We propose to apply chip interleaving and iterative detection to self-encoded multiple access (SEMA) communications. In SEMA, the spreading code is obtained from user bit information itself without using a pseudo noise code generator. The proposed scheme exploits the inherent diversity in self encoded spread spectrum signals. Chip interleaving not only increases the diversity gain, but also enhances the performance of iterative detection. We employ user-mask and interference cancellation to decouple self-encoded multiuser signals. This paper describes the proposed scheme and analyzes its performance. The analytical and simulation results show that the proposed system can achieve a 3 dB power gain and possess a diversity gain that can yield a significant performance improvement in both Rayleigh and multipath fading channels.Index Terms: Chip-interleaving, interference cancellation, iterative detection, self-encoded multiple access (SEMA), spread spectrum.

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In this paper, we apply iterative detection to typical time hopping (TH) pulse position modulation (PPM) ultra wideband (UWB) spread spectrum systems. Unlike a typical TH-PPM UWB which employs repetition code, the proposed system uses self-encoded code which is updated by data rab = I T covered data user information itself. To take advantage of self-encoded spread spectrum, we apply iterative detection to the TH-PPM UWB T T system. By means of simulation, we will investigate the bit error T T rate (BER) performance of the proposed system in additive white gaussian noise (AWGN) channels and also fading channels. TWe observe a significant BER performance improvement over conventional TH-PPM UWB systems.