Ericsson initiated development of the Bluetooth technology in 1994, but today the specification is developed, published and promoted by the Bluetooth Special Interest Group (SIG) . Bluetooth wireless technology is a worldwide specification for a low-cost, low power consuming radio solution that provides links between different types of devices. It uses the globally available 2.4 GHz ISM (Industrial, Scientific and Medical) band.
As a provider of short-range connectivity, Bluetooth is initially replacing cables and proprietary wireless systems within existing applications. There are numerous applications in use today that benefit from Bluetooth technology, such as laptop-to-mobile handset connections, synchronisation between PCs and PDAs or smartphones, and headset-to-handset connections.

As Bluetooth devices become cheaper and more widely available, new applications will be developed that would not have been viable using wired or proprietary wireless technology. These new applications will take many forms, depending on the context in which they are used: fringe of LAN connectivity for PDAs and smartphones in large corporate offices, connecting domestic appliances to home networks, or the much vaunted public access services.

One way to divide the application areas supported by Bluetooth is:
o Cable replacement: The original design objective of Bluetooth was to eliminate the need for cable, e.g. between phone and headset or keyboard and computer. However there are many other application areas, e.g. automotive or medical, where this could be useful.
o Network Access: Another early application scenario was ad-hoc networking, where devices form networks on the fly, when they are in proximity of one another or when handheld devices connect to an IP network to use its services. An important device in this context is the Network Access Point.
o Location-based services: An example of a location-based service is the m-Express scenario where a person equipped with a Bluetooth device walks around in an exhibition area. For each exhibition booth the person passes, the location-based service pushes information about the booth to the device.

Bluetooth is a public standard and in the following sections it will be explained how it is maintained, updated and expanded.

The Bluetooth Special Interest Group

The Bluetooth Special Interest Group (SIG) was formed in February 1998. Today the Bluetooth SIG includes promoter companies like 3Com, Ericsson, IBM, Intel, Agere Systems, Microsoft, Motorola, Nokia and Toshiba, and thousands of Adopter/Associate member companies.
The assignment of the SIG originally was to monitor the technical development of short-range radio and to create an open global standard, thus preventing the technology from becoming the property of a single company. This work resulted in the release of the first Bluetooth Specification in July 1999.
The further development of the Specification still is one of the main issues for the SIG. Other important tasks are interoperability requirements, frequency band harmonization and promotion of the technology.
The Bluetooth Qualification Program guarantees global interoperability between devices regardless of the vendor and regardless of the country in which they are used. During the test procedure, which all devices must pass, it must be verified that they meet all requirements regarding: radio link quality, lower layer protocols, profiles and information to end-users.

Piconets: Bluetooth networks

Bluetooth units that come within range of each other can set up ad hoc point-to-point and/or point-to-multipoint connections. Units can dynamically be added or disconnected to the network and two or more Bluetooth units sharing a channel form a piconet. Several piconets can be established and linked together in ad hoc scatternets to allow communication and data exchange in flexible configurations as shown in the figure below.
If several other piconets are within range they each work independently and each have access to full bandwidth. Each piconet is established by a different frequency-hopping scheme. All users participating in the same piconet are synchronized to this hopping scheme/pattern. Unlike infrared devices, Bluetooth units are not limited to line-of-sight communication because a radio-based link is used. To control traffic of each piconet’s hopping scheme, one of the participating units becomes a master of the piconet, while all other units become slaves.

With the current Bluetooth Specification, up to seven slaves can actively communicate with one master. However, there can be 254 units attached to a master, 7 in active mode as slaves and the remaining 247 in parked mode.

Bluetooth Radio Characteristics
The Bluetooth Specification defines a short range (around 10 meters) or optionally a medium range (around 100 meters) radio link capable of voice or data transmission to a maximum capacity of 720 kilobits per second per channel.
Radio frequency operation is in the unlicensed industrial, scientific and medical band at 2.40 to 2.48GHz, using a spread spectrum, frequency hopping, full-duplex signal at a nominal rate of 1600 hops/sec. The signal hops among 79 frequencies at 1 MHz intervals to give a high degree of interference immunity. RF output is specified as 0dBm (1mW) in the 10m-range version and -30 to +20dBm (100mW) in the longer-range version. When producing the radio specification, high emphasis was put on specifying a design that enables low cost, minimum power consumption and a small chip size required for implementation in mobile devices.
o Voice: Up to three simultaneous synchronous voice channels can be used, or one channel that simultaneously supports asynchronous data and synchronous voice. Each voice channel supports a 64kb/s synchronous (voice) channel in each direction.
o Data: The asynchronous data channel can support maximal 723.2kb/s asymmetric (and still up to 57.6kb/s in the return direction), or 433.9 kb/s symmetric.

