Per-path-per-weight Beamforming And Power Control In CDMA System

It is well-known that as the key multiple access technology in 3G, beyond 3Gand wireless LAN system, recently, the CDMA technology has achieved manydelightful developments both in the theory research and practical application.High data rate transmission of multimedia service requires the CDMA system toincrease the received power. As the same time, the complexity of propagationinduced by decreasing coverage radius of cells will bring much moreinterference. Since the capacity is limited by the interference from itself, in theCDMA fields, the effective method of suppressing interference is still important.Using space-time coding in CDMA systems can improve diversity gain, but can notenhance the ability to suppress multiple access interference (MAI). In frequencyselective fading channel, MAI introduced by multidelay paths would not be deletedcompletely by temporal correlation. Even if joint using Rake receiver and space-timecoding, MAI will increase when the number of subscriber increases.The beamforming combined with power control can effectively suppress MAI. Butthe beamforming method currently adopted is mainly per-user-per-weight (PUPW), inwhich one user's all delay paths are allocated same weight vector. In macro-cellenvironment, the angular separation between each path of the same user is relative small,and this approach is more effective. But in micro-or pico-cell environment, the angularseparation between each path of the same user is relatively large, using the PUPWbeamforming scheme can not ensure the main lobe direct to the desired user while thenull direct to the interference users. For further improving the performance of CDMA in micro-or pico-cell, we integratebeamforming, power control and space-time coding, mainly consider downlink problem,and research the optimization of the per-path-per-weight beamforming (PPPW)combined with power control. Main Content of this thesis Charter 1 summarizes the researching actuality of downlink beamforming for CDMAsystems, and analyzes the effect using per-path-per-weight (PPPW) beamformingcombined power to improve the performance of CDMA systems in pico-and micro-cell.Finally introduces the researching purport and main content of this thesis. Charter 2 analyzes the relationship between uplink and downlink beamforming signalmodel. If the DOAs are identical, the differences between uplink and downlink channelresponses are mainly determined by carrier frequency and fading coefficients. Theinfluence of carrier frequency is determined and the influence of fading coefficients israndom. Summarizes DCCM algorithm of TDD and FDD systems, including DOAestimation, frequency transformation and frequency calibration, and the frequencycalibration is introduced in detail. Compare the optimizing models of joint beamformingand power control between downlink and uplink. The uplink situation is a typical linearoptimizing problem, and the downlink situation is a complex no-linear optimizingproblem which can be solved by virtual uplink beamforming and power controltechnology (V-UBPCT). Charter 3 introduces the concept of code filter and analyzes the principle of PPPWbeamforming. Since the array response of long spreading sequence CDMA is circularstationarity, in frequency selective fading channel, based on Differential MinimumMean Squared (DMMSE) criterion, constructs a new blind PPPW beamforming model.Proves the generalized solution and analyzes the iterative algorithm based on maximumeigen-value decomposition and RLS algorithm. This scheme divides a frequency selective fading channel into several frequencyno-selective subchannels which have independent DOA and time delay. Based on theidea of code filter, it takes the desired user's spreading sequence as a perpetual trainingsequence. Under constrains of DMMSE criterion, it implements blind PPPWbeamforming, multipath signal separating and interference suppressing in eachsubchannel. Simulations analyze the SINR performance of our scheme and conventional Rakereceiver when existing strong near-far effect. Charter 4 constructs a joint uplink PPPW beamforming and power control model,derives the SINR formula, analyzes the relationship between transmitted power andbeamforming weights, presents the iterative algorithm to generating the beamformingweight and transmitted power vectors, and proves the convergence and optimality of thisalgorithm. The optimal solution of the beamforming weights and transmitted powers isobtained by taking into account the data information of all users, and minimizes thepower radiated by the mobile terminals while maintaining the SINR requirements. Simulations show the beam pattern, SINR and total transmitted power curves of ourmethod and PUPW scheme when the angular spreading increases. Charter 5 introduces the principle of space-time block coding, constructs anoptimizing model of joint downlink beamforming and power control for orthogonalspace-time block coding CDMA systems with two array antennas. In which each useronly has one spreading code, two array antennas maintain equal transmitting power forone user, and total radiated power of whole users is minimized while maintaining theSINR threshold requirements. Derives the modified V-UBPCT of this scheme andproves its convergence and optimality. For decreasing the complexity introduced by multipath, a simplified algorithm aboutaforementioned modified V-UBPCT is presented by using equivalent one-path channelvectors (EOCVs) to replace multipath channel vectors. Simulations show the beam pattern, SINR and total transmitted power curves of ourmethod and conventional space-time coding scheme when the users increases. Charter 6 extends the idea of space-time coding on multiple antennas to space-timecoding on multiple beam, constructs an optimizing model of joint downlink PPPWbeamforming and power control for orthogonal space-time block coding CDMA systems,derives the iterative algorithm to generating the beamforming weight and transmittedpower vectors. Extending the aforementioned idea to difference space-time block coding CDMAsystems, the receiver will get the maximum diversity gain even if without channelestimation. Though this scheme decreases the complexity of receiver, it will introducemore noises and interference, and increase the total transmitted power. Simulations show the beam pattern, SINR and total transmitted power curves of ourtwo methods and PUPW scheme when the angular spreading increases. Charter 7 summarizes the conclusions of this thesis. The innovative work of this thesis 1. A new blind PPPW beamforming method based on Differential MinimumMean Squared (DMMSE) criterion is proposed. It is adapted to long spreadingsequence CDMA system with antenna array in frequency selective fadingchannel. It takes the desired user's spreading sequence as a perpetual training sequenceand avoids tracking the channel fading coefficients. Simulations show in fast fading...