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An energy-efficient chain-based cooperative sleep/wake-up routing protocol for wireless sensor network Dina M

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An energy-efficient chain-based cooperative sleep/wake-up routing protocol for wireless sensor network

Dina M. El-Feky
Computers and Automatic Control Dept.
Faculty of Engineering, Tanta University
Tanta, Egypt
[email protected]

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Nada M. El-shennawy
Computers and Automatic Control Dept.
Faculty of Engineering, Tanta University
Tanta, Egypt
[email protected]

Mahmoud M. Fahmy
Computers and Automatic Control Dept.
Faculty of Engineering, Tanta University
Tanta, Egypt
[email protected]

Abstract—In recent years, wireless sensor networks (WSNs) have a rapid development and they attracted a great deal of research attention because of their wide-range applications. A WSN consists of hundreds or thousands of distributed sensor nodes that often deploy in remote or hostile areas to monitor physical or environmental conditions. This data is then sent to the base station. The energy of these nodes is very limited, and sensing and transmitting data consume energy. The most critical parameter in WSNs is network lifetime. So an efficient routing protocol with sleep/wake-up scheduling mechanism is essential to reduce the energy consumption and increase the network lifetime. This paper proposes an energy-efficient chain-based cooperative routing protocol based on node sleep/wake-up mechanism for WSNs. The proposed protocol is implemented and compared with two efficient protocols, LEACH and CBCCP, using MATLAB. Simulation results show that the proposed algorithm achieves better performance and conserves more energy than the other two protocols.
Keywords—Wireless sensor networks; Clustering; Energy consumption; sensing coverage
I. INTRODUCTION
Wireless sensor networks (WSNs) support a wide range of applications, such as war battles, manufacturing, surveillance, targeting systems, health needs, home automation, smart building and monitoring disaster areas 1, 2 . A WSN is a wireless network that consists of hundreds or thousands of low cost and low power sensor nodes which are randomly deployed in a monitoring field to sense and monitor the data, and then this data is passed to the main location 3. Examples of sensing data are temperature, pressure, humidity, lightning conditions, noise levels and presence or absence of a certain kind of object. In a large-scale WSN, high density sensor nodes are used. These sensor nodes are equipped with limited energy batteries, and it is difficult and not practical to replace or recharge these batteries because of high cost or geographic reasons. Because of the limited resource of sensor nodes, effective routing protocols have to be designed to prolong network lifetime and to reduce energy consumption. Also node scheduling is of prime importance in order to increase the network lifetime and preserve sufficient sensing coverage and reliability. Energy consumption can be reduced and network lifetime can be increased by turning off redundant nodes and activating another set of nodes, providing good sensing coverage.
WSN routing protocols can be classified on the basis of network structures as: flat, hierarchical and location-based 4. In a flat structure, all sensor nodes have the same role. The base station sends queries to different regions and waits for the sensor response, such as Sensor Protocols for Information via Negotiation (SPIN) and Direct Diffusion (DD) 5. In hierarchical routing protocols, sensor nodes have different roles; this type is also called cluster routing. Nodes are classified according to their energy into high and low energy nodes. Cluster routing processes have two steps: cluster selection and routing. Low-Energy Adaptive Clustering Hierarchy (LEACH) 6 and Threshold sensitive Energy Efficient sensor Network (TEEN) 7 are hierarchical routing protocols. In location-based routing, the node location is the main parameter in this routing as in Geographical Adaptive Fidelity (GAF) 8 and Geographical and Energy-Aware Routing (GEAR) 9.
Minimizing energy consumption and maximizing network lifetime are the main goals for WSNs. The LEACH 6 uses a cluster approach. LEACH can maximize the energy efficiency by dynamically changing cluster head and the result shows that LEACH increases energy efficiency eight times over Minimum Transmission Energy routing protocol (MTE) and Direct Routing (DR).Cluster heads (CHs) can directly send data to the base station which consumes a lot of energy of CHs. But multi-hop communication is more efficient in terms of energy as used in Hybrid Energy-Efficient Distributed (HEED) protocol 10. In HEED cluster formation is done on the basis of node residual energy and intra-cluster communication cost to prolong network lifetime. The result shows that HEED increases network lifetime by approximately two times than LEACH.
Power-Efficient Gathering in Sensor Information Systems (PEGASIS) 11 is a chain-based protocol which reduces energy consumption and increases network lifetime by making nodes communicate only with the nearest neighbors. It is assumed that every node should know the location information about all other nodes. One of the sensor nodes on the chain acts as the head node and sends data to the base station. The performance of PEGASIS protocol is better for twice at least than LEACH protocol. In 8, an algorithm called Geographical Adaptive Fidelity (GAF) is developed and it uses geographic location information for dividing the area into virtual grids. Within each virtual grid, nodes will elect one sensor node staying awake to sense and forward data to the base station and then they go to sleep. Analysis and simulation results show that GAF consumes 40% to 60% less energy than an unmodified ad hoc routing protocol. In the Chain Based Cluster Cooperative Protocol (CBCCP) 12 uses more benefits by using both types of communication at inter and intra cluster level. Reducing energy in communication to prolong the network lifetime is the main goal of CBCCP. The result shows that CBCCP consumes six times less energy than LEACH.
In this paper, energy efficient routing and scheduling protocol is proposed based on energy efficiency and node life time to increase the total network lifetime. CBCCP can be improved on the higher level by taking into account sleep and wake scheduling which we propose in this paper. The proposed algorithm uses a sleep/wake-up mechanism. It is implemented using MATLAB and is compared with LEACH6 and CBCCP12.
The paper is organized as follows. Section II introduces the architecture of wireless sensor networks. In Section III, the routing and scheduling protocols are reviewed. In Section IV, the proposed protocol is presented. Comparison of performance of the proposed protocol with LEACH and CBCCP is shown in Section V. In Section VI, conclusions and trends for future work are given.
II. W IRELESS SENSOR NETWORKS (WSNS)

