Subcarrier, Bit and Power Allocation for Multiuser OFDM-Based Multi-Cell Cognitive Radio Systems

We study the subcarrier, bit and power allocation problem for multiuser OFDM-based multi-cell cognitive radio (CR) systems in which one or more spectrum holes exist between multiple primary user (PU) frequency bands. The cognitive radio users (CRUs) are able to share any portion of the frequency band with other CRUs and the PUs as long as this does not interfere unduly with the PUs´ transmissions. Both cochannel interference (CI) from other CRUs as well as mutual interference (MI) between the CRUs and the PUs are considered. The resource allocation problem is formulated as a multi-dimensional knapsack problem and a relatively simple, greedy max-min algorithm is proposed to solve it. Simulation results show that the max-min algorithm yields solutions which are close to (within 5% of) optimal. Sharing of the whole band can provide a substantial performance improvement over schemes which use guard bands to protect PU frequency bands and do not allow CRUs to use the PU bands.