| Wireless sensor networks is a kind of wireless networks consisting of a largenumber of stationary or mobile sensors, in which sensors communicate with eachother by self-organization and multi-hop manner. Wireless sensor networks achievedata collection, processing and transmission. Due to the features of low powerconsumption, low-cost, distributed and self-organization, wireless sensor networks arewidely used in military, aerospace, anti-explosion, disaster relief, environment,medical treatment, health, home, industry, business and other fields.Wireless sensor networks are data-centric networks. In order to obtain accuratedata, hundreds of thousands, or even more sensor nodes are deployed in themonitoring area. Sensor nodes are assembled with communication module, perceptionmodule and calculation modules. The energy of sensor nodes is largely consumed byCPU and wireless transceiver. In general, relatively high power is consumed bywireless communication. According to statistics, the energy consumption of datatransmission accounted for80%of the entire sensor network energy consumption.However, the sensor nodes are usually powered by batteries. In other words,completing the sensor node deployment, it is difficult to replace the batteries.Therefore, how to keep the energy balance in wireless sensor networks to effectivelyextend the life cycle is one of the main problems of the study.Many definitions of life cycle of wireless sensor networks are defined. Webelieve that the life cycle of a wireless sensor network starts from its work to oneexhausted sensor appearing. Topology of wireless networks usually includes starnetwork, mesh network, blending network (hierarchical network). As the wirelesssensor network topology with characteristics of large number, large density, complexstructure and dynamics, optimization to enhance the complexity of the networklifecycle is important. In MAC layer, ineffective energy consumption is largely caused by the four aspects:①The idle listening: A sensor node needs to receive datatransmitted by neighboring nodes. Because when transmission is unknown, thecommunication module in the sensor node keeps its state as listener, making a lot ofenergy consumption in ineffective listening.②Conflict retransmission: Inmany-for-one communication process, the signals will interfere with each other, sothat the receiving node cannot collect accurate data. Therefore, the energy is wastedon repeatedly transmitting the data to ensure the completeness of data.③Crosstalk:Because communication signals interfere with each other, the node will receive a lotof useless or irrelevant noise data. So the energy is wasted on receiving invalidinformation.④Control overhead: When a node data is transferred, data framesattach a lot of control information. Such as packet switching, handshake protocol andfixed assignment protocol need to establish periodic allocation table, then thisdisabling control information increases the amount of data communication, so that theenergy wasted in the invalid information transmission. Since idle listening is too long,the node is listening but no data is transmitted. The largely ineffective energy routingprotocol layers, as many-for-one data aggregation form, will make some nodes loadimbalance and early failure. All levels of energy consumption will affect the entirenetwork life cycle. Therefore, it is necessary to propose energy improvement programat all levels of response.Research and contribution of this paper as following aspects:1.State of the art and significance of wireless sensor network in the domesticand international study are given; the wireless sensor network applications invarious fields as well as its importance are summarized. The keytechnologies of wireless sensor networks, characteristics, limitations, andmany others are discussed and analyzed deeply; the current problems andchallenges faced by wireless sensor networks are revealed.2. The limitations of wireless sensor network make difficult to replace energynode, so it is necessary to extend the network lifetime as much as possible.By analyzing the architecture and topology of the sensor network, energyconsumption on the various levels of the physical layer, MAC layer, routing, transport layer are analyzed. Via analyzing primary energy consumption, putforward a strategy to extend the network lifetime of wireless sensornetworks. On the basis of PMAC, the relative improvement program isproposed. Regular wireless sensor network collects and transmits data.Changes in environment information are burst. Due to the occurrence ofunexpected events will generate a lot of data, which will slow down datatransceiver into a stable cycle after a period of time. With the reduction indata traffic, it is allowed that nodes become into hibernation cycle for energysavings. Thus, according to the node data flow status life cycle of wirelesssensor network will be divided into three periods: Intensive traffic periods,the normal flow of time and idle time. And the four types of time slotsinclude minimum listening period, listening longest period and the shortestsleep period and longest sleep period. Even in the case of very large flow, itcan continue to maintain a reasonable period of dormancy and listening.3.In the case of static sink node, propose a role relationships based routingselection algorithm. Based on sensor nodes existing energy situation,relationships and membership are built. According to the node relationships,sink node harsh energy consumption is shared. Rational use of remainingenergy of nodes is necessary. The routing algorithm based on rolemembership relations constructs the role and relationship between the nodes.According to the routing algorithm based on role membership relations,information transmits through these two relationships. The role ofrelationship and membership is based on two parameters: remaining energyand communication cost. On the one hand, reduce the consumption ofnetwork, on the other hand, protect reasonable transmission of information.4.In the dynamic environment of the sink node, put forward a progressiveprogram of latency communication on the basis of delay tolerate level. In thecourse of static sink node, due to poor energy consumption of relay nodeswill lead to relay nodes near sink nodes exhaust. In order to solve theproblem of energy hole, many methods based on mobile sink node are proposed. In the case of delay tolerance, delay tolerance level need to bechecked. In some cases, data is not necessarily to send out immediately. Thecollected data can be considered to be stored, until the e mobile sink nodeapproaches to transmit data. Under the conditions of the network delay level,mobile sink node with delay tolerance maximizes the network lifecycle. |
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