Modeling For Communication Channel Between A Train And Ground Based On WSNs

With the rapid increasing of global population and the quickening pace of life, the transportation industry has achieved great development. Concomitantly, the security issue of transportation has been paid more and more attention. As a high speed train is one of the most important passenger transports, its security is the focus of domestic and foreign scholars.As a new technology, wireless sensor networks (WSNs) have obtained widespread approval of the international community, because they have been successfully applied to the fields of industrial control, health care and military. In this thesis, WSNs will be applied in the monitoring and early warning of surrounding environment of a high speed rail. The sensor nodes around the high speed rail send the monitored environment information to the ground sink nodes. Next, the sink nodes receive the information from the sensor nodes and then transmit them to the high speed trains. The trains make decisions according to the received information from sink nodes. In this way, the train operation safety would be improved significantly. Thus, the modeling of communication channel between the train and sink nodes has very important significance.In view of the characteristics of high speed trains, such as high moving speed and deterministic moving direction, etc., the train-ground communication channel is modeled as a finite-state Markov chain and an improved method of a channel modeling is developed in this thesis. Just as the current works about modeling of the train-ground communication channel, the location extent of a train is taken into consideration. First, the location extent of a train is divided into some large intervals based on pass loss model. And then, each large interval is partitioned uniformly into smaller intervals. Finally, the channel of each smaller interval is modeled as a finite-state Markov chain.This thesis is organized as follows:In the first part, some knowledge about the wireless channel model is summarized, and some typical channel fading models is presented, including large scale fading models and small scale fading models. For the large scale fading models, we introduce the pass loss model and shadowing fading model. For the small scale fading models, we introduce the Rayleigh fading model, Rician fading model and Nakagami fading model.In the second part, we state a improved channel modeling method firstly. And then, we present a deployment scheme of WSNs on a viaduct. Next, we use MATLAB to simulate the signal-to-noise ratio (SNR) of the train-ground communication channel under a viaduct environment, and the channel model is given in the simulation. Due to the open terrain, shadowing fading of the channel is not considered for this case. Finally, the model accuracy of communication channel is improved by comparing our proposed model with an existing channel model.In the third part, considering a tunnel environment of a high speed railway, we first present a deployment scheme of WSNs in the tunnel. And then, we use MATLAB to simulate the signal-to-noise ratio (SNR) of a train-ground communication channel under a tunnel environment, and the channel model is given in the simulation. Due to the relatively closed environment, we consider the shadowing fading of the channel in our simulation. Finally, under the shadowing fading environment, the effectiveness in improving accuracy of channel model is illustrated by comparing our method with an existing channel model.