An Internally Coded Time-Hopping Spread-Time CDMA Scheme for UWB Systems and its Performance Analysis

We consider an internally coded multiple access technique for ultra wide-band systems which combines time-hopping (TH) and spread-time (ST) techniques using a super-orthogonal encoder. In this method, the duration of each bit is divided into N
_s
frames. The outputs of a super-orthogonal encoder and a PN sequence specify the frame number, in which the data is transmitted in spread-time CDMA form using the second PN sequence. We consider soft decision before Viterbi decoding at the receiver. We obtain the performance of the proposed method. We also consider the uncoded ST-CDMA system and compare its performance with our method. The results indicate that our method has much more better performance while it has the same bandwidth as the uncoded ST-CDMA system