Remaining-Energy Based Routing Protocol for Wireless Sensor Networks Millad Ghane and Amir Rajabzadeh Department of Computer Engineering, Razi University, Daneshgah Ave., Kermanshah Iran [email protected], [email protected] Abstract—Consumption of energy in sensor network is one of the most important goals of designing a routing protocol. An energy efficient routing protocol will decrease number of transmitted and received packets, because main consumption part of routing is using antennas and signals. This paper presents an energy efficient routing protocol, called Remaining-Energy Based Routing (REB-R). The idea behind REB-R is broadcasting remaining energy along with data in data packet instead of calculating a parameter, related to remaining energy, and broadcasting it. REB-R is compared to two well-known protocols, AODV and T-ANT, and simulation is done by NS-2 framework. In order to compare REB-R with both of them, T-ANT has been implemented inside NS-2 and an add-on has been added to current AODV implementation to support energy consumption. For 200 nodes in area, REB-R uses less than 50% of energy consumption of the others, and number of saved nodes is less than 20% for T-ANT and AODV but REB-R saves all of them in simulation time. Keywords—Routing, Wireless Sensor Networks, Remaining energy, ns-2, WSN I. INTRODUCTION Role of sensor network in monitoring and gathering information from environment is significant. Volcano monitoring [1, 2, 3], keep tracking of vital signals of patients [4, 5], monitoring a bridge [6] and measuring environmental properties like temperature, pressure, humidity and etc. are among sensor networks applications in monitoring and measuring issues. Mobile nodes are also an interesting issue in sensor networks. These nodes move across environment and after gathering information form environment, they send it to workstation for further processing. Event detection in environment is another interesting application of sensor networks. Surveillance of entities is an example in this field. In this issue, nodes are listening to environment and wait for an event to take place, and then they will report position of event to workstation. A good implementation of this application field is CodeBlue project [4]. They used event detection mechanism to track location of individuals, such as patients, nurses, doctors or even medical equipments in hospitals. This location tracking is done in three dimensional (3D) to precisely find location of each entity. To achieve this precise localization, a number of radio beacons are fixed in locations around environment to find 3D position of entities. Physicians and emergency department personnel are able to access entities’ location by interfaces like handheld PDAs and Web-based clients through Hourglass system [4]. A different approach to application of sensor networks is their usage in battlefields. Simon et al. [15] build a sensor network system consist of scattered nodes around the field, forming a sensor network. This system reveals the sniper’s location at the moment sniper begins shooting. Average accuracy of location of sniper and latency time of finding are 1 meter and 2 seconds, respectively. Nodes in sensor network are tiny, low-cost, low-power, multi-functional [7] and low memory capacity sensors, thus important factors have to be considered when designing routing protocols. Security [13, 16], data aggregation methods [12], reliability [14, 13] and energy consumption are among important factors to be considered. Activities of energy consumption of sensor nodes are sensing, computation and communication [14, 11]. Communication consumes more energy in compare to other two activities [17, 11], so effect of computation and sensing is almost disregarded and minimization of number of packets across network can take us to our goal. Because of equipping sensors with batteries for energy source, the energy factor plays a crucial role. These batteries usually are not replaceable [9] (solar energy is not always an option [9]), so when battery goes off, node dies and will be disconnected from network. It’s the reason why energy is most considerable factor in sensor network and life of network depends on it [7]. Disconnection of a critical node from network causes network to come near to its lifetime. Since these critical nodes are living in bottleneck of many routing paths to sink, and consume a lot of energy for relaying packets [18, 11], their death will put out of action those paths [11]. Also dying non-critical nodes will reduce precision of measuring parameter which network is trying to collect data. Remaining-Energy Based Routing (REB-R) protocol leads nodes to broadcast their energy level alongside the data to their neighbors and let nodes choose their parent with highest energy level and forward data to it. Simulations have been done by an event-based framework called, Network Simulator 2 (NS-2). REB-R is compared against AODV, a MANET protocol, and T-ANT, an