Other

Mitsubishi Denki Kabushiki Kaisha

Sirikiat Ariyavisitakul

Susumu Yoshida

Tsutomu Takeuchi

Fumio Ikegami

Masaaki Sasada

Digital communication system

A digital communication system, in which digital information is represented by a quaternary information symbol (11, 01, 00, 10) and the double step phase shift, each step represented by (.pi./4, 3.pi./4, 5.pi./4, 7.pi./4), is performed per 1/2 time slot in correspondence to each information symbol, so that the number of phase shift per unit time in the case of the identical transmission rate can be decreased to 1/2, as compared with a .DELTA..theta./2-DSK system, and expansion of the bandwidth can be decreased to 1/2.

The present invention provides a digital communication system in which one time slot is divided into a first half section and a second half section and the carrier phase difference .theta. between each neighboring first half section is set to either (.pi., 0) with respect to a binary information symbol (1,0) or (0, .pi./2, .pi., 3/2.pi.) with respect to a quaternary information symbol (11, 01, 00, 10). In addition, the phase difference .psi. between the first half and the second half of any time slot is a constant value .psi..sub.0 (for example, .pi.rad) irrespective of the symbol, or .psi..sub.i determined with respect to a symbol (for example, +.pi./2 with respect to a symbol 1 or -.pi./2 with respect to a symbol 0). Therefore, an arbitrary complementary characteristic can be obtained when differentially demodulated in a multipath fading channel, irrespective of the amplitude characteristic of a demodulation signal.

The present invention provides a communication system which employs a signal whose carrier phase is shifted by a constant amount .DELTA..theta. per time slot in correspondence to each symbol (1 or 0) transmitted, and the phase shift is performed by .DELTA..theta./2 (or -.DELTA..theta./2) in the first 1/2 time slot and further by .DELTA..theta./2 (or -.DELTA..theta./2) in the second 1/2 time slot thereby to improve the bit error rate in multipath propagation.

Growing community of inventors

Kyoto, Japan

Sirikiat Ariyavisitakul