| Due to the development of communication service in recent years,there is an increasing demand for the growth of transmission data rate.Therefore,the multiple-input multiple-output(MIMO)spatial multiplexing technology with multiple arrays at both ends of the communication link is used to achieve the improvement of the performance of the communication system.Considering the possibility of millimeter wave band data transmission in open scenes,this thesis mainly analysis spatial multiplexing conditions in MIMO systems with only Line of Sight(Lo S)when using directional antennas.The analysis of spatial multiplexing mainly focuses on the influencing factors of actual channels and antennas.The important parameters include the number of antennas at the receiving and transmitting ends,transmission distance,transmission frequency,antenna array size,antenna beamwidth,antenna pointing,etc.The specific research contents are as follows:Firstly,according to the influence of channel eigenvalues on channel capacity and spatial multiplexing,optimal spatial multiplexing and effective spatial multiplexing are defined.Then conduct environment modeling and directional antenna modeling for the Lo S MIMO system.At the same time,channel eigenvalues analysis are performed for the Lo S MIMO system based on the principle of spatial multiplexing,and it is found that the parameters that affect channel eigenvalues are subchannel gain difference and subchannel orthogonality.Secondly,based on the millimeter wave transmission scenario model in an open environment,a spatial multiplexing analysis of Lo S MIMO based on isotropic antennas was conducted,and the optimal and effective spatial multiplexing conditions based on isotropic antennas were obtained.By adjusting the relationship between the number of antennas,transmission distance,and antenna spacing,the optimal spatial multiplexing condition,namely the Rayleigh condition,can be achieved.At the same time,the maximum number of data streams that can be simultaneously transmitted during largescale MIMO and long-distance transmission is derived,and the characteristic values of the same size for each stream are obtained.Considering that it is difficult to obtain a explicit expression of the eigenvalues of the channel gain matrix in higher order conditions,the effective spatial multiplexing conditions for transmitting up to two data streams in parallel are derived,as well as the impact on channel capacity under different spatial multiplexing conditions.Finally,according to the environment model and antenna model,the optimal and effective spatial multiplexing conditions for Lo S MIMO based on directional antennas are obtained.Compared with the use of isotropic antenna,the use of directional antenna increases the two parameters of antenna beamwidth and antenna pointing,which makes the conditions for spatial multiplexing more stringent.Comprehensive theoretical analysis and simulation verification show that the spatial multiplexing condition of directional antenna not only needs to meet the Rayleigh condition,but also needs the symmetry of the transceiver antenna gain or higher requirements on the beamwidth based on the ideal antenna modeling.When the number of transmitting antennas is always two,the gain of subchannels can be the same by adjusting the antenna pointing.At this time,only the orthogonality of subchannels affects spatial multiplexing.As the number of receiving antennas increases,different antenna pointing modes and antenna numbers will affect the orthogonality of the sub channel.Although directional antenna cannot increase the farthest effective spatial multiplexing distance,within this farthest effective spatial multiplexing distance,the narrower antenna beamwidth can bring better spatial multiplexing effect and greater channel capacity. |
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