Architecture of a typical wireless sensor network
Wireless sensor network is a distributed, self-organizing network of many sensors (sensors) and actuators interconnected via a radio channel. Moreover, the coverage area of such a network can range from several meters to several kilometers due to the ability to relay messages from one element to another.
One of the first prototypes of a sensor network can be considered the SOSUS system, designed to detect and identify submarines. Wireless sensor network technologies began to actively develop relatively recently - in the mid-90s. However, only at the beginning of the 21st century the development of microelectronics made it possible to produce sufficiently cheap materials for such devices. element base. Modern wireless networks are mainly based on the ZigBee standard. A considerable number of industries and market segments (manufacturing, various types of transport, life support, security) are ready for the implementation of sensor networks, and this number is constantly increasing. The trend is due to the increasing complexity of technological processes, the development of production, and the expanding needs of individuals in the segments of security, resource control and use of inventory. With the development of semiconductor technologies, new practical tasks and theoretical problems arise related to the applications of sensor networks in industry, housing and communal services, and households. The use of inexpensive wireless sensor-based parameter monitoring devices opens up new areas for the use of telemetry and control systems, such as:
It should be noted that despite the long history of sensor networks, the concept of building a sensor network has not finally taken shape and has not been expressed in specific software and hardware (platform) solutions. The implementation of sensor networks at the current stage largely depends on the specific requirements of the industrial task. The architecture, software and hardware implementation is at the stage of intensive technology formation, which draws the attention of developers in order to find a technological niche for future manufacturers.
Wireless sensor networks (WSNs) consist of miniature computing devices - motes, equipped with sensors (temperature, pressure, light, vibration level, location sensors, etc.) and signal transceivers operating in a given radio range. Flexible architecture and reduced installation costs distinguish wireless smart sensor networks from other wireless and wired data transfer interfaces, especially when we're talking about about a large number of interconnected devices, a sensor network allows you to connect up to 65,000 devices. The constant reduction in the cost of wireless solutions and the increase in their operational parameters make it possible to gradually reorient from wired solutions in systems for collecting telemetric data, remote diagnostics, and information exchange. "Sensor network" is a well-established term today. Sensor Networks), denoting a distributed, self-organizing, resistant to failure of individual elements network of maintenance-free devices that do not require special installation. Each sensor network node may contain various sensors for monitoring the external environment, a microcomputer and a radio transceiver. This allows the device to take measurements, independently carry out initial data processing and maintain communication with an external information system.
802.15.4/ZigBee relayed short-range radio technology known as Sensor Networks. WSN - Wireless Sensor Network), is one of the modern trends in the development of self-organizing fault-tolerant distributed systems monitoring and managing resources and processes. Today, wireless sensor network technology is the only wireless technology that can be used to solve monitoring and control tasks that are critical to the operating time of sensors. Sensors integrated into a wireless sensor network form a geographically distributed self-organizing system for collecting, processing and transmitting information. The main area of application is control and monitoring of measured parameters of physical environments and objects.
The accepted IEEE 802.15.4 standard describes wireless channel access control and the physical layer for low-speed wireless personal area networks, that is, the two lower layers according to the OSI network model. The “classical” sensor network architecture is based on a typical node, which includes an example of a typical RC2200AT-SPPIO node:
A typical node can be represented by three types of devices:
Currently, wireless sensor network technology is rapidly developing. Wireless sensor networks are distributed, self-organizing networks that are resistant to the failure of individual elements that exchange information wirelessly. Each network element has an autonomous power source, a microcomputer, and a receiver/transmitter. The network coverage area can range from several meters to several kilometers, depending on the type of module and antenna, and also due to the ability to relay messages from one element to another. Data exchange between two end devices can be carried out through a repeater if the operating range of these devices does not allow their mutual detection. Thus, devices with a short range can communicate with each other using a repeater system.
The following main standards for low-power wireless networks are distinguished:
wireless sensor network transmission
1 .2.2 Application of sensor networks
Typically, WSN is used to collect data from devices equipped with sensors: temperature, humidity, lighting, that is, monitoring. For example, miniature sensors can be used in medicine to monitor patients. The devices that the patient carries with him can monitor the functioning of vital organs and notify the doctor in case of any dangerous situations.
