Cooperative spectrum sharing with distributed secondary user selection

In this paper, we propose a two-phase protocol based on cooperative relaying for a secondary system to achieve spectrum access along with a primary system. The primary system comprises of a transmitter-receiver pair PT-PR, and the secondary system comprises of M transmitter-receiver pairs ST_i -_i, i ε {1, 2, ⋯ ,M}. The secondary pair ST_b -_b, b ε {1, 2, ⋯ ,M} which is able to provide the best performance for the primary system, is selected to access the spectrum, with ST_b serving as a cooperative relay for the primary system. In the first transmission phase, PT transmits the primary signal to PR, which is also received by ST_b and _b, where it is decoded. At ST _b, the primary signal is regenerated and linearly combined with the secondary signal by assigning fractions α and (1 - α) of the available power to the primary and secondary signals respectively. This combined signal is then broadcasted by ST_b in the second transmission phase, and PR combines the signal it received in the two phases to decode for the primary signal. Theoretical and simulation results confirm that the outage performance for both primary and secondary systems are improved with a larger M by using the proposed scheme.