MICROWAVE LINK TECHNOLOGY IN COMMUNICATIO

MICROWAVE LINK TECHNOLOGY IN COMMUNICATION

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ABSTRACT:

Bluetooth technology is considered to be the most advanced technologies in

the communication engineering. It is the low power microwave wireless link,

which does not require the line of sight positioning. In this paper the

working and the modes of operation of the bluetooth enabled devices and

their secure data transmission is discussed. The power required for the

operation of the bluetooth devices is very small. The networking between the

bluetooth-enabled devices is done with the microwave link. The network

formed by the bluetooth-enabled devices is known as pico net. It works in

the frequency range of 2.56 GHZ ISM band and it prefers the frequency

hopping technique. The competing technologies with the bluetooth

technology and the advantages of the bluetooth technology over the other

devices used for the microwave communication are explained. As a whole

the paper gives precious information about the advanced bluetooth

technology.


INTRODUCTION:

Bluetooth is a high-speed, low-power microwave

wireless link technology, designed to connect phones, laptops, PDAs and

other portable equipment together with little or no work by the user. Unlike

infrared, Bluetooth does not require line-of-sight positioning of connected

units. The technology uses modifications of existing wireless LAN

techniques but is most notable for its small size and low cost. The current

prototype circuits are contained on a circuit board 0.9cm square, with a

much smaller single chip version in development. It is envisioned that

Bluetooth will be included within equipment rather than being an optional

extra. When one Bluetooth product comes within range of another, (this can

be set to between 10cm and 100m) they automatically exchange address and

capability details. They can then establish a 1 megabit/s link (up to 2 Mbps

in the second generation of the technology) with security and error

correction, to use as required. The protocols will handle both voice and data,

with very flexible network topography.

Moreover, Bluetooth devices won't drain precious

battery life. The Bluetooth specification targets power consumption of the

device from a "hold" mode consuming 30 micro amps to the active

transmitting range of 8-30 milliamps (or less than 1/10th of a watt). The

radio chip consumers only 0.3mA in standby mode, which is less than 3 %

of the power used by a standard mobile phone. The chips also have excellent


power-saving features, as they will automatically shift to a low-power mode

as soon as traffic volume lessens or stops.

WORKING OF BLUETOOTH:

Bluetooth technology achieves its goal by

embedding tiny, inexpensive, short-range transceivers into the electronic

devices that are available today. The radio operates on the globally available

unlicensed radio band, 2.45 GHz. It means there will be no hindrance for

international travelers using Bluetooth-enabled equipment. It supports data

speeds of up to 721 Kbps, as well as three voice channels. The bluetooth

modules can be either built into electronic devices or used as an adaptor. For

instance in a PC they can be built in as a PC card or externally attached

through the USB port.

Each device has a unique 48-bit address from the

IEEE 802 standard. Connections can be point-to-point or multipoint. The

maximum range is 10 meters but can be extended to 100 meters by

increasing the power. Bluetooth devices are protected from radio

interference by changing their frequencies arbitrarily up to a maximum of


1600 times a second, a technique known as frequency hopping. They also

use three different but complimentary error correction schemes. Built-in

encryption and verification is provided.

POWER CLASSES OF BLUETOOTH:

Bluetooth devices are classified according to three

different power classes, as shown in the following table.

Power Class Maximum Output Power1 100 mW (20 dBm)2 2.5 mW (4 dBm)3 1 mW (0 dBm)

But beyond unfettering devices by replacing the

cables, Bluetooth radio technology provides a universal bridge to existing

data networks, a peripheral interface, and a mechanism to form small private

ad hoc groupings of connected devices away from fixed network

infrastructures. Designed to operate in a noisy radio frequency environment,

the Bluetooth radio uses a fast acknowledgment and frequency-hopping

scheme to make the link robust. Bluetooth radio modules avoid interference

from other signals by hopping to a new frequency after transmitting or

receiving a packet. Compared with other systems operating in the same

frequency band, the Bluetooth radio typically hops faster and uses shorter

packets. This makes the Bluetooth radio more robust than other systems.

Short packages and fast hopping also limit the impact of domestic and

professional microwave ovens. Use of Forward Error Correction (FEC)


limits the impact of random noise on long-distance links. The encoding is

optimized for an uncoordinated environment

SECURITY IN BLUETOOTH:

Bluetooth guarantees security at the bit level.

