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Communication system |
| RE39111 |
Communication system
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| Patent Drawings: | |
| Inventor: |
Oshima |
| Date Issued: |
May 30, 2006 |
| Application: |
10/119,793 |
| Filed: |
April 11, 2002 |
| Inventors: |
Oshima; Mitsuaki (Kyoto, JP)
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| Assignee: |
Matsushita Electric Industrial Co., Ltd. (Osaka, JP) |
| Primary Examiner: |
Chevalier; Robert |
| Assistant Examiner: |
|
| Attorney Or Agent: |
Wenderoth, Lind & Ponack, L.L.P. |
| U.S. Class: |
348/726; 386/123; 386/46 |
| Field Of Search: |
386/46; 386/109; 386/111; 386/112; 386/27; 386/33; 386/123; 375/1; 375/260; 375/265; 348/21; 348/24; 348/22; 348/608; 348/636; 348/723; 348/725; 348/737; 348/726 |
| International Class: |
H04N 5/91; H04N 5/455 |
| U.S Patent Documents: |
3824548; 3909721; 3959726; 4048572; 4227152; 4271527; 4303939; 4303941; 4309726; 4525846; 4535352; 4564858; 4581639; 4630287; 4636876; 4751478; 4769819; 4794447; 4800426; 4817192; 4855692; 4873701; 4891806; 4903125; 4937844; 4940954; 4958360; 5007088; 5029003; 5038219; 5038402; 5050188; 5063445; 5086340; 5087975; 5105442; 5115453; 5128758; 5134464; 5142353; 5164963; 5166924; 5168509; 5170413; 5181112; 5197061; 5214656; 5218622; 5243629; 5267021; 5282019; 5291289; 5311547; 5311550; 5377051; 5398073; 5400084; 5452015; 5481412; 5555275; 5561468; 5565926; 5565932; 5576902; 5598220; 5600672; 5638112; 5802241; 5819000; 5892879; 5999569; 6049651; 6256357 |
| Foreign Patent Documents: |
2095435; 0031193; 0122805; 0282298; 0311188; 0329158; 0365431; 0392538; 0448492; 0485105; 0485108; 0485108; 0490552; 0506400; 0525641; 0531046; 0540231; 0540231; 2 187 611; 53-108215; 53-137657; 57-39629; 58-161427; 58-161547; 61-70861; 62-133842; 63-28145; 63-180222; 63-180280; 64-5135; 64-68144; 64-74836; 2-94814; 2-141049; 2-154583; 2-166979; 2-195732; 2-218279; 2-260726; 3-048587; 3-69295; 04-196822; 5-75568; 5-167633; 5-218978; 5-327807; 7-79415; 7-99522; 7-264148; 7-322219; 85/04541; 86/07223; 89/08366; 91/20137; 92/14343; 92/22162 |
| Other References: |
IEEE Transactions on Information Theory, vol. 18, No. 1, Jan. 1972, New York, US; pp. 2-14, Cover: `Broadcast channels`. cited by examiner.
IEEE Global Telecommunications Conference 1991, 2-5/12/1991, Phoenix, US; IEEE New York, US, 1991: pp 40-46, Hoeher et al.: "Performance of an RCPC--coded OFDM--based digital audio broadcasting (DAB) system". cited by examiner.
Biglieri et al. `Introduction to Trellis-Coded Modulation with Applications` 1991, MacMillan, New York, US. cited by examiner.
IEEE International Conference on Communications, May 23-26, 1993, Geneva, CH; New York, US, 1993; pp. 1081-1085, Fazel & Ruf: `Combined multilevel coding and multiresolution modulation`. cited by examiner.
European Transactions on Telecommunications and Related Technologies, vol. 4, No. 3, May 1993, Italy; pp. 325-334, Seshadri & Sundberg `Multi-level block coded modulations with unequal error protection for the Rayleigh fading channel`. cited byexaminer.
4th International Workshop on HDTV, Sep. 1991, Torino, IT, Elsevier 1992; pp. 61-69, Uz et al.: "Multiresolution source and channel coding for the digital broadcast of HDTV". cited by examiner.
SMPTE Journal, vol. 101, No. 8, Aug. 1992, Scarsdale, NY US; pp. 538-549, Schreiber `Spread--spectrum television broadcasting`. cited by examiner.
Signal Processing: Image Communication, vol. 4, Aug. 1992, Amsterdam NL; pp. 283-292, Uz et al.: `Combined multiresolution source coding and modulation for digital broadcast of HDTV`. cited by examiner.
Multidiminsional Systems and Signal Pocessing, vol. 3, No. 2-3, May 1992, NL pp. 161-187, Vetterli Et and Uz: `Multiresolution coding techniques for digital television: a review`. cited by examiner.
B-277, pi/4-shift QPSK Subcarrier Transmission; Ryutaro Ohmoto, Hiroyuki Ohtsuka. cited by examiner.
B-231, Bit Error Rate Characteristics of OFDM in Multipath Environment; Masafumi Saito, Shigeki Moriyama, Osamu Yamada. cited by examiner.
Shigeki Moriyama et al., "Delay Propagation Characteristics at VHF and UHF bands in Urban Area", 1991 Spring National Convention Record, The Institute of Electronics, Information and Communication Engineers, Part 2, p. 406, Mar. 15, 1991. cited byother.
Yasuhiro Ito et al., "Adaptive Weighted Code Division Multiplexing (AW-CDM) Transmission System for Terrestrial Digital Television Broadcasting", ITE Technical Report vol. 17, No. 13, pp. 27-32, Feb. 25, 1993. cited by other.
Shinji Matsumoto et al., "200 Mb/s 16 QAM Digital Radio-Relay System Operating in 4 and 5 GHz Bands", Japan Telecommunications Review, Jan. 1982, vol. 24, No. 1, pp. 65-73. cited by other.
M. Pecot et al., "Compatible Coding of Television Images, Part 2. Compatible System", Signal Processing Image Communication, Oct. 2, 1990, No. 3, pp. 259-268. cited by other.
Mitsuaki Oshima, "Constellation-Code Division Multiplex for Digital HDTV", IEEE, 1992, pp. 1086-1092. cited by other.
Tricia Hill et al., "A Performance Study of NLA 64-State QAM", IEEE Transactions on Communications, vol. COM-31, Jun. 1983, No. 6, pp. 821-826. cited by other.
Hideki Ishio et al., "A Proposal of a Carrier Digital Transmission System Using Multi-Level APSK", pp. 1-20. cited by other.
Shanmugam, "Digital and Analog Communication Systems" 1979, p. 272. cited by other.
Khaled Fazel et al., Combined multilevel coding and multiresolution modulation, Feb. 8, 1993, pp. 1081-1085. cited by other.
P. Hoeher et al., Performance of an RCPC-Coded OFDM-based Digital Audio Broadcasting (DAB) System, IEEE Global Telecommunications Conference "Globecom '91", Dec. 2-5, 1991, vol. 1 of 3, pp. 2.1.1-2.1.7. cited by other.
K. M. Uz et al., Combined multiresolution source coding and modulation for digital broadcast of HDTV*, 1992, pp. 283-292. cited by other.
K. M. Uz et al., Multiresolution Source and Channel Coding for Digital Broadcast of HDTV, 1992, pp. 61-69. cited by other.
Nambi Seshadri et al., Multi-Level Block Coded Modulations with Unequal Error Protection for the Rayleigh Fading Channel, vol. 4, No. 3, May-Jun. 1993, pp. 325-334. cited by other.
William F. Schreiber, Spread-Spectrum Television Broadcasting, SMPTE Journal, Aug. 1992, pp. 538-549. cited by other.
Martin Vetterli et al., Multiresolution Coding Techniques for Digital Television: A Review, Multidimensional Systems and Signal Processing, vol. 3, May 1992, pp. 161-187. cited by other.
Ezio Biglieri et al., Introduction to Trellis-Coded Modulation with Applications, Apr. 6, 1992, pp. 173-207. cited by other.
English Language Abstract of European Patent No. 93 30 7575. cited by othe- r.
Kazuhiko Nitadori, Synthesis of Multichannel Orthogonal VSB Signals by Quadrature Method, 1976 International Conference on Communications, Jun. 14-16, 1976, vol. 1, pp. 3-25--3-29. cited by other.
Thomas M. Cover, Broadcast Channels, IEEE Transactions on Information Theory, Jan. 1972, pp. 2-14. cited by other.
"Optimum Weighted PCM for Speech Signals", Sundberg, IEEE Transactions on Communications, vol. COM-26, No. 6, Jun. 1978, pp. 872-881. cited by othe- r.
J. A. C. Bingham, "Multicarrier Modulation for Data Transmission: An Idea Whose Time Has Come ", IEEE Communications Magazine, vol. 28, May 1990, pp. 5-8 and 11-14. cited by other.
B. Hiroaki, "An Orthogonally Multiplexed QAM System Using the Discreter Fourier Transform", IEEE Transactions on Communications, vol. Com-29, No. 7, Jul. 1981, pp. 982-999. cited by other.
L. J. Cimini, Jr., "Analysis and Simulation of a Digital Mobile Channel Using Orthogonal Frequency Division Multiplexing", IEEE Transactions on Communications, vol. Com-33, No. 7, Jul., 1985 pp. 665-675 and Annex. cit- ed by other. |
|
| Abstract: |
At the transmitter side, carrier waves are modulated according to an input signal for producing relevant signal points in a signal space diagram. The input signal is divided into, two, first and second, data streams. The signal points are divided into signal point groups to which data of the first data stream are assigned. Also, data of the second data stream are assigned to the signal points of each signal point group. A difference in the transmission error rate between first and second data streams is developed by shifting the signal points to other positions in the space diagram expressed at least in the polar coordinate system. At the receiver side, the first and/or second data streams can be reconstructed from a received signal. In TV broadcast service, a TV signal is divided by a transmitter into, low and high, frequency band components which are designated as a first and a second data streams respectively. Upon receiving the TV signal, a receiver can reproduce only the low frequency band component or both the low and high frequency band components, depending on its capability. Furthermore, a communication system based on an OFDM system is utilized for data transmission of a plurality of subchannels, wherein the subchannels are differentiated by changing the length of a guard time slot or a carrier wave interval of a symbol transmission time slot, or changing the transmission electric power of the carrier. |
| Claim: |
What is claimed is:
1. A receiving apparatus comprising: a channel selector connected to a variable oscillator for changing a frequency of an oscillation signal of said variable oscillator; amixer connected to said variable oscillator for converting a received signal by using said oscillation signal, into a an M-value VSB modulation modulated signal, where M is an integer; a demodulator for demodulating said M-value VSB modulation modulatedsignal to reproduce an encoded signal; and a trellis decoder for trellis decoding said encoded signal to obtain a trellis-decoded signal, wherein said received signal is a time division multiplexed signal transmitted by a time division multiplexing, andis demodulated as an 8-value VSB modulation modulated signal in a first mode and is demodulated as an N-value VSB modulation modulated signal in a second mode, where N is an integer less than 8.
2. The receiving apparatus in accordance with claim 1, wherein said trellis-decoded signal is an encoded video signal, and wherein said apparatus further comprises a video decoder for decoding said trellis-decoded signal to obtain a videosignal.
3. The receiving apparatus in accordance with claim 2, wherein the video decoder is an MPEG decoder.
4. A receiving apparatus comprising: a channel selector operable to change a frequency of an oscillation signal of a variable oscillator; a mixer operable to convert a received signal by using the oscillation signal into a VSB modulatedsignal; a demodulator operable to demodulate the VSB modulated signal into an N-level demodulated signal and an 8-level demodulated signal, where N is an integer less than 8; and a trellis decoder operable to trellis decode the 8-level demodulatedsignal to obtain a trellis-decoded signal, wherein the received signal is a time division multiplexed signal transmitted by a time division multiplexing.
5. The receiving apparatus in accordance with claim 4, wherein the trellis-decoded signal is an encoded video signal, and wherein said apparatus further comprises a video decoder operable to decode the trellis-decoded signal to obtain a videosignal.
6. The receiving apparatus in accordance with claim 5, wherein the video decoder is an MPEG decoder. |
| Description: |
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a communication system for transmission/reception of a digital signal through modulation of its carrier wave and demodulation of the modulated signal.
2. Description of the Prior Art
Digital signal communication systems have been used in various fields. Particularly, digital video signal transmission techniques have been improved remarkably.
Among them is a digital TV signal transmission method. So far, such digital TV signal transmission system are in particular use for e.g. transmission between TV stations. They will soon be utilized for terrestrial and/or satellite broadcastservice in every country of the world.