WSNs are considered one of the most developing technologies. A WSN consists of spatially distributed sensing nodes which are used to control environmental or physical conditions, as pressure, sound, motion, temperature, vibration or pollutants, and pass this data to the main location through the network 3 as shown in Fig.1.

Fig. 1. Wireless sensor network architecture
The sensor node is the main component in a WSN. It consists of four basic units: sensing unit, processing unit, transceiver unit and power unit, as shown in Fig.2. There are many additional components such as power generator, mobilizer and location finding system. The sensing unit consists of two parts: sensors and analog-to-digital converters. The analog signals are generated from the sensors and converted to digital signals by the analog-to-digital converters; then they are fed into the processing unit. The processing unit is responsible for managing the procedures to make the cooperation between sensor nodes to execute the specified sensing tasks. Each sensor node is connected to the network by the transceiver unit 13.
III. ROUTING PROTOCOLS
In a WSN, sensor nodes communicate with each other to send collected data to the base station. This is the major role of routing algorithms. Sensor nodes are equipped with low battery power and it is difficult to replace or recharge these batteries, so WSN lifetime is limited. To prolong WSN lifetime, we need efficient routing and scheduling algorithms. There are many routing protocols which are used with WSN such as LEACH 6 and CBCCP 12.
A. LEACH protocol
LEACH 6 is proposed to reduce energy consumption and prolong network lifetime. The operation of LEACH can be divided into rounds as shown in Fig.3. Each round begins with a set-up phase where clusters are organized, then the second phase which is a steady-state phase where data is sent form the nodes to the cluster head (CH) and then to the base station. LEACH uses received signal strength of nodes to organize clusters. First, it uses a function for determining the probability P of a node that wants to be a CH. Then the CH nodes send advertisement messages to the other nodes with the same transmit energy. Each non-CH node chooses its cluster by determining the CH that can be reached based on the lowest energy that is used to send data to CH. Finally, the cluster is organized and nodes can send data to CH which aggregates data and sends it to the base station.

