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Performance analysis of a rate varying space-time coding scheme

In this paper, a rate-varying space time coding scheme is proposed to improve the performance of the MIMO radio link under a high mobility communication system. Unlike the traditional fixed rate space time coding scheme, the proposed scheme keeps choosing the pre-coding matrix randomly in each transmission period to deliver a certain signal vector until the vector is successfully decoded by the receiver. Because the number of transmission period is based on the channel quality, the proposed scheme can obtain a random coding rate to suit the fast-varying channel. The effective channel gain (ECG) of each signal can be designed in this scheme to obtain a optimal percoder because the ECG consist of the channel matrix and the percoding matrix which we can choose. Surprisingly, it is shown that the impulse function is the best probability density function (PDF) of the ECG to achieve the best symbol error rate (SER)performance under mean constraint. Thus, an optimal pre-coding method and a Gaussian pre-coding method for comparison are designed under that criterion. Further more, the PDF of ECG of each signal in the two method are presented to show the performance accurately. Finally, numerical results are presented to verify the proposed scheme. It is shown that the scheme is more flexible under a high mobility channel.