Authentication is controlled by the user by using a 128 bit key. Radio signals

can be coded with 8 bits or anything upto 128 bits. The Bluetooth radio

transmissions will conform to the safety standards required by the countries

where the technology will be used with respect to the affects of radio

transmissions on the human body. Emissions from Bluetooth enabled

devices will be no greater than emissions from industry-standard cordless

phones. The Bluetooth module will not interfere or cause harm to public or

private telecommunications network.

The Bluetooth base band protocol is a combination

of circuit and packet switching. Slots can be reserved for synchronous

packets. Each packet is transmitted in a different hop frequency. A packet

nominally covers a single slot, but can be extended to cover up to five slots.

Bluetooth can support an asynchronous data channel, up to three

simultaneous synchronous voice channels, or a channel, which

simultaneously supports asynchronous data and synchronous voice. It is thus

possible to transfer the date asynchronously whilst at the same time talking

synchronously at the same time. Each voice channel supports 64 kb/s

synchronous (voice) link. The asynchronous channel can support an

asymmetric link of maximally 721 kb/s in either direction while permitting

57.6 kb/s in the return direction, or a 432.6 kb/s symmetric link.


MODES OF OPERATION: An interesting aspect of the technology is the instant

formation of networks once the bluetooth devices comes in range to each

other. A piconet is a collection of devices connected by Bluetooth

technology in an ad hoc fashion. A Piconet can be a simple connection

between two devices or more than two devices. Multiple independent and

non-synchronized piconets can form a scatter net. Any of the devices in a

Pico net can also be a member of another by means of time multiplexing. I.e.

a device can be a part of more than one Pico net by suitably sharing the time.

The Bluetooth system supports both point-to-point

and point-to-multi-point connections. When a device is connected to another

device it is a point-to-point connection. If it is connected to more that one

(up to 7) it is a point to multipoint connection. Several Pico nets can be

established and linked together ad hoc, where each Pico net is identified by a

different frequency hopping sequence. All users participating on the same

Pico net are synchronized to this hopping sequence. If a device is connected

to more than one Pico net it communicates in each Pico net using a different

hopping sequence. A Pico net starts with two connected devices, such as a

portable PC and cellular phone, and may grow to eight connected devices.

All Bluetooth devices are peer units and have identical implementations.

However, when establishing a Pico net, one unit will act as a master and the

other(s) as slave(s) for the duration of the Pico net connection. In a Pico net


there is a master unit whose clock and hopping sequence are used to

synchronize all other devices in the Pico net.

All the other devices in a Pico net that are not the

master are slave units. A 3-bit MAC address is used to distinguish between

units participating in the Pico net. Devices synchronized to a Pico net can

enter power-saving modes called Sniff and hold mode, in which device

activity is lowered. Also there can be parked units, which are synchronized

but do not have a MAC addresses. These parked units have an 8-bit address;

therefore there can be a maximum of 256-parked devices

Voice channels use either a 64 kbps log PCM or the

Continuous Variable Slope Delta Modulation (CVSD) voice-coding scheme,

and never retransmit voice packets. The voice quality on the line interface

should be better than or equal to the 64 kbps log PCM. The CVSD method


was chosen for its robustness in handling dropped and damaged voice

samples. Rising interference levels are experienced as increased background

noise: even at bit error rates up 4%, the CVSD coded voice is found.

COMPETING TECHNOLOGIES:

Besides Bluetooth many other technologies exist

like IrDA, Home RF provides similar or related services. A quick glance

into their scope and properties would help putting all of these into

perspective. The features of Bluetooth first (for the sake of comparison)

• Operates in the 2.56 GHZ ISM band which is globally available

• Uses FHSS

• Can support up to 8 devices in a piconet

• Omni-directional, non line of sight transmission through walls

• 10m to 100m range

• Low cost, $20

• 1mW power

• Extended range with external power amplifier (100 meters)

IrDA

IrDA is an international organization that creates

and promotes interoperable, low-cost infrared data interconnection

standards. IrDA has a set of protocols covering all layers of data transfer and

in addition has some network management and interoperability designs.

Features:


• Range: From contact to at least 1metre. Can be extended to 2 meters.

A low power version relaxes the range objective for operation from

contact through at least 20 cm between low power devices and 30 cm

between low power and standard power devices.

• This implementation affords 10 times less power consumption. These

parameters are termed the required maximum ranges by certain

classes of IrDA

• Featured devices and sets the end user expectation for discovery,

recognition and performance.

