Using Bluetooth technology to implement a home wireless network system

Author: Zhang Zhi-rong Qian Ying, Zeng Zhou, School of Precision Instruments and optoelectronic engineering, Tianjin University
　　
Abstract: using Bluetooth technology, you can quickly connect to personal computers, mobile phones, PDAs, digital cameras, printers, televisions, air conditioners, washing machines, and other household appliances and office equipment without cables, A convenient and practical "wireless micro-network" is formed to provide users with great convenience and new service functions can be derived. The Bluetooth Network technology enables traditional household informatization and is closely integrated with the information expressway-communication network.
　　
Keywords: Bluetooth mini-network Wireless Access Frequency Hopping spectrum Expansion protocol stack
　　
Introduction
　　
An important aspect of today's informatization is the rapid development of the Internet and mobile communication. It makes great changes to people's lifestyle, work style, and way of thinking. It also stimulates people's increasing demands for various data sources and network services outside the computer. The emergence and development of smart home networks have injected new vigor and vitality into the information society. The increasingly mature bluetooth technology has undoubtedly contributed to this new wave.
A home network is a network formed by connecting all information devices in the home before the information network of the home and society is connected. Obviously, the most ideal technology for connecting to a home network is wireless communication technology, which replaces the intricate cables in traditional networks with microwave. Currently, there are many products and standards related to this technology, such as butterfly, diamond, proxim, shavewave, and other companies. The most representative of these technologies are Bluetooth and homerf. The advantage of Bluetooth lies in the unification of global standards, interoperability, and convenient fast, flexible, secure, low-cost, low-power data and voice communication, therefore, Bluetooth technology has great potential in the home wireless network system.
　　
System Design
　　
The Bluetooth carrier is used in the world's GHz engineering medical (ISM) frequency band and uses the Frequency Hopping (FHSS) technology ). The frequency hopping rate is 1600 times per second. A maximum of 79 1 MHz bandwidth channels can be obtained at a GHz center frequency. The Bluetooth device uses gfsk modulation. The transmission rate is 1 Mb/s. The actual effective rate is up to kb/s, and the transmission distance is 10 m. Voice Transmission uses Continuous Variable Slope modulation coding (CVSD) technology, while communication protocols use time division multiple access (TDMA) protocol. All types of data and voice devices that follow the Bluetooth protocol can be connected to public network systems (such as Internet and Intranet) wirelessly ).
The Bluetooth system is based on point-to-point (Point-to-Point Protocol) connections. Several Bluetooth devices are wirelessly connected to a topology micro-Network (piconet) of the master and slave devices in micrograph 1 ). Each piconet bluetooth device is composed of one master device and several slave devices (slave). The master device is responsible for communication protocol operation. The MAC address is expressed in three bits, that is, eight devices can be addressable in one micro-network (the number of connected devices is actually unlimited, but only eight devices can be activated at the same time, one of them is primary, and seven are slave ). Figure 1 shows the topology of a Master/Slave Device in the micro-network. In addition, the Bluetooth system supports point-to-point communication to form a distributed network, that is, one master device can be another piconet slave device, and each slave device can also be another piconet master device.
　　　
1. hardware composition
Figure 2 hardware structure of the device 3 hardware structure of the master device the hardware structure of the system mainly includes: antenna unit, GHz power amplifier module, bluetooth module, audio codecs, embedded microprocessor system, interface circuit and some auxiliary circuits. In addition, the main device includes the Ethernet interface and embedded Modem. Figure 2. Figure 3 shows the hardware structure of the master and slave devices of the system. The system antenna is a micro-antenna, so the antenna can be small in size and light in quality. The air interface is based on the antenna level of 0 dBm and complies with the FCC (Federal Communications Commission) ISM band standard with the level of 0 dBm. Because Bluetooth uses the frequency hopping technique, the antenna must be a broadband antenna with a frequency starting from 2.402 GHz and a frequency ending from 2.480 GHz. To resist multi-path interference, the system is designed as a variety of antennas. The system's power amplifier operates in the 24 GHz ISM band that can be used worldwide. The power amplifier bandwidth is 2400 ~ 24835 MHz. The system designed communication distance is 10 m (0 dB ). If the transmit power is increased to 20 dB (100 MW), the distance will reach 100 MB. The microprocessor system of the main device adopts an embedded system, which is a key technical difficulty in the system. From a certain point of view, the master device acts as a smart gateway. It is the core part of the home wireless network system. It needs to complete the conversion and information sharing among various communication protocols in the home wireless network, as well as the data exchange function between the communication networks, it also manages and controls various slave devices. Taking into account what ordinary home users can accept, microprocessor uses non-PC cheap equipment, Master, Slave Device processor uses embedded Internet technology and high performance microprocessor. The Bluetooth module converts some baseband protocols and integrates the voice data streams sent by the digital voice processing circuit with the data sent by the microprocessor, after being encoded and modulated, it is sent to the Power Amplifier for amplification and then sent to the wireless device. This module consists of two main units.
