Soft-Information Aided Channel Estimation With IQ Imbalance for Alternate-Relaying OFDM Cooperative Systems

In this letter, we exploit the feature of data redundancy associated with alternate-relaying cooperative systems to develop an iterative channel estimation algorithm in the context of orthogonal frequency division multiplexing (OFDM) transmission. Our attention is also focused on the problem of in-phase/quadrature-phase (IQ) imbalance which is typically associated with OFDM transmission. Analytical analysis indicates that instead of estimating a family of parameters including IQ imbalance occurring at the source, relays, and destination, and channel impulse responses (CIRs) between the source-destination link, and relays-destination links, we can estimate one parameter called the equivalent CIR. In addition, we illustrate how to perform data detection using the estimated parameter. By employing expectation-maximization algorithm, we show that soft information provided by the detector can be combined with pilot symbols in an efficient way to enhance the estimation process. Simulations experiments have confirmed the efficiency of the proposed approach.