A low-rate code-spread and chip-interleaved time-hopping UWB system

We consider a code-spread and chip-interleaved time-hopping (TH) multiple-access scheme for multiuser ultra-wideband (UWB) communications. In such a system, each user´s chip sequence is interleaved by a user-specific distinct random interleaver, and the receiver is a low-complexity chip-level iterative multiuser detector (MUD) which performs simple Rake-type combining to collect the energy dispersed in multipath UWB channels. To further reduce the receiver complexity, time reversal (TR), a transmitter preprocessing technique, is also considered. When power control is employed along with TR, a single-tap receiver can be utilized which offers a desirable bit error rate (BER) performance with a significantly reduced sampling rate. Furthermore, the zigzag Hadamard (ZH) code is proposed as the low-rate code for both channel coding and spreading in the code-spread TH-UWB system. With its capacity-approaching capability and low encoding/decoding complexity, the parallel concatenated ZH code is a promising coding scheme for UWB applications.