　　　
Figure 2 device-to-hardware structure
　　　
Figure 3 hardware structure of the master device
　　
(1) radio frequency (RF) unit. The RF unit power of the bluetooth module also meets the requirements of the FCC for the ISM band. Therefore, unpredictable interference sources may occur during use. The Bluetooth module is specially designed with fast validation and frequency hopping to ensure link stability. In the 2.4 GHz ISM band, a jump is made at a pseudo-random rate of 1600 times/s at a total of 79 frequencies (at a GHz center frequency, A maximum of 79 channels with 1 MHz bandwidth can be obtained. This can effectively prevent signal interference and weaken. Compared with other systems that work in the same frequency band, Bluetooth is faster and data packets are shorter, which makes Bluetooth more stable than other systems. In addition, the system also uses the Time Division Duplex (TDD) solution to achieve full duplex transmission. The use of FEC blocks random noise on long-distance links.
(2) baseband (baseband, BB) and Link Management (linkmanager, lm) units. BB is responsible for the transmission of frequency hopping and Bluetooth data and information frames; Lm is responsible for the establishment and removal of connections. Their functions include: support for SCO and ACL connection methods; Error Control, which can adopt multiple checking and error correction methods, including forward Correction Code (FEC ); physical Layer authentication and encryption; Link Management. The digital speech processing circuit consists of the Speech Encoding and decoder and the speech interface circuit. The audio codecs adopt the CVSD encoding method. CVSD (Continuous Variable Slope Delta Modulation) is a continuous variable slope incremental modulation. It is an adaptive incremental modulation technology that can obtain high-quality audio encoding without resending voice packets. CVSD encoding is good at processing lost and corrupted voice samples. Even if the bit error rate reaches 4%, the CVSD encoding speech is still audible. The voice interface circuit includes the standard audio input and output, and the necessary audio amplification. The RS232, USB, UART, I2C interface, and telephone line interface are set in the system interface section. In addition, the main device also has Ethernet interface and ADSL Jack. RS232, USB, and UART are connected to computers, smart headsets, PDAs, and smart appliance devices to exchange information. The RS232 serial port in the main device is also used for field parameter setting and program upgrade. Embedded Modem is the physical interface between the system and external communication networks (Internet and public telephone networks. Embedded Modem uses a simple and flexible implementation method to reduce the complexity of the system and reduce the dependence of general household users on the basic modem operation skills. embedded Modem needs to complete the basic functions of modem, connect the home wireless network to an external communication network. According to the modem development status, the system modem adopts the ADSL high-speed modem standard. You can directly connect to a LAN through an Ethernet interface. The system can connect to the DSL through the internal high-speed data tunnel and the embedded Modem, and log on to the Internet through the signal splitter of the ADSL modem, in this way, you can enjoy the various information and services provided by the ISP service provider. The auxiliary circuit includes the LCD circuit, keyboard control circuit, and power management circuit.
2 software protocol stack
The software (protocol stack) Unit of the system is an independent operating part and is not bundled with any operating system. It complies with the established Bluetooth specifications. The system's protocol stack adopts a layered structure, data Stream filtering and transmission, frequency hopping and data frame transmission, connection establishment and release, link control, data disassembly, service quality, protocol reuse and reuse, and other functions are completed respectively. The protocol stacks of the master and slave devices are slightly different, as shown in Figure 4 and figure 5, but they are roughly divided into three layers: The underlying protocol, the intermediate protocol, and the high-level protocol.
　　
(1) underlying protocol. This layer includes baseband BB and Link Management (LM ). These protocols have been fixed in the bluetooth module. The underlying protocol is very transparent to applications and is responsible for establishing physical RF links between bluetooth units to form a micronetwork. Lm also needs to complete security tasks such as authentication and encryption, this includes generation and exchange of encryption keys, link check, baseband packet size control, power mode and clock cycle of Bluetooth wireless devices, and connection status of the Bluetooth unit in the micronetwork.
(2) Intermediate protocol. This is part of the protocol to be developed in the system. Including Logical Link Control and Adaptation Protocol L2CAP and Service Discovery Protocol (SDP) serial Port simulation protocol RFCOMM, Telephone Control Protocol TCS (only in the master device protocol stack) and PPP protocol. The Logical Link Control and Adaptation Protocol (L2CAP) is used to adapt the baseband protocol to the high-level protocol, and provides high-level data businesses and classification extraction through Protocol reuse, reuse, and restructuring. It allows high-level protocols and applications to receive or send up to 64000 bytes of L2CAP packets. The service Search Protocol (SDP) is an extremely important part and serves as the basis for all usage modes. It provides a mechanism for upper-layer applications to discover available services and their features in the network. The SDP can query device information, services, and features, and establish connections between two or more Bluetooth devices after the query. SDP supports three query modes: search by service type, search by service attribute, and browsed by business attributes ). The serial port simulation protocol RFCOMM is also located on The L2CAP. It simulates the RS232 control and data signal on the Bluetooth baseband, provides transmission capabilities for advanced businesses that use serial lines as transmission mechanisms (such as Object Exchange OBEX protocol. This protocol was developed by bsig of the Bluetooth Special Interest Group based on the ETSI standard ts07.10. Telephone Control protocols include the telephone control specification binary (TCS bin) protocol and a set of telephone control commands (AT/| commands ). The TCS bin defines the call control signaling required to establish voice and data calls between bluetooth devices; at/| commands is a set of commands that can be used to control mobile phones and modem in multi-use mode. It is also developed based on ITU/| T q.931.
(3) high-level agreement. The general principle of designing high-level protocols is to try to absorb existing mature protocols. The Protocols adopted by the system are PPP and UDP/TCP/IP. PPP running and serial port simulation protocols above RFCOMM are used to implement point-to-point