Relay Selection Algorithms For Analog Network Coding OFDM Systems

Two relay selection schemes for Analog Network Coding (ANC) OFDM systems areproposed. One uses OFDM Symbol-Based Max-Min-Min Selection Criterion to selectonly one relay for signal transmission, and the other uses a carrier-Based Max-MinSelection Criterion to select multiple relays for signal transmission. Using afrequency-domain fully-uncorrelated Rayleigh fading channel, asymptotic Symbol ErrorRate (SER) performance is derived for both schemes, and it shows they both can achievefull diversity. It is further shown that the analytical results match the simulation resultsaccurately in the high SNR region. Moreover, the analytical results, though derived forfully uncorrelated channels, match the simulated SER performance even for correlatedchannels. Additionally, two Cyclic Prefix (CP) handling schemes are proposed for thecarrier-based selection criterion.Cooperation diversity consists on using relay nodes to combat the effects of fadingchannels by means of spatial diversity. Physical-layer Network Coding (PNC) is used tomake the two way relay network achieve a higher bandwidth efficiency than thetraditional four-phase and three phase bidirectional relaying schemes. To reduceimplementation complexity, simpler PNC schemes such as Analog Network Coding (ANC)with Amplify and Forward (AF) protocol were presented in previous works. ANC hasbeen already applied to Orthogonal Frequency Division Multiplexing (OFDM) forbroadband wireless communications.In order to achieve high order of spatial diversity to combat fading, multi-antennarelay can be deployed. However, as the multiple antennas are geographically co-located,the received signals on each individual antenna may experience dependent fading. Analternative spatial diversity approach is through multi-relay cooperation, which posesother design challenges, e.g., synchronization, if all the relays participate in thetransmission. As a result, Relay Selection (RS) has been proposed to achieve full diversitythrough a multi-relay network at a lower implementation cost.