Research On Adaptation Technology Of The Physical Layer In The Underground Multimedia Sensor Network Based On MB-OFDM-UWB

Multimedia wireless sensor network is promised to have great application value in the underground wireless monitoring system. MB-OFDM-UWB technique, as a typical ultra-wideband technique, is applicable to underground coal mine for the advantages such as high transmission rate, low power consumption and high multi-path resolution. To improve the performance of the multimedia wireless sensor network in the mine, this paper concentrated on some key physical-layer techniques of the multimedia wireless sensor network in the underground wireless monitoring based on MB-OFDM-UWB wireless communication technique.The underground coal mine is a typical confined space where complex multi-path propagation will result in frequency selective fading in the wireless channel. The adaptive technique can take full advantage of the dynamic characteristic of wireless channel for performance optimization by changing some channel parameters. According to the dynamic wireless channel of the underground coal mine, the adaptive technique is analyzed for better performance. This paper discussed adaptive modulation in single user system for simple monitoring environment and dynamic resource allocation in multi-user system for the complex monitoring environment.The wireless system of MB-OFDM-UWB and some typical Ultra-wideband wireless channels are analyzed and modeled at first, and the CM3 mode recommended by IEEE 802.15.3a is brought in as the optimum propagation model of coal mine considering the propagation environment.As to the simple monitoring environment of single user, this paper mainly analyzed and implemented adaptive modulation in MB-OFDM-UWB system. Firstly, the fixed threshold for a given BER and channel mode CM3 was obtained from the figure based on the fixed threshold adaptive algorithm with low complexity. Then the grouped-sub-Carrier algorithm was proposed, including four schemes to calculate the SNR in each sub-band, and the performance of BER and throughput were compared. The result of simulation showed that every kind of adaptive modulation shows better performance than the fixed mode one.With respect to the complex monitoring environment of multi-user, this paper focused on dynamic resource allocation in MB-OFDM-UWB system. Firstly, some algorithm based on amplitude adaptation optimization, namely BABS, ACG and RBS, were introduced. Then RBS improved algorithm was proposed to meet the demands of ultra-wideband wireless sensor network, such as low complexity and power restriction.As presented above, the performance of multimedia sensor network in the underground wireless monitoring based on MB-OFDM-UWB wireless communication technique is improved.