Most existing works on orthogonal frequency division multiple access (OFDMA) multihop cellular networks have assumed half-duplex relay, which suffers from spectral inefficiency since it requires additional resources for relaying. In order to alleviate this half-duplex loss, a new relay transmission scheme using dirty paper coding (DPC) is proposed. By alternately forwarding the messages to two mobile stations (MSs) via two fixed relay stations (FRSs) for each subcarrier, the base station (BS) predicts and pre-cancels the inter-relay interference between FRSs in advance. This proposed DPC-aided transmission scheme matches well with the nature of the quasi-static fading channel between FRSs. We also propose a two step resource allocation algorithm to select the appropriate MSs and to maximize the achievable sum rate. Numerical results demonstrate that the achievable sum rate of the proposed DPC-aided multihop cellular networks is significantly increased by utilizing the multi-user and multi-relay diversity gain as well as pre-cancelling the inter-relay interference between FRSs.