Security

As radio signals can be easily intercepted, Bluetooth devices have built-in security to prevent eavesdropping or falsifying the origin of messages (spoofing). The main security features are:
o Challenge-response routine for authentication, which prevents spoofing and unwanted access to critical data and functions.
o Stream cipher – for encryption, which prevents eavesdropping and maintains link privacy.
o Session key generation – session keys can be changed at any time during a connection.

Three entities are used in the security algorithms:

o The Bluetooth device address (48 bits) is a public entity unique for each device. The address can be obtained through the inquiry procedure.
o A private user key (128 bits) is a secret entity. The private key is derived during initialization and is never disclosed.
o A random number (128 bits) is different for each new transaction. The random number is derived from a pseudo-random process in the Bluetooth unit.

In addition to these link-level functions, frequency hopping and the limited transmission range also help to prevent eavesdropping.

Stack layout

The specification itself does not prescribe what should be hardware and what should be software. It merely defines the different layers in the protocol stack and their interfaces. The different layers in the protocol are described below.
The Bluetooth radio specification describes the radio interface and is controlled by the baseband. The baseband in turn is either used by the Audio layer for voice transmission or the Link Manager for data transmissions.
The Link Manager (LM) software runs on the CPU core. The LM discovers other LM’s and communicates with them via the Link Manager Protocol (LMP) to perform its service provider role and to use the services of the underlying Link Controller.
The Radio, Baseband, Audio and Link Manager layers are often referred to as the core layers. The next layer is the Host Controller Interface (HCI) that is the common interface between the Bluetooth host (e.g. a portable PC) and the Bluetooth core.
The Logical Link Control and Adaptation Protocol (L2CAP) takes care of its segmentation and reassembly to allow larger data packets to be carried over a Bluetooth baseband connection. L2CAP is used by higher-level protocols like:
o Service Discovery Protocol (SDP): Allows applications to find out about available services in the devices they connect to and also provide information about the devices’ own services to other devices.
o RFCOMM protocol: RFCOMM is a serial port emulation protocol. It is mainly aimed at easing the transition of cabled applications to the wireless world and is used by applications (and profiles) for as different purposes as networking, Infrared Data Association (IrDA) interoperability and telephony.
o Telephony Control protocol (TCS): The telephony control protocol is used for transmitting audio by supporting telephony functions, including call control and group management. It can also be used for data calls.

On top on these protocols are profiles and on top of the profiles are the applications.

3.9.6. Profiles
To ensure interoperability at a higher level than protocols the Bluetooth SIG has specified a number of Profiles, which provide high-level functionality, specified in a form akin to an Application Programmers Interface (API). Profiles can be divided into two main groups:
o Generic profiles: The generic profiles provide a high level interface for interacting with other devices. They are Generic Access Profile (GAP) and the Service Discovery Application Profiles (SDAP), which is an abstraction on top of the Service Discovery Protocol.
o Application specific profiles: These profiles are targeted toward (a) specific application scenarios, such as fax, telephony, headset, and imaging, but also (b) application areas such as automotive, medical, etc. New application specific profiles will be developed continuously by working groups under the Bluetooth SIG.
The main profiles with relevance to LBS are used for network connection, positioning, access roaming and exchanging information, such as maps, links, promotional material and are the following:
o Generic Object Exchange Profile (GOEP): The GOEP is used for transferring objects between Bluetooth devices. Any content with a defined MIME type can be transferred.
o Personal Area Network (PAN) Profile: The PAN profile currently addresses the following (a) Ethernet encapsulation, (b) ad-hoc single piconet IP PAN, (c) master forwarding, and (d) Network Access Point thus expanding on the existing LAN profile, which is expected to become obsolete.
o Local Positioning Profile (LP): A Bluetooth device with the LP profile can use another position-aware Bluetooth device, i.e. the other Bluetooth device knows its exact geographic position, within range to determine its own position.
o Personal Area Network – Access Point Roaming Profile (PAN-APR): The PAN-ARP profile is an extension to the PAN specifying functionality for access roaming, e.g. hand-over from one access point to another and identification of logical networks.

