Bluetooth: technology and its application

It is possible that it is with these words of the medieval Danish king Harald II Sinezuby (Harald II Bluetooth) that his other nickname is connected - the "unifier", after 1000 years which became the name of the new wireless communication interface... and he said: "may all be reunited."

What is bluetooth? This is a wireless technology created in 1998 by a group of companies: Ericsson, IBM, Intel, Nokia, Toshiba. Currently, Bluetooth is being developed by Bluetooth SIG (Special Interest Group), which also includes Lucent, Microsoft and many others.

The main purpose of Bluetooth is to provide economical (from the point of view of current consumption) and cheap radio communication between various types of electronic devices, and considerable importance is attached to the compactness of electronic components, which makes it possible to use Bluetooth in small-sized devices the size of a watch.

The Bluetooth interface allows you to transfer both voice (at a speed of 64 Kbps) and data. For data transmission, asymmetric (721 Kbps in one direction and 57.6 Kbps in the other) and symmetric methods (432.6 Kbps in both directions) can be used. A transceiver operating at a frequency of 2.4 GHz, which is a Bluetooth chip, allows you to establish communication within 10 or 100 meters, depending on the degree of power. The difference in distance is, of course, large, but the connection within 10 m allows you to maintain low power consumption, compact size and a fairly low cost of components. Thus, a low-power transmitter consumes only 0.3 mA in standby mode and an average of 30 mA when exchanging information.

Bluetooth operates on the principle of FHSS (Frequency-Hopping Spread Spectrum). Briefly, this can be explained as follows: the transmitter breaks the data into packets and transmits them according to a pseudo-random frequency hopping algorithm (1600 times per second), or to a pattern composed of 79 sub-frequencies. Only those devices that are configured for the same transmission pattern can “understand” each other - for external devices, the transmitted information will be ordinary noise.

The main structural element of the Bluetooth network is the so-called "piconet" - a combination of 2 to 8 devices running on the same template. In each piconet, one device acts as a master, and the rest as a slave. Master defines a template on which all slave devices of its piconet will work, and synchronizes its work. The Bluetooth standard provides for the connection of independent and not even synchronized piconets (up to 10) into the so-called "scatternet" (I have not yet seen the correct Russian translation of this term, but one of the options for translating the verb to scatter sounds like "scatter"). To do this, each pair of piconets must have at least one common device that will be a master in one and a slave in another. Thus, within a single scatternet with a Bluetooth interface, a maximum of 71 devices can be connected at the same time, however, no one restricts the use of gate devices that use the same Internet for further communication.

The frequency range of Bluetooth in most countries is free of licensing, but in France, Spain and Japan, due to legal restrictions, it is necessary to use frequencies other than those indicated above.

Speaking about wireless communications, one cannot but address the issue of security of such a connection. In addition to the focus with frequency patterns and the need to synchronize the transceiver, the Bluetooth standard provides encryption of transmitted data with an effective key from 8 to 128 bits and the ability to select one-way or two-way authentication (of course, you can do without authentication at all), which allows you to set the strength of the resulting encryption in accordance with the laws of each individual country (in some countries the use of strong cryptography is prohibited :). In addition to encryption at the protocol level, application-level encryption can be applied - no one restricts the use of arbitrarily strong algorithms here.

Often you have to come across the opinion that the Bluetooth devices within the range of communication can simply connect and begin to exchange information that may not be suitable for third-party ears or eyes. In fact, the automatic exchange of information between Bluetooth devices is carried out only at the hardware level, i.e. solely to determine the very fact of connectivity. But at the application level, the user decides whether to enter or prohibit automatic communication. Thus, the use of Bluetooth is no more dangerous than an Internet connection, in which all nodes are also electrically connected, but this does not mean obtaining unconditional access to any resource.

It is also worth noting that the Bluetooth standard was developed with the expectation of low power, so its impact on the human body is minimized.

The main focus of using Bluetooth should be the creation of so-called personal networks (PANs, or private area networks), which include such diverse devices as mobile phones, PDAs, MP3 players, computers, and even microwave ovens with refrigerators (this is something that has not been connected to network ). The ability to transmit voice allows you to embed the Bluetooth interface in cordless phones or, for example, wireless headsets for cell phones. The possibilities of using Bluetooth in practice are endless: in addition to synchronizing the PDA with a desktop computer or connecting relatively low-speed peripherals such as keyboards or mice, the interface makes it easy to organize a home network at a low cost. Moreover, the nodes of this network can be any devices that have a need for information or have the necessary information.

Let's compare Bluetooth with another equally well-known wireless interface - IEEE 802.11, especially since both solutions are already available in a wide market. The main differences between them can be reduced to the following:

As you can easily see, the Bluetooth interface is much better suited for use in those wireless communication devices where a fairly low price is required, there is no need for high speeds and preferably low power consumption. However, as already noted, the creation of combined networks is possible, especially since IEEE 802.11 works on a completely different principle of encoding the transmitted data, therefore, being at the same operating frequency, both standards will hear each other physically, but each other's signals will be regarded by each of them like extraneous noise.

An important aspect in the development of Bluetooth is the fact that this technology is not subject to licensing and its use does not require payment of any royalties (although it does require the signing of a free agreement). This policy has allowed many companies to energetically get involved in the development of Bluetooth devices, which were demonstrated in large numbers at CeBIT 2001.

The greatest interest, of course, is caused by devices that provide a transition from existing interfaces to Bluetooth. One of them was the Industrial Bluetooth Serial Port Adapter of the Swedish company connectBlue . As the name implies, this device is intended for industrial use and allows you to connect any devices equipped with a serial port to Bluetooth:

A typical use case may be, for example, configuring industrial installations with a laptop.

Specifications:

• range of action - up to 10 m,
• transfer rate - 300-115200 Kbit,
• supply voltage - 9-30 Volts.

Belkin, famous, in particular, for its products for the USB bus, introduced a range of Bluetooth devices: