Wireless Networking
A wireless network is a flexible data communications system, which uses wireless media such as radio frequency technology to transmit and receive data over the air, minimizing the need for wired connections (What is Wireless LAN, White Paper). Wireless networks are used to augment rather than replace wired networks and are most commonly used to provide last few stages of connectivity between a mobile user and a wired network.
Wireless networks use electromagnetic waves to communicate information from one point to another without relying on any physical connection. Radio waves are often referred to as radio carriers because they simply perform the function of delivering energy to a remote receiver. The data being transmitted is superimposed on the radio carrier so that it can be accurately extracted at the receiving end. Once data is superimposed (modulated) onto the radio carrier, the radio signal occupies more than a single frequency, since the frequency or bit rate of the modulating information adds to the carrier. Multiple radio carriers can exist in the same space at the same time without interfering with each other if the radio waves are transmitted on different radio frequencies. To extract data, a radio receiver tunes in one radio frequency while rejecting all other frequencies. The modulated signal thus received is then demodulated and the data is extracted from the signal.
Wireless networks offer the following productivity, convenience, and cost advantages over traditional wired networks:
- Mobility: provide mobile users with access to real-time information so that they can roam around in the network without getting disconnected from the network. This mobility supports productivity and service opportunities not possible with wired networks.
- Installation speed and simplicity: installing a wireless system can be fast and easy and can eliminate the need to pull cable through walls and ceilings.
- Reach of the network: the network can be extended to places which can not be wired
- More Flexibility: wireless networks offer more flexibility and adapt easily to changes in the configuration of the network.
- Reduced cost of ownership: while the initial investment required for wireless network hardware can be higher than the cost of wired network hardware, overall installation expenses and life-cycle costs can be significantly lower in dynamic environments.
- Scalability: wireless systems can be configured in a variety of topologies to meet the needs of specific applications and installations. Configurations can be easily changed and range from peer-to-peer networks suitable for a small number of users to large infrastructure networks that enable roaming over a broad area.
Bluetooth and 802.11b have the potential to dramatically alter how people use devices to connect and communicate in everyday life. Bluetooth is a low-power, short-range technology for ad hoc cable replacement; it enables people to wirelessly combine devices wherever they bring them.
Conversely, 802.11b is a moderate-range, moderate-speed technology based on Ethernet; it allows people to wirelessly access an organizational network throughout a campus location. Although the technologies share the 2.4 GHz band, have some potentially overlapping applications, and have been pitted against each other in the press, they do not compete and can even been successfully combined for corporate use.
One thing is clear, wireless technologies will continue to evolve and offer organizations and end users higher standard of life by making us more mobile and increasing our ability to interact with each other, removing distance as a barrier. There will be a time when a traveler can sit in any airport or hotel and surf the Web or connect to the home office and work. Users will be able to surf or work in places such as malls, parks, or (with smaller handheld computers) just walking down the street. Internet service providers will install larger wireless networks allowing users to connect from anywhere in the city. All of these things are possible with wireless technology.
One day soon, the network will follow you instead of you following it.
Source: http://www.tutorial-reports.com/wireless/introduction.php
802.11
802.11 is an evolving family of specifications for wireless local area networks (WLANs) developed by a working group of the Institute of Electrical and Electronics Engineers (IEEE). There are several specifications in the family and new ones are occasionally added.
All the 802.11 specifications use the Ethernet protocol and Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) for path sharing. The original modulation used in 802.11 was phase-shift keying (PSK). However, other schemes, such as complementary code keying (CCK), are used in some of the newer specifications. The newer modulation methods provide higher data speed and reduced vulnerability to interference.
Wireless LAN
WLAN allows you at home to share an Internet connection in all rooms, without having to drill holes and put in Network cables between all the rooms.
