Research On The Key Technologies Of Broadband Internet Applications For Passenger Train

More than 100 million passengers have to be isolated from the Internet while traveling on train up to billions of hours in China, which shows that it's not only the demand to promote the railway service quality, but also a great potential market for providing the broadband Internet services on passenger trains. Then, the state of the art is surveyed for the Internet applications on passenger train firstly and it is concluded that WiFi is the most appropriate technology which is technically and economically feasible, but the following two questions must be resolved in advance, that is the railway wireless coverage and train-ground internetworking. Hence, an integrated access mode based 4-layer architecture model is proposed for the broadband Internet applications on passenger train, and the two questions are decomposed into 4 key technologies, those are 1) how to realize the broadband train-ground internetworking within a single AP's overlay; 2) how to realize the seamless handoff among the APs; 3) how to realize the broadband wireless overlay along the railway and 4) how to realize the efficient communication for the fast moving users.To realize the stable and broadband train-ground internetworking with WiFi, which is always not designed for the mobile scenario, a mobile communication model and a simulation system are built up for IEEE 802.11a. Following, its performance under various mobile conditions is investigated, especially for the influence of different configurations, e.g., frame duration and bit rate. According to the simulation results, a new scheme for the broadband train-ground internetworking with WiFi is presented, which called TGI@11a. With TGI@11a, its bit error rate (BER) is decreased from 5‰to 0.4‰, and its effective bit rate is increased from 6Mbps to 20Mbps.To analysis the complete process of the mobile node which handoff from one AP to another, a special and a general inter-AP handoff concepts are presented firstly, and then a general inter-AP handoff model for the broadband train-ground internetworking is built up. Based on this model, a RSM (Radio-Signal-Measurement) based handoff decision model and a fast handoff algorithm are designed, which can decrease the network disrupt time to several milliseconds and can maintain the link quality during the pre-and-post handoff process, while the mobile node is moving along the serial APs with the passenger train.To realize the wireless overlay along the railway, which is always more than hundreds of kilometers, a number of new concepts such as banyan-tree topology, multi-hop wireless link, invalid risk degree and influence factor are presented firstly, and a dynamical minimum spanning tree algorithm is proposed too. Based on the banyan-tree topology, a multi-portal bus structure and a multi-radio Mesh node structure are designed for the railway wireless mesh network. Finally, an illustrative implementation proposal is designed for a railway with 300Km distance. Theoretical analysis and illustrative implementation proposal show that the banyan-tree topology is suitable for the implementation of railway broadband wireless overlay with low latency, high throughput and robust characters, and it is feasible to deploy because it only requires fewer portals to the wired network and is more flexible to adjust.Because most users of the railway wireless Mesh network are fast moving, a layer-2 forwarding policy of MAC bridge for fast moving users is proposed firstly, which can realize the forwarding path update in real-time after the frequent handoff with low bandwidth cost. Following, a state reporting mechanism and a tail-node forwarding policy are proposed, which support the network status detecting and predicating, and adjust the forwarding path automatically. Theoretical analysis shows that the railway wireless Mesh network can work efficiently and continuously.To verify the theoretical research results, several open experimental platforms are developed utilizing with the open source codes, based on the X86/arm hardware and Linux operation system, e.g., M-Gateway, M-Router and S-Center. Furthermore, the railway wireless Mesh network testbed is set up with these open platforms. Experimental results show that, the railway wireless Mesh network can expand the broadband Internet along the railway with low latency, high throughput and robust characters, and extend to the fast moving passenger train continuously and rather stably.