Communication system

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.

Description

[0001]This application is a continuation-in-part of application Ser. No. 07 / 857,627, filed Mar. 25, 1992.[0002]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, 200...

AI Technical Summary

Benefits of technology

[0015]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 groundsground.

[0019]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.

[0021]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.

[0022]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.

Problems solved by technology

However, the TV broadcast service is a public business and cannot go further without considering the interests and benefits of viewers.

This causes the corresponding NTSC channels to be unavailable during the transmission of the HDTV signal.

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 fromform, it can be intercepted more or less at such signal attenuating regions although its reproduced picture is low in quality.

This disadvantage is critically hostile to the development of any digital TV system.

Images