antcolony protocol for sensor networks. Both of the above protocols are among distributed type just like REB-R. Results are compared with average energy consumption of nodes and number of alive nodes. When number of scattered nodes in area is 200, REB-R uses 42.77% and 42.5% of total average energy of T-ANT and AODV respectively. Percentage of number of alive nodes of T-ANT and AODV are 18.47% and 17.74% respectively, but REBR saves all of nodes in simulation time. Rest of paper is organized as follows. Section 2 describes related works. In Section 3, proposed protocol, REB-R, is presented in details. First subsection explains packet structure. Second subsection in Section 3, describes the REB-R. Section 4 represents simulations and experimental results. In this section, results of simulation for all of protocols, AODV and T-ANT and REB-R, are compared to each other and shown in figures, and finally Section 5 reveals some conclusions. II. RELATED WORKS Distinguished aspect of designing protocols in sensor networks field is minimizing consumed energy. If number of exchanged packets is minimized, consumed energy will be at its minimum value [18]. Many methods have been introduced to reduce transmitted packets. Two general categorizations of introduced protocols are distributed and non-distributed protocols. In non-distributed protocols, main job of protocols is done in a center. Running an algorithm on workstation and broadcast routing results to network is main subcategory of non-distributed protocols. Bari et al. [7] have implemented a protocol which uses genetic algorithm to find optimal parent for each node. After calculations, it broadcasts to each node a message about their routing information. Classical MANET and wireless routing protocols like AODV, DSDV and so forth can be used for sensor networks but overhead of control packets and enormous routing table is a huge disadvantage. In these protocols, computations and protocol codes are so much hard and big, that are considerable. Wireless routing protocols are designed to work in environments that energy issue is not worried. Using these protocols in routers has huge impact on performance of network and packets are routed faster. In distributed protocols, core of protocol is not centered and it is distributed among nodes. Hierarchical is a wellknown subcategory of distributed protocols. In hierarchical algorithms, clustering techniques are used to group nodes and route packets toward sink [8, 9, 18]. Some clustering protocols are based on ant-colony principles and use their behavior to achieve their energy efficient goals [10]. Hierarchical protocols are categorized to dynamic and static classes. In dynamic class, routing paths are changed during lifetime of network. This changing in routing is done in order to remove centrality of gathering information from a node, and balance work load among nodes [8, 9]. For static class, topology of network is usually static and therefore nodes are immobile. Leu and Li [18] have proposed an algorithm where it deploys a polar coordinate system for routing packets. In [18], some fixed and immobile nodes known as manager nodes are placed in area and their duty is to collect data from sensors and send it to sink through their intra-network. Location of manager nodes is expressed by the protocol. In hierarchical protocols, overall measuring of a property is our aim. The main disadvantage of these type of protocols is aggregating data from whole network, and workstation could not ask for a specific node’s data, although it is possible to collect information from a specific node, but it needs a complex mechanism. Least battery energy consumption is its advantage. Hierarchical protocols partition network into levels and each node belongs to one. Lower nodes only communicate with one-level higher ones. Partitioning will reduce amount of packets transmitted through network. As an example, in T-ANT [10], some nodes gather around each other and form a cluster, and then they will select one among them as cluster head and try to aggregate data and send it to sink through cluster head. Similar to T-ANT, LEACH [8] and HEED [9] protocols have been proposed which T-ANT outperforms them. III. REB-R PROTOCOL Assume we have a network with sensor nodes spread in the area. Sink node which is a special node with unlimited energy is positioned in the center. Positioning sink node in center is just another assumption and does not interfere with REB-R in any way. For network model we have following assumption [9, 10]: · Nodes in network are stationary. · Nodes are unaware of their location. · All nodes have similar capabilities, i.e. processing and communications capabilities. · Nodes are left unattended in area after deployment. · Each node has fixed transmission power capability, i.e. radio ranges of nodes are equal, and transmission energy of one bit from node u to node v is the same as from node v to node u. · Nodes are scattered with homogeneous spatial