Two-way decode-and-forward(DF) relay technique is an efficient method to improve system performance in 5G networks.However,traditional orthogonal frequency division multiplexing(OFDM) based two-way relay systems only consider a per-subcarrier relay strategy,which treats each subcarrier as a separate channel,which results in significant sum rate loss,especially in fading environments.In this paper,a joint coding scheme over multiple subcarriers is involved for multipair users in two-way relay systems to obtain multiuser diversity.A generalized subcarrier pairing strategy is proposed to permit each user-pair to occupy different subcarriers during the two transmission phases,i.e.,the multiple access and broadcast phases.Moreover,a low complexity joint resource allocation scheme is proposed to improve the spectrum efficiency with an additional multi-user diversity gain.Some numerical simulations are finally provided to verify the efficacy of our proposal. Two-way decode-and-forward (DF) relay technique is an efficient method to improve system performance in 5G networks. Still, the traditional orthogonal frequency division multiplexing (OFDM) based two-way relay systems only consider a per-subcarrier relay strategy, which treats each subcarrier as a separate channel, which results in significant sum rate loss, especially in fading environments. In this paper, a joint coding scheme over multiple subcarriers is involved for multipair users in two-way relay systems to obtain multiuser diversity. A generalized subcarrier pairing strategy is proposed to permit each user-pair to occupy different subcarriers during the two transmission phases, ie, the multiple access and broadcast phases. Moreover, a low complexity joint resource allocation scheme is proposed to improve the spectrum efficiency with an additional multi-user diversity gain.Some numerical simulations are finally provided to verify the efficacy of our proposal.