This question appears in Mumbai University > Wireless Networks subject

Marks: 5 & 10 M

Year: May 2014, Dec 2014

1. Replacement of Wired sensor networks

i. Wired sensor networks include gauges measuring temperature, fluid levels, humidity, and other attributes on pipelines, pumps, generators, and manufacturing lines.

ii. Many of these run as separately wired networks, sometimes linked to a computer but often to a control panel that flashes lights or sounds an alarm when a temperature rises too high or a machine vibrates too much.

iii. Also wired in are actuators, which let the control panel slow down a pump or start a fan in response to the sensor data.

iv. With advances in silicon radio chips, cleverly designed routing algorithms and network software; wireless sensor networks are in use.

v. Wireless sensor networks eliminate wires and their installation and maintenance costs.

vi. Wireless sensor networks can use several different wireless technologies, including IEEE 802.11 WLANs, Bluetooth, and radio frequency identification (RFID).

vii. However, most of the applications use low-power radios having a range of about 30 to 200 feet and data rates of up to around 300 kbps.

2. Sensor nodes

i. A wireless sensor network contains a large number of tiny sensor nodesthat are densely deployed either inside the phenomenon to be sensed or very close to it.

ii. Sensor nodes consist of sensing, data processing, and communicating components.

iii. The position of sensor nodes need not be engineered or predetermined.

iv. This allows random deployment in inaccessible terrain or disaster relief operations.

v. Thus the sensor network protocols and algorithms must possess self-organizing capabilities.

vi. Another unique feature of sensor networks is the cooperative effort of sensor nodes. Sensor nodes are fitted with an inboard processor. Instead of sending the raw data to the nodes responsible for the fusion, they use their processing abilities to locally carry out simple computations and transmit only required and partially processed data.

3. Wireless ad-hoc network

i. Wireless sensor network applications require wireless ad hoc networking techniques.

ii. However, there are many differences between wireless sensor network and wireless ad hoc networks.

iii. The number of sensor nodes in a wireless sensor network can be several orders of magnitude higher than the nodes in a wireless ad hoc network.

iv. In a wireless sensor network, sensor nodes are densely deployed.

v. Sensor nodes are prone to failure.

vi. The topology of a wireless sensor network changes very frequently.

vii. Sensor nodes mainly use broadcast communication paradigms whereas most traditional ad hoc networks are based on point-to-point communications.

viii. Sensor nodes are limited in power, computational capabilities, and memory.

ix. Sensor nodes may not have global identification because of the large amount of overhead and large number of sensors.

x. Another factor that distinguishes wireless sensor networks from traditional mobile ad hoc networks (MANETs) is that the end goal is the detection/estimation of some event(s) of interest, and not just communication.

xi. To improve detection performance, it is often quite useful to fuse data from multiple sensors. Data fusion requires the transmission of data and control messages. This need may impose constraints on network architecture.

xii. The large number of sensing nodes may congest the network with information. To solve this problem, some sensors, such as cluster heads, can aggregate the data, perform some computation (e.g., average, summation, highest value, etc.), and then broadcast the summarized new information.

4. Low power consumption

i. Since large numbers of sensor nodes are densely deployed, neighbour nodes may be very close to each other. Hence, multihop communication in wireless sensor networks is expected to consume less power than traditional single hop communication.

ii. Furthermore, the transmission power level can be kept low, which is highly desirable in covert operations. Multihop communication can effectively overcome some of the signal propagation effects experienced in long-distance wireless communication.

iii. One of the most important constraints on sensor nodes is the low power consumption requirement.

iv. Sensor nodes carry limited, generally irreplaceable power sources.

v. Therefore, while traditional networks aim to achieve high quality of service (QoS) provisions, wireless sensor network protocols must focus primarily on power conservation.

vi. They must have built-in trade-off mechanisms that give the end-user the option of prolonging network lifetime at the cost of lower throughput or higher transmission delay.