Poisson process (it does not really affect protocol). Nodes sent packets to each other simultaneously and conflicts of packets may occur in the network. A. Packet Structure Figure 1 shows packet structure which REB-R uses. Simplicity and being short are two main advantages of this structure. Type (1 bit) Energy (32 bits) Data (32 bits) Figure 1 - Overhead of packet structure for REB-R A node broadcasts two types of packets, one is FWD_ROUTE and the other is DATA. For these two types, we use a bit to represent packet’s state and the mentioned is “type” bit, and “type” bit is 1 for FWD_ROUTE and 0 for DATA. For “energy” part, we can use single precision floating number or number of residual packets, where it is calculated by dividing battery energy level at the beginning, to energy value required to send/receive packets. For “Data” part, we could use integer values or double values. Integer values are simple and their computation takes less time, but on the other hand double values are complex and have heavy computation time. It is a tradeoff between speed and precision. For our simulations, we have used double values to achieve better precision. In Algorithm 1 and Algorithm 2, highest energy represent energy of current parent. PARENT_NODE points to current parent, and FIRST_TTL is a variable stored in node describing value of the first received TTL. B. REB-R algorithm After nodes being placed, sensor nodes wait for a packet from sink. Sink starts network activities by broadcasting a FWD_ROUTE packet to all of its neighbors. When packet received by each node, its TTL (time-to-live) is stored as FIRST_TTL and this node will broadcast a fresh new FWD_ROUTE packet with previous packet’s TTL incremented by one, as new TTL. By this action, forwarding route shapes in levels. Level-one nodes are nodes neighbor to sink, level-two nodes are nodes neighbor to level-one nodes and other levels are shaped liked this pattern. From now on, each node that receives a FWD_ROUTE packet with TTL smaller than or equal to FIRST_TTL is recorded as nominee for parent node of this node in future. If TTL is greater than FIRST_TTL packet will be dropped to avoid retransmission of extra packets. If this packet is broadcasted, it has no usage for nodes; as explained above, we don’t have interest in packets with greater TTL than the recorded FIRST_TTL and they are discarded. During making future nominee list, if a packet is collected and it has minimum TTL and maximum energy, sender will be selected as current forwarding node. Afterwards, during steady state, current node will be changed to a node among future nominee list which has maximum energy. Sink’s job ends at this point and from now on, it just waits for information to come along by sensor nodes. As mentioned previously, sensor nodes are using batteries to operate and if this battery dies, node will die. Stopping operation of a node will cause network topology to change, so every fixed intervals sink broadcasts a FWD_ROUTE packet to refresh current forward route. Refreshing forwarding route has benefits for new nodes which have been added to system. When a new node is added to network, it just waits for next round of interval to happen. When sink starts forwarding route phase, this node catches the FWD_ROUTE packets and it start to participate in network’s activity. We must have a timer in each node to clear each nodes neighbor’s list at beginning of every interval and reset node’s state to start state. In node’s life, there are some times that node has no parent. During these times, the node simply does nothing and waits for a FWD_ROUTE packet. These times occur in two situations. Suppose a node is isolated and deserted far from network that its signal is not received by any nodes. In this situation FWD_ROUTE packets are not received by them and they just do not do anything. The other situation is when a new node is joined to network and it have to wait to receive FWD_ROUTE packet. Figure 2 - Starting point of network. Sink sends FWD_ROUTE packet. Figure 3 - Forming reverse forwarding path to sink for level one nodes From energy level encapsulated in packets, forwarding route will change. In wireless communications, when a node broadcasts a packet, it will be collected by its neighbors, and we make sure around neighbors take energy level of all possible parents with only one packet transmission which holds data too. From time to time, current parent of a node has an energy level which is lower than the node broadcasting its energy level in data phase. sends its current energy level along with data. This behavior will help other nodes which select this node as nominee to know energy level at every moment and to change their parent node to a node with maximum energy level at any time. Selecting node with maximum energy will balance energy in a specific area of environment. Algorithm 1 – Parsing forwarding packets // When a FWD_ROUTE packet is received, // this method is called Parse_FWD() { if