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INTRODUCTION
Wireless communication is the transfer of information over a distance without the use of electrical conductors or "wires". The distances involved may be short (a few meters as in television remote control) or long (thousands or millions of kilometers for radio communications). Wireless communication is generally considered to be a branch of telecommunications.
It encompasses various types of fixed, mobile, and portable two-way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of wireless technology include GPS units, garage door openers and or garage doors, wireless computer mice, keyboards and headsets, satellite television and cordless telephones.
Wireless operations permits services, such as long-range communications, that are impossible or impractical to implement with the use of wires. The term is commonly used in the telecommunications industry to refer to telecommunications systems (e.g. radio transmitters and receivers, remote controls, computer networks, network terminals, etc.) which use some form of energy (e.g. radio frequency (RF), infrared light, laser light, visible light, acoustic energy, etc.) to transfer information without the use of wires. Information is transferred in this manner over both short and long distances.
In 1895, Guglielmo Marconi opened the way for modern wireless communications by transmitting the three-dot Morse code for the letter S over a distance of three kilometers using electromagnetic waves. From this beginning, wireless communications has developed into a key element of modern society.
From satellite transmission, radio and television broadcasting to the now ubiquitous mobile telephone, wireless communications has revolutionized the way societies function.
Wireless communications and the economic goods and services that utilise it have some special characteristics that have motivated specialised studies. First, wireless communications relies on a scarce resource namely, radio spectrum. Second, use of spectrum for wireless communications required the development of key complementary technologies; especially those that allowed higher frequencies to be utilised more efficiently. Finally, because of its special nature, the efficient use of spectrum required the coordinated development of standards. Those standards in turn played a critical role in the diffusion of technologies that relied on spectrum use.
1 PRINCIPLES OF WIRELESS COMMUNICATIONS
Wireless communications begin with a message that is converted into an electronic signal by a device called a transmitter. There are two types of transmitters: analog
and digital. An analog transmitter sends electronic signals as modulated radio waves. The analog transmitter modulates the radio wave to carry the electronic signal and then sends the modified radio signal through space. A digital transmitter encodes electronic signals by converting messages into a binary code, the series of zeros and ones that are the basis of all computer programming. The encoded electronic signal is then sent as a radio wave. Devices known as receivers decode or demodulate the radio waves and reproduce the original message over a speaker.
Wireless communications systems involve either one-way transmissions, in which a person merely receives notice of a message, or two-way transmissions, such as a telephone conversation between two people. An example of a device that only receives one-way transmission is a pager, which is a high-frequency radio receiver. When a person dials a pager number, the pager company sends a radio signal to the desired pager. The encoded signal triggers the pager s circuitry and notifies the customer carrying the pager of the incoming call with a tone or a vibration, and often the telephone number of the caller. Advanced pagers can display short messages from the caller, or provide news updates or sports scores.
Two-way transmissions require both a transmitter and a receiver for sending and receiving signals. A device that functions as both a transmitter and a receiver is called a transceiver. Cellular radio telephones and two-way radios use transceivers, so that back-and-forth communication between two people can be maintained. Early transceivers were very large, but they have decreased in size due to advances in technology. Fixed-base transceivers, such as those used at police stations, can fit on a desktop, and hand-held transceivers have shrunk in size as well. Several current models of handheld transceivers weigh less than 0.2 kg (0.5 lb). Some pagers also use transceivers to provide limited response options. These brief return-communication opportunities allow paging users to acknowledge reception of a page and to respond using a limited menu of options.
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Abstract
wireless communication may be used to transfer information over short distances (a few meters as in television remote control) or long distances (thousands or millions of kilometers for radio communications). The term is often shortened to "wireless". This paper completely deals about a wireless communication, specially about a wireless technology zigbee (802.15.4)IEE, where ZigBee is a standard that defines a set of communication protocols for low-data-rate short-range wireless networking, this paper includes entire architecture of this wireless technology, then it states about the frequencies of operation and its data rates ,interoperability, device types, device roles, zigbee network topologies, zigBee and IEE 802.15.4 communication basics, association and disassociation, binding, zigbee self forming and self healing characteristics, and detail about zigBee and IEE 802.15.4 networking layer functions about then it states about the real time examples where it is been mostly preferred, they are about Home automation security system and light control system.
