An Adaptive Transmission Scheme Robust to Variant Moving Speeds

Coherent space-time codes perform not so excellent in high moving speed case due to the inaccurate channel estimation. However, differential space-time code is appealing in this case because no channel estimation is needed. While in low and middle signal-to-noise ratio regions differential space-time codes are inferior to the coherent ones. To achieve an excellent performance in a various moving speed environments, we develop an adaptive transmission scheme in this paper where coherent space-time code is applied in low and middle moving speed cases, while differential space-time code is used in high moving speed case. Because the proposed scheme adopts the space-time codes wisely according to the moving speed, it outperforms the scheme which purely utilizes coherent space-time code or differential space-time code and thus is suitable for various moving speed environments. Moreover, two differential space-time codes based on differential Alamouti code are proposed in this paper with the merits of low decoding complexity, suitable for general number of transmit antennas and no code rate loss. The effectiveness of the proposed scheme and the proposed differential space-time codes is supported by numerical simulations.