The TV broadcast systems including HDTV, PCM music, FAX, and other information service are now demanded to increase desired data in quantity and quality for satisfying millions of sophisticated viewers. In particular, the data has to beincreased in a given bandwidth of frequency allocated for TV broadcast service. The data to be transmitted is always abundant and provided as much as handled with up-to-date techniques of the time. It is ideal to modify or change the existing signaltransmission system corresponding to an increase in the data amount with time.
However, the TV broadcast service is a public business and cannot go further without considering the interests and benefits of viewers. It is essential to have any new service appreciable with existing TV receivers and displays. Moreparticularly, the compatibility of a system is much desired for providing both old and new services simultaneously or one new service which can be intercepted by either of the existing and advanced receivers.
It is understood that any new digital TV broadcast system to be introduced has to be arranged for data extension in order to respond to future demands and technological advantages and also, for compatible action to allow the existing receivers toreceive transmissions.
The expansion capability and compatible performance of prior art digital TV system will be explained.
A digital satellite TV system is known in which NTSC TV signals compressed to an about 6 Mbps are multiplexed by time division modulation of 4 PSK and transmitted on 4 to 20 channels while HDTV signals are carried on a single channel. Anotherdigital HDTV system is provided in which HDTV video data compressed to as small as 15 Mbps are transmitted on a 16 or 32 QAM signal through ground stations.
Such a known satellite system permits HDTV signals to be carried on one channel by a conventional manner, thus occupying a band of frequencies equivalent to same channels of NTSC signals. This causes the corresponding NTSC channels to beunavailable during transmission of the HDTV signal. Also, the compatibility between NTSC and HDTV receivers or displays is hardly concerned and data expansion capability needed for matching a future advanced mode is utterly disregarded.
Such a common terrestrial HDTV system offers an HDTV service on conventional 16 or 32 QAM signals without any modification. In any analogue TV broadcast service, there are developed a lot of signal attenuating or shadow regions within itsservice area due to structural obstacles, geographical inconveniences, or signal interference from a neighbor station. When the TV signal is an analogue form, it can be intercepted more or less at such signal attenuating regions although its reproducedpicture is low in quality. If TV signal is a digital form, it can rarely be reproduced at an acceptable level within the regions. This disadvantage is critically hostile to the development of any digital TV system.
SUMMARY OF THE INVENTION
It is an object of the present invention, for solving the foregoing disadvantages, to provide a communication system arranged for compatible use for both the existing NTSC and introducing HDTV broadcast services, particularly via satellite andalso, for minimizing signal attenuating or shadow regions of its service area on the grounds.
A communication system according to the present invention intentionally varies signal points, which used to be disposed at uniform intervals, to perform the signal transmission/reception. For example, if applied to a QAM signal, thecommunication system comprises two major sections: a transmitter having a signal input circuit, a modulator circuit for producing m numbers of signal points, in a signal vector field through modulation of a plurality of out-of-phase carrier waves usingan input signal supplied from the input circuit, and a transmitter circuit for transmitting a resultant modulated signal; and a receiver having an input circuit for receiving the modulated signal, a demodulator circuit for demodulating one-bit signalpoints of a QAM carrier wave, and an output circuit.
In operation, the input signal containing a first data stream of n values and a second data stream is fed to the modulator circuit of the transmitter where a modified m-bit QAM carrier wave is produced representing m signal points in a vectorfield. The m signal points are divided into n signal point groups to which the n values of the first data stream are assigned respectively. Also, data of the second data stream are assigned to m/n signal points or sub groups of each signal point group. Then, a resultant transmission signal is transmitted from the transmitter circuit. Similarly, a third data stream can be propagated.
At the p-bit demodulator circuit, p>m, of the receiver, the first data stream of the transmission signal is first demodulated through dividing p signal points in a signal space diagram into n signal point groups. Then, the second data streamis demodulated through assigning p/n values to p/n signal points of each corresponding signal point group for reconstruction of both the first and second data streams. If the receiver is at P=n, the n signal point groups are reclaimed and assigned the nvalues for demodulation and reconstruction of the first data stream.
Upon receiving the same transmission signal from the transmitter, a receiver equipped with a large sized antenna and capable of large-data modulation can reproduce both the first and second data streams. A receiver equipped with a small sizedantenna and capable of small-data modulation can reproduce the first data stream only. Accordingly, the compatibility of the signal transmission system will be ensured. When the first data stream is an NTSC TV signal or low frequency band component ofan HDTV signal and the second data stream is a high frequency band component of the HDTV signal, the small-data modulation receiver can reconstruct the NTSC TV signal and the large-data modulation receiver can reconstruct the HDTV signal. As understood,a digital NTSC/HDTV simultaneously broadcast service will be feasible using the compatibility of the signal transmission system of the present invention.
More specifically, the communication system of the present invention comprises: a transmitter having a signal input circuit, a modulator circuit for producing m signal points, in a signal vector field through modulation of a plurality ofout-of-phase carrier waves using an input signal supplied from the input, and a transmitter circuit for transmitting a resultant modulated signal, in which the main procedure includes receiving an input signal containing a first data stream of n valuesand a second data stream, dividing the m signal points of the signal into n signal point groups, assigning the n values of the first data stream to the n signal point groups respectively, assigning data of the second data stream to the signal points ofeach signal point group respectively, and transmitting the resultant modulated signal; and a receiver having an input circuit for receiving the modulated signal, a demodulator circuit for demodulating p signal points of a QAM carrier wave, and an outputcircuit, in which the main procedure includes dividing the p signal points into n signal point groups, demodulating the first data stream of which n values are assigned to the n signal point groups respectively, and demodulating the second data stream ofwhich p/n values are assigned to p/n signal points of each signal point group respectively. For example, a transmitter 1 produces a modified m-bit QAM signal of which first, second, and third data streams, each carrying n values, are assigned torelevant signal point groups with a modulator 4. The signal can be intercepted and reproduced the first data stream only by a first receiver 23, both the first and second data streams by a second receiver 33, and all the first, second, and third streamsby a third receiver 43.
More particularly, a receiver capable of demodulation of n-bit data can reproduce n bits from a multiple-bit modulated carrier wave carrying an m-bit data where m>n, thus allowing the communication system to have compatibility and capabilityof future extension. Also, a multi-level signal transmission will be possible by shifting the signal points of QAM so that a nearest signal point to the origin point of I-axis and Q-axis coordinates is spaced nf from the origin where f is the distanceof the nearest point from each axis and n is more than 1.
Accordingly, a compatible digital satellite broadcast service for both the NTSC and HDTV systems will be feasible when the first data stream carries an NTSC signal and the second data stream carries a difference signal between NTSC and HDTV. Hence, the capability of corresponding to an increase in the data amount to be transmitted will be ensured. Also, at the ground, its service area will be increased while signal attenuating areas are decreased.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of the entire arrangement of a signal transmission system showing a first embodiment of the present invention;
FIG. 2 is a block diagram of a transmitter of the first embodiment;
FIG. 3 is a vector diagram showing a transmission signal of the first embodiment;
FIG. 4 is a vector diagram showing a transmission signal of the first embodiment;
FIG. 5 is a view showing an assignment of binary codes to signal points according to the first embodiment;
FIG. 6 is a view showing an assignment of binary codes to signal point groups according to the first embodiment;
FIG. 7 is a view showing an assignment of binary codes to signal points in each signal point group according to the first embodiment;
FIG. 8 is a view showing another assignment of binary codes to signal point groups and their signal points according to the first embodiment;
FIG. 9 is a view showing threshold values of the signal point groups according to the first embodiment;
FIG. 10 is a vector diagram of a modified 16 QAM signal of the first embodiment;
FIG. 11 is a graphic diagram showing the relation between antenna radius r.sub.2 and transmission energy ratio n according to the first embodiment; FIG. 12 is a view showing the signal points of a modified 64 QAM signal of the first embodiment;
FIG. 13 is a graphic diagram showing the relation between antenna radius r.sub.3 and transmission energy ratio n according to the first embodiment;
FIG. 14 is a vector diagram showing signal point groups and their signal points of the modified 64 QAM signal of the first embodiment;
FIG. 15 is an explanatory view showing the relation between A.sub.1 and A.sub.2 of the modified 64 QAM signal of the first embodiment;
FIG. 16 is a graph diagram showing the relation between antenna radius r.sub.2, r.sub.3 and transmission energy ratio n.sub.16, n.sub.64 respectively according to the first embodiment;
FIG. 17 is a block diagram of a digital transmitter of the first embodiment;
FIG. 18 is a signal space diagram of a 4 PSK modulated signal of the first embodiment;
FIG. 19 is a block diagram of a first receiver of the first embodiment;
FIG. 20 is a signal space diagram of a 4 PSK modulated signal of the first embodiment;
FIG. 21 is a block diagram of a second receiver of the first embodiment;
FIG. 22 is a vector diagram of a modified 16 QAM signal of the first embodiment;
FIG. 23 is a vector diagram of a modified 64 QAM signal of the first embodiment;
FIG. 24 is a flow chart showing an action of the first embodiment;
FIGS. 25(a) and 25(b) are vector diagrams showing an 8 and a 16 QAM signal of the first embodiment respectively;
FIG. 26 is a block diagram of a third receiver of the first embodiment;
FIG. 27 is a view showing signal points of the modified 64 QAM signal of the first embodiment;
FIG. 28 is a flow chart showing another action of the first embodiment;
FIG. 29 is a schematic view of the entire arrangement of a signal transmission system showing a third embodiment of the present invention;
FIG. 30 is a block diagram of a first video encoder of the third embodiment;
FIG. 31 is a block diagram of a first video decoder of the third embodiment;
FIG. 32 is a block diagram of a second video decoder of the third embodiment;
FIG. 33 is a block diagram of a third video decoder of the third embodiment;
FIG. 34 is an explanatory view showing a time multiplexing of D.sub.1, D.sub.2, and D.sub.3 signals according to the third embodiment;
FIG. 35 is an explanatory view showing another time multiplexing of the D.sub.1, D.sub.2, and D.sub.3 signals according to the third embodiment;
FIG. 36 is an explanatory view showing a further time multiplexing of the D.sub.1, D.sub.2, and D.sub.3 signals according to the third embodiment;
FIG. 37 is a schematic view of the entire arrangement of a signal transmission system showing a fourth embodiment of the present invention;
FIG. 38 is a vector diagram of a modified 16 QAM signal of the third embodiment;
FIG. 39 is a vector diagram of the modified 16 QAM signal of the third embodiment;
FIG. 40 is a vector diagram of a modified 64 QAM signal of the third embodiment;
FIG. 41 is a diagram of assignment of data components on a time base according to the third embodiment;
FIG. 42 is a diagram of assignment of data components on a time base in TDMA action according to the third embodiment;
FIG. 43 is a block diagram of a carrier reproducing circuit of the third embodiment;
FIG. 44 is a diagram showing the principle of carrier wave reproduction according to the third embodiment;
FIG. 45 is a block diagram of a carrier reproducing circuit for reverse modulation of the third embodiment;
FIG. 46 is a diagram showing an assignment of signal points of the 16 QAM signal of the third embodiment;
FIG. 47 is a diagram showing an assignment of signal points of the 64 QAM signal of the third embodiment;
FIG. 48 is a block diagram of a carrier reproducing circuit for 16.times. multiplication of the third embodiment;
FIG. 49 is an explanatory view showing a time multiplexing of D.sub.V1, D.sub.H1, D.sub.V2, D.sub.H2, D.sub.V3, and D.sub.H3 signals according to the third embodiment;
FIG. 50 is an explanatory view showing a TDMA time multiplexing of D.sub.V1, D.sub.H1, D.sub.V2, D.sub.H2, D.sub.V3, and D.sub.H3 signals according to the third embodiment;
FIG. 51 is an explanatory view showing another TDMA time multiplexing of the D.sub.V1, D.sub.H1, D.sub.V2, D.sub.H2, D.sub.V3, and D.sub.H3 signals according to the third embodiment;
