Bluetooth Technology Overview
BLUETOOTH
Abstract
Bluetooth Technology Overview
Bluetooth is a Radio Frequency (RF) specification for short-range, point-to-point and point-to-multi-point voice and data transfer. Bluetooth will enable users to connect to a wide range of computing and telecommunications devices without the need for proprietary cables that often fall short in terms of ease-of-use. The technology represents
an opportunity for the industry to deliver wireless solutions that are ubiquitous across a
broad range of devices. The strength and direction of the underlying Bluetooth standard
will ensure that all solutions meet stringent expectations for ease-of-use and
interoperability.
Bluetooth, named for Denmark's first Christian king and not a dire dental condition, is the name of a technology specification for small form factor, low-cost, short-range radio links between PCs, handhelds, mobile phones, and other computing and electronic devices. The Bluetooth SIG (Special Interest Group) is an industry group consisting of leaders in the telecommunications and computing industries that are driving development of the technology and bringing it to market. Over 2000 companies have executed the Bluetooth adopter’s agreement and are members of the Bluetooth SIG.
Bluetooth technology provides a 10-meter personal bubble that supports simultaneous transmission of both voice and data for multiple devices.
Bluetooth wireless technology is designed to be as secure as a wire with up to 128-bit public/private key authentication, and streaming cipher up to 64-bit based on A5 security. The encryption strength can be very robust which is good for establishing a secure link, but there may be export problems when shipping from the US. Different hardware with smaller encryption key lengths may be required to meet US export controls.
One of the goals of the Bluetooth SIG is to make wireless connections easy and simple to use. To ensure the best possible customer Bluetooth experience as well as interoperability with other Bluetooth devices, the Bluetooth SIG is developed a logo program, which validates compliance with the published Bluetooth specification as well as interoperability with other Bluetooth devices. Bluetooth devices that successfully complete the Bluetooth testing criteria have the right to bear the official Bluetooth logo.
THE BLUETOOTH TECHNOLOGY
Introduction
Bluetooth is a global standard for wireless connectivity. Bluetooth is based on a
short-range radio. Designwise three main goals of Bluetooth were small size,low cost and low power consumption. Bluetooth technology facilitates the replacement of the cables normally used to connect one device to another, with one universal short-range radio link. For example, Bluetooth radio technology built into both the mobile telephone and the laptop could replace the traditional (serial) cable used today to connect these
devices. Printers, Personal Digital Assistants (PDAs), desktop computers, fax machines,
keyboards, joysticks, mice or any other digital device can be part of the Bluetooth
system.
Beyond facilitating the replacement of cables, Bluetooth technology can also act as a universal medium to bridge the existing data networks; a peripheral interface for
existing devices; and a mechanism to form small private adhoc groupings of connected
devices away from fixed network infrastructures.
Two Bluetooth devices can talk to each other when they come within a range of 10 meters to each other. Due to their dependence on a radio link, as opposed to alternate
technology such as an infrared connection, Bluetooth devices do not require a line-of-sight connection in order to communicate. Therefore, a laptop could print information
on a printer in the adjoining room, or the microwave in the kitchen could send a
message to the mobile phone in the living room indicating that the meal is ready.
The idea that resulted in Bluetooth technology arose in 1994. Ericsson Mobile
Communication initiated a study to investigate the feasibility of a low-power, low cost
radio interface between mobile phones and their accessories. The aim of the study was
to eliminate cables between mobile phones and PC cards, handsets and desktop
devices, etc.
In February 1998, Ericsson, Nokia, IBM, Toshiba and Intel formed a Special Interest Group (SIG). The group contained two market leaders in mobile telephony, two in laptop computing and one in digital signal processor technology.
About Bluetooth
This Bluetooth technology achieves its goal by embedding small, inexpensive, short-range radio transceivers into the devices that are available today, either directly or
through an adapter such as a PC Card. The radio operates on the globally available
unlicensed radio band, 2.4 GHz, and supports data speeds of up to 723.2 Kbps.
Bluetooth can also support up to three voice channels. The Bluetooth specification targets very low power consumption (less than 100 mW) in the active state.
The Bluetooth radio is designed to operate in a noisy radio frequency environment. It
uses a fast acknowledgement 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, which also operate in the 2.4 GHz radio band.
The bluetooth system consists of a radio unit,link control unit,support unit for link management and host terminal interface functions. The host controller interface(HCI) provides the means for a host device to access the Bluetooth hardware capabilities. For eg, a laptop or a personal computer can be a host device and the PC card inserted in the PC is the bluetooth device. All commands from host to the Bluetooth module and events from module to the host got through the HCI interface.
Network topology
The Bluetooth system supports both point-to-point and point-to-multi-point connections. Several Piconets 1 can be established and linked together in an adhoc manner. Each such Piconet is identified by a different frequency hopping sequence. All users participating on the same Piconet are synchronized to this hopping sequence.
The Piconet
Bluetooth devices can interact with one or more other Bluetooth devices in several different ways. The simplest scheme is when only two devices are involved. This is referred to as point-to-point. One of the devices acts as the master and the other as a
slave. This adhoc network is referred to as a Piconet.
As a matter of fact, a
Piconet is any such Bluetooth
network with one master 2 and one or
more slaves. A diagram of a Piconet
is provided in the adjoining figure. In
the case of multiple slaves, the
communication topology is referred
to as point-to-multipoint. In this
case, the channel (and bandwidth) is
shared among all the devices in the
Piconet. There can be up to seven active slaves in a Piconet. Each of the active slaves
has an assigned 3-bit Active Member address. There can be additional slaves, which
remain synchronized to the master, but do not have an Active Member address. These
slaves are not active and are referred to as parked. For the case of both active and
parked units, all channel access is regulated by the master. A parked device has an 8-bit
Parked Member Address, thus limiting the number of parked members to 256. A parked
device remains synchronized to the master clock and can quickly become active and
begin communicating in the Piconet.
