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* BLUETOOTH TECHNOLOGY

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*INTRODUCTION

*Bluetooth is a wireless low power technology for short range, point to point and point to multi point voice and data transfer using radio transmission.

*It was developed at 1994 at Ericsson in Sweden.

*Originally it was build to eliminate the need for cable connections between PDAs and notebook PCs. Later the goals were to enable different devices through a commonly accepted standard for wireless connectivity. 

*It operates on 2.45 GHz radio signals and has an effective range of 10 metres.

*Devices need not be pointing towards each other, as signals are omni-directional.

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Bluetooth Specifications*STANDARD

It is mainly based on the IEEE 802.15 standard. Unlike other wireless standards, the Bluetooth Core Specification provides product developers both link layer and application layer definitions, which support data and voice applications.

The IEEE 802.11communications standard defines the protocol for two types of networks; Ad-hoc and client/server.

The Ad-hoc network is a simple network where communications are established between multiple stations in a given coverage area without the use of an access point or server. The 802.11- standard specifies the etiquette that each station must observe so that all units have fair access to the wireless media

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*SPECTRUM

Bluetooth technology operates in the unlicensed industrial, scientific and medical (ISM) band at 2.4 to 2.485 GHz, using a spread spectrum, frequency hopping, full-duplex signal at a nominal rate of 1600 hops/sec. The 2.4 GHz ISM band is available and unlicensed in most countries.

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*INTERFERENCE

Bluetooth technology's adaptive frequency hopping (AFH) capability was designed to reduce interference between wireless technologies sharing the 2.4 GHz spectrum. This is done by the technology detecting other devices in the spectrum and avoiding the frequencies they are using. The devices hop randomly between frequencies up to 1600 times per second. So, if another device using a 2.4 GHz frequency, then the interference lasts only for about 1/1600 of a second. By then, the devices hop to another frequency.

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*RANGE

Range is application specific and although a minimum range is mandated by the Core Specification, there is not a limit and manufacturers can tune their implementation to support the use case they are enabling. 

Range may vary depending on class of radio used in an implementation:

•Class 3 radios – have a range of up to 1 meter or 3 feet.

•Class 2 radios – most commonly found in mobile devices – have a range of 10 meters or 33 feet.

•Class 1 radios – used primarily in industrial use cases – have a range of 100 meters or 300 feet

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*POWER

Bluetooth technology is designed to have very low power consumption. This is reinforced in the specification by allowing radios to be powered down when inactive.

The Power consumption based on various Bluetooth classes are:

• Class 1: Max Power – 100mW

• Class 2: Max Power – 2.5mW

• Class 3: Max Power – 1mW

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*BLUETOOTH TOPOLOGY

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*The two main topologies are: Piconet Topology and Scatternet Topology.

PICONET TOPOLOGY:•A piconet consists of upto 8 BWTenabled devices.

•When piconet is established, one device sets up frequency-hoppingpattern and other devices synchr--onize their signals to the samepattern.•Each piconet has a differentfrequency-hopping pattern.

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*SCATTERNET TECHNOLOGY:

•Scatternet consists of several piconetsconnected by devices participating inmultiple piconet.

• There is a ‘BRIDGE’ connecting 2piconets which is also a slave individual piconets.

Advantages of Scatternet :

•Higher throughput.

•Multi-hop connections between devices indifferent piconets.

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*BLUETOOTH PROTOCOLS

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APPLICATION FRAMEWORK

AND SUPPORT

HOST CONTROLLER INTERFACE

LINK MANAGER AND L2CAP

RADIO AND BASEBAND

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*RADIO PROTOCOL

• Responsible for the modulation and demodulation of data into RF signals.

• The radio layer describes the physical characteristics a Bluetooth device’s receiver-transmitter component must have.

*BASEBAND PROTOCOL

• Responsible for channel coding and decoding.

• Digitizes the signals received by the radio for passing up the stack.

• Formats the data it receives from the Link Controller (upper protocol) for transmission over the channel.

*LINK CONTROLLER

• Responsible for establishing and maintaining the links between Bluetooth units.

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*The Link Manager Protocol (LMP)

• Handles link setup, authentication, link configuration and security procedures.

• Establishes all connections with the help of baseband protocol.

