Title:

Communication system

Document Type and Number:

United States Patent RE39927

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 first and 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.

Inventors:

Oshima, Mitsuaki (Kyoto, JP)
Sakashita, Seiji (Osaka, JP)

Plaque It!

CROSS-REFERENCE TO RELATED APPLICATIONS

~~This application is a continuation-in-part of application Ser. No. 07/857,627, filed Mar. 25, 1992, pending.~~ This is a reissue application of U.S. Pat. No. 5,600,672, issued Feb. 4, 1997, and a divisional application of reissue application No. 09/244,037, filed Feb. 4, 1999, which is also a reissue application of U.S. Pat. No. 5,600,672, issued Feb. 4, 1997 which is a Continuation-In-Part of application Ser. No. 07/857,627, filed Mar. 25, 1992 now abandoned. Further reissue divisional applications have been filed, all of which are reissues of U.S. Pat. No. 5,600,672. These further applications are: 09/677,421, filed Oct. 5, 2000; 09/678,014, filed Oct. 5, 2000; 09/677,420, filed Oct. 5, 2000; 09/680,177, filed Oct. 5, 2000; 09/680,176, filed Oct. 5, 2000; 09/686,467, filed Oct. 12, 2000; 09/686,463, filed Oct. 12, 2000; 09/686,466, filed Oct. 12, 2000; 09/688,028, filed Oct. 12, 2000; 09/686,464, filed Oct. 12, 2000; 09/686,465, filed Oct. 12, 2000; 09/666,012, filed Sep. 19, 2000; 09/667,525, filed Sep. 21, 2000; 09/667,438, filed Sep. 21, 2000; 09/668,068, filed Sep. 25, 2000; 09/669,916, filed Sep. 25, 2000; 09/672,948, filed Sep. 29, 2000; 09/672,946, filed Sep. 29, 2000; 09/672,947, filed Sep. 29, 2000; 10/133,347, filed Apr. 29, 2002; 10/133,364, filed Apr. 29, 2002; 10/692,469, filed Oct. 24, 2003; 10/693,526, filed Oct. 27, 2003; 10/635,468, filed Aug. 7, 2003; 10/690,297, filed Oct. 27, 2003; 10/860,666, filed Jun. 4, 2004; 10/782,411, filed Feb. 20, 2004; 10/783,588, filed Feb. 23, 2004; 10/773,811, filed Feb. 9, 2004; 10/882,126, filed Jun. 30, 2004; 10/885,572, filed Jul. 7, 2004; 10/911,680, filed Aug. 5, 2004; and 11/038,006, filed Jan. 19, 2006.

Claims:

What is claimed is:

1. A signal transmission and reception apparatus for transmitting and receiving an n-level VSB signal, the apparatus comprising a transmitter and a receiver; said transmitter comprising: a compression means for compressing an input video signal to a digital video compression signal; an error correction encoding means for adding an error correction code to the digital video compression signal to produce an error correction coded signal; a modulation means for modulating the error correction coded signal to an n-level VSB modulation signal, said modulation means comprising a means for allocating code points along a uniaxial modulation coordinate system, and a filter means having a plurality of coefficients which are a series of impulse responses defined by plotting timebase responses to the VSB modulation signal along the in-phase axis and its orthogonal axis for filtering a series of said code points allocated along the uniaxial modulation coordinate system; and a transmission means for transmitting the modulation signal, and said receiver comprising: a means for receiving a transmitted n-level VSB modulation signal; a demodulation means for demodulating the received n-level VSB modulation signal into a digital reception signal; an error correction means for error correcting the digital reception signal to obtain an error-corrected digital signal; and an expanded means for expanding the error-corrected digital signal to obtain a video output signal.

2. ~~A transmission and reception apparatus according to claim 1, wherein the error correction means comprises a trellis decoder.~~

3. ~~A transmission and reception apparatus according to claim 2, wherein the trellis decoder is associated with a plurality of memories which each holds a number of selectable correct codes.~~

4. A transmission and reception apparatus according to claim 1, wherein the digital reception signal is divided into a high priority signal and a low priority signal, and wherein said error correction means comprises a high code gain first error correction means and a low code gain second error correction means, said first error correction means correcting the high priority signal.

