Code Hopping - Direct Sequence Spread Spectrum to Compensate for Intersymbol Interference in an Ultra-wideband System

We propose code hopping - direct sequence spread spectrum (CH-DSSS) with binary phase shift-keying (BPSK) modulation to compensate for intersymbol interference (ISI) in an Ultra-wideband system. The central idea is that code hopping (CH) affects ISI amplitudes that are produced by both the cross-and the auto-correlation properties of spreading codes for codewords; not just by the latter as occurs without CH. We also propose a low complexity CH pattern search algorithm to find good CH patterns. To evaluate the performance of the CH-DSSS system, an exact bit error rate (BER) expression is derived for a Rake receiver, and the computational speed to evaluate it is further increased by applying the Beaulieu series method (BSM) without sacrificing accuracy. Computational results for Gold and Walsh-Hadamard codes show that significant gains can be obtained by CH for both the average BER and the outage probability (e.g. a 6 dB gain in outage probability for a non-line of sight channel).