As the technology becomes more sophisticated, the need for facile wireless communication has led the human brain to renovate the orthodoxy bottlenecked conventions being used. Computing will inevitably be indispensable and ubiquitous – a scenario that has no place for wires. Bluetooth provides several irksome issues that have plagued implementation of wireless technology handling both data and voice transmissions.
What is Bluetooth?
Bluetooth is the global defacto standard for wireless connectivity based on low-cost, short-range radio link that resides on a micro chip. Bluetooth wireless technology is a system solution comprising hardware, software and Interoperability requirements. Bluetooth is a standard for a small, cheap radio chip to be plugged in to computers, printers, mobile phones etc.
How does it work?
There are four basic parts to any Bluetooth system: Radio (RF) that receives and transmits data and voice, a Base band or link control unit that processes the transmitted and received data, link management software that manages the transmission and supporting application software.
The Bluetooth radio is a short distance, low power radio operating in the unlicensed spectrum of 2.4 GHz and using a nominal antenna power of 0 dBm (range 10mts) Optionally a range of 100 meters (about 328 feet) may be achieved by using an antenna power of 20 dBm. Data is transmitted at the rate of up to 1Mbps maximum. But communication protocol overhead limits the practical data rate to a little over 721 Kbps.
Radio communication is subjected to noise and interference, as the 2.4 GHz frequencies is shared between all devices in Pico nets. So the Bluetooth specification has solved this problem by employing what is called as spectrum spreading, in which the Bluetooth radio hops among different frequencies very quickly. There are 79 hops starting at 2.402 GHz; and stopping at 2.1.80GHz, each of which is displaced by 1 MHz. Frequency hoping also provides data security because two packets of data is never sent over the same frequency consecutively and the changing frequency is unpredictable.
In wireless communication the baseband is the hardware that turns the radio signals (transmit/ received) into a digital form that can be processed by the host application. In other words it can convert the digital or voice data into a form that can be transmitted using a radio signal, according to a protocol that allows. Virtually all wireless communication accomplishes this feat by putting the data into Packets. It also contains information on how the data was compressed. When the data is received it is checked for accuracy, un-packetized, reassembled, de-composed & possibly filtered in some way . The baseband processor handles all the tasks & in Bluetooth it is called as Link Controller.
The Bluetooth link is the method of data transmission which supports two link types: Synchronous Connection Oriented (SCO) used primarily for voice communications and Asynchronous Connection Less (ACL) links for packet data. Each link type support sixteen different packet types that are used based on the application.
Link Controller& Link manager:
It a supervisory function that handles all the Bluetooth baseband functions and supports the Link manager. It sends &. Receives data, requests the identification of the sending device authenticates the link, sets up the type of link, determines what type of frame to use on a packet by packet basis, directs how devices will listen for transmissions from other devices or puts them on hold. It is software that runs on a microprocessor and manages the communication between. Bluetooth devices .Each Bluetooth device has its own Link Manager that discovers other remote Link Manager, & communicates with them to handle link setup, authentication, configuration & other protocols.
Network Topology :
Bluetooth devices are generally organized into groups of two to eight devices called Piconets, consisting of a single master device and one or more slave devices. A device may additionally belong to more than one piconet, either as a slave in both or as a master of one piconet and a slave in another. These bridge devices effectively connect piconets into a scatternet. A diagram of a Bluetooth scatternet is shown in figure above. Bluetooth operates in the unlicensed ISM frequency band that is generally cluttered with signals from other devices-garage door openers, baby monitors, and microwave ovens, to name just a few. This pattern, moving through 1,600 different frequencies per second, is unique to the particular piconet. Each frequency “hop” is a time slot during which data packets are transferred. A packet may actually span up to five time slots, in which case the frequency remains constant for the duration of that transfer.
P.Aditya (ECE 2/4)
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