5. ~~A transmission and reception apparatus according to claim 4, wherein the high priority signal carries the address data for all data.~~

6. ~~A transmission and reception apparatus according to claim 4, wherein the first error correction means comprises a trellis decoder.~~

7. ~~A signal transmission and reception apparatus according to claim 1, further comprising a band path filtering means for filtering the n-level VSB modulation signal before being transmitted.~~

8. A signal transmission and reception apparatus for transmitting an n-level VSB signal, comprising: a compression means for compressing an input video signal into a digital video compression signal; an error correction encoding means for adding an error correction code to the digital video compression signal to produce an error correction coded signal; a modulation means for modulating the error correction coded signal to an n-level VSB modulation signal, said modulation means comprising a means for allocating code points along a uniaxial modulation coordinate system, and a filter means having a plurality of coefficients which are a series of impulse responses defined by plotting timebase responses to the VSB modulation signal along the in-phase axis and its orthogonal axis for filtering a series of said code points allocated along the uniaxial modulation coordinate system; and a transmission means for transmitting the modulation signal.

9. ~~A signal transmission apparatus according to claim 8, further comprising a band path filtering means for filtering the n-level VSB modulation signal before being transmitted.~~

10. A signal receiving apparatus comprising: a tuner for receiving a transmission signal containing a digital modulation signal and an analog modulation signal and for selecting the digital modulation signal using a local oscillation signal; an interference detecting means for detecting interference caused by the analog modulation signal from the digital modulation signal selected by the tuner; a notch filter means responsive to the interference detected by the interference detecting means for removing a carrier of the analog modulation signal in a same frequency band as a frequency band of the digital modulation signal; an error ratio calculating means for calculating a bit error ratio of an output of the notch filter means; and an automatic frequency correcting means for changing a frequency of the local oscillation signal of the tuner according to a level of the interference detected by the interference detecting means and the bit error ratio calculated by the error ratio calculating means to compensate for a frequency offset of the carrier of the analog modulated signal.

11. ~~A signal receiving apparatus according to claim 10, wherein the digital modulation signal is an n-level VSB modulation signal.~~

12. A signal receiving apparatus comprising: a tuner for receiving a transmission signal containing at least one of a VSB modulated signal and a QAM modulated signal and for selecting one of the VSB modulated signal and the QAM modulated signal to obtain a selected signal; an analog-to-digital converter for converting the selected signal into a series of digital codes; a transversal filter provided on an orthogonal axis for suppressing a transmission distortion of the series of digital codes with respect to both orthogonal axes to obtain a series of filtered digital codes allocated on the orthogonal axes; a carrier recovery means for phase-compensating a carrier of the filtered digital codes allocated on the orthogonal axis outputted from the transversal filter; and a control means for producing a control signal to extract detected codes at equal time intervals from the VSB modulated signal; a clock reproducing means for phase synchronizing entire codes of the QAM modulated signal where the selected signal is the QAM modulated signal and for phase synchronizing codes of the VSB modulated signal intermittently at predetermined intervals when the selected signal is the VSB modulated signal; and a decoding means for decoding an output of the carrier recovery means.

13. A signal transmission system comprising a transmission apparatus and a receiving apparatus, said transmission apparatus comprising: a mapper operable to map a data stream to produce a mapped signal; a selector operable to select between tap coefficients for a VSB modulation mode and tap coefficients for a QAM modulation mode; first and second FIR filters operable to filter the mapped signal to produce a VSB modulated signal when said selector selects the tap coefficients for the VSB modulation mode and to produce a QAM modulated signal when said selector selects the tap coefficients for the QAM modulation mode; and a transmitter operable to transmit at least one of the VSB modulated signal and the QAM modulated signal; and said receiving apparatus comprising: a receiver operable to receive a transmitted signal; a selector operable to select between tap coefficients for a VSB demodulation mode and tap coefficients for a QAM demodulation mode; first and second FIR filters operable to filter, when said selector selects the tap coefficients for the VSB demodulation mode, the VSB modulated signal to produce a mapped signal of the VSB modulated signal, and to filter, when said selector selects the tap coefficients for the QAM demodulation mode, the QAM modulated signal to produce a mapped signal of the QAM modulated signal; and a de-mapper operable to de-map at least one of the mapped signal of the VSB modulated signal and the mapped signal of the QAM modulated signal to produce the data stream.

14. A signal transmission apparatus comprising: a mapper operable to map a data stream to produce a mapped signal; a selector operable to select between tap coefficients for a VSB modulation mode and tap coefficients for a QAM modulation mode; first and second FIR filters operable to filter the mapped signal to produce a VSB modulated signal when said selector selects the tap coefficients for the VSB modulation mode and to produce a QAM modulated signal when said selector selects the tap coefficients for the QAM modulation mode; and a transmitter operable to transmit at least one of the VSB modulated signal and the QAM modulated signal.