FIRST_TTL has not been initialized { FIRST_TTL is initialized to packet’s TTL. PARENT_NODE is initialized to sender. Record sender’s energy as highest energy. Add sender to future nominees list. Increment TTL of received packet by one. Integrate current energy level with incremented TTL to a FWD_ROUTE packet and send the packet. Figure 4 - Forming reverse forwarding path to sink for level two nodes } else if packet’s TTL is less than or equal to FIRST_TTL { Add sender to future nominees list. if packet’s TTL is less than the smallest received TTL till now { PARENT_NODE is set to sender node. Record sender’s energy as highest energy till now. Increment TTL of received packet by one. Integrate current energy level with incremented TTL to a FWD_ROUTE packet and send the packet. Figure 5 - Reverse forwarding route to sink node after forward phase As shown in Figure 1 and described previously, node sends its current energy level along with data. This behavior will help other nodes which select this node as nominee to know energy level at every moment and to change their parent node to a node with maximum energy level at any time. Selecting node with maximum energy will balance energy in a specific area of environment. From energy level encapsulated in packets, forwarding route will change. As you know, in wireless communications, when a node broadcasts a packet, it will be collected by its neighbors, and from this characteristic we make sure neighbors around found energy level of all possible parents with only one packet transmission which holds data too. From time to time, current parent of a node has an energy level which is lower than the node broadcasting its energy level in data phase. As shown in Figure 1 and described previously, node } } Drop packet. } Nodes and formation of their paths are shown through figures. Figure 2 shows node formation within environment and starting point of network that at this time no reverse forwarding route is formed and sink starts network activities by sending a FWD_ROUTE packet. At Figure 3, level-one nodes are forming around sink and their reverse forwarding path is shown. In this point, each node in level one knows who its parent is and following that, they are sending a FWD_ROUTE packet to their neighbors to form level-two nodes. Figure 4 demonstrates how level-two nodes and their routes are taking shape. These routes are constructed by level-one nodes where they broadcast a FWD_ROUTE packet to their neighbors. When all forwarding paths are Algorithm 2 – Parsing data packets // When a data packet from a node arrives to a node, // this method is called. Parse_DATA() { if sender of packet has energy level more than highest energy and is a member of the future nominees list { PARENT_NODE is initialized to sender. Record sender’s energy as highest energy till now. } if packet’s destination is this node { Aggregate received data. } nominees list and that node would have chance to be selected as this node’s parent, and when TTL has minimum value among received TTL, beside of adding sender node to future nominees list, sender is selected as parent. We used FIRST_TTL to build a list of neighbor nodes. Doing so, nodes will select open-handed among their neighbors which are only a few hops more than selected parent away from sink node. There is a chance that a node with maximum hops away from sink is selected, but above selection is only made if selected node has maximum residual energy. It’s obvious that selecting such a node uses more hops therefore more energy of whole network but our goal is to balance the energy in network. The situation is described before on Figure 5. Thus, the bigger the future lists, the more energy-balanced network, the longer lifetime of network. Step-by-step procedure of reverse forwarding route formation is shown in Algorithm 1. Drop packet. } constructed, nodes are ready to send data to sink and this state is shown in Figure 5. At the time the data timer expires in each node, they send their sensed data to sink by forwarding their data to their parent node. In Figure 5, as you see Node A does not select Node B as its parent and selects a route that is farther than selecting Node B. Situations like this may occur sometimes based on network’s delay or maybe packets collision. If you notice to Figure 6 route is corrected but this option will remain in nodes record and node looks at it as an extra option to reach sink. In future longer path may be selected if it has maximum energy level among nominees. Although this situation is not encouraged but if it does happen we take advantage of it. Two situations will be occurred when facing FWD_ROUTE packets. When the TTL value of packet is greater than FIRST_TTL, the packet will be dropped. We drop these packets for two reasons: 1. Forwarding such packets does not have any useful information for routing. REB-R uses minimum values of TTL for building routing path to sink, thus TTL values greater than FIRST_TTL are not considered and will be dropped. 