Code hopping: Direct sequence spread spectrum to compensate for intersymbol interference in an ultra-wideband system

Ultra-Wideband (UWB) has been attracting many researchers for its potential to support a high bit rate in a short range wireless communication system. In order to achieve the high bit rate, a short spreading code is often preferred to a long spreading code in a Direct Sequence Spread Spectrum (DSSS) UWB system. As the symbol period is decreased to support the high bit rate, intersymbol interference (ISI) gets severe in the multipath fading channel. In this thesis, we propose Code Hopping - Direct Sequence Spread Spectrum (CH-DSSS) to compensate for ISI in a UWB system. We also propose a CH pattern search algorithm to find a suboptimal hopping pattern.;To evaluate the performance of the proposed CH-DSSS system, we derive an exact bit error rate (BER) expression in the CH-DSSS system using a Rake receiver for the multipath fading channel. Then, we increase a computational speed by applying the Beaulieu series method (BSM) without sacrificing accuracy. The performance of the CH-DSSS system is evaluated with the Intel channel model that has been adopted by the IEEE 802.15.3a task group. We generate 7000 channels and compute average BER and outage probability.;Computational results show that significant gains are obtained by CH both in the average BER and in the outage probability. Especially, CH with the Gold sequence of length 31 is found to be very good for a non-line of sight (NLOS) channel. Our most important result is for the Gold sequence with 10 Rake fingers at 193.1 Mbps in the NLOS channel, where CH is shown to achieve a 6 dB gain for the outage probability over the system that uses a single optimized sequence all the time.