A Reduced Overhead OFDM Relay System with Clusterwise TMRC Beamforming

We consider a relay clustering system using decode and forward (DF) relaying, orthogonal frequency division multiplexing (OFDM), and transmit maximal ratio combining beamforming (TMRC-BF) at the relays. We address channel estimation at the destination for the above system. A cluster pairing scheme with corresponding pilot designs is proposed. It reduces both necessary pilot overhead and computational complexity by half. Simulation results show that if the signal to noise ratio (SNR) of pilots for channel estimation for TMRC-BF at the relays is kept above a threshold (5 dB below the SNR of the pilots sent to the destination by the cluster pairing strategy), nearly optimal channel estimation performance can be achieved.