Spread spectrum communication system utilizing differential code shift keying

摘要

A spread spectrum data communication system utilizing a modulation technique referred to as differential code shift keying (DCSK) transmits data in the form of time shifts between consecutive circularly rotated waveforms of length T known as spreading waveforms. A plurality of bits are transmitted during each symbol period which is divided into a plurality of shift indexes with each shift index representing a particular bit pattern. The spreading waveform is rotated by an amount in accordance with the data to be transmitted or is conveyed in the difference between two consecutive rotations. A correlator employing a matched filter having a template of the chirp waveform pattern is used to detect the amount of rotation of the chirp within the received signal for each symbol. The received data is fed into a shift register and circularly rotated. For each rotation shift, the matched filter generates a correlation sum. The shift index chosen for each symbol corresponds to the shift index that yields the maximum correlation sum. Differential shift indexes are generated by subtracting the currently received shift index from the previously received shift index. The differential shift index is then decoded to yield the originally transmitted data.