FIG. 52 is a diagram showing a signal interference region in a known transmission method according to the fourth embodiment;
FIG. 53 is a diagram showing signal interference regions in a multi-level signal transmission method according to the fourth embodiment;
FIG. 54 is a diagram showing signal attenuating regions in the known transmission method according to the fourth embodiment;
FIG. 55 is a diagram showing signal attenuating regions in the multi-level signal transmission method according to the fourth embodiment;
FIG. 56 is a diagram showing a signal interference region between two digital TV stations according to the fourth embodiment;
FIG. 57 is a diagram showing an assignment of signal points of a modified 4 ASK signal of the fifth embodiment;
FIG. 58 is a diagram showing another assignment of signal points of the modified 4 ASK signal of the fifth embodiment;
FIGS. 59(a) and 59(b) are diagrams showing assignment of signal points of the modified 4 ASK signal of the fifth embodiment;
FIG. 60 is a diagram showing another assignment of signal points of the modified 4 ASK signal of the fifth embodiment when the C/N rate is low;
FIG. 61 is a block diagram of a transmitter of the fifth embodiment;
FIGS. 62(a) and 62(b) are diagrams showing frequency distribution profiles of an ASK modulated signal of the fifth embodiment;
FIG. 63 is a block diagram of a receiver of the fifth embodiment;
FIG. 64 is a block diagram of a video signal transmitter of the fifth embodiment;
FIG. 65 is a block diagram of a TV receiver of the fifth embodiment;
FIG. 66 is a block diagram of another TV receiver of the fifth embodiment;
FIG. 67 is a block diagram of a satellite-to-ground TV receiver of the fifth embodiment;
FIG. 68 is a diagram showing an assignment of signal points of an 8 ASK signal of the fifth embodiment;
FIG. 69 is a block diagram of a video encoder of the fifth embodiment;
FIG. 70 is a block diagram of a video encoder of the fifth embodiment containing one divider circuit;
FIG. 71 is a block diagram of a video decoder of the fifth embodiment;
FIG. 72 is a block diagram of a video decoder of the fifth embodiment containing one mixer circuit;
FIG. 73 is a diagram showing a time assignment of data components of a transmission signal according to the fifth embodiment;
FIG. 74(a) is a block diagram of a video decoder of the fifth embodiment;
FIG. 74(b) is a diagram showing another time assignment of data components of the transmission signal according to the fifth embodiment;
FIG. 75 is a diagram showing a time assignment of data components of a transmission signal according to the fifth embodiment;
FIG. 76 is a diagram showing a time assignment of data components of a transmission signal according to the fifth embodiment;
FIG. 77 is a diagram showing a time assignment of data components of a transmission signal according to the fifth embodiment;
FIG. 78 is a block diagram of a video decoder of the fifth embodiment;
FIG. 79 is a diagram showing a time assignment of data components of a three-level transmission signal according to the fifth embodiment;
FIG. 80 is a block diagram of another video decoder of the fifth embodiment;
FIG. 81 is a diagram showing a time assignment of data components of a transmission signal according to the fifth embodiment;
FIG. 82 is a block diagram of a video decoder for D signal of the fifth embodiment;
FIG. 83 is a graphic diagram showing the relation between frequency and time of a frequency modulated signal according to the fifth embodiment;
FIG. 84 is a block diagram of a magnetic record/playback apparatus of the fifth embodiment;
FIG. 85 is a graphic diagram showing the relation between C/N and level according to the second embodiment;
FIG. 86 is a graphic diagram showing the relation between C/N and transmission distance according to the second embodiment;
FIG. 87 is a block diagram of a transmission of the second embodiment;
FIG. 88 is a block diagram of a receiver of the second embodiment;
FIG. 89 is a graphic diagram showing the relation between C/N and error rate according to the second embodiment;
FIG. 90 is a diagram showing signal attenuating regions in the three-level transmission of the fifth embodiment;
FIG. 91 is a diagram showing signal attenuating regions in the four-level transmission of a sixth embodiment;
FIG. 92 is a diagram showing the four-level transmission of the sixth embodiment;
FIG. 93 is a block diagram of a divider of the sixth embodiment;
FIG. 94 is a block diagram of a mixer of the sixth embodiment;
FIG. 95 is a diagram showing another four-level transmission of the sixth embodiment;
FIG. 96 is a view of signal propagation of a known digital TV broadcast system;
FIG. 97 is a view of signal propagation of a digital TV broadcast system according to the sixth embodiment;
FIG. 98 is a diagram showing a four-level transmission of the sixth embodiment;
FIG. 99 is a vector diagram of a 16 SRQAM signal of the third embodiment;
FIG. 100 is a vector diagram of a 32 SRQAM signal of the third embodiment;
FIG. 101 is a graphic diagram showing the relation between C/N and error rate according to the third embodiment;
FIG. 102 is a graphic diagram showing the relation between C/N and error rate according to the third embodiment;
FIG. 103 is a graphic diagram showing the relation between shift distance n and C/N needed for transmission according to the third embodiment;
FIG. 104 is a graphic diagram showing the relation between shift distance n and C/N needed for transmission according to the third embodiment;
FIG. 105 is a graphic diagram showing the relation between signal level and distance from a transmitter antenna in terrestrial broadcast service according to the third embodiment;
FIG. 106 is a diagram showing a service area of the 32 SRQAM signal of the third embodiment;
FIG. 107 is a diagram showing a service area of the 32 SRQAM signal of the third embodiment;
FIG. 108(a) is a diagram showing a frequency distribution profile of a conventional TV signal, FIG. 108(b) is a diagram showing a frequency distribution profile of a conventional two-layer TV signal, FIG. 108(c) is a diagram showing thresholdvalues of the third embodiment, FIG. 108(d) is a diagram showing a frequency distribution profile of two-layer OFDM carriers of the ninth embodiment, and FIG. 108(e) is a diagram showing threshold values for three-layer OFDM of the ninth embodiment;
FIG. 109 is a diagram showing a time assignment of the TV signal of the third embodiment;
FIG. 110 is a diagram showing a principle of C-CDM of the third embodiment;
FIG. 111 is a view showing an assignment of codes according to the third embodiment;
FIG. 112 is a view showing an assignment of an extended 36 QAM according to the third embodiment;
FIG. 113 is a view showing a frequency assignment of a modulation signal according to the fifth embodiment;
FIG. 114 is a block diagram showing a magnetic recording/playback apparatus according to the fifth embodiment;
FIG. 115 is a block diagram showing a transmitter/receiver of a portable telephone according to the eighth embodiment;
FIG. 116 is a block diagram showing base stations according to the eighth embodiment;
FIG. 117 is a view illustrating communication capacities and traffic distribution of a conventional system;
FIG. 118 is a view illustrating communication capacities and traffic distribution according to the eighth embodiment;
FIG. 119(a) is a diagram showing a time slot assignment of a conventional system;
FIG. 119(b) is a diagram showing a time slot assignment according to the eighth embodiment;
FIG. 120(a) is a diagram showing a time slot assignment of a conventional TDMA system;
FIG. 120(b) is a diagram showing a time slot assignment according to a TDMA system of the eighth embodiment;
FIG. 121 is a block diagram showing a one-level transmitter/receiver according to the eighth embodiment;
FIG. 122 is a block diagram showing a two-level transmitter/receiver according to the eighth embodiment;
FIG. 123 is a block diagram showing an OFDM type transmitter/receiver according to the ninth embodiment;
FIG. 124 is a view illustrating a principle of the OFDM system according to the ninth embodiment;
FIG. 125(a) is a view showing a frequency assignment of a modulation signal of a conventional system;
FIG. 125(b) is a view showing a frequency assignment of a modulation signal according to the ninth embodiment;
FIG. 126(a) is a view showing a frequency assignment of an OFDM signal of the ninth embodiment, wherein no weighting is applied;
FIG. 126(b) is a view showing a frequency assignment of an OFDM signal of the ninth embodiment, wherein two channels of two-layer OFDM are weighted by transmission electric power;
FIG. 126(c) is a view showing a frequency assignment of an OFDM signal of the ninth embodiment, wherein carrier intervals are doubled by weighting;
FIG. 126(d) is a view showing a frequency assignment of an OFDM signal of the ninth embodiment, wherein carrier intervals are not weighted;
FIG. 127 is a block diagram showing a transmitter/receiver according to the ninth embodiment;
FIG. 128 is a block diagram showing a Trellis encoder according to the fifth embodiment;
FIG. 129 is a view showing a time assignment of effective symbol periods and guard intervals according to the ninth embodiment;
FIG. 130 is a graphic diagram showing a relation between C/N rate and error rate according to the ninth embodiment;
FIG. 131 is a block diagram showing a magnetic recording/playback apparatus according to the fifth embodiment;
FIG. 132 is a view showing a recording format of track on the magnetic tape and a travelling of a head;
FIG. 133 is a block diagram showing a transmitter/receiver according to the third embodiment;
FIG. 134 is a diagram showing a frequency assignment of a conventional broadcasting;
FIG. 135 is a diagram showing a relation between service area and picture quality in a three-level signal transmission system according to the third embodiment;
FIG. 136 is a diagram showing a frequency assignment in case the multi-level signal transmission system according to the third embodiment is combined with FDM;
FIG. 137 is a block diagram showing a transmitter/receiver according to the third embodiment, in which Trellis encoding is adopted;
FIG. 138 is a block diagram showing a transmitter/receiver according to the ninth embodiment, in which a part of low frequency band signal is transmitted by OFDM;
FIG. 139 is a diagram showing an assignment of signal points of the 8-PS-APSK signal of the first embodiment;
FIG. 140 is a diagram showing an assignment of signal points of the 16-PS-APSK signal of the first embodiment;
FIG. 141 is a diagram showing an assignment of signal points of the 8-PS-PSK signal of the first embodiment;
FIG. 142 is a diagram showing an assignment of signal points of the 16-PS-PSK (PS type) signal of the first embodiment;
FIG. 143 is a graphic diagram showing the relation between antenna radius of satellite and transmission capacity according to the first embodiment;
FIG. 144 is a block diagram showing a weighted OFDM transmitter/receiver according to the ninth embodiment;
FIG. 145(a) is a diagram showing the waveform of the guard time and the symbol time in the multi-level OFDM according to the ninth embodiment, wherein multipath is short;
FIG. 145(b) is a diagram showing the waveform of the guard time and the symbol time in the multi-level OFDM according to the ninth embodiment, wherein multipath is long;
FIG. 146 is a diagram showing a principle of the multi-level OFDM according to the ninth embodiment;
FIG. 147 is a diagram showing subchannel assignment of a two-layer signal transmission system, weighted by electric power according to the ninth embodiment;
FIG. 148 is a diagram showing relation among the D/V ratio, the multipath delay time, and the guard time according to the ninth embodiment;
FIG. 149(a) is a diagram showing time slots of respective layers according to the ninth embodiment;
FIG. 149(b) is a diagram showing time distribution of guard times of respective layers according to the ninth embodiment;
FIG. 149(c) is a diagram showing time distribution of guard times of respective layers according to the ninth embodiment;
FIG. 150 is a diagram showing relation between multipath delay time and transfer rate according to the ninth embodiment, wherein three-layer signal transmission effective to multipath is realized; and
FIG. 151 is a diagram showing relation between multipath delay time and C/N ratio according to the ninth embodiment, wherein two-dimensional, matrix type, multi-layer broadcast service can be realized by combining the GTW-OFDM and the C-CDM (orthe CSW-OFDM).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment 1
One embodiment of the present invention will be described referring to the relevant drawings.
FIG. 1 shows the entire arrangement of a signal transmission system according to the present invention. A transmitter 1 comprises an input unit 2, a divider circuit 3, a modulator 4, and a transmitter unit 5. In action, each input multiplexsignal is divided by the divider circuit 3 into three groups, a first data stream D1, a second data stream D2, a third data stream D3, which are then modulated by the modulator 4 before being transmitted from the transmitter unit 5. The modulated signalis sent up from an antennal 6 through an uplink 7 to a satellite 10 where it is intercepted by an uplink antenna 11 and amplified by a transponder 12 before being transmitted from a downlink antenna 13 towards the ground.
The transmission signal is then sent down through three downlinks 21, 32, and 41 to a first 23, a second 33, and a third receiver 43 respectively. In the first receiver 23, the signal intercepted by an antenna 22 is fed through an input unit 24to a demodulator 25 where its first data stream only is demodulated, while the second and third data streams are not recovered, before being transmitted further from an output unit 26.
Similarly, the second receiver 33 allows the first and second data streams of the signal intercepted by an antenna 32 and fed from an input unit 34 to be demodulated by a demodulator 35 and then, summed by a summer 37 to a single data streamwhich is then transmitted further from an output unit 36.
The third receiver 43 allows all the first, second, and third data streams of the signal intercepted by an antenna 42 and fed from an input unit 44 to be demodulated by a demodulator 45 and then, summed by a summer 47 to a single data streamwhich is then transmitted further from an output unit 46.
