Wireless sensor networks
Wireless sensor network (WSN) - a wireless system, which is a distributed, self-organizing and robust to
failures of individual elements of a network whose nodes are special devices - prodigals. WSN - a wireless network, transmission of information in
which is produced from one node to another, until the packet reaches the remote gateway. From the gateway information comes to
parent computer, which performs information processing, or passes it on.
Mote is a dress size is usually not more than one cubic inch. The board placed the processor, memory - flash and operational,
analog and analog-digital converters, radio frequency transceiver, power supply and sensors. Sensors can be very
diverse, and they are connected via both digital and analog connectors. Most widely used temperature sensors, pressure, humidity,
light, vibration, less often - magneto, chemical (eg, measuring the content of CO, CO2), audio, and some others [1]. Set
sensors used depends on the functions performed by wireless sensor networks. Nutrition Mota made from a small battery. Prodigals
used only for collection, primary processing and transmission of sensory data. Appearance Motov produced by various manufacturers,
shown in Fig. 6.1
Figure 6.1 – Mote appearance.
The main functional processing of data collected motami, carried out on the node, or gateway, which is powerful enough
kompyuter.Problema receiving sensory information gathered motami, is solved as follows. Prodigals can share among themselves information
using transceivers operating at radio frequencies. This is, first, sensory information is read from sensors, and secondly, information
on the status of devices and the results of the data. Information is transferred from one Motov other chain, and eventually coming to the Gateway
prodigals throw him the accumulated information. If part of Motov fails, the work of a sensor network after reconfiguration must continue.
But in this case, of course, decreases the number of information sources [2].
The benefits of technology of wireless sensor networks can be effectively used for various applications related to
distributed collection, analysis and transmission of information [3]. Wireless sensor networks - a new promising technology, and all associated
projects are mainly in the development stage. Describe the main areas of application of this technology:
- Defense and security;
- Control environment;
- Monitoring of industrial equipment;
- Security systems;
- Monitoring the status of agricultural land;
- Energy management;
- Control of ventilation, air conditioning and lighting;
- Fire alarm;
- Stock control;
- Monitoring the transport of goods;
- Monitoring the physiological state of man;
- Control staff, etc.
The presented list is extremely small and virtually unlimited. From the rather large number of examples of the use of wireless sensor networks distinguish the two.
Wine industry - occupation, requiring the myriad variety of information. The wine is bought and sold not by weight or volume (as, for example,
cereals or vegetables), and its price depends largely on the location and year of cultivation and harvest. The quality of wine is influenced by many factors, and experienced winemakers
carefully takes into account the tiniest details to achieve the best bouquet of the drink. But if you use a sensor network, we can "sow" the vineyard
wireless sensors and continuously monitor temperature, humidity and other parameters important for the maturation of each vine. A few farms in the valley
Villamet (Oregon), Intel researchers have launched a pilot sensor network. The project is led professional ... psychologist Richard Beckwith (Richard Bechwith),
research using a technology known as "participant observation". He observes, on the one hand, for the experts who gather information
with sensors placed on the plantation, on the other - for the growers themselves, to understand what criteria are important in the field of viticulture for those and others and how
This information is linked together [4].
An example of another of the implemented project is the deployment of sensor network based on the Air Force in Florida, USA. The system demonstrated
good opportunity to recognize the various metal objects, including moving. Application of sensor network allowed to detect the penetration
people and vehicles in a controlled area and track their movements. To solve these problems were used prodigals equipped with magnetoelectric and
temperature sensors. Currently, the project scope expanded, and a wireless sensor network is already installed on the range of 10 000x500 m.
Appropriate application software developed by several American universities [2].
One of the main problems of the WSN is the limited capacity of batteries installed in motah. Replace the battery on motah, in most cases the problem is rather
complicated. That is why to date to reduce energy consumption issues involved large numbers of people. The subjects of works ranges from highly specialized issues
associated with the creation of individual components of network facilities (transceivers, microcontrollers, sensors, etc.) with low cost and low power consumption to the problems
that arise in the operation of sensor networks (issues relating to the organization of the network, software development, etc.) [5]. But the most important
problem is the data. The main problems in this area are:
- Reducing the cycle of reception and transmission of data;
- Finding the best routes data;
- Select the network topology;
- Resistance to change in the topology;
- Etc.
Although there are already a large number of developments, but all these developments is not complete, because they can not apply for any number of tasks.
For each specific task, it is necessary to organize your approach to resheniyu.Imenno why are the present work is to develop a new protocol
will be based on ant algorithms. The main objective for this protocol is the optimal route search data from Motov to the main computer
as well as the possibility of choosing the optimal route in the event that one or more Motov failure.
Protocol СТР
The protocol provides data to one of several possible receivers of data, thereby providing a link to one of many at the network level.
