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ENERGY-BASED WIRELESS SENSOR NETWORKS TO IMPROVE THE AODV PROTOCOL


Jin Chun,Liu Xing,Renzi
Chongqing University of Posts and Telecommunications ChongQing China
[email protected]

 

 

Abstract
  The fatal weakness of wireless sensor is the problem of energy consumption. The AODV protocol is based on the minimum number of hops. However, it may not be the optimal routing. Considering from the perspective of remaining energy of nodes, we found this protocol is more likely to result in the death of nodes. In order to solve this problem, we divided the nodes into three stages according to the residual energy of them. Then we improved each phase of the protocol in order to ensure the maximize life of each node, so that the survival time of entire network would be improved obviously.

Keywords: wireless sensor; energy; optimal routing; nodes; survival time.
1 Introduction
  Mobile Ad—hoc Network is a multi-hop temporary autonomous system that consisted with a group of mobile nodes with wireless transceiver devices. Since each node can be mobile, as a result, it may cause changes in network topology.

  If each network node is required to have a router function at the same time, the corresponding routing protocol must be able to adapt to the changing link between the nodes, that is, fast-switching. However, because each node does not rely on fixed infrastructure, nodes can only rely on batteries to obtain energy. So the energy is limited.

  The energy conservation is essential for nodes rely on battery-powered. If energy of one node is run out, the entire network will be affected. If many routings run through the same node or two nodes use the same routing path, the energy of nodes will be depleted rapidly. Therefore, the routing mechanism decides the length of life of the Mobile Ad—hoc Network. This paper began with the study on efficiency of the energy usage, carried out some simple modifications on the AODV routing protocol to ensure that the energy consumption of each node is as fair as possible in order to improve the life of the entire network.

2 Introduction of AODV protocol

2.1 Routing Discovery
  AODV routing protocol is an on-demand routing protocol. Only when two nodes need for communication and the source node hasn't reach the destination node of the routing, the routing discovery process occurs[2]. The discovery mechanism of AODV is broadcasting routing. If one node would like to link with another node when the routing table has not reached the destination node of the routing entry, it will broadcast a RREQ message. When relay nodes received the message, if it is the destination node or has routing leading to the destination node, it will send a RREP message to source node. When the RREP message arrives at the source node, the source node can establish routing to the destination node.
2.2Routing maintenance
  When movements of nodes in the MANET cause the network topology changed, it resulting in part of the routing entries in the routing table can not be reused. If is caused by the movement of source node, we can only initiate routing discovery process from the source node again; While if relay node, we send an RRER message to upstream node when the failure routing node is detected. Related routing entries will be updated when the node has received RRER message. Then it will try to repair the routing. If the repair is unsuccessful, a routing discovery process will be initiated from the source node again.
2.3 Defects of AODV protocol on the balance of energy
  When traditional AODV routing protocol establish routing from the source node to the destination node, it chooses routings that newer or with less routing hops. It will cause a high frequency of use of certain nodes in the network if we don't consider the current residual energy of nodes. If many routings run through the same node, the speed of the energy consumption in one node will be greatly increased, so that the surplus energy in the node will be soon run out of. On the other hand, as a result of this unfair routing mechanism, many nodes died while some other nodes consume almost no energy. If we work in certain circumstances that we've defined the entire network can not work any more when 1/3 of the nodes found dead, the life of the network is short.

3. The improvement of the protocol
3.1 Definition of the work stage of nodes
  Each node in network has an energy value. In this paper, we divide it into three stages according to the energy value of the node including full of energy stage, energy preservation stage and energy weak phase stage. When the residual energy of nodes is greater than 80% of the initial energy, we call it full of energy stage; when the residual energy of nodes is less than 5% of the initial energy, we call it energy weak phase stage; other situation is called energy preservation stage. If nodes are in the full of energy stage, they work according to the original protocol; while if the energy weak phase stage, nodes don't transmit any information-only to receive and send information; while if the energy preservation stage, they work according to the following protocol.
3.2 Routing protocol when nodes in the energy preservation stage
  Since the AODV protocol is based on the minimum number of hops and the routing has protection mechanisms, once the routing table is determined, the routing path will not be changed almost.
This will lead to a number of relay nodes die of excessive energy consumption.

We discuss the following two cases.

