Research On Differentiated Service Reliable Transmission For LTE-R System

In recent years, the high-speed railway of China develops very fast and has made many remarkable achievements. However, compared to the great success of the high-speed railway construction, the development of the railway communication system is relatively backward. Considering the existing GSM for railway (GSM-R) communication system can not meet the requirements of future high-speed rail system, such as high redundant reliable communication and high-definition video surveillance and other multimedia services, the International Union of Railways has decided to adopt LTE for railway (LTE-R) as the next generation of railway communication system. LTE system designed as a high-speed broadband transmission system, can solve the problems of the existing high-speed railway communication system effectively with its special design considerations for mobility and broadband system, and ensure the high-speed railway communication system evolve from GSM-R to LTE-R smoothly.The control informations related to the safety operation of railway, such as voice information of train dispatching and data information of train controlling, are important in high-speed railway communication system. In the GSM-R system, the information is transmited via circuit switched system. However, LTE system is designed as a packet switched system, then how to ensure the reliable transmission of this information has became a research hot topic of the LTE high-speed railway communication system.Based on the network architecture and service types of the GSM-R system, this thesis first studies the services and network architecture of LTE high-speed railway communication system, analyzes the advantages of LTE system when applied to high-speed railway communication system, and the feasible evolutions for the GSM-R evolution to LTE-R.Then, this thesis studies the reliable transmission of voice information of train dispatching and defines a new type of bearer and QoS parameters for the service based on the concept of bearer in LTE system and the scheduling algorithms of MAC layer in LTE system; analyzes the performance of MAX C/I, Round Robin, Proportional Fair, for real-time service; and compares the delay performances of M-LWDF and EXP algorithms. After that, this thesis proposes a modified algorithm based on M-LWDF algorithm, which introduces the QCI parameter into it, and allocates the channel resources considering the channel condition and fairness as well as the QCI priority. The proposed algorithm increases the scheduling priority of the train dispatching information and improves the QoS performance of the service.As for the reliable transmission of high-speed train controlling information, based on the existing physical channel of LTE downlink, this thesis troduces a concept of sub-control channel into the downlink physical for the train controlling information, the sub-control channel gives high priority to the resource allocation of the control-related information, and makes backup for DCIs of the information on the sub-control channel. Meanwhile, taking the reliable transmission requirement of the information into account, the modulation and coding scheme is modified to ensure the reliable and efficient transmission of the train controlling information by decresing the MCS order of the train controlling information, when the resource of the sub-control channel is sufficient.