Various multirate time-hopping UWB systems and performance evaluation

We consider multirate time-hopping ultra-wideband (TH-UWB) communication systems where each user can have several multirate services. We investigate both the constant spreading factor scheme, which uses multicode, and variable spreading factor scheme, which uses constant chip time and variable frame number. For multicode structure, we consider two methods. In the first, one kind of signature (PN) code is used to distinguish users and their diverse services alike. Whereas in the second one different users and different services of the same user are distinguished through two kinds of signature codes, namely PN code and Walsh code, respectively. For the variable spreading factor scheme, one signature code is assigned to each user and different services are differentiated by time multiplexing. We evaluate and compare the performance of these multirate TH-UWB systems in the uncoded and coded schemes. Our results indicate that while the multicode structure with two kinds of signature codes outperforms the other structures in the uncoded scheme, the structure with one kind of signature code (PN code) performs the best for the coded scheme. We also show that even though the coded scheme considered requires the same bandwidth as the uncoded scheme, the coded scheme significantly outperforms the uncoded scheme of all three methods.