*Host Controller Interface

• The Host Controller Interface (HCI) defines uniform methods for accessing and controlling the lower layers of the protocol stack (baseband and the link manager).

*Logical Link Control and Adaptation Protocol (L2CAP)

• Responsible for:

Establishing connections across existing ACL ( Asynchronous Connection-oriented) links or requesting an ACL link if one does not already exist.

• Allow many different applications to use a single ACL link through multiplexing.

• Repackaging the data packets it receives from the higher layers into the form expected by the lower layers.

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*Service Discovery Protocol

Defines procedures for-

• Discovering services of other devices.

• Determining the characteristics of those services.

*Telephony Control Protocol Specification (TCS) defines call

• Control signaling for establishing speech and data calls between Bluetooth devices, providing them with telephony services.

*Object Exchange Protocol

• Is a specification for Object data exchange over IR(InfraRed links).

• Examples for using OBEX include exchanging business cards and synchronizing calendar applications.

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*MASTER- SLAVE MODEL

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*Bluetooth Networks use a master/slave model to control when and where devices can send data.

In this model, a single master can be connected upto seven different slave devices. Any slave device can only be connected to a single master device.

The master can send datato any of its slaves and requestdata from them. But, slaves areonly allowed to transmit to andreceive from their master. Theyare not even allowed to talk to other slaves in the same piconet.

* All the slaves synchronize their clocks and hopping sequences to that of the master. A Time Division Duplex (TDD) scheme is used where master and slave alternatively

transmit.

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*HOW DOES THE TECHNOLOGY WORK?

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*The OSI Physical (PHY) layer is represented by the radio and the baseband.

-The Radio is responsible for transmitting and receiving the analog sinal upto a specified range depending upon the radio characteristics.

-The Baseband is responsible for channel coding and decoding and low level timing control and management of the link within the domain of a single packet transfer.

-The Link Controller (LC) is responsible for carrying out link level operations in response to higher level commands from the Link Manager (LM). The LC will manage the process of establishing a link once commanded by LM and will maintain the link once established. The Bluetooth uses a Bluetooth socket to transfer data

between devices.The socket transfers the data serially, which means one

byte at a time.

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*PACKETS:

*Now let us discuss about the Bluetooth packet structure that are used for communication over ACL links. The packets are broken down into their constituent parts such as access code, packet header, payload header, and payload. Each packet type has a different level of error correction and protection and different size payloads.

*The Access code is used to detect the presence of a packet and to address the packet to a specific device. The header packet contains control information associated with the packet such as the address of the Slave for which the packet is intended. Finally, the payload contains the message information.

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*MODULATION CHARACTERISTICS

*The Bluetooth modulation scheme is GFSK (Gaussian Frequency Shift Keying) with a symbol rate of 1Ms/s and modulation index between 0.28~0.35. The Gaussian-shaped, binary FSK modulation minimizes transceiver complexity. Using positive frequency deviation a binary one is represented while a binary zero is represented by a negative frequency deviation.

*During one time slot the data can change value every 1us, so the transmit frequency oscillates back and forth around the channel center frequency. The minimum deviation can never be smaller than 115kHz. Maximum frequency deviation is between 140 kHz and 175 kHz.

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*AT THE RECEIVER END*3 Types of Hardware is required to

complete the conversion, they are:

I.DAC CONVERTER:This device is used to convert digital signal to analog signal. In this case when binary data arrives as input of this device, it takes them as digital signal and converts it as analog signal using some conversion protocol(eg: NRZ,RZ,quadrant etc.)

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II.Base Band Generator:In this stage the converted analog signal is amplified to the acceptable amplitude for transmission.

In this process:

Consider a carrier wave (sine wave) of frequency fc and amplitude A given by:

c(t) = A.sin(2πfct),.Let m(t) represent the modulation waveform. For this example we shall take the modulation to be simply a sine wave of a frequency fm, a much lower frequency (such as an audio frequency) than fc:

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m(t) = M.cos(2πfmt + Φ)

where M is the amplitude of the modulation. We shall insist that M<1 so that (1+m(t)) is always positive. Amplitude modulation results when the carrier c(t) is multiplied by the positive quantity (1+m(t)):

y(t)= [1 + m(t)].c(t)

= [1 + M.cos(2πfmt + Φ)].A.sin(2πfct)

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*III. RADIO:*Now that the signal is amplified to an acceptable range, the radio transmits the analog signal to the receiver device. Hence the format of the raw data conversion is done.