Like networking via coax-cable
(10base2) or via coax-cables (10baseT
/ 100baseT
/ 1000baseT),
WLAN networking is a world-wide standard :
802.11b : maximum bandwidth : 11 Mbps
802.11g : maximum bandwidth : 54 Mbps
Most 802.11g installations allow dual-speed operations, allowing wireless
connection of 802.11b - 11Mbps clients and of 802.11g - 54 Mbps clients.
WLAN Access-point :
Allows multiple systems with WLAN network cards to connect to the network, for
communication with other wireless systems and/or systems connected via network
cables ( like a network
hub, but using wireless communication instead of cables)
Range:
Depending on the WLAN devices and where it is used (outside or in a building
with walls), you can have a wireless connection between 50 meter (side a
building through walls and floors) and 500 m (outside with no items between
Access Point and client).
Concerns:
The lack of default security of Wireless connections is fast becoming an issue, especially in the UK, where many Broadband (ADSL) connections are now offered together with a Wireless Basestation/ADSL Modem/firewall/Router access point. Further, many laptop PCs now have Wireless Networking built in (cf. Intel 'Centrino' campaign) thus eliminating the need for an additional plug-in (PCMCIA) card. This might even be enabled, by default, without the owner ever realising it, thus 'broadcasting' the laptop's accessibility to any computer nearby.
Wireless LAN Standards Click Here
OFDM
Short for Orthogonal Frequency Division Multiplexing, an FDM modulation technique for transmitting large amounts of digital data over a radio wave. OFDM works by splitting the radio signal into multiple smaller sub-signals that are then transmitted simultaneously at different frequencies to the receiver. OFDM reduces the amount of crosstalk in signal transmissions. 802.11a WLAN, 802.16 and WiMAX technologies use OFDM.In frequency-division multiplexing, multiple signals, or carriers, are sent simultaneously over different frequencies between two points. However, FDM has an inherent problem: Wireless signals can travel multiple paths from transmitter to receiver (by bouncing off buildings, mountains and even passing airplanes); receivers can have trouble sorting all the resulting data out.
Orthogonal FDM deals with this multipath problem by splitting carriers into smaller subcarriers, and then broadcasting those simultaneously. This reduces multipath distortion and reduces RF interference (a mathematical formula is used to ensure the subcarriers' specific frequencies are "orthogonal," or non-interfering, to each other), allowing for greater throughput.
OFDM is at the heart of 802.11a wireless-LAN technology, which can offer throughput of up to 54M bit/sec (the 802.11a specification calls for up to 52 subcarriers). It is also used in ADSL over copper telephone wires.
MIMO
Next-generation wireless local area network (WLAN) services target specifications of up to 100Mbps at ranges up to 100m. This requires a drastic increase in bandwidth efficiency since current WLAN systems rarely achieve throughputs of 54Mbps due to channel attenuation and dispersion and sharing of resources between users within a cell.
Multiple antenna transmission allows significantly boosting the capacities of future WLANs without needing to increase bandwidth or transmit power.Multiple antenna systems are the key to the high-capacity wireless universe. Indeed, they allow increasing the rate, improving the robustness, or accommodating more users in the cell.
One can upgrade a link with multiple antennas at transmit, receive or both sides. The latter is often called referred to as Multiple-Input Multiple-Output (MIMO).
HIPERLAN
Short for high performance radio local area network. Developed by the European Telecommunications Standards Institute, HiperLAN is a set of WLAN communication standards used chiefly in European countries. HiperLAN is similar to the IEEE 802.11 WLAN standards used in the U.S.
There are two types of HiperLAN:
* HiperLAN/1: provides communications at up to 20 Mbps in the 5 GHz band.
* HiperLAN/2: provides communications at up to 54 Mbps in the 5 GHz band.
HiperLAN/2 is compatible with 3G (third-generation) WLAN systems for sending and receiving data, images, and voice communications. HiperLAN/2 has the potential, and is intended, for implementation worldwide in conjunction with similar systems in the 5-GHz RF band.Like 802.11, HiperLAN serves to ensure the possible interoperability of different manufacturers' wireless communications equipment that operate in this spectrum.
