Adaptive Subband Selection in OFDM-Based Cognitive Radios for Better System Coexistence

In an environment of shared radio spectrum, multiple systems may interfere with each other and cause significant impacts on system coexistence. In this paper we propose an adaptive subband selection technique based on orthogonal frequency division multiplexing (OFDM) to avoid interference for better system coexistence when multiple systems are operating in the same unlicensed industrial, scientific and medical (ISM) bands. Under the assumption that the interference power level and the interfered frequency bands are identified at the receiver, interference thresholds, determined over both Gaussian and multipath fading channels, are applied to adaptively select the transmission subbands so that interference is avoided and the system coexistence issues are relaxed. To verify the effectiveness of the proposed adaptive subband selection method, the system bit error rates (BERs) under different interference levels are simulated and compared.