2. Forwarding these packets will bring chaos to network. Unnecessary packets are broadcasted to whole network and they will not only be broadcasted forever (because the TTL we use in REB-R increases crossing each hop) but also consume the whole energy of every node in network. Because such behaviors are not encouraged, we drop mentioned packets. And about TTL values less than or equal to FIRST_TTL, we will take action as follow. If TTL is equal to FIRST_TTL, we just add node to future Figure 6 - Changing route path a period of time after start of network for Figure 2 First phase of our protocol has been fully discussed. At this phase we created reverse forwarding route to sink node and future parent nominees of each node. This important phase in REB-R prepares nodes to transmit their sensed data to sink node. When a node collects data from environment, it tries to send data through its selected parent node which is changed in time. As the data arrives to sink and crosses from nodes, it causes the forwarding route to change to best available one. Using the energy part in data packets traveling through network makes this action possible. Data packets not only contain the data but also energy level of transmitter. Energy part in data packets plays a key role. When packet is received by node, node looks up in its future list for sender node. If it finds node, nominee list is updated by new energy level, and parent node could be changed to this node when energy level of this node is more than current parent node. For transmitting data to sink node any kind of aggregation algorithm can be used and REB-R is independent of this algorithm. In our simulations we used a simple aggregation strategy; we just make average of incoming and sensed data within a node and then transmit it through forwarding route to sink. Figure 6 shows how forwarding route to sink node change through time as energy of nodes are consumed due to transmission and reception of packets. As you see from Figure 3 comparing to Figure 2, some nodes are forced to select a specific node for their life time, so those nodes are among nodes which their energy diminishes faster than other nodes and we lose sensor nodes of that area. Although the results have shown REB-R performs outstandingly better than other protocols in number of dead nodes. Parent nodes of sensors are changed rapidly before network achieves its optimal structure. An example about how protocol works in steady state may help to understand it properly. Suppose time 0.0 is when sink starts network activities by sending FWD_ROUTE packet. Time passes and network goes to its steady state, and during this time nodes have selected their parents. At time 32.46, node 23 has broadcasted the data to its parent and data timer is set to be expired again one second later in 33.46. Among nodes in area, suppose nodes 46, 2, 78 and 124 have selected node 23 as their parent. Data timers on above nodes are set to be expired 32.84, 32.57, 32.89 and 33.23, respectively. When data timer expires on these nodes, they begin to send their collected or aggregated data to node 23 as destination. During consecutive timers on 32.46 and 33.46, node 23 captures all incoming packets and it will collect every data which their destinations are node 23. After aggregating its data with received data at 33.46 it will send the aggregated data to its parent. It should be mentioned during this process, future nominee list and their corresponding energy level is update as protocol considers this change. IV. SIMULATION AND RESULTS For performance comparison of our proposed protocol with other protocols, we have used Network Simulator 2 (NS-2) framework which is capable of simulating network protocols to weigh against other protocols. NS-2 is an event-driven simulator which simulates a network with a specific topology for network researches, and it supports simulation of TCP, routing and multicast protocols over wired and wireless networks in local and satellite environments. In sensor network applications, topology usually is not static form, so results vary. To cover this variation, we have simulated our protocols with different topologies of nodes which are distributed according to homogeneous spatial Poisson process; it scatters nodes randomly in a manner which nodes are almost near and in touch to each other. In Figures 7, 8, 9, 11, 12 and 13, graphs represent average value of parameter and 90% of simulation results. In order to eliminate influence of out of order data samples, 5% of high values and 5% of low values are omitted. Bottom and top of bar represent minimum and maximum values of this 90% samples. A. Simulations parameters For our simulation experiments, we have assumed that nodes are scattered in a square 670x670 area. Transmission and reception energy of packets are assumed to be equal and static values as 10µJ and initial energy of each node is valued at 1J. Sink node’s initial energy similar to other experiments