"Turn" Bluetooth technology and its system principle

The UMTS "Bluetooth" technology is made up of the world-renowned 5 big companies-Ericsson (Ericsson), Nokia (Toshiba), International Business Machines (IBM) and Intel, A new technology for wireless communications, announced in May 1998. It is for: 1 Bluetooth Technology "Bluetooth" was originally the European medieval Danish emperor Hnddⅱ name, he for the unification of the fragmented Sweden, Finland, Denmark has the immortal credit. Ericsson, a Swedish company that is about to become the world's most versatile wireless technology, may have a eminence meaning.

Bluetooth technology is an open and global specification for wireless data and voice communication, which is based on low-cost near-distance wireless connection and establishes a specially connected short-range radio technology for stationary and mobile device communication environments. Its substance is to establish a universal Radio air Interface (Radio air interface) and its control software open standards, so that the communication and computer integration, so that the different manufacturers of portable equipment in the absence of wire or cable interconnection, can be in the close range of interoperability, Interoperable performance (interoperability). Its program is written in a 9mmx9mm microchip.

The role of Bluetooth technology is to simplify the communication between small network devices (such as mobile PCs, PDAs, mobile phones) and between these devices and the Internet, eliminating the cordless phone or mobile phone, modem, head-to-head/receiver, PDAs, computer, printer, slide projector, Add wires, cables, and connectors between LAN, etc. Moreover, this technology can be extended to completely different new devices and new applications. For example, if you put Bluetooth technology into your mobile phone and laptop, you can get rid of the annoying connection cable between your mobile phone and your laptop and make it communicate wirelessly. Printers, PDAs, desktops, fax machines, keyboards, game joysticks, and all other digital devices can be part of a Bluetooth system. In addition, Bluetooth wireless technology provides a common interface for existing digital networks and peripherals to form a personal, specially connected device group away from fixed networks.

"Bluetooth" Technology radio transceiver link distance of up to 30 feet, not limited to the line range, even the equipment is not in the same room can be linked to each other, and can link multiple devices, up to 7, which can be linked to the device around the user, forming a "personal domain network" (Personal areanetwork).

2 Bluetooth system

Before understanding the structure of Bluetooth system, first familiar with the Bluetooth system a few commonly used terminology.

*piconet: All devices connected by Bluetooth technology are considered to be a piconet. A piconet can be just two connected devices, such as a laptop computer and a mobile phone, or 8 devices connected to one another. In a piconet, all devices are units of the same level, with the same permissions. However, at the beginning of the Piconet network, one of the units is defined as master, and the other units are defined as slave.

*master Unit: The main unit, in one piconet, whose clock and frequency hopping sequence are used to synchronize the devices of other units.

*slave units: From the unit, that is, all devices in piconet that are not master.

* Scatternet: several independent and unsynchronized piconet form a scatternet. * MAC address: Used to distinguish the 3-bit length of each unit in the piconet.

Parked units: Pause unit, which is a device in piconet that is synchronized with the network but does not have a MAC address.

*sniff and hold mode: A mode of operation that synchronizes with the network but goes to sleep to conserve energy.

The Bluetooth system generally consists of the following 4 functional units:

* Antenna Unit

* Link Control (firmware) unit

* Link Management (software) unit

* Bluetooth Software (protocol) unit

2.1 Day Line Unit

Bluetooth requires the antenna part of the volume is very small, light weight, so the Bluetooth antenna belongs to the Microstrip antenna. The Bluetooth air interface is built on the basis of an antenna level of 0 dbm. The air interface follows the federal communication Commission (FCC, the Federal Communications Commission) standard for ISM bands with a level of 0 dbm. If the global level reaches more than a few MW, you can use the extended Spectrum feature to add additional services. The spectrum expansion function is achieved by starting at a frequency of 2.402GHz and terminating at 2.480GHz with an interval of 1MHz of 79 hops. For some local regulations, Japan, France and Spain have reduced their bandwidth. The maximum frequency hopping rate is 1660 hops/s. The ideal connection range is 100mm~10m, but the distance can be extended up to 100m by increasing the transmit level.

Bluetooth works in the global 2.4GHzISM (ie, industrial, scientific, medical) frequency bands. The data rate for Bluetooth is 1mb/s. The ISM band is a band that is open to all radio systems, so using one of these bands will encounter an unpredictable source of interference. For example, some home appliances, cordless telephones, car door opener, microwave ovens and so on, may be interference. To this end, Bluetooth specifically designed a fast confirmation and frequency hopping scheme to ensure that the key path stability. Frequency hopping technology is divided into a number of frequency hopping channel (hop channel), in a single connection, the radio transceiver in accordance with a certain code sequence (that is, a certain rule, technically called "pseudo-random Code", is "false" random code) constantly from one channel "Jump" to another channel, Only the sending and receiving parties are communicating according to this law, while the other disturbances cannot be interfered by the same rules; the instantaneous bandwidth of the hops is very narrow, but by extending the spectrum technology, the narrow band is extended to a wide frequency band, which can make the effect of the interference become very small. The Time Division Duplex (Time division Duplex, TDD) scheme is used for full-duplex transmission.

