Mobile Computing Assignment
APPLICATION OF WIRELESS SENSOR NETWORKS
FOR
ENVIRONMENTAL MONITORING AND DEVELOPMENT OF AN ENERGY EFFICIENT CLUSTER BASED ROUTING
Wireless Sensor Networks (WSNs) have attracted the attention of many researchers.
Wireless Sensor Networks (WSNs) are used for various applications such as habitat monitoring, automation, agriculture, and security. Since numerous sensors are usually deployed on remote and inaccessible places, the deployment and maintenance should be easy and scalable. Wireless sensor network consists of large number of small nodes. The nodes then sense environmental changes and report them to other nodes over flexible network architecture. Sensor nodes are great for deployment in hostile environments or over large geographical areas.
Advances in wireless networking, micro-fabrication and integration (for examples, sensors and actuators manufactured using micro-electromechanical system technology, or MEMS), and embedded microprocessors have enabled a new generation of massive-scale sensor networks suitable for a range of commercial and military applications.
These nodes are having different node identification & they will sense the temperature & light of there surrounding location and send it to the base station node which is connected through USB port to the computer by the use of MoteView & MoteConfig environment. The data acquisition board that we have used is MDA100CB (Mote Data Acquisition). The programming of the sensor nodes is done by MoteConfig & live data is viewed through MoteView environment. The nodes that we have used are MicaZ; the MDA100CB board is fixed over these nodes by means of 51 Input/output pins.
We introduce a set of cluster heads, head-set, for cluster-based routing. The head-set members are responsible for control and management of the network. On rotation basis, a head-set member receives data from the neighboring nodes and transmits the aggregated results to the distant base station.
In a typical sensor network, each sensor node operates un-tethered and has a microprocessor and a small amount of memory for signal processing and task scheduling. Each node is equipped with one or more sensing devices such as acoustic microphone arrays, video or still cameras, infrared (IR), seismic, or magnetic sensors. Each sensor node communicates wirelessly with a few other local nodes within its radio communication range.
The Information collected by and transmitted on a sensor network describes conditions of physical environments for example, temperature, humidity, or vibration and requires advanced query interfaces and search engines to effectively support user-level functions. Sensor networks may inter-network with an IP core network via a number of gateways. A gateway routes user queries or commands to appropriate nodes in a sensor network. It also routes sensor data, at times aggregated and summarized, to users who have requested it or are expected to utilize the information. A data repository or storage service may be present at the gateway, in addition to data logging at each sensor. The repository may serve as an intermediary between users and sensors.
They involve deploying a large number of small nodes. The nodes then sense environmental changes and report them to other nodes over flexible network architecture. The sensor nodes leverage the strength of collaborative efforts to provide higher quality sensing in time and space as compared to traditional stationary sensors, which are deployed in the following two ways:
§ Sensors can be positioned far from the actual phenomenon, i.e. something known by sense perception. In this approach, large sensors that use some complex techniques to distinguish the targets from environmental noise are required.
§ Several sensors that perform only sensing can be deployed. The position of the sensors and communications topology is carefully engineered. They transmit time series of the sensed phenomenon to central nodes where computations are performed and data are fused.
A wireless sensor network is a collection of nodes organized into a cooperative network.
The difference between wireless sensor networks and ad-hoc networks are outlined below:
§ The number of sensor nodes in a sensor network can be several orders of magnitude higher than the nodes in an ad hoc network.
§ Sensor nodes are densely deployed.
§ Sensor nodes are prone to failures.
§ The topology of a sensor network changes very frequently.
§ Sensor nodes mainly use broadcast communication paradigm whereas most ad hoc networks are based on point-to-point communication.
§ Sensor nodes are limited in power, computational capacities, and memory.
§ Sensor nodes may not have global identification (ID) because of the large amount of overheads and large number of sensors.
§ Sensor networks are deployed with a specific sensing application in mind whereas ad-hoc networks are mostly constructed for communication purpose.
To summarize, the challenges we face in designing sensor network systems and applications include:-
1. Limited hardware: Each node has limited processing, storage, and communication capabilities, and limited energy supply and bandwidth.
2. Limited support for networking: The network is peer-to-peer, with a mesh topology and dynamic, mobile, and unreliable connectivity. There are no universal routing protocols or central registry services.
