A survey of wireless sensor networks deployment techniques Michał Marks Institute of Control and Computation Engineering Warsaw University of Technology Research and Academic Computer Network (NASK) DSTIS - Decision Support for Telecommunications and Information Society September 4 7, 2009
Outline A survey of wireless sensor networks deployment techniques 2 Introduction to positioning in Wireless Sensor Networks Key properties in WSN designing Positioning taxonomy classification criteria Examples coverage tracking Summary and conclusions
Previously on DSTIS A survey of wireless sensor networks deployment techniques 3 DSTIS 2008: WSN Localization Problem Source: http://www.dei.unipd.it/~schenato/ LOCALIZATION Goal: Estimation of the network nodes location Ad hoc network consisting of a set of sensors with initially unknown positions
Positioning nodes in WSN A survey of wireless sensor networks deployment techniques 4 Different meaning of the positioning Source: D Agents http://agent.cs.dartmouth.edu/ DEPLOYMENT Goal: Positioning the nodes so as to meet the aim of successfully transferring data from the sources to the base station and, ultimately, to optimize some network performance metric. A set of sensors to be placed in considered area
WSN Positioning Classification - preliminary A survey of wireless sensor networks deployment techniques 5 WSN POSITIONING LOCALIZATION DEPLOYMENT (PLACEMENT)
Definition of Wireless Sensor Network A survey of wireless sensor networks deployment techniques 6 In the past, a number of early, mostly US-based research projects established a de facto definition of a wireless sensor network as a large-scale ad hoc, multi-hop, unpartitioned network of largely homogenous, tiny, resource-constrained, mostly immobile sensor nodes that would be randomly deployed in the area of interest. Romer, K.; Mattern, F., The design space of wireless sensor networks, IEEE Wireless Communications, Volume 11, Issue 6, 2004, 54-61
WSN world is changing A survey of wireless sensor networks deployment techniques 7 Wireless Sensor Network 1 Mobile Sensor 2 Wireless Sensor 3 Networks and Actor Networks Wireless Multimedia Sensor Networks MOSES Laboratory; University of Notre Dame Carnegie Mellon University CROSSBOW Solutions 1.Wang, Y., Dang, H., Wu, H. A survey on analytic studies of Delay-Tolerant Mobile Sensor Networks: Research Articles. Wirel. Commun. Mob. Comput. 7, 10 (Dec. 2007), 1197-1208. 2.Akyildiz, I. F., Kasimoglu, I. H., Wireless Sensor and Actor Networks: Research Challenges, Ad Hoc Networks Journal, 2, 4 (Oct. 2004) pp. 351-367. 3.Akyildiz, I. F., Melodia, T., Chowdhury, K. R., A survey on wireless multimedia sensor networks. Comput. Netw. 51, 4 (Mar. 2007), 921-960.
Initial assumptions and WSN development A survey of wireless sensor networks deployment techniques 8 WSN DEFINITION PROPERTIES large-scale ad hoc, multi-hop, unpartitioned network of largely homogenous, tiny, resource-constrained, mostly immobile sensor nodes that would be randomly deployed in the area of interest. 1. NETWORK SIZE 2. NETWORK TOPOLOGY 3. HETEROGENITY 4. SIZE, RESOURCES 5. MOBILITY 6. DEPLOYMENT
WSN development: 1. Network size A survey of wireless sensor networks deployment techniques 9 The network size may vary from a few nodes to thousands of sensor nodes. The number of nodes participating in a sensor network is mainly determined by requirements relating to network connectivity and coverage, and by the size of the area of interest. Possible values: all from a few nodes to thousands of nodes Examples: Application Size (number of nodes) Torre Aquila (monitoring Heritage Buildings) 16 Glacsweb (glacier monitoring) 32 Argo (ocean monitoring) 3338
Example 1: Argo Project #1 A survey of wireless sensor networks deployment techniques 10 Argo is a global array of 3,000 free-drifting profiling floats that measures the temperature and salinity of the upper 2000 m of the ocean. This allows, for the first time, continuous monitoring of the temperature, salinity, and velocity of the upper ocean, with all data being relayed and made publicly available within hours after collection. ARGO project - http://www.argo.ucsd.edu
Example 1: Argo Project #2 A survey of wireless sensor networks deployment techniques 11
