Interference-free overlay cognitive radio network based on cooperative space time coding

In this paper, we propose a two-phase overlay spectrum sharing protocol based on cooperative decode-and-forward relaying which allows the secondary system to gain spectrum access along with the primary system. In the proposed scheme, the secondary system operates simultaneously in the same frequency band as the primary system, which supports the relaying functionality. We show that by using a space time block code (STBC) design in two time phases in the secondary system, the subsequent interference from the secondary system to the primary system and vice versa can be completely removed. Consequently, it is possible to achieve spectrum access for secondary system without compromising on the performance of the primary system. Performance of the primary system and the secondary system is analyzed in terms of outage probability, and simulation results are shown to validate the efficiency of the proposed scheme.