To improve the outage performance of a wireless body area network (BAN), exploitation of the diversity in the channel obtained by letting different nodes cooperate and relay signals for each other is an attractive solution. We carry out multi-link channel measurements and modeling for all realistic locations of the on-body sensor nodes and for three different motion scenarios in a typical office environment to develop equivalent channel model for simple and practical cooperative transmission schemes. Using the developed model the performance of the transmission schemes are evaluated and compared. Incremental decode and forward relaying is found to be consistently better than the other schemes with gains of up to 16dB at 10% outage probability, and an average gain of more than 5.9dB for any location of the coordinator node. The best location of the coordinator node based on the performance is also determined. Such insights will be very useful in designing BANs.

We propose an incremental relaying protocol in conjunction with partial relay selection with the aim of making efficient use of the degrees of freedom of the channels as well as improving the performance of dual hop relaying with partial relay selection (DRPRS). Specifically, whenever the direct link from the source to the destination is not favorable to decoding, the destination will request the help of the opportunistic relay providing highest SNR of the links from the source. Theoretical analyses, as well as simulation results, verify that our scheme outperforms the DRPRS scheme in terms of bit error probability.

In incremental relaying, the destination uses a checking system and requires a retransmission from the relay in case an error happens. After receiving the signal from the relay, the destination combines the signals from the source and the relay and performs detection. However, the combined signal is actually worse because of the erroneous signal from the source. Our scheme eliminates the detrimental signal from the source and uses only the fresh signal from the relay, resulting in a large performance improvement and reduced complexity. The symbol error rate (SER) and its upper bound are established to analyze the power allocation strategy. Simulations verify the rightness of the theoretic studies, and many benefits of cooperative ARQ schemes are revealed.

In terms of outage behavior, it has been shown that incremental relaying achieves the best performance among cooperative diversity protocols such as: Amplify-And-Forward (AF), Decode-And-Forward (DF), and Selection Decode-And-Forward (SDF). Exploiting a limited feedback from the destination, incremental relaying lets the relay forward the signal received from the source whenever an error happens at the destination, then, the signals from both the source and the relay are combined to make a decision. Noticing that the signal from the source, indicated by the error, is detrimental, we propose a new scheme not using that signal but only making a decision based on the fresh signal from the relay. Large performance improvement and complexity reduction are attained as we show in the analysis and simulation results. Theoretical results are derived and shown to match with the simulation counterparts.