PEACE: Polarization Enabled Active Cooperation Scheme Between Primary and Secondary Networks

In this paper, we present a two-phase cooperative transmission and relay scheme between a primary network and a secondary network to address spectrum underutilization and spectrum inefficiency. By placing orthogonally dual-polarized antennas (ODPAs) and enabling polarization signal processing functionalities at secondary users (SUs), the cochannel interference caused by multiple independent transmissions from primary and secondary networks can be mitigated. A framework design, including system description, signaling plan, and key enabling techniques, is studied to perform Polarization Enabled Active CoopEration (PEACE) between primary users (PUs) and SUs. In the presented PEACE framework, polarization zero forcing and oblique projection polarization filtering are utilized to address interference from SUs to the primary network and to separate SUs signals, respectively. We provide theoretical analysis to maximize the sum achievable channel capacity under certain transmission rates and power constraints to evaluate PEACE performance. To solve the original nonconvex optimization problem, it is effectively approximated to a convex problem, which can be tackled quite efficiently. Closed-form solutions to optimal power allocation of SUs are, respectively, obtained by a centralized algorithm and a distributed algorithm. Extensive numerical results are given to illustrate the performance and to examine the features of the PEACE framework and the proposed algorithms.