Channel Modeling And Applications Of Hybrid-diversity MIMO Systems

Multi-input multi-output (MIMO) system uses multiple antenna elements in bothtransmitter and receiver, which increases spectral efficiency and channel capacity withoutadditional system bandwidth and transmitting power. Due to the great advantages, MIMO systemhas wide application prospect in wireless communications.Different diversity techniques of MIMO systems have different advantages anddisadvantages. The hybrid diversity, which makes combination of different diversity techniques,also received much attention. For MIMO systems with hybrid diversity, statistical characteristicsof sub-channels are difficult to understand due to effects of various diversities, and that’s whyexisting models often have various degrees of defects. The main objects of our research are howto grasp statistical characteristics of sub-channels of MIMO systems with hybrid diversity andhow to establish more accurate channel models.During the study of modeling hybrid-diversity MIMO system, it is concluded thatcorrelations of orthogonal sub-channels can be further reduced by increasing distance betweenantennas, which may be valuable for six-polarization MIMO systems. Yet defects also exist inpower and correlations of past models of six-polarization MIMO systems, which results ininaccurate conclusions under most conditions. New modeling methods of six-polarization arecarried out. Based on the new modeling methods, performances of six-polarization MIMOsystems are also discussed.The main achievements and innovations on such aspects are listed as follows:1. On condition of neglecting correlations of orthogonal sub-channels and effect ofpolarization of spatial-diversity antenna on sub-channels’ correlations, research work of signalpropagation is carried out based on simplified physical models which suit such condition.Problems of past models and correct theory of modeling are pointed out. A new simplifiedstatistical model, which reflects effects of various diversities correctly, is established based oncomposite application of power matrix and correlation matrix.2. Effect of polarization of spatial-diversity antenna on sub-channels’ correlations is provedbased on complicated physical models. This effect is often neglected in past models. In order tocompensate for this effect in modeling theory, a new simplified statistical model, which reflects effect of polarization of spatial-diversity antenna on sub-channels’ correlations, is established asan expansion of the new model mentioned above.3. On condition of considering correlations of orthogonal sub-channels, correlationsbetween sub-channels are analysed in detail. It is indicated that the traditional modeling method,which caluates correlation coefficients of hybrid-diversity MIMO system from correlationcoefficients spatial-diversity MIMO system and polarization-diversity MIMO system, is not ableto avoid inaccurate correlation coefficients. A new statistical model for complicated condition isestablished directly from statistical characteristics of hybrid-diversity MIMO system in spite ofthe traditional modeling method.4. Inaccurate power information of Kronecker product model in past research work isreplaced by an extra power matrix, which result in a Kronecker product model with correctpower of sub-channels.5. Defects of Kronecker product model itself are analysed. It is indicated that Kroneckerproduct model usually results in inaccurate correlation coefficients when applied tosix-polarization MIMO system. Instead of Kronecker product model, other modeling methodsare suggested for six-polarization MIMO system in order to get more accurate conclusions.6. It is indicated that six-polarization MIMO systems may not achieve maximal diversityindependent communication modes during studing of modeling six-polarization MIMO systems.Conclusion from studing of modeling hybrid-diversity MIMO systems is also taken into account,which results in a six-polarization MIMO system with hybrid-diversity. Simulation results ofsuch system show that six-polarization MIMO systems does not achieve performance limit of sixantenna systems because that correlations of six-polarization MIMO systems can be furtherreduced by appling of hybrid-diversity.