Abstract
In Wireless Sensor Network (WSN), the routing protocols have been given attention because most of the routing protocols are application and architecture dependent. This chapter presents routing protocols for wireless sensor networks and also classifies routing in WSN. Chapter gives five main classifications of routing protocols in WSN which are data-centric, hierarchical, location-based, network flow and QoS aware and opportunistic routing protocols. The focus has been given on advancement of routing in WSN in form of opportunistic routing, in which the sensor nodes utilize broadcasting nature of wireless links and the data packets can be transmitted through different paths. The routing protocols for WSN are described and discussed under the appropriate classification. A table of comparison of routing protocols on the basis of power usage, data aggregation, scalability, query basis, overhead, data delivery model and QoS parameters has been presented.
TopIntroduction
The recent advancements in the micro-electro-mechanical systems (MEMS) technology, communication techniques in wireless networks and nanotechnology give arise to develop small sensor nodes that are low-cost multifunctional energy constrained devices (Akkaya & Younis, 2005; Akyildiz, Su, Sankarasubramaniam, & Cayirci, 2002). These nodes can communicate over radio frequencies in small distances. The sensors constitute sensing, data processing and communicating hardware and software components. Wireless Sensor networks (WSN) are the dense collection of such sensors. The WSNs gather and communicate the physical or chemical data to monitor and control physical or chemical environments from remote stations with accuracy.
In most of the applications the position of the sensors need not to be engineered or pre-determined and this allows the distribution of the sensor nodes randomly. The WSN left unattended in most of the applications for long time. Hence, the protocols designed for WSN must contain the self-organizing capabilities. Rather than sending only raw data the sensor nodes should also be capable of carrying out some simple computations on raw data and transmit only the useful data towards the sink/base station.
Networking the unattended densely scattered sensor nodes has significant impact on many applications like disaster management, security, battle field surveillance (Dargie & Poellabauer, 2010). Routing WSN is very challenging task because WSNs are having different characteristics than conventional networks. First of all, as the sensor nodes are randomly deployed, global addressing is not possible. Hence, the user cannot apply classical IP-based protocols to WSNs. Second, the sensor nodes are constrained with respect to energy, transmission power, processing capacity, and storage capacity and therefore require resource management. Third, in contrast to classical communication in networks, the communications in WSN always require the flow of data from multiple sensor nodes (sources) towards the sink/base stations (Figure 1). Fourth, the data gathered from different regions in WSN have significant redundancy because multiple sensor nodes can generate the same data within particular area of deployment. Due to these types of differences, to solve the problem of data routing in WSN many algorithms has been proposed till date. These algorithms consider almost every characteristic of WSN. The sensor nodes organize themselves to form different topologies for communication which are discussed in the following section along with communication framework.
Figure 1.
Wireless sensor network example
The organization of chapter is as follows. Rest of this section will briefly summarize the communication in WSN and classification of routing protocols in WSN. In the Section 2, various design issues for routing protocols in WSNs are covered. Section 3 summarizes all types of routing protocols available under different classifications like Data centric, hierarchical, location based, Network flow and QoS, and opportunistic routing. Section 4 concludes the chapter with comparison tables of the studied routing algorithms and points out the good approach for routing in WSN.
Key Terms in this Chapter
Data aggregation: Data aggregation is defined as the process of removing the duplicate data packets by combining the received and sensed data by a node. The data aggregation has been done by the nodes which are intermediate to source and sink/base station.
Quality-of-Service (QoS): Quality-of-service is subjected to low-level, networking device observable attributes mainly bandwidth, delay, jitter, and packet loss rate. The QoS attributes in WSN are mainly dependent on the application like event detection level, tracking accuracy, event classification error and missing reports.
Network Lifetime: Generally defined as the time during which the network is operational. In other words the lifetime of network is defined as the operational time of the network during which it is able to perform the dedicated task(s).
Opportunistic Routing: Opportunistic routing uses broadcast nature of wireless links and tries to solve all of communication problems in WSN. Any sensor node can overhear the packet, but, only one will forward the packet towards next-hop. The next-hop selection process is based on opportunistic decisions/rules.
Communication Overhead: The total number of packets are to be transferred or transmitted from one node to another is known as the communication overhead. It includes the overhead of routing process, routing table and packet preparation in a sensor node.
Broadcast: The nature of communication of the wireless medium networks like WSN which allows the nodes to transmit the data to every other node in the routing table. Opportunistic routing protocols utilizes the broadcasting nature of WSN to transmit data with good quality-of-service.
Deployment: The setting up of the network components in a network is known as deployment. In other words, the setting up of a functional sensor network in real world application/environment is known as deployment of.
Topology: Topology is the way of arranging the entities of a network in such a way that it can operate efficiently and provide good quality-of-service. In other words, the organization of the all network components is known as topology.
Sink/Base Station (BS): A sink/base station is the type of sensor node which possesses high power, large memory and it is the entity, where information is required. Sink/base Station can be a part of the wireless sensor network field like sensor/actuator or it could be the node outside the field of sensors. It can also act as a gateway to other sensor nodes in the WSN field.
Scalability: The ability of a sensor network to always perform equally irrespective of the increasing or decreasing size of the network. It is an important factor in WSN because there are thousand number of nodes present in the network.
Routing: Routing is the process transmitting the data packet from source to destination via best routes within the network. It is basically the technique for the propagation of packets between multiple nodes.