A spatial incremental relaying-based user transparent ARQ protocol

In this paper, we propose an incremental decode-and-forward (DF) relaying scheme; in our proposed scheme, we make use of the free spatial dimensions over which the relay node will forward the source node data. The relay node will help in providing an automatic repeat request (ARQ) service for the source node that is completely transparent to the source node. The proposed ARQ service will not require any additional complexity at the source node transmitter and will not incur any rate loss. We provide a complete analysis for the symbol error rate (SER) of our proposed scheme. In addition, we derive SER upper-bounds to calculate the diversity order achieved by our scheme. Numerical simulations are conducted that support our derived SER expressions as well as the calculated diversity orders. The results show the significant performance gains of our proposed scheme, in terms of the system SER and the diversity order, compared to the system where no relay is deployed.