WSN usually constitutes a tree structure rooted at gateways, and leaves - prodigals. CTP uses frames to update the routing and construction
tree network.
At fig.6.2 example tree network. The gateway is the root and other nodes form the set of routes that connect to this root. In the CTP is available
addressing, so the node does not send the packet on a particular root, and implicitly selects the root of the tree, by selecting the recipient's next shipment.
Figure 6.2 – Example collection tree.
Protocol CTP uses 2 aspect ratio: data frame and frame routing. CTP was designed for networks with relatively low traffic, because Bandwidth
channel should be enough to send the frame routing in a time when the transmitted data frames.
CTP uses the expected number of hops (ETX) as the gradient routing. The root has ETX 0. ETX ETX node is a parent plus ETX connection with
parent. Ultimately, PAGES, given the current route, select route with a smaller value of ETX. ETX - appears as a 16-bit decimal floating point
number of fixed-point within a tenth. For example ETX with a value of 45, appears as ETX 4.5, and the ETX with a value of 10 is presented as ETX 1.
Protocol Tymo
Tymo - an implementation of the protocol Dymo in TinyOS [3], which is a routing protocol for mobile ad-hoc networks. First, the protocol was developed
to find routes over IP level. Since the protocol Dymo, a reactive protocol, then he obviously does not keep the network topology. If necessary, send
data node establishes a route to the destination. Due to a small exchange of information on routing, reduced network traffic, which saves bandwidth
bandwidth. Due to the small volumes of stored information about routing, Dymo easily built in limited mote memory .
When a node is necessary to obtain a route, it distributes Route Request (RREQ) - Package zaporashivayuschy route between the sender and receiver. This package
distributed throughout the network or within a certain number of neighboring nodes. When a packet reaches the target (or host has a new route to the goal), the node sends
Route Replay (RREP). This response is very similar to Route Request, the only difference being that the package has a unicast route and does not require a response.
When nodes receive a RREQ or RREP, they remain in the cache of information about the sender, so they know the path to the source of the package, which can be
used later (if the path is not out of date), without sending RREQ. Nodes are able to accumulate the path followed by the package in the package itself. So
manner when the nodes send RREQ or RREP in response package can get information more than the path between two nodes.
When the routes are not used for a long time, they are removed. If the site will ask to send a package through a remote route is generated Route
Error (RERR) message to notify the sender node (and other sites) that the requested route is no longer available. As another mechanism
service route, Dymo uses serial numbers and counters transitions to determine the usefulness and quality of the route.
Review of systems modeling WSN
Each network requires a different approach to development. That is why the development of sensor networks and software to its great importance to have a system
simulation. Modeling systems allow you to develop hardware and software for Motov at much lower cost than in the case
use of real devices. So they allow various different parameters, that provides the information necessary to decide
advantage of those or other parameters in a given situation. Even more useful fall simulation system for developing and testing protocols
data.
At the current time there are a large number of systems modeling as specialized (TOSSIM, SWAN, Em *, GloMoSim, etc.) and general-purpose
(NS2, OMNet + +, etc.).
TOSSIM - a simulator applications TinyOS. It is a library of TinyOS. Tossim - simulation of discrete events. Event reports on data from the sensor,
on the timer, the packet data or the completion of the calculations. It follows that TOSSIM - emulates the event for wireless sensor systems
which prodigals are running TinyOS.
TOSSIM is installed on your computer along with a set of tools needed to create, compile, install and debug applications for wireless
sensor networks. Working with data tools via the command line.
The main advantage of TOSSIM is that the emulator allows you to simulate the applications that are written for real Motov. Compiler TOSSIM `and replaces
Several low-level application components that interact with the real hardware resources Mota, components that interact with the program
implementations of these devices in the emulator.
TOSSIM converts interrupt the computer in the event emulator and arranges them in turn, this turn of events emulator controls the execution of an application for TinyOS
separate simulated Mota. Event occurs causing an interrupt handler, which sends signals to the events and calls the team TinyOS, imitating what
happens in real motah. These events and the team run TinyOS tasks and initiate the generation of further events emulator.
Another of the well-known simulation environment - is the environment AnyLogic. Wednesday AnyLogic allows the use of different paradigms of simulation (continuous and
discrete event simulation, multi-agent approach), and combine them. Important advantages of the system are:
- Object-oriented approach to modeling;
- Visual development environment with rich functionality;
- The possibility of using the language Java.
The system AnyLogic introduced the concept of active object (AO) - extension of the classical objects, which are used in object-oriented languages
programming. In AnyLogic active object may also include other elements.