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*The technology of Bluetooth centers around a 9mm x 9mm microchip, which functions as a low cost and short range radio link. Bluetooth Technology provide a 10 meter personal bubble that support simultaneous transmission of both voice and data for multiple devices. Up to 8 devices can be connected in a piconet, and up to 10 piconets can exist within the 10 meter bubble.

*In order to establish new connections the procedures inquiry and paging are used.

• INQUIRY- If two Bluetooth devices know absolutely nothing about each other, then one must run a query to try to discover the other, and any device listening for such a request will respond with its address, and possibly its name and other information.

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• PAGING- Now, both the devices know each other’s addresses which was found in the enquiry step. Now, Paging is done which is the process of forming a connection between two bluetooth devices.

• After the connection has been established a device can be in any of the four nodes:

oActive mode: In this mode, the device is actually transmitting or receiving date.

oSniff mode: This is a power saving mode where the device is sleeping and is only listening for transmission.

oHold mode: In this mode, a device can sleep for a defined period and then returns back to active mode.

oPark node: It is the deepest sleep mode. A device enters this mode when its master asks it to, and again wakes up, on its master’s command.

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ENQUIRY PAGING

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*OBTAINING BLUETOOTHTECHNOLOGY

QUALIFICATION

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In order to obtain qualification of a component or product, the manufacturer may use a test house for two services:

oThe test house is contracted to make tests to a Bluetooth test specification, and to produce a test report containing the results of the tests.

oAn employee of the test house who is appointed by the Bluetooth SIG as a Bluetooth Qualification Body(BQB) reviews evidence submitted by the manufacturer in a Compliance Folder (CF), and if satisfactory, the BQB submits the product to the Bluetooth Qualification Administrator(BQA) for listing on the Bluetooth Qualified Products List (BQPL).

The list that follows gives more details on the tests necessary for qualification:

oRF tests are required to made once for each new PCB design.

oUSB, UART or BCSP variants need not be retested for RF as the HCI does not affect the radio performance.

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oThe Bluetooth Qualification Body(BQB) may require one or more BB timing tests to be repeated for each new PCB design.

oBoth module manufacturers and end product users can use a software component that is prequalified at Baseband(BB) and LM.

oIf the new design includes the upper layer stack components or Bluetooth profiles, these must also be qualified.

oSoftware components affecting profiles must also be qualified. This could be done by developing and qualifying your own profile software components, or by buying in prequalified software components and integrating them into the end product.

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*WHY CONVERT TODIGITAL?

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*It is possible to directly modulate analog signals into a radio without converting them into digital format. Then why we do not go for this?

There are several reasons:

-Digital signals tend to be more robust in the noisy environment

-Encoding into a digital format means easy error detection and error correction.

Ofcourse in the case of Bluetooth wireless technology, the baseband is designed to handle only digital signals, so transmitting analog signals is not even an option.

Bluetooth specification forces a low data rate, so the codecs are required to compress the signal as well as convert them to digital from analog.

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*TRANSMISSION*Bluetooth uses either a 64 kb/s log PCM format (A-law

or m-law) or a 64 kb/s CVSD(Continuous Variable Slope Delta Modulation) for audio transmission.

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*BLUETOOTHSECURITY

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In any wireless networking setup, security is a concern. Devices can easily grab radio waves out of the air, so people who send sensitive information over a wireless connection need to take precautions to make sure those signals aren't intercepted. Bluetooth technology is no differentBluetooth offers several security modes, and device

manufacturers determine which mode to include in a Bluetooth-enabled gadget. In almost all cases, Bluetooth users can establish "trusted devices" that can exchange data without asking permission.

When any other device tries to establish a connection to the user's gadget, the user has to decide to allow it. Service-level security and device-level security work together to protect Bluetooth devices from unauthorized data transmission. Security methods include authorization and identification procedures that limit the use of Bluetooth services to the registered user and require that users make a conscious decision to open a file or accept a data transfer.