Research Of Resource Allocation Scheme In Wireless Communication System Of Urban Railway Based On OFDM

In the wireless communication system of urban railway,mobile communication technology is an important means to ensure the communication quality of various users.Facing the communication needs of huge passenger groups and the high reliability requirements of train operation,an efficient and reasonable resource allocation scheme plays a key role in improving system performance.Since the train operating environment of urban railway is different from traditional cellular communication,there are many types,a large and unfixed total number of public users,and the current demand for resource allocation schemes of public users in urban railway is not obvious.In addition,according to the operation of trains,the scenarios are divided into two categories: only train users,T2T(Train-to-Train)and T2G(Train-to-Ground)mixed users,and the research and application of the resource allocation schemes in these two types is not yet clear.Although there are some studies on the resource allocation of urban railway,the consideration angles,optimization models,research objects,and research methods are all different.Therefore,the research objects of this thesis include public users,train users,T2 T and T2 G mixed users in urban railway.Based on OFDM(Orthogonal Frequency Division Multiplexing)technology,The thesis studies the wireless resource allocation scheme to improve the overall performance in wireless communication system of urban railway.The main contents of the thesis are as follows:Firstly,according to the communication requirements of public users and the changing characteristics of wireless channels,we study the problem of OFDM adaptive resource allocation for public users.The architecture of the public wireless communication system and the communication mode of single public user are analyzed respectively.Based on the minimum bit error rate criterion under the constraints of bit and power,a resource allocation model is established.And the Fischer adaptive algorithm is used to complete the bit allocation and power allocation.The complexity analysis and simulation results show that the Fischer algorithm can ensure the communication reliability of public user and the effectiveness of service transmission.Secondly,considering the communication mode and requirements of train users,the problem of adaptive OFDM resource allocation for train users is studied.Under the network architecture of train-to-ground communication network,this thesis establishes an optimization model based on the rate maximization criterion by combining the total power constraints and the power constraints of each user.And the Water-Filling algorithm is used for power allocation and its performance is verified by simulation.At the same time,the Water-Filling algorithm is combined with MIMO(multiple input multiple output)-OFDM technology to expand,and the simulation verifies the further improvement of channel capacity.Combined with the characteristics of the train-to-ground communication network,a better combination of transceiver antennas is determined for it.Finally,the resource allocation problem for T2 T and T2 G mixed users is studied.We separately analyze T2 T and T2 G hybrid network architecture,and the spectrum reuse mode of T2 T and T2 G mixed users.On the basis of CSI(Channel State Information)feedback delay,a non-convex optimization model that maximizes the sum of T2 G users transmission rates is constructed.The constraints include power constraints,spectrum reuse constraints,interruption probability constraints for T2 T users,and transmission rate constraints for T2 G users.The feasible region is analyzed based on the linear programming theory,the distribution power is solved by the Dichotomy,and the maximum matching of the bipartite graph is solved by the Hungarian algorithm.Simulation results show that the resource allocation scheme based on Dichotomy and Hungarian algorithm is feasible and reliable in T2T and T2G hybrid networks.