An iterative CFO estimator for QO-STBC uplink MC-CDMA MIMO systems

In the present paper, we propose an iterative blind CFO estimator for the hybrid quasi-orthogonal space-time block coding (QO-STBC) [3] MC-CDMA system with four transmit antennas. The design of the proposed scheme started with the development of a multiply constrained minimum output energy (MCMOE)-based blind detector, in which a set of correlators is constructed to collect each multipath signal from the user-of-interest and suppress multiple access interference (MAI). The CFO estimate can be determined by minimizing the output power of the MCMOE detector, which approximates to a quadratic function in terms of CFO by using the first-order Taylor series expansion. To reduce the computational complexity, we find the solution to the quadratic function as the CFO estimate, instead of searching the peak location of the output power spectrum of the MCMOE detector. Finally, further performance enhancement is achieved by using an iterative scheme in which the CFO-compensated data is sent to the MCMOE detector as the input of the next iteration. Numerical results have been conducted to verify that the proposed blind estimator can achieve the precise CFO estimation with a few iterations.