Performance analysis of Doppler shift effects on OFDM-based and MC-CDMA-based cognitive radios

摘要

The present development of high data rate wireless applications has led to extra bandwidth demands. However, finding a new spectrum bandwidth to accommodate these applications and services is a challenging task because of the scarcity of spectrum resources. In fact, the spectrum is utilized inefficiently for conventional spectrum allocation, so Federal Communications Commission has proposed dynamic spectrum access mechanism in cognitive radio, where unlicensed users can opportunistically borrow unused licensed spectrum, which is a challenge to obtain contiguous frequency spectrum block. This also has a significant impact on multicarrier transmission systems such as orthogonal frequency division multiplexing (OFDM) and multicarrier code division multiple access (MC-CDMA). As a solution, this paper develops non-contiguous OFDM (NC-OFDM) and non-contiguous MC-CDMA (NC-MC-CDMA) cognitive system. The implementation of NC-OFDM and NC-MC-CDMA systems provides high data rate via a large number of non-contiguous subcarriers without interfering with the existing transmissions. The system performance evaluates NC-OFDM and NC-MC-CDMA for mobile scenario where each propagation path will experience Doppler frequency shift because of the relative motion between the transmitter and receiver. The simulation results of this paper proved that NC-OFDM system is a superior candidate than NC-MC-CDMA system considering the mobility for cognitive users. Copyright (c) 2013 John Wiley & Sons, Ltd.