| MIMO (Multiple-input Multiple-output) communication system can do an excellent work in the competing against the wireless channel fading, improving the spectrum effectiveness and enhancing the system channel capacity. The performance of MIMO multiaerial system is determined by the spatial correlation function that characterizes system channel features. In this article, channel model of wireless MIMO system with Y-shaped taken as receiving end is innovatively put forward and the research on the array element correlation changes of Y-shaped array under different incoming signal distribution and the influence of mutual coupling effect under two-dimensional plane and three dimensional conditions to wireless MIMO system with Y-shaped taken as receiving end. The whole work can be shown as follows:Firstly, taken Y-shaped array antenna as the model, the correlation accurate formula among the wireless array elements is deduced when the incoming signal is taken the forms of uniform distribution, Gaussian distribution and Laplace distribution respectively, meanwhile the correlation approximation formula is deduced according to the trigonometric formula and modified Bessel function,discovering that this formula is also applicable to the UCA. Simulated analysis is conducted on the effects of various elements such as extension angle, array element interval and array element number to Y-shaped array special correlation when the incoming signal is taking the form of uniform distribution, Gaussian distribution. According to numerical analysis done by matlab software, the conclusion has been made that approximate calculation has a good computational efficiency and it can further applied in the other performance research and simulation of MIMO system.Secondly, analysis is conducted on the influence of cross coupling effect to the multi-antenna system performance and a simplified analysis is also carried out on MIMO system antenna model with equivalent analysis method, thus we can obtain impedance matrix and coupling matrix of receiving end. The general expressions of array element correlation of Y-shaped array and UCA under the cross coupling is deduced. The conclusion can made through the simulation and comparison with matlab software that correlation among the antenna elements will fluctuate around the correlation without cross coupling. The smaller distance among the antenna array elements, the stronger the effect of cross coupling to the correlation.Thirdly, according to the problem that under the cross coupling, the channel capacity of MIMO antenna array will sharply reduce when the array elements interval is smaller and DOA greater, MIMO receiving antenna model based on the Y-shaped array structure is put forward too. Based on constructing network equivalent model, the general expressions of Y-shaped array channel correlation with or without cross coupling is deduced. Under the condition when the incoming wave angular spectrum is Gaussian distribution, the analysis on the effect of Bodard incoming signal central arrival angle and angle spread to the Y-shaped array and UCA system channel capacity is conducted. The simulation results show that Y-shaped wireless MIMO system with Y-shaped array taken as receiving end has a stronger cross coupling resistance and stable channel capacity, its channel capacity is better then that of UCA wireless array so it can effectively improve the array cross coupling and promote the system performance. Fourthly, based on two dimensional Y-shaped antenna array, three dimensional spatial channel models are put forward, in which Y-shaped is taken as the receiving antenna array and the general channel model of MIMO is extended to the three dimensional spatial domain. The equivalent network model of wireless MIMO antenna array is established under the effect of cross coupling and the cross coupling correlation expression is deduced, in which the receiving end is taken the form of Y-shaped under three dimensional conditions. This expression is applied to analyze the effects of direction extension angel, pitching extension angel, central arrival angle and arrival pitching angle of incoming signal to the system channel capacity respectively when the receiving end is taken the forms of Y type under the cross coupling. Matlab simulation is used to analyze effects of various angle extensions under cross coupling to the wireless MIMO system array elements correlation and a comparison between it and UCA is made thus the relevant conclusions are made correspondingly. Compared to UCA, channel capacity of antenna system channel capacity with Y-shaped taken as receiving end is more stable and has more powerful cross coupling resistance under three dimensional conditions. |
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