3. Limited support for software development: The tasks are typically real-time and massively distributed, involve dynamic collaboration among nodes, and must handle multiple competing events. Global properties can be specified only via local instructions. Because of the coupling between applications and system layers, the software architecture must be co-designed with the information processing architecture.
Installation
Supported Platforms
MoteConfig is supported on the following operating systems:
Windows XP Home
Window XP Professional
Windows 2000 with SP4
Installing MoteView on a Windows PC
Before you can use MoteView you have to install it on a PC. The requirements necessary to properly install MoteView are below:
1. A PC with one of the following operating systems
Windows XP Home/Professional
Windows 2000 with SP4
2. An NTFS file system.
3. Screen resolution must be at least 800 × 600 or the interface will require scrollbars.
4. Administrative privileges to write to Windows registry.
5. Prior to installing MoteView, it is highly recommended that you shut down all the programs running on your computer.
MoteView Overview
MoteView is designed to be an interface between a user and a deployed network of wireless sensors. MoteView provides the tools to simplify deployment and monitoring. It also makes it easy to connect to a database, to analyze, and to graph sensor readings.
The hardware features of the Mote Processor Radio (MPR) platforms and Mote Interface Boards (MIB) for network base stations and programming interfaces. It is intended for understanding and leveraging Crossbows Smart Dust hardware design in real-world sensor network, smart RFID, and ubiquitous computing applications.
MPR2400 (MICAz)
Product Summary
The MICAz is the latest generation of Motes from Crossbow Technology. The MPR2400 (2400 MHz to 2483.5 MHz band) uses the Chipcon CC2420, IEEE 802.15.4 compliant, ZigBee ready radio frequency transceiver integrated with an Atmega128L microcontroller.
The same MICA family, 51 pin I/O connector, and serial flash memory is used; all application software and sensor boards are compatible with the MPR2400.
Photo of the MPR2400MICAz with standard antenna
Block Diagram and Schematics for the MPR2400 / MICAz
51-pin Expansion Connector
Thermistor
The thermistor, sensor is a highly accurate and highly stable sensor element. With proper calibration, an accuracy of 0.2 °C can be achieved. The thermistor's resistance varies with temperature. The resistance vs. temperature graph is non-linear. The sensor is connected to the analog-digital converter channel number 1 (ADC1) thru a basic resistor divider circuit.
MIB520 USB Interface Board
The MIB520 provides USB connectivity to the IRIS and MICA family of Motes for communication and in-system programming. It supplies power to the devices through USB bus. MIB520CB has a male connector while MIB520CA has female connector.
Photo of top view of an MIB520CA
ISP (In System Processor)
The MIB520 has an on-board in-system processor (ISP) an Atmega16L located at U14 to program the Motes. Code is downloaded to the ISP through the USB port. Next the ISP programs the code into the Mote.
Mote Programming Using the MIB520
Programming the Motes requires having MoteWorks/TinyOS installed in your host PC. The IRIS, MICAz and MICA2 Motes connect to the MIB520 for UISP programming from USB connected host PC.
States of a sensor node
The damaged or malfunctioning sensor states are not considered. Each sensor node joins the network as a candidate. At the start of each iteration, a fixed number of sensor nodes are chosen as cluster heads; these chosen cluster heads acquire the active state. By the end of election phase, a few nodes are selected as members of the head-sets; these nodes acquire associate state. At the end of an election phase, one member of a head-set is in active state and the remaining head-set members are in associate state.
In an epoch of a data transfer stage, the active sensor node transmits a frame to the base station and goes into the passive associate state. Moreover, the associate, which is the next in the schedule to transmit to the base station, acquires the active state. During an epoch, the head-set members are distributed as follows: one member is in active state, a few members are in associate state, and a few members are in passive associate state.
During the transmission of the last frame of an epoch, one member is active and the remaining members are passive associates; there is no member in an associate state. Then, at the start of the next epoch, all the head-set members become associate and one of them is chosen to acquire the active state. At the end of an iteration, all the head-set members acquire the non-candidate state. The members in non-candidate state are not eligible to become a member of an head-set. At the start of a new round, all non-candidate sensor nodes acquire candidate state; a new round starts when all the nodes acquire non-candidate state.
