By Aashish Jindal

INTRODUCTION

There are various generations in the development of wireless communication networks as : (1) First generation (1G) , is traditional analog cellular and much for the voice only. (2) 2G, is digital standard for voice that allows low speed data transfer. (3) 3G , it has the basis of packet switching. In packet switching data is digitized, broken into small chunks called packets, surrounded it with information that allows it to be verified by the receiver and sent off. The receiver gets the packets, verifies them and reassembles the data.

The benefits of 3G are huge, treating voice as just another kind of data means that far more traffic can be carried in the same amount of bandwidth. This is important as bandwidth is the most scarcest resource for mobile communications. But the main obstacle behind 3G is the cost.

In an attempt to standardize data transfer and synchronization between disparate mobile devices in the short-distance range, Intel and Microsoft established in 1998 a major industry consortium that included IBM, Ericsson, Toshiba, Nokia and Puma Technology code named Bluetooth which was widely advertised as just over the horizon. The idea behind Bluetooth is that, it is a wireless protocol meant to replace all cables used in computers and other electronic gear. Bluetooth is designed to use a very low power signal to connect devices that are within the ten meters range of each other. The target price for the chipset needed to make any device to understand Bluetooth is around $10.Actual transceivers cost more than that. Right now Bluetooth PC cards for laptops and desktops are in the neighborhood of $100.

Bluetooth is a technology standard using short-range radio links. The standard defines a uniform structure for a wide range of devices to communicate with each other, with minimal user effort. Its key features are robustness, low complexity, low power and low cost. The technology also offers access to wireless LANs, the mobile phone network and the Internet for a host of home appliances and portable handled interfaces.

Wireless :

Wireless media is any media that does not use electrical or optical conductors to transmit electronic signals. It can be either line of sight communication as in case of infrared or non line of sight as in case of radio links. An access point is a transceiver that accepts wireless signals from other devices and provides a wired connection to LAN.

Wireless LANs :

Using Radio Frequency (RF) Technology, wireless LANs receive and transmit data over the air, minimizing the need for wired connections. In a typical wireless LAN configuration, a transmitter/receiver (transceiver) device, called an access point, connects to the wired network from a fixed location using standard cabling. At a minimum the access point receives, buffers and transmits data between wireless LAN and the wired network infrastructure. .

End users access the wireless LAN through wireless-LAN adapters, which are implemented as PC cards in computers. These cards provide an interface between the client network operating system (NOS) and the airwaves via an antenna.

Bluetooth :

The Bluetooth Special Interest Group (SIG) is an industry group consisting of the leaders in the telecommunication and the computing industries , that are driving development of the technology and bringing it to the market. This group is in charge of developing the bluetooth specification.

Bluetooth enables the creation of wireless Internet gateways that allows Bluetooth equipped devices to access the Internet quickly and easily. It enables users to connect a wide range of computing and telecommunications devices easily and simply, without the need to buy, carry, or connect cables. It delivers opportunities for rapid ad hoc connections, and the possibility of automatic, unconscious, connections between devices. It will virtually eliminate the need to purchase additional or proprietary cabling to connect individual devices. Also it is the idea of SIG group that because Bluetooth wireless technology can be used for a variety of purposes, it will also potentially replace multiple cable connections via a single radio link.It creates the possibility of using mobile data in a different way, for different applications such as "Surfing on the sofa", "The instant postcard", "Three in one phone" and many others.

Alternatives To Bluetooth Technology :

There are couple of ways to get around using wires. One is to carry information between components via beam of light in the Infrared spectrum. It is used in most TV remote systems, and with a standard called IrDA. Bluetooth borrows from those specifications to enable file sharing and data transfers between devices. Infrared is reliable and cheap communication but there are certain drawbacks of this technology. First , Infrared is "line of sight". Secondly, Infrared is almost always a "one-to-one" technology.

