Study On And Application Of Smart Antennas In TD-SCDMA Systems

The technology of smart antenna in the TD-SCDMA (Time Division -Synchronous Code Division Multiple Access) system is comprehensively and deeply studied. The radio transmission of system is described wholly and the whole simulation model and simulation link is set up. Theoretical analysis and simulation of smart antenna, which is a key technology of TD-SCDMA, is made and performance of smart antenna system is evaluated comprehensively from the point of link level and system level. Smart antenna algorithms fit for TD-SCDMA are proposed and their applications are also considered. The concepts of sectorial smart antenna and edge interferences are proposed. The optimum principle of sectorial beam and two channel distribution schemes to solve the edge interference are illustrated.The author's major contributions are as follows:1. A Space-Time channel model used for smart antenna simulation in TD-SCDMA system is proposed which is based on plentiful published measurement results and models. Basic and main properties of Space-time channel, especially angular spread and correlated fading are included in the model. Parameters used in the model are summarized from a mass of published measurement results, which assures the model precise and mature. The Power Delay Profile characteristic of the model is the same as that recommended by 3GPP, so the consistency of the TD-SCDMA model is ensured.2. A discrete time system model of the TD-SCDMA air interface is described in the equivalent lowpass domain. Based on the model an integrated physical layer simulation link of TD-SCDMA is setup. The uplink STJD (Space-Time Joint Detection) algorithms is analyzed with its space processing, space-time processing and output SNR performance considered. A directional interference model is introduced for the first time and the simulation results with interference considered and not under different interference case are given which are important to the design or selection of TD-SCDMA uplink algorithms.3. An improved channel estimation method based on conventional Steiner estimator is presented which can depress effect of interference and noise on estimator. Three improved interference spatial covariance matrix estimation methods, namely, Post-Processing method, Midamble Signal Cancellation method and Data Signal Cancellation are proposed. The front two improved methods give better performance and the last one performs better only under low SNR sceario compared to the conventional Idle Windows method.4. Concepts of chip level beamforming (for user) and symbol level beamforming (for code channel) are firstly proposed and their difference is simulated in TD-SCDMA system. The downlink algorithm of TD-SCDMA, namely Transmit Beamforming algorithm, is analyzed and different criteria, algorithms and realizations of transmit beamforming are simulated. An optimum multi-user detection approach for TD-SCDMA terminals has been proposed which gives better performance compared to conventional JD methods and simplified JD methods.5. System simulation model based on TD-SCDMA standard has been built. In the model the smart antenna models with different criteria for TD-SCDMA uplink and downlink has been set up and the wraparound model is introduced. Characteristic of uplink inter-cell interference of TD-SCDMA system is simulated which is the basis for application of spatial covariance matrix. The difference of spatial covariance matrix between uplink and downlink has been analyzed and simulated. The simulation results are important references for application of tramsmit beamforming methods with interference suppression creterition. System simulation results of smart antenna under various conditions are given.6. Sectorization is extensively used in cell communication systems. A scheme combined smart antenna and sectorial antenna is proposed which is an effective method to realize sectorization together with smart antenna. An optimization criterion of minimizing inter-sector interference subject to an in-sector pattern ripple constraint is given. Inter-sector interference at edges between adjoint sectors and ilk code phenomenon of TD-SCDMA systems are analyzed. Two DCA methods based on DOA estimation are proposed to suppress edge interferences. Time slot allocation methods can effectively combat MAI at sector edges and then balances performances of users at different area; Channelized code allocation method can efficiently depress the infection of ilk-code phenomenon of TD-SCDMA system.