Bluetooth Technology

Bluetooth is the 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 telecommunication 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 readily available across a wide range of devices. The strength and direction of the underlying Bluetooth standards will ensure that all solutions meet stringent expectations for ease of use and interoperability.

Bluetooth Technology usage model

The technology is designed to be small and inexpensive. Bluetooth technology has no line-of-sight requirements making it a potential replacement for infrared ports. Bluetooth can operate through walls or from within your briefcase. Portable PCs can wirelessly connect to printers, transfer data to desktop PCs or PDAs, or interface with cellular phones for wireless WAN (Wide Area Networking) access to corporate networks or Internet.

You can also browse all incoming e-mails and read those you select in the mobile phone’s display. When your portable PC receives e-mail, you’ll get an alert on your mobile phone!

Positioning wireless technologies

It is important to understand the different wireless communication standards that are emerging in respect to Bluetooth. To understand the relative positioning of each wireless standard, it is important to appreciate the three primary usage scenarios for wireless connectivity.
· Wireless Personal Area Networking (WPAN). Applicable in scenarios that are personal in nature like synchronization of data between you PDA and a desktop PC.
· Wireless Local Area Networking (WLAN). Focused on organizational connectivity with the intent of providing members of a workgroup access to corporate network resources without inhibiting user’s mobility. The region of coverage is finite as dictated by the access points.
· Wireless wide Area Networking (WWAN). Addresses the need to stay connected while traveling. This has been facilitated by cellular technologies either through cellular telephone or through PC card cellular modems.

Bluetooth lingo

· Piconet: Devices connected in an ad hoc fashion, that is, not requiring predefinition and planning, as with a standard network. Two to eight devices can be networked into a piconet. It is a peer network, that is, once connected, each device has equal access to the others. However, one device is defined as master, and the others as slaves.

· Scatternet: Several piconets may form a larger scatternet, with each piconet maintaining independence.
· Master unit: The master in a piconet whose clock and hopping sequence synchronizes the other devices.
· Slave unit: Devices in a piconet that are not the master.
· MAC address: Three bit address that distinguishes each unit in a piconet.
· Parked units: Piconet devices that are synchronized but don't have MAC addresses.
· Sniff and hold mode: Power-saving mode of a piconet device.

Transmission types and rates

The baseband (single channel per line) protocol combines circuit and packet switching. To assure that packets do not arrive out of order, slots (up to five) can be reserved for synchronous packets. As noted earlier, a different hop signal is used for each packet. Circuit switching can be either asynchronous or synchronous. Up to three synchronous (voice) data channels, or one synchronous and one asynchronous data channel, can be supported on one channel. Each synchronous channel can support a 64 Kb/s transfer rate, which is fully adequate for voice transmissions. An asynchronous channel can transmit as much as 721 Kb/s in one direction and 57.6 Kb/s in the opposite direction. It is also possible for an asynchronous connection to support 432.6 Kb/s in both directions if the link is symmetric.

Radio frequency and spectrum hopping

What if there's a lot of radio noise? Won't that interfere with Bluetooth connections? As a rule, the answer is no. It is designed to use fast acknowledgement and frequency hopping, which will make connections robust. It is packet-based, and will jump to a new frequency after each packet is received, which not only helps limit interference problems, but also adds to security. Data rates are one megabyte/second, including headers. Full duplex transmissions (both directions at once) are accomplished via time division multiplexing.
The Bluetooth radio chip functions at 2.4 gigahertz, which is in the unlicensed ISM (Industrial Scientific Medical) band. It separates the 2.4 gigahertz frequency band into 79 hops one megahertz apart, starting with 2.402 and ending with 2.480 (though this bandwidth is narrower in Japan, France, and Spain). This spread spectrum is used to hop from one channel to another, pseudo-randomly, which adds a strong layer of security. Up to 1600 hops per second can be made. The standard frequency range is 10 centimeters to 10 meters, and can be extended to at least 100 meters by increasing transmission power.

Connection protocol

Bluetooth connections are established via the following techniques:
· Standby: Devices not connected in a piconet are in standby mode. In this mode, they listen for messages every 1.28 seconds over 32 hop frequencies (fewer in Japan, Spain, and France).
· Page/Inquiry: If a device wishes to make a connection with another device, it sends out a page message, if the address is known, or an inquiry followed by a page message, if it is unknown. The master unit sends out 16 identical page messages on 16 hop frequencies to the slave unit. If there is no response, the master retransmits on the other 16 hop frequencies. The inquiry method requires an extra response from the slave unit, since the MAC address is unknown to the master unit.

· Active: Data transmission occurs.
· Hold: When either the master or slave wishes, a hold mode can be established, during which no data is transmitted. The purpose of this is to conserve power. Otherwise, there is a constant data exchange. A typical reason for going into hold mode is the connection of several piconets.
· Sniff: The sniff mode, applicable only to slave units, is for power conservation, though not at as reduced a level as hold. During this mode, the slave does not take an active role in the piconet, but listens at a reduced level. This is usually a programmable setting.

· Park: Park mode is a more reduced level of activity than the hold mode. During it, the slave is synchronized to the piconet, thus not requiring full reactivation, but is not part of the traffic. In this state, they do not have MAC addresses, but only listen enough to keep their synchronization with the master and check for broadcast messages.
Data transmission

As noted earlier, data can be transmitted both synchronously and asynchronously. The Synchronous Connection Oriented (SCO) method is used primarily for voice, and Asynchronous Connectionless (ACL) is primarily for data. Within a piconet, each master-slave pair can use a different transmission mode, and modes can be changed at any time. Time Division Duplex (TDD) is used by both SCO and ACL, and both support 16 types of packets, four of which are control packets that are the same in each type. Because of the need for smoothness in data transmission, SCO packets are generally delivered via reserved intervals, that is, the packets are sent in groups without allowing other transmissions to interrupt. SCO packets can be transmitted without polling by the sending unit. ACL links support both symmetric and assymetric transmissions.

Bandwidth is controlled by the master unit, which determines how much of the total each slave unit can use. Slaves cannot transmit data until they have been polled by the master, and the master can broadcast messages to the slave units via ACL link.