Sidelobe Reduction in Non-Contiguous OFDM-Based Cognitive Radio Systems Using a Generalized Sidelobe Canceller

Atif Elahi,Fawad Zaman,Ijaz Qureshi,Zafar Khan

doi:10.3390/app5040894

Abstract

In orthogonal frequency division multiplexing (OFDM), sidelobes of the modulated subcarriers cause high out-of-band (OOB) radiation, resulting in interference to licensed and un-licensed users in a cognitive radio system environment. In this work, we present a novel technique based on a generalized sidelobe canceller (GSC) for the reduction of sidelobes. The upper branch of the GSC consists of a weight vector designed by multiple constraints to preserve the desired portion of the input signal. The lower branch has a blocking matrix that blocks the desired portion and preserves the undesired portion (the sidelobes) of the input signal, followed by an adaptive weight vector. The adaptive weight vector adjusts the amplitudes of the undesired portion (the sidelobes) so that when the signal from the lower branch is subtracted from the signal from the upper branch, it results in cancellation of the sidelobes of the input signal. The effectiveness and strength of the proposed technique are verified through extensive simulations. The proposed technique produces competitive results in terms of sidelobe reduction as compared to existing techniques.

Highlights

The rapid growth in wireless communication methods and devices is a major reason for spectrum scarcity
Both the accuracy and the reliability of the proposed technique are discussed for the reduction of sidelobe suppression of the orthogonal frequency division multiplexing (OFDM) signal
The performance comparison of the proposed technique has been done in terms of normalized power spectral density (PSD) with already existing techniques in this area

Summary

Introduction

The rapid growth in wireless communication methods and devices is a major reason for spectrum scarcity. CR has the ability to dynamically permit secondary users (SU) to operate in those spectral domains that are not being used by the primary users (PU) at certain times and localities (interweave mode) [1,2,3]. Efficient techniques are needed at the transmitter side to control the shapes of the transmitted signal so that both SU and PU can share the same spectrum resources with minimum interference. Orthogonal frequency division multiplexing (OFDM) is the best candidate for the CR [4,5,6], with the ability to divide the available wideband channel into multiple narrow band orthogonal channels/subcarriers and to transmit those subcarriers in parallel. Some attributes of OFDM include spectral efficiency, multipath delay spread, robustness to channel fading, etc. Due to the large sidelobes of the OFDM subcarriers, CR based on OFDM experiences high out-of-band (OOB)

Methods

Results

Conclusion