Effects of Bit Allocation on Non-Contiguous Multicarrier-Based Cognitive Radio Transceivers

In this paper, we evaluate a cognitive radio transceiver employing both non-contiguous multicarrier modulation (NC-MCM) and adaptive bit allocation. Although NC-MCM and bit allocation have potential benefits with respect to enabling dynamic spectrum access (DSA) and increasing throughput, they also require the transmission of overhead information between the transmitter and the receiver. To reduce this overhead information, operating parameters can be assigned to a block of subcarriers, at the cost of some throughput. The trade-offs between subcarrier block size and two different bit allocation approaches for several DSA scenarios are assessed in this work. The results show that as percentage of available spectrum decreases, the throughput loss of systems employing larger subcarrier block sizes rapidly increases. Nevertheless, larger block sizes also yield greater reductions in transmission overhead.