Relay-based cooperative communications can achieve spatial diversity gains, enhance coverage and potentially increase capacity. If considered for large networks, traditional relaying scheme suffer from spectral inefficiency that can be improved through network coding at a physical layer. These considerations motivate the complex field network coding (CFNC) scheme proposed in this paper. As opposed to network coding over Galois field, where wireless links cannot improve throughput limitations as the number of sources increases, CFNC achieves throughput as high as 1/2 symbol per source per time slot. With improved throughput, CFNC-based relaying achieves full diversity gain regardless of the channel signal-to-noise-ratio (SNR) and the underlying constellation, and is general enough to incorporate transmissions from sources to a common destination as well as information exchange among the sources at the same time.