1.Because the routing path will hardly be changed when the routing table is determined, when the source node sends data to the destination node frequently, it will lead to a number of relay nodes die of excessive energy consumption. In order to avoid this, once relay nodes forwarding a message, automatic counting table will cumulate a time. When the cumulate value overrun a certain value will prompted to the source node re-select the routing, and node itself is selected automatically reduce the priority level. If the source node to select this node for the relay node again, Then their priority was to select a lower level again, when it request re-select routing next time. Should be noted here, if the two nodes of equal priority when the relay competition, following the principle of minimal hops. Source node in accordance with the priority of the surrounding nodes considered for selection relay node. Figure 1,if N1 sending data to N2 lead excessive energy consumption in N0, N1 may send data to N2 through N3, N4 or N5,N6, which prolong the life span of N0.

2.A number of list routing are use the same relay node, This situation is likely to result in the node's energy drain easily. In order to avoid this situation, Similarly the establishment of a table. If a node elected to three different routing table at the same time, then automatically reduces its priority level, After this node to be selected more than one routing table each time, and its priority level will be lower. Of course, for some reason, this node have been kicked out by one of routing tables, then its priority will be a corresponding increase in level. If the two nodes of equal priority when the relay competition, the same following the principle of minimal hops. Figure 2, if N1 send data to N6, N2 send data to N5, N3 send data to N4, they will select N0 as routing, but after a while, N3 may select N7 as the routing to send data to N4, N1 will send data to the N6 through N8 and N9, which reduce the N0 energy consumption due to heavy load.

4. Simulation and Analysis

4.1 Simulation parameters
This article uses simulation OPENT, Set the network size: 100m X 100m; 50 nodes; Initial energy:

5J; Packet size: 500Byte; Data aggregation and the amount of energy used

message a distance d using our radio model, the radio   expends:

To receive this message, the radio    

If the node is less than 0.002J energy is that the death of the node; the entire network is death if 30% of nodes dead in the network.

4.2 Analysis

 

Figure3 the minimum energy consumption of nodes

. Simulate the original protocol with the energy statistics. Figure 3 is the smallest energy consumption node, simulation shows that the smallest energy consumption took place on the 38th node, we can find that the 38th is on the edge of the network, which based on least hop count on the AODV routing, so it transmitted less data and consume less energy. Similarly, in Figure 4, if the node is in the middle part of the network, it will consume energy more quickly. The largest energy consumption jitter among 14th, 2nd, 30th nodes, and stabilize on the 30th node at last, from which we can conclude they are in the middle part of the network.

Figure3 the minimum energy consumption of nodes
Figure4.the maximum energy consumption of nodes
Figure5. Comparison of energy consumption
Figure4.the maximum energy consumption of nodes     Figure5. Comparison of energy consumption
Figure7. node energy consumption Figure7. node energy consumption

           Figure6. Network lifetime

        Figure7. node energy consumption
Figure8. Network lifetime
Figure 5 is the comparing analysis of maximum, minimum and average energy consumption nodes, the maximum energy consumption nodes exhausted at 311th seconds, from which the average energy consumption become smooth. While , the minimum energy consumption node did not consume a little until the end of simulation, which shows greatest unfairness of AODV.In Figure 6, we can see the entire network died in the 410th second. In Figure 8, improved protocol prolong the network lifetime to 523 seconds, Figure 7 is one of the nodes' energy consumption map, from the chart we can see that the node's energy  consumption is in linear increase at
Figure8. Network lifetime

the beginning, and then in non - linear and moderate increase, which fully shows protocol will prolong the life span of the node and entire network.
5. Summary
  Some nodes of the wireless sensor network died of excessive energy consumption due to overload. It will increase the energy consumption in network and play negative impacts on the life-cycle. To address this issue, this article divides node into three work stages according to the energy value of it. We solved the problem that nodes died of excessive energy consumption due to overload through the routing choose priority. The OPNET simulation results show that: the improved protocol has extend the working hours of the nodes and improved the survival time of the network apparently compared with the original protocol.

 

 

References

[1] Li la yuan, LI Chun-lin. Computer network technology. 2. Beijing: National Defense Industry Press ,2004:158-169.
[2] WANG Shao—qing.Nie Jing—nan.Enhanced AODV routing protocol based on energy eficient.Computer Engineering and Applications.2007,43(28):150—152.
[3] Based on AODV in Ad Hoc Network Routing Protocol energy balance. Research and Development.

 

 

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