Mobiles Ad-Hoc Networks
In the next generation of wireless communication systems, there will be a need for the rapid deployment of independent mobile users. Significant examples include establishing survivable, efficient, dynamic communication for emergency/rescue operations, disaster relief efforts, and military networks. Such network scenarios cannot rely on centralized and organized connectivity, and can be conceived as applications of Mobile Ad Hoc Networks(MANET).
A MANET is an autonomous collection of mobile users that communicate over relatively bandwidth constrained wireless links. Since the nodes are mobile, the network topology may change rapidly and unpredictably over time. The network is decentralized, where all network activity including discovering the topology and delivering messages must be executed by the nodes themselves, i.e., routing functionality will be incorporated into mobile nodes.
The set of applications for MANETs is diverse, ranging from small, static networks that are constrained by power sources, to large-scale, mobile, highly dynamic networks. The design of network protocols for these networks is a complex issue. Regardless of the application, MANETs need efficient distributed algorithms to determine network organization, link scheduling, and routing. However, determining viable routing paths and delivering messages in a decentralized environment where network topology fluctuates is not a well-defined problem. While the shortest path (based on a given cost function) from a source to a destination in a static network is usually the optimal route, this idea is not easily extended to MANETs. Factors such as variable wireless link quality, propagation path loss, fading, multiuser interference, power expended, and topological changes, become relevant issues. The network should be able to adaptively alter the routing paths to alleviate any of these effects. Moreover, in a military environment, preservation of security, latency, reliability, intentional jamming, and recovery from failure are significant concerns. Military networks are designed to maintain a low probability of intercept and/or a low probability of detection. Hence, nodes prefer to radiate as little power as necessary and transmit as infrequently as possible, thus decreasing the probability of detection or interception. A lapse in any of these requirements may degrade the performance and dependability of the network.
The concepts and operational requirements associated with the current idea of MANETs are discussed in the mobile computing and networking literature, notably documents and standards developed by the MANET Working Group of the Routing Area of the Internet Engineering Task Force
(IETF).
Wireless Sensor Networks
A wireless ad hoc sensor network consists of a number of sensors spread across a geographical area. Each sensor has wireless communication capability and some level of intelligence for signal processing and networking of the data.
Some examples of wireless ad hoc sensor networks are the following:
1. Military sensor networks to detect and gain as much information as possible about enemy movements, explosions, and other phenomena of interest.
2. Sensor networks to detect and characterize Chemical, Biological, Radiological, Nuclear, and Explosive (CBRNE) attacks and material.
3. Sensor networks to detect and monitor environmental changes in plains, forests, oceans, etc.
4. Wireless traffic sensor networks to monitor vehicle traffic on highways or in congested parts of a city.
5. Wireless surveillance sensor networks for providing security in shopping malls, parking garages, and other facilities.
6. Wireless parking lot sensor networks to determine which spots are occupied and which are free.
The above list suggests that wireless ad hoc sensor networks offer certain capabilities and enhancements in operational efficiency in civilian applications as well as assist in the national effort to increase alertness to potential terrorist threats.
Two ways to classify wireless ad hoc sensor networks are whether or not the nodes are individually addressable, and whether the data in the network is aggregated. The sensor nodes in a parking lot network should be individually addressable, so that one can determine the locations of all the free spaces. This application shows that it may be necessary to broadcast a message to all the nodes in the network. If one wants to determine the temperature in a corner of a room, then addressability may not be so important. Any node in the given region can respond. The ability of the sensor network to aggregate the data collected can greatly reduce the number of messages that need to be transmitted across the network. This function of data fusion is discussed more below.
The basic goals of a wireless ad hoc sensor network generally depend upon the application, but the following tasks are common to many networks:
1. Determine the value of some parameter at a given location: In an environmental network, one might one to know the temperature, atmospheric pressure, amount of sunlight, and the relative humidity at a number of locations. This example shows that a given sensor node may be connected to different types of sensors, each with a different sampling rate and range of allowed values.
