Data Transmission Protocol In Wireless Underground Sensor Network

To overcome the low efficiency of existing rescue positioning techniques,we develop a wireless underground sensor network(WUSN)-based satellite-aided rescue positioning network.However,as its core networking module,WUSN is required to face with many difficulties different from wireless sensor network(WSN),especially in terms of data transmission.To this end,this thesis analyzes three main characteristics of WUSN: frequency selectivity,heterogeneity and high pathloss,and further studies the optimal data transmission protocol in WUSN.The contents of this thesis are listed as follows.Firstly,the problem with the routing protocol from underground sensor nodes to underground sink nodes in WUSN data transmission is studied.Aiming at the frequency selectivity of WUSN,a distributed routing protocol based on Q-learning technique is proposed.In our WUSN system,because of conductive media such as steel bars in the underground environment formed by collapsed buildings after the earthquake,its wireless channel between underground sensor nodes will encounter an extremely time-varying frequency selectivity.To this end,we map the WUSN network with this frequency selectivity into a multi-layer network,and further mathematically describe its routing problem.On this basis,we give a solution based on Q-learning algorithm,so that the underground sensor nodes in WUSN can continuously learn the environment to optimize its routing,and then gradually improve the data transmission performance.In addition,we also apply simulation experiments to verify the convergence and effectiveness of the proposed routing algorithm,and to analyze the influence of algorithm parameters on various performance indexes in WUSN,such as packet delivery success rate,average transmission rate,and so on.Secondly,the problem with the reliability requirement of the data collection from underground sink nodes in WUSN data transmission is studied.Aiming at the high pathloss of WUSN,a data return protocol to guarantee the reliability combined with energy harvesting technology is proposed.In our WUSN system,the underground sink node needs to transmit data to the aboveground access point,which will suffer a high pathloss.To this end,we introduce energy harvesting technology into WUSN,which can meet its demand of extremely high energy consumption to a large extent,and then form a new type of network,i.e.,wireless powered underground sensor network(WPUSN).Further,the underground sensor can be replenished by a radio frequency energy harvesting technique and transmit geological data to the nearby aboveground access point in real time.Based on a time division multiple access(TDMA)protocol,we thus can balance the downlink energy transfer and uplink information transmission in WPUSN by adjusting their time allocation.In this paradigm,we discuss and give its optimal allocation scheme with analytical expressions.The protocol adopting this scheme for passing data back to the aboveground access point,realizes the maximum network throughput under the guarantee of reliability.Thirdly,the problem with the high-rate requirement of the data collection from underground sink nodes in WUSN data transmission is studied.Aiming at the heterogeneity of WUSN,a data return protocol to guarantee the transmission rate combined with multiple input multiple output(MIMO)technology is proposed.For our WUSN system,although the WPUSN framework mentioned above can solve its energy-consumption problem and guarantee its communication reliability,its energy reserve among underground sink nodes only depends on their channel quality and cannot be reallocated.Therefore,in the strongheterogeneous underground environment,it thus is required to encounter a seriously unfair energy and task allocation among underground sink nodes,which greatly limits the rate performance of WPUSN.To this end,we introduce the MIMO technique into WPUSN,which is able to adjusting the power allocation,and then establish a MIMO-based WPUSN network(MIMO-WPUSN).That is,the aboveground access point in MIMO-WPUSN is equipped with multiple antennas,and can apply the beamforming technology to designedly transfer energy for diverse underground sink nodes.In this paradigm,we discuss and present the joint optimal scheme about the beamforming weight and the time allocation with analytical expressions.The protocol adopting this scheme for passing data back to the aboveground access point,maximizes the network throughput under the guarantee of both communication reliability and transmission rate.In a word,the routing protocol and the data return protocols proposed in this paper constitute the data transmission protocol in WUSN,which provide theoretical guidance for the realization of WUSN and facilitate the establishment of intelligent rescue system...