15. A signal receiving apparatus comprising: a receiver operable to receive a signal of at least one of a VSB modulated signal and a QAM modulated signal; a selector operable to select between tap coefficients for a VSB demodulation mode and tap coefficients for a QAM demodulation mode; first and second FIR filters operable to filter, when said selector selects the tap coefficients for the VSB demodulation mode, the VSB modulated signal to produce a mapped signal of the VSB modulated signal, and to filter, when said selector selects the tap coefficients for the QAM demodulation mode, the QAM modulated signal to produce a mapped signal of the QAM modulated signal; and a de-mapper operable to de-map the mapped signal of VSB modulated signal to produce a data stream of the VSB modulated signal, and de-map the mapped signal of the QAM modulated signal to produce a data stream of the QAM modulated signal.

16. A signal transmission and receiving method comprising a transmission method and a receiving method, said transmission method comprising: mapping a data stream to produce a mapped signal; selecting between tap coefficients for a VSB modulation mode and tap coefficients for a QAM modulation mode; filtering, by first and second FIR filters, the mapped signal to produce a VSB modulated signal when the tap coefficients for the VSB modulation mode are selected, and to produce a QAM modulated signal when the tap coefficients for the QAM modulation mode are selected; and transmitting the modulated signal; and said receiving method comprising: receiving a transmitted signal; selecting between tap coefficients for a VSB demodulation mode and tap coefficients for a QAM demodulation mode; filtering, by first and second FIR filters, when the tap coefficients for the VSB demodulation mode are selected, the VSB modulated signal to produce a mapped signal of the VSB modulated signal, and filtering, when the tap coefficients for the QAM demodulation mode are selected, the QAM modulated signal to produce a mapped signal of the QAM modulated signal; and de-mapping the mapped signal to produce the data stream of the VSB modulated signal or the data stream of the QAM modulated signal.

17. A signal transmission method comprising: mapping a data stream to produce a mapped signal; selecting between tap coefficients for a VSB modulation mode and tap coefficients for a QAM modulation mode; filtering, by first and second FIR filters, the mapped signal to produce a VSB modulated signal when the tap coefficients for the VSB modulation mode are selected, and to produce a QAM modulated signal when the tap coefficients for the QAM modulation mode are selected; and transmitting at least one of the VSB modulated signal and the QAM modulated signal.

18. A signal receiving method comprising: receiving a signal of at least one of a VSB modulated signal and a QAM modulated signal; selecting between tap coefficients for a VSB demodulation mode and tap coefficients for a QAM demodulation mode; filtering, by first and second FIR filters, when the tap coefficients for the VSB demodulation mode are selected, the VSB modulated signal to produce a mapped signal of the VSB modulated signal, and filtering, when the tap coefficients for the QAM demodulation mode are selected, the QAM modulated signal to produce a mapped signal of the QAM modulated signal; and de-mapping the mapped signal of the VSB modulated signal to produce a data stream of the VSB modulated signal, and de-mapping the mapped signal of the QAM modulated signal to produce a data stream of the QAM modulated signal.

Description:

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication system for transmission and 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 systems are in particular use for transmission between TV stations. They will soon be utilized for terrestrial and/or satellite broadcast service in every country of the world.

The TV broadcast systems including HDTV, PCM music, FAX, and other information services are now demanded to increase desired data in quantity and quality for satisfying millions of sophisticated viewers. In particular, the data has to be increased 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 signal transmission 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 compatible with existing TV receivers and displays. More particularly, 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 both the existing and advanced receivers.

It is understood than 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 compatibility to allow the existing receivers to receive transmissions.

The expansion capability and compatible performance of the 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 ~~muitiplexed~~ multiplexed by time division modulation of 4 PSK and transmitted on 4 to 20 channels while HDTV signals are carried on a signal channel. Another digital 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 the channel by a conventional manner, thus occupying a band of frequencies equivalent to the same channels of NTSC signals. This causes the corresponding NTSC channels to be unavailable during the 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 its service area due to structural obstacles, geographical inconveniences, or signal interference from a neighbor station. When the TV signal is an analogue ~~from~~ form , it can be intercepted more or less at such signal attenuating regions although its reproduced picture is low in quality. If the 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 newly introduced HDTV broadcast services, particularly via satellite and also, for minimizing signal attenuating or shadow region of its service area on the ~~grounds~~ ground .

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 and reception. For example, if applied to a QAM signal, the communication 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 using an 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 signal points 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 vector field. 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 if is first demodulated through dividing p signal points in a signal space diagram into n signal point groups. Then, the second data stream is 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 n values 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 sized antenna 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 of an 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 simultaneous 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 ~~point,~~ points in a signal vector field through modulation of a plurality of out-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 values and 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 signal points of each 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 output circuit, 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 of which p/n values are assigned to p/n signal points of each signal point group respectively. For example, a transmitter produces a modified m-bit QAM signal of which first, second, and third data streams, each carrying n values, are assigned to relevant signal point groups with a modulator. The signal can be intercepted and the first data stream only reproduced by a first receiver, both the first and second data streams can be reproduced by a second receiver, and all the first, second, and third streams can be reproduced by a third receiver.

