Research On Handoff Of The Train Video Surveillance System In Urban Rail Transit

The rail transport have became the best choice of public transport in the big and prosperity cities of the countries by virtue of its fast, punctuality, high-volume high-security, low pollution, low energy consumption and conservation of land and other characteristics. But as more and more passengers, the train safety issues are gradually revealed, especially inside the train compartments. Because of the places of the train is not fixed and the mobility of the carriage environment, the interior can easily become targets of criminals and terrorists. So, it is imminent to build the train video surveillance system suitable for urban rail transit is imminent.The train video surveillance system of the urban rail transit is composed of two parts, video surveillance network and car video surveillance images transmission network. The article briefly describes the car video surveillance network and focuses on the handoff phenomenon in the part of the car Video surveillance images transmission. Taking into account the mobility of the train, the train-ground communication network should combined with the wireless network technology. With the increase of the speed of the train, the handoff phenomenon in the train-ground communication network must be resolved in a timely manner to ensure real-time and continuity of the vehicle image transmission. The paper analyzes the insufficient of handover in the traditional WLAN network. In accordance with trigger lag problem in the traditional handoff trigger mechanism and high delay and packet-lost rate in the traditional handoff schemes three aspects, the paper proposed optimization methods.After analysis of the deficiencies of the traditional WLAN network, the article proposes a new type of wireless network technology:Wireless Mesh Network. Then the performance of the WLAN networks and the wireless Mesh network is contrasted in the paper, the results indicate that the coverage, network delay and network throughput of the wireless Mesh network are better than the traditional WLAN network. Therefore, this article proposes applying the wireless mesh networks to the train video surveillance system of Urban Rail Transit, and builds the train-ground communication system architecture of URT based on the wireless mesh networks.In accordance with problems such as trigger lag, ping-pong effect and false handover in current handover trigger mechanism, this paper proposes a collaboration handover trigger mechanism based on speed and virtual relay, the mechanism combines the redundant coverage of double-layer interweave network and the wireless mesh node peculiar relaying functions. The improved scheme proposes intertwined site, based on specific proposed when a layer of the network as a main handover layer, the mesh node of another layer of it as the virtual relay points of the main handover layer network. These virtual relay points on the one hand increase the network coverage, and more importantly, they are seen as the point of handover trigger and execution in this paper. The simulation result indicated that the improved scheme can early trigger handover and avoid the ping-pong handover and false handover.Finally, we proposed a cooperation handover scheme on the basis of the car double MMS, the scheme is still based on the redundant coverage of double-layer interweave network. The double MMS work simultaneously in different networks, an MMS is responsible for handover and another MMS is responsible for maintaining communications to the base station of the cooperative cell to ensure the normal train-ground communication. The improved scheme in this paper achieves a true sense of the seamless handover and zero packet loss and reduce the handover interrupt rate and delay after verified by mathematical analysis and simulation comparison and meets the demand of the car video surveillance image transmission.