Reliability Analysis For Relay-based D2D Communication System Under The Scenario Of High-speed Railway Emergency

With the rapid development of high-speed railway, the safety of high-speed trains has become an increasingly hot topic, the existing railway communication system GSM-R, gradually can not meet the increasing requirement for safety. The former Ministry of Railways has proposed to develop new technologies to ensure traffic safety and prevent the train rear-ended when the signal equipment is broken, achieving informatization and automation, building a reliable and smooth integrated digital mobile communication network. The communication system based on the LTE and LTE-R has been proposed as the next generation of railway communication system. As one of the technologies of LTE, D2D communication can establish direct communication between adjacent users. Using unlicensed spectrum for communication can effectively reduce the load of base station, reduce transmission delay, improve spectrum utilization efficiency and system reliability. Since the trains can not communicate directly, the introduction of D2D communication technology can make the two approaching trains communicate directly in an emergency scenario which can brake ttimely and slow downto prevent trains rear-ended. While departing from the emergency scenario, D2D communication will be cancled immediately.This paper researcheson the reliability of D2D communication in LTE-R.This paper proposes two innovations. Firstly, D2D communication is introduced, to research the reliability of D2D communication withno relay and single-hop relay in short distance.Secondly, in the longer distance, a interference cancellation scheme is proposed, which is based on multi-hops relay transmission of D2D communication. The contents and innovations are as follows:In the first innovation of this paper, D2D communication is introduced into the high-speed rail emergency communication. Through analyzing system reliability this paper researches the safety of the trains using D2D communication under emergency scenario.System reliability is judged by the outage probability. To further improve reliability, this paper presents a single-hop relay transmission scheme. With the processing delay increasing, the transmission distance greatly increases. Through simulation, the scheme can effectively reduce the outage probability and greatly improve the reliability of the system. So the safety of emergency communication of high-speed trains is protected well.In the second innovation, to expand the coverage of D2D emergency communication, this paper presents a multi-hops relay scheme. Based on that, two high-speed trains can use multi-hops transmission communication by several relay base stations. Because of the interference between two adjacent relays, this paper proposes an iterative algorithm based on interleaving of wireless multi-hop relay scheme.The scheme is based on IDMA algorithm and uses BER to measure system reliability. Through simulation analysis, this paper proves that this algorithm is simple, with low system complexity, and its performance is excellent So this algorithm can effectively reduce the system transmission BER, improve system reliability and make sure the high-speed rail safe which is under emergency.