Analysis of the performance of asynchronous sequence segment keying communication systems

The application of CDMA-type techniques to an HF environment with time-invariable path delays is considered. For an ideal CDMA system, a set of completely uncorrelated sequences with ideal impulsive autocorrelation functions should be used. In a conventional CDMA system, the out-of-phase crosscorrelation functions (CCFs) of the sequences are quasi-ideal rather than exactly zero; therefore, the superimposed CCF components will lead to co-channel interference which increases with the number of users. This progressive degradation will eventually limit the number of users. Sequence segment keying (SSK) provides a solution to this problem by reducing cochannel interference to zero at the expense of nonideal autocorrelations, which are not a significant disadvantage in practice as shown by Quirke and Darnell (see 5th IMA Int. Conf. on Cryptograph & Coding, 1995)