As understood, the three discrete receivers 23, 33, and 43 have their respective demodulators of different characteristics such that their outputs demodulated from the same frequency band signal of the transmitter 1 contain data of differentsizes. More particularly, three different but compatible data can simultaneously be carried on a given frequency band signal to their respective receivers. For example, each of three, existing NTSC, HDTV, and super HDTV, digital signals is divided intoa low, a high, and a super high frequency band components which represent the first, the second, and the third data stream respectively. Accordingly, the three different TV signals can be transmitted on a one-channel frequency band carrier forsimultaneous reproduction of a medium, a high, and a super high resolution TV image respectively.
In service, the NTSC TV signal is intercepted by a receiver accompanied with a small antenna for demodulation of a small-sized data, the HDTV signal is intercepted by a receiver accompanied with a medium antenna for demodulation of medium-sizeddata, and the super HDTV signal is intercepted by a receiver accompanied with a large antenna for demodulation of large-sized data. Also, as illustrated in FIG. 1, a digital NTSC TV signal containing only the first data stream for digital NTSC TVbroadcasting service is fed to a digital transmitter 51 where it is received by an input unit 52 and modulated by a modulator 54 before being transmitted further from a transmitter unit 55. The demodulated signal is then sent up from an antenna 56through an uplink 57 to the satellite 10 which in turn transmits the same through a downlink 58 to the first receiver 23 on the ground.
The first receiver 23 demodulates with its demodulator 25 the modulated digital signal supplied from the digital transmitter 51 to the original first data stream signal. Similarly, the same modulated digital signal can be intercepted anddemodulated by the second 33 or third receiver 43 to the first data stream or NTSC TV signal. In summary, the three discrete receivers 23, 33, and 43 all can intercept and process a digital signal of the existing TV system for reproduction.
The arrangement of the signal transmission system will be described in more detail.
FIG. 2 is a block diagram of the transmitter 1, in which an input signal is fed across the input unit 2 and divided by the divider circuit 3 into three digital signals containing a first, a second, and a third data stream respectively.
Assuming that the input signal is a video signal, its low frequency band component is assigned to the first data stream, its high frequency band component to the second data stream, its super-high frequency band component to the third datastream. The three different frequency band signals are fed to a modulator input 61 of the modulator 4. Here, a signal point modulating/changing circuit 67 modulates or changes the positions of the signal points according to an externally given signal. The modulator 4 is arranged for amplitude modulation on two 90.degree.-out-of-phase carriers respectively which are then summed to a multiple QAM signal. More specifically, the signal from the modulator input 61 is fed to both a first 62 and a second AMmodulator 63. Also, a carrier wave of cos(2.pi.fct) produced by a carrier generator 64 is directly fed to the first AM modulator 62 and also, to a .pi./2 phase shifter 66 where it is 90.degree. shifted in phase to a sin(2.pi.fct) form prior totransmitted to the second AM modulator 63. The two amplitude modulated signals from the first and second AM modulators 62, 63 are summed by a summer 65 to a transmission signal which is then transferred to the transmitter unit 5 for output. Theprocedure is well known and will not further be explained.
The QAM signal will now be described in a common 8.times.8 or 16 state constellation referring to the first quadrant of a space diagram in FIG. 3. The output signal of the modulator 4 is expressed by a sum vector of two, A cos 2.pi.fct and B sin2.pi.fct, vectors 81, 82 which represent the two 90.degree.-out-of-phase carriers respectively. When the distal point of a sum vector from the zero point represents a signal point, the 16 QAM signal has 16 signal points determined by a combination offour horizontal amplitude values a.sub.1, a.sub.2, a.sub.3, a.sub.4 and four vertical amplitude values b.sub.1, b.sub.2, b.sub.3, b.sub.4. The first quadrant in FIG. 3 contains four signal points 83 at C.sub.11, 84 at C.sub.12, 85 at C.sub.22, and 86 atC.sub.21.
C.sub.11 is a sum vector of a vector 0-a.sub.1 and a vector 0-b.sub.1 and thus, expressed as C.sub.11=a.sub.1 cos 2.pi.fct-b.sub.1 sin 2.pi.fct=A cos (2.pi.fct+.pi./2).
It is now assumed that the distance between 0 and a.sub.1 in the orthogonal coordinates of FIG. 3 is A.sub.1, between a.sub.1 and a.sub.2 is A.sub.2, between 0 and b.sub.1 is B.sub.1, and between b.sub.1 and b.sub.2 is B.sub.2.
As shown in FIG. 4, the 16 signal points are allocated in a vector coordinate, in which each point represents a four-bit pattern thus to allow the transmission of four bit data per period or time slot.
FIG. 5 illustrates a common assignment of two-bit patterns to the 16 signal points.
When the distance between two adjacent signal points is great, it will be identified by the receiver with much ease. Hence, it is desired to space the signal points at greater intervals. If two particular signal points are allocated near toeach other, they are rarely distinguished and error rate will be increased. Therefore, it is most preferred to have the signal points spaced at equal intervals as shown in FIG. 5, in which the 16 QAM signal is defined by A.sub.1=A.sub.2/2.
The transmitter 1 of the embodiment is arranged to divide an input digital signal into a first, a second, and a third data or bit stream. The 16 signal points or groups of signal points are divided into four groups. Then, 4 two-bit patterns ofthe first data stream are assigned to the four signal point groups respectively, as shown in FIG. 6. More particularly, when the two-bit pattern of the first data stream is 11, one of four signal points of the first signal point group 91 in the firstquadrant is selected depending on the content of the second data stream for transmission. Similarly, when 01, one signal point of the second signal point group 92 in the second quadrant is selected and transmitted. When 00, one signal point of thethird signal point group 93 in the third quadrant is transmitted and when 10, one signal point of the fourth signal point group 94 in the fourth quadrant is transmitted. Also, 4 two-bit patterns in the second data stream of the 16 QAM signal, or e.g. 16four-bit patterns in the second data stream of a 64-state QAM signal, are assigned to four signal points or sub signal point groups of each of the four signal point groups 91, 92, 93, 94 respectively, as shown in FIG. 7. It should be understood that theassignment is symmetrical between any two quadrants. The assignment of the signal points to the four groups 91, 92, 93, 94 is determined by priority to the two-bit data of the first data stream. As the result, two-bit data of the first data stream andtwo-bit data of the second data stream can be transmitted independently. Also, the first data stream will be demodulated with the use of a common 4 PSK receiver having a given antenna sensitivity. If the antenna sensitivity is higher, a modified typeof the 16 QAM receiver of the present invention will intercept and demodulate both the first and second data stream with equal success.
FIG. 8 shows an example of the assignment of the first and second data streams in two-bit patterns.
When the low frequency band component of an HDTV video signal is assigned to the first data stream and the high frequency component to the second data stream, the 4 PSK receiver can produce an NTSC-level picture from the first data stream and the16- or 64-state QAM receiver can produce an HDTV picture from a composite reproduction signal of the first and second data streams.
Since the signal points are allocated at equal intervals, there is developed in the 4 PSK receiver a threshold distance between the coordinate axes and the shaded area of the first quadrant, as shown in FIG. 9. If the threshold distance isA.sub.T0, a PSK signal having an amplitude of A.sub.T0 will successfully be intercepted. However, the amplitude has to be increased to a three times greater value or 3A.sub.T0 for transmission of a 16 QAM signal while the threshold distance A.sub.T0being maintained. More particularly, the energy for transmitting the 16 QAM signal is needed nine times greater than that for sending the 4 PSK signal. Also, when the 4 PSK signal is transmitted in a 16 QAM mode, energy waste will be high andreproduction of a carrier signal will be troublesome. Above all, the energy available for satellite transmitting is not abundant but strictly limited to minimum use. Hence, no large-energy-consuming signal transmitting system will be put into practiceuntil more energy for satellite transmission is available. It is expected that a great number of the 4 PSK receivers are introduced into the market as digital TV broadcasting is soon in service. After introduction to the market, the 4 PSK receiverswill hardly be shifted to higher sensitivity models because a signal intercepting characteristic gap between the two, old and new, models is high. Therefore, the transmission of the 4 PSK signals must not be abandoned.
In this respect, a new system is desperately needed for transmitting the signal point data of a quasi 4 PSK signal in the 16 QAM mode with the use of less energy. Otherwise, the limited energy at a satellite station will degrade the entiretransmission system.
The present invention resides in a multiple signal level arrangement in which the four signal point groups 91, 92, 9394 are allocated at a greater distance from each other, as shown in FIG. 10, for minimizing the energy consumption required for16 QAM modulation of quasi 4 PSK signals.
For clarifying the relation between the signal receiving sensitivity and the transmitting energy, the arrangement of the digital transmitter 51 and the first receiver 23 will be described in more detail referring to FIG. 1. Both the digitaltransmitter 51 and the first receiver 23 are formed of known types for data transmission or video signal transmission e.g. in TV broadcasting service. As shown in FIG. 17, the digital transmitter 51 is a 4 PSK transmitter equivalent to the multiple-bitQAM transmitter 1, shown in FIG. 2, without AM modulation capability. In operation, an input signal is fed through an input unit 52 to a modulator 54 where it is divided by a modulator input 121 to two components. The two components are thentransferred to a first two-phase modulator circuit 122 for phase modulation of a base carrier and a second two-phase modulator circuit 123 for phase modulation of a carrier which is 90.degree. out of phase with the base carrier respectively. Twooutputs of the first and second two-phase modulator circuits 122, 123 are then summed by a summer 65 to a composite modulated signal which is further transmitted from a transmitter unit 55.
The resultant modulated signal is shown in the space diagram of FIG. 18.
It is known that the four signal points are allocated at equal distances for achieving optimum energy utilization. FIG. 18 illustrates an example where the four signal points 125, 126, 127, 128 represent 4 two-bit patterns, 11, 01, 00, and 10respectively. It is also desired for successful data transfer from the digital transmitter 51 to the first receiver 23 that the 4 PSK signal from the digital transmitter 51 has an amplitude of not less than a given level. More specifically, when theminimum amplitude of the 4 PSK signal needed for transmission from the digital transmitter 51 to the first receiver 23 of 4 PSK mode, or the distance between 0 and a.sub.1 in FIG. 18 is A.sub.T0, the first receiver 23 successfully intercept any 4 PSKsignal having an amplitude of more than A.sub.T0.
The first receiver 23 is arranged to receive at its small-diameter antenna 22 a desired or 4 PSK signal which is transmitted from the transmitter 1 or digital transmitter 51 respectively through the transponder 12 of the satellite 10 anddemodulate it with the demodulator 24. In more particular, the first receiver 23 is substantially designed for interception of a digital TV or data communications signal of 4 PSK or 2 PSK mode.
FIG. 19 is a block diagram of the first receiver 23 in which an input signal received by the antenna 22 from the satellite 12 is fed through the input unit 24 to a carrier reproducing circuit 131 where a carrier wave is demodulated and to a.pi./2 phase shifter 132 where a 90.degree. phase carrier wave is demodulated. Also, two 90.degree.-out-of-phase components of the input signal are detected by a first 133 and a second phase detector circuit 134 respectively and transferred to a first136 and a second discrimination/demodulation circuit 137 respectively. Two demodulated components from their respective discrimination/demodulation circuits 136 and 137, which have separately been discriminated at units of time slot by means of timingsignals from a timing wave extracting circuit 135, are fed to a first data stream reproducing unit 232 where they are summed to a first data stream signal which is then delivered as an output from the output unit 26.
The input signal to the first receiver 23 will now be explained in more detail referring to the vector diagram of FIG. 20. The 4 PSK signal received by the first receiver 23 from the digital transmitter 51 is expressed in an ideal form withouttransmission distortion and noise, using four signal points 151, 152, 153, 154 shown in FIG. 20.