The second alternative to wires, cable synchronizing, is a little more troublesome than Infrared. In synchronizing, PDA (personal digital assistant) is attached to the computer and made sure that data on the PDA and the data on the computer match and made sure that one has the correct cable or cradle to connect the two , but this type of synchronizing can be a real problem sometimes.

Bluetooth has the capability of automatic synchronization of PDA, laptop, cell phones etc. bluetooth has borrowed some things from the existing wireless standards including Motorola’s Piano, Digital Enhanced Cordless Telecommunications (DECT) , IEEE 802.11 and IrDA etc.

The IEEE 802.11 Standard :

It defines 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 station in a given coverage area without the use of an access point or server. Each station must observe , so that all units have fair access to the wireless media.

The client/server network uses an access point that controls the allocation of the transmit time for all stations and allows mobile stations to roam from cell to cell. The access point is used to handle traffic from the mobile radio to the wired or wireless backbone of this network.

The Name : Bluetooth

The name of Bluetooth comes from a Dutch ruler " Harald Bluetooth" in the late 900 A.D. , who ruled greater part of Denmark and Norway during his reign. He managed to unite Denmark and part of Norway into a single kingdom then introduced Christianity into Denmark.

Bluetooth Features :

Bluetooth communicates over a frequency of 2.54 gigahertz , which has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM). A number of devices already take advantage of the same radio-frequency band. Making sure that Bluetooth and these other devices don’t interfere with one another has been a crucial part of the design procedure. Bluetooth

•  
• Uses GFSK (gaussian frequency shift keying modulation)
•  
• Uses FHSS (frequency hopping spread spectrum )
•  
• Can support upto 8 devices in a piconet
•  
• Omni-directional, non line of sight transmission through walls
•  
• 10 mt. To 100 mt. range
•  
• 1 mW power
•  
• Extended range with external power amplifiers (100 mts.)
•  
• Simultaneous handle both voice and data
•  
• Uses time devision duplex system
•  

Functional Blocks In Bluetooth System :

The Bluetooth system consists of a radio unit , a link control unit, and a support unit for link management and host terminal interface functions.

Frequency-Hopping Spread Spectrum Technology :

In the frequency hopping technique data is modulated with a carrier signal that hops from frequency to frequency as a function of time over a wide band of frequencies. The carrier frequency changes periodically. This technique reduces interference because an interfering signal from a narrowband system will only affect the spread spectrum signal if both are transmitting at the same frequency at the same time. Thus the aggregate interference is very low ,resulting in little or no bit errors.

A hoping code determines the frequencies that radio transmits and in which order. To properly receive the signal , the receiver must be set to some hoping code and listen to the incoming signal at the right time and correct frequency. It is possible to have operating radios use spread spectrum within the same frequency band and not interfare,assuming they are using different hopping sequence. While one radio is transmitting at a particular frequency, the other radio is using a different frequency. A narrowband carrier that changes frequency in a pattern is known to both receiver and transmitter.

Time Division Duplexing :

Duplexing to provide simultaneous, two way communication services is done in time division. Transmit and receive occur on the same frequency but at the different times on a fixed interval. And because of relative speed of switching between the two functions, simultaneous , two way communication is preserved.

ARCHITECTURAL OVERVIEW

RADIO MODULE

Bluetooth radio is an integral part of the Bluetooth device as it provides an electrical interface for transfer of packets on a modulated carrier frequency using wireless bearer services. The radio requires a very small and efficient antenna ( smart antenna), a good RF front end on chip, power controller, GFSK modulator and a transmit/receive switch for it works as a transceiver.

Bluetooth Radio Modem IC:

The radio modem performs the GFSK modulation and demodulation, symbol and frame timing recovery. The modem also contains a fully integrated radio transceiver and frequency hopping synthesizers on a single chip.

