?Introduction
??????? The world today is advancing at a very high rate, and within this change is the world of wireless technology. Wireless and radio technologies have been at the heart of many disruptive businesses and activities. The people of today want hassle free and compact products, which can be used at any time or at any place. Wireless is the possible solution to meeting the needs or wants of the society. This paper will discuss the emerging wireless technology such as Bluetooth. This paper gives an in depth look on how the different technologies are being used today. By doing this, we will discuss how Bluetooth technology works, its origin, context, and implementation.
What is Bluetooth?
If you look around at the moment, you can find that your keyboard is connected to the computer, as well as a printer, mouse; monitors and so on are connected by cables. Cables have become a problem at many offices, homes and other establishments. Most of us have experienced trying to figure out what cable goes where, and ended up tangled in the details. Bluetooth essentially aims to fix this problem. This is considered a cable-replacement technology.
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Bluetooth is an open standard specification for a radio frequency (RF)-based, short-range connectivity technology that promises to change the face of computing and wireless communication. It is designed to be an inexpensive, wireless networking system for all classes of portable devices, such as laptops, PDAs (personal digital assistants), and mobile phones. It also will enable wireless connections for desktop computers, making connections between monitors, printers, keyboards, and the CPU cable-free. The idea of a cable-free, or wireless, technology was initially conceived by Ericsson in 1994, when the company began a study to investigate the feasibility of a low-power, low-cost radio interface between mobile phones and their accessories. The company?s goal was to eliminate the need for cables. The original idea was to create a small, inexpensive radio chip that could be used in mobile computers, printers, mobile phones, and so on, to transmit data between these devices. The radio chip, of course, would replace cables. The projected cost of the chip was around $5, and it was to require low power so that it could be used in devices that rely on battery life.
Open specification:
The Bluetooth Special Interest Group (SIG) has produced a specification for Bluetooth wireless communication that is publicly available and royalty free.
Short-range wireless:
There are many short-range digital communications among computing and communications devices; today much of that communication takes place over cables. These cables connect to multitude of devices using a wide variety of connectors with many combinations of shapes, sizes and number of pins; this plethora of cables can become quite burdensome to user. With Bluetooth technology, this technology can communicate without wires over a single air interface, using radio waves to transmit and receive data. Bluetooth wireless technology is specifically designed for short-range communications; one result of this very low power consumption, making the technology well suited for use with small, portable personal devices that typically are powered by batteries.
?Voice and Data ?
Voice appliances such as mobile telephones are also used for data applications such as information access or browsing. Trough voice recognition, computers can be controlled by voice, and through voice synthesis, computers can produce audio output in addition to visual output. Some wireless communication technologies are designed to carry only voice while others handle only data traffic. Bluetooth wireless communication makes provisions for both voice and data, and thus it is an ideal technology for unifying these worlds by enabling all sorts of devices to communicate using either or both of these content types.
Name and History
The name of Bluetooth came from Danish Viking King, Harald Blatand (Blatand in Danish means Bluetooth). He was a king of Denmark around the turn of the last millennium. He managed to unite Denmark and part of Norway into a single kingdom, and then introduced Christianity in to Denmark. He left a large monument, the Jelling rune stone, in memory of his parents. He was killed in 986 during a battle with his son, Svend Forkbeard. The name was adopted because Bluetooth wireless technology is expected to unify the telecommunication and computing industries.
Bluetooth is a standard developed by a group of electronics manufactures that allow any sort of electronic equipment such as computers, cell phones, keyboards, and headphones to make their own connections without wires. It is getting popular because it can connect any Bluetooth device to another. Imagine any type of device that handles information or data (phones, PDAs, cameras, music players, etc.). If each device is enabled with Bluetooth, the information can be shared among the devices
???? Bluetooth is split into two sections: Bluetooth Specification and Bluetooth Profile.