2. Detect the occurrence of events of interest and estimate parameters of the detected event or events: In the traffic sensor network, one would like to detect a vehicle moving through an intersection and estimate the speed and direction of the vehicle.
3. Classify a detected object: Is a vehicle in a traffic sensor network a car, a mini-van, a light truck, a bus, etc.
4. Track an object: In a military sensor network, track an enemy tank as it moves through the geographic area covered by the network.
In these four tasks, an important requirement of the sensor network is that the required data be disseminated to the proper end users. In some cases, there are fairly strict time requirements on this communication. For example, the detection of an intruder in a surveillance network should be immediately communicated to the police so that action can be taken.
Wireless ad hoc Sensor Network Requirements include the following:
1. Large number of (mostly stationary) Sensors: Aside from the deployment of sensors on the ocean surface or the use of mobile, unmanned, robotic sensors in military operations, most nodes in a smart sensor network are stationary. Networks of 10,000 or even 100,000 nodes are envisioned, so scalability is a major issue.
2. Low energy use: Since in many applications the sensor nodes will be placed in a remote area, service of a node may not be possible. In this case, the lifetime of a node may be determined by the battery life, thereby requiring the minimization of energy expenditure.
3. Network self-organization: Given the large number of nodes and their potential placement in hostile locations, it is essential that the network be able to self-organize; manual configuration is not feasible. Moreover, nodes may fail (either from lack of energy or from physical destruction), and new nodes may join the network. Therefore, the network must be able to periodically reconfigure itself so that it can continue to function. Individual nodes may become disconnected from the rest of the network, but a high degree of connectivity must be maintained.
4. Collaborative signal processing: Yet another factor that distinguishes these networks from MANETs is that the end goal is detection/estimation of some events of interest, and not just communications. To improve the detection/estimation performance, it is often quite useful to fuse data from multiple sensors. This data fusion requires the transmission of data and control messages, and so it may put constraints on the network architecture.
5. Querying ability: A user may want to query an individual node or a group of nodes for information collected in the region. Depending on the amount of data fusion performed, it may not be feasible to transmit a large amount of the data across the network. Instead, various local sink nodes will collect the data from a given area and create summary messages. A query may be directed to the sink node nearest to the desired location.
Sensor types and System Architecture:
With the coming availability of low cost, short range radios along with advances in wireless networking, it is expected that wireless ad hoc sensor networks will become commonly deployed. In these networks, each node may be equipped with a variety of sensors, such as acoustic, seismic, infrared, still/motion videocamera, etc. These nodes may be organized in clusters such that a locally occurring event can be detected by most of, if not all, the nodes in a cluster. Each node may have sufficient processing power to make a decision, and it will be able to broadcast this decision to the other nodes in the cluster. One node may act as the cluster master, and it may also contain a longer range radio using a protocol such as IEEE 802.11 or Bluetooth.
Moreinfo: http://www.computer.org/computer/homepage/0804/GEI/r8041.pdf
Software Defined Radio
Imagine a radio technology that could configure a wireless device to work with any communications system, be it a cellular phone, a pager, a WI-FI transceiver, an FM or AM radio, a satellite communications terminal and even a garage door opener. This would offer both cost and time savings for consumers, who would only need to buy one radio to meet multiple communications needs. And more importantly, that same technology could facilitate interoperability among the communications systems used by military, police and rescue-relief teams, who currently cannot always communicate with each other, even sometimes in critical, life-threatening situations because of incompatible radio systems.
This unique radio technology is called Software Defined Radio (SDR) and it works much like desktop computing, where a single hardware platform can carry out many functions based on the software applications loaded. SDR uses software to perform radio-signal processing functions instead of using resistors, capacitors, feedback loops, or application-specific integrated circuits. Frequency tuning, filtering, synchronization, encoding and modulation are now performed in software on high-speed reprogrammable devices such as digital signal processors (DSP), field programmable field array (FPGA), or general purpose processors (GPP). RF components are still needed for generation of high frequencies or for signal amplications and radiation but SDR aims at reducing the count to a minimum.