3.9.7. Value for LBS
To summarize Bluetooth is an ad hoc networking protocol that is meant to replace cables between computers, mobile phones and peripherals. It is now included as a standard module in most communicating consumer electronics items from laptops to printers to TV picture viewing appliances and surveillance cameras. It was originally standardized by mobile phone manufacturers as a way to make electronic devices communicate with mobile phones over short distances of at most a few dozen meters.
Bluetooth is a peer-to-peer network where all devices can behave in symmetric roles and offer or access services to and by other devices. It is used in collective game playing of mobile phone games and exchanging ringing tones, for submitting pictures taken by cameras on mobile phones onto the Internet, or for printing, or for viewing on a TV set and so on. Bluetooth devices constantly pry their surroundings for other Bluetooth enabled devices, and automatically exchange handshakes with them, unless explicitly instructed to restrict their attention to a few predominated devices.
Bluetooth can still be considered a new technology even though the experience about building and operating large-scale networks is scarce, but has growing momentum and most new models of mobile phones, PDAs and laptops and therefore almost every user will have a capable terminal in the near future.
In the specification there is also defined how WAP over Bluetooth should be supported and it can be expected that this will be supported in mobile phones, too. Currently there is on-going work on a positioning profile. With respect to LBS Bluetooth has two roles. Firstly, it can function as a positioning grid to build mobile location services on, and secondly, it can be joined to user scenarios of various mobile location services by any other location method.

Bluetooth as Part of a Mobile Location Service Scenario
Looking at Bluetooth as part of a more general set-up for mobile location services, the situation changes for the better, when compared to using Bluetooth as a positioning method.
Bluetooth is a costless way to transmit content at a high bandwidth over short distances, and desired Bluetooth devices can be made accessible to any mobile phone that happens to pass by. This is one possible use of Bluetooth in Mobile Location based services.
Service provisioning over Bluetooth requires the adoption of one or two mechanisms. Either the services are based on the proximity of users to a Bluetooth enabled “info point” operated by some organisation, or the services must be built upon a peer-to-peer scenario. Both mechanisms are analysed in further detail below.

Info point based Bluetooth services
A possible candidate for a Bluetooth enabled info point is any kiosk similar to Internet enabled information kiosks. In the case of info kiosks, mobile location is trivially solved, because the location of each kiosk is known and the user will have to be in a neighbourhood of some 20m from it. On the basis of this assurance, the kiosk can offer information based on its own location directly to a passing mobile phone that has enabled its Bluetooth to pry its surroundings. Its services would then be found behind an appropriate device name and icon on the user’s mobile phone and could be browsed at will.
Another option is to offer Bluetooth as an option to store information that the user has already dug up on the kiosk on her mobile phone for further reference. Such info could be images, maps, music or even video related to the contents available on the kiosk. In both scenarios, the advantages of Bluetooth are:
o Automatic knowledge of the user’s location
o Broadband connectivity
o Free transmission of even a high volume of content
The main disadvantage is the necessity of the user to reside close to an info kiosk.

Peer-to-peer based Bluetooth services
In the peer-to-peer mechanism, users distribute Bluetooth services themselves. Some such services are already operational in Europe’s undergrounds, although hardly by anybody’s design. In a phenomenon known as “Bluejacking” a person allows his or her mobile phone to pry its surroundings. If the phone detects another Bluetooth user, the first user tries to guess the second user by her alias username, then takes a photo of her with his mobile phone and sends it over to her via Bluetooth.
Effectively, this Bluetooth user scenario has created a peer-to-peer chat group or dating service without anybody planning it. Also the location problem is solved automatically by the short range of Bluetooth connectivity and subsequent human intelligence. Such services are more appropriately called “proximity based services” than Location Based Services, but they still fall in the category of services where both mobile content and the location of its users are relevant.
It is a rather safe bet that such “services” as Bluejacking are going to be a hit among mobile users, because their appeal resides in similar human emotions that have caused SMS and Internet chat to succeed. These services are obviously less attractive as businesses, because they do not involve any charges. But they should still be welcomed, because in them lies a grain of potentially very high revenues in the future.