Phase Noise Effects on Signal Detection for Uwb/wimax Coexistence

Abstract

The effect of local oscillator (LO) phase noise of an ultra-wide band (UWB) receiver on the detection of a nearby WiMAX receiver is investigated. An expression for the spectrum broadening effect due to the phase noise is derived, and a practical method is presented to estimate the in-band interference due to the phase noise interaction with an interfering adjacent channel signal. INTRODUCTION After the Federal Communications Commission (FCC) authorized the unlicensed use of the frequency band between 3.1 to 10.6 GHz for UWB communication systems [1], interference problems became a concern. One of the systems that share the frequency spectrum with UWB is the worldwide interoperability for microwave access (WiMAX) system. Based on the IEEE 802.16 standard, WiMAX is currently utilizing several frequency bands below 11 GHz, such as the unlicensed 5 GHz band, the licensed 3.5 GHz band, and the licensed 2.5 GHz band [2]. Since the WiMAX system is expected to share the frequency spectrum with UWB, an active WiMAX device detection scheme is highly desirable for UWB devices. Detecting WiMAX downlink signal is a possible approach, but it has the drawback that it will confine the available frequency spectrum for the UWB device even when no WiMAX receiver is present. As shown in Figure 1, the radius of the UWB system is confined to about 10 m, and so detecting the LO leakage signal from a nearby WiMAX mobile terminal receiver could be used by a UWB device to detect the presence of that WiMAX receiver [3]. However, the detection sensitivity is of major concern due to the very low level of the incoming leakage signal power. In particular, the phase noise of the UWB detector’s RF oscillator can degrade the overall detection sensitivity due to the spectrum broadening effect. In this paper, we evaluate the effect of receiver phase noise on the in-band interference in an additive white Gaussian noise (AWGN) environment and apply the result to the detection of a WiMAX mobile terminal (MT) by a UWB device. SIGNAL DETECTION FOR UWB/WIMAX COEXISTENCE When a WiMAX MT is in the receive mode, a small portion of the receiver LO signal power leaks to the antenna and radiates as shown in Figure 1. Typically, a leakage signal power level of –70 to –90 dBm is expected at the antenna port [4]. This signal is received at the UWB antenna, and is either ( ) ( ) = W r t n t (1) or ( ) ( ) ( ) = + W r t s t n t (2) where ( ) s t and ( ) W n t denote the received leakage signal from the WiMAX MT and the received noise, respectively. We assume that a UWB device relies on a Discrete Fourier Transform (DFT) to discriminate the unmodulated leakage signal from the background noise. The UWB device determines that ( ) s t is absent if the magnitude WiMAX Access Point Downlink UWB Interference Range LO le ak ag e WiMAX MT

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Cite this paper

@inproceedings{Park2009PhaseNE, title={Phase Noise Effects on Signal Detection for Uwb/wimax Coexistence}, author={Sanghoon Park and Lawrence E. Larson and Laurence B. Milstein}, year={2009} }