Time-frequency Cooperative Multi-antenna Transmission Technology

With the advancement of technology, mobile communication channel environment is becoming increasingly complex. In many new communication scenario, channel fading characteristics already exhibited by more than a single time domain selective fading or a frequency domain selective fading, but a time and frequency domains simultaneously fading feature. The traditional time-domain signals in the frequency domain selective channels have better performance, but the poor performance under the time domain selective fading channel, and the traditional frequency-domain signals in the time domain despite fading channels perform well, but have poor performance in frequency domain selective fading channels. Thus, in the time-frequency double selective fading channel, the traditional time-domain signals and frequency domain signals are hard to get a good error performance.In order to solve this problem, this paper chooses the time-frequency collaborative signal form, to make full use of the characteristics that the time domain signals anti Doppler frequency shift, and the frequency domain signals anti multipath, so as to fight against the time and frequency selective fading caused by the Doppler frequency shift and multi-path delay spread. Researches show that the time-frequency cooperative way based on the weighted fractional Fourier transform performs well in time-frequency doubly selective channel conditions. In order to further improve the capacity of the system, we can also use the airspace resources, and multi antenna technology is just the best technology of using airspace resources. But if it is simply to combine the time-frequency cooperative signal with the multi antenna system, there are clearly many problems, but also can not give full play to the potential of the system.So this paper studies the multi antenna transmission technology of the time frequency cooperative signal. Based on the analysis of the time-frequency collaborative signal constraints and compensation characteristics, this paper gives the combination form between the complete time-frequency collaborative signals and the multi antenna system. Simulation results show that the frequency doubly selective channel, its performance is better than both of the traditional time domain signal multi antenna system and frequency domain signal multi antenna system. Through the further analysis of weighted form of time-frequency collaborative signal, we found that different components have different ability to adapt different sub channels, if each component is mapped to the corresponding sub channel, component form must be able to obtain better performance than the complete form. For this, we propose a specific scene in which two base station joint for serving a mobile user, and it can be abstracted into a system model in which one channel presents time selective fading, the other channel shows frequency selective fading. The simulation results show that in this scenario, the performance of the component signal form is better than the full signal form when combining the time-frequency cooperative signal with the multi antenna. On this basis, taking into account the transformation order influence the error performance seriously when the signal frequency cooperative multi-antenna system is large, this paper presents a method of transformation order selection. The simulation results show that using this method, the performance of time-frequency cooperative multi-antenna transmission system has been further optimized.