In practice, the real four signal points appear in particular extended areas about the ideal signal positions 151, 152, 153, 154 respectively due to noise, amplitude distortion, and phase error developed during transmission. If one signal pointis unfavorably displaced from its original position, it will hardly be distinguished from its neighbor signal point and the error rate will thus be increased. As the error rate increases to a critical level, the reproduction of data becomes lessaccurate. For enabling the data reproduction at a maximum acceptable level of the error rate, the distance between any two signal points should be far enough to be distinguished from each other. If the distance is 1A.sub.R0, the signal point 151 of a 4PSK signal at close to a critical error level has to stay in a first discriminating area 155 denoted by the hatching of FIG. 20 and determined by |0-a.sub.R1|.gtoreq.A.sub.R0 and |0-b.sub.R1|.gtoreq.A.sub.R0. This allows the signal transmission systemto reproduce carrier waves and thus, demodulate a wanted signal. When the minimum radius of the antenna 22 is set to r.sub.0, the transmission signal of more than a given level can be intercepted by any receiver of the system. The amplitude of a 4 PSKsignal of the digital transmitter 51 shown in FIG. 18 is minimum at A.sub.T0 and thus, the minimum amplitude A.sub.R0 of a 4 PSK signal to be received by the first receiver 23 is determined equal to A.sub.T0. As the result, the first receiver 23 canintercept and demodulate the 4 PSK signal from the digital transmitter 51 at the maximum acceptable level of the error rate when the radius of the antenna 22 is more than r.sub.0. If the transmission signal is of modified 16- or 64-state QAM mode, thefirst receiver 23 may find it difficult to reproduce its carrier wave. For compensation, the signal points are increased to eight which are allocated at angles of (.pi./4+n.pi./2) as shown in.degree. FIG. 25(a) and its carrier wave will be reproducedby a 16.times. multiplication technique. Also, if the signal points are assigned to 16 locations at angles of n.pi./8 as shown in FIG. 25(b), the carrier of a quasi 4 PSK mode 16 QAM modulated signal can be reproduced with the carrier reproducingcircuit 131 which is modified for performing 16.times.frequency multiplication. At the time, the signal points in the transmitter 1 should be arranged to satisfy A.sub.1/(A.sub.1+A.sub.2)=tan(.pi./8).
Here, a case of receiving a QPSK signal will be considered. Similarly to the manner performed by the signal point modulating/changing circuit 67 in the transmitter shown in FIG. 2, it is also possible to modulate the positions of the signalpoints of the QPSK signal shown in FIG. 18 (amplitude-modulation, pulse-modulation, or the like). In this case, the signal point demodulating unit 138 in the first receiver 23 demodulates the position modulated or position changed signal. Thedemodulated signal is outputted together with the first data stream.
The 16 PSK signal of the transmitter 1 will now be explained referring to the vector diagram of FIG. 9. When the horizontal vector distance Al of the signal point 83 is greater than A.sub.T0 of the minimum amplitude of the 4 PSK signal of thedigital transmitter 51, the four signal points 83, 84, 85, 86 in the first quadrant of FIG. 9 stay in the shaded or first 4 PSK signal receivable area 87. When received by the first receiver 23, the four points of the signal appear in the firstdiscriminating area of the vector field shown in FIG. 20. Hence, any of the signal points 83, 84, 85, 86 of FIG. 9 can be translated into the signal level 151 of FIG. 20 by the first receiver 23 so that the two-bit pattern of 11 is assigned to acorresponding time slot. The two-bit pattern of 11 is identical to 11 of the first signal point group 91 or first data stream of a signal from the transmitter 1. Equally, the first data stream will be reproduced at the second, third, or fourthquadrant. As the result, the first receiver 23 reproduces two-bit data of the first data stream out of the plurality of data streams in a 16-, 32-, or 64-state QAM signal transmitted from the transmitter 1. The second and third data streams arecontained in four segments of the signal point group 91 and thus, will not affect on the demodulation of the first data stream. They may however affect the reproduction of a carrier wave and an adjustment, described later, will be needed.
If the transponder of a satellite supplies an abundance of energy, the forgoing technique of 16 to 64-state QAM mode transmission will be feasible. However, the transponder of the satellite in any existing satellite transmission system isstrictly limited in the power supply due to its compact size and the capability of solar batteries. If the transponder or satellite is increased in size thus weight, its launching cost will soar. This disadvantage will rarely be eliminated bytraditional techniques unless the cost of launching a satellite rocket is reduced to a considerable level. In the existing system, a common communications satellite provides as low as 20 W of power supply and a common broadcast satellite offers 100 W to200 W at best. For transmission of such a 4 PSK signal in the symmetrical 16-state QAM mode as shown in FIG. 9, the minimum signal point distance is needed 3A.sub.T0 as the 16 QAM amplitude is expressed by 2A.sub.1=A.sub.2. Thus, the energy needed forthe purpose is nine times greater than that for transmission of a common 4 PSK signal, in order to maintain compatibility. Also, any conventional satellite transponder can hardly provide a power for enabling such a small antenna of the 4 PSK firstreceiver to intercept a transmitted signal therefrom. For example, in the existing 40 W system, 360 W is needed for appropriate signal transmission and will be unrealistic in the respect of cost.
It would be understood that the symmetrical signal state QAM technique is most effective when the receivers equipped with the same sized antennas are employed corresponding to a given transmitting power. Another novel technique will however bepreferred for use with the receivers equipped with different sized antennas.
In more detail, while the 4 PSK signal can be intercepted by a common low cost receiver system having a small antenna, the 16 QAM signal is intended to be received by a high cost, high quality, multiple-bit modulating receiver system with amedium or large sized antenna which is designed for providing highly valuable services, e.g. HDTV entertainments, to a particular person who invests more money. This allows both 4 PSK and 16 QAM signals, if desired, with a 64 DMA, to be transmittedsimultaneously with the help of a small increase in the transmitting power.
For example, the transmitting power can be maintained low when the signal points are allocated at A.sub.1=A.sub.2 as shown in FIG. 10. The amplitude A(4) for transmission of 4 PSK data is expressed by a vector 96 equivalent to a square root of(A.sub.1+A.sub.2).sup.2+(B.sub.1+B.sub.2).sup.2. Then, |A(4)|.sup.2=A.sub.1.sup.2+B.sub.1.sup.2A.sub.T0.sup.2+A.sub.T0.sup.2=2A.- sub.T0.sup.2 |A(16)|.sup.2=(A.sub.1+A.sub.2).sup.2+(B.sub.1+B.sub.2).sup.2=4A.sub.T0.s- up.2+4A.sub.T0.sup.2=8.sub.T0.sup.2|A(16)|/|A(4)|=2
Accordingly, the 16 QAM signal can be transmitted at a two times greater amplitude and a four times greater transmitting energy than those needed for the 4 PSK signal. A modified 16 QAM signal according to the present invention will not bedemodulated by a common receiver designed for symmetrical, equally distanced signal point QAM. However, it can be demodulated with the second receiver 33 when two threshold A.sub.1 and A.sub.2 are predetermined to appropriate values. At FIG. 10, theminimum distance between two signal points in the first segment of the signal point group 91 is A.sub.1 and A.sub.2/2A.sub.1 is established as compared with the distance 2A.sub.1 of 4 PSK. Then, as A.sub.1=A.sub.2, the distance becomes 1/2. Thisexplains that the signal receiving sensitivity has to be two times greater for the same error rate and four times greater for the same signal level. For having a four times greater value of sensitivity, the radius r.sub.2 of the antenna 32 of the secondreceiver 33 has to be two times greater than the radius r.sub.1 of the antenna 22 of the first receiver 23 thus satisfying r.sub.2=2r.sub.1. For example, the antenna 32 of the second receiver 33 is 60 cm diameter when the antenna 22 of the firstreceiver 23 is 30 cm. In this manner, the second data stream representing the high frequency component of an HDTV will be carried on a signal channel and demodulated successfully. As the second receiver 33 intercepts the second data stream or a higherdata signal, its owner can enjoy a return of high investment. Hence, the second receiver 33 of a high price may be accepted. As the minimum energy for transmission of 4 PSK data is predetermined, the ratio n.sub.16 of modified 16 APSK transmittingenergy to 4 PSK transmitting energy will be calculated to the antenna radius r.sub.2 of the second receiver 33 using a ratio between A.sub.1 and A.sub.2 shown in FIG. 10.
In particular, n.sub.16 is expressed by ((A.sub.1+A.sub.2)/A.sub.1).sup.2 which is the minimum energy for transmission of 4 PSK data. As the signal point distance suited for modified 16 QAM interception is A.sub.2, the signal point distance for4 PSK interception is 2A.sub.1, and the signal point distance ratio is A.sub.2/2A.sub.1, the antenna radius r.sub.2 is determined as shown in FIG. 11, in which the curve 101 represents the relation between the transmitting energy ratio n.sub.16 and theradius r.sub.2 of the antenna 22 of the second receiver 23.
Also, the point 102 indicates transmission of common 16 QAM at the equal distance signal state mode where the transmitting energy is nine times greater and thus will no more be practical. As apparent from the graph of FIG. 11, the antenna radiusr.sub.2 of the second receiver 23 cannot be reduced further ever if n.sub.16 is increased more than 5 times. The transmitting energy at the satellite is limited to a small value and thus, n.sub.16 preferably stays not more than 5 times the value, asdenoted by the hatching of FIG. 11. The point 104 within the hatching area 103 indicates, for example, that the antenna radius r.sub.2 of a two times greater value is matched with a 4.times. value of the transmitting energy. Also, the point 105represents that the transmission energy should be doubled when r.sub.2 is about 5.times. greater. Those values are all within a feasible range.
The value of n.sub.16 not greater than 5.times. value is expressed using A.sub.1 and A.sub.2 as: n.sub.16=((A.sub.1+A.sub.2)/A.sub.1).sup.2.ltoreq.5 Hence, A.sub.2.ltoreq.1.23A.sub.1.
If the distance between any two signal point group segments shown in FIG. 10 is 2A(4) and the maximum amplitude is 2A(16), A(4) and A(16)-A(4) are proportional to A.sub.1 and A.sub.2 respectively. Hence, (A(16)).sup.2.ltoreq.5(A(14)).sup.2 isestablished.
The action of a modified 64 ASPK transmission will be described as the third receiver 43 can perform 64-state QAM demodulation.
FIG. 12 is a vector diagram in which each signal point group segment contains 16 signal points as compared with 4 signal points of FIG. 10. The first signal point group segment 91 in FIG. 12 has a 4.times.4 matrix of 16 signal points allocatedat equal intervals including the point 170. For providing compatibility with 4 PSK, A.sub.1.gtoreq.A.sub.T0 has to be satisfied. If the radius of the antenna 42 of the third receiver 43 is r.sub.3 and the transmitting energy is n.sub.64, the equationis expressed as: r.sub.3.sup.2={6.sup.2/(n-1)}r.sup.12
This relation between r.sub.3 and n of a 64 QAM signal is also shown in the graphic representation of FIG. 13.
It is understood that the signal point assignment shown in FIG. 12 allows the second receiver 33 to demodulate only two-bit patterns of 4 PSK data. Hence, it is desired for having compatibility between the first, second, and third receivers thatthe second receiver 33 is arranged capable of demodulating a modified 16 QAM form from the 64 QAM modulated signal.
The compatibility between the three discrete receivers can be implemented by three-level grouping of signal points, as illustrated in FIG. 14. The description will be made referring to the first quadrant in which the first signal point groupsegment 91 represents the two-bit pattern 11 of the first data stream.
In particular, a first sub segment 181 in the first signal point group segment 91 is assigned the two-bit pattern 11 of the second data stream. Equally, a second 182, a third 183, and a fourth sub segment 184 are assigned 01, 00, and 10 of thesame respectively. This assignment is identical to that shown in FIG. 7.
The signal point allocation of the third data stream will now be explained referring to the vector diagram of FIG. 15 which shows the first quadrant. As shown, the four signal points 201, 205, 209, 213 represent the two-bit pattern of 11, thesignal points 202, 206, 210, 214 represent 01, the signal points 203, 207, 211, 215 represent 00, and signal points 204, 208, 212, 216 represent 10. Accordingly, the two-bit patterns of the third data stream can be transmitted separately of the firstand second data streams. In other words, two-bit data of the three different signal levels can be transmitted respectively.
As understood, the present invention permits not only transmission of six-bit data but also interception of three, two-bit, four-bit, and six-bit, different bit length data with their respective receivers while the signal compatibility remainsbetween three levels.
The signal point allocation for providing compatibility between the three levels will be described.
As shown in FIG. 15, A.sub.1.gtoreq.A.sub.T0 is essential for allowing the first receiver 23 to receive the first data stream.
It is needed to space any two signal points from each other by such a distance that the sub segment signal points, e.g. 182, 183, 184, of the second data stream shown in FIG. 15 can be distinguished from the signal point 91 shown in FIG. 10.