Bluetooth Controller IC :

The controller implements the basebands protocol and functions. On the receive side it performs error detection and de-scrambling. The link controller hardware implements the basic, repetitive actions of paging, inquiry, page and inquiry scan etc. It also provides a USB and audio CODEC interface to the host system.

Radio Bands And Channels :

The Bluetooth system is operating in the 2.4 GHz ISM (Industrial ,Scientific,Medicine) band. In a vast majority of countries around the world the range of this frequency band is 2400 - 2483.5 MHz. Some countries have however national limitations in the frequency range. In order to comply with these national limitations, special frequency hopping algorithms have been specified for these countries. It should be noted that products implementing the reduced frequency band will not work with products implementing the full band. The products implementing the reduced frequency band must therefore be considered as local versions for a single market.

In some countries 23 channels instead of 79 are used.

The hoping sequence is unique for the piconet and is determined by the Bluetooth device address of the master ; the phase in the hoping sequence is determined by the Bluetooth clock of the master. The channel is divided into time slots, each 625 microsec in length, where each slot corresponds to an RF hop frequency. The nominal hop rate is 1600 hops/s. All Bluetooth devices participating in the piconet are time and hop-synchronized to the channel.

Channel spacing is 1 MHz. In order to comply with out-of-band regulations in each country, a guard band is used at the lower and upper band edge.

The Modulation is GFSK (Gaussian Frequency Shift Keying). A binary one is represented by a positive frequency deviation, and a binary zero is represented by a negative frequency deviation.

------------------------------------------------------------------------------------------------------------

BASEBAND MODULE

It is the most comprehensive part of the Bluetooth protocol and most important. Baseband is the layer that controls the radio. The frequency hop sequence are provided by this layer. It is the physical layer of the Bluetooth which manages physical channels and links apart from other services like error correction, data whitening, hop selection and Bluetooth security. Baseband lies on the top of the Bluetooth radio in Bluetooth stack and essentially acts as a link controller and works with link manager for carrying out link levels routines like link connection and power control. Baseband also manages asynchronous and synchronous links, handles packets and does paging and inquiry to access and inquire the Bluetooth devices. Baseband transceiver applies a TDD (time division duplex) scheme, therefore apart from different hoping frequency, the time is also slotted. On the channel, information is exchanged through packets. Each packet is transmitted on a different hop frequency. A packet nominally covers a single slot, but can be extended to cover up to five slots.

The Bluetooth protocol uses a combination of circuit and packet switching. Slots can be reserved for synchronous packets. 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. Each voice channel supports a 64 kb/s synchronous (voice) channel in each direction. The asynchronous channel can support maximal 723.2 kb/s asymmetric (and still up to 57.6 kb/s in the return direction), or 433.9 kb/s symmetric.

The Bluetooth system provides a point-to-point connection (only two Bluetooth units involved), or a point-to-multipoint connection. In the point-to-multipoint connection, the channel is shared among several Bluetooth units. Two or more units sharing the same channel form a piconet . One Bluetooth unit acts as the master of the piconet, whereas the other unit(s) acts as slave(s). Up to seven slaves can be active in the piconet. The device that initiates the connection is the master of the piconet.In addition, many more slaves can remain locked to the master in a so-called parked state. These parked slaves cannot be active on the channel, but remain synchronized to the master. Both for active and parked slaves, the channel access is controlled by the master.

Multiple piconets with overlapping coverage areas form a scatternet. Each piconet can only have a single master. However, slaves can participate in different piconets on a time-division multiplex basis. In addition, a master in one piconet can be a slave in another piconet. The piconets shall not be frequency-synchronized. Each piconet has its own hopping channel.

Physical Links :

Between master and slave(s), different types of links can be established. Two link types have been defined:

• Synchronous Connection-Oriented (SCO) link
•  
• Asynchronous Connection-Less (ACL) link
•  

1.SCO Link

The SCO link is a symmetric, point-to-point link between the master and a specific slave. The SCO link reserves slots and can therefore be considered as a circuit-switched connection between the master and the slave. The SCO link typically supports time-bounded information like voice. The master can support up to three SCO links to the same slave or to different slaves. A slave can sup-port up to three SCO links from the same master, or two SCO links if the links originate from different masters. SCO packets are never retransmitted.

