Multipoint-to-point and point-to-multipoint space-time network coding
Traditional cooperative communications can improve communication reliability. However, the simultaneous transmissions from multiple relays are challenging in practice due to the issue of imperfect frequency and timing synchronization. In this work, we propose space-time network codes (STNCs) that overcome the issue of imperfect synchronization, reduce the large transmission delay, and still provide full spatial diversity in multipoint-to-point (M2P) and point-to-multipoint (P2M) transmissions. Relays form single linearly-coded signals from the overheard symbols and transmit them to the destination, where multiuser detection is utilized to detect the desired symbol. For a network of N client nodes, M2P and P2M STNCs result in a diversity order of N with only 2N time slots, a significant reduction from N2 time slots in traditional cooperative communications using TDMA.