Code shift keyed spread spectrum for ocean acoustic telemetry

摘要

Code shift keyed spread spectrum (CSK-SS) transmits information bysending symbols consisting of various phases of a finite length spreadspectrum code. In its rudimentary form, a symbol interval of length T ispartioned into N chips, modulated with cyclic shift of an underlyinglength N code sequence. The information is demodulated using an FFTmatched filter, which realizes periodic correlation. The informationrate of the basic system is (1/T)log₂N bits/second. Wediscuss the application of CSK-SS to acoustic telemetry, with an aimtowards improving the spectral efficiency by overlaying multiple codes.The demodulator is a mismatched filter (equalizer) that trades off SNRfor a reduction in the ISI self-noise caused by the overlay. In thisway, increased spectral efficiency is possible at the expense of poorerperformance in the presence of channel impairments such as phase offsetand timing jitter