Opportunity Detection for OFDMA Systems with Timing Misalignment

Accurate detection of spectrum opportunities within the frequency band of an orthogonal frequency division multiple access (OFDMA) system is a critical requirement for the realization of a coexisting cognitive radio. In this paper, we analyze the opportunity detection performances of energy detection and ESPRIT algorithms in the presence of timing misalignments in uplink (UL) OFDMA. For the energy detector, the statistics of subcarrier power are derived, and the accuracy of these derivations is verified through simulations. The feasibility of opportunity detection in an asynchronous UL-OFDMA system is proven. Also, it is shown that energy detection has a considerably better performance than the ESPRIT algorithm especially when the subcarrier assignments change frequently.