Spectrum Sharing Based on Overlay Cognitive Full-Duplex Two-Way OFDM Relaying: Protocol Design and Resource Allocation

A secondary relay is used to assist bidirectional communication between two primary nodes, and thus, is allowed to use part of the licensed spectrums to transmit its own messages. All involved links are orthogonal-frequency-division-multiplexing-modulated into multiple subcarriers, and the secondary relay is full-duplex capable such that it can receive and transmit signals within the same frequency band. In the first time slot, the two primary nodes transmit to the secondary relay over the same subset of subcarriers, and meanwhile, the secondary relay transmits its own messages over the remaining subcarriers; in the second time slot, the secondary relay broadcasts the superimposed primary signals over possibly another subset of subcarriers and continues transmitting the secondary messages over the remaining subcarriers. We aim to maximize the secondary data rate while satisfying the requirements of the two primary nodes, and formulate a resource allocation problem that tackles spectrum partition, subcarrier pairing, and power allocation jointly. An asymptotically optimal solution is developed with polynomial complexity; in particular, a variant version of the classic Hungarian method is proposed to solve spectrum partition and subcarrier pairing jointly. We further show that the proposed Hungarian-variant method can solve a generalized class of "partition-and-pairing" problems efficiently.