| Multiple-Input Multiple-Output (MIMO) technology based on transmit and receive diversity technology increases the capcity, data rate and spectral efficiency of wireless communication systems, and resists the fading effectively, realizes the reliable communication. Space-Time Codes (STC) make use of transmit diversity technology, introduce space and time correlation on the transmitter, so not only diversity gain but coding gain can be achieved on the receiver. The performance of STC depends on the number of antennas and temporal and spatial coding of the signal.In this paper, the Space-Time Block Codes and STC with optimal power allocation are analyzed by exploring the model of STC. For the fast fading channel, Differential Space-Time Codes and Unitary Space-Time modulation are introduced, and amplitude-phase Double Differential Space-Time Codes are derived, which controls the transmission power of the system by the amplitude coefficient, and selects the modulation symbols by the phase coefficient. Based on the above, the impact of amplitude coefficient ratio on amplitude-phase Double Differential Space-Time Codes is discussed, and an optimal selection scheme in amplitude coefficient is given. Meanwhile, the maximum data rate is achieved by selecting the optimal amplitude and phase coefficents adaptively using M2M4 SNR estimate algorithm under a BER.The design of STC is based on frequency nonselective fading channels. For frequency selective fading channels, how to use STC is a problem deserving to research. Now, a general solution is that combining STC with OFDM, but it is supposed that the channel changes slowly, so there is enough time to transmit the training sequence for channel estimation. For fast fading channels, this paper adopts interlace and deinterlace methods, solves the combination problem of amplitude-phase Double Differential Space-Time Codes and OFDM, which is more suitable for frequency selective fading channels, for it doesn't need channel estimation. |
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