Research On Multi-Antenna Data Access System In High-Speed Railway Environment And Handoff Algorithms

With the development of communication and Internet technology, in mobile environment, demand for high-rate data communication system is increasing. Especially in situations such as railway and subway, travelling for long time, people’s demand for office on railway, entertainment, news and information is increasing. In the situation of high speed railway, it’s hard to satisfy these requirements. However, the scenario above has these characteristics. The coaches are closed strictly, the users round up, and the process of handoff is frequent because of high speed. Which bring difficulties when data communication in high-speed mobile environment. In order to improve the quality of communication in high speed railway environment and reduce the effects of frequent handoff, in this paper, we have put forward a data access system for high speed railway environment and a fast handoff algorithm triggered by location.First, in order to overcome the problem that the closed coach can block the signal and which will result in the attenuation of signal, and that terminals round up can result in signaling storm, in this paper, we put forward a kind of data access system based on a multi-antennas gateway outside the train. The framework includes terminals in the train, gateway on the train and the access point along the way (cellular base station or access point in802.11). Users create communication link with the gateway via inner wireless interfaces of the gateway. The gateway is responsible for gathering data, and then forward the packets to the available APs along of the road through the multi-antennas equipped. This kind of architecture based on vehicle antenna, completely overcomes the shielding of signal. At the same time, numbers of handoff procedure between terminals in train and APs along the road is instead by one handoff procedure between the gateway and APs, which effectively reduce the handoff management signal and then avoid the signaling storm.Second, using of the regularity of railway and subway lines, in this paper, we propose a fast handoff algorithm based on location learning (A Location Aware-based Handoff Algorithm, LAB-HA). First of all, by the method of learning, the gateway establishes a table of AP along the railway, which records the information of location where it starts to handoff and the probability of successful handoff. Secondly, according to the predictability of vehicle motion, in the same SSID, we can optimize the procedure of authentication. Then, when the train moving, it can use the positioning equipment, such as GPS and cellular, to update the information of location periodically. For instance, when the gateway moves to the certain location, the handoff procedure between the gateway and APs is triggered by the signal of location. Whether it handoff successfully or not is used to update the information in the table list above.Third, in this paper, using NS3network simulator, we set up the data access system network architecture based on802.11protocol. By changing the state machine process in MAC layer, the LAB-HA we algorithm has been realized based on802.11. In scenarios of train moving at the speed of100km/h and300km/h, we have simulated the fast transmit algorithm in802.11(FT-802.11) and LAB-HA algorithm. Then we have analyzed the performances of networks, such as handoff latency, packet loss rate and throughput. Finally, QoS mechanism in802.11MAC has been introduced to distinguish data packets and control packets, in order to improve the priority of control packets. Having also simulated and analyzed performances of LAB-HA algorithm with QoS mechanism.From the results, it can be seen that LAB-HA algorithm can effectively reduce handoff latency and packet loss rate, can also effectively improve the overall throughput of the whole system at the same time. After introducing the QoS mechanism, LAB-HA algorithm in802.11can further reduce handoff latency and packet loss rate. Thus it come to a conclusion, the proposed data access system and location aware handoff algorithm can be used in the environment of high-speed railway and subway and this paper can be a reference for related researches.