The technology is being promoted by the US Department of Defence to replace tens of thousands of single protocol, single use radios with a common platform that could be reprogrammed to ensure interoperability. Military and public safety organizations from around the world are also considering this technology to solve their interoperability problems. The Software Defined Radio Forum (SDRF) is also promoting the technology but for commercial applications.
Software-defined radio (SDR), sometimes shortened to software radio (SR), refers to wireless communication in which the transmitter modulation is generated or defined by a computer, and the receiver uses a computer to recover the signal intelligence.? To select the desired modulation type, the proper programs must be run by microcomputers that control the transmitter and receiver.
A typical voice SDR Transmitter, such as might be used in mobile two-way radio or cellular telephone communication, consists of the following stages.? Items with asterisks represent computer-controlled circuits whose parameters are determined by the programming (software).
* Microphone
* Audio amplifier
* Analog-to-digital converter (ADC) that converts the voice audio to ASCII data *
* Modulator that impresses the ASCII intelligence onto a radio-frequency (RF) carrier *
* Series of amplifiers that boosts the RF carrier to the power level necessary for transmission
* Transmitting antenna
A typical SDR Receiver designed to intercept the above-described voice SDR signal would employ the following stages, essentially reversing the transmitter's action.? Again, items followed by asterisks represent programmable
circuits.
* Receiving antenna
* superheterodyne system that boosts incoming RF signal strength and converts it to a constant frequency
* Demodulator that separates the ASCII intelligence from the RF carrier *
* Digital-to-analog converter (DAC) that generates a voice waveform from the ASCII data *
* Audio amplifier
* Speaker, earphone, or headset
The most significant asset of SDR is versatility.Wireless systems employ protocols that vary from one service to another. Even in the same type of service, for example wireless fax, the protocol often differs from country to country.
A single SDR set with an all-inclusive software repertoire can be used in any mode, anywhere in the world.Changing the service type, the mode, and/or the modulation protocol involves simply selecting and launching the requisite computer program, and making sure the batteries are adequately charged if portable operation is contemplated.
Goal of SDR
The ultimate goal of SDR engineers is to provide a single radio transceiver capable of playing the roles of cordless telephone, cell phone, wireless fax, wireless e-mail system, pager, wireless videoconferencing unit, wireless Web browser, Global Positioning System (GPS) unit, and other functions still in the realm of science fiction, operable from any location on the surface of the earth, and perhaps in space as well.
More Info : http://www.broadcastpapers.com/broadband/WiproSDRadio.pdf
RF-ID
Its a technology similar in theory to bar code identification. With RFID, the electromagnetic or electrostatic coupling in the RF portion of the electromagnetic spectrum is used to transmit signals. An RFID system consists of an antenna and a transceiver, which read the radio frequency and transfer the information to a processing device, and a transponder, or tag, which is an integrated circuit containing the RF circuitry and information to be transmitted.
RFID systems can be used just about anywhere, from clothing tags to missiles to pet tags to food -- anywhere that a unique identification system is needed. The tag can carry information as simple as a pet owners name and address or the cleaning instruction on a sweater to as complex as instructions on how to assemble a car. Some auto manufacturers use RFID systems to move cars through an assembly line. At each successive stage of production, the RFID tag tells the computers what the next step of automated assembly is.
One of the key differences between RFID and bar code technology is RFID eliminates the need for line-of-sight reading that bar coding depends on. Also, RFID scanning can be done at greater distances than bar code scanning. High frequency RFID systems (850 MHz to 950 MHz and 2.4 GHz to 2.5 GHz) offer transmission ranges of more than 90 feet, although wavelengths in the 2.4 GHz range are absorbed by water (the human body) and therefore has limitations.
RFID is also called dedicated short range communication (DSRC).
