Filterbank Multicarrier and Multicarrier CDMA for Cognitive Radio Systems

Abstract

Recent works in cognitive radio (CR) have suggested multicarrier communication based on orthogonal frequency-division multiplexing (OFDM) for CR networks. In this paper, we propose two alternative multicarrier techniques. The first one, filterbank-based OFDM-OQAM (OFDM-offset quadrature amplitude modulation), allows to maximize the secondary users' spectral efficiency by eliminating the need for guard bands. Also, OFDM-OQAM's filterbank spectral estimator has greater dynamic range than the conventional fast fourier transform in OFDM, which further reduces the probability of undesirable collisions between the secondary users (SU) and primary users (PU). However, OFDM-OQAM still requires an SU base station for distributed sensing. For cases where such is not available, or when sensing information cannot be conveyed, we suggest another multicarrier technique, namely multicarrier code division multiple access (MC-CDMA). While MC-CDMA does not achieve comparably high spectral efficiency as OFDM-OQAM, the spreading gain of MC-CDMA results in graceful degradation in the case of collisions between PUs and SUs. Furthermore, compared to direct sequence (DS) CDMA, MC-CDMA allows to exclude narrowband PU interferers locally at the SU receiver, hence improving SU performance. We show that MC-CDMA makes it possible to operate the SU network without distributed sensing and hence no need for a base station infrastructure and/or a signaling channel.