BlueTooth is a standard used in short-range radio links, intended to replace the wired connections between electronic devices.
This technology allows the instant connections of voice and information between multiple devices in real time. The transmission mode used ensures protection against interference and security in the transmission of information.
Main features :
• low complexity
• low consumption
• low price
BlueTooth is a small chip that works in a globally available frequency band. Communication can be achieved point to point or multi-point.
All devices must be equipped with a chip that emits and receives the frequency of 2,4 GHz available worldwide. In addition to information, there are three channels of voice.
Information can be exchanged up to 1 megabit per second, or 2 megabits per second in the second generation. A scheme of \frequency hopping\ allows the devices to communicate inclusive in the regions where there are large electromagnetic interference.
The Bluetooth standard works in the 2.4 GHz band.
It's the frequency band of the scientific and medical industries. Bandwidth in Europe and the United States is between 2,400 to 2,483 MHz and it covers a part of the France and the Spain. The bandwidth to the Japan is between 2,471 to 2,497 MHz.
If the system can be used anywhere in the world is because radio transmitters cover 2,400 and 2,500 MHz and it is possible to select the appropriate frequency. This standard is open to all radio systems and must take into account interference from baby monitors, controls for the gates of garages, wireless phones and ovens to microwaves.
In general, communications equipment must accept any interference.
Transmission equipment are classified into 3 groups according to the level of emission power. Equipment recipient must have a sensitivity of at least 70 dBm, and the tau of permissible error must be less than or equal to 0.1%.
|Device||power mW (dBm) class||range (approximate)|
|Class 1||100 mW (20 dBm)||100 meters|
|Class 2||2.5 mW (4 dBm)||10 meters|
|Class 3||1 mW (0 dBm)||1 meter|
It must be incorporated into portable devices, that is why she must have a very limited consumption (up to 97 times less than a mobile phone). If BlueTooth devices don't exchange information, they establish a waiting to save energy.
Transmission power which is used is 1 mW with a range of 10 m, 100 mW for a range up to 100 m.
The connections have a maximum range of 10 meters, but using amplifiers it is possible to reach up to 100 meters, with a slight distortion. It must be remembered that these devices have been created to be used in closed environments and short distance.
It is necessary to pay attention to the devices that work in the same frequency band.
For example, just as it is forbidden to use mobile phones in aircraft, it is possible to prohibit the use of any device that integrates a Bluetooth chip, because it can interfere with navigation elements.
It was designed to maintain a constant communication, even moving and inside briefcases, and so it can operate without the user noticing.
The versatility of the design of BlueTooth technology allows easy design and the layout of networks between different devices.
BlueTooth is designed to work in a multiuser environment. The standard sets out two types of configurations to support a considerable number of items and develop networks and subnets.
The structure that manages this technology consists of a piconet and in a slightly more complex structure, a Scatternet.
Up to eight users or devices can form a piconet and up to ten piconet can coexist in the same area. Knowing that each link is codified and protected from parasites and loss of connection, Bluetooth can be regarded as a very safe short range wireless network.
The pico network consists of several devices that are in the same radio coverage where they share the same channel. It is comprised between two and eight of these units. Each device is based on the standard IEEE 802.19 for WLAN, while the Scatternet which is formed by the connection of the pico network between them, has a maximum of ten inter-connexions.
The Scatternet was introduced to the problem of the low bandwidth available to each user of a piconet if there is a large amount of connected units.
Performance, overall and individual users of a Scatternet is better than all users have when they are in the 1 MHz channel.