More particularly, a receiver capable of demodulation of n-bit data can reproduce n bits from a multiple-bit modulated carrier wave carrying m-bit data where m>n, thus allowing the communication system to have compatibility and capability of 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 distance of 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, on the ground, the 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 relationship between antenna radius r ₂and 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 relationship between antenna radius r ₃and 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 relationship between A ₁and A ₂of the modified 64 QAM signal of the first embodiment;

FIG. 16 is a graph diagram showing the relationship between antenna radius r ₂and r ₃and transmission energy ratio n ₁₆and n ₆₄respectively 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 flowchart showing the operation of the first embodiment;

FIG. 25 (a) and 25 (b) are vector diagrams respectively showing an 8 and a 16 QAM signal of the first embodiment;

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 flowchart showing another the operation 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 ₁, D ₂, and D ₃signals according to the third embodiment;

FIG. 35 is an explanatory view showing another time multiplexing of D ₁, D ₂, and D ₃signals according to the third embodiment;

FIG. 36 is an explanatory view showing a further time multiplexing of D ₁, D ₂, and D ₃signals 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× multiplication of the third embodiment;

FIG. 49 is an explanatory view showing a time multiplexing of D _V1, D _H1, D _V2, D _H2, D _V3, and D _H3signals according to the third embodiment;

FIG. 50 is an explanatory view showing a TDMA time multiplexing of D _V1, D _H1, D _V2, D _H2, D _V3, and D _H3signals according to the third embodiment;

FIG. 51 is an explanatory view showing another TDMA time multiplexing of the D _V1, D _H1, D _V2, D _H2, D _V3, and D _H3signals 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 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 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 and FIGS. 59 (c) and 59 (d) are diagrams respectively showing the slice levels of the modulated 4 ASK signal in subchannels 1 and 2 ;

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 shows a 4- and 8-level VSB transmitter according to the fifth embodiment of the invention;

FIG. 62 (a) is a wave spectrum diagram of the ASK signal, i.e., a multi-value VSB signal before filtering, in the fifth embodiment of the invention and FIG. 62 (b) is a wave spectrum diagram showing the characteristics of the filtered VSB signal;

FIG. 63 is a block diagram of a 4-, 8-, and 16-level VSB receiver in the fifth embodiment of the invention;

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 (a) is an 8-level VSB constellation map in the fifth and sixth embodiments of the invention;

FIG. 68 (b) is an 8-level VSB constellation map in the fifth and sixth embodiments of the invention;

FIG. 68 (c) is an 8-level VSB signal-time waveform diagram in the fifth and sixth embodiments of the invention;

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 ₁signal of the fifth embodiment;

FIG. 83 is a graphic diagram showing the relationship 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 relationship between C/N and level according to the second embodiment;

FIG. 86 is a graphic diagram showing the relationship between C/N and transmission distance according to the second embodiment;

FIG. 87 is a block diagram of a ~~transmission~~ transmitter 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 relationship 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 the 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 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 relationship between C/N and error ~~rake~~ rate according to the third embodiment;

FIG. 102 is a graphic diagram showing the relationship between C/N and error rate according to the third embodiment;

FIG. 103 is a graphic diagram showing the relationship between shift distance n and C/N needed for transmission according to the third embodiment;

FIG. 104 is a graphic diagram showing the relationship between shift distance n and C/N needed for transmission according to the third embodiment;

FIG. 105 is a graphic diagram showing the relationship 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 threshold values 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 (a) is a block diagram of a trellis encoder (ratio ½) in embodiments 2 , 4 , and 5 ,

FIG. 128 (b) is a block diagram of a trellis encoder (ratio ⅔) in embodiments 2 , 4 , and 5 ,

FIG. 128 (c) is a block diagram of a trellis encoder (ratio ¾) in embodiments 2 , 4 , and 5 ,

FIG. 128 (d) is a block diagram of a trellis decoder (ratio ½) in embodiments 2 , 4 , and 5 ,

FIG. 128 (e) is a block diagram of a trellis decoder (ratio ⅔) in embodiments 2 , 4 , and 5 ,

FIG. 128 (f) is a block diagram of a trellis decoder (ratio ¾) in embodiments 2 , 4 , and 5 ;

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 relationship 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~~ traveling 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 relationship 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 relationship 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 multilevel OFDM according to the ninth embodiment;

FIG. 147 is a diagram showing subchannel assignment of a two-layer signal transmission system, weighted electric power according to the ninth embodiment;

FIG. 148 is a diagram showing relationship 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 the relationship between multipath delay time and transfer rate according to the ninth embodiment, wherein a three-layer signal transmission effective to multipath is realized; and

FIG. 151 is a diagram showing the relationship between multipath delay time and C/N ratio according to the ninth embodiment, wherein two-dimensional, matrix type, multilayer broadcast service can be realized by combining the GTW-OFDM and the C-CDM (or the CSW-OFDM).

