移动自组网翻译

0 IntroductionMobile terminal in Ad hoc networks has a portable, light and facility qualities while the limited energy depends on batteries under the urgent and hazardous circumstance, which will have an impact on connectivity of the whole topological network and reduce the quality of communication when the nodes run out of energy due to failing to charge up and then stops. Currently, there are some various effective works about minimum energy in Ad hoc networks. There are Medium Access Control (MAC) layer mechanism, 2.5 layer mechanism and network energy-saving mechanism, respectively, as classified according to network hierarchy. PAMAS[1] protocol and 802.11PSM [2] protocol are used in MAC layer; minimum energy protocol in 2.5 layer includes Span [3] protocol for connection of backbone set and on-demand protocol deciding states of the nodes by network traffic as well as minimum transmission power routing (MTPR), minimum battery consumption routing (MBCR), and minimum-maximum battery consumption routing are all minimum energy protocol in the network layer.By exploiting multi-path in Ad hoc network, energy can be minimized, frequent routing updating can be reduced, data transmission rate can be improved and wireless network bandwidth can be increased. Source Transmit Power Selection Algorithm referred to in reference [7] is, currently, an efficient, multi-path and energy-minimized routing algorithm with disjoint nodes. However, due to properties of multicast in wireless transmission, if there are multi path transmitting data simultaneously, it will give rise to great collision problems, such as, high packets loss rate, bad transmitting performance of data. Hence, if we employ multi-path, we should exploit related strategy to lower the collision and choose minimum possibility of collision to conduct communication.In this paper, we proposed Energy Collision-Constrained Algorithm, (ECCA) and correlation factor was introduced to weigh the collision probability between node-disjoint multi-path when transmitting data simultaneously, then a upper limit for correlation factor was calculated according to service requirements, finally a minimum energy node-disjoint multi-path routing was found to satisfy the limit.1 the theory of energy in Mobile Ad hoc network1.1 energy model in Ad hoc networkIn nature, there are difference between wireless transmission and wire transmission: a link exists between two nodes in a traditional wire network, which refers to they can directly communicate through the physical medium while, in Ad hoc wireless network, referring to sending nodes try to send signals in high enough power to make Signal-to-Noise in the received nodes greater than threshold value which can ensure bit error rate in transmission lower than some value to ensure right transmission.Assume that the nodes in the network exploit omnidirectional aerial as well as regulate power dynamically, besides, every node has a maximum transmission power . This paper is based on wireless transmitting energy model in reference [7,8], inwhich signal power sent by sending nodes is decreased by ,where d is distancebetween source and destination ,generally, m is 2 or 4. If the node i want tocommunicate with the node j, the minimum sending power of the node i is :To simplify the calculation and simulation afterwards as well as without loss of generality, we assume k=1, therefore, the equation 1 can be changed to:In mobile Ad hoc network, if the node i can communicate with the node j, then the sending power of the node I must meet:The channel in wireless Ad hoc network is unidirectional due to the influence of emission frequency and geographical position. For example, the required power is lower when transmitted from uphill mountains to downhill, vice versa. Observed in unidirectional channel as follow:1.2 topological graph for energyWith the development off Global Positioning System (GPS), it’s become probability to achieve low-cost GPS in Ad hoc nodes, and the nodes may know where its physical position is as follow:1)firstly, locate the position of every node in the network and assign a related IDto every node to make all nodes form a node set by exploiting GPS2)as for random nodes , if , then there exists a link from i to j.to carry out energy management, we must assign a weight and the set “V” formed by all linksFigure1 topological graph for energy1.3 source transmission power selection (STPS)Assume that Q is the sub-graph which is formed by the energy topological graph with only M disjoint nodes. However, as for moving nodes frequently, the power of every node can be considered as the biggest weight in all borders. And the required power E(Q) equals the total power of all nodes. As shown in the following equations:Where . This is much difference compared to the traditional networks. For Ad hoc network, its energy is based on nodes, and equals the total power of all nodes, while it’s based on borders and equals the total weight of all borders in a traditional network. The equation 6 is for a traditional network:Figure 2 source transmission power selectionIn figure 2, it’s an sub-graph G’ of energy topological graph G with only M disjoint nodes. By observing, we find there is only border in the middle of nodes except the source node and destination node, so the nodes in the middle are constants while the power of sources have M kinds of choices. The total power E(Q) of sub-graph Q can be changed as follow:Where transmission power of source node is p(s) .2node-disjoint multi-path collision problemsthe properties of WMA (Wireless Multicast Advantage) refers to when one node is sending message, all nodes can received messages in its bound of power. In Figure 3, and are the distance from the node i to j, respectively. If the node jwants to communicate with the node k, in traditional networks, the power of thenode i equals , while in Ad hoc networks, the power of the node Iequals p(i)= according to the properties of WMA, apparently, it’s minimum energy. Rather , it’s this properties that results in collision problems.Assume , when the node i wants to send data packets to the node j, and the power of the node i is still ,and for this reason, the collision will happen.Figure 3.WMA propertiesTo reduce