Bluetooth Technology And Usage Computer Science Essay

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ABSTRACT: Bluetooth is a novel technology of short range distance wireless communications. In recent years Bluetooth technology has been regarded as a in expensive solution for wireless communication. The main design application of blue tooth has been focused on replacing cables between handheld devices. One of the most popular applications using Bluetooth technology in future is wireless telecommunication such as public internet access via Bluetooth devices. Bluetooth is radio frequency specification for short range distances and point to point, point to multipoint voice and data transfer. Bluetooth operates in ISM band with 2.4GHz frequency range. It provides connection between stationary and mobile communication environments. It delivers rapid, ad hoc network opportunities and also it provides automatic, unconscious connections between devices in future. In this report mainly we discuss about modulation and coding techniques in Bluetooth technology.

1. INTRODUTION: Bluetooth is a communication protocol it provides wireless communication between different types of devices like mobile phone, PDAs, laptops, digital cameras and desktops. Exchange of data can be done by using radio wave. The data exchange can be done securely Bluetooth is used for relatively short range distances about few meters (10 to 100). Bluetooth is a wireless personal area network (WPAN). The design architecture of Bluetooth is mainly providing low power wireless transmission over short range distances to a relative low cost.

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The word Bluetooth comes from the name Harold Bluetooth. He was the late 10th century king of Denmark and Norway. The specification of Bluetooth was developed in 1994 by Jaap Haartsen. He had worked in Ericsson mobile platform. In 1998 the Bluetooth SIG (special interest group) was formed by different company's they are Ericsson, IBM, Nokia, Intel and Toshiba. The main purpose of this group is to spread Bluetooth technology and also to develop Bluetooth standard. Since 1998 onwards this group grown up and now it consists of 9000 companies in Bluetooth SIG group. Bluetooth is based on IEEE 802.15 standard. It handles communication standards for wireless personal area networks.

The choice of frequency band one of the major factors in system design. The Bluetooth operates in the unlicensed 2.4GHz ISM (industrial scientific and medical) band. In term unlicensed means anybody just go to shop and bye a device and start to transmit data without requiring any permission. It means anybody can use this band. Bandwidth of ISM band is about 800MHz depends on country. United states use 2.40-2.4835GHz range. Advantage of this band is no need of line of sight communication because microwave can travel through mater also. Interference is the problem to use this band several modulation techniques' is used to reduce this problem. Frequency hopping is used in Bluetooth technology to reduce interference and fading in a channel.

Bluetooth system supports point to point, point to multipoint communication. In point to multipoint connection several Bluetooth devices can share the single channel two are more Bluetooth devices sharing the channel from piconet. The network consist of 8 devices in a group is called piconet. It consists of one master and up to seven slaves in a wireless group master devices can communicate with other slaves. By using Bluetooth technology protocol master device can interconnect up to seven active devices remaining 250 devices be inactive. Master device can get into active states at any time of remaining devices at any time slave can become the master. The master can switch in round robin fashion from one device to another devices the specification of Bluetooth can allow one or more piconets work together to form a Scatternet.

In this report we discuss physical layer and modulation techniques of Bluetooth technology in section2. In section3, coding technique in Bluetooth Technology. In section 4 applications of Bluetooth. Finally, section5 has the conclusion.

2. PHYSICAL LAYER:

Physical layer concerns transmission and reception of wireless waveforms and processing of digital data including protocol processing. Physical layer mostly concerned with modulation and demodulation of digital data this take is done out by transceivers. Mostly in sensor network one of the challenges to find modulation techniques and design architecture of transceiver. It is simple, low cost and robust to provide required service.

In wireless sensor networks some of the important design consideration to design physical layer and transceiver. Low power consumption, low cost, less complexity to implement, small transmission power, required data rate, mobility, most of time the hardware system should switched off or operated in low power standby mode.

2.1 MODULATION TECHNIQUE:

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Bluetooth is short range communication device using radio waves. It is operating the frequency of 2.4GHz ISM band with a bandwidth of 80MHz depending on what country you are in. To overcome problems of saturated air waves Bluetooth developers provide several modulation techniques one is FSK, GFSK and spread spectrum via frequency hopping.

In Bluetooth mainly we are using frequency shift keying modulation scheme. In FSK positive deviation can represent with binary one and negative deviation can represent with binary zero with respect to center frequency.

Fig 1.frequency shift keying []

The data rate in FSK is very low compare to f1and f2 frequencies. Bluetooth operates in GHz but also it allows MHz data rates. For a given bandwidth to minimize error rate, f1and f2 must be choosing according to this equation.f1-f2=1.43/Tb here Tb is time allocated for digital one or zero. The advantage of FSK is generation of signals is very easy, making it a low cost technique. FSK system is insensitive to additive noise due to this reason information is contained in the frequency of the signal is being sent. The receiver and transmitter must know what center frequency is and what range of deviation allowed. In Bluetooth maximum deviation of center frequency is 175 KHz .To demodulate the signal at receiver side we must need frequency discriminator it demodulates the signal. The Drawback of this system is it does not use bandwidth effectively due to these reason the frequency transmission from one to zero the modulator may cause to change in frequency output. Due to change in output the required bandwidth to transmit signal is more. but in ISM band limited bandwidth spectrum .to overcome this problem Gaussian frequency shift keying is used in Bluetooth technology.

GFSK: Gaussian frequency shift keying is a variant of a frequency shift keying modulator. every signal can be represented as -1(0)or1.in GFSK Gaussian filter is used to smoothen the binary values the signal passes through Gaussian filter which limits the spectral width. By using Gaussian filter we can improve efficient bandwidth usage.

