Hybrid overlay/underlay cognitive radio with spectral null composite sequence

Hybrid overlay/underlay mechanism is a smart way for secondary users to access spectrum in cognitive radio (CR). In this way, secondary users coexist with primary users in the same frequency band. For all we know, in the RF end, multicarrier modulation has been the major technique to realize this kind of spectrum access mechanism. From the perspective of system baseband, we proposed a promising system to help secondary users accessing spectrum in hybrid overlay/underlay mechanism, called composite sequence cognitive radio (CS-CR). In this system, we design a composite sequence, which is compounded by spectral null codes and m sequence. With our design composite sequence, secondary users can transmit low power over a wide frequency band and have spectral nulls in the band where primary users have been used. Bit error performance of primary and secondary users in AWGN channel is simulated in our system. The simulation results indicate that secondary users can guarantee the quality of service (QoS) of primary users, and also suppress the interference from primary users at the same time.