WSN development: 2. Network topology #1 A survey of wireless sensor networks deployment techniques 12 One important property of a sensor network is the maximum number of hops between any two nodes in the network. In its simplest form, a sensor network forms a single-hop network, with every sensor node being able to directly communicate with every other node. In multi-hop networks nodes may forward messages over multiple hops. The sensor network architecture can be flat where all sensors play the same role in communication all nodes acts as routers. We can also consider a tired architecture. The most common is two-tier where sensors are split into clusters; each is led by an cluster head node. Possible values: I dim single-hop, multi-hop, II dim flat, layered (tiered)
WSN development: 2. Network topology #2 A survey of wireless sensor networks deployment techniques 13 Examples: Application Torre Aquila (monitoring Heritage Buildings) Grape (Agricultural Wireless Sensor Network) Glacsweb (glacier monitoring) Network topology flat, ad-hoc, multi-hop two-tier, multi-hop two-tier, multi-hop
Example 2: Glacsweb Project #1 A survey of wireless sensor networks deployment techniques 14 Elsevier: Quaternary Science Reviews
Example 2: Glacsweb Project #2 A survey of wireless sensor networks deployment techniques 15 The base station is located on the surface of the glacier. Due to the significant radio losses in the upper ice layer, the nodes are unable to communicate directly with base station. In order to establish (or enhance) these communication links, the base station is connected to some of the nodes (called anchor nodes) via a serial cable. These anchor nodes are responsible for communicating with the remaining network on behalf of the base station. Spatial view Two-tier network configuration Elsevier: Quaternary Science Reviews
WSN development: 3. Heterogenity A survey of wireless sensor networks deployment techniques 16 Early sensor network visions anticipated that sensor networks would typically consist of homogeneous devices that were mostly identical from a hardware and software point of view. However, in many prototypical systems available today, sensor networks consist of a variety of different devices. Nodes may differ in the type and number of attached sensors; some nodes may act as gateways to long-range data communication networks (e.g., GSM networks or satellite networks). Possible values: homogeneous, heterogeneous Examples: Application Torre Aquila (monitoring Heritage Buildings) Argo (ocean monitoring) Glacsweb (glacier monitoring) Heterogenity heterogeneous homogeneous homogeneous
Example 3: Torre Aquila The system contains many kinds of sensors, whose operation is quite different. Deformation and environmental parameters can be sampled at a low rate, but vibration must be monitored at a high rate, which consequently demands efficient reporting of the resulting high volume of data. A survey of wireless sensor networks deployment techniques 17
WSN development: 4. Size, resources #1 A survey of wireless sensor networks deployment techniques 18 Depending on the actual needs of the application, the form factor of a single sensor node may vary from the size of a shoe box (e.g., a weather station) to a microscopically small particle (e.g., for military applications). Similarly, the cost of a single device may vary from a few Euros to a hundreds of Euros. Varying size and cost constraints directly result in corresponding varying limits on the energy available, as well as on computing, storage, and communication resources. Possible values: brick, matchbox, grain, dust Examples: Application Node length Node cost Torre Aquila (monitoring Heritage Buildings) 13 cm >=120$ Argo (ocean monitoring) 110 cm ~ 15000$ Glacsweb (glacier monitoring) 16 cm ~ 320$
WSN development: 5. Mobility A survey of wireless sensor networks deployment techniques 19 Sensor nodes may change their location after initial deployment. Mobility can result from environmental influences such as wind or water, sensor nodes may be attached to or carried by mobile entities passive mobility. Sensor nodes may possess automotive capabilities active mobility. David Pescovitz photo Berkeley lab Wildsensing project Oxford University
WSN development: 5. Mobility A survey of wireless sensor networks deployment techniques 20 Mobility may apply to all nodes within a network or only to subsets of nodes. The degree of mobility may also vary from occasional movement with long periods of immobility in between, to constant travel. Possible values: I dim active, passive II dim mobile, stationary, mixed. Examples: Application Mobility Wildsensing University of Oxford passive, mixed, 30 mobile, 28 stationary Torre Aquila - University of Trento Mobile Sensor Swarms Univ. of Notre Dame stationary mobile