• Bi-directional communication is the basis of all specifications

• Data transmission from 9600 b/s with primary speed/cost steps of 115

kb/s and maximum speed up to 4 Mb/s

• Data packets are protected using a CRC (CRC-16 for speeds up to

1.152Mb/s and CRC-32 at 4 Mb/s).

IrDA vs. Bluetooth

Bluetooth and IrDA are both critical to the

marketplace. Each technology has advantages and drawbacks and neither

can meet all users' needs. Bluetooth's ability to penetrate solid objects and its

capability for maximum mobility within the piconet allows for data

exchange applications that are very difficult or impossible with IrDA. For

example, with Bluetooth a person could synchronize their phone with a PC

without taking the phone out of their pocket or purse (this is not possible

with IrDA). The omni-directional capability of Bluetooth allows

synchronization to start when the phone is brought into range of the PC.

The Bluetooth standard defines the layers 1 and 2 of

the OSI model. The application framework of Bluetooth is aimed to achieve


interoperability with IrDA and WAP. In addition, a host of other

applications will be able to use the Bluetooth technology and protocols.

HOMERF:

The HOMERF is a subset of the International Telecommunication Union

(ITU) who is working on the development of a standard for inexpensive RF

voice and data communication. Currently, the HomeRF Working Group

specification provides for wireless Ethernet transmission.

• Range: Maximum 40 meters

• Data rates of 1.2Mbps

The HomeRF Working Group has also developed

the Shared Wireless Access Protocol (SWAP). SWAP is an industry

specification that permits PCs, peripherals, cordless telephones and other

devices to communicate voice and data without the usage of cables. SWAP

is similar to the CSMA/CA protocol of IEEE 802.11 but with an extension

to voice traffic. The SWAP system can either operate as an adhoc network

or as an infrastructure network under the control of a connection point. In an

adhoc network, all stations are peers and control is distributed between the

stations and supports only data. In an infrastructure network, a connection

Point is required so as to coordinate the system and it provides the gateway

to the PSTN (Public Switched Telephone Network). Walls and floors don't

cause any problem in its functionality and some security is also provided

through the use of unique network IDs. It is robust, reliable and minimizes

the impact of radio interference.


Features:

• Operates in the 2.45 GHz range of the unlicensed ISM band

• Range: upto 150 feet

• Employs frequency hopping at 50 hops per second

• It supports both a TDMA service to provide delivery of interactive

voice and CSMA/CA service for delivery of high speed data packets

• The network is capable of supporting upto 127 nodes

• Transmission Power : 100mW

• Data Rate : 1Mbps using 2FSK modulation and 2 Mbps using 4 FSK

modulation

• Voice connections : upto 6 full duplex conversations

• Data Security : Blowfish encryption algorithm (over 1 trillion codes)

• Data Compression : LZRW3-A algorithm

SWAPvsBluetooth

Currently SWAP has more installed base compared to Bluetooth but it

is believed that Bluetooth is eventually going to prevail. Bluetooth is a

technology to connect devices without cables. The intended use is to provide

short-range connections between mobile devices and to the Internet via

bridging devices to different networks (wired and wireless) that provide

Internet capability. HomeRF S0WAP is a wireless technology optimized for

the home environment. Its primary use is to provide data networking and


dial tones between devices such as PCs, cordless phones, Web Tablets and a

broadband cable or DSL modem. Both technologies share the same

frequency spectrum but do not interfere when operating in the same space.

CONCLUSION:

Thus the paper is presented on the advanced

microwave link technology. The secure data transmission and the modes of

operation of the bluetooth-enabled devices are explained. The features of it

over other advancing technologies are discussed. Bluetooth has a

tremendous potential in moving and synchronizing information in a

localized setting. Potential for Bluetooth applications is huge, because we

transact business and communicate more with people who are close by than

with those who are far away - a natural phenomenon of human interaction.

The Bluetooth wireless technology in, e.g., PANs will most likely change

the future way how we handle and access information, similar to how the

mobile phone has changed our behavior in terms of information over the

past ten years.


CONTACT:

Dony Rojerson.M

Albert Ravish . J

Room: 366,S.G.Bobraj Block,

Karunya Hostels,

Karunya Nagar,

Coimbatore.

641114

E-mail: [email protected]

Mobile: 9894317719


mailto:[email protected]

MICROWAVE LINK TECHNOLOGY IN COMMUNICATIO

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