Fig. 2. Components of sensor node

Fig. 3 . LEACH algorithm flowchart 6
B. Node scheduling algorithm
This algorithm 14 is proposed to minimize the number of active nodes and preserve the original sensing coverage. The process of this algorithm consists of two phases: self-scheduling phase and sensing phase. The self-scheduling phase is composed of two steps. First, each node advertises its position and listens to advertisement messages from other nodes to get neighboring nodes’ position information. Second, each node calculates its sensing area and compares it with the sensing area of its neighbors to decide if this node goes to sleep or not, based on Eq.1.

The neighbor set of node i is defined as
N (i) = {n ? ? | d (i, j) ? r, n ? i} (1)
where ? is a node set in the deployment region, d (i, j) denotes the distance between node i and node j as shown in Figs 4.
After each round, the remaining energy of the nodes is decreased with time and its sensing radius is gradually reduced as shown in Fig. 5, so a threshold W of energy consumption is added for each sensor node as explained in 15.

Fig. 4. Illustration of the nodes coverage area 14

Fig. 5. Changes in nodes detection range 15
Assume U is the initial energy of nodes. When the energy of nodes decreases to a threshold W with time, a working node starts to send wake-up commands to its sleeping neighbor nodes. Sleeping nodes wake up and re-enter the self-scheduling phase with the working nodes and establish a queue sort mechanism according to the remaining energy of nodes in the neighbor nodes set. This is to avoid choosing the nodes whose energy below the threshold W as working nodes again in the new scheduling algorithm 15.

C. CBCCP Routing protocol
The main goal of this protocol is to reduce energy in communication to prolong the network lifetime. CBCCP 12 begins its work by dividing the field into a static set of clusters arranged as levels. Each cluster selects one node randomly to act as CH. At the first cluster (level 1) there is only one CH. But upper levels of clusters have one CH and some cluster coordinator nodes (CCOs), the number of CCOs in each level is equal to the number of cluster level -1 as shown in Fig. 6. In this protocol, the data collected at each cluster is sent from CH to CCO in the upper level. This means that the CH of each cluster is responsible for collecting data of its level and CCO is responsible for receiving data of lower level. The method used for sending data reduces energy consumption and prolongs the network lifetime.
IV. PROPOSED PROTOCOL
The main problem of WSNs is the network lifetime. To increase the network lifetime we need an efficient routing and scheduling algorithm to enhance the energy used. In this paper, an energy-efficient chain-based cooperative sleep/wake-up routing protocol is proposed to prolong the network lifetime by using sleep/wake-up mechanism. The proposed protocol is divided into two phases: scheduling phase by using a sleep/wake-up mechanism and a clustering phase based on cluster levels. We assume that the WSN consists of N sensor nodes randomly deployed in the sensing field. The sensor nodes are stationary and each node knows its location; each node knows its neighbors and where they exist; each node knows its sensing area. The sensing area of a node is defined as the area that can be monitored by a node, when it is in the active state. Each node belongs to exactly one cluster; after node-scheduling, each node can be off-duty (sleep) state or on-duty (wake-up) state; during clustering each node can be a normal node, a cluster head (CH) or a cluster coordinator (CCO) 12.
A. Scheduling phase
In this phase, each node advertises its sensing range to its neighbor nodes and listens to the messages from its neighbors that contain the sensing range of these nodes. The sleep/wake-up mechanism 14 works on the basis of comparing the sensing area of the node with its neighbors. If the sensor node is fully covered by its neighbors, this node goes to sleep without any problem in sensing data to reduce its energy consumption. The sleeping nodes can wake-up when the residual energy of the wake-up nodes is less than the proposed threshold energy by sending wake-up command to sleeping neighbor nodes. The sleeping nodes wake-up and re-enter the self-scheduling phase to make the less energy nodes sleep; at this point another round starts.
B. Clustering phase
The clustering phase starts once the network is installed to construct a static level of clusters. For each cluster, one CH and a number of CCOs are selected randomly based on the cluster level. The numbers of CCOs depend on the cluster level. Any node can be selected as CH or CCO in which energy is greater than a threshold level. When any CH or CCO consumes energy up to the threshold level, a clustering process is affected and new CH and CCO are selected in each cluster. Then the cluster is organized and the nodes in each cluster send collected data to CH with the help of relay nodes. The CH collects and aggregates data and sends it to the next level cluster and received by the CCO. It is forwarded to the next level CCO in the next cluster. This process continues until the data is forwarded to the base station 12. The flowchart of the proposed protocol is shown in Fig 7.