Bluetooth Specification
Technical features
? Bluetooth operates in the unlicensed 2.4 GHz Industrial Scientific Medical (ISM) frequency band as shown in Figure 4 below. It uses 79 channels between 2.402 GHz to 2.480 GHz. It uses power of 1mW to 100mW. The nominal range is 10 meters, but can be extended to more than 100 meters by increasing the transmission power to 100mW. The gross data rate is 1Mbps. Bluetooth uses a combination of packet and circuit switching technologies for transmission.
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?? While developing the specification, high emphasis was placed on developing a design that would enable single chip CMOS implementations, thereby reducing cost, power consumption, and the chip size required for implementation in mobile devices. A single chip CMOS, such as the one shown in Figure 5 on the next page, is already available from multiple manufacturers. This device contains the RF radio, baseband controller and microprocessor on a single CMOS integrated circuit.
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Access Technology
Since Bluetooth operates in the unlicensed ISM band that is also used by other devices such as 802.11 networks, baby monitors, garage door openers, microwave ovens etc, there is possibility of interference (Helsinki University of Technology, 2000). To avoid interference, Bluetooth uses an access technology called Frequency Hop Spread Spectrum (FHSS). The band where Bluetooth operates is divided into 79 channels of 1 MHz each. Each channel is divided into time slots consisting of 625 ?sec in length. After a packet is sent on one frequency, both the devices retune their radios to a different frequency, effectively hopping at a rate of 1600 hops per second through different time slots. In this way, Bluetooth devices use the entire ISM band and if a transmission is compromised by interference on one channel, the retransmission will always be on a different (hopefully clear) channel.
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Protocol Stack
The key feature of the Bluetooth specification is that it allows devices from many different manufacturers to work with one another. To this end, Bluetooth defines a software stack, as shown in Figure 7 below. This enables applications to find other Bluetooth devices in their area, discover what services they can offer, and use those services. Bluetooth protocol stack is divided into three groups depending upon their functionality. Those groups are:
1. Transport protocol group
2. Middleware protocol group
3. Application group.
1. Transport protocol Group
?Radio (RF)? The radio modulates and demodulates data for transmission and reception on air.
Baseband/Link Controller? Instantiates air interface, determines master ? slave relationship between the devices, and also defines frequency-hopping sequences based upon time division duplex for a packet based polling scheme. It also sends various packet types for synchronous, asynchronous traffic and determines packet processing procedure, error detection, encryption, packet ransmission and retransmission.
Link Manager ? Reserves bandwidth for data (L2CAP layer) and audio. For authentication, it follows challenge ? response approach and supervises devise pairing and encryption of data flow. It also supports power control by negotiating low activity baseband modes of operation.
Host Controller Interface (HCI) ? Handles the communications between a separate host and a Bluetooth module. It allows higher layers of the stack, including applications, to access the baseband, link manager, and other hardware registers through a single standard interface. HCI enables interoperability among host devices and Bluetooth modules developed by different vendors. It also abstracts transport dependencies and provides a common device driver interface to various devices.
L2CAP? Supports protocol multiplexing by allowing multiple protocols and applications to share the air interface. It segments large packets used by higher layers to smaller packets for baseband transmission. It also exercises admission control and coordinates with lower layers to maintain the desired level of service.
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2. Middleware Protocol Group
RFCOMM? It serves as a serial port abstraction. It multiplexes serial communications over a single serial link supports legacy applications that use serial communication provides reliable data stream, multiple connections, flow control and serial cable like settings. Ex: USB, RS-232.
Service Discovery Protocol? Discovers available services and locates needed services establishes a communication channel between 2 devices to find out about services that are available to the device. Some other service discovery protocols such as JINI and UDNP can be used in conjunction with Bluetooth SDP protocol.
Infrared Object Exchange (OBEX)? Exchanges well defined objects. It is a requirement for exchanging data among devices to define the format, both syntax and semantics of that data, Infrared object exchange, developed by Infrared Data Association (IrDA), for peer-to-peer communication. Data objects such as electronic business cards (Vcard format), email (Vmessage format) and calendar entries (Vcal format) are exchanged.