FIG. 152 is a timing chart of a 3-level hierarchical television signal at each time slot when GTW-OFDM of the ninth embodiment is combined with C-CDM (or CSW-OFDM);

FIG. 153 shows the relationship between the multipath signal delay time, C/N ratio, and transmission rate when GTW-OFDM of the ninth embodiment is combined with C-CDM (or CSW-OFDM), and is used to describe the hierarchical broadcasting method using three-dimensional matrix structure;

FIGS. 154A-C together form a frequency distribution graph of power weight OFDM in the ninth embodiment;

FIG. 155 shows the position on the time axis of a 3-level hierarchical television signal at each time slot when guard time-OFDM of the ninth embodiment is combined with C-CDM;

FIG. 156 is a block diagram of the transmitter and the receiver in the fourth and fifth embodiments of the invention;

FIG. 157 is a block diagram of the transmitter and the receiver in the fourth and fifth embodiments of the invention;

FIG. 158 is a block diagram of the transmitter and the receiver in the fourth and fifth embodiments of the invention;

FIG. 159 (a) is a signal point positioning diagram in 16-level VSB in the fifth embodiment of the invention;

FIG. 159 (b) is a signal point positioning (8-level VSB) diagram in 16-level VSB in the fifth embodiment of the invention;

FIG. 159 (c) is a signal point positioning (4-level VSB) diagram in 16-level VSB in the fifth embodiment of the invention;

FIG. 159 (d) is a signal point positioning (16-level VSB) diagram in 16-level VSB in the fifth embodiment of the invention;

FIG. 160 (a) is a block diagram of an ECC encoder in the fifth and sixth embodiments of the invention;

FIG. 160 (b) is a block diagram of an ECC decoder in the fifth and sixth embodiments of the invention;

FIG. 161 is an overall block diagram of a VSB receiver in the fifth embodiment of the invention;

FIG. 162 is a block diagram of a the receiver in the fifth embodiment of the invention;

FIG. 163 is a graph of the error rate and C/N ratio curve in 4-level VSB and TC 8-level VSB in the fourth embodiment of the invention;

FIG. 164 is an error rate curve of subchannel 1 and subchannel 2 in 4-level VSB and TC-8-level VSB in the fourth embodiment of the invention;

FIG. 165 (a) is a block diagram of the Reed-Solomon encoder in the second, fourth, and fifth embodiments of the invention;

FIG. 165 (b) is a block diagram of the Reed-Solomon decoder in the second, fourth, and fifth embodiments of the invention;

FIG. 166 is a flowchart of Reed-Solomon error correction and operation in the second, fourth and fifth embodiments of the invention;

FIG. 167 is a block diagram of the deinterleaver in the second, third, fourth, fifth and sixth embodiments of the invention;

FIG. 168 (a) is an interleave/deinterleave table for the second, third, fourth, and fifth embodiments of the invention;

FIG. 168 (b) shows the interleave distance in the second, third, fourth, and fifth embodiments of the invention;

FIG. 169 is a comparison redundancy in 4-level VSB, 8-level VSB, and 16-level VSB in the fifth embodiment of the invention;

FIG. 170 is a block diagram of a television receiver for receiving the high priority signal of the second, third, fourth, and fifth embodiments of the invention;

FIG. 171 is a block diagram of the receiver and transmitter in the second, third, fourth, and fifth embodiments of the invention;

FIG. 172 is a block diagram of the receiver and transmitter in the second, third, fourth, and fifth embodiments of the invention; and

FIG. 173 is a block diagram of an ASK magnetic recording and reproducing apparatus according to the sixth embodiment of the invention;

FIG. 174 is a block diagram showing a circuitry arrangement of QAM/VSB compatible modulator for multi-level transmission according to Embodiment 5 .

FIG. 175 is a block diagram showing another circuitry arrangement of the QAM/VSB modulator for multi-level transmission according to Embodiment 5 .

FIG. 176 illustrates a third modification of the QAM/VSB modulator of Embodiment 5 .

FIG. 177 is a block diagram showing a Trellis decoder in the demodulator of Embodiment 5 .

