Estimating Timing and Frequency Offset along with Channel in Multi-Relay Cooperative Networks Using Amplify and Forward Network

Orthogonal synchronization has been a major problem in Cooperative Orthogonal Frequency Division Multiplexing (CO-OFDM) under the influence of both carrier frequency offset and timing offset with unknown channel gains. CO-OFDM network performance can be improved by employing Amplify-and-Forward (AF) relay strategy. The OFDM network comprises of many sub-carriers which requires an adjustment of transmit frequencies in order to avoid Inter-Carrier-Interference (ICI) which would otherwise destroy the orthogonality of subcarriers and lead to severe performance degradation. Symbol timing offset between transmitter and receiver due to multipath propagation that exist in cooperative channels often cause erroneous decoding and Inter-Symbol-Interference (ISI). Multi-relay cooperative networks affected by Multiple Carrier Frequency Offsets (MCFO’s), Multiple Timing Offsets (MTO’s) and unknown channel gains are estimated by MaximumLikelihood (ML) estimation and Maximum Ratio Combining (MRC). Simulation results show that, through the ML decoding method, cooperative system results in significant improvement in Symbol Error Rate (SER).