Telephony Control Specification (TCS)? Used for controlling telephone calls that might be used either for audio or for data. It uses binary encoding so they are called TCS-BIN. It also supports call control and group management.
3. Application Group
Refers to software that resides above the protocol stack as defined by SIG, This software supplied by device manufacturers exercises the protocol stack to accomplish some functions that benefits the user of a Bluetooth device.????????????????????
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? There are some similarities between Open System Interconnect (OSI) standard reference model and Bluetooth protocol stack, which are shown above in Figure 8. Although Bluetooth protocol stack does not exactly match the OSI model, it is useful to compare because the OSI model is an ideal well-partitioned stack. The comparison serves to highlight the division of responsibilities in the Bluetooth stack.
The Physical Layer is responsible for transmission, framing, and error control over a particular link. This overlaps the link controller task and the control end of the baseband, including error checking and correction.
The Network Layer is responsible for data transfer across the network, independent of the media and specific topology of the network. This encompasses the higher end of the link controller, setting up and maintaining multiple links, and also covering most of the Link Manager (LM) task. The Transport Layer is responsible for the reliability and multiplexing of data transfer across the network to the level provided by the application, and thus overlaps at the high end of the LM and covers the Host Controller Interface (HCI), which provides the actual data transport mechanisms.
The Session Layer provides the management and data flow control services, which are covered by L2CAP and the lower ends of RFCOMM/SDP. The Presentation Layer provides a common representation for Application Layer data by adding service structure to the units of data, which is the main task of RFCOMM/SDP. Finally the
Application Layer is responsible for managing communications between host applications.
Topologies
Bluetooth communication occurs between a master device and a slave device. Bluetooth devices are symmetric such that the same device may operate as a master and also the slave. The two different topologies through which the Bluetooth devices communicate are
1. Piconet ?????????????????????????? 2. Scatternet
Two or more radio devices together from ad-hoc networks called piconets. All units with a piconet share the same channel. Each piconet has one master device and one or more slaves. There may be up to seven active slaves at a time within a piconet. Inactive slaves in unconnected state may continue to reside within the piconet in Stand by mode (sb) as shown in the Figure 12.
??? A master is the only one that may initiate a Bluetooth communication link. However, once a link is established, the slave may request a master/slave switch to become the master. The master controls how the total available bandwidth is divided among the slaves by deciding when and how often to communicate with each slave. Using Time Division Multiplexing, the timeslots are divided between multiple devices depending upon data transfer requirements. To form a piconet, the Bluetooth device needs to understand two parameters: the hopping pattern of the radio it wishes to connect to and the phase within that pattern.
?? Multiple piconets with overlapping areas are called Scatternets. A device can be a master in a piconet or a slave in more than a piconet as shown in Figure 13. Each piconet may have only one master, but slaves may participate in different piconets on a time division multiplex basis. More piconets in the area i.e., bigger the scatternet have more collisions and more retransmissions which will cause the data rates to fall.
Addressing
Each Bluetooth device has a 48 bit unique address, which is referred as BD_ADDR. An active slave within a piconet is identified by a 3 bit Active Device Address (AM_ADDR), which separates it from the inactive/parked slaves in the piconet. Those parked slaves are assigned an 8 bit address called Parked Member Address (PM_ADDR).
CONCLUSION:
There is huge interest for Bluetooth in Industrial, Scientific and Medical Markets. We are starting to see the first applications move from trials to roll out.
Most of this business is using Bluetooth as an instant cable replacement. For a compelling Simple Cable Replacement solution lots of issues must be solved. Issues of User interface, visual prompts, power consumption, data integrity not to mention expensive and time consuming Bluetooth qualification.
Brain boxes have solved all these issues with a range of pre qualified, low cost, simple to use, software free Bluetooth products. We have solutions and advice for virtually every type of cable replacement application.
By : Nirav Prajapati
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