Multiuser pilot pattern for uplink multicarrier systems with frequency-dependent I/Q imbalance

This paper deals with the optimization of the multiuser (MU) pilot design for orthogonal-frequency-division-multiple-access (OFDMA) systems perturbed by the I/Q imbalance (IQI) impairment. For the frequency-selective Rayleigh propagation channels, the proposed approach exploits the decoupled direct and image channels, and the knowledge of the effective channel statistics to realize dual linear-minimum-mean-square-error (LMMSE) channel estimators. We develop the pilot power distribution and positioning approach for the training sequence design under the channel mean-square-error (MSE) minimization criterion considering the existence of IQI and guard bands. For the pilot power allocation, we formulate the problem into semi-definite programming whereas positions are assigned with either a heuristic greedy method or fairness instigating genetic combinatorial optimization. Simulation results indicate that with the proposed pilot design, it is possible to achieve a better MSE performance than the conventional MU channel estimation methods and introduce user fairness when selecting pilot composition from the shared pool of resources.