The small size of the devices makes it possible to carry out not only “superficial” observations of the patient, but also to examine the internal organs of a person. So, when performing gastroscopy in public hospitals and clinics, a special device with a gastroscopic tube is used, but not all patients can swallow it. Devices in the form of tablets for conducting such studies already exist on the market. These battery-powered devices have enough energy to operate continuously for 24 hours and send readings to another device that the patient carries with them during that time. After this, the doctor can analyze the results and make an accurate diagnosis.
Sensors can be used to automatically turn on lighting when a person enters a room, or used to control some devices (in a smart home system).
Sometimes it is necessary to monitor the mobility or destruction of any objects where it is difficult to lay cables. For this, it is again more profitable to use sensor networks, since the sensors have an autonomous power source and are wireless.
Also, wireless sensor network technology can be used to transmit audio data - as an intercom system, multimedia system with low power consumption.
Wireless technologies and telecommunication networks created on their basis have a number of well-known advantages, including flexible architecture and low installation costs. Currently, the most popular and most popular wireless communication systems in the consumer market include: cellular communications, WiFi and Bluetooth. Each of them is characterized by range and transmission speed, operating frequency range, functionality and scope of application, as well as other characteristics that determine the architecture and structural features of telecommunication networks deployed on their basis (Fig. 3). In the architectural aspect, the main difference between WSN and classical telecommunication radio networks is the use of a large number of subminiature smart sensors in the network to transmit small amounts of telemetric information over medium distances (10-100 m).
Rice. 3. Massive wireless systems transmission of information via radio channel
In operational terms, the main distinctive features of WSN are the requirements for stable operation in conditions of dynamic changes in the network topology due to the movement of sensors, autonomous power supply and significant limitations in energy consumption and computing performance of microprocessors, memory, transceivers and other microelectronic components built into network nodes. At the same time, the operating conditions of the WSN provide for the transmission of small amounts of information at low speed. Taking into account the demands of the telecommunications market in the specific area of monitoring and managing objects via wireless communications under the auspices of IEEE ( Institute of Electrical and Electronics Engineers) in 2003, the official IEEE 802.15.4 specification was released and received standard status. According to the developers' plans, the new standard was supposed to provide a connection range comparable to WiFi, but at the same time have less power consumption due to the low data transfer rate. Among the most important tasks are also ensuring real-time operation using time slots, preventing access collisions and comprehensive support for network protection. 802.15.4 compliant devices must be able to manage power consumption and monitor the quality of connections. Since May 2007, 802.15.4 devices have been certified in Russia, the radiation power of which does not exceed 10 mW in open areas and 100 mW indoors.
802.15.4 defines two lower layers seven-level network model OSI: physical ( PHY) and channel ( MAC). The physical layer determines the method of data transmission, the communication interface, hardware features and parameters necessary for building a network. In practice, the physical layer controls the operation of the transceiver, selecting channels, control signals and transmit power levels.
In accordance with the specification of the 802.15.4 standard, 27 channels in three frequency ranges are reserved at the physical level for data exchange: 868 MHz, 910 MHz, 2.4 GHz, which allows the use of the standard in frequency bands that are unlicensed in most countries of the world (Fig. 4). In the territory Russian Federation Only the 2.4 GHz band is available for use. In this range, 16 channels of 5 MHz width are defined with carrier frequencies calculated in accordance with the expression:
Fc = 2405 + 5 (k - 1) MHz, k = 1.16.
Rice. 4. 802.15.4 physical layer frequency ranges.
The first version of the 802.15.4 standard defined two physical layers with wideband direct spread spectrum modulation DSSS (Direct Sequence Spread Spectrum): the first is in the 868/915 MHz band with a transmission rate of 20 and 40 kbit/s, respectively, and the second is in the 2450 MHz band with a transmission rate of 250 kbit/s. In 2006, permissible data rates at 868/915 MHz frequencies were increased to 100 and 250 kbit/s. In addition, four physical layer specifications have been defined depending on the modulation method: while maintaining wideband DSSS modulation, it is possible to use both binary and quadrature phase shift keying in the 868/915 MHz band ( QPSK - Quadrature Phase Shift Keying). Since 2007, the IEEE 802.15.4a version of the standard has increased the number of physical layers to six by including a layer with ultra-wideband radio technology Ultra WideBand (UWB) for high speed data transfer , as well as level specifications with radio technology Chirp Spread Spectrum (CSS), based on expanding the frequency spectrum using the method of linear frequency modulation. Physical layer UWB defined by allocated frequencies in three ranges: below 1 GHz, 3-5 GHz and 6-10 GHz, and for CSS spectrum allocated in the 2450 MHz band of the unlicensed range ISM. In 2009, the IEEE 802.15.4c and IEEE 802.15.4d standards expanded the available frequency ranges. These specifications determine the possibility of using transceiver devices with quadrature phase shift keying (QPSK) at the physical level. Quadrature phase-shift keying, QPSK) or with higher order phase shift keying ( M-PSK) at a frequency of 780 MHz, and at a frequency of 950 MHz - Gaussian frequency shift keying ( Gaussian frequency-shift keying, GFSK) or binary phase shift keying ( Binary phase-shift keying, BPSK). In addition, the IEEE 802.15.4d study group in 2009 included the newly opened bands 314-316 MHz, 430-434 MHz, and 779-787 MHz in China into the specifications, and defined an amendment to the existing 802.15.4-2006 standard to support the band 950-956 MHz in Japan.
