In this letter, we consider a new communication scenario in cellular networks, which is called intra-cell communications (ICC), for which user pairs within the same cell exchange information through the base station (BS). A network coding based protocol is proposed to assist ICC in OFDMA networks to improve the spectral efficiency. In the uplink, each user accesses the BS following the OFDMA principle, while in the downlink, the BS transmits to each of the user pairs using the OFDMA principle. To do so, the BS performs bit level XOR (BLX) operation on the information bits received from each user pair. The output is then transmitted back to the same user pair through subcarrier sharing. We formulate the joint uplink/downlink subcarrier assignment and power allocation problem to maximize the weighted sum rate. While the formulated problem is non-convex, an asymptotically optimal, yet low complexity algorithm is proposed. Simulation results are presented to verify that the proposed protocol outperforms subcarrier pairing and assignment schemes which require no subcarrier sharing in both uplink and downlink.
