Performance Evaluation of Quality of Service in IEEE 802.15.4-Based Wireless Sensor Networks

1. Introduction

Wireless Sensor Networks(WSN) have gained world-wide attention in recent years due to the advances made in wireless communication, information technologies and electronics field (Akyildiz, Su, Sankarasubramaniam, & Cayirci, 2002; Yick, Mukherjee & Ghosal, 2008).The concept of wireless sensor networks is based on a simple equation: Sensing + CPU + Radio = Thousands of potential applications (Hill, 2003) . It is an “In situ” sensing technology where tiny, autonomous and compact devices called sensor nodes or motes deployed in a remote area to detect phenomena, collect and process data and transmit sensed information to users via radio frequency (RF) channel.

WSN term can be broadly sensed as devices range from laptops, PDAs or mobile phones to very tiny and simple sensing devices. At present, most available wireless sensor devices are considerably constrained in terms of computational power, memory, efficiency and communication capabilities due to economic and technology reasons. That’s why most of the research on WSNs has concentrated on the design of energy and computationally efficient algorithms and protocols, and the application domain has been confined to simple data-oriented monitoring and reporting applications. WSNs nodes are battery powered which are deployed to perform a specific task for a long period of time, even years.

The basic block diagram of a wireless sensor node is presented in Figure 1. It is made up four basic components: a sensing unit, a processing unit, a transceiver unit and a power unit. A MICAZ mote is shown in Figure 2.

Figure 1.

Architecture of a wireless sensor node

Figure 2.

MICAZ mote

Moog Crossbow, n.d.

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  Sensing Unit: Sensing units are usually composed of two subunits: sensors and analog to digital converters (ADCs). Sensor is a device which is used to translate physical phenomena to electrical signals. The analog signals produced by the sensors based on the observed phenomenon are converted to digital signals by the ADC and then fed into the processing unit.

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  Processing Unit: The processing unit mainly provides intelligence to the sensor node. The processing unit consists of a microprocessor, which is responsible for control of the sensors, execution of communication protocols and signal processing algorithms on the gathered sensor data. For example, the processing unit of a smart dust mote prototype is a 4 MHz Atmel AVR8535 micro-controller with 8 KB instruction flash memory, 512 bytes RAM and 512 bytes EEPROM. TinyOS operating system is used on this processor, which has 3500 bytes OS code space and 4500 bytes available code space.

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  Transceiver Unit: The transceiver unit enables wireless communication with neighbouring sensor nodes and the outside world. It consists of a short range radio which usually has single channel at low data rate and operates at unlicensed bands of 868-870 MHz (Europe), 902-928 MHz (USA) or near 2.4 GHz (global ISM band). The Chipcon’s CC2420 is included in the MICAZ mote that was built to comply with the IEEE 802.15.4 standard (802.15.4, 2006) for low data rate and low cost wireless personal area networks.