Physical-Layer Modeling of UWB Interference Effects

Abstract : The NETEX program is focused initially on understanding the effects of interference from ultra-wideband (UWB) transmitters on legacy military radio receivers, nearly all of which are narrowband (NB) relative to the UWB signal, which can have a bandwidth on the order of 1 GHz. The purpose of this report is to document a set of mathematical models which have been developed to analyze the impact of UWB signals on NB receivers. This analysis work is being done in parallel with a UWB interference testing program being conducted by other parties. There are two main components to the work presented here. The first is a detailed analysis of the power spectral density (PSD) of the UWB signal, which shows the distribution of the UWB transmit power over frequency. The PSD is determined by (1) the spectrum of the basic UWB pulse; and (2) pulse position modulation/dithering and pulse amplitude modulation. A clear understanding of the PSD is important, because the main factor that determines the impact on a NB receiver is the total average UWB interference power within the receiver passband. This is demonstrated by the second main component of the report, which is a set of models describing the impact of UWB interference on several different representative receiver types, both digital and analog. The PSD gives the average power-per-Hz as a function of frequency for the UWB signal. The UWB PSD models developed here allow the PSD to be computed analytically for a wide range of different UWB signal types, and include the effects of pulse-position modulation (PPM), random or periodic pseudo-random dithering of the pulse position, modulation or random (or pseudo-random) coding of the pulse amplitude, modulation symbols that include multiple UWB frames (giving integration gain), and modulation of the actual pulse repetition frequency (PRF) by either a periodic PRF-modulating signal or by a random process such as a data signal.