Compared to other systems working in the same frequency band, Bluetooth is faster and the packets are shorter, which makes Bluetooth more stable than other systems. The use of FEC (Forwarderrorcorrection, forward error correction) inhibits the random noise of long-distance links, and frequency-hopping transceivers using binary FM (FM) technology are used to suppress interference and prevent fading.

2.2 Link Control (firmware) unit in the current Bluetooth product, 3 ICS are used as join controllers, baseband processors, and RF transmission/receivers, in addition to the use of 30~50 individual tuning elements.

The baseband link controller handles baseband protocols and some other low-level general protocols.

The baseband controller has 3 error correction options:

*1/3 Proportional forward Error correction (FEC) code;

*2/3 Proportional forward error correcting code;

* Data automatic request re-send scheme.

The purpose of the FEC (forward error correction) scheme is to reduce the number of times the data is re-sent and to reduce the load. However, to achieve error-free transmission of data, FEC is bound to generate some unnecessary overhead bits and reduce the data transfer rate. This is because the packet is elastically defined for whether FEC is used. The header always has a 1/3 ratio of FEC code protection, which contains useful key path information.

In an unnumbered ARQ scheme, the data transmitted in a single timeslot must be acknowledged at the next timeslot. Only the data will send the acknowledgement message back to the originator after the receiver has passed header error detection and cyclic redundancy detection, otherwise an error message is returned. For example, the voice channel of Bluetooth uses continuous Variableslope Dalta modulation (abbreviated as CVSD, continuous variable slope increment modulation technology) voice coding scheme to obtain high-quality audio encoding of transmission. The CVSD code excels at handling lost and corrupted voice samples, even if the bit error rate reaches 4%,CVSD encoded voice or audible.

and Cambridge Consultants Company Cambridge Silicon Radio. Their views were raised. This company's man door product is a single-chip transmitter and a connection controller. The company calls Bluecore and Bluestack. This is a complete Bluetooth, does not require external saw filters, ceramic capacitors or sensors, product integration is very high, using 0.18 or 0.15pm technology, can be almost without increasing the cost of the baseband circuit to add to the chip.

2.3 Key Path Management (software) unit

The link management (LM) software module carries data settings, authentication, link hardware configuration, and other protocols for the link. LM is able to discover other remote LM and communicate with it via the LMP (Key Path Management protocol). The LM module provides the following services:

(1) Sending and receiving data.

(2) The name of the request.

(3) Link address query.

(4) Establish a connection.

(5) authentication.

(6) Link mode negotiation and establishment.

(7) determines the type of frame.

(8) Set the device to sniff mode. Master can only send data in a specific time slot regularly.

(9) Set the device to hold mode. The device that works in hold mode for energy saving stops receiving data for a longer period of time, averaging every activation of the link, which is defined by LM, LC (link Controller) specific operation.

(10) Set the device to pause mode when the device does not need to transmit or receive data but still need to remain synchronized. A device in suspend mode periodically activates and tracks synchronization while checking the page message.

(11) Establish a network connection. All devices are in standby (standby) state until the connection within the piconet is established. In this mode, the disconnected unit periodically "listens" to information every 1.28s. Whenever a device is activated, it listens to the 32 hops that are planned for the unit. The number of hop points varies by geographic region, and the 32 figure applies to most countries except Japan, France and Spain. The device that is the master initializes the connector first, and if the address is known, establishes a connection through a pager (page) message, and if the address is unknown, a connection is established through a inquiry (query) message that is followed by the page message. In the initial paging state, The master unit sends a string of 16 identical page blanking points on the 16 hop frequencies assigned to the paging unit. If there is no answer, master continues paging on the remaining 6 frequency points in the order of activation. Slave The maximum latency for messages received from Master is twice times the activation cycle (2.56s), and the average late time is half of the activation cycle (0.6s). Iqnuiry is mainly used to find Bluetooth devices, such as co-cooked printers, fax machines and other similar devices with unknown addresses, inquiry messages are very similar to page messages, but Inquriy messages require an additional data string cycle to collect all responses.

