Research On The Radio Coverage Characteristics In Confined Space

Wireless communication in the confined space is an important way to guarantee the safe operation of the mobile vehicle, safety of the person and information exchange. Antenna types, layout optimization and efficient radio coverage is important basis of wireless communication systems in confined space, which fundamentally determines the quality and reliability of wireless communication systems. In the confined space electromagnetic waves generated by antennas interact strongly with the environment, which makes electric field intensity distribution is non-uniform. So research the laws of radio coverage in confined space is the base of antenna system layout and optimization. The existing models usually divide the field coverage into antennas and radio wave propagations, and study of characteristics and laws in the limited space independently, which ignore the effect of the antenna on the radio coverage. In this paper the research content is combined with the key project of national natural science funds titled "antenna theory and technology which support efficient radio coverage in confined space", and take the mobile communication system for railway (GSM-R) as an application background. The radio coverage features associated with transmitting antenna is studied in railway tunnel. It is of great significance for the layout and optimization of antenna and the radio coverage performance evaluation of wireless communication system in tunnel. The main innovative works of this paper have the following several aspects.1. Ray tracing method in tunnel environment based on image method is established, and radio coverage features in the tunnel with different cross sections generated by linearly and circularly polarized wave is studied using this method. The radio coverage characteristics generated by antennas in actual tunnel is studied, which verifies the correctness of the theoretical results.2. A waveguide modal prediction model is proposed which includes antenna parameters (beam width, beam direction) and antenna position. The influence of the antenna parameters on radio coverage and time delay characteristics in tunnels is analyzed by using this prediction model, and the theory formula of wideband time delay is deduced. It can be found that different antenna parameters will excite different amplitudes of the waveguide modes, which affects the radio coverage characteristics.3. The influence of the antenna parameters on the break point in tunnel is analyzed, and a prediction fitting formula of break point location which is including the antenna parameters is given using the method of curve fitting, which provides an effective way for quick estimating the radio coverage characteristics.4. Using the FDTD method combined with the equivalence principle, a full wave prediction method for predicting the radio coverage characteristics generated by antennas in confined space is established, and the parallelization of the algorithm is achieved. The radio coverage characteristics in the rectangular and arched tunnels which generated by antenna is analyzed. The radio coverage characteristics are analyzed when the locomotive exists in the tunnel.5. A wireless link integration simulation model which includes of the digital baseband model, transmitting and receiving antennas, and railway environment is built using the finite difference time domain method. The modulation and demodulation method similar to GMSK which is applied in GSM-R is employed. The effect of the wireless propagation environment on the received RF signal and baseband digital signal is analyzed. The phenomenon that the spark pulse of the railway overhead line-pantograph system causes the bit errors is studied.