GFSK use a bandwidth bit period product of 0.5and modulation index in between 0.28 and 0.35. Minimum frequency deviation of every transmission is

Fmin={Fmin+;Fmin-} Fmin means less of above frequencies which corresponds to 10 10 sequence but it should be no smaller then ±80% of frequency deviation of

Fig 2.GFSK modulation []

00001111 sequences the minimum frequency deviation is no smaller then 115KHz. The time difference between ideal symbol period and actual time is called crossing error. It must be less than ±1/8 of a symbol period. Implementation of this method is more expensive because its need extra filters before FM modulator. Some of the Bluetooth modules use regular FSK because to avoid extra cost.

2.1.2 SPREAD SPECTRUM: Spread spectrum is one of digital coding technique used in wireless Bluetooth technology. By using spread spectrum the narrow band signal spreads over larger portion of available radio frequency band. it increase number of bits transmitted and amount of bandwidth used. Advantage of the spread spectrum is more resistant to interference and more secure against interception. This technology used in card less phones, WLANs. The spread signal having low power density it can spread over expanded band width of transmitter. Result this technology having resistance to variety of conditions like interference, jamming, interception. In Bluetooth systems the spread signal spectrum by using frequency hopping technique.

Fig.3.spread spectrum signal[]

By using pseudo random sequence the transmitter change one frequency to another frequency at a specific hop rate. Normal hop rate is 1600 hop/sec throughout 79 different channels each channel spaced apart from 2402 to 2480MHz.

Several Bluetooth devices can share single channel by using piconet. Piconet can support 8 inter connected devices like one master and seven slaves. The relationship is formed during the connection of piconet. The devices that can participate in piconet are synchronized in terms of time and hop of the same channel. Every device has internal clock system to determine timing and hopping of transceiver. The timing and hopping of piconet channel is determined by clock of the master. Once piconet is established the master clock communicates with slaves.

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One of the advantages of spread spectrum can be seen from below equation developed by Shannon in the 1940's while constructing his famous theory of classical information

C=Wlog2 (1+s/n) ; c=channel capacity, w=bandwidth, s/n=signal to noise ratio.

In the above equation we can see that if bandwidth increases it increases the channel capacity to transmit error free information. Shannon theory tells that increase in bandwidth is high we can send message with error free. Actual detection of original signal is impossible to get, still there exist a threshold point of interferences this called jamming margin, it directly related to process gain. Gm=W/R; here Gm is process gain, W=bandwidth, R= rate of information transfer. Due to this reason Bluetooth technology uses spread spectrum frequency hopping to reduce interference in the channel and also gives the signal improved security.

Different countries are used different frequency bands in Bluetooth technology as shown bellow.

Country

Frequency range

RF Channels

Europe &USA

2400 -2483.5 MHz

F=2402+kMHz

K=0,..,78

France

2446.5 -2483.5 MHz

F=2454+kMHz

K=0,..,22

Japan

2471 - 2497 MHz

F=2473 +k MHz

K=0,..,22

Spain

2445 -2475 MHz

F=2449+k MHz

K=0,...,22

3. CODING TECHNIQUS: data link layer is placed directly above physical layer of network model. Coding techniques is done in data link layer. The main features of data link layer are Packetization of data, channel setup and access, error control and security. In Bluetooth technology data transmission is done in the form of packets. Variable frame length packet format is used in Bluetooth technology. The general packet format is

Fig.5. the packet format of Bluetooth

3.1 ACCESS CODE: Bluetooth contains 72 bit access code it identifies the packets to transmit over Bluetooth channel. All data packets can share same access code in a channel. Access code is used for to find out which device is in range this technique is called device paging. It is also used for inquires (to find new devices). Each Bluetooth device can monitor the access code of packet. If any devices are not mentioned address directly or indirectly rest of packet ignored. It is also used for determine receive timing. Access code is false tolerant.

3.2 PACKET HEADER: Bluetooth consist of 18 bit packet header. 18 bit header contains the following information i.e. 3 bit is used for target device address it means device address on the Bluetooth channel it also provide broadcast address. Four bit is used for to identify the type packet data, 3 bit is used for flow control, packet ACKs, sequencing each field take one bit. Remaining 8 bit header is used for CRC. Each bit is transmitted three times in a row to protect a header from transmission errors.

3.3 PAYLOAD: payload field carries the actual data of the packet. Payload mainly consist of three segments i.e. payload header, payload body, payload CRC. It indicates the length of the packet and flow control, fields for logic channels. Total bits (0-2745) scheduled into five slots because Bluetooth time slot is 625µsec then it sends maximum 625bits. Payload mainly consists of two fields i.e. voice and data fields it also called as synchronous and asynchronous field. ACL packets have only data fields and SCO packets have only voice field. DV packets have both the fields voice field has a fixed length. It is 240 bits for HV packets and 80 for DV packets.

3.4 ERROR CORRECTION: error correction is very important for communication system. Bluetooth devices use three types of error correction schemes 1/3FEC, 2/3FEC and ARQ. FEC means forward error correction it means if receiver detects an error then it will try to rectify the error before passing. The main purpose is reducing number of re transmission when an error is occurred. ARQ scheme if any error occurred it request to retransmit data. It is used for error free environment. The choice of error correction scheme is depends on implementation.

4. APPLICATIONS: Bluetooth technology has huge applications. The following list represents only small set of potential applications.

Wireless communication between mobile phone and hands free headset.

Link between mobile phone and laptops.

It is used for to transmit health sensor data from medical devices to mobile phones.

Dial up internet access is used for PDAs and personal computers.

Bluetooth is used in wireless mouse and keyboard.