Bluetooth
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Bluetooth
Bluetooth is awireless specification defines a low-power, low-cost technology that provides a standardized platform for eliminating cables between mobile devices and facilitating connections between products. Unlike many other wireless standards, the Bluetooth wireless specification includes both link layer and application layer definitions for product developers. Radios that comply with the Bluetooth wireless specification operate in the unlicensed, 2.4 GHz radio spectrum ensuring communication compatibility worldwide. These radios use a spread spectrum, frequency hopping, full-duplex signal at up to 1600 hops/sec. The signal hops among 79 frequencies at 1 MHz intervals to give a high degree of interference immunity. While point-to-point connections are supported, the specification allows up to seven simultaneous connections to be established and maintained by a single radio. The name "bluetooth" comes from King Harad Bluetooth of what is now Denmark. He was king from 940 and 985 AD and was known as a great comminicator and a unifier of Europe. The hope is that bluetooth will also be a great commincator and unify europe.
Bluetooth 1.1
The most significant change to Bluetooth in Version 1.1 involves authentication. Bluetooth communications are encrypted for security. When two Bluetooth devices try to establish a link, one of the first things they do is exchange keys confirming their identities. If the keys don't match, the two devices won't talk to each other. Under Bluetooth 1.0b, the two devices could get into an irreconcilable race condition during the initial link negotiation. The devices would execute the algorithm to generate the key, but each device would generate a different key. The problem revolves around timing. Generating the correct key depends on which device initiates the conversation (the master) and how fast the responding device (the slave) replies to the master's communications. If the slave can process information faster than the master, the ensuing race condition can leave each device calculating that it is the master. Based on that error, the devices fail to generate matching keys. Bluetooth 1.1 rectifies this problem by more thoroughly defining the steps required for device authentication. Specifically, Version 1.1 requires that each device confirm its role in the master/slave relationship by reconciling and/or acknowledging which device initiated interaction.
Bluetooth 1.2
The newer Bluetooth 1.2 specification, which is supported by very few products so far but is fully backwards compatible, uses Adaptive Frequency Hopping (AFH) to reduce interference from other devices that use the 2.4 GHz spectrum. That includes 802.11b and 802.11g (Wi-Fi) wireless LAN technologies, some cordless phones, and microwave ovens. AFH better adjusts to the local environment to avoid "bumping into" other transmission technologies, which in turn helps ensure that both systems are able to transmit at full bandwidth.
Bluetooth 2.0
This version is backwards compatible with 1.x. The main enhancement is the introduction of Enhanced Data Rate (EDR) of 2.1 Mbit/s. This has the following effects:
* 3 times faster transmission speed (up to 10 times in certain cases).
* Lower power consumption through reduced duty cycle.
* Simplification of multi-link scenarios due to more available bandwidth.
* Further improved BER (Bit Error Rate) performance.
Bluetooth Classes
* Class 3 (1 mW) is the rarest and allows transmission of 10 centimetres
(3.9 inches), with a maximum of 1 metre (3.2 feet)
* Class 2 (2.5 mW) is most common and allows a quoted transmission distance of
10 metres (32 ft)
* Class 1 (100 mW) has the longest range at up to 100 metres. This class of
product is readily available.
Bluetooth Ident
Every device has a unique 48-bit address. On computers running Linux the address and class of a USB Bluetooth dongle may be found by entering "hciconfig hci0 class" as root ("hci0" may need to be replaced by another device name). Every device also has a 24-bit class identifier. This provides information on what kind of a device it is (Phone, Smartphone, Computer, Headset, etc), which will also be transmitted when other devices perform an inquiry.
Devices also have friendly "Bluetooth names" which can be set by the user, and will appear when another user scans for devices and in lists of paired devices. However since the Bluetooth address is permanent a pairing will be preserved even if the Bluetooth name is changed. Most phones have the Bluetooth name set to the manufacturer and model of the phone.