the great collision problems caused by using multi-path, we employed the disjoint path in the traditional networks. It includes node-disjoint and link-disjoint path. The former is better than the latter according to the collision problems. However, there still exist great collision problem between multi-path , even if the nodes are disjoint. Figure 4, two node-joint path, S-b-c-D and S-d-e-D, when b sends data packets to c, d can also receive the packets due to the weight in on the border (b, c) is greater up to 5 than that of on border (b, d). hence, when from b to c, the collision will happen. Similarly, when c sends packets to D, the node d and e can neither send packets or receive packets.Therefore, there still exist collision problems while transmitting data simultaneously, even though the nodes are disjoint. To solve this problem, a correlation factor was introduced to weigh the probability of collision in a group of node-joint.Definition 1 the correlation factor 入of two node-disjoint path: assume the correlation factor 入is the number of the borders of two node-disjoint in G’, andG’ is the sub-graph of the energy topological graph in two node-disjoint path. Figure.4 is illustrated by the two node-disjoint path, S-b-c-D and S-d-e-D.There are three such links in G’(b, d), (c, d), (c, e). the only common property is :one node belongs to S-b-c-D and another belongs to S-d-e-D. therefore, the correlation factor 入in figure 2 is 3.Figure 4. node-disjoint paths (入=3)Definition 2the correlation factor in k piece of nodes 入: a sub-graph G’ of energy topological graph G, and the k is the number of the two random borders belonging to k pieces of node-disjoint in G’.3Based on ECCA algorithmThis paper proposed two steps of ECCA:1)according to the loss packet rate required by the specific application andnetwork simulation experiments, we calculated a upper limit for collision, namely when the correlation factor in used node-disjointpaths, this will meet the requirement that specific application to losspackets rate.2)On the condition of the appropriate correlation factor less than , try tofind the most energy-saving group of node-disjoint paths with k pieces ofborders.To avoid overusing some node and make its energy run out quickly, bytrials, we define a threshold value , when choosing nodes, try not to usethose which the remains of energy is less than unless not using thisnode to find a group node-disjoint paths required.3.1 ECCA AlgorithmAssume that the source node S has M close nodes and the requiredpower of these close nodes are, respectively, and the relatedborders to these power are respectively.Input: networks energy topological graph GOutput: correlation factor , most energy-saving node-disjointpaths with k borders.Initialize: set m=k, the power of source node.Step1 modify energy topological graph G, delete the power of sourcenode, unable to cover to the borders ，attain the relatedpower of source nodes.Step2 for n=1 to k{operate algorithm on modified the topological graph , only usethose without marks which the remaining energy is greater than nodeand find a shortest path and mark the middle nodes in this path.}If node-disjoint path can’t be found ,then directly turn to step4; if it’s found,then determine the power of all nodes, attain the sub-graph of , marked .Step3relative to the sub-graph,calculate the transmission power of thesource node, and find the correlation factorcalculate the total transmission power by theequationstep4 set m=m+1, repeatedly run step1 to step4 until m>M.step5choose the smallest group of gathering energy, the total consumed power for the minimum energy which meets is :(8)3.2 the analysis of algorithm complexityAssume n as the number of node in the networks, so the complexity ofDijstra algorithm. The number of close nodes of the source node is at most the n-1, therefore, the algorithm complexity of the whole algorithm is , namely.3.3 the analysis of performanceaccording to the loss packet rate required by the specific application and network simulation experiments, we calculated a upper limit forcollision , namely when the correlation factor in usednode-disjoint paths, this will meet the requirement that specific application to loss packets rate.4.simulation analysissimulate a network which contains 80 hosts distribute in the grid of 50mX50m, the bound of MTU of every node is 100m,and set a=2. so the maximum power of every node is 10000. 40 CBRs will be produced by the upper traffic at random, the average lasting time of every connection corresponds to the time of 200 packets transmitted. The length of every packet is 512 bytes, the rate is 4 packets/s. data link exploits IEEE802.11 protocol, and the bandwidth is 2 Mbps. The initialized energy of every node is set to 20J, variance ranges from 0 to 2 by Gauss. The simulation time is 1200s. k=2 in ECCA. The simulation is produced as the number of the nodes are 20,30,40,50,60,70,80. the random chosen source and destination nodes in the simulation is the average value by 10 times of experimentations.4.2 the result of simulationFigure5. the comparison of loss packets rateThe first simulation compared the loss packets rate of two algorithm as shown in figure5. the benefit of ECCA compared with STPS is not finding the minimum energy but choosing the energy-saving path which can meet the condition of limit collision by correlation factor.The second one compared the energy consumption of two algorithm as shown infigure6. by choosing different the value of , we can compare the totaltransmission power , due to the path attained by ECCA. These two algorithm is much similar, and that shows the more strict the limit for collision, the more energy will be consumed. In general, compared with STPS, the increased volume of the total transmission power is very small.Figure5 comparison of power consumptionFigure7. comparison of seek timeWe compared the seek time of ECCA and STPS by simulation as shown in figure7. some calculations are added due to correlation factor in algorithm, so it took much time to seek the time. However, when the seek time respectively is 2,4,6 in ECCA, compared with the minimum energy algorithm STPS, it increases 0.02s,0.06s,0.07s respectively. Therefore, the seek time of ECCA is better. Reference:。