Encoding Research On Anti-interference For Wireless Channel In CBTC

With the development of science and technology, CBTC(Communication Based Train Control) system has been widely used. At present, the CBTC is mostly based on the IEEE 802.11 standards to transfer wireless information. However, due to the working frequency of IEEE 802.11 is open in the ISM band, it is inevitable to be disturbed. Therefore, it is of practical significance to improve the reliability of CBTC information transmission by using appropriate anti jamming scheme under the existing conditions.According to the structure of CBTC communication system and the IEEE 802.11 standard, combined with the propagation characteristics of radio waves in free space and in the tunnel, summed up the radio propagation model for CBTC. Then analyzes the wireless interference types of CBTC system. The advantages and disadvantages of anti jamming scheme through the analysis of several present common, the present economic system, better compatibility, is the encoding technology to increase the anti-interference performance of CBTC.Then using the OPNET network simulation tool and select the appropriate modules to construct a CBTC wireless communication model, including the scene without interference source two models, and the simulation results of two models are compared and analyzed. It can be seen that when the interference source is consistent with the transmit power of CBTC system, the media access delay, retransmission Attempts and bit error rate of the whole system are increased, and the receiving delay of CBTC system is reduced, so the transmission power of CBTC system can be considered in practiceAfter considering the use of encoding technology to enhance the reliability of information transmission scheme in CBTC. First, analysis of the current CBTC is often used in encoding scheme based on CRC-32, and according to the characteristics of CBTC wireless channel is now deteriorating the environment of simulation is improved, using SIMULINK simulation tool model. Then according to the characteristics of CRC-32 can not error correction, the serial concatenated encoding form(BCH code +CRC-32+ interleaver) the original scheme was improved. By comparing the improved scheme, the bit error rate is reduced and the reliability of the information transmission is improved.. Finally, according to the development of communication technology, has get more attention with the current Turbo code and CRC-32 code and simulation model were compared, analyzed the possible replacement of CRC-32 code Turbo code.