A Cooperative Group-Based Sensor Network for Environmental Monitoring Miguel Garcia1, Jaime Lloret2 Instituto de Investigación para la Gestión Integrada de Zonas Costeras Universidad Politécnica de Valencia Camino de Vera s/n, 46022 Valencia, Spain 1
[email protected],
[email protected]
Abstract. Sensor networks can be used in many types of environments. The environmental monitoring is one of the most used. Communications in sensor networks should be as efficient as possible and collaborative methods can enhance their performance. In this work, we propose a monitoring group-based sensor network which uses the cooperation between groups. When a group detects an event, it warns the alert, jointly with the parameters measured, to its neighboring groups. Cooperation with other groups could change the direction of the alert propagation and the level of the alert. According this cooperation, the sensor network will be efficient and the sensors will have a longer lifetime. Keywords: cooperative group-based networks, environmental monitoring.
1
Introduction and Related Works
One of the main features of the sensor networks algorithms is their efficiency. Many sensor networks use an ad-hoc communication to a sink node [1]. This node is responsible for carrying out the management processes in the sensor network. When the data are managed, it sends information to the ad-hoc network. Sensors are also responsible for routing the information. The logic communication between the sensor network and the sink node is centralized. In these cases, the network intelligence rests on a single point and this gives the disadvantages of centralized networks. A group-based network is a network split into groups or areas according to some features [2]. A group is a small number of interdependent nodes with complementary operations that interact in order to share resources or computation time, or to acquire content or data and produce joint results. So far, in this type of group-based networks when an event is detected by a node, the node sends this information to all members of the group. In addition, the groups can share information and the information can reach all nodes of the network. This feature is adequate if we want to distribute an event to the whole sensor network. An example from the same authors is given in [3]. A. Nosratinia et al. present a work about cooperative communication in wireless networks, but from the physical level point of view, in [4]. They show several techniques and conclude the work indicating that the wireless devices may increase
their effective quality of service via cooperation. The work shown in [5] presents a cooperative architecture for sensor networks. The architecture is based on 6 layers. The first 3 layers are performed at the node and the next 3 layers require communication between nodes. The authors state that this type of networks can make improvements in: signal processing, communication, synchronization, geolocation, power saving, etc. Another work where the authors use cooperative sensor networks is presented in [6]. A stochastic sensor scheduling framework is applied to the position estimation of multiple emitter targets using a cooperative sensor network. We have shown several works where the authors use the cooperative term to develop different node roles in the networks. In our case, we propose an environmental monitoring network based on the cooperation between groups. The events detected in a group will only be transmitted to the closest groups. The rest of this paper is organized as follows. In section 2 is described the cooperative group-based network design. Section 3 shows its operation and messages exchanged. Finally, in section 4 we will show the conclusion and future works.
2
Cooperative Group-Based Sensor Network Description
This proposal of cooperative sensor networks is based on the group-based idea presented in [3] by J. Lloret et al. The group-based network formation is performed in the same manner but here we introduce cooperation issues. In addition, each group selects the best connection between neighbors through the proximity and the nodes’ capacity [7]. In order to have an efficient group-based sensor network, the groups will communicate with their neighboring groups. When a group detects an event, it warns the alert, jointly with the parameters measured, routing the information to its neighboring groups (not to all groups) based on the position of each group. The position of the sensors (it could be entered manually or using GPS [8]) and a positionbased routing algorithm [9] are used to know the group situation. Neighboring groups will reply to the first group if any of the parameters is changed in the place of that group in order to take the appropriate actions. Cooperation with other groups could change the direction of the alert propagation and the level of the alert. In Fig. 1 shows a group-based topology example. In a group-based network, all groups will be aware of an event produced inside the Group 1. The network efficiency would be yet higher than in a regular topology [2]. But, in cooperative group-based networks this efficient is greater, because only the neighboring groups will be aware of it. The other groups could be in sleep mode. The sleep groups will be saving energy and they would not transmit unnecessary information.
3
Cooperative Group-Based Sensor Network Operation
We define 3 alert levels. Level_1 means the maximum alert level and Level_3 the lowest. This cooperative group-based architecture runs following the next steps: 1. A sensor detects a warning event.
pNew
pNew Cooperative Group‐based New event Sensor Network
Group‐based Sensor Network
pIni
Group 2
Group 2
Group 1
Group 3
New event
Group 1
pIni
Group 3
Group 9
Group 9 Group 8
Group 8 Group 6
Group 4
Group 6 Group 4
Group 5
Group 5
Fig. 1. Comparison of group-based and cooperative group-based sensor networks.