FIG. 15 shows that they are spaced by 2/3A.sub.2. In this case, the distance between the two signal points 201 and 202 in the first sub segment 181 is A.sub.2/6. The transmitting energy needed for signal interception with the third receiver 43is now calculated. If the radius of the antenna 32 is r.sub.3 and the needed transmitting energy is n.sub.64 times the 4 PSK transmitting energy, the equation is expressed as: r.sub.3.sup.2=(12r.sub.1).sup.2/(n-1)
This relation is also denoted by the curve 221 in FIG. 16. For example, if the transmitting energy is 6 or 9 times greater than that for 4 PSK transmission at the point 223 or 222, the antenna 32 having a radius of 8.times. or 6.times. valuerespectively can intercept the first, second, and third data streams for demodulation. As the signal point distance of the second data stream is close to 2/3A.sub.2, the relation between r.sub.1 and r.sub.2 is expressed by:r.sub.2.sup.2=(3r.sub.1).sup.2/(n-1) Therefore, the antenna 32 of the second receiver 33 has to be a little bit increased in radius as denoted by the curve 223.
As understood, while the first and second data streams are transmitted trough a traditional satellite which provides a small signal transmitting energy, the third data stream can also be transmitted through a future satellite which provides agreater signal transmitting energy without interrupting the action of the first and second receivers 23, 33 or with no need of modification of the same and thus, both the compatibility and the advancement will highly be ensured.
The signal receiving action of the second receiver 33 will first be described. As compared with the first receiver 23 arranged for interception with a small radius r.sub.1 antenna and demodulation of the 4 PSK modulated signal of the digitaltransmitter 51 or the first data stream of the signal of the transmitter 1, the second receiver 33 is adopted for perfectly demodulating the 16 signal state two-bit data, shown in FIG. 10, or second data stream of the 16 QAM signal from the transmitter1. In total, four-bit data including also the first data stream can be demodulated. The ratio between A.sub.1 and A.sub.2 is however different in the two transmitters. The two different data are loaded to a demodulation controller 231 of the secondreceiver 33, shown in FIG. 21, which in turn supplies their respective threshold values to the demodulating circuit for AM demodulation.
The block diagram of the second receiver 33 in FIG. 21 is similar in basic construction to that of the first receiver 23 shown in FIG. 19. The difference is that the radius r.sub.2 of the antenna 32 is greater than r.sub.1 of the antenna 22. This allows the second receiver 33 to identify a signal component involving a smaller signal point distance. The demodulator 35 of the second receiver 33 also contains a first 232 and a second data stream reproducing unit 233 in addition to thedemodulation controller 231. There is provided a first discrimination/reproduction circuit 136 for AM demodulation of modified 16 QAM signals. As understood, each carrier is a four-bit signal having two, positive and negative, threshold values aboutthe zero level. As apparent from the vector diagram, of FIG. 22, the threshold values are varied depending on the transmitting energy of a transmitter since the transmitting signal of the embodiment is a modified 16 QAM signal. When the referencethreshold is TH.sub.16, it is determined by, as shown in FIG. 22: TH.sub.16=(A.sub.1+A.sub.2/2)/(A.sub.1+A.sub.2)
The various data for demodulation including A.sub.1 and A.sub.2 or TH.sub.16, and the value m for multiple-bit modulation are also transmitted from the transmitter 1 as carried in the first data stream. The demodulation controller 231 may bearranged for recovering such demodulation data through statistic process of the received signal.
A way of determining the shift factor A.sub.1/A.sub.2 will be described with reference to FIG. 26. A change of the shift factor A.sub.1/A.sub.2 causes a change of the threshold value. Increase of a difference of a value of A.sub.1/A.sub.2 setat the receiver side from a value of A.sub.1/A.sub.2 set at the transmitter side will increase the error rate. Referring to FIG. 26, the demodulated signal from the second data stream reproducing unit 233 may be fed back to the demodulation controller231 to change the shift factor A.sub.1/A.sub.2 in a direction to increase the error rate. By this arrangement, the third receiver 43 may not demodulate the shift factor A.sub.1/A.sub.2, so that the circuit construction can be simplified. Further, thetransmitter may not transmit the shift factor A.sub.1/A.sub.2, so that the transmission capacity can be increased. This technique can be applied also to the second receiver 33.
FIGS. 25(a) and 25(b) are views showing signal point allocations for the C-CDM signal points, wherein signal points are added by shifting in the polar coordinate direction (r, .theta.). The previously described C-CDM is characterized in that thesignal points are shifted in the rectangular coordinate direction, i.e. XY direction; therefore it is referred to as rectangular coordinate system C-CDM. Meanwhile, this C-CDM characterized by the shifting of signal points in the polar coordinatedirection, i.e. r, .theta. direction, is referred to as polar coordinate system C-CDM.
FIG. 25(a) shows the signal allocation of 8PS-APSK signals, wherein four signal points are added by shifting each of 4 QPSK signals in the radius r direction of the polar coordinate system. In this manner, the APSK of polar coordinate systemC-CDM having 8 signal points is obtained from the QPSK as shown in FIG. 25(a). As the pole is shifted in the polar coordinate system to add signal points in this APSK, it is referred to as shifted pole-APSK, i.e SP-APSK in the abbreviated form. In thiscase, coordinate value of the newly added four QPSK signals 85 are specified by using a shift factor S.sub.1 as shown in FIG. 139. Namely, 8PS-APSK signal points includes an ordinary QPSK signal points 83 (r.sub.0, .theta..sub.0) and a signal point((S.sub.1+1)r.sub.0, .theta..sub.0) obtained by shifting the signal point 83 in the radius r direction by an amount of S.sub.1r.sub.0. Thus, a 1-bit subchannel 2 is obtained in addition to a 2-bit subchannel 1 identical with the QPSK.
Furthermore, as shown in the constellation diagram of FIG. 140, eight new signal points, represented by coordinates (r.sub.0+S.sub.2r.sub.0, .theta..sub.0) and (r.sub.0+S.sub.1r.sub.0+S.sub.2r.sub.0, .theta..sub.0), can be added by shifting theeight signal points (r.sub.0, .theta..sub.0) and (r.sub.0+S.sub.1r.sub.0, .theta..sub.0) in the radius r direction. As this allows two kinds of allocations, a 1-bit subchannel is obtained and is referred to as 16PS-APSK which provides the 2-bitsubchannel 1, 1-bit subchannel 2, and 1-bit subchannel 3. As the 16-PS-APSK disposes the signal points on the lines of .theta.=1/4 (2n+1).pi., it allows the ordinary QPSK receiver explained with reference to FIG. 19 to reproduce the carrier wave todemodulate the first subchannel of 2-bit although the second subchannel cannot be demodulated. As described above, the C-CDM method of shifting the signal points in the polar coordinate direction is useful in expanding the capacity of information datatransmission while assuring compatibility to the PSK, especially to the QPSK receiver, a main receiver for the present satellite broadcast service. Therefore, without losing the first generation viewers of the satellite broadcast service based on thePSK, the broadcast service will advance to a second generation stage wherein the APSK will be used to increase transmittable information amount by use of the multi-level modulation while maintaining compatibility.
In FIG. 25(b), the signal points are allocated on the lines of .theta.=.pi./8. With this arrangement, the 16 PSK signal points are reduced or limited to 12 signal points, i.e. 3 signal points in each quadrant. With this limitation, these threesignal points in each quadrant are roughly regarded as one signal point for 4 QPSK signals. Therefore, this enables the QPSK receiver to reproduce the first subchannel in the same manner as in the previous embodiment.
More specifically, the signal points are disposed on the lines of .theta.=.pi./4, .theta.=.pi./4+.pi./8, and .theta.=.pi./4-.pi./8. In other words, the added signals are offset by an amount .+-..theta. in the angular direction of the polarcoordinate system from the QPSK signals disposed on the lines of .theta.=.pi./4. Since all the signals are in the range of .theta.=.pi./4.+-..pi./8, they can be regarded as one of QPSK signal points on the line of .theta.=.pi./4. Although the errorrate is lowered a little bit in this case, the QPSK receiver 23 shown in FIG. 19 can discriminate these points as four signal points angularly allocated. Thus, 2-bit data can be reproduced.
In case of the angular shift C-CDM, if signal points are disposed on the lines of .pi./n, the carrier wave reproduction circuit can reproduce the carrier wave by the use of an n-multiplier circuit in the same manner as in other embodiments. Ifthe signal points are not disposed on the lines of .pi./n, the carrier wave can be reproduced by transmitting several carrier information within a predetermined period in the same manner as in other embodiment.
Assuming that an angle between two signal points of the QPSK or 8-SP-APSK is 2.theta..sub.0 in the polar coordinate system and a first angular shift factor is P1, two signal points (r.sub.0, .theta..sub.0+P.sub.1.theta..sub.0) and (r.sub.0,.theta..sub.0-P.sub.1.theta..sub.0) are obtained by shifting the QPSK signal point in the angular .theta. direction by an amount .+-.P.sub.1.theta..sub.0. Thus, the number of signal points is doubled. Thus, the 1-bit subchannel 3 can be added and isreferred to as 8-SP-PSK of P=P1. If eight signal points are further added by shifting the 8-SP-PSK signals in the radius r direction by an amount S.sub.1r.sub.0, it will become possible to obtain 16-SP-APSK (P, S.sub.1 type) as shown in FIG. 142. Thesubchannels 1 and 2 can be reproduced by two 8PS-PSKs having the same phase with each other. Returning to FIG. 25(b), as the C-CDM based on the angular shift in the polar coordinate system can be applied to the PSK as shown in FIG. 141, this will beadopted to the first generation satellite broadcast service. However, if adopted to the second generation satellite broadcasting based on the APSK, this polar coordinate system C-CDM is inferior in that signal points in the same group cannot beuniformly spaced as shown in FIG. 142. Accordingly, utilization efficiency of electric power is worsened. On the other hand, the rectangular coordinate system C-CDM has good compatibility to the PSK.
The system shown in FIG. 25(b) is compatible with both the rectangular and polar coordinate systems. As the signal points are disposed on the angular lines of the 16 PSK, they can be demodulated by the 16 PSK. Furthermore, as the signal pointsare divided into groups, the QPSK receiver can be used for demodulation. Still further, as the signal points are also allocated to suit for the rectangular coordinate system, the demodulation will be performed by the 16-SRQAM. Consequently, thecompatibility between the rectangular coordinate system C-CDM and the polar coordinate system C-CDM can be assured in any of the QPSK, 16PSK, and 16-SRQAM.
The demodulation controller 231 has a memory 231a for storing therein different threshold values (i.e., the shift factors, the number of signal points, the synchronization rules, etc.) which correspond to different channels of TV broadcast. Whenreceiving one of the channels again, the values corresponding to the receiving channel will be read out of the memory to thereby stabilize the reception quickly.
If the demodulation data is lost, the demodulation of the second data stream will hardly be executed. This will be explained referring to a flow chart shown in FIG. 24.
Even if the demodulation data is not available, demodulation of the 4 PSK at Step 313 and of the first data stream at Step 301 can be implemented. At Step 302, the demodulation data retrieved by the first data stream reproducing unit 232 istransferred to the demodulation controller 231. If m is 4 or 2 at Step 303, the demodulation controller 231 triggers demodulation of 4 PSK or 2 PSK at Step 313. If not, the procedure moves to Step 310. At Step 305, two threshold values TH.sub.8 andTH.sub.16 are calculated. The threshold value TH.sub.16 for AM demodulation is fed at Step 306 from the demodulation controller 231 to both the first 136 and the second discrimination/reproduction circuit 137. Hence, demodulation of the modified 16 QAMsignal and reproduction of the second data stream can be carried out at Steps 307 and 315 respectively. At Step 308, the error rate is examined and if high, the procedure returns to Step 313 for repeating the 4 PSK demodulation.
As shown in FIG. 22, the signal points 85, 83, are aligned on a line at an angle of cos(.omega.t+n.pi./2) while 84 and 86 are off the line. Hence, the feedback of a second data stream transmitting carrier wave data from the second data streamreproducing unit 233 to a carrier reproducing circuit 131 is carried out so that no carrier needs to be extracted at the timing of the signal points 84 and 86.
The transmitter 1 is arranged to transmit carrier timing signals at intervals of a given time with the first data stream for the purpose of compensation for no demodulation of the second data stream. The carrier timing signal enables to identifythe signal points 83 and 85 of the first data stream regardless of demodulation of the second data stream. Hence, the reproduction of carrier wave can be triggered by the transmitting carrier data to the carrier reproducing circuit 131.
It is then examined at Step 304 of the flow chart of FIG. 24 whether m is 16 or not upon receipt of such a modified 64 QAM signal as shown in FIG. 23. At Step 310, it is also examined whether m is more than 64 or not. If it is determined atStep 311 that the received signal has no equal distance signal point constellation, the procedure goes to Step 312. The signal point distance TH.sub.64 of the modified 64 QAM signal is calculated from: TH.sub.64=(A.sub.1+A.sub.2/2)/(A.sub.1+A.sub.2)This calculation is equivalent to that of TH.sub.16 but its resultant distance between signal points is smaller.
