Effects of hopping codes in TH-SS UWB signals

In this paper, we study the hopping code effects on the time-hopping spread-spectrum (TH-SS) ultra-wideband (UWB) signals to address the achievability of the desired signal properties. Specifically, we investigate the code features leading to the low averaged spectral power level and good receiver performance. For the former concern, an explicit relation between the hopping code and the power spectral density (PSD) is derived. Then two practical propositions about the averaged spectral power level are developed. For the receiver performance, we discuss the code features leading to low noise, narrowband interference (NBI). and multiple-access interference (MAI) by virtue of the filter interpretation of the RAKE combiner which is conventionally adopted in a UWB receiver. Notably, our work suggests focusing on finding/constructing those hopping sub-codes with proper spectrum properties instead of the entire codes.