FIG. 178 is a block diagram of a receiver of Embodiment 5 for interception of VSB multi-level transmitted signals emitted in the air.

FIG. 179 is illustrates another arrangement of the QAM/VSB compatible receiver of Embodiment 5 .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

EMBODIMENT 1

One embodiment of the present invention will be described referring to the relevant drawings.

In the preferred embodiment of the invention both the transmission apparatus, which comprises a transmitter for transmitting a digital HDTV signal or other digital signal and a receiver for receiving the transmitted signal, and the recording and reproducing apparatus, which records the digital HDTV signal or other digital signal on a magnetic tape or other recording medium and reproduces the recorded signal from said medium, are described.

It should be noted, however, that the configuration, operation, and principle of the digital modulator and demodulator, error correction encoder and decoder, and the encoder and decoder for image coding the HDTV signal are common to the transmission apparatus and the recording and reproducing apparatus, and apply essentially the same technologies. Therefore, to more concisely describe each embodiment, the block diagrams for either the transmission apparatus or the recording and reproducing apparatus are referenced in the description of each embodiment. In addition, the configuration of each embodiment of the invention can be achieved by means of any multi-value digital modulation method, e.g., QAM, ASK and PSK, positioning signal points in a constellation, and for brevity the embodiments of the present invention are described using only one modulation method. FIG. 1 shows the entire arrangement of a signal transmission system according to the first embodiment of the present invention. A transmitter 1 comprises an input unit 2 , divider circuit 3 , a modulator 4 , and a transmitter unit 5 . In operation, each input multiplex signal is divided by the divider circuit 3 into three groups, a first data stream D 1 , a second data stream and, a third data stream D 3 , which are then modulated by the modulator 4 before being transmitted from the transmitter unit 5 . The modulated signal is sent up from an antenna 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 31 , 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 24 to 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, combined by a mixer 37 into a single data stream which is then transmitted further from an output unit 36 .

The third receiver 43 allows all of 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, combined by a mixer 47 into a single data stream which 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 different sizes. 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 into low, high, and 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 for simultaneous reproduction of medium, high, and super high resolution TV images respectively.

The NTSC TV signal is intercepted by a receiver accompanied by a small antenna or demodulation of small-sized data; the HDTV signal is intercepted by a receiver accompanied by a medium antenna for demodulation of medium-sized data, and the super HDTV signal is intercepted by a receiver accompanied by 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 TV broadcasting service is fed to a digital transmitter 51 where it is received by an input unit 52 and modulated by a ~~demodulator~~ modulator 54 before being transmitted further from a transmitter unit 55 . The ~~demodulated~~ modulated signal is then sent up from an antenna 56 through 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 into the original first data stream signal. Similarly, the same modulated digital signal can be intercepted and demodulated by the second receiver 33 or third receiver 43 into 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 data stream. The three different frequency band signals are fed to a modulator input 61 of the modulator 4 . Here, a signal point shifting circuit 67 shifts the positions of the signal points according to an externally given signal. The modulator 4 is arranged for amplitude modulation on two 90°-out-of phase carriers respectively which are then combined into a multiple QAM signal. More specifically, the signal from the modulator input 61 is fed to both a first AM modulator 64 62 and a second AM modulator 63 . Also, a carrier wave of cos(2πfct) produced by a carrier generator 64 is directly fed to the first AM modulator 64 62 and also, to a π/2 phase shifter 66 where it is 90° shifted in phase to a sin(2πfct) form prior to being transmitted to the second AM modulator 63 . The two amplitude modulated signals from the first and second AM modulators 64 62 , 63 are combined by a summer 65 into a transmission signal which is then transferred to the transmitter unit 5 for output. The procedure is well known and will not be further explained.

The QAM signal will now be described in a common 4×4 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, Acos2πfct and ~~Bcos~~ Bsin 2πfct, vectors 81 and 82 which respectively represent the two 90°-out-of-phase carriers. 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 of four horizontal amplitude values a ₁, a ₂, a ₃, and a ₄and four vertical amplitude values b ₁, b ₂, and b ₃, and b ₄. The first quadrant in FIG. 3 contains four signal points 83 at c ₁₁, 84 at c ₁₂, 85 at c ₂₂, and 86 at c ₂₁.

c ₁₁is a sum vector of a vector 0 -a ₁and a vector 0 -b ₁and thus, expressed as c ₁₁=a ₁cos2πfct−b ₁sin2πfct=Acos (2πfct+dπ/2).