If the signal point distance in the first sub segment 181 is A.sub.3, the distance between the first 181 and the second sub segment 182 is expressed by (A.sub.2-2A.sub.3). Then, the average distance is (A.sub.2-2A.sub.3)/(A.sub.1+A.sub.2) whichis designated as d.sub.64. When d.sub.64 is smaller than T.sub.2 which represents the signal point discrimination capability of the second receiver 33, any two signal points in the segment will hardly be distinguished from each other. This judgement isexecuted at Step 313. If dip is out of a permissive range, the procedure moves back to Step 313 for 4 PSK mode demodulation. If d.sub.64 is within the range, the procedure advances to Step 305 for allowing the demodulation of 16 QAM at Step 307. If itis determined at Step 308 that the error rate is too high, the procedure goes back to Step 313 for 4 PSK mode demodulation.
When the transmitter 1 supplied a modified 8 QAM signal such as shown in FIG. 25(a) in which all the signal points are at angles of cos(2.pi.f+n.pi./4), the carrier waves of the signal are lengthened to the same phase and will thus be reproducedwith much ease. At the time, two-bit data of the first data stream are demodulated with the 4-PSK receiver while one-bit data of the second data stream is demodulated with the second receiver 33 and the total of three-bit data can be reproduced.
The third receiver 43 will be described in more detail. FIG. 26 shows a block diagram of the third receiver 43 similar to that of the second receiver 33 in FIG. 21. The difference is that a third data stream reproducing unit 234 is added andalso, the discrimination/reproduction circuit has a capability of identifying eight-bit data. The antenna 42 of the third receiver 43 has a radius r.sub.3 greater than r.sub.2 thus allowing smaller distance state signals, e.g. 32- or 64-state QAMsignals, to be demodulated. For demodulation of the 64 QAM signal, the first discrimination/reproduction circuit 136 has to identify 8 digital levels of the detected signal in which seven different threshold levels are involved. As one of the thresholdvalues is zero, three are contained in the first quadrant.
FIG. 27 shows a space diagram of the signal in which the first quadrant contains three different threshold values.
As shown in FIG. 27, when the three normalized threshold values are TH1.sub.64, TH2.sub.64, and TH3.sub.64, they are expressed by: TH1.sub.64=(A.sub.1+A.sub.3/2)/(A.sub.1+A.sub.2) TH2.sub.64=(A.sub.1+A.sub.2/2)/(A.sub.1+A.sub.2) andTH3.sub.64=(A.sub.1+A.sub.2-A.sub.3/2)/(A.sub.1+A.sub.2)
Through AM demodulation of a phase detected signal using the three threshold values, the third data stream can be reproduced like the first and second data stream explained with FIG. 21. The third data stream contains e.g. four signal points201, 202, 203, 204 at the first sub segment 181 shown in FIG. 23 which represent 4 values of two-bit pattern. Hence, six digits or modified 64 QAM signals can be demodulated.
The demodulation controller 231 detects the value m, A.sub.1, A.sub.2, and A.sub.3 from the demodulation data contained in the first data stream demodulated at the first data stream reproducing unit 232 and calculates the three threshold valuesTH1.sub.64, TH2.sub.64, and TH3.sub.64, which are then fed to the first 136 and the second discrimination/reproduction circuit 137 so that the modified 64 QAM signal is demodulated with certainty. Also, if the demodulation data have been scrambled, themodified 64 QAM signal can be demodulated only with a specific or subscriber receiver. FIG. 28 is a flow chart showing the action of the demodulation controller 231 for modified 64 QAM signals. The difference from the flow chart for demodulation of 16QAM shown in FIG. 24 will be explained. The procedure moves from Step 304 to Step 320 where it is examined whether m=32 or not. If m=32, demodulation of 32 QAM signals is executed at Step 322. If not, the procedure moves to Step 321 where it isexamined whether m=64 or not. If yes, A.sub.3 is examined at Step 323. If A.sub.3 is smaller than a predetermined value, the procedure moves to Step 305 and the same sequence as of FIG. 24 is implemented. If it is judged at Step 323 that A.sub.3 isnot smaller than the predetermined value, the procedure goes to Step 324 where the threshold values are calculated. At Step 325, the calculated threshold values are fed to the first and second discrimination/reproduction circuits and at Step 326, thedemodulation of the modified 64 QAM signal is carried out. Then, the first, second, and third data streams are reproduced at Step 327. At Step 328, the error rate is examined. If the error rate is high, the procedure moves to Step 305 where the 16 QAMdemodulation is repeated and if low, the demodulation of the 64 QAM is continued.
The action of carrier wave reproduction needed for execution of a satisfactory demodulating procedure will now be described. The scope of the present invention includes reproduction of the first data stream of a modified 16 or 64 QAM signal withthe use of a 4 PSK receiver. However, a common 4 PSK receiver rarely reconstructs carrier waves, thus failing to perform a correct demodulation. For compensation, some arrangements are necessary at both the transmitter and receiver sides.
Two techniques for the compensation are provided according to the present invention. A first technique relates to transmission of signal points aligned at angles of (2n-1) .pi./4 at intervals of a given time. A second technique offerstransmission of signal points arranged at intervals of an angle of n.pi./8.
According to the first technique, the eight signal points including 83 and 85 are aligned at angles of .pi./4, 3.pi./4, 5.pi./4, and 7.pi./4, as shown in FIG. 38. In action, at least one of the eight signal points is transmitted during sync timeslot periods 452, 453, 454, 455 arranged at equal intervals of a time in a time slot gap 451 shown in the time chart of FIG. 38. Any desired signal points are transmitted during the other time slots. The transmitter 1 is also arranged to assign a datafor the time slot interval to the sync timing data region 499 of a sync data block, as shown in FIG. 41.
The content of a transmitting signal will be explained in more detail referring to FIG. 41. The time slot group 451 containing the sync time slots 452, 453, 454, 455 represents a unit data stream or block 491 carrying a data of Dn.
The sync time slots in the signal are arranged at equal intervals of a given time determined by the time slot interval or sync timing data. Hence, when the arrangement of the sync time slots is detected, reproduction of carrier waves will beexecuted slot by slot through extracting the sync timing data from their respective time slots. Such a sync timing data S is contained in a sync block 493 accompanied at the front end of a data frame 492, which is consisted of a number of the sync timeslots denoted by the hatching in FIG. 41. Accordingly, the data to be extracted for carrier wave reproduction are increased, thus allowing the 4 PSK receiver to reproduce desired carrier waves at higher accuracy and efficiency.
The sync block 493 comprises sync data regions 496, 497, 498, - - - containing sync data S1, S2, S3, - - - respectively which include unique words and demodulation data. The phase sync signal assignment region 499 is accompanied at the end ofthe sync block 493, which holds a data of I.sub.T including information about interval arrangement and assignment of the sync time slots.
The signal point data in the phase sync time slot has a particular phase and can thus be reproduced by the 4 PSK receiver. Accordingly, I.sub.T in the phase sync signal assignment region 499 can be retrieved without error thus ensuring thereproduction of carrier waves at accuracy.
As shown in FIG. 41, the sync block 493 is followed by a demodulation data block 501 which contains demodulation data about threshold voltages needed for demodulation of the modified multiple-bit QAM signal. This data is essential fordemodulation of the multiple-bit QAM signal and may preferably be contained in a region 502 which is a part of the sync block 493 for ease of retrieval.
FIG. 42 shows the assignment of signal data for transmission of burst form signals through a TDMA method.
The assignment is distinguished from that of FIG. 41 by the fact that a guard period 521 is inserted between any two adjacent Dn data blocks 491, 491 for interruption of the signal transmission. Also, each data block 491 is accompanied at frontend a sync region 522 thus forming a data block 492. During the sync region 522, the signal points at a phase of (2n-1).pi./4 are only transmitted. Accordingly, the carrier wave reproduction will be feasible with the 4 PSK receiver. More specifically,the sync signal and carrier waves can be reproduced through the TDMA method.
The carrier wave reproduction of the first receiver 23 shown in FIG. 19 will be explained in more detail referring to FIGS. 43 and 44. As shown in FIG. 43, an input signal is fed through the input unit 24 to a sync detector circuit 541 where itis sync detected. A demodulated signal from the sync detector 541 is transferred to an output circuit 542 for reproduction of the first data stream. A data of the phase sync signal assignment data region 499 (shown in FIG. 41) is retrieved with anextracting timing controller circuit 543 so that the timing of sync signals of (2n-1).pi./4 data can be acknowledged and transferred as a phase sync control pulse 561 shown in FIG. 44 to a carrier reproduction controlling circuit 544. Also, thedemodulated signal of the sync detector circuit 541 is fed to a frequency multiplier circuit 545 where it is 4.times. multiplied prior to transmitted to the carrier reproduction controlling circuit 544. The resultant signal denoted by 562 in FIG. 44contains a true phase data 563 and other data. As illustrated in a time chart 564 of FIG. 44, the phase sync time slots 452 carrying the (2n-1).pi./4 data are also contained at equal intervals. At the carrier reproducing controlling circuit 544, thesignal 562 is sampled by the phase sync control pulse 561 to produce a phase sample signal 565 which is then converted through sample-hold action to a phase signal 566. The phase signal 566 of the carrier reproduction controlling circuit 544 is fedacross a loop filter 546 to a VCO 547 where its relevant carrier wave is reproduced. The reproduced carrier is then sent to the sync detector circuit 541.
In this manner, the signal point data of the (2n-1).pi./4 phase denoted by the shaded areas in FIG. 39 is recovered and utilized so that a correct carrier wave can be reproduced by 4.times. or 16.times. frequency multiplication. Although aplurality of phases are reproduced at the time, the absolute phases of the carrier can be successfully be identified with the used of a unique word assigned to the sync region 496 shown in FIG. 41.
For transmission of a modified 64 QAM signal such as shown in FIG. 40, signal points in the phase sync areas 471 at the (2n-1).pi./4 phase denoted by the hatching are assigned to the sync time slots 452, 452b, etc. Its carrier can hardly bereproduced with a common 4 PSK receiver but successfully with the first receiver 23 of 4 PSK mode provided with the carrier reproducing circuit of the embodiment.
The foregoing carrier reproducing circuit is of COSTAS type. A carrier reproducing circuit of reverse modulation type will now be explained according to the embodiment.
FIG. 45 shows a reverse modulation type carrier reproducing circuit according to the present invention, in which a received signal is fed from the input unit 24 to a sync detector circuit 541 for producing a demodulated signal. Also, the inputsignal is delayed by a first delay circuit 591 to a delay signal. The delay signal is then transferred to a quadrature phase modulator circuit 592 where it is reverse demodulated by the demodulated signal from the sync detector circuit 541 to a carriersignal. The carrier signal is fed through a carrier reproduction controller circuit 544 to a phase comparator 593. A carrier wave produced by a VCO 547 is delayed by a second delay circuit 594 to a delay signal which is also fed to the phase comparator593. At the phase comparotor 594, the reverse demodulated carrier signal is compared in phase with the delay signal thus producing a phase difference signal. The phase difference signal sent through a loop filter 546 to the VCO 547 which in turnproduces a carrier wave arranged in phase with the received carrier wave. In the same manner as of the COSTAS carrier reproducing circuit shown in FIG. 43, an extracting timing controller circuit 543 performs sampling of signal points contained in thehatching areas of FIG. 39. Accordingly, the carrier wave of a 16 or 64 QAM signal can be reproduced with the 4 PSK demodulator of the first receiver 23.
The reproduction of a carrier wave by 16.times. frequency multiplication will be explained. The transmitter 1 shown in FIG. 1 is arranged to modulate and transmit a modified 16 QAM signal with assignment of its signal points at n.pi./8 phase asshown in FIG. 46. At the first receiver 23 shown in FIG. 19, the carrier wave can be reproduced with its COSTAS carrier reproduction controller circuit containing a 16.times. multiplier circuit 661 shown in FIG. 48. The signal points at each n.pi./8phase shown in FIG. 46 are processed at the first quadrant b the action of the 16.times. multiplier circuit 661, whereby the carrier will be reproduced by the combination of a loop filter 546 and a VCO 541. Also, the absolute phase may be determinedfrom 16 different phases by assigning a unique word to the sync region.
