Front-End Narrowband Interference Mitigation for DS-UWB Receiver

Narrow band interference (NBI) suppression is one of major issues for ultra wideband (UWB) wireless communication system operating over huge spectrum occupied by narrow band wireless systems. In this paper, we propose an interference mitigation scheme based on complex-valued adaptive notch filter, which smartly exploits the substantial correlation difference of signals and removes the NBIs in UWB signal with noise by estimating the corresponding central frequencies. To obtain high speed convergence and maintain small signal distortion, a low complexity gradient algorithm for one-order basic adaptive notch filter cell is deduced. Considering that the data rate prior to despreading is extremely high, a novel time-division multiplexing (TDM) parallel approach for eliminating a single NBI is presented, which effectively simplify the hardware design especially in high speed digital signal processing. Based on the one-order basic adaptive notch filter cell, three different implementations including direct forms, linear cascade forms and TDM parallel cascade forms to eliminate multiple NBIs are developed and discussed. Theoretical analysis and simulation results indicate that the proposed scheme possesses the advantages of high convergence speed, small distortion and high stability. Furthermore, the propose scheme utilized as a preprocessing unit prior to despreading can considerably improve the interference tolerance margin of UWB systems, leading to it's suitable for the low complexity direct sequence (DS)-UWB receiver.

I. Introduction

In the last decade, there has been a great interest in ultra-wideband (UWB) techniques. UWB radio is particularly promising for short-range high-rate wireless communications, since it potentially combines reduced complexity with low power consumption, low probability of intercept, high-accuracy positioning, and immunity to multipath fading due to discontinuous transmission [1], [2]. First report and order released by Federal Communications Commissions (FCC) in 2002 defines UWB transmissions to have a fractional bandwidth greater than 20%, or a transmission bandwidth of at least 500 MHz [3]. Since UWB systems are planned to coexist with other legacy narrow band systems, the transmission power of the UWB devices is strictly limited so that the pre-existing narrow band systems will be affected by the UWB signals only at a negligible level. Specifically, the average power spectral density (PSD) can not exceed −41.3 dBm/MHz over the frequency band from 3.1 to 10.6 GHz, and it must be even lower outside this band, depending on the specific application.