| With the high-speed development of urban rail transportation, and improvement of quality in constom service, the construction of security defense system has been paid more attention in the past decade. As one of the most important part in security defense system, train video surveillance system has limited investigation in real-time transmission of video data. This thesis involves consideration of realistic situation in urban rail by utilizing WLAN and3G network, which have been proved as complementary advantages, and show improvement of real-time performance within the system in a cost effective way.With the background above, a customized vehicle gateway has been researched by using embedded technology. It can be used in wireless video surveillance urban rail train system in order to have real-time transmission of video data, while the network is converting. First of all, an overall scheme of data transmission in train wireless video surveillance system has been designed, with additional analysis on MAC layer protocol in WLAN, a train handoff mechanism based on RFCS (RF Channel Switched) has been proposed to achieve less time during video data transmission in WLAN. Secondly, this work has been focusing on the design process of gateway software and hardware platform:SamSung’s S3C6410board, along with ARM11’s kernel have been used as main processor, chip selection and circuit design have been done by using camera module, WIFI module and3G module. Gateway software platform uses the Windows CE operating system, which accomplish the construction of system by applying custom kernel. Under this constructed system, module driver has been designed and transplanted. On top of this, with Directshow architecture, video collection and compression have been studied, which realize the function of video surveillance terminal for gateway. Finally, by transplanting the gateway mobile hotspot application, data transmission channel conversion issues in all of the video surveillance terminals have been solved, which makes the success in gateway’s core function. Also, real-time transmission in wireless video surveillance system can be achieved by using RTP/UDP/IP as video data transfer protocol and programming of VS2005and Socket networks.At the end of this thesis, RFCS mechanism has been simulated, which shows that handoff delay in RFCS mechanism is far less than that of the traditional WLAN mechanism. Additional, gateway performance has been tested; the result shows that the design scheme of this gateway can meet the requirement of real-time video transmission. |
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