Sensor Network for Better, Efficient and Automated (BEA) Farming

Diagram representing overall architecture for BEA farming

Wireless sensor networks have wide variety of applications . I would like to brief on how WSN can be used for better,efficient and automated farming. I and my friends got this idea during a casual discussion. So this articles belongs to them also. [:)].

Sensor network can be used in agriculture to monitor, the moisture content in soil , the fertility of soil, the surrounding weather conditions of the farm. Various sensor nodes can be deployed in the farm which have the capability to monitor the moisture,fertility and temperature. These sensor nodes can in turn give data to a gateway or a farmers mobile. Mobile is one of the very common devices it can act as gateway to collect data from all the senors nodes deployed in the farm. The data can be obtained whenever the farmer goes to his farm along with his mobile or there can be gateway, which aggregates the data from all the senor nodes in the farm, and sends it to the farmers mobile.

Once the data is available at the farmer's mobile he can send this data to experts or his friends or use this data himself to get any advice on farming if necessary. The data obtained on moisture level can be used to water the whole farm appropriately , such that none of the part of the farm will be over watered neither will less watered. Actuators can be used to take appropriate decisions based on sensor readings . There can be server to which all farmers can connect using their mobile and get necessary data. The server can also be used to store the data provided by the farmers. In this way all the agriculture lands can be connected , the data provided by all farmers can be used for various research purposes like to check what fertilizer level and moisture level has resulted in best yield. The data collected from many farmers at a place will help in building a detailed picture of farming at that respective place.

The shared server can also be used to share information such as , crops that can be grown on particular type of soil, best agriculture practices , present price for a particular type of crop etc. These information can be sent to farmers mobile so that farmers are updated with latest happenings.

The sensor nodes can be connected to the gateway or mobile using 802.15.4 (Low rate Wireless Personal Area network ) and the mobile and server can be connected using Internet or using other mobile communication system such as GSM or CDMA. The common sensors that can be used are soil moisture sensor, soil nutrients sensor , temperature sensor and rain sensors.

The diagram below makes the explanation given above more clearer.

The diagram given above is taken from the link given below.

http://www.ubicomp.in/uagri/

Design Issues in WSN

Wireless sensor networks are made of large number of tiny sensor nodes, which have limited power and less processing capability. The life time of the individual sensor node is not easily predictable and also the network needs to be formed autonomously as it is not possible to manually set up the sensor network for all applications. The sensor network also consists of several different kind of nodes hence heterogeneity needs to be supported. The number of sensor nodes in the network is not constant through out the life time of the network it may vary because of addition of senor nodes or reduction of nodes due to their death . The major factors that need to considered while designing sensor network are listed below.

Fault Tolerance: Possibility of node failure and change of topology of network is quite high in case of WSN. Hence the designer of network should make the network robust and reliable even in case of node failures and topology changes. The network should function smoothly and normally irrespective of node failures and topology changes.

Life Time: WSN are supposed to work for a quite long time with low power consumption. They are supposed to last at-least for 6 months to 1 year. We need to keep in mind that every node in WSN may be powered using just a 3 V battery and this should be sufficient for the entire life time of the node . The design of protocols of WSN should be such that the node consumes as less energy as possible. This will help in making the WSN last longer.

Scalability: The design of WSN should support addition of new nodes any time and also the design should support large number of nodes because some applications in WSN may require quite a huge number of sensor nodes.

Date Aggregation: The sensor nodes in WSN are located close to each other hence the possibility of similar data being generated by the nodes next to each other is quite high. So the data needs to be aggregated and the duplicate data needs to be avoided because the transmission and reception data is the most costly affair in WSN.The data needs to be aggregated at different levels in WSN so that only the necessary data is transmitted and recevied and the redundant data is not communicated.

Cost: The cost of each sensor node is supposed to be 1$ , as WSN can have large number of sensor nodes the total cost of the network can become a quite expensive affair. So the designer of WSN needs to decide on the optimal number of nodes necessary for the application.

Environment: The environment in which the WSN is deployed can be very demanding , so the design of WSN should be such that WSN should be able to survive regardless of the conditions in which WSN s deployed.

Heterogeneity Support: The protocols designed for WSN should support different kinds of sensor nodes and also be able to support variety of applications.

Autonomous Operations: The WSN should be able to organize , reorganize and operate autonomously because sometimes WSN deployed in places where human habitation is not possible.

Limited Memory and Processing Capability : The sensor nodes have very limited memory, power and processing capabilities , so all designs of WSN should not be demanding in terms of processing requirements or memory requirements .

