Cyclic Code Shift Keying: A Low Probability of Intercept Communication Technique
SPACE AND NAVAL WARFARE SYSTEMS CENTER SAN DIEGO CA
Pagination or Media Count:
A low probability of intercept LPI, or low probability of detection LPD communication technique known as cyclic code shift keying CCSK is described. We discuss the basic concepts of CCSK and describe a system based on the use of random or pseudorandom codes for biphase modulation. We use simulation to show that the bit error rate BER for CCSK can be closely estimated by using existing equations that apply to M-ary orthogonal signaling MOS. Also, we show that significantly fewer computations are required for CCSK than for MOS when the number of bits per symbol is the same. We show that using biphase modulation results in waveforms that have a large time-bandwidth product and very low input signal-to-noise ratio SNR and thus inherently have an LPI by a radiometer. We evaluate detection by a radiometer and show that LPI can be achieved by using codes of lengths great than about 212 i.e., by transmitting more than about 12 bits per symbol. Results illustrate the effect that the CCSK symbol length and error probability, and the radiometer integration time and probability of false alarm PFA, have on detection by a radiometer. We describe a variation of CCSK called truncated CCSK TCCSK. In this system, the code on length 2k is cyclically shifted, then truncated and transmitted. Although shortened, the truncated code still represents k bits of information, thus leading to an increased data rate. We evaluate radiometer detection of TCCSK and it is shown that tile probability of detection is increased compared with the detection of CCSK.
- Radio Communications