Network Coded Modulation with HDF Strategy and Optimized Beam-Forming in 2-Source 2-Relay Network

The paper address the Network Coded Modulation (NCM) with Hierarchical Decode and Forward (HDF) strategy in the 2-source 2-relay scenario with SIMO (Single-Input Multiple-Output) fading channels. The NCM/HDF technique is known to be vulnerable to the mutual phase rotations of the signals from the sources. We use additional degrees of freedom in SIMO channels and create a specific receiver beam-forming tailored for given NCM/HDF strategy. We derive a closed form solution of the NCM/HDF specific beam-former and apply it on example NCMs. We evaluate the performance in terms of the mean and the outage hierarchical rates. It is shown that these rates significantly benefit from the beam-forming and that the resulting rate significantly outperforms classical (non WNC (Wireless Network Coding)) channel sharing techniques.