The arrangement of the 16.times. multiplier circuit will be explained referring to FIG. 48. A sum signal and a difference signal are produced from the demodulated signal by an adder circuit 662 and a subtractor circuit 663 respectively andthen, multiplied each other by a multiplier 664 to a cos 2.theta. signal. Also, a multiplier 665 produces a sin 2.theta. signal. The two signals are then multiplied by a multiplier 666 to a sin 4.theta. signal.
Similarly, a sin 8.theta. signal is produced from the two, sin 2.theta. and cos 2.theta., signals by the combination of an adder circuit 667, a subtracter circuit 668, and a multiplier 670. Furthermore, a sin 16.theta. signal is produced bythe combination of an adder circuit 671, a subtractor circuit 672, and a multiplier 673. Then, the 16.times. multiplication is completed.
Through the foregoing 16.times. multiplication, the carrier wave of all the signal points of the modified 16 QAM signal shown in FIG. 46 will successfully be reproduced without extracting particular signal points.
However, reproduction of the carrier wave of the modified 64 QAM signal shown in FIG. 47 can involve an increase in the error rate due to dislocation of some signal points from the sync areas 471.
Two techniques are known for compensation for the consequences. One is inhibiting transmission of the signal points dislocated from the sync areas. This causes the total amount of transmitted data to be reduced but allows the arrangement to befacilitated. The other is providing the sync time slots as described in FIG. 38. In more particular, the signal points in the n.pi./8 sync phase areas, e.g. 471 and 471a, are transmitted during the period of the corresponding sync time slots in thetime slot group 451. This triggers an accurate synchronizing action during the period thus minimizing phase error.
As now understood, the 16.times. multiplication allows the simple 4 PSK receiver to reproduce the carrier wave of a modified 16 or 64 QAM signal. Also, the insertion of the sync time slots causes the phasic accuracy to be increased during thereproduction of carrier waves from a modified 64 QAM signal.
As set forth above, the signal transmission system of the present invention is capable of transmitting a plurality of data on a single carrier wave simultaneously in the multiple signal level arrangement.
More specifically, three different level receivers which have discrete characteristics of signal intercepting sensitivity and demodulating capability are provided in relation to one single transmitter so that any one of them can be selecteddepending on a wanted data size to be demodulated which is proportional to the price. When the first receiver of low resolution quality and low price is acquired together with a small antenna, its owner can intercept and reproduce the first data streamof a transmission signal. When the second receiver of medium resolution quality and medium price is acquired together with a medium antenna, its owner can intercept and reproduce both the first and second data streams of the signal. When the thirdreceiver of high resolution quality and high price is acquired with a large antenna, its owner can intercept and reproduce all the first, second, and third data streams of the signal.
If the first receiver is a home-use digital satellite broadcast receiver of low price, it will overwhelmingly be welcome by a majority of viewers. The second receiver accompanied with the medium antenna costs more and will be accepted by notcommon viewers but particular people who want to enjoy HDTV services. The third receiver accompanied with the large antenna at least before the satellite output is increased, is not appropriate for home use and will possibly be used in relevantindustries. For example, the third data stream carrying super HDTV signals is transmitted via a satellite to subscriber cinemas which can thus play video tapes rather than traditional movie films and run movies business at low cost.
When the present invention is applied to a TV signal transmission service, three different quality pictures are carried on one signal channel wave and will offer compatibility with each other. Although the first embodiment refers to a 4 PSK, amodified 8 QAM, a modified 16 QAM, and a modified 64 QAM signal, other signals will also be employed with equal success including a 32 QAM, a 256 QAM, an 8 PSK, a 16 PSK, a 32 PSK signal. It would be understood that the present invention is not limitedto a satellite transmission system and will be applied to a terrestrial communications system or a cable transmission system.
Embodiment 2
A second embodiment of the present invention is featured in which the physical multi-level arrangement of the first embodiment is divided into small levels through e.g. discrimination in error correction capability, thus forming a logicmulti-level construction. In the first embodiment, each multi-level channel has different levels in the electric signal amplitude or physical demodulating capability. The second embodiment offers different levels in the logic reproduction capabilitysuch as error correction. For example, the data D.sub.1 in a multi-level channel is divided into two, D.sub.1-1 and D.sub.1-2, components and D.sub.1-1 is more increased in the error correction capability than D.sub.1-2 for discrimination. Accordingly,as the error detection and correction capability is different between D.sub.1-1, and D.sub.1-2 at demodulation, D.sub.1-1 can successfully be reproduced within a given error rate when the C/N level of an original transmitting signal is so low as disablethe reproduction of D.sub.1-2. This will be implemented using the logic multi-level arrangement.
More specifically, the logic multi-level arrangement consists of dividing data of a modulated multi-level channel and discriminating distances between error correction codes by mixing error correction codes with product codes for varying errorcorrection capability. Hence, a more multi-level signal can be transmitted.
In fact, a D.sub.1 channel is divided into two sub channels D.sub.1-1 and D.sub.1-2 and a D.sub.2 channel is divided into two sub channels D.sub.2-1 and D.sub.2-2.
This will be explained in more detail referring to FIG. 87 in which D.sub.1-1 is reproduced from a lowest C/N signal. If the C/N rate is d at minimum, three components D.sub.1-2, D.sub.2-1 and D.sub.2-2 cannot be reproduced while D.sub.1-1, isreproduced. If C/N is not less than c, D.sub.1-2 can also be reproduced. Equally, when C/N is b, D.sub.2-1 is reproduced and when C/N is a, D.sub.2-2 is reproduced. As the C/N rate increases, the reproducible signal levels are increased in number. The lower the C/N, the fewer the reproducible signal levels. This will be explained in the form of relation between transmitting distance and reproducible C/N value referring to FIG. 86. In common, the C/N value of a received signal is decreased inproportion to the distance of transmission as expressed by the real line 861 in FIG. 86. It is now assumed that the distance from a transmitter antenna to a receiver antenna is La when C/N=a, Lb when C/N=b, Lc when C/N=c, Ld when C/N=d, and Le whenC/N=e. If the distance from the transmitter antenna is greater than Ld, D.sub.1-1, can be reproduced as shown in FIG. 85 where the receivable area 862 is denoted by the hatching. In other words, D.sub.1-1, can be reproduced within a most extended area. Similarly, D.sub.1-2 can be reproduced in an area 863 when the distance is not more than Lc. In this area 863 containing the area 862, D.sub.1-1 can with no doubt be reproduced. In a small area 854, D.sub.2-1 can be reproduced and in a smallest area865, D.sub.2-2 can be reproduced. As understood, the different data levels of a channel can be reproduced corresponding to degrees of declination in the C/N rate. The logic multi-level arrangement of the signal transmission system of the presentinvention can provide the same effect as of a traditional analogue transmission system in which th amount of receivable data is gradually lowered as the C/N rate decreases.
The construction of the logic multi-level arrangement will be described in which there are provided two physical levels and two logic levels. FIG. 87 is a block diagram of a transmitter 1 which is substantially identical in construction to thatshown in FIG. 2 and described previously in the first embodiment and will no further be explained in detail. The only difference is that error correction code encoders are added as abbreviated to ECC encoders. The divider circuit 3 has four outputs1-1, 1-2, 2-1, and 2-2 through which four signals D.sub.1-1, D.sub.1-2, D.sub.2-1, and D.sub.2-2 divided from an input signal are delivered. The two signals D.sub.1-1 and D.sub.1-2 are fed to two, main and sub, ECC encoders 872a, 873a of a first ECCencoder 871a respectively for converting to error correction code forms.
The main ECC encoder 872a has a higher error correction capability than that of the sub ECC encoder 873a. Hence, D.sub.1-1 can be reproduced at a lower rate of C/N than D.sub.1-2 as apparent from the CN-level diagram of FIG. 85. Moreparticularly, the logic level of D.sub.1-1 is less affected by declination of the C/N than that of D.sub.1-2. After error correction code encoding, D.sub.1-1 and D.sub.1-1 are summed by a summer 874a to a D.sub.1 signal which is then transferred to themodulator 4. The other two signals D.sub.2-1 and D.sub.2-2 of the divider circuit 3 are error correction encoded by two, main and sub, ECC encoders 872b, 873b of a second ECC encoder 871b respectively and then, summed by a summer 874b to a D.sub.2signal which is transmitted to the modulator 4. The main ECC encoder 872b is higher in the error correction capability than the sub ECC encoder 873b. The modulator 4 in turn produces from the two, D.sub.1 and D.sub.2, input signals a multi-levelmodulated signal which is further transmitted from the transmitter unit 5. As understood, the output signal from the transmitter 1 has two physical levels D.sub.1 and D.sub.2 and also, four logic levels D.sub.1-1, D.sub.1-2, D.sub.2-1, and D.sub.2-2based on the two physical levels for providing different error correction capabilities.
The reception of such a multi-level signal will be explained. FIG. 88 is a block diagram of a second receiver 33 which is almost identical in construction to that shown in FIG. 21 and described in the first embodiment. The second receiver 33arranged for intercepting multi-level signals from the transmitter 1 shown in FIG. 87 further comprises a first 876a and a second ECC decoder 876b, in which the demodulation of QAM, or any of ASK, PSK, and FSK if desired, is executed.
As shown in FIG. 88, a receiver signal is demodulated by the demodulator 35 to the two, D.sub.1 and D.sub.2, signals which are then fed to two dividers 3a and 3b respectively where they are divided into four logic levels D.sub.1-1, D.sub.1-2,D.sub.2-1, and D2-2. The four signals are transferred to the first 876a and the second ECC decoder 876b in which D.sub.1-1 is error corrected by a main ECC decoder 877a, D.sub.1-2 by a sub ECC decoder 878a, D.sub.2-1 by a main ECC decoder 877b,D.sub.2-2 by a sub ECC decoder 878b before all sent to the summer 37. At the summer 37, the four, D.sub.1-1, D.sub.1-2, D.sub.2-1, and D.sub.2-2, error corrected signals are summed to a signal which is then delivered from the output unit 36.
Since D.sub.1-1 and D.sub.2-1 are higher in the error correction capability than D.sub.1-2 and D.sub.2-2 respectively, the error rate remains less than a given value although C/N is fairly low as shown in FIG. 85 and thus, an original signal willbe reproduced successfully.
The action of discriminating the error correction capability between the main ECC decoders 877a, 877b and the sub ECC decoders 878a, 878b will now be described in more detail. It is a good idea for having a difference in the error correctioncapability to use in the sub ECC decoder a common coding technique, e.g. Reed-Solomon or BCH method, having a standard code distance and in the main ECC decoder, another encoding technique in which the distance between correction codes is increased usingReed-Solomon codes, their product codes, or other long-length codes. A variety of known techniques for increasing the error correction code distance have been introduced and will no more explained. The present invention can be associated with any knowntechnique for having the logic multi-level arrangement.
The logic multi-level arrangement will be explained in conjunction with a diagram of FIG. 89 showing the relation between C/N and error rate after error correction. As shown, the straight line 881 represents D.sub.1-1 at the C/N and error raterelation and the line 882 represents D.sub.1-2 at same.
As the C/N rate of an input signal decreases, the error rate increases after error correction. If C/N is lower than a given value, the error rate exceeds a reference value Eth determined by the system design standards and no original data willnormally be reconstructed. When C/N is lowered to less than e, the D.sub.1 signal fails to be reproduced as expressed by the line 881 of D.sub.1-1 in FIG. 89. When e.ltoreq.C/N<d, D.sub.1-1 of the D.sub.1 signal exhibits a higher error rate than Ethand will not be reproduced.
When C/N is d at the point 885d, D.sub.1-1 having a higher error correction capability than D.sub.1-2 becomes not higher in the error rate than Eth and can be reproduced. At the time, the error rate of D.sub.1-2 remains higher than Eth aftererror correction and will no longer be reproduced.
When C/N is increased up to c at the point 885c, D.sub.1-2 becomes not higher in the error rate than Eth and can be reproduced. At the time, D.sub.2-1 and D.sub.2-2 remain in no demodulation state. After the C/N rate is increased further to b',the D.sub.2 signal becomes ready to be demodulated.
When C/N is increased to b at the point 885b, D.sub.2-1 of the D.sub.2 signal becomes not higher in the error rate than Eth and can be reproduced. At the time, the error rate of D.sub.2-2, remains higher than Eth and will not be reproduced. When C/N is increased up to a at the point 885a, D.sub.2-2 becomes not higher than Eth and can be reproduced.
As described above, the four different signal logic levels divided from two, D.sub.1 and D.sub.2, | | | |
