Interference Excision in Spread Spectrum Communications Using Adaptive Positive Time-Frequency Analysis
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Research Article Interference Excision in Spread Spectrum Communications Using Adaptive Positive Time-Frequency Analysis ¨ ¸ uk ¨ Sridhar Krishnan and Serhat Erkuc Department of Electrical and Computer Engineering, Ryerson University, Toronto, ON, Canada M5B 2K3 Received 26 July 2006; Revised 10 February 2007; Accepted 24 May 2007 Recommended by Richard Kozick This paper introduces a novel algorithm to excise single and multicomponent chirp-like interferences in direct sequence spread spectrum (DSSS) communications. The excision algorithm consists of two stages: adaptive signal decomposition stage and directional element detection stage based on the Hough-Radon transform (HRT). Initially, the received spread spectrum signal is decomposed into its time-frequency (TF) functions using an adaptive signal decomposition algorithm, and the resulting TF functions are mapped onto the TF plane. We then use a line detection algorithm based on the HRT that operates on the image of the TF plane and detects energy varying directional elements that satisfy a parametric constraint. Interference is modeled by reconstructing the corresponding TF functions detected by the HRT, and subtracted from the received signal. The proposed technique has two main advantages: (i) it localizes the interferences on the TF plane with no cross-terms, thus facilitating simple filtering techniques based on thresholding of the TF functions, and is an efficient way to excise the interference; (ii) it can be used for the detection of any directional interferences that can be parameterized. Simulation results with synthetic models have shown successful performance with linear and quadratic chirp interferences for single and multicomponent interference cases. The proposed method excises the interference even under very low SNR conditions of −10 dB, and the technique could be easily extended to any interferences that could be represented by a parametric equation in the TF plane. Copyright © 2007 S. Krishnan and S. Erk¨uc¸u¨ k. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
In spread spectrum (SS) communications, the message signal is modulated and spread over a wider bandwidth with a pseudonoise (PN) code also known at the receiver, and transmitted over the channel. The increase of the bandwidth yields a processing gain, defined as the ratio of the bandwidth of the transmitted signal to the bandwidth of the message signal, and it provides a high degree of interference suppression. However, there is a tradeoff between increasing the processing gain and the available frequency spectrum. In the case of a jammer with high power, the SS system may not be able to suppress the interference. Therefore, excising the interference prior to despreading the received signal is necessary to increase the performance of the system. Most interference suppression techniques are designed to deal
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