It is now assumed that the distance between 0 and a ₁in the orthogonal coordinates of FIG. 3 is A ₁, between a ₁and a ₂is A ₂, between 0 and b ₁is B ₁, and between b ₁and b ₂is B 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 desirable to space the signal points at greater intervals. If two particular signal points are allocated near to each other, they are rarely distinguished and the error rate will be increased. Therefore, it is most preferable to have the signal points spaced at equal intervals as shown in FIG. 5, in which the 16 QAM signal is defined by A ₁= 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 of the 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 first quadrant 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 the third signal point group 93 in the third quadrant is transmitted and when 10 , one signal point of the fourth signal point group 94 is the fourth quadrant is transmitted. Also, 4 two-bit patterns in the second data stream of the 16 QAM signal, or e.g. 16 four-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 , and 94 respectively, as shown in FIG. 7 . It should be understood that the assignment is symmetrical between any two quadrants. The assignment of the signal points to the four groups 91 , 92 , 93 , and 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 and two-bit data of the second data stream can be transmitted independently. Also, the first data stream will be demodulated by using a common 4 PSK receiver having a given antenna sensitivity. If the antenna sensitivity is higher, a modified type of the 16 QAM receiver of the present invention will intercept and demodulate both the first and second data ~~stream~~ streams 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 the 16- 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 is A _TO, a PSK signal having an amplitude of A _TOwill successfully be intercepted. However, the amplitude has to be increased to a three times greater value or 3 A _TOfor transmission of a 16 QAM signal while the threshold distance A _TOis maintained. More particularly, the energy needed for transmitting the 16 QAM signal is 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 and reproduction 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 practice until more energy for satellite transmission is available. It is expected that a great number of the 4 PSK receivers will be introduced into the market as digital TV broadcasting is placed in service. After introduction to the market, the 4 PSK receivers will hardly be shifted to higher sensitivity models because a signal intercepting chacteristic 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 using less energy. Otherwise, the limited energy at a satellite station will degrade the entire transmission system.

The present invention resides in a multiple signal level arrangement in which the four signal point groups 91 , 92 , 93 , and 94 are allocated at a greater distance from each other, as shown in FIG. 10, for minimizing the energy consumption required for 16 QAM modulation of quasi 4 PSK signals.

For clearing the relationship 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 digital transmitter 51 and the first receiver ~~2 3~~ 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-bit QAM 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 into two components. The two components are then transferred 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° out of phase with the base carrier respectively. The two outputs of the first and second two-phase modulator circuits 122 and 123 are then combined by a summer 65 into 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 ~~allcated~~ allocated at equal distances for achieving optimum energy utilization. FIG. 18 illustrates an example where the four signal points 125 , 126 , 127 , and 128 represent 4 two-bit patterns, 11 , 01 , 00 , and 10 respectively. It is also desirable 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 the minimum 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 ₁in FIG. 18 is A _TO, the first receiver 23 must successfully intercept any 4 PSK signal having an amplitude of more than A _TO.

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 and demodulate it with the demodulator 24 25 . In more detail, 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 10 is fed through the input unit 24 to a carrier reproducing circuit 131 where a carrier wave is demodulated and to a π/2 phase shifter 132 where a 90° phase carrier wave is demodulated. Also, two 90°-out-of-phase components of the input signal are respectively detected by a first phase detector circuit 133 and a second phase detector circuit 134 and are respectively transferred to first 136 and second discrimination/demodulation circuits 136 and 137 . 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 timing signals from a timing wave extracting circuit 135 , are fed to a first data stream reproducing unit 232 where they are combined into 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 without transmission distortion and noise, using four signal points 151 , 152 , 153 , and 154 , as shown in FIG. 20 .

In practice, the real four signal points appear in particular extended areas about the ideal signal positions 151 , 152 , 153 , and 154 respectively due to noise, amplitude distortion, and phase error developed during transmission. If one signal point is unfavorably displaced from its original position, it will hardly be distinguished from its neighboring signal point and the error rate will thus be increased. As the error rate increases to a critical level, the reproduction of data becomes less accurate. 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 1 A _R0, the signal point 151 of a 4 PSK signal close to a critical error level has to stay in a first discrimination area 155 denoted by the hatching of FIG. 20 and determined by | 0 -a _R1|>A _R0and | 0 -b _R1|>A _R0. This allows the signal transmission system to reproduce carrier waves and thus, demodulate a wanted signal. When the minimum radius of the antenna 22 is set to r ₀, the transmission signal of more than a given level can be intercepted by any receiver of the system. The amplitude of a 4 PSK signal of the digital transmitter 51 shown in FIG. 18 is minimum at A _T0and thus, the minimum amplitude A _R0of a 4 PSK signal to be received by the first receiver 23 is determined to be equal to A _T0. As a result, the first receiver 23 can intercept 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 ₀. If the transmission signal is of a modified 16- or 64-state QAM mode, the first 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 (π/4+nπ/2) as shown in FIG. 25 (a) and its carrier wave will be reproduced by a 16× multiplication technique. Also, if the signal points are assigned to 16 locations at angles of nπ/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 reproducing circuit 131 which is modified for performing 16× frequency multiplication. At the time, the signal points in the transmitter 1 should be arranged to satisfy A ₁/(A ₁+A ₂)=tan(π/8).

