WSNs are typically composed of a large number of low-cost, low-power, multifunctional wireless devices deployed over a geographical area in an ad hoc fashion and without careful planning. Individually, sensing devices are resource constrained
and therefore are only capable of a limited amount of processing and communication. It is the coordinated effort of these sensing devices, however, that bears promise for a significant impact on a wide range of applications in several fields, including science and engineering, military settings, critical infrastructure protection, and environmental monitoring. Harnessing the potential benefits ofWSNs requires a high-level of self-organization and coordination among the sensors to perform the tasks required to support the underlying application. At the heart of this collaborative effort to achieve communications is the need for the wireless sensor nodes to self-organize into a multihop wireless network. Consequently, the design of efficient communications and network protocols for WSNs becomes crucial for wireless sensor nodes to carry out successfully the mission for which they are deployed. The establishment of a multihop wireless network infrastructure for data transfer requires the establishment of communication links between neighboring sensor nodes. Unlike communication over a guided medium in wired networks, however, communication in wireless networks is achieved in the form of electromagnetic signal transmission through the air. This common transmission medium must therefore be shared by all sensor network nodes in a fair manner. To achieve this goal, a medium access control protocol must be utilized. The choice of the medium access control protocol is the major determining factor in WSN performance. A number of access control protocols have been proposed for WSNs. The objective of this chapter is to discuss the fundamental design issues of medium access control for WSN methods and to provide an overview of these protocols. a description of the basic requirements of access control protocols is provided. We categorize the major media access control techniques used in shared medium access networks.We discuss specific requirements of access control methods for WSNs and describes several media access control (MAC) protocols for these networks.
Communication among wireless sensor nodes is usually achieved by means of a unique channel. It is the characteristic of this channel that only a single node can transmit a message at any given time. Therefore, shared access of the channel
requires the establishment of a MAC protocol among the sensor nodes. The objective of the MAC protocol is to regulate access to the shared wireless medium such that the performance requirements of the underlying application are satisfied [5.4–5.7]. From the perspective of the Open Systems Interconnection (OSI) Reference Model (OSIRM), the MAC protocol functionalities are provided by the lower sublayer of the data link layer (DLL). The higher sublayer of the DLL is referred as the logical link control (LLC) layer. The subdivision of the data link layer into two sublayers is necessary to accommodate the logic required to manage access to a shared access communications medium. Furthermore, the presence of the LLC sublayer allows support for several MAC options, depending on the structure and topology of the network, the characteristics of the communication channel, and the quality of service requirements of the supported application.
Figure 5.1 depicts the OSI reference model and the logical architecture of the DLL for shared medium access in wireless networks. The physical layer (PHY) typically includes a specification of the transmission medium and the topology of
the network. It defines the procedures and functions that must be performed by the physical device and the communications interface to achieve bit transmission and reception. It also coordinates the various functions necessary to transmit a stream of bits over the wireless communication medium. The major services provided by the physical layer typically include the encoding and decoding of signals, preamble generation and removal to achieve synchronization, and the transmission and reception of bits.
Keyword :
wireless sensor networks ,sensor networks ,the network ,sensor nodes ,protocols ,transmission ,sensors ,sensor node ,sensor ,protocol ,preamble ,packets ,packet ,networks ,neighbors ,medium access control ,wireless sensors ,wireless sensor network ,wireless networks ,wireless ,topologies ,tinyos ,time slots ,simulation ,scheme ,schedule ,receiver ,rate control ,probability ,power consumption ,node topology ,mac protocols ,mac protocol ,low-power ,latency ,energy efficient ,energy consumption ,energy ,duty cycle ,deployed ,data packets ,contention ,congestion control ,congestion ,collisions ,cluster ,channel ,algorithms ,algorithm ,adaptive ,ad hoc ,access control protocol.
The characteristics of the communication channel, and the quality of service requirements of the supported application.