Performance analysis of coded secondary relaying in overlay cognitive radio networks

We study the error and diversity-multiplexing tradeoff (DMT) performance of a (secondary) multi-user relay network, where a class of finite field network codes are applied in the relays to efficiently provide spatial diversity. To eliminate spectral efficiency loss induced by half-duplex limitation we adopt the cognitive radio overlay spectrum sharing concept and consider aligning the relays´ operation with that of a primary system. To compensate the interference introduced by the secondary relaying, the secondary destination also transmits the primary signals to boost the signal power of the primary system. We also consider exploiting Automatic Repeat Request (ARQ) feedback signals from the secondary destination to minimize the energy consumption of the secondary system. In addition, by allowing multiple secondary sources to transmit non-orthogonally, the performance can be further enhanced.