Here, a case of receiving a QPSK signal will be considered. Similarly to the manner performed by the signal point setting circuit 67 in the transmitter shown in FIG. 2, it is also possible to modulate the positions of the signal points 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. The demodulated 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 A ₁of the signal point 83 is greater than A _TOof the minimum amplitude of the 4 PSK signal of the digital transmitter 51 , the four signal points 83 , 84 , 85 , and 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 first discriminating area of the vector field shown in FIG. 20 . Hence, any of the signal points 83 , 84 , 85 , and 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 a corresponding 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 fourth quadrant. 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 are contained in four segments of the signal point group 91 and thus, will not affect 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 is strictly 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 and thus weight, its launching cost will soar. This disadvantage will rarely be eliminated by traditional techniques unless the cost of launching a satellite rocket is reduced by to a considerable level. In the existing system, a common communications satellite provides as low as 20 W of power and a common broadcast satellite offers 100 W to 200 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~~ needed is 3 A _T0as the 16 QAM amplitude is expressed by 2 A ₁=A ₂. Thus, the energy needed for the 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 first receiver 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 with respect to 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 be preferred for use with 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 a medium or large sized antenna which is designed fro providing highly valuable services, e.g. HDTV entertainment, to a particular person who invests more money. This allows both 4 PSK and 16 QAM signals, if desired, with a 64 ~~DMA~~ QAM , to be transmitted simultaneously 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 ₁=A ₂as shown in FIG. 10 . The amplitude A( 4 ) for transmission of 4 PSK data is expressed by a vector 96 equivalent to the square root of (A ₁+A ₂) ²+(B ₁+B ₂) ². Then,
|A(4)| ₂=A ₁ ²+B ₁ ²=A ² _T0+A ² _T0=2A ² _T0
|A(16)| ₂=(A ₁+A ₂) ²+(B ₁+B ₂) ²=4A ² _T0+4A ² _T0=8A _T0
|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 be demodulated 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 values A ₁and A ₂are preset to appropriate values. In FIG. 10, the minimum distance between two signal points in the first segment of the signal point group 91 is A ₁and A ₂/ 2 A ₁is established as compared with the distance 2 A ₁of 4 PSK. Then, as A ₁=A ₂, the distance becomes ½. This explains 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 ₂of the antenna 32 of the second receiver 33 has to be two times greater than the radius r ₁of the antenna 22 of the first receiver 23 thus satisfying r ₂= 2 r ₁. For example, the antenna 32 of the second receiver 33 is 60 cm diameter when the antenna 22 if the first receiver 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 higher data signal, its owner can enjoy a of high return of investment ~~return~~ . 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 ₁₆of modified 16 APSK transmitting energy to 4 PSK transmitting energy will be calculated according to the antenna radius r ₂of the second receiver 33 using a ratio between A ₁and A ₂shown in FIG. 10 .

In particular, n ₁₆is expressed by ((A ₁+A ₂)/A ₁) ²which is the minimum energy for transmission of 4 PSK data. As the signal point distance suited for modified 16 QAM interception is A ₂, ~~The~~ the signal point distance for 4 PSK interception is 2 A ₁, and the signal point distance ratio is A ₂/ 2 A ₁, the antenna radius r ₂is determined as shown in FIG. 11, in which the curve 101 represents the relationship between the transmitting energy ratio n ₁₆and the radius r ₂of 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 radius r ₂of the second receiver 23 cannot be reduced further even if n ₁₆is increased more than 5 times.

The transmitting energy at the satellite is limited to a small value and thus, n ₁₆preferably stays not more than 5 times the value, as denoted by the hatching of FIG. 11 . The point 104 within the hatching area 103 indicates, for example, that the antenna radius r ₂of a two times greater value is matched with a 4× value of the transmitting energy. Also, the point 105 represents that the transmission energy should be doubled when r ₂is about 5× greater. Those values are all within a feasible range.

The value of n ₁₆not greater than 5× value is expressed using A ₁and A ₂as:
n ₁₆=((A ₁+A ₂)/A ₁) ²<5
Hence, A ₂<1.23A ₁.

If the distance between any two signal point group segments shown in FIG. 10 is 2 A( 4 ) and the maximum amplitude is 2 A( <

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