The master will send SCO packets at regular intervals, the so-called SCO interval to the slave in the reserved master-to-slave slots. The SCO slave is always allowed to respond with an SCO packet in the following slave-to-master slot unless a different slave was addressed in the previous master-to-slave slot. If the SCO slave fails to decode the slave address in the packet header, it is still allowed to return an SCO packet in the reserved SCO slot.

2. ACL Link

In the slots not reserved for SCO links, the master can exchange packets with any slave on a perslot basis. The ACL link provides a packet-switched connection between the master and all active slaves participating in the piconet.Between a master and a slave only a single ACL link can exist. For most ACL packets, packet retransmission is applied to assure data integrity.

A slave is permitted to return an ACL packet in the slave-to-master slot if and only if it has been addressed in the preceding master-to-slave slot. If the slave fails to decode the slave address in the packet header, it is not allowed to transmit.

ACL packets not addressed to a specific slave are considered as broadcast packets and are read by every slave. If there is no data to be sent on the ACL link and no polling is required, no transmission shall take place.

PHYSICAL CHANNEL

The channel is represented by a pseudo-random hopping sequence hopping through the 79 or 23 RF channels. The hopping sequence is unique for the piconet and is determined by the Bluetooth device address of the master; the phase in the hopping sequence is determined by the Bluetooth clock of the master. The channel is divided into time slots where each slot corresponds to an RF hop frequency. Consecutive hops correspond to different RF hop frequencies. The nominal hop rate is 1600 hops/s. All Bluetooth units participating in the piconet are time- and hop-synchronized to the channel.

Time Slots :

The channel is divided into time slots, each 625 µs in length. The time slots are numbered according to the Bluetooth clock of the piconet master. In the time slots, master and slave can transmit packets.

A TDD scheme is used where master and slave alternatively transmit. The master starts its transmission in even-numbered time slots only, and the slave starts its transmission in odd-numbered time slots only. The packet start is aligned with the slot start. Packets transmitted by the master or the slave may extend over up to five time slots.

The RF hop frequency remains fixed for the duration of the packet. For a single packet, the RF hop frequency to be used is derived from the current Bluetooth clock value. For a multi-slot packet, the RF hop frequency to be used for the entire packet is derived from the Bluetooth clock value in the first slot of the packet. The RF hop frequency in the first slot after a multi-slot packet is used the frequency as determined by the current Bluetooth clock value.

Packet Format:

The data on the piconet channel is conveyed in packets. The general packet format is shown in fig. Each packet consists of 3 entities : the access code, the header, and the payload.

Each packet starts with an access code. If a packet header follows, the access code is 72 bits long, otherwise the access code is 68 bits long. This access code is used for synchronization, DC offset compensation and identification. The access code identifies all packets exchanged on the channel of the piconet. Each piconet uses a unique access code to identify the packets.

The header contains the information for packet acknowledgement, packet numbering for out of order packet reordering, flow control , slave address and error check for headers.

Payload data formats come in two basic forms : real time audio and data. ACL link contain only data while SCO link may contain both. The payload also carries a 16 bit length CRC ( cyclic redundancy check ) for error detection and correction in the payload. SCO packet do not contain CRC.

HOST CONTROLLER INTERFACE

The link manager protocol (LMP), baseband and radio are typically implemented in the Bluetooth hardware modules. These modules can interface to the host using different interfaces. However, all Bluetooth controllers should implement the Bluetooth Host Controller Interfaces(HCI). Essentially this interface provides a uniform method of accessing the Bluetooth baseband capabilities. The HCI exist across 3 sections : Host, Transport Layer, Host Controller. Some link controller hardware may include an HCI layer above the link manager. The firmware layer is used to isolate the Bluetooth baseband and link manager from a transport protocol such as USB or RS-232 . This allows a standard host processor interface to bluetooth hardware. An HCI driver on the host is used to interface a Bluetooth application with the transport protocol. Three transport mechanism are supported : USB, RS-232 and UART.

