Research On Access Technology For D2D Communication Mode Under Emergency Scenarios Of High-speed Railway

With the technology development of China’s railway, High-speed Railway plays an indispensable role and makes people’s life much more convinent, however, its running safety has obtained more and more public concern.The existing railway wireless communication system GSM-R, has been gradually unable to meet the growing demands for High-speed Railway (HSR) new services, for example, video monitoring and so on.The relevant departments of the China Railway Corporation (original Ministry of Railways) put forward to study the new technology, to ensure the safety of trains under signal equipment failure or other emergency scenarios. It aims to realize the informatization and automation, building a reliable and comprehensive integrated digital dispatching mobile communication network.International Union of Railways (UIC) proposed that GSM-R could skip 3G communication stages, and a directly transition to LTE-R. UE can communicate directly via authorized bandwidth by establishing a communication link between adjacent terminals through D2D technology, which is a key technology of LTE communication system with prominent advantages of reducing transmission delay, reducing the base load and improving spectral efficiency and so on.Direct communication between normal traveling trains is not permitted, in line with relevant provisions of the railway.However, under emergency scenarios, D2D communication technology has been taken account of getting permission, which can make the fault trains quickly establish communication with adjacent train. In order to avoid collision and crash, proximal trains can communicate with fault train by D2D can slow down or even apply emergency brake in effective time.Due to D2D communication in HSR emergency scenario has some new features compared to public cellular networks, a few questions must be considered:(1) when to introduce the D2D communication, (2) access control management, (3) whether the D2D communication will be interrupted when the train terminals perform handover.In this paper, the above-mentioned issues were analyzed and discussed; we divide the HSR emergency scennarios into two types and do lots of work on wireless network coverage scenario for centralized resource allocation mode.The timing to introduce D2D communication to HSR emergency is analyzed according to the present rules on railway.For access control of D2D communication, direct communication mode and radio relay communication mode are available based on the distance of the trains. Orthogonal resource sharing based on train control business and D2D communication business is proposed to avoid physical system interference of different types of data services.The distance threshold for train to choose direct communication mode or radio relay communication mode is 6km and the required frequency resource to ensure D2D communication is about 3 RB, which is conformed by simulation.For the frequent handover of HSR terminals, D2D communication and train’s communication with eNB combined handover based on resource reservation is proposed in this paper, in order to ensure the communication reliability of the D2D in the emergency scene. Through the simulation and analysis of the scheme, we verify that the failure probability of D2D communication when train terminals perform handoff is within the acceptable limits, to prove the feasibility of the scheme.