WSN development: 6. Deployment A survey of wireless sensor networks deployment techniques 21 The deployment of sensor nodes in the physical environment may take several forms. Nodes may be deployed at random (e.g., by dropping them from an aircraft) or installed at deliberately chosen spots. The actual type of deployment affects important properties such as the expected node density, node locations, regular patterns in node locations, and the expected degree of network dynamics. Possible values: random, deterministic. Examples: Application Argo (ocean monitoring) Torre Aquila (monitoring Heritage Buildings) Glacsweb (glacier monitoring) Deployment random deterministic deterministic
From properties to classification A survey of wireless sensor networks deployment techniques 22 WSN DEFINITION PROPERTIES large-scale ad hoc, multi-hop, unpartitioned network of largely homogenous, tiny, resource-constrained, mostly immobile sensor nodes that would be randomly deployed in the area of interest. 1. NETWORK SIZE 2. NETWORK TOPOLOGY 3. HETEROGENITY 4. SIZE, RESOURCES 5. MOBILITY 6. DEPLOYMENT
Classification criteria for WSN positioning techniques A survey of wireless sensor networks deployment techniques 23 1. HETEROGENITY Homogeneous, heterogeneous 2. MOBILITY Stationary, mobile, mixed networks 3. DEPLOYMENT Deterministic, random 4. OBJECTIVES Area coverage Network connectivity Network longevity Data fidelity Ability to tracking the objects Fault tolerance Effective transmission
A survey of wireless sensor networks deployment techniques 24 Classification tree Coverage Mobile networks Deterministic Deployment Tracking Fault tolerant Coverage Deterministic Deployment Tracking Stationary networks Fault tolerant Heterogeneous nodes Random Deployment Coverage topology control Localization Coverage Deterministic Deployment Tracking Positioning in Wireless Sensor Networks Mixed networks (some nodes are mobile) Fault tolerant Random Deployment Coverage topology control Localization Coverage Deterministic Deployment Tracking Stationary networks Fault tolerant Homogeneous nodes Random Deployment Coverage topology control Localization Coverage Mobile networks Deterministic Deployment Tracking Fault tolerant
A survey of wireless sensor networks deployment techniques 25 Coverage #1 Coverage Mobile networks Deterministic Deployment Tracking Fault tolerant Coverage Deterministic Deployment Tracking Stationary networks Fault tolerant Heterogeneous nodes Random Deployment Coverage topology control Localization Coverage Deterministic Deployment Tracking Positioning in Wireless Sensor Networks Mixed networks (some nodes are mobile) Fault tolerant Random Deployment Coverage topology control Localization Coverage Deterministic Deployment Tracking Stationary networks Fault tolerant Homogeneous nodes Random Deployment Coverage topology control Localization Coverage Mobile networks Deterministic Deployment Tracking Fault tolerant
Coverage #2 A survey of wireless sensor networks deployment techniques 26 Maximal coverage of the monitored area is the objective that has received the most attention in the literature. Some of the papers, especially early ones, use the ratio of the covered area to the size of the overall deployment region as a metric for the quality of coverage.
Coverage -> Tracking A survey of wireless sensor networks deployment techniques 27 Since 2001, however, most work has focused on the worst case coverage, usually referred to as least exposure, measuring the probability that a target would travel across an area or an event would happen without being detected.
Example sensor repositioning to improve coverage #1 A survey of wireless sensor networks deployment techniques 28 Lets assume that we have a mobile sensor network and the goal is to maximize the area covered with minimal overhead in terms of travel distances and inter-sensor message traffic. The main idea is that each sensor assesses the coverage in its neighborhood and decides whether it should move to boost the coverage. To assess the coverage, a sensor node creates a Voronoi polygon with respect to neighboring sensors.
Example sensor repositioning to improve coverage #2 A survey of wireless sensor networks deployment techniques 29 The intersection of the disk that defines the sensing range and the Voronoi polygon represents the area the sensor can cover. If there are uncovered areas within the polygon, the sensor should move to cover them.
