Impact of Chip Duty Factor on DS, TH and DS-TH UWB Systems in Realistic Environment

In this paper, the impact of chip duty factor (DF) on direct sequence (DS), time hopping (TH) and hybrid DS-TH ultra wideband (UWB) systems is investigated in realistic environments. Rake receivers are designed to perform energy capture (EC) on received UWB signals over multipath and multi-user environment in the presence of narrowband interference. It is found that by applying lower DF in the signal design, multipath resolvability can be increased and system performance can be improved. However, in contrary to the common belief, lower DF does not always contribute to performance improvement. On the other hand, it is observed that at extremely low DF, EC capability may be compromised, causing performance degradation. The optimum DF values for respective systems are determined and discussed in this paper. Additionally, the strength and tradeoff for DS, TH and DS-TH UWB systems employing varying DF are investigated and compared over multipath and multi-user environment. In a multipath environment, a selective Rake receiver with less than 10 fingers is found to be sufficient for energy capture. In a single user environment, DS-UWB system has the most superior performance, followed by DS-TH-UWB and TH-UWB systems. And in a multi-user environment, DS-TH-UWB is found to outperform the rest, followed by DS-UWB and TH-UWB systems. key words: UWB, chip duty factor, DS, TH, DS-TH, energy capture