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

Abstract

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. OPEN ACCESSAppl. Sci. 2015, 5 895

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

“…However, due to the high sidelobes of the OFDM subcarriers, CR based OFDM experience high out-of-band radiation (OOBR) that may interfere with either LUs or secondary users (SUs) in the contiguous bands. 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. These techniques undergo different penalties; therefore, proper hybridization of two or more techniques may result in a better OOBR reduction.…”

Techniques for the suppression of sidelobes in a non-contiguous orthogonal frequency division multiplexing framework

“…It adjusts the amplitudes of sidelobes, such that when the signals from the upper and lower branch add with each other, a signal with minimum OOBR results. The expressions for u q , u a and B are available in Elahi et al (2015) and are given by:…”

“…In the first level, the OOBR is minimized using methods which are represented by precoding matrices; these include CC (Brandes method) (Brandes et al 2005), CC (Pagadarai method) (Pagadarai et al 2008b), ACC ) and ANCC (Lopes and Panaro 2013), while in the second level further minimization of OOBR is achieved using GSC (Elahi et al 2015). …”

“…category are called the frequency domain methods, including subcarrier weightings (SW) (Cosovic et al 2006), advanced subcarrier weightings (ASW) , cancellation carriers (CC) (Brandes et al 2005;Pagadarai et al 2008b), advanced cancellation carriers (ACC) Rady et al 2015), CC using (genetic algorithm) GA and (differential evolution) DE (Elahi et al 2016), active and null cancellation carriers (ANCC) (Lopes and Panaro 2013), constellation expansion (CE) (Pagadarai et al 2008a;Li et al 2009;Selim et al 2012), CE using GA (Khan and Yoo 2015) and generalized sidelobe canceller (GSC) (Elahi et al 2015), etc. where the OOBR elimination process is carried out before the IFFT.…”

A Haar Wavelet Decision Feedback Channel Estimation Method in OFDM Systems

“…Orthogonal frequency division multiplexing (OFDM) system [1][2][3][4][5] has been widely used in modern wireless communication systems due to its high spectrum efficiency and strong multipath fading resistance ability. The cyclic prefix (CP) is used as the guard interval in each OFDM symbol to reduce the inter-symbol interference (ISI) and inter-carrier interference (ICI) greatly.…”