STBC MIMO OFDM Systems with Implementation Impairments

Multi-input multi-output (MIMO) systems are often realized with low cost front-end architectures, e.g. the so called direct conversion architectures. However, such systems are very sensitive to imperfections in the analog front-end, resulting in radio frequency (RF) impairments such as in-phase/quadrature-phase (IQ) imbalance and carrier frequency offset (CFO). The RF impairments in such low cost front-end systems are unavoidable and can result in a severe performance degradation. In this paper we propose a generally applicable equalization technique for space-time block coded (STBC) MIMO orthogonal frequency division multiplexing (OFDM) communication systems. The Alamouti based STBC scheme is examined in detail. It is shown that the compensation scheme can be easily extended to other higher order STBC systems. We consider a digital compensation scheme for joint transmitter and receiver IQ imbalance along with front-end filter mismatch, CFO and frequency selective channel distortions.