Internally coded TH--UWB--CDMA system and its performance evaluation

A new time-hopping ultrawideband (TH-UWB) CDMA scheme for indoor wireless communications is presented. In the proposed method, the duration of each bit is divided into Ns₁ frames, each one containing Ns₂ subframes. Two pseudorandom sequences are assigned to each user. During each bit interval, based on the output of a super-orthogonal encoder and the user´s first dedicated pseudorandom sequence, the transmitter selects one of the Ns₁ frames and then transmits Ns₂ narrow pulses in that frame, one in each of the Ns₂ subframes. The location of the pulse in each subframe is determined by the user´s second dedicated PN sequence. Four different detection techniques are considered at the receiver front end, namely thresholded hard decision, strict hard decision, soft decision and chip-based decision. Their performances are analysed and the results are compared with those of the previously introduced coded and uncoded TH-UWB systems. The results indicate that the proposed scheme has the best performance without requiring any extra bandwidth. It is also shown that the chip-based decoding technique works better in moderate and high SNRs while the soft decision method has better performance in low SNRs.