Election Phase
In the proposed model, the number of clusters, k, are pre-determined for the wireless sensor network. At the start, a set of cluster heads are chosen on random basis. These cluster heads send a short range advertisement broadcast message. The sensor nodes receive the advertisements and choose their cluster heads based on the signal strengths of the advertisement messages. Each sensor node sends an acknowledgment message to its cluster head. Moreover, for each iteration, the cluster heads choose a set of associates based on the signal analysis of the acknowledgments.
A head-set consists of a cluster head and the associates. The head-set, which is responsible to send messages to the base station, is chosen for one iteration of a round. In an epoch of an iteration, each member of the headset becomes a cluster head. All the head-set members share the same time slot to transmit their frames. Based on uniform rotation, a schedule is created for the head-set members for their frame transmissions; only the active cluster head transmits a frame to the base station. Moreover, a schedule is created for the data acquisition and data transfer time intervals for the sensor nodes that are not members of the head-set.
Data Transfer Phase
Once clusters, head-sets, and TDMA-based schedules are formed, data transmission begins. The non-cluster head nodes collect the sensor data and transmit the data to the cluster head, in their allotted timer slots. The cluster-head node must keep its radio turned on to receive the data from the nodes in the cluster. The associate members of the head-set remain in the sleep mode and do not receive any messages. After, some pre-determined time interval, the next associate becomes a cluster head and the current cluster head becomes a passive head-set member. At the end of an epoch, all the head-set members have become a cluster head for once. There can be several epochs in iteration. At the end of an iteration, the head-set members become non-candidate members and a new head-set is chosen for the next iteration. Finally, at the end of a round, all the nodes have become non-candidate members.
Quantitative Analysis
In this section, we describe a radio communication model that is used in the quantitative analysis of our protocol. The energy dissipation, number of frames, time for message transfer, and the optimum number of clusters are analytically determined.
Radio Communication Model
We use a radio model, where for a shorter distance transmission, such as within clusters, the energy consumed by a transmit amplifier is proportional to r2. However, for a longer distance transmission, such as from a cluster head to the base station, the energy consumed is proportional to r4. Using the given radio model, the energy consumed to transmit an l-bit message for a longer distance, d, is given by:
ET = lEe + lel d 4 (5.1)
Similarly, the energy consumed to transmit an l-bit message for a shorter distance is given by:
ET = lEe + le sd 2 (5.2)
Moreover, the energy consumed to receive the l-bit message is given by:
ER = lEe + lEBF (5.3)
Equation 5.3 includes the cost of beam forming approach that reduces energy consumption. The constants used in the radio model are given in Table.
Sample parameter values of the radio communication model used in our quantitative analysis.
Election Phase
For a sensor network of n nodes, the optimal number of clusters is given as k. All nodes are assumed to be at the same energy level at the beginning. The amount of consumed energy is same for all the clusters. At the start of the election phase, the base station randomly selects a given number of cluster heads. First, the cluster heads broadcast messages to all the sensors in their neighborhood. Second, the sensors receive messages from one or more cluster heads and choose their cluster head using the received signal strength. Third, the sensors transmit their decision to their corresponding cluster heads. Fourth, the cluster heads receive messages from their sensor nodes and remember their corresponding nodes. For each cluster, the corresponding cluster head chooses a set of m associates, based on signal analysis. For uniformly distributed clusters, each cluster contains n/k nodes. Using Equation 5.2 and Equation 5.3, the energy consumed by a cluster head is estimated as follows: 
The first part of Equation represents the energy consumed to transmit the advertisement message; this energy consumption is based on a shorter distance energy dissipation model. The second part of Equation 5.4 represents the energy consumed to receive 
messages from the sensor nodes of the same cluster.
FUNDAMENTALS OF CLUSTER BASED ROUTING
Using the equation, the energy consumed by non-cluster head
sensor nodes is estimated as follows:
The first part of Equation 5.5 shows the energy consumed to receive messages from k cluster heads; it is assumed that a sensor node receives messages from all the cluster heads. The second part of Equation 5.5 shows the energy consumed to transmit the decision to the corresponding cluster head.
Data Transfer Phase
During data transfer phase, the nodes transmit messages to their cluster head and cluster heads transmit an aggregated messages to a distant base station. The energy consumed by a cluster head is as follows: 
The first part of Equation shows the energy consumed to transmit a message to the distant base station. The second part of Equation 5.6 shows the energy consumed to receive messages from the remaining nodes that are not part of the head-set.
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