Applications of Sensor Networks

Wireless Sensor Networks are used to build wide variety of applications . The apps range from agriculture apps to defense apps. All applications involve many sensor nodes, which collect data from the deployed site and this collected data is used for some specific purpose. I will give some examples of applications which are built using sensor networks.

• Military or Defense Applications
• Agriculture Applications
• Environment and Weather Monitoring Applications
• Habitat Monitoring Applications
• Applications for Home Automation
• Applications for Industries
• Traffic Surveillance and Road Monitoring Applications
• Applications for Health Monitoring , which is very broad area called as Body Area Network
• Pollution Monitoring Applications
• Applications to predict Natural Calamities
• Applications for Surveillance and Intrusion Prevention
• Structure Monitoring Applications like bridge monitoring apps

Addressing in WSN

Several approaches have been proposed for addressing in WSN(Wireless Sensor Network) . I will brief about some approaches which I have read.

"Lease based addressing for event driven wireless sensor networks" proposes to use a network level unique address to use a node temporarily. Three phases are proposed by this paper, they are boot up phase , address request phase and address release phase. Initially when the node boots up, it assigns itself a link local address and waits for the broadcast message from sink. Once the node receives the broadcast message from sink it send address request message to sink. The sink maintains a table of address assigned and table of address unassigned. If the sink has any unassigned address then the sink assigns an unique address to the requesting node. The node utilizes this address for required duration and then releases the address , the node uses release address message for this purpose.

"Distributed address assignment" specified in ZigBee standard provides a method to distribute addresses available at the coordinator among all nodes. It gives a mathematical formula, which is utilized to distibute address among the nodes. The coordinator distributes the available addresses to its immediate children, every router child is given equal number of addresses and non router child is given a single address. Every router node in turn assigns available addresses to its children (differentiating between router child and non router child). This method may not be very relevant if the network does not grow uniformly .

"A novel approach for dynamic address assignment in wireless sensor networks" proposes to use only a part of available addresses for initial distribution . This initial distribution is done as specified in ZigBee. Later if any other node requires more addresses then it requests for more addresses from its parent, which is allocated if the parent has required number of addresses else the request is relayed till the initial server. Th parent also may ask some of its children to return unused addresses if the parent is in need of addresses. This method is applicable even if the network grows non uniformly.

"Dynamic Address Allocation for Management and Control in WSN" proposes a novel method. The address server sends a broadcasts message once the network starts up and in turn all nodes select an address dynamically(randomly selected) and send the selected address to the server. The server checks if the address is already in use and if so the server asks the respective node (which ever is newer) to select another address using redo message. If the address is unique then the node is confirmed about the address using assign message. This process continues until the node gets an unique address.

"An energy efficient node address naming scheme for WSN" provides procedures for cluster based sensor networks. Along with the above specified methods there are several other approaches for addressing in WSN, one can refer to the references in the above papers for information on other approaches.

Save Energy - The Buzz Word in Sensor Network

WSN(Wireless Sensor Network)applications use sensor nodes which are mostly powered using a 3 V battery.Sensor networks are supposed to last at least for six months ,hence the available energy needs to be used very prudently. This is similar to usage of available financial sources during recession,every penny needs to be spent after much thought. Lot of research has been done and is being done in the field of optimal usage of energy in sensor networks.

I will be briefing about some of these energy saving methods in WSN. All different procedures and methods given here are from papers or patents which I have come across.

Dynamic Power Management(DPM) specifies five modes of operations for each sensor node.Each mode consumes different amount of power. The mode of operation of sensor node varies from being fully active to deep sleep state. Maximum energy is consumed in fully active state and least is consumed in deep sleep state. A method called as Dynamic Voltage Scaling (DVS) is also proposed , the operating frequency and operating voltage is varied according to the sensor node's mode. The components in sensor node such as transceiver , processor, sensors are dynamically switched off or put to sleep in different modes. By these dynamic changes in the sensor nodes energy conservation achieved in the sensor nodes. The table below summarizes the different sates of the sensor node.

State Processor Memory Sensor Radio
S0 Active Active On Tx, Rx
S1 Idle Sleep On Rx
S2 Sleep Sleep On Rx
S3 Sleep Sleep On Off
S4 Sleep Sleep Off Off

After DPM lets see how a protocol called "LEACH" to uses energy optimally. LEACH is one of the well known protocol in WSN. In this protocol data aggregation is done at Cluster heads before further forwarding data , this in turn reduces the amount of data being transferred and saves lot of energy, which would be otherwise consumed for transmission and reception of the un-aggregated data. In WSN data transmission or data reception is the most energy consuming activity compared any other activity so data aggregation at various levels helps in conservation of energy. LEACH also saves energy by making all nodes(other than cluster head) go to sleep when they do not having anything to communicate. All nodes are allocated different time slots to communicate by the cluster head hence the nodes are awake only during their time slot. The figure below shows Cluster Heads, normal nodes and Sink in LEACH protocol.