Fig. 6. Inter-cluster communication with the help of cluster coordinators

Fig. 7. Proposed protocol flowchart

V. PROTOCOL EVALUATION AND SIMULATION RESULTS

The proposed protocol is implemented and evaluated using MATLAB. Our protocol is compared with the most famous protocols: LEACH 6 and CBCCP 12. The used performance metrics in our comparison are the number of dead nodes, the number of sent packets to the base station and the sum of nodes energy. The network specification used is shown in Table. 1.
The performance metric of number of dead nodes is indicated in Fig.8. From the figure, we see that the proposed algorithm has the lowest number of dead nodes. In the both LEACH and CBCCP protocols, nodes are dying fast as compared to the proposed protocol. So these protocols have high number of dead nodes. But the proposed protocol uses a sleep/wake-up mechanism which increases the node lifetime and decrease the number of dead nodes.
The sum of nodes energy is shown in Fig.9. The proposed algorithm outperforms the other algorithms in the sum of nodes energy which cause prolonged network life-time. This results from the use of a sleep/wake-up mechanism which increases the nodes energy and nodes lifetime. On the contrary, in case of the other protocols, nodes are dying fast. So these protocols have low sum of nodes energy.
TABLE I. VALUES OF THE PARAMETERS USED IN SIMULATION 12.
Simulation Parameters Column
Area of simulation 200 × 200 m2
Number of nodes 1000
?fs (energy used in short distant communication) 10 pJ/bit/m2
?mp (energy used in long distant communication) 0.0013 pJ/bit/m4
l (length of data) 4000 bit
Ee (Initial energy of the nodes) 0.5 J
ET (Transmitting energy) 50 nJ/bit
ER (Reception Energy) 50 nJ/bit
Ebf (Energy consumption in Beam Forming) 5 nJ/bit
Sensing range, r 10m

Fig. 8. Number of dead node VS. round
In Fig.10, the numbers of sent packets to the base station are shown. As the results show, LEACH has the highest number of sent packets to the base station because it uses more clusters than the proposed algorithm that has a finite number of clusters. But, the proposed algorithm has a higher number of sent packets than CBCCP because the use of a sleep/wake-up mechanism to increase the network lifetime.

Fig. 9. Sum of energy of node VS. round
VI. CONCLUSION AND FUTURE WORKS
In recent years, WSNs have a rapid development and they attracted a great deal of research attention. The main essential parameter of WSNs is the network lifetime, so we need an energy efficient routing protocol to prolong the network lifetime. In this paper, energy efficient chain based cooperative sleep/wake-up routing protocol is proposed. This protocol reduces energy consumption and therefore increases network lifetime. The proposed protocol is implemented and evaluated using MATLAB. It is compared with LEACH and CBCCP. The simulation results indicate that the proposed algorithm exceed the others in the number of dead nodes and the sum of nodes energy performance metrics. Although our algorithm achieves the goals of increasing network lifetime and maintaining network performance, it still has space for improvement. For instance, our protocol is based on the assumption that the coverage area of each node is a circle. In practice, obstacles, weather or other factors may affect the coverage area and change its shape to irregular and asymmetric. Evaluating the sensitivity of our scheme to these factors is necessary. In addition, the trade-off between the percentage of active nodes and the percentage of system sensing coverage is also part of our future work.

Fig. 10. Number of packets sent to BS VS. round

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