Spectrum Sensing of OFDMA Systems for Cognitive Radios

In order to fully exploit wireless radio resource and then increase spectrum efficiency, cognitive radios shall sense and cognize environments so that the secondary system(s) may coexist with primary communication systems. In this paper, we acquire an effective set of cognitive information under a proposed spectrum sensing cycle for orthogonal frequency division multiple access (OFDMA) systems. To avoid interfering with primary systems, detecting existence of the primary system by tracking fundamental symbol rate of the primary system and measuring RSSI is the first step in coexistence. Furthermore, using cyclic property of OFDMA signal, we can precisely determine existence of a specific OFDMA system and its frequency band, via Neyman-Pearson criterion. Simulation results show that near perfection detection is achieved even at low SINR. With a priori knowledge of frame structure in potential primary systems, communication parameters, such as data transmission rate and resource allocation, are extracted by decoding frame header. Finally, we can determine available radio resource with respect to cognitive radios using rate-distance relationship, while guarantee interference to primary systems. Moreover, by parametric adjustment, our sensing procedure can be applied to any state-of-the-art OFDMA systems nowadays.