Research On Spatial-temporal Channel Modeling Of Wireless Anication System And The Effects Of Antenna Array Orientation On Channel Characteristics

In the conventional wireless communication system, both of the transmitter and receiver use single-antenna to transmit the signal. With the rapid development of multimedia communications in wireless Internet, the demands of broadband high-speed data communication service is growing day by day. Capacity of conventional single-antenna transceiver communication system has been far from satisfying the needs of actual use, and reliability need to be improved. The study on utilization of multi-input multi-output (MIMO) system at both ends of the wireless link, conclude that the transmission rate of the system communication can be improved several times without increasing the frequency spectrum resources and transmit power. Therefore, MIMO has become an important technology in the field of wireless communications. However, the implementation of large capacity, the improvement of other performances and performance advantages and disadvantages of various signal processing algorithms in MIMO system and the MIMO system are greatly dependent on the characteristics of MIMO channel. This requires that we acquire the channel characteristics very well and create the channel model to promote the development of other MIMO technologies. Meanwhile, the effect on the channel characteristics from the correlation between the antennas cannot be ignored due to the use of multiple antennas,In connection with the above two issues, the main contents in this as follows:Firstly, the necessity of channel modeling is introduced, followed by a review of the existing radio channel model as well as the space channel model and analysis of the advantages and disadvantages of each model. To provide a theoretical basis on improved spatial model that will be proposed later, the principles of geometrically based single bounce scattering model are highlighted.Secondly, for the particular scattering environment that the number of scatterers in the regions that are adjacent to the mobile station (MS) is very small or equals zero, a hollow circular inverted parabolic spatial channel model is proposed. What’s more, this paper has presented a technique to derive the probability density functions (PDFs) of time of arrival (TOA) in simply formulas for an arbitrary spatial distribution. Employing this channel model, we have also derived the PDFs of angle of arrival (AOA) and AOA/TOA. Simulation analysis show that compared to the previous model, the presented model gains a better versatility. The theoretical values of AOA derived by the model matches the experimental data better, which verified the rationality of this model.Thirdly, given the poor estimation accuracy and the poor flexibility for the existing spatial channel models for macrocell and microcell, we present an improved spatial statistical channel model. The channel model assumes scatterers at an inverted parabolic spatial distribution around MS within a circle. The BS and MS are included in the region in order to flexibly simulate outdoor macrocell and microcell environments. Employing this channel model, we derive the PDFs of AOA and AOA/TOA. Simulation analysis show that compared to the geometrically based single bounce circular model (GBSBCM) and the Gaussian distribution model, the improved model matches the experimental data better, and the parameters estimated by the model are in line with the theory and experience. Meanwhile, taking the practical factors of the directional antenna and the movement of MS into account, we have also analyzed the impacts of a directional antenna at BS with the main-lobe width2α on the Doppler spectra. The results revise the Clarke model. This model has provided a powerful tool to appraise space-time processing algorithm for MIMO system and for simulation of wireless communications system. The estimate parameters will be used to compute the spatial correlation coefficient.Lastly, antenna correlations are researched and exact and approximate analytic formulas of coefficient with several distributions of power angle spectrum in two types of antenna array are derived. From the simulation results, we obtain the application scope of the approximate expressions. The simulation results show that the approximate formula can replace the exact formula to simplify the calculation when the range of incidence angle is small. At the same time, the impact of various factors on the correlation coefficient is studied. Next, comparisons of the correlation coefficient among the estimated wave angular spectrum distribution of improved model and another three distributions show that the correlation coefficient corresponding to improved model is less than another three kinds of situations when the antenna spacing is greater than0.7wavelengths and the center angle of arrival equals zero. Finally, the antenna array orientation on the performance of the channel is discussed. To reach the low correlation between the antennas, the normal of transceiver arrays should point to the direction of average angle of arrival and the direction of average angle of departure as much as possible, respectively.