Example sensor repositioning to improve coverage #3 A survey of wireless sensor networks deployment techniques 30 So, the sensor node is pulled towards the farthest Voronoi vertex (point A) to fix the coverage hole in the polygon. However, the sensor will be allowed to travel only a part of a distance between the node S and point A. The authors proposed 3 different methods how to calculate this distance.
Example sensor repositioning to improve coverage #5 A survey of wireless sensor networks deployment techniques 31 Initial deployment Final deployment Wang, G., Cao, G., La Porta, T., Proxy-Based Sensor Deployment for Mobile Sensor Networks, IEEE MASS, October 2004
A survey of wireless sensor networks deployment techniques 32 Tracking - example Coverage Mobile networks Deterministic Deployment Tracking Fault tolerant Coverage Deterministic Deployment Tracking Stationary networks Fault tolerant Heterogeneous nodes Random Deployment Coverage topology control Localization Coverage Deterministic Deployment Tracking Positioning in Wireless Sensor Networks Mixed networks (some nodes are mobile) Fault tolerant Random Deployment Coverage topology control Localization Coverage Deterministic Deployment Tracking Stationary networks Fault tolerant Homogeneous nodes Random Deployment Coverage topology control Localization Coverage Mobile networks Deterministic Deployment Tracking Fault tolerant
Example monitoring movements #1 A survey of wireless sensor networks deployment techniques 33 Monitoring movements in and out of a facility served by two roads The facility is modeled as a circle of radius 1 centered at the origin. It is assumed that any sensor placed inside the facility will not be able to operate. Two roads serve the facility, one horizontal going East, one vertical going North. Jourdan, D., de Weck, O., Multi-objective genetic algorithm for the automated planning of a wireless sensor network to monitor a critical facility
Example monitoring movements #2 A survey of wireless sensor networks deployment techniques 34 Objective 1: Coverage The first objective is the coverage, by which is meant the ability of the network to monitor movements in and out of the facility. A series of radial lines stemming from the facility are generated, and represent the possible directions from which agents can enter or exit the facility. A sensor covers a line if its distance with the line is less than sensing range. The coverage is equal to the number of lines covered by the sensors, divided by the total number of lines.
Example monitoring movements #3 A survey of wireless sensor networks deployment techniques 35 Objective 2: Survivability The second objective is the survivability of the network, by which is meant the likelihood that sensors will not be found. Each point in the area is assigned a probability of detection. This probability depends on the proximity of the facility or the roads. It is assumed that if a sensor is placed close to a road (where most of the activity takes place) or to the facility, it is more likely to be found and disabled.
Example monitoring movements #4 A survey of wireless sensor networks deployment techniques 36 Objective 3: Number of sensors Solution:
Example monitoring movements #5 A survey of wireless sensor networks deployment techniques 37 Solution Coverage Survivability Number of sensors b 0,99 0,74 9 c 0,96 0,66 7 d 1,00 0,44 5
Conclusions A survey of wireless sensor networks deployment techniques 38 The deployment problem is one of the most fundamental issue in WSN designing. How many wireless sensor nodes should be used and where should they be placed in order to optimize network performance? This is a difficult question to answer for a decision maker due to conflicting objectives of deployment costs, overall network lifetime and wireless transmission reliability. I have tried to present a categorization of various strategies for positioning nodes in WSNs. We have considered stationary, mobile and mixed networks with homogenous or heterogeneous nodes. We have made an attempt to identify the various objectives and enumerate the different models and formulations.
A survey of wireless sensor networks deployment techniques 39 Thank You for attention
Questions about deployment A survey of wireless sensor networks deployment techniques 40 How many sensor nodes are needed to meet the overall system objectives? For a given network with a certain number of sensor nodes, how do we precisely deploy these nodes in order to optimize network performance? When data sources change or some part of the network malfunctions, how do we adjust the network topology and sensor deployment? Cassandras, C.G. Wei Li, Sensor Networks and Cooperative Control, 44th IEEE Conference on Decision and Control, 2005, 4237-4238
WSN development: 4. Size, resources #2 A survey of wireless sensor networks deployment techniques 41 ARGO TORRE AQUILA GLACSWEB
A survey of wireless sensor networks deployment techniques 42