Research On Key Technology For The Downlink Of The TD-SCDMA System Over Rician Fast Fading Channels

As one of the third generations of terrestrial-based mobile communicationsystem standards, Time Division-Synchronous Code Division Multiple Access(TD-SCDMA) system has been widely implemented since it granted its first license in2009. With the development of the construction of network for the TD-SCDMAsystem, variously applied scenarios should be considered, such as high speed railway.To make mobile station (MS) run on the safety and the steady, commonly, thecharacteristics of environments should be analysed firstly, and its accurate simulationmodel should also be established. Then, the effects of the circumstances on thereceived signal of the MS will be studied. At last, the scheme for solving thecorresponding problems should be put forward. Based on the above analyses, theproject founded by the Science and Technology Innovation Foundation of Tianjinunder Grant10FDZDGX00400has been set up, and three key technologies onchannel simulator, frequency offset (FO) estimator, and estimation for channel fadingcoefficients (CFCs) have been considerably studied in this dissertation. The mainresearch contents and contributions are as follows:First, the characteristics of wireless propagation environments are introduced,and the pros and cons about several methods of frequency-flat Rayleigh simulatorbased on sum-of-sinusoids are analysed. In order to overcome these deficiencies, twoimproved methods are proposed to simulate the uncorrelated Rayleigh fadingprocesses by applying a smart parameter computation method to the arrival angle andemploying some parameters and functions that differ from those in the existingmodels. Meanwhile, the statistical properties of these two models are derived andverified by simulation. Based on the above methods and the zero-mean stochasticsinusoid, a new stochastic frequency-flat Rician fading simulation model is proposed.Its properties are presented and verified. Then, an approach is presented to generatethe frequency-selective Rician fading waveforms. The proposed methods can not onlysatisfy requiments of this dissertation, but also use for the multiple-inputmultiple-output channel simulation by revising them.Second, the effects of FO on the performance of radio mobile system areanalysed, and the methods about the correction of the FO are studied. Unfortunately, all of the aforementioned works are unavailable for the Rician fading channels.Furthermore, to the best of our knowledge, all the existing methods are unable toprovide satisfactory frequency estimation for frequency-flat or frequency-selectiveRician fast fading channels when the carrier frequency offset (CFO) and Doppler shiftcoexist. To solve the problems for these situations, two FO estimation algorithms areproposed for the downlink of the TD-SCDMA system over frequency-flat andfrequency-selective Rician fast fading channels, respectively. The proposedalgorithms present second-order and fourth-order statistics of the signals whichcontain unknown CFO, unknown Rice factor, unknown Doppler shift, additive whiteGaussian noise (AWGN), etc. Based on flexible parameters setting and concretemathematical operations for these statistics, an expression for FO estimation isderived in closed-form. The simulation results are provided to illustrate the accuracyand reliability of the proposed method. The same realized steps of the proposedapproaches are found by comparing them, so the computational load is low, which cansatisfy the downlink of the TD-SCDMAsystem extremely.Finally, the estimated methods for CFCs are summarized. Aiming at thedeficiencies over the Rician fading channels and reckoning without the CFO for theexisting algorithms, the burst structure is slightly modified, and the characteristics ofthe CFCs over the modified burst are studied. Then, the CFCs with a residualfrequency offset (RFO) for each block of the modified burst structure is modeled as alinear function of time, which is analysed and verified by theory and computersimulation, respectively. Based on this approximation, a new scheme is proposed toestimate the frequency selective Rician CFCs for the downlink of the TD-SCDMAsystem in the presence of a RFO. In addtion, taking account of the case where theAWGN and additive interference coming from other users coexist, the algorithm forthe CFCs in this condition is proposed. The simulation results illustrate that theproposed method leads to small mean square error.