Low complexity turbo equalization for LTE uplink with transmitter IQ imbalance

In this paper, we propose two improved turbo equalizers for Long Term Evolution (LTE) uplink in presence of transmitter (Tx) in-phase and quadrature-phase imbalance (IQI) which are known at the receiver. For multi-user multiple-input multiple-output (MU-MIMO) single-carrier frequency division multiple access (SC-FDMA) systems, we derive a optimal joint linear turbo equalizer under minimum mean-square error (MMSE) criterion. For the special scenario where there is only one user equipment (UE) and it occupies all sub-carriers, we derive an optimal widely linear MMSE (WLMMSE) turbo equalizer. Both of two equalizers are implemented in discrete frequency domain and only cause slightly increase in computational complexity compared to the conventional turbo equalizers. Simulation results show that both the proposed equalizers outperform the conventional turbo equalizers under corresponding scenarios.