2. It senses other parameters (it could be done using a multi-sensor). 3. The node assigns an alert level for each neighboring group and routes the information for each group using a position-based routing algorithm [9]. 4. The destination group senses the same parameters when it receives the information. 5. If the parameters are close, the neighboring groups will accept the alert level, if they are not close, they change the level according to the measured parameters and send the new parameters to the source group. 6. When the source group receives the information, it analyzes the level that should give to the neighboring groups and sends them the new level. Then go to step 4. Fig. 2 shows the flow chart of the steps explained. Taking into account Fig. 1 (right side), the messages sent are shown in Fig. 3. Let’s imagine that a plague of insects produces an event in Group 1, and the other parameters sensed are the wind direction and speed (now called pIni). Nodei calculates the level for each group and sends the alert and pIni to all nodes in its group. Each message will be also routed to the appropriate neighboring groups as in [3]. The information reaches Group 2, Group 8 and Group 6. Let’s suppose that the wind comes from east, so Group 2 has level_1, Group 8 has level_2 and the Group 6 has level_3. The p process is executed in each group when the information arrives. Fig. 4 shows the algorithm. If the parameters sensed are close to the initial parameters, the alert level does not vary. Let’s suppose that Group 6 detects changes in the wind direction (pNew). This group will send the new wind direction to Group 1, and then this group will estimate the new alert level.
4
Conclusion
In this paper we have presented a cooperative group-based sensor network. When a sensor detects a new event, an alert is sent to its group and it is distributed to neighboring groups. The cooperation between groups is used to send messages between groups in order to obtain the right alert level. This system is going to be developed as a fire detection system where the wind, humidity and temperature parameters are also measured. There are other application environments such as Rural and agricultural monitoring and natural crisis.
Nodei of Group 1 event
Initial parameters calculus
event
Group 2
Group 1
Group 8
Group 6
event + pIni
Alert level calculation according to the neighbor group position
To calculate initial parameters
Level_2
info + lev_2
ack
ack
To calculate the alert level according to the neighbor group position
What does level assign to the group?
Level_1
info + lev_1
Process p
info + lev_3 ack + pNew
info + lev_new ack
Fig. 3. Messages exchanged.
Level_3
If (pNew ≤ pIni*1.1 || pNew ≥ pIni*0.9)
Process P
Send ack to source group Alert level assigned = OK Does it change the value of the parameter?
No
Alert level = OK
Yes
Fig. 2. Cooperative architecture operation.
Else Send ack + pNew End
Fig. 4. Process p operation.
References 1. Akyildiz, I.F., Weilian Su, Sankarasubramaniam, Y. and Cayirci, E., “A survey on sensor networks”, IEEE Communications Magazine, vol.40, no.8, pp. 102-114, Aug 2002. 2. Lloret J., Palau C., Boronat F., Tomas J., “Improving networks using group-based topologies”, Computer Communications, vol. 31, issue 14, pp. 3438-3450, Sept. 2008. 3. Lloret, J., Garcia, M., Tomas, J. and Boronat, F., “GBP-WAHSN: A Group-Based Protocol for Large Wireless Ad Hoc and Sensor Networks”, Journal of Computer Science and Technology, vol. 23, no. 3, pp. 461-480, Springer US. May 2008. 4. Nosratinia, A., Hunter, T.E. and Hedayat, A., “Cooperative communication in wireless networks”, IEEE Communications Magazine, vol.42, no.10, pp. 74-80, Oct. 2004. 5. Agre, J. and Clare, L., “An integrated architecture for cooperative sensing networks”, Computer, vol.33, no.5, pp.106-108, May 2000. 6. Sciacca L. J., and Evans R., “Cooperative sensor networks with bandwidth constraints”, Battlespace Digitization and Network-centric Warfare Conference, vol. 4741, 192-201. Orlando, FL, USA. April 2002. 7. Garcia, M., Bri, D., Boronat, F. and Lloret, J., "A New Neighbour Selection Strategy for Group-Based Wireless Sensor Networks," 4th Int. Conf. on Networking and Services, ICNS 2008, pp.109-114, 16-21 March 2008. 8. E. D. Kaplan, “Understanding GPS: Principles and Applications”. Artech House. Boston, MA, 1996. 9. I. Stojmenovic, “Position based routing in ad hoc networks”, IEEE Communications Magazine, Vol. 40, No. 7, pp. 128-134. July 2002.
