CFO and IQ Imbalance Parameter Estimation in Cooperative OFDM Links

In a distributed cooperative environment, synchronization is a major issue. Especially when OFDM is employed in the physical layer, frequency offset synchronization is of great significance. In addition, transmitter and receiver IQ imbalances are known to be important implementation issues in OFDM systems. In this paper, the use of a strategy is investigated that enables blind estimation of Carrier Frequency Offsets (CFOs) of each transmitter (along with receiver IQ parameters), in a cooperative scenario when OFDM (with either amplify and forward or Space-frequency Coded) is employed in the physical layer for frequency selective channels, even when the transmitter and receiver IQ imbalances and phase noise are present. This is possible by a block precoding strategy involving adjacent OFDM symbol blocks, as well as multiplication of the symbols to be transmitted by a random PSK sequence. This precoding strategy involves negligible loss in rate. Computer simulations are presented to demonstrate the effectiveness of the algorithm.