At the link level The IEEE 802.15.4 specification standard defines mechanisms for interaction of network elements at the physical layer to ensure the formation of data fragments (frames), error checking and correction, and sending frames to the network layer. In this case, the MAC sublayer ( media access control) The link layer regulates multiple access to the physical medium with time division, manages transceiver communications and ensures security.
IEEE 802.15.4 provides two-way half-duplex data transmission while supporting AES 128 encryption. Channel access is based on the principle Carrier Sense Multiple Access With Collision Avoidance (CSMA/CA) - multiple access with carrier sense and collision avoidance." CSMA/CA is a network protocol that uses the principle of listening to a carrier frequency. A device that is ready to transmit data sends jam signal ( congestion signal) and listens to the air. If a "stranger" is detected jam signal, then the transmitter “falls asleep” for a random period of time, and then tries again to start transmitting the frame. This way, the transmission can only come from one device, which improves network performance. In this case, data is transmitted in relatively small packets, which is typical for the traffic of control and monitoring signals in a WSN. An important feature of the standard is the mandatory confirmation of message delivery.
A feature of devices networked according to the IEEE 802.15.4 standard is low power consumption due to the transceiver going into sleep mode when there is no data to send and maintaining the connection in this mode. When developing the standard, the main emphasis was on the speed of configuration and reconfiguration processes. In particular, the transition of the receiver to the active state lasts about 10-15 ms, and connecting new devices to the network - from 30 ms. In this case, the duration of reconfiguration and connection of devices depends on the constant “listening” of the routers to the network.
Types of network nodes. The standard defines two types of network nodes: full-featured device FFD (Fully Function Device), which can implement both the function of coordinating work and setting network parameters, and operate in standard node mode; device with limited functionality RFD (Reduced Function Device), having only the ability to communicate with fully functional devices. Any network must have at least one FFD, which implements the coordinator function. Each device has a 64-bit identifier, but in some cases, for a limited area, a short 16-bit identifier may be used for connections in personal network PAN (personal area network).
Network topologies. At the link level, the IEEE 802.15.4 standard provides general recommendations for constructing a network topology. Networks can be peer-to-peer P2P (peer-to-peer, point-to-point), or have a star topology. Based on structure P2P Arbitrary connection structures can be formed, limited only by the communication range between pairs of nodes. Taking this into account, various options for the topological structure of a WSN are possible, in particular a “tree” of clusters - a structure in which RFD, being "leaves of the tree", associated with only one FFD, and most nodes in the network are FFD. A mesh network topology is also possible, formed on the basis of cluster “trees” with a local coordinator for each cluster and containing a global network coordinator.
Rice. 5. IEEE 802.15.4 network topology options
The standard also supports a more structured “star” topology, in which the coordinator ( FFD) network must be the central node of the personal network being formed ( PAN) with a unique identifier. Other devices can then join the network, which is completely independent from other networks with a similar topology.
The 802.15.4 standard describes the two lower layers of the OSI network model, without defining the requirements for the upper layers and the conditions for their compatibility. Solving these problems required the development of special communication protocols. The most famous are the alliance protocols ZigBee, which was created in 2002 by the world's largest companies specializing in the development of software and hardware for information and communication systems. Among more than two hundred members of the alliance ZigBee, coordinating work on technology promotion and production technical means for wireless sensor networks - Texas Instruments, Motorola, Philips, IBM, Ember, Samsung, NEC, Freescale Semiconductor, LG, OKI and many others. Corporation Intel, although he is not a member of the alliance ZigBee actively supports his activities. ZigBee developed and ratified a standard in 2004 that includes a complete protocol stack for wireless sensor networks. Standard ZigBee is based on the IEEE 802.15.4 standard, which describes only the physical and media access layers for low-power wireless data networks. In contrast, the document ZigBee includes a description of network management processes, compatibility and device profiles, as well as information security, (Fig. 6). At the network level in ZigBee routing mechanisms and formation of the logical network topology are determined.