and like real applications is set to infinite, thus neither transmitting nor receiving packets would not change energy level of sink node. Infinity value for energy level of sink node comes from this concept that this node is a data collector node and must be online at anytime to take delivery of data packets. The only control packet REB-R uses, FWD_ROUTE, is for building forwarding route from each node to sink. Constructing this route takes time and this time is not fixed and it is related to the number of nodes. For transmitting acquired data to sink node, data timer is set to 1 second. For AODV parameters, we used the default ones in NS-2, but for sending our specific data we added another timer to protocol, to send us data every seconds, like REB-R and T-ANT. T-ANT parameters are also changed to reach one second of transmission of data. Unlike AODV, T-ANT protocol has mechanism of broadcasting data to sink node as default. For T-ANT experiments, all parameters except timers’ interval are those introduced in its paper. Cluster head selection phase interval is set to 8 seconds, join phase interval is 3 seconds, and ant releasing takes place each 4 seconds. Radio range of each node and sink node is set to 200. T-ANT paper assumes nodes have awareness of their neighbors and recognize them but we did not apply the supposition. When network starts, each node sends a FNA (Find Neighbors Around) packet and asks for neighbors to respond to him by RFNA (Response FNA) packet, and then neighbor list in each node is generated. Since AODV does this implicitly by on-demand routing and REB-R actually uses FWD_ROUTE packet types to recognize its neighbors so we are not worried about finding neighbors in those protocols. But TANT needs to know its neighbors before network is started. In original paper [10], authors assume nodes are aware of their neighbors from beginning. Number of nodes is another parameter to system which along in the simulation, by changing it, we get different results. This number varies among 50, 100 and 200. The results are shown in diagrams. Each protocol is simulated with a specific topology for 2000 seconds, and results shown here are based on this timing. B. Experimental results Within this part, we will demonstrate results of our experiments and compare them to each other. The features to compare are average consumption of energy of all nodes % of average consumed energy and average number of alive nodes. In all of them REB-R surpasses both of T-ANT and AODV. 1) Average consumed energy: We have simulated our proposed protocols along with other protocols for 50 times with 50 different topologies in each round. At the end of every round, consumed energy of each node is determined and summing all of them together yields total energy consumed in all of nodes, and dividing it by number of nodes, concludes average value. 120 100 80 AODV 60 T-ANT 40 REB-R 20 0 0 100 200 300 Figure 10 - Comparison of average consumed energy AODV T-ANT REB-R Figure 7 - Consumed energy for 50 nodes % of consumed energy 120 100 80 60 40 20 0 AODV T-ANT REB-R Figure 8 - Consumed energy for 100 nodes % of consumed energy 120 100 80 60 40 20 0 AODV T-ANT 2) Average number of alive nodes: Along with average consumed energy simulation, we measured number of alive nodes in network. Like average consumed energy, numbers of active nodes are summed together and divided by number of nodes, expressing average nodes currently active. Figure 11 reveals comparison of number of alive nodes in simulation against protocols for 50 nodes. REB-R does not have any dead nodes in simulation time but AODV performs well with more than 90% of alive nodes and TANT performs near REB-R performance. In Figure 12 comparison is done for 100 nodes. Like previous results REB-R does not have dead nodes but T-ANT saves only 80% of nodes, and AODV as expected saves around 30%. Figure 13 indicates that T-ANT does not perform well and like AODV less than 20% of nodes are saved for both of them, but like other results, REB-R achieves perfect value. Looking for reason for this behavior will guide us to complexity of T-ANT and amount of control packages which are traveling in network and consume more energy just like AODV. Figure 14 certifies our conclusion about behavior of converging T-ANT to AODV when number of nodes increases. In this figure, T-ANT’s result converges to AODV result. For 50 nodes, they perform like each other but when number of nodes grow and reaches 100, T-ANT is behind of REB-R and for 200 nodes, T-ANT perform like AODV. As it is obvious in results, REB-R protocols leads network toward long life and high performance. REB-R Figure 9 - Consumed energy for 200 nodes Figure 10 shows average consumption of energy against number of nodes in environment. This figure shows how REB-R performs outstandingly when number of nodes grows. AODV reaches its maximum available value just for 100 nodes and uses 100% of energy of a node in average. For 200 nodes, REB-R