1.INTRODUCTION
Wireless operations permits services, such as long range communications, that are impossible or impractical to implement with the use of wires. The term is commonly used in the telecommunications industry to refer to telecommunications systems (e.g. radio transmitters and receivers, remote controls, computer networks, network terminals, etc.) which use some form of energy (e.g radio frequency (RF), infrared light, laser light, visible light, acoustic energy, etc.) to transfer information without the use of wires. Information is transferred in this manner over both short and long distances. In which my pick and, i would like exhibit about a wireless technology called as zigbee.
ZigBee is a standard that defines a set of communication protocols for low-data-rate short-range wireless networking. ZigBee-based wireless devices operate in 868 MHz, 915 MHz, and 2.4 GHz frequency bands. The maximum data rate is 250 K bits per second. ZigBee is targeted mainly for battery-powered applications where low data rate, low cost, and long battery life are main requirements.
In many ZigBee applications, the total time the wireless device is engaged in any type of activity is very limited; the device spends most of its time in a power-saving mode, also known as sleep mode. As a result, ZigBee enabled devices are capable of being operational for several years before their batteries need to be replaced.
ZIGBEE IS HIGHLY RELIABLE
Wireless communication is inherently unreliable. Prove this to yourself by walking around with your cell phone, then step into an elevator. Anyone who has used a cell phone has experienced dropped calls or poor reception. It s all because radio waves arejust that: waves. They run into interference patterns, can be blocked by metal, water or a lot of concrete, and vary depending on many complex factors including antenna design, power amplification, and even weather conditions.
Wireless control, however, doesn t usually have the same remedies normally associated with a cell phone call, of moving to find better reception, or waiting to try back later.
The ZigBee Alliance understands this, and so the ZigBee specification reflects this need.
ZigBee achieves high reliability in a number of ways:
IEE 802.15.4 with O-QPSK and DSS
CSMA-CA
16-bit CRCs
Acknowledgments at each hop
Mesh networking to find reliable route
End-to-end acknowledgments to verify data made it to the destination.
ZIGBEE IS COST EFFECTIVE
Most of the entries in the table are the price for a combination MCU and radio. That s right, a single chip solution yields prices in the $3 to $5 range, on average. One of the entries, the Freescale MC13203, is a stand-alone radio that can be combined with any MCU or CPU.
The final two entries, the Digi International XBee and the Panasonic PAN802154, are complete, ready-to-ship, precertified modules. Connect a couple of AA or AA batteries and a sensor or actuator to these boards, put it in some plastic enclosure, and ship your product. These prices are for low-volume sales. OEM and higher volume (10,000 _ units) knock off about a dollar, as a rule of thumb. And, as the competition for the 802.15.4 market stiffens, the prices will likely be brought down even further. Some have predicted that the 802.15.4 radio market will see prices around $1 in quantity over the next three to five years.
But the low cost of ZigBee isn t just about low silicon costs. In addition to low MCU and
radio costs, developing applications for ZigBee is cheap in other ways:
It uses the 2.4 GHz spectrum for worldwide distribution.
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WIRLESS COMMUNICATION
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introduction
Short and long distance transferring of data without the use of electrical wires.
Forms of energy like radio frequency(RF), infrared light, laser light etc are used to transfer information without the use of wires
wireless communications has revolutionized the way societies function.
INFRARED WIRELESS TRANSMISSION
Uses propagation of light waves in the infrared band as a transmission medium for communication
point-to-point system
The transmitter and receiver must be pointed at each other
Path from the transmitter to the receiver must be clear of obstructions
Also called directed LOS systems
Links can be temporarily created for a data exchange session between two users
diffuse systems
Link is always maintained between any transmitter and any receiver.
Transmitter employs a wide transmit beam and the receiver has a wide field-of-view
LOS path is not required
Suited to the wireless LAN application
BLUETOOTH
Technology which enable short-range wireless voice and data communication anywhere in the world.
Replacement of cables.
No need for line of site connection in order to communicate.
Facilitates connections of devices within a range of 10m.
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