If the standard means AnyLogic not enough to build a model (or their use inconvenient), there is the possibility of using the language Java. In the simplest case,
this amounts to a description of actions committed during the transition to another state, triggering a timer or a message arrives. In addition, you can add your own
Java code to the active object, and use third-party libraries. This makes the system easily expandable AnyLogic [6].
NS2 - known simulator networks open source. This is a system of discrete event simulation network. NS is widely used for modeling protocols and
research networks. The system supports a number of popular network protocols. Allows you to create models of wired and wireless networks. This system
allows implementation of virtually any model due to the possibility finish simulator. [9]
Based on the foregoing, we can conclude that at present there are a large number of tools for modeling the FSU. All have their pluses and minuses. For
task are the most acceptable simulator TOSSIM. This option is selected for the following reasons:
- Simulator designed specifically for FSU;
- Emuliruer that applications written for real Motov;
- Free distribution;
- Allows you to emulate the work of the FSU running TinyOS, which is the standard for faketicheski.
Review of methods of interaction sites WSN
To provide for interaction sites FSE can use a sufficiently large number of methods, such as:
- Probability theory;
- Computational Mathematics;
- The theory of stochastic processes;
- Optimization algorithms, etc.
Consider several existing methods.
The method of collective data. The essence of the method is as follows. Once the network connectivity drops sharply as a result of failure of nodes around
the base station, the remaining nodes are combined into clusters and transmit the information gathered collectively, using the principle of coherent information transfer. This
significantly increases the distance that can transmit nodes and, thus, can be expected to improve connectivity and extend the lifetime. Under time
Life Network is the period of time before the fall of connections below a certain threshold [10].
Algorithm for multi-hop data transmission. The essence of the algorithm lies in the fact that sending messages from one network to another point along the chain of intermediate nodes instead of
Direct long-distance transmission. To synchronize the nodes are encouraged to use the recurrent wave propagation service messages, outgoing
from the center of the network, in addition to the converging wave data. Oncoming waves must be separated in time to prevent crossings. Optimal
is the mode when the control wave is emitted by the base station immediately after the arrival of the wave with the data, because doing so maximizes your width
network. The minimum allowable distance between the waves depends on the width of the network and the time of passage through the waves one level. [11]
The method of determining the coordinates in the FSU. The method is to find the geographic location of objects a wireless network, which in turn simplifies
formation in the standard ZigBee, routing tables. To implement this method used methods Kolmanovskii filtering and methods of the theory of stochastic
processes.
Ant algorithms. These algorithms are widely known. This method gives good results in solving optimization problems of large sizes. Enough
worked well for the calculation of telecommunication and computer networks. Currently, good results for solving such complex problems,
as the traveling salesman problem, graph coloring, optimization problem of network traffic, etc. [12]
Ant algorithms
The idea of ant algorithm - modeling of the behavior of ants associated with their ability to quickly find the shortest path from the nest to a food source and
adapt to changing conditions, finding a new shortest route.
1. The first ant finds a food source (F) in any way (a), and then returns to the nest (N), leaving behind a trail of pheromones (b).
2. Then the ants choose one of four possible ways, and then strengthen it and make it attractive.
3. The ants choose the shortest route, because the longer stronger pheromones have evaporated.
Described above is presented in Fig. 6.3.
Figure 6.3 – Example of finding the shortest route ants.(Animation: volume – 29,5 KB; size –
114x279; number of shots – 7; delay between shots – 1000 ms; delay between first and lst shots – 2000 ms; number of repetition cycles – 6).
Among the experiments on the choice between two paths of unequal length, leading from the colony to a power source, biologists noticed that, as a rule, the ants use
shortest route. [6] [10] model of this behavior is as follows:
* Ant (so-called "Blitz") is random from the colony.
* If it finds a food source, then returns to the nest, leaving behind a trail of pheromone.
* These pheromones attract other ants near most likely to go this route.
* Returning to the nest they will strengthen the pheromone trail.
* If there are 2 routes, then by a shorter, for the same time, would get more ants than the long.
* The short route will become more attractive.
* Long road, eventually disappear due to evaporation of pheromones.
Step in the solution using ant algorithms
In order to construct a suitable ant algorithm for solving any problem, you need:
1. submit the task as a set of components and conversions, or a set of undirected weighted graphs, where the ants can build solutions;
2. determine the value of pheromone trail;
3. heuristics to determine the behavior of ants, when building a solution;
4. if possible, to implement an effective local search;
5. select a specific ACO algorithm and apply for solving the problem;
6. nastroit option ACO algorithm.
Also, are the determining factor:
- The number of ants;
- Balance between the study and use;
- A combination of greedy heuristics or local search;
- The moment when the pheromone is updated.
It is expected that further implementation of the algorithm described above will create a new data transfer protocol in wireless sensor networks, which enables
find the shortest routes package, with an optimal distribution of information flows across the network.
