Active Interference Cancellation Technique Research Articles

Constellation expanded active interference cancellation technique for suppression of out-of-band radiation in OFDM based cognitive radios

Cognitive radio is a novel technology to address the problem of spectrum under-utilization, by allowing the secondary users to dynamically use the spectrum of the primary users. OFDM is a potential candidate for the physical layer of cognitive radio, due to its inherent features of spectrum shaping, spectrum analysis and robustness to multipath. OFDM based cognitive radio, however suffers from out-of-band radiation (OOBR). In cognitive radio, suppression of OOBR is much more important as the interference to the primary users needs to be kept to the minimum possible level. In the literature, time and frequency characteristics of the transmitted signal have been exploited to minimize the OOBR. In this paper, we investigate the possibility of combining merits of the constellation expansion (CE) technique and the active interference cancellation (AIC) technique for suppression of OOBR. We show through simulations that the joint technique based on CE and AIC achieves much better OOBR reduction, with a slight degradation in error performance.

Performance Evaluation of AIC Technique for Single and Multiple Primary Bands in OFDM based Cognitive Radios

Cognitive radio has emerged as an efficient approach to address the problem of spectrum under-utilization. OFDM has been proposed as a potential candidate for the physical layer of cognitive radios due to its inherent characteristics of spectrum shaping, spectrum analysis and robustness to frequency selective fading. One of the major problems of OFDM is high Out Of Band Radiation (OOBR). This is an undesired phenomenon especially if the nearby band is occupied by primary (or licensed) user. Among the proposed techniques to overcome this problem, Active Interference Cancellation (AIC) is considered to be one of the efficient techniques. In this paper, we evaluate the performance of this technique for single and multiple primary bands in OFDM based cognitive radios. For the case of single primary band, it is shown through simulations that narrower primary bands and use of more number of cancellation carriers increases the OOBR reduction in the desired band. For the case of multiple primary bands, the AIC technique is shown to provide better OOBR reduction for larger inter primary band spacing, lesser number of primary bands and more number of cancellation carriers. We also evaluate the bandwidth efficiency for single and multiple primary bands. The bandwidth efficiency shows a linear decrease with the increase in number of cancellation carriers. Multiple primary band system has more bandwidth efficiency degradation than the single primary band system.