Fig.6. Configuration of 802.15.4 and ZigBee protocol stacks
In addition to the 802.15.4 / ZigBee standards, specifications of other wireless communication standards based on IEEE 802.15.4 - 2005 can be used to create WSNs, in particular WirelessHART And ISA100. However, currently in the field of wireless sensor network technologies ZigBee is the standard best supported by fully compatible hardware and software available on the market. In addition, protocols ZigBee Allow network devices to sleep b O most of the time, which significantly increases the operating life of the units when powered by battery sources. In FSU based ZigBee"device profiles" mode or profiles for various sensors, which are compatible at the protocol stack level and can be networked, transmit, receive and relay information. At the same time, only the device for which it is intended will “understand” this information.
Currently, a fairly large number of different ZigBee-products ranging from IEEE 802.15.4 standard transceiver chips to ready-made OEM modules with built-in network stack software ZigBee. All standard devices ZigBee depending on the level of complexity, they are divided into three classes, the highest of which - the coordinator - manages the process of network formation, stores data about its topology and serves as a gateway for transmitting data collected from all WSN sensors for further processing. In a network, as a rule, only one is used PAN coordinator. A medium-complex device - a router - is capable of relaying messages, supporting all network topologies, and also performing the functions of a cluster coordinator. And finally, the simplest device - an ordinary node - is only capable of transmitting data to the nearest router.
So the standard ZigBee supports a network with a cluster architecture (Fig. 7), formed from ordinary nodes united into clusters through routers. Cluster routers request sensor data from devices and, relaying them to each other, transfer them to the coordinator, who usually communicates with IP-network, where it sends information for accumulation and final processing.
Rice. 7. Typical network topology ZigBee
Net ZigBee is self-organizing, that is, all nodes are able to independently determine and adjust data delivery routes. Data is transmitted using radio transmitters from one node to another along the chain, and as a result, the nodes closest to the gateway dump all the accumulated information to the gateway. This information includes data read from touch sensors, as well as data about the status of devices and the results of the information transfer process. If some of the devices fail, the operation of the sensor network should continue after reconfiguration. Wireless nodes operate under the control of a special application. Typically, all sensor network nodes use the same control program to ensure their functionality and execution of network protocols.
So the standard ZigBee is practically the only standard in the field of WSN technologies that most fully describes a set of seven levels classical scheme open systems interactions ( OSI) and at the same time - to the greatest extent supported by the availability of production of fully compatible hardware and software products (Fig. 8).
In addition to solutions based ZigBee possible options for implementing WSN using proprietary platforms (for example, from Sensicast, Millennial Net, Iris, Mia2, Telos, Dust Networks etc.), which use either proprietary or IEEE 802.15.4-based transceivers. The network stack of proprietary platforms is implemented based on proprietary algorithms and protocols that provide a number of advantages over ZigBee, but do not ensure compatibility of solutions from different manufacturers. Standard ZigBee the network in general looks like a “cluster tree” and requires planning the placement of devices of various types ( FFD, RFD) at the network design stage. At the same time, most nodes are end devices and are unable to relay messages, as a result of which there must be at least one router node within the range of each of them. This requires optimization of the arrangement of devices of various classes.
The specifics of network protocols for WSNs require solving energy efficiency problems, since in autonomous power supply network nodes from batteries, the minimum energy consumption determines the temporary operating life of the node.
IN ZigBee the lowest power consumption is achieved with synchronized access to the medium ( beacon mode), allowing you to set the "sleep" mode for both, RFD(terminal) devices and FFD ( routers). With a complex network topology and especially random traffic generation, it is practically impossible to implement best option environment access schedules. In accordance with the standard, multiple access using the algorithm is more technologically advanced CSMA/CA. However, in this mode, all coordinators must constantly be in channel listening mode, and therefore a fixed power supply is required to power the routers. In this case, only end devices will operate from autonomous sources (batteries), and routers and PAN- coordinator - from the power supply network.
