Research On Forwarding Performance And Handover Scheme In High-speed Railway Scenario Based On Double Mobile Relays

With the rapid develop of high-speed railway, China’s existing GSM-R (Global System for Mobile Communications-Railway, an exclusive global system for mobile communications) has failed to meet the demands of information construction of railway. In particular, it is unable to provide public network users with a seamless, high-speed and stable broadband access system. Therefore, it is imperative to do researches on a new broadband access scheme which is applicable to high-speed rail. Actually, International Railway Union has made it clear that railway mobile communication systems must be gradually transferred from GSM-R to LTE-R (Long Term Evolution for Railway) which is applicable to high-speed railway. But there still stand many problems remaining to be solved in the way of the transition. And this paper focuses on two of these problems.High-speed trains are generally made of totally-enclosed aluminum-alloy stainless steel, whose body will have serious penetration loss when radio waves pass through. In GSM-R system, public network users are directly communicated with base station, so it is impossible for GSM-R system to provide public users with high-speed and stable broadband access. To solve this problem, this paper discusses an access solution based on double-AF (Amplify-and-Forward) mobile relay for public network users. By relaying, a poor-quality wireless link between base station and users can be decomposed into two good-quality wireless links, so that communication can avoid the influence of train body loss effectively. In the paper, double AF mobile relaying system model based on high-speed railway scenario is established, the mathematical expressions of average SER (Symbol Error Rate) of the system, outage probability and spectrum efficiency are worked out in a closed form and the performance of this system is discussed through simulation. At the end of this paper, a conclusion is drawn:mobile relaying system based on the double AF has lower average SER, lower outage probability and higher spectrum efficiency than that of traditional non-relaying system.Because high-speed trains are moving forward in high speed and passenger are sitting very close to each other, the high-speed railway mobile communication system will suffer frequent group handover. The traditional hard handover scheme’s handover failure rate is very high, and is easy to bring communication to be interrupted in the process of handover. What’s more,"ping-pong effect" will happen in some cases. This paper advances a handover scheme based on double mobile relay’s coordination, establishes a system model, analyzes the relationship between the handover trigger probability and speed of the train as well as the handover position and works out a close-form mathematical expression of handover trigger probability. Additionally, the author discusses the handover failure rate as well as the communication interrupt rate of the traditional hard handover scheme, thus getting their close-form mathematical expressions. In the end, the author analyzes, through simulation, the handover trigger probability, compares the handover failure rate and communication interrupt rate of the scheme proposed in this paper with that of the traditional hard handover scheme. Finally, the author draws the following conclusion:when the train speed is higher, the handover trigger probability is smaller; when the handover position is closer to the edge of the cell, the handover trigger probability become larger. Compared with the traditional hard handover scheme, the scheme proposed in this paper has a lower handover failure rate, and the communication interrupt rate shall never larger than1. The closer to the edge of the cell, the lower the communication interrupt rate is.