In paper titled "Power Efficient Organization of Wireless Sensor Network" authors try to use only the optimal number of sensor nodes from all available sensor nodes to cover a given area. By this unnecessary sensor nodes are made to sleep and unnecessary redundant data is avoided and also one can rotate between sleeping and active sensor nodes.

In paper tilted " Power efficient Topologies for Wireless Sensor Networks" authors propose a method to find a sensor network topology which consumes least power to cover given area, in other words the sensor nodes are placed such that they cover the given area by utilizing minimum number of sensor nodes.

There are some more protocols such as S-MAC, STEM, SMACS which try use to available energy in best possible way , if interested one can find them in Google. As I told earlier the efficient usage of energy in one of the most important and one of most researched topics in Wireless Sensor Network, hence one can find many articles, papers and patents on the same.

Wireless Sensor Networks - A New Network Paradigm

Welcome to the world of sensor networks , where small is big and unity is strength. In this fascinating domain of sensors one needs to think at micro level rather than at the macro. The designer of this network needs to think one hundred times before he decides to introduce communication of few bytes of data. Even a three volt battery is considered to be considerably huge source of energy to a sensor node., and the sensor node itself is as big as a dollar. Wireless sensor network collects data utilizing a group of tiny sensor nodes and here the data as a whole is more important than the individual sensor node collecting the . Hence it is appropriate to say that "In sensor network small is big and unity is strength ".

Wireless sensor network consists of a group of tiny sensor nodes, distributed in a wide geographic area, forming an ad-hoc network, collecting and conveying information regarding the area under surveillance. The data collected by these sensor nodes is aggregated and analyzed at a more capable node called as sink or gateway or base station. Wireless sensor network combine simple wireless communication,minimal computation facilities and some sort of sensing of the physical environment and this leads to a new paradigm of networks that can be deeply embedded in our physical environment,fueled by the low cost and wireless communication facilities.

Wireless sensor networks have many wide variety of applications . Some of the examples being

• Military Applications : In battlefield sensor network can be used to monitor enemy movements, to monitor various defense equipments. to detect biological and chemical attacks and to evaluate damage caused by the war.


• Environmental Applications : Sensor networks can be used, to monitor habitats, to monitor forest fire, to monitor the pollution caused, to monitor weather conditions etc...


• Traffic Surveillance: WSN can be used to monitor traffic on land or water or in air.


• Industrial Applications: WSN can be used to monitor equipments, processes, conditions inside a factory and also can be used to detect leakage of gas/chemicals etc..


• Home Applications: The applications at home that can be built using WSN range form home automation to intruder detection.


• Health Applications: Another branch called Body Area Networks is carved specifically to concentrate on health applications using senor network.


• Precision Agriculture: Examples for this include monitoring of fertility and humidity in soil using sensor network.

Each wireless sensor network needs to be designed according to the applications for which it will be used. The number of nodes present in the network, the redundancy required, the precision necessary, the periodicity of collection of data all depends on the application to which the sensor network is used.Wireless sensor networks are self organizing, autonomous, fault tolerant,scalable, long lasting and are able to survive with less energy consumption and are generally low cost.

A typical sensor node in a WSN is made up of, a micro controller such as MSP430FG4618 which is specially designed for low power consumption , a transceiver such as CC2420 which works in ISM band, sufficient memory,power supply and sensors such as temperature sensor, photo sensor ,IR sensor .

If we see from software perspective then a sensor node has necessary drivers, a tiny operating system such as TinyOS, MAC layer modules such as 802.15.4 or S-MAC or STEM , Network Layer modules such as Zigbee Specification or LEACH or gossiping or SPIN , Security modules for data confidentiality, authentication , data integrity and Applications such as data aggregation apps, in node processing apps, senor collaboration module .

Sensor network was considered among top ten technologies in the world. Sensor network is also one of researched topic in many leading universities and companies. Research mainly concentrates on reducing power consumption, lighter protocols, self organization , autonomous operation , lighter OS. Time is not far when many of our day today applications will be built and powered using sensor networks.

Note: I have refered several books, articles , IEEE papers to write all the artciles on sensor networks . I have tried to explain my understanding of sensor networks through these articles in my blog. In some cases I have used the orginal author's examples and diagrams. I am thankful to all the orginal authors.