Rice. 8. Protocol stack ZigBee
A number of foreign companies use private technical solutions and proprietary network protocol stacks to reduce power consumption, including component-level solutions. In addition to the technical characteristics of transceiver chips, microcontrollers and other wireless module components, power consumption is significantly affected by the operating mode of the network application and the intensity of data exchange. There are operating modes with an intensive work cycle and with a low exchange rate. In duty cycle-intensive applications, the bulk of power consumption comes from the air interface - packet reception/transmission, synchronization and frequency locking. Moreover, in the case of a predominance of long packets in the traffic, the consumption of the transceiver dominates, and in the case of the predominant transmission of short packets, the consumption of the radio part initialization and frequency auto-calibration circuits comes to the fore. In applications with low traffic intensity, indicators such as the presence and effectiveness of low-power modes for sensor chips, microcontrollers and transceivers begin to play a role.
A typical energy consumption profile of a wireless node is shown in Fig. 9. Absolute values are given for a device with a range of less than 1 GHz; for devices in the 2.4 GHz range, current consumption will be approximately twice as high.
An example of our own network protocol stack solutions is the one developed by the company Texas Instruments simple protocol Simpliciti(Fig. 10) open source. The protocol is intended for WSNs of the IEEE 802.15.4 standard with self-contained battery power and electronic components based on a system-on-chip (for example, CC430, CC1110/2510), or based on a combination of low-power MSP430 series controllers and any of the transceivers T.I. series MSP430 + CC1XXX/CC25XX. The protocol ensures minimization of energy consumption with support for sleep mode of network nodes and can be used in WSNs for various applications, including: intrusion sensors, light sensors, CO sensors, water, gas, electricity meters, applications RFID with active tags, etc.
Rice. 9. Example of a wireless node power profile
Fig. 10. Protocol stack structure Simpliciti
Another example of a private solution to create a WSN for remote control devices is the proposed Texas Instruments protocol RemoTITM, supported by relevant wireless devices and meeting the specification ZigBee® RF4CE(Fig. 11). Protocol RemoTI is based on the IEEE 802.15.4 standard with the addition of a network interaction layer and a set of basic control commands and includes: support for multiple channels; secure transactions; energy saving modes; a simple mechanism for combining devices for collaboration.
Rice. eleven. Protocol stack structure RemoTI
The most well-known platforms that meet the basic basic requirements for sensor networks (low power consumption, long operating time, low-power transceivers and the presence of sensors) should also include: MicaZ, TelosB, Intel Mote 2. Most development companies produce both equipment (assemblies, sensors) and software that meet these standards. Currently, several companies have achieved the greatest success, among which they stand out for the depth and completeness of their developments Crossbow And Sentilla.
Overview of modern wireless technologies
Sensor architecture
A touch sensor consists of hardware and software, like any other telecommunications node. In general, the sensor consists of the following
subsystems: perception, data processing, monitoring, communication and power supply (Figure 1.1).
Figure 1.1 – General architecture of the sensor.
The perception subsystem usually consists of an analog device that takes certain statistics and an analog-to-digital converter. The data processing subsystem contains CPU and memory, allowing you to store not only the data generated by the sensor, but also service information that is necessary for the correct and full functioning of the communication subsystem. The monitoring subsystem allows the sensor to collect environmental data such as humidity, temperature, pressure, magnetic field, air chemical analysis, etc. The sensor can also be supplemented with a gyroscope and accelerometer, which makes it possible to build a positioning system.
Progress in the field of wireless communications and miniaturization of microcircuits are opening new horizons in information and computer technologies. In addition to multi-hop networks, there are more complex routing protocols where the next node is selected based on an analysis of its characteristics, for example, energy level, reliability, and the like. The situation becomes more complicated when the nodes of a wireless sensor network move - the network topology becomes dynamic.
To implement a sensor as a small telecommunications device (no more than one cubic centimeter), many technical aspects must be taken into account. The CPU frequency must be at least 20 MHz, volume random access memory at least 4 KB, transfer speed at least 20 Kbps. Optimizing the hardware will reduce the size of the sensor, but will entail an increase in its price. The operating system (OS) must be optimized taking into account the architecture of the central processor used. Limited resources and small memory size encourage placing the OS in ROM. Currently, the open-source Tiny OS is widely used, allowing flexible control of sensors from different manufacturers. In the field of networking, the limited power supply in sensors imposes significant limitations on
the use of radio technologies that can be used in sensor networks. It should also be noted that the limited performance of the central processor does not allow the use of standard IP network routing protocols
– the high complexity of calculating the optimal path algorithm will overload the central processor. To date, a large number of special routing protocols for sensor networks have been developed.
