Analysis And Identification Of The Pseudo Code And Scrambling Code In WCDMA Communication System

Wideband Code Division Multiple Access(WCDMA)system has high data rate,strong confidentiality and anti-interception ability.It is the most widely used 3G mobile communication technology in the world.WCDMA permit multiple users to transmit information simultaneously on the same channel or frequency band in which correlation character of codes is used to extract different signal.It is necessary to study on the pseudo codes.This article mainly work on the analysis and identification of address code,which are used in the uplink Dedicated Physical Data Channel(DPDCH)of WCDMA communication system.By analyzing the structure of the WCDMA signal,it is pointed out that the signal is essentially a kind of long scrambled direct sequence spread signal,and can be modeled as a synchronized virtual multi-user DS-CDMA signal.On this basis,the energy accumulation algorithm is employed for the synchronization of received signal.By comparing with the most widely used maximum norm method,the performance of energy accumulation method is proved to be better.After synchronized,the shortened scrambling code waveform can be estimated by the expectation maximization(EM)algorithm.The corresponding code sequence then be reconstructed.Based on the LFSR sequence’s structural features,the complete correct sequence can be recovered by estimating the generating polynomial and the initial state,which are completed by an improved W-H transform.Compared with the traditional WH transform,improved W-H transform method can greatly lower the required large amount of computation,computer memory,and calculation time.Finally,inspired by heuristic algorithm reducing problem calculation amount,we research the LFSR sequence generation polynomial estimation problem more deeply from the view of combinatorial optimization.By transforming the original problem to a combinatorial optimization problem,using simulated annealing and local search algorithm to find its optimal solution,and analyzing the objective function values distribution during entire solution space,we can find that the optimal solution of LFSR sequence generator polynomial estimation problem can only be fined by travelling the whole solution domain.If we apply some methods to decrease the feasible solution range,the computational complexity can be effectively reduced.Several sections are contained in this article:First of all,we need to learn the key knowledge of WCDMA signal,such as the signal structure,the spread spectrum and scrambling technique,and the types and generation methods of different codes,so that we can establish its mathematical model.Since the WCDMA signal is essentially a kind of long scrambled direct sequence spread signal,it can be modeled as a synchronized virtual multi-user DS-CDMA signal and the energy accumulation algorithm is used for the synchronization of received signal.By eliminating the influence of pseudo random(PN)code and anti-phase and find the maximum accumulated energy value,the energy accumulation method can estimate the starting point of the information code really well.After synchronized,the received signal is divided into multiple grids whose length is equal to the Spread-spectrum factor,and then reform a new multi-user short code DSSS signal.Using the expectation maximization(EM)algorithm to estimate the short spreading code waveform and reconstruct its sequence,which is part of the scrambling code.Repeat this operation to recover multiple segments of short spreading codes,which can be sequentially spliced to obtain truncated long scrambling codes.Secondly,the scrambling code sequence estimated by the EM algorithm may contains some error codes,and complete correct sequence can be recovered by estimating the generating polynomial and the initial state.Constructing linear system of equations over binary operations of GF(2)on feedback coefficients and initial states,according to the LFSR feature,solving them by Gauss elimination,and the solution is what we need.Since the system of equations may contain errors,the second largest value of spectral coefficients is taken as the most likely solution,which is calculated by Walsh-Hadamard(W-H)transform.We propose an improved W-H transform method because of the large amount of computation and computer memory,and it can effectively reduce the amount of calculation,while the estimation performance is not bad.Finally,we research the LFSR sequence generation polynomial estimation problem more deeply from the view of combinatorial optimization.We learn the development process and application areas of heuristic algorithm at first.Next,the principle and operation steps of local search algorithm and simulated annealing algorithm are emphatically studied.The problem of solving linear system of equations over binary operations of GF(2)can be transformed to a combinatorial optimization problem,which comes from the LFSR sequence generation polynomial estimation problem.Simulated annealing and local search algorithm are used to find the optimal solution.Simulation result shows that the algorithm works well with lower generation polynomial order,but the order increases,the performance decreases.By analyzing the objective function values distribution during entire solution space,we can find that the shape of the objective function is so special that search direction can not be adjusted according to its value change in the iterative process,and the optimal solution can only be fined by travelling the whole solution domain.The performance of the algorithm totally depends on the search range,and heuristic algorithm is not suitable for the LFSR sequence generation polynomial estimation problem.If we apply some methods to decrease the feasible solution range,the computational complexity can be effectively reduced.