Using HCI , a Bluetooth application can access Bluetooth hardware without knowledge of the transport layer or other hardware implementations details. Hardware module usually implement the lower layers-radio, baseband and LMP. Then the data to be sent to LMP and baseband travels over the physical buses like USB. A driver for this bus is required on the "host" , that is the PC, and a "host controller interface" is required on the Bluetooth hardware card to accept data over the physical bus.

HCI FUNCTIONAL ENTITIES :

The HCI is broken into 3 separate parts :

1.  
2. HCI Firmware ( Location : Host Controller ) HCI firmware is located on the host controller, (e.g. The actual Bluetooth hardware device ). The HCI firmware implements the HCI commands for the Bluetooth hardware by accessing baseband commands , Link manager commands, hardware status registers, control registers, and event registers.
3.  
4. HCI Driver ( Location : Host ) This is the driver for host controller interface, which is located on the host ( e.g. Software entity) above the physical bus, and formats the data to be accepted by the Host Controller on the Bluetooth hardware.
5.  
6. Host Controller Transport Layer (Location : Intermediate Layers ) The HCI driver and Firmware communicate via the Host Controller Transport Layer , i.e. a definition of the several layers that may exist between the HCI Driver on the host system and the HCI Firmware in the Bluetooth hardware. These intermediate layers, the Host Controller Transport Layer, should provide the ability to transfer data without intimate knowledge of the data being transferred.
7.  

The Bluetooth protocol stack can be divided into four layers according to their purpose including the aspect whether Bluetooth SIG has been involved in specifying these protocols.

The Bluetooth Core protocols comprise exclusively Bluetooth-specific protocols developed by the Bluetooth SIG. RFCOMM and the TCS binary protocol have also be developed by the Bluetooth SIG . The Bluetooth Core protocols (plus the Bluetooth radio) are required by most of Bluetooth devices, while the rest of the protocols are used only as needed.

Together, the Cable Replacement layer, the Telephony Control layer, and the Adopted protocol layer form application-oriented protocols enabling applications to run over the Bluetooth Core protocols.

Link Manager Protocol (LMP):

The link manager protocol is responsible for link set-up between Bluetooth devices. This includes security aspects like authentication and encryption by generating, exchanging and checking of link and encryption keys and the control and negotiation of baseband packet sizes.

Furthermore it controls the power modes and duty cycles of the Bluetooth radio device, and the connection states of a Bluetooth unit in a piconet.

Logical Link Control And Adaptation Protocol (L2CAP) :

The Bluetooth logical link control and adaptation protocol (L2CAP) adapts upper layer protocols over the baseband. It can be thought to work in parallel with LMP in difference that L2CAP provides services to the upper layer when the payload data is never sent at LMP messages.

L2CAP provides connection-oriented and connectionless data services to the upper layer protocols with protocol multiplexing capability, segmentation and reassembly operation, and group abstractions. L2CAP permits higher level protocols and applications to transmit and receive L2CAP data packets up to 64 kilobytes in length.

Service Discovery Protocol (SDP) :

Discovery services are crucial part of the Bluetooth framework. These services provide the basis for all the usage models. Using SDP, device information, services and the characteristics of the services can be queried and after that, a connection between two or more Bluetooth devices can be established.

Other Protocols :

Like SDP, RFCOMM is layered on top of the L2CAP. As a ‘cable replacement’ protocol, it provides transport capabilities for high-level services (e.g. OBEX protocol) that use serial line as a transport mechanism.