does not even consume half energy of a node in average. T-ANT for 100 nodes exceeds 50% of energy a node and keeps it distance from AODV. Number of alive nodes % of consumed energy Number of nodes 80 70 60 50 40 30 20 10 0 60 50 40 30 20 10 0 AODV T-ANT REB-R Figure 11 - Comparison of alive nodes for 50 nodes Number of alive nodes REFERENCES 120 [1] 100 80 60 40 20 0 AODV T-ANT REB-R Number of alive nodes Figure 12 - Comparison of alive nodes for 100 nodes 250 200 150 100 50 0 AODV T-ANT REB-R Average number of alive nodes Figure 13 - Comparison of alive nodes for 200 nodes 250 200 AODV 150 T-ANT 100 REB-R 50 0 0 100 200 300 Number of nodes Figure 14 - Comparison of average alive nodes V. CONCLUSION Leading nodes of sensor networks toward consuming less energy is a gigantic problem for designing routing protocols. Many protocols are offered for minimizing network’s total dissipation of energy. Some protocols rely on grouping nodes and therefore routing packets through one of them, and others are designing routing path by algorithms which run on sink node. This paper presents a routing protocol which route packets based on decision a node makes from energy level that neighbors transmit along with data. G. Werner-Allen, J. B. Johnson, M. Ruiz, J. Lees and M. Welsh, “Monitoring volcanic eruptions with a wireless sensor network”, Proc. Second European Workshop on Wireless Sensor Networks (EWSN’05), 2005 [2] G. Werner-Allen, K. Lorincz, J. Johnson, J. Lees and M. Welsh, “Fidelity and yield in a volcano monitoring sensor network”, 7th USENIX Symposium on Operating Systems Design and Implementation (OSDI 2006), pp. 381-396, 2006. [3] G. Werner-Allen, K. Lorincz, M. Ruiz, O. Marcillo, J. B. Johnson, J. Lees and M. Welsh, “Deploying a wireless sensor network on an active volcano”, IEEE Internet Computing, Volume 10, Issue 2, pp. 18-25, March 2006. [4] D. Malan, T. Fulford-Jones, M. Welsh and S. Moulton, “CodeBlue: An ad hoc sensor network infrastructure for emergency medical care”, Proc. MobiSys 2004 Workshop on Applications of Mobile Embedded Systems (WAMES 2004), June 2004. [5] T. Gao, D. Greenspan, M. Welsh, R. R. Juang and A. Alm, “Vital signs monitoring and patient tracking over a wireless network”, Proc. of the 27th Annual International Conference of the IEEE EMBS, Shanghai, pp.102-105, September 2005. [6] R.G. Lee, K.C. Chen, C.C. Lai, S.S. Chiang, H.S. Liu and M.S. Wei, “A backup routing with wireless sensor network for bridge monitoring system”, Measurement, Elsevier, Volume 40, Issue 1, pp. 55-63, January 2007. [7] A. Bari, S. Wazed, A. Jaekel and S. Bandyopadhyay, “A genetic algorithm based approach for energy efficient routing in two-tiered sensor networks”, Ad Hoc Networks, Elsevier, Volume 7, Issue 4, pp. 665-676, June 2009. [8] W.B. Heinzelman, A.P. Chandrakasan and H. Balakrishnan, “An application-specific protocol architecture for wireless microsensor networks”, IEEE Transactions on Wireless Communications, Volume 1, No. 4, pp. 660-670, October 2002. [9] O.Younis and S. Fahmy, “Heed: a hybrid, energy-efficient, distributed clustering approach for ad hoc sensor networks”, IEEE Transactions on Mobile Computing, pp. 366-379, October 2004. [10] S. Selvakennedy, S. Sinnappan and Y. Shang, “A biologically-inspired clustering protocol for wireless sensor networks”, Computer Communications, Elsevier, Volume 30, Issues 14-15, pp. 2786-2801, October 2007. [11] J.Y. Choi, H.S. Kim, I. Baek and W.H. Kwon, “Cell based energy density aware routing: a new protocol for improving the lifetime of wireless sensor networks”, Computer Communications, Volume 28, Issue 11, pp. 1293-1302, July 2005. [12] P. von Rickenbach and R. Wattenhofer, “Gathering correlated data in sensor networks”, Workshop on Discrete Algothrithms and Methods for MOBILE Computing and Communications, ACM (2004), pp. 6066. [13] K.F. Ssu, C.H. Chou and L.W. Cheng, “Using overhearing technique to detect malicious packet-modifying attacks in wireless sensor networks”, Computer Communications, Volume 30, Issues 11-12, pp. 2342-2352, September 2007. [14] I.F. Akyildiz, W. Su, Y. Sankarasubramaniam and E. Cayirci, “Wireless sensor network: a survey”, Computer Networks, pp. 393-422, 2002. [15] G. Simon, M. Maroti, A. Ledeczi, G. Balogh, B. Kusy, A. Nadas, G. Pap, J. Sallai and K. Frampton, “Sensor network-based countersniper system”, Proc. of 2nd International Conference on Embedded Networked Sensor Systems, pp. 1-12, 2004. [16] S. Madria, J. Yin, “SeRWA: A secure routing protocol against wormhole attacks in sensor networks”, Ad Hoc Networks, Elsevier, Volume 7, Issue 6, pp. 1051-1063, August 2009. [17] A. Bachir, D. Barthel, M. Heusse and A. Duda, “O(1)-Reception routing for sensor networks”, Computer Communications, Volume 30, Issue 13, pp. 2603-2614, September 2007. [18] F.Y. Leu and G.C. Li, “A scalable sensor network using a polar coordinate system”, Signal Processing, Volume 87, Issue 12, pp. 29782990, December 2007.
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