Suppression of Mutual Interference in Noncontiguous Orthogonal Frequency Division Multiplexing Based Cognitive Radio Systems

Atif Elahi,Ijaz Mansoor Qureshi,Tahir Saleem,Noor Gul,Fawad Zaman

doi:10.1155/2017/1860134

Abstract

Orthogonal frequency division multiplexing (OFDM) is a favourable technology for dynamic spectrum access (DSA) due to the flexibility in spectrum shaping. In spite of that, high sidelobes of OFDM subcarriers bring in considerable interference to the nearby users, particularly in OFDM based cognitive radio (CR) networks, where the secondary users (SUs) are capable of accessing the spectrum opportunistically. In this paper, two new techniques for the suppression of high sidelobes are proposed. The proposed techniques composed of an optimization scheme are followed by generalized sidelobe canceller. The proposed techniques can be considered as a two-level suppression technique in the sense that in the first level the sidelobe is reduced by using cancellation carriers (CCs), whose amplitudes are determined using genetic algorithm (GA) and differential evolution (DE), while in the second level further reduction of sidelobe is achieved using generalized sidelobe canceller (GSC). Simulation results show the power spectral density (PSD) performance of the proposed techniques in comparison with already existing techniques, demonstrating that the proposed techniques minimize the out-of-band radiation (OOBR) significantly, thus qualifying for more effective spectrum sharing.

Highlights

To tackle the problem of spectrum overcrowding, Mitola [1,2,3] was the first to give the concept of cognitive radio (CR)
We propose two new techniques: generalized sidelobe canceller (GSC) combined with cancellation carriers (CCs) using genetic algorithm (GA) and GSC combined with CC using differential evolution (DE)
The efficiency of our proposed techniques for this scenario is compared with the current techniques, including CC [7, 8], advanced cancellation carriers (ACC) [11], advanced subcarrier weightings (ASW) [12], CC using GA and DE [9], and GSC [32], as shown in Figures 4 and 5

Summary

Introduction

To tackle the problem of spectrum overcrowding, Mitola [1,2,3] was the first to give the concept of cognitive radio (CR). Different techniques including cancellation carriers (CCs) [7, 8], CC using genetic algorithm (GA) and differential evolution (DE) [9], active and null cancellation carriers (ANCC) [10], advanced cancellation carriers (ACC) [11], advanced subcarrier weightings (ASW) [12], subcarrier weightings (SW) [13], filtering [14], windowing [15, 16], adaptive symbol transition (AST) [17], active interference cancellation (AIC) [18,19,20], insertion of guard bands [21, 22], multiple choice sequence (MCS) [23], spectral precoding schemes [24,25,26,27,28], constellation expansion (CE) [29,30,31], and sidelobes reduction using generalized sidelobe canceller (GSC) [32] are proposed to address the OOBR problem. Small bold letter represents a vector, the capital bold letter represents matrix, and I represents the identity matrix while O represents the null matrix

System Model

The Proposed Methodologies

Simulation Results

II III

Conclusion