If a device already connected in piconet has no data transfer for a longer period of time, Bluetooth also supports energy-saving mode of operation. Aster can put salve into hold mode, in which only one internal counter is working. The slave can also be actively asked to be placed in hold mode. Once in hold mode it is commonly used to connect several piconet or low energy devices, such as temperature sensors. In addition to hold mode, Bluetooth supports two other energy-saving modes of operation: Sniff (breathing) mode and park (pause) mode. In sniff mode, slave reduces the rate of "listening" to messages from Piconet, and the "breathing" interval can be adjusted appropriately to the application requirements. In park mode, the device still synchronizes with piconet but no data is transferred. The device working in park mode abandons the MAC address, occasionally listens to master's messages and resumes synchronization, checking broadcast messages. If we line up these modes of work in ascending order of energy efficiency, then the following are: Breathing mode, hold mode, and pause mode.

(12) Connection type and packet type. The connection type defines what type of packet can be used in a special connection. Bluetooth baseband technology supports two types of connections: synchronous directional Connection (synchronous Connection oriented, hereinafter referred to as SCO) type, mainly used for transmitting voice; asynchronous no connection (asynchronous connectionless, ACL) type, primarily for transmitting packets.

Different slave-to-master pairs in the same piconet can use different connection types, and you can change the connection type arbitrarily in one phase. Each connection type can support a maximum of 16 different types of packets, including 4 control groupings, which are the same for SCO and ACL. Both connection types use TDD (Time Division Duplex Transfer Scheme) for full-duplex transmission.

The SCO connection is a symmetric connection that transmits packets using the reserved timeslot. After the connection is established, master and slave can send SCO data without being selected. SCO packets can either transmit voice or transmit data, but only use it to re-send the damaged portion of data when transmitting data.

An ACL link is a directed sending packet that supports both symmetric and asymmetric connections. Master is responsible for controlling the link bandwidth and determining how much bandwidth and connection symmetry each slave in the piconet can occupy. Slave can only be transmitted if it is selected. The ACL link also supports receiving the broadcast messages that master sends to all slave in piconet.

(13) authentication and confidentiality. The Bluetooth baseband section provides users with protection and information security mechanisms at the physical level.

Authentication is based on the "Request Response" algorithm. Authentication is a key part of a Bluetooth system that allows a user to create a trusting domain for a personal Bluetooth device, such as allowing only the owner's own laptop to communicate through the owner's own mobile phone. Encryption is used to protect the personal information of the connection. The key is managed by the top level of the program. Network transport protocols and applications can provide users with a strong security mechanism.

2.4 Software (Protocol) unit

The Bluetooth baseband protocol combines circuit switches and packet switches for voice and data transmission. Each channel supports a kb/s sync (voice) link. The asynchronous channel supports either side up to 721kb/s and the return direction 57.6kb/s asymmetric link, also can support 43.2kb/s symmetric connection. Therefore, it can cope with very large data ratios on the cellular system quickly enough. In general, its link range is 100mm~10m, and if the transmission power is increased, its link range can be extended to 100m. The Bluetooth software Architecture specification requires devices that are compliant with Bluetooth to support basic levels of interoperability. This level of compliance is determined by different applications.

Bluetooth devices need to support some basic interoperability feature requirements. For some devices, this requirement involves wireless modules, air protocols, and application-layer protocols and pair-like interchange formats. The Bluetooth1.0 standard consists of two files. One called Foundationcore, which specifies the design criteria. The other is called Foundationprofile, which prescribes the principle of interoperability. But for other devices, such as headphones, this is a much simpler requirement. Bluetooth devices must be able to identify and load the corresponding software with each other to support higher level performance of the device.

Bluetooth has different requirements for different levels of devices (such as PCs, handhelds, mobile phones, headsets, etc.), for example, you can't expect a Bluetooth headset to provide an address book. But mobile phones, handheld computers and laptops need to have more features.

The Software (protocol) structure should have the following functions:

• Setup and fault diagnosis tools;

• Can automatically identify other equipment;

• Replace the cable connection;

• Communication with peripherals;

• Audio communication and call control;

• Commercial card transactions and directory network protocols.

The Bluetooth Software (protocol) unit is a standalone operating system that is not bundled with any operating system. Bluetooth specifications for several different commercial operating systems are being perfected.

3 concluding remarks

With the rapid development of mobile communications in recent years, portable computers such as laptops (Laptop), Laptops (Notebook), handheld computers (HPC) and personal digital aids (PDAs) have also developed rapidly, and the rapid development of the Internet, There is a growing demand for the transmission of data messages beyond telephone communications.

"Bluetooth" technology to the various portable computers and cellular mobile phone with the radio plating Road, so that the computer and communication more closely together, so that people can be anywhere to exchange and transfer of data information. Therefore, the computer industry, mobile communications industry, "Bluetooth" technology attaches great importance to the future of wireless mobile data communications business has a huge boost, it is expected in recent years wireless data communications business will grow rapidly. "Bluetooth" technology is considered one of the most significant advances in wireless data communication.

"Turn" Bluetooth technology and its system principle