In this paper, we study the application of physical layer network coding to the joint design of uplink and downlink transmissions, where the base station and the relay have multiple antennas, and all mobile stations only have a single antenna. A new network coding transmission protocol is proposed, where uplink and downlink transmissions can be accomplished within two time slots. Since each single antenna user has poor receive capability, precoding at the base station and relay has been carefully designed to ensure that co-channel interference can be removed completely. Explicit analytic results have been developed to demonstrate that the multiplexing gain achieved by the proposed transmission protocol is, much better than existing time sharing schemes. To further increase the achievable diversity gain, two variations of the proposed transmission protocols have also been proposed when there are multiple relays and the number of the antennas at the base station and relay is increased. Monte-Carlo simulation results have also been provided to demonstrate the performance of the proposed network coded transmission protocol.