We consider a two-hop distributed relaying network using orthogonal space-time block codes (OSTBC), where several relays using Decode-Forward (DF) support the transmission from one source to one destination. In order to mitigate the impact of error propagation for DF, an inter-relay cooperation (IRC) scheme allowing message exchanges among the relays was presented in our previous work based on punctured channel codes. Specifically, one of the relays that decodes the source message correctly re-generates and broadcasts the punctured bits as side information to support the relays with decoding errors for re-decoding. Subsequently, only the error-free relays transmit to the destination using OSTBC. It was shown that this IRC scheme may increase the number of error-free relays when at least one relay decodes the source message correctly. In this paper we focus on the scenario that all relays fail to decode the source message correctly. To this end, an improved IRC scheme is presented based on received signal exchange, in which the whole or part of the received frame are exchanged among the relays to apply signal combining. Additionally, the total energy consumption for signal transmission, baseband processing and RF circuit at all relays is evaluated for practical preferences. It is shown that the improved scheme outperforms our original scheme significantly with respect to the overall system throughput.
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