The development of data transmission technology in sensor networks is one of the most important tasks when building a sensor network, since its specific architectural and system characteristics impose a whole host of strict restrictions, among which the following should be emphasized:
Limited energy reserves, which means the range is limited;
Limited processor performance;
Simultaneous operation large quantity nodes in a limited space;
Equivalence of nodes, client-server architecture is not applicable due to its characteristic delays;
Operating in an unlicensed frequency spectrum;
Low cost.
Currently, the development of sensor networks is based on the IEEE 802.15.4 Zigbee standard, which I mentioned above. Additionally, I note that the Zigbee alliance assumes that radio access of the ZigBee standard will be used in applications such as monitoring, production automation, sensors, security, control, household appliances and much more. Thus, sensor network applications can be divided into several main categories:
Security, emergencies and military operations;
Medicine and health;
Weather, Environment and Agriculture;
Factories, factories, houses, buildings;
Transport systems and cars.
I will consider cases of specific applications of sensor networks in the above categories. Sensor networks can, at a minimum, be used in the following scenarios.
Application of sensor networks
Wireless sensor networks have the unique characteristics of easy deployment, self-organization, and fault tolerance. Emerging as a new paradigm for information collection, wireless sensor networks have been used for broad applications related to health, environmental control, energy, food safety and manufacturing.
Over the past few years, there have been many indications that sensor networks will become a reality. Several sensor node prototypes have been created, including Motes at Berkeley, uAMPS at MIT, and GNOMES at Rice. The elementary functions of sensor networks are positioning, sensing, tracking and detection. Besides military applications, there have also been civil applications based on elementary functions, which can be divided into habitat control, environmental surveillance, healthcare and other commercial
applications. Additionally, Sibley recently created a mobile sensor called the Robomote, which is equipped with wheels and can move around the field.
In one of the first attempts to use sensor networks for civilian applications, Berkeley and Intel Research Laboratory used the Mote sensor network to monitor storm readings on the Great Duck Islands, Maine in the summer of 2002. Two-thirds of the sensors were installed off the coast of Maine, collecting the necessary (useful) information in real time on the world wide web (Internet). The system worked for more than 4 months and provided data
For 2 months after the scientists left the island due to bad weather conditions (winter). This habitat monitoring application represents an important class of sensor network applications. Most importantly, network sensors are capable of collecting information in dangerous environments that are inhospitable to people. During the monitoring studies, design criteria were considered, including design creation, creation of a sensor system with the possibility of remote access and data management. Numerous attempts have been made to achieve the requirements, leading to the development of a set of prototype sensor network systems. The sensor system used by Berkeley and Intel Research Laboratory, although primitive, was effective in collecting interesting environmental data and providing scientists with important information.
Sensor networks have found applications in the fields of observation and prediction (guessing). A living example of such an application is the Automated Local Evaluation in Real-Time (ALERT) system developed by the National Weather Service with a wireless network of sensors. Equipped with meteorological/hydrological touch devices,Sensors in a given environment typically measure several properties of ,local weather such as water level, temperature, wind. Data is transmitted via line-of-sight radio communication through sensors at the base station. The Flood Forecast Model was adapted to process the data and issue automatic warnings. The system provides important information rainfall and water levels in real time to assess the possibility of potential flooding anywhere in the country. The present (current) ALERT system is installed throughout the West Coast of the United States and is used for flood warnings in California and Arizona.
Recently, sensor systems have been intensively used in the healthcare sector, used by patients and doctors for glucose tracking and monitoring, cancer detectors and even artificial organs. Scientists suggest the possibility of implanting biomedical sensors into the human body for various purposes. These sensors transmit information to external computer system through wireless interface. Several biomedical sensors are integrated into an application system to determine the diagnosis and treatment of disease. Biomedical sensors herald a more advanced level of medical care.
The main difference between wireless sensor networks and traditional computer and telephone networks is the lack of permanent infrastructure that belongs to a specific operator or provider. Each user terminal in a sensor network has the ability to function not only as an end device, but also as a transit node, as shown in Figure 1.2.
Figure 1.2 – Example of connecting network sensors
