Bluetooth Protocol
2.2.6 Bluetooth Protocol
In May 1998, Ericsson, Nokia, Toshiba, IBM and Intel jointly proposed Bluetooth technology, with the tenet of providing a short-distance, low-cost wireless transmission technology. Bluetooth is a wireless data communication technology. Its transmission rate is 1Mbps, and transmission distance is approximately 10 meters. With Bluetooth technology, the communication among PDA, laptop computer and cell phones can be more efficient and faster. Therefore, Bluetooth successfully simplifies the interconnection between the portable devices and the Internet. Its application can be extended to domestic apparatus and automobiles,
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thus forming a huge wireless network. The Bluetooth system is composed of several functional units: wireless unit, link control unit, link management unit and relevant software. Bluetooth technology works at the global universal frequency 2.4 GHz ISM, and the transmission rate is 1 Mb/s, using Time Division Duplex (TDD) to realize Full Duplex Transmission (FDT). The system infrastructure is illustrated in Fig. 2.8.
Figure 2.8 The system framework of Bluetooth In the 2.4 GHz frequency interval, the client device does not need to apply for
access to the frequency. And most countries have similar regulations concerning the use of this frequency. Thus Bluetooth has the following features:
(1) Short transmission distance: Now the work distance of Bluetooth is less than 10 meters, and it can reach 100 meters after RF power is amplified. This range guarantees that Bluetooth has a high transmission rate, while rarely interfered by other apparatus and products.
(2) Frequency-hopping spread spectrum technology: The frequency interval
2.4 machine and subordinate machine, frequency of hopping is 1600 ps. Frequency- hopping technology is used to guarantee higher security and anti-jamming performance of Bluetooth wireless links. The air interface of Bluetooth is based on the PWL of antenna that is 0dBm. The air interface conforms to relevant standards of ISM issued by FCC. When the global PWL reaches more than 100mW, spread spectrum can be used to realize some supplementary operations. Spread spectrum function is realized by 79 points at an interval of 1 MHz between 2.402 GHz and 2.480 GHz. As a result of consideration of local regulations, bandwidth has been narrowed down in Japan, France and Spanish, where the maximum hopping rate is 1660 ps.
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(3) Time division multiple access (TDMA) technology: The basic band rate of Bluetooth is 1Mbps, and transmission is executed in the form of data packet according to time slots (TS), 0.625ms per TS. Much higher rate of transmission is not excluded in the future. Each Bluetooth equipments sends data packets within its own TS, which effectively avoids “collision” and “hidden terminal” in wireless communication.
(4) Network technology: Several piconets can be connected in sequence and identified according to the sequence of hopping. All users within the same picot synchronize with the sequence. And the topological structure is described as multi-piconet structure. In a multi-piconet structure composed of 10 independent piconets, the data transmission rate can exceed 6Mb/s.
(5) Voice support: The voice channel adopts the CVSD coding solution, and does not resend voice datagram. CVSD is good at dealing with lost and damaged voice sampling, and even if the error rate reaches 4%, it is still recognized after processed by CVSD.
(6) Error correction technology: Bluetooth uses Forward Error Correction (FEC), which aims to reduce the resending of data and load of data transmission. However, to realize errorless transmission, FEC has to generate some bit of extra load, thus lowering the data transmission rate. That is because datagram has flexible definition as to whether to use FEC. The datagram head has at least 1/3 part of protective FEC code, which includes useful link information. Within a numberless ARQ solution, the data transmitted in a time slot must be confirmed in the next time slot. It is until data have been proven errorless at the receiving terminal through header-error-check and cyclic redundancy checks that the confirmation message will be sent back to the sending terminal. Otherwise an error message will be returned.
The baseband of Bluetooth can provide security and encryption mechanism for users at the physical layer. Authentication is the key part in the Bluetooth system, which allows the user to establish a trust domain for the personal Bluetooth device.
Encryption is used to protect personal information. The key is managed by the upper part of program. Network protocols and applications can provide a stronger security mechanism for the user.
The standardization of Bluetooth can be divided into three phases. The first phase began from 1997, in which three enterprises including Ericsson determined the business model through negotiation. The second phase began from May 1998, in which the first version of Bluetooth technical regulation was published. In the third phase authentication of machine format was taken into account.
In the first version of technical regulation, the data transmission rate is prescribed as 1Mbps (nominal value), and the transmission distance is about 10 meters (when the transmission power is 1mW), with frequency 2.4GHz. In this frequency band there are 99 channels with 1MHz each. Frequency hopping 1600ps is allowed. When data is transmitted, the maximum currency is 30mA, which can
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drop to below 0.3mA in standby. Moreover, it is estimated that in 2001 the data transmission would be increased to 10Mbps to meet the need of image transmission.
As described above, authentication should be made in the physical layer as well as between machines from different manufacturers. Although the authentication in the physical layer started with LSI from the fourth quarter of 1999, the experiment on interconnection between machines produced by different manufacturers still waits for the Qualification Program, technical parameters of which was accomplished in the middle of 2000. However, Bluetooth SIG has determined so-called Branding system. Equipment manufacturers test according to the sequence prescribed by the program before submitting it to the authentication organization. The machine that is authenticated will be given the mark of Bluetooth technology. If Bluetooth equipment without this mark is sold, Bluetooth SIG will fine its manufacturer and claims fees of patent.
The Bluetooth interface can be integrated into the laptop computers or connected with computers via PCI card or USB. Bluetooth is an independent technical standard, which does not depend on any other technical regulations.
(1) Personal LAN The Bluetooth interface can be integrated to the cell phone or connected via
appended device. The application models of telephone include: hand-free telephone using Bluetooth; the wireless connection between laptop computer and cell phone. Thus, the application of Bluetooth to laptop computer, cell phone and office phone can realize personal communication in its true sense. This “personal LAN” uses cell phone as gateway, rendering more convenient information exchange among portable devices.
(2) Domestic wireless networking Although there are various domestic apparatus and devices, Bluetooth technology
makes interconnection among all these devices wireless except power supply, including refrigerator, washing machine, TV and microwave over.
(3) Mobile office Bluetooth enables laptop computers and cell phone to access the printer, DC,
recorder, etc., thereby creating a mobile office. (4) Internet access Bluetooth standard defines interfaces for Internet, LAN and WAN. Therefore a
single Bluetooth standard is enabled to establish connections with various networks. Equipments with built-in Bluetooth chip can access to the Internet.
(5) E-commerce application The security feature of Bluetooth will tremendously extend the existing
e-commerce systems, and structure the e-payment systems in various consumption circumstances.
(6) Others Bluetooth can apply to other devices including HID devices, data and voice
access points. Many companies are developing products with Bluetooth features, which enable access to resources in LAN. In the future, WAN and personal
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information network will be developed, which will enable users to move anywhere without disconnection to the networks.