Multi-Antenna Relay Nodes in OFDM Systems

In this paper we study different ways of embedding multi-antenna relay nodes to OFDM systems. We compare the performance of half-duplex amplify and forward, amplify and forward within the cyclic prefix and decode and forward relays in combination with multi-stream MIMO communication. We show that the eigenvalue spread of the effective channel matrix is much higher for the amplify and forward relaying protocols compared to the decode and forward protocols. Thus, decode and forward relays offer better spatial multiplexing possibilities. In particular we test the performance of the different relaying protocols for a 4times4times4 relay network in the downlink of a metropolitan area network. We show that amplify and forward within the cyclic prefix outperforms half-duplex amplify and forward and decode and forward relaying for a SNR up to 20 dB. Only at higher SNR decode and forward performs better due to its higher spatial multiplexing possibilities.