Abstract
In this article, we propose a dynamic multiple-input multiple-output (MIMO) mode switching scheme between spatial multiplexing and diversity modes, which also includes adaptive modulation. At each transmission, we select the modulation level and the MIMO mode that maximize the spectral efficiency while satisfying a given target bit error rate. The dynamic MIMO mode scheme considers instantaneous spectral efficiency whereas the conventional static scheme considers only the average SNR. As for adaptive modulation, a new method is proposed to compute the SNR thresholds for adaptive modulation in each MIMO mode, and it can avoid the computational difficulty of the conventional Lagrangian (optimal) method at high average SNR. To deal with the case where the rates of the two MIMO modes are the same, we also propose a new measure based on the BER exponent, which has lower computational complexity than a conventional measure. Numerical results show that the proposed dynamic mode switching improves over the conventional static mode switching in terms of average spectral efficiency.
Highlights
Today’s wireless communication systems demand high data rate and spectral efficiency with increased reliability
Multiple-input multiple-output (MIMO) systems have been popular techniques to achieve these goals because increased data rate is possible through spatial multiplexing scheme [1] or improved diversity order is possible through transmit diversity scheme [2]
In Step 3, we propose the mode selection rule based on the instantaneous spectral efficiency (ISE) as well as the rule which can be applied to the case when both of the two MIMO modes have the same data rate
Summary
Today’s wireless communication systems demand high data rate and spectral efficiency with increased reliability. We propose a dynamic MIMO mode switching scheme which considers instantaneous channel condition in conjunction with rate adaptation. The adaptive modulation part is based on the existing methods [5,7,8,9,11], we compare the performance of the existing techniques, and propose a sub-optimal method to obtain the SNR thresholds for the average BER constraint. The modulation level and the MIMO mode are selected according to the current channel condition. In Step 3, we propose the mode selection rule based on the ISE as well as the rule which can be applied to the case when both of the two MIMO modes have the same data rate.
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