More Info : http://www.tutorial-reports.com/wireless/rfid/
NanoTechnology
Nanotechnology as a collective term refers to technological developments on the nanometer scale, usually 0.1-100nm. (One nanometer equals one thousandth of a micrometer or one millionth of a millimeter.) The term sometimes applies to any microscopic technology.
Due to the small size at which nanotechnology operates, physical phenomena not observed at the macroscopic scale dominate. These nanoscale phenomena include quantum size effects and short range forces such as van der Waals forces. Furthermore the vastly increased ratio of surface area to volume promotes surface phenomena. More...
Quantum Computers
A quantum computer is any device for computation that makes direct use of distinctively quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data. In a classical (or conventional) computer data are measured by bits; in a quantum computer the data are measured by qubits. The basic principle of quantum computation is that the quantum properties of particles can be used to represent and structure data, and that devised quantum mechanisms can be used to perform operations with these data. More..
Positioning
Outdoor Positioning
GPS
Global Positioning System, a worldwide middle earth orbit (MEO) satellite navigational system formed by 24 satellites orbiting the earth and their corresponding receivers on the earth. The satellites orbit the earth at approximately 12,000 miles above the surface and make two complete orbits every 24 hours. The GPS satellites continuously transmit digital radio signals that contain data on the satellites location and the exact time to the earth-bound receivers. The satellites are equipped with atomic clocks that are precise to within a billionth of a second. Based on this information the receivers know how long it takes for the signal to reach the receiver on earth. As each signal travels at the speed of light, the longer it takes the receiver to get the signal, the farther away the satellite is. By knowing how far away a satellite is, the receiver knows that it is located somewhere on the surface of an imaginary sphere centered at the satellite. By using three satellites, GPS can calculate the longitude and latitude of the receiver based on where the three spheres intersect. By using four satellites, GPS can also determine altitude.GPS was developed and is operated by the U.S. Department of Defense. It was originally called NAVSTAR (Navigation System with Timing and Ranging). Before its civilian applications, GPS was used to provide all-weather round-the-clock navigation capabilities for military ground, sea, and air forces.
GPS has applications beyond navigation and location determination. GPS can be used for cartography, forestry, mineral exploration, wildlife habitation management, monitoring the movement of people and things and bringing precise timing to the world.
- Trimble - All about GPS Tutorial
- Differential GPS Tutorial
- O'Reilly Differential GPS tutorial
- GPS Raw data, theory, antennas
Indoor Positioning
Many positioning systems designed to determine or track a user's location have been proposed over the years. Those systems fall into three categories: global location systems, wide-area location systems based on cellular networks, and indoor location systems.
A typical global location system is the Global Positioning System (GPS) , which receives signals from multiple satellites and employs a triangulation process to determine physical locations with an accuracy of approximately 10 m. However, GPS is inefficient for indoor use or in urban areas where high buildings shield the satellite signals.
Several cellular-network-based wide-area location systems have been proposed in recent years . The technological methods of location determination involve measuring the signal strength, the angle of signal arrival, and/or the time difference of signal arrival. However, the accuracy of wide-area location systems is highly limited by the cell size. Moreover, the effectiveness of systems for an indoor environment is also limited by the multiple reflections suffered by the radio frequency (RF) signal.
For an indoor environment, several systems based on various technologies such as infrared (IR), ultrasound , video surveillance , and radio signal are emerging. Among these systems, radio-signal-based approaches—more specifically, the wireless local-area network (WLAN) (IEEE 802.11b, also named Wi-Fi) radio-signal-based positioning system—have drawn great attention in recent years.
Using Wireless Networks
RF-Based Indoor Positioning System RADAR- Microsoft Research
WLAN-Based Indoor Positioning System - IBM Research
Sources:
This information provided is partly from my views on the subject and mostly derived from websites such as www.wikipedia.org, www.webopedia.com, www.whatis.com , http://www.tutorial-reports.com and many other internet sources, i thank them all.
Praneeth Katakolla
