Many-to-many communications via space-time network coding
The mutual cooperative communication between multiple nodes in a wireless network is efficiently achieved through a novel concept of Space-Time Network Coding (STNC). Unlike the conventional point-to-point cooperative communications between two nodes with N relay nodes deployed in between, simultaneous transmissions from the different N nodes acting as source/relay nodes are performed within 2N time-slots. In particular, the communication is split into two phases: 1) Broadcasting Phase and 2) Cooperation Phase. In the Broadcasting Phase, each node broadcasts its data symbol to the other nodes in the network in its own time-slot, alternatively; while in the Cooperation Phase, in each time-slot, a set of (N-1) nodes transmit while a single destination node receives the other nodes' transmissions. Specifically, each node employing a selective Decode-and-Forward (DF) cooperative protocol, performs a linear combination of the other nodes data symbols and all the (N-1) nodes simultaneously transmit their signals to a single receiving node; which then performs joint multiuser detection to separate the different nodes' symbols. Exact symbol-error-rate (SER) expressions for arbitrary order M-ary Phase Shift Keying (M-PSK) modulation are derived. In addition, an asymptotic SER approximation is also provided which is shown to be tight at high signal-to-noise ratio (SNR). Finally, the analytical results confirm that for a network of N nodes, a full diversity order of (N-1) per node is achieved by the proposed STNC cooperative communication scheme.