1. A Piconet is a collection of devices connected via Bluetooth technology in an adhoc fashion. A Piconet
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 Piconet, one unit will act as a master and the other(s) as slave(s) for the duration of the Piconet
connection.
2. By definition, the Bluetooth unit that initiates the connection (to one or more slave units) represents the
master. The names ‘master’ and ‘slave’ only refer to the protocol on the channel: the Bluetooth units
themselves are identical; that is, any unit can become a master of a Piconet. Once a Piconet has been
established, master-slave roles can be exchanged.
1
The Scatternet
When two Piconets are close to each other, they have overlapping coverage areas. This scenario is provided for in the Bluetooth specification and is referred to as a scatternet. A typical example: one might have a Piconet consisting of the mobile phone and the PC in one’s cubicle, while the person in the neighboring cubicle may have a Piconet consisting of a mobile phone, headset, and business card scanner.
Slaves in one Piconet can participate in another Piconet as either a master or slave. This is accomplished through time division multiplexing. In a scatternet, the two (or more) Piconets are not synchronized in either time or frequency. Each of the Piconets operates in its own frequency-hopping channel while any devices in multiple Piconets participate at the appropriate time via time division multiplexing. In the previous example, the person in cubicle #1 may use the neighbour’s business card scanner on mutually agreed upon terms.
Frequency Hopping
Bluetooth technology uses a frequency hopping technique, which means that every packet is transmitted on a different frequency. In most countries, 79 channels can be used. With a fast hop rate (1600 hops per second), good interference protection is achieved. Another benefit is a short packet length. If some other device is jamming the transmission of a packet, the packet is resent in another
frequency determined by the frequency scheme of the master. Note that this case only refers to situations where there are two or more simultaneous
active piconets or a non-Bluetooth device using the same frequency in range. The error correction algorithms are used to correct the fault caused by jammed transmissions
625µs
200µs
Figure 4. Three-slot and five-slot long packets reduce overhead compared to one-slot packets. 220 s switching time after the packet is needed for changing the frequency.
Subsequent time slots are used for transmitting and receiving. The nominal slot length is 625 s. A packet nominally covers a single slot, but can be extended to cover three or five slots, as depicted in Figure 4. In multi-slot packets the frequency remains the same until the entire packet is sent. When using a multi-slot packet, the data rate is higher because the header and a 220 s long switching time after the packet are needed only once in each packet. On the other hand, the robustness is reduced: in a crowded environment the long packets will more probably be lost.
The Bluetooth Clock
Every Bluetooth unit has an internal system clock, which determines the timing and hopping of the transceiver. The Bluetooth clock is derived from a free running native
clock, which is never adjusted and is never turned off. For synchronization with other
units, only offsets are used. These offsets, when added to the native clock, provide
temporary Bluetooth clocks, which are mutually synchronized. The Bluetooth clock has
no relation to the time of day and can therefore be initialized to any value. The Bluetooth clock provides the heart beat of the Bluetooth transceiver. Its resolution is at least half the TX or RX slot length, or 312.5 s. The Bluetooth clock has a cycle of about a day. If the clock is implemented with a counter, a 28-bit counter is required that wraps around at 2 28 -1. The LSB ticks in units of 312.5 s, giving a clock rate of 3.2 KHz.
Applications
Home
The Three-in-one Phone
With Bluetooth support, one handset will be able to provide multiple functionality. When
at home, the phone functions as a cordless phone, connected to the fixed line. When on
the move, it functions as a mobile phone connected to the mobile network. Additionally,
when the phone comes within range of another mobile phone with built-in Bluetooth
technology, it functions as a walkie-talkie.
The Internet Bridge
An extension of this model could be a mobile computer that allows surfing the Internet
irrespective of the location of the user, and regardless of whether the user is cordlessly
connected through a mobile phone (cellular) or through a wireline connection (e.g.
PSTN, ISDN, LAN, xDSL).
Smart Home
Homes equipped with Bluetooth devices may be able to recognise the arrival of its
bonafide residents and unlock the door on their arrival. The device will also adjust heat
to a preset temperature. While this is happening, the data from the individual’s PDA
may be exchanged with the home electronic board, and the family calendar is updated
to reflect the scheduled activities in the office.
Office
The Automatic Synchronizer
The Bluetooth technology will also allow automatic synchronization of the desktop,
mobile computer, PDAs and the mobile phone. For instance, as soon as one enters
his/her office the address list and calendar in the PDA will automatically be updated to
agree with the one in the desktop, or vice versa.
The Interactive Conference
In meetings and conferences, one can transfer selected documents instantly with
selected participants, and exchange electronic business cards automatically, without any
wired connections.
In another similar application, one can access one’s PDA to send the presentation to the
electronic whiteboard. The minutes of the meeting are also recorded on a PDA and
wirelessly transferred to other participants before they leave the meeting.
Travelers
Automatic Check-in
The Bluetooth enabled mobile phone or the PDA can present the electronic ticket to the
airline system without one having to go through the queue at the check-in counters.
The airline's on-line system performs the identification via the ID-tag feature built into
the mobile phone or the PDA and confirms the reserved seat.
In the airport waiting lounge, kiosks could be equipped with Bluetooth-enabled Internet
ports. Via these ports, one could connect the Bluetooth-enabled laptops, PDAs, and
other devices to access the office or home-based servers via the airline server. The