On top of the link and transport protocols, the applications still need some specific protocols to complete the protocol stack. In the Bluetooth architecture, the application-specific protocols are added on top of RFCOMM or directly on the L2CAP. The object-exchange applications have been defined to use the OBEX protocol on RFCOMM. PPP for different Internet services, which can include services on top of TCP/IP or new WAP services, is also mapped over RFCOMM. AT-commands and TCS binary protocol are used to communicate with modems and different types of phones.

The enumerated application-specific protocols offer the basic functionality in the Bluetooth environment and they provide only the cable-replacement capabilities. Features such as broadcasting, point-to-multipoint topologies, and scatternet possibilities are not really utilized by these current high-level protocols and usage models. Thus, there are numerous possibilities for developers to create more applications, the nature of which can be totally different from the existing ones.

CONCLUSION

Bluetooth debuts amid much promise and criticism as it tries to sink its teeth into an already crowded wireless market. Bluetooth had a glorious freshman year, as the patronage of wealthy benefactors like Ericsson and IBM promised to remove all marketing obstacles to this hopeful wireless technology. This technology was going to use short-range radios to replace all those cables between the notebook and the handheld, the cell phone, the printer and practically anything else the mobile professional uses to hook up to a computer. Now Bluetooth is facing a case of the sophomore jinx where nothing seems to be going right.

One cavity in Bluetooth's fortunes is Microsoft Corp. The software giant decrees that Windows XP shall not support Bluetooth. So much for having the notebook exchange numbers with the cellular phone. But the consolation prize is that Microsoft's next iteration of Windows CE, code-named Talisker, will use Bluetooth, so handhelds have a brighter wireless future

Today Bluetooth is being sold as separate accessory items, but it does not make sense for anyone to go out and buy a lot of Bluetooth equipment,Nothing will happen in the market until Bluetooth is embedded in new devices. When one can go out and purchase a Bluetooth phone, PDA and PC with a small incremental, embedded cost point, then Bluetooth will really become pervasive."

Despite a pessimistic short-term outlook, Bluetooth has great potential in industrial niches. Symbol Technologies Inc.,N.Y.-based maker of inventory scanners and mobile data-management systems, is working on Bluetooth chipsets that will be incorporated into a cordless bar-code ring scanner to replace a cabled scanner. Given Bluetooth's 30-foot range, the wearer might even be able to leave the receiving unit at a central location, thereby creating a lighter system.

Bluetooth and 802.11b use the same 2.4GHz radio frequency, and some experts are still debating how the two can best be negotiated. For instance, there must be an internal machine protocol so devices (like a notebook) using Bluetooth and 802.11b don't transmit data simultaneously on the same radio frequency. Externally, a protocol needs to be worked out to minimize radio transmission between devices on 802.11b and Bluetooth frequencies.

Power requirement for the 802.11b connection is much greater, so one is much more limited as far as the devices are concerned. By contrast, Bluetooth is a chip level technology that can be embedded on very small devices like cell phones, so it's really something that could be more pervasive in the mainstream.

Bluesocket also is trying to solve a significant problem with Bluetooth, as it lacks a specification for handing-off access. When a user moves from the coverage area of one Bluetooth access point to another, the connection breaks and must be reestablished at the next access point. This is unlike cell phones, where two transmission towers briefly provide a connection with the user at the border of two coverage areas just before handoff occurs. Bluesocket has written its handoff specification to be backward-compatible so no changes are required in existing handsets. The company has submitted its design to the Bluetooth SIG.

The challenge, according to IBM, is creating a technology that works out of the box and costs no more than what it's replacing. Users are not going to spend $100 to get a networked Bluetooth printer if they can do the same with a $10 cable. To be successful, Bluetooth must not be oversold.

Despite the challenges, the new, more realistic Bluetooth seems to be shaking the sophomore jinx and entering its third year with its eyes fixed on graduation. Hopefully it will graduate with honors to take its place in the wireless world.