Asymptotic Symbol Error Probabilities of MIMO (multiple inputs and multiple outputs) Diversity Configurations and A Novel Close Loop Code Division MIMO Diversity Scheme

Abstract

This paper derives, in an unconventional way, the asymptotic symbol error rate (ASEP) for existing MIMO diversity configurations. The ASEP contains only the term of the inverse SNR raised to the system diversity order (DO). It is an explicit function of the MIMO DO, its array gain (AG) resulting from increased DO and the SNR gaps under the same DO. When both transmit (Tx) and receive (Rx) antennas exceed one, the inter-channel interference (ICI) from different Tx antennas coming into the same Rx antenna makes it very difficult to obtain the full system DO, which equals the product of the number of Tx and the number of Rx antennas. ICI is cancelled in the Alamouti and dominant eigen-mode transmission (DET) MIMO diversity schemes [1,4] by creating effective orthogonal Tx-Rx channel matrix. Walsh orthogonal codes or code division (CD) schemes are also used in the open-loop (OL) MIMO diversity configuration, e.g. in WCDMA standard [2] without any bandwidth (BW) efficiency loss or processing gain. The paper proposes to use CD for the OL MIMO to not only avoid ICI and but also trade bandwidth for AG. It also proposes a CD scheme for the closed-loop (CL) MIMO diversity with the channel knowledge (CK) at the Tx. Compared to the existing CL DET and OL CD schemes, the CL CD scheme is much simpler and has about 1dB SNR improvement for a 2×2 system. Simulation results show good agreements with the theoretical analysis.