Bi-directional relaying is an efficient way of exchanging messages between two devices through a relay. However, in multipath fading environments, using relays can increase the effective delay spread of the communication channel, causing inter-symbol interference in OFDM systems. In this paper, we look at the effect of using channel shorteners at relays to reduce the effective delay spreads to within the cyclic prefix length. We will also look at the improvement in energy efficiency of the system through using a combination of channel shortener and a shorter cyclic prefix.
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