A Study On Space-Time Diversity Receiving And Related Techniques

In mobile wireless communication systems users and obstacles are locate in different area, therefore multi-path signals have the spatial and temporal coupling signature. Separate temporal signal processing or spatial signal processing doesn't utilize the spatial and temporal structural signature of the signals and channels, so they can only improve the quality and capacity of wireless networks limitedly. Space-time processing (STP) can take the advantages of both spatial and temporal signal processing, and utilizes the space-time structural characters of the radio communication channels sufficiently, so it can make up the shortcoming of the spatial or temporal domain processing, and improve network capacity, coverage and quality of radio communication systems.This thesis focuses on the space-time diversity receiving and related techniques. In detail, the main contributions of the thesis include:1) Angle diversity receiving for the multipath signalsThe multi-path propagation may cause the transmitted signal to arrive at the receiver along several paths with different DOAs and different delays. Multipath propagation results in delay spread and angle spread of the received signals. The signals propagating along different paths arrive at the destination with different DOAs and different delays, which leads to ISI in the received signals. In regard to multipath propagation, a method of angle diversity receiving was presented. By using several beamformers we performed spatial filtering for each ray of the desired user's signal to extract each component of the multipath signals respectively, and then the extracted multipath components were combined after proper delay with maximal ratio combining (MRC), which can improve SINR of output signal effectively. Considering the problem that the temporal diversity gain is obtained less by the MRC, we also proposed a MMSE combining and equalization scheme, in which the output from all the beamformers were combined and equalized simultaneity to suppress the ISI in the combined signal.2) Beamforming for CDMA signals and 2D-RAKE receiverOn despreading the DS-CDMA signals, the multipath signals whose delays exceed one chip will be seemed as noise. But it is not the same circumstance when to perform beamforming for the despreaded array signals, because the multipath signals with different delays are became coherent signals after dispreading and can be utilized.The Code Filtering beamforming method proposed by Naguib in reference [69] can only form a large gain in one of multipath signals of desired user, and other multipath signals are seemed as noise. Namely, Code Filtering method only utilizes one multipath component, while other components don't be utilized. To solve this problem, in this paper we proposed a improved Code Filtering beamforming method by which all the multipath components of desired user are utilized when to perform beamforming after code filtering processing. Based on these above, we improved the time-space cascaded 2D-RAKE receiver, and proposed a novel time-space cascaded 2D-RAKE receiver.3) Space-time two dimension joint diversity receivingSeparate time diversity receiving or space diversity receiving doesn't utilize the spatial and temporal structural signature of the signals and channels, which limits their diversity gains and interference suppressing ability. In regard to the shortcoming of one dimension diversity receiving methods, we proposed a space-time two dimension joint diversity receiving method, which can perform diversity receiving for desired user's multipath signals with different DOAs and different delays in both spatial domain and temporal domain jointly and suppress CCI and noise, so it can improve the output SNR of the desired user's signals.The CDMA technology has been widely accepted by the current wireless communication systems. The space-time processing for CDMA systems relates to the conventional 2D-Rake receiver. We proposed a joint space-time diversity receiving method for DS-CDMA system to solve the problem of the space-time processing of the direct sequence spread spectrum (DSSS) signals in the frequency selective fading channel. For each multipath component of the deserved user's signal, there was a bank of same correlators connected with each element of the antenna array to despread the signals received on each antenna respectively. Several such banks of correlators were used to despread every component of the deserved user's multi-path signals respectively, and then the despread signals outputted from all banks of correlators were combined jointly by exploiting the Minimum Mean Squared Error (MMSE) criterion.In order to reduce the calculating complexity of the weight coefficients, we also proposed a complexity-reduced space-time diversity receiving method for DS-CDMA system. Simulation results show that the proposed methods are demonstrated to be superior to the conventional 2D-Rake receiver.