Robust noise variance and channel estimation for SC-FDE UWB systems under narrowband interference

In this study, the noise variance and channel estimation problems are investigated over the UWB channel with narrowband interference (NBI). We first give two ways to construct the samples of noise variance using the least square (LS) channel estimates, by which we model the estimation problem of noise variance as parameter estimation of an exponential distribution and turn the NBI detection in the LS channel estimates into a general constant false alarm rate (CFAR) problem. Then, a robust noise variance estimator based on order statistic is presented to avoid the impact of NBI, and its estimation variance is also analyzed. In addition, a low complexity robust channel estimation (RCE) scheme is provided without requiring any knowledge of channel statistics including finite delay spread. The RCE scheme includes three new steps, namely the identification of the NBI signal by a CFAR detector, the recovery of channel estimates at the jammed frequency bins by either utilizing the conjugate symmetry property of the UWB channel or median filtering, and finally noise reduction through threshold filtering. Simulation results demonstrate the superior performance of the proposed schemes compared to the existing methods.

I. Introduction

RECENTLY [1], frequency-domain equalization (FDE) techniques have been proposed for ultra-wideband (UWB) systems employing block transmission. It has been shown that the SC-FDE UWB is a promising candidate for UWB communications due to its advantages over previous solutions in terms of performance and implementation issues [1]. To achieve good spectral efficiency, UWB systems operating over extremely wide frequency bands will have to coexist with current narrowband systems operating on a very small slice of the UWB bandwidth with much higher power levels. Therefore, it is very important to design the UWB receivers robust to such narrowband interference (NBI). Similar to conventional multi-carrier communications [2], in a UWB system with NBI, robust noise variance and channel estimates are very important for the coherent receiver to recover the data reliably. Hence, NBI must be effectively coped with in the estimation of noise variance and channel coefficients at the receiver. However, to the best of our knowledge, research on noise variance and channel estimation for SC-FDE UWB systems in the presence of NBI has not received much attention so far.