GSM full name: Global System for Mobile Communications, Chinese for the Global System for Mobile Communications, commonly known as the "GSM", is a mobile communications technology standards originated in Europe, is the second generation of mobile communications technology, the development of which is to allow the world to ** ** with the use of a mobile phone network standard, allowing users to use a mobile phone can travel around the world. The purpose of its development is to enable all parts of the world to ** use the same cell phone network standard, so that users can use a cell phone to travel around the world. China introduced the use of this technology standard in the early 1990s, before it has been the use of cellular analog mobile technology, that is, the first generation of GSM technology (December 31, 2001, China closed the analog mobile network). Currently, China Mobile and China Unicom each have a GSM network, which is the world's largest mobile communication network.The GSM system includes several frequency bands such as GSM 900:900MHz, GSM1800:1800MHz and GSM-1900:1900MHz.
The GSM system has several important features: good anti-theft copying ability, large network capacity, rich resources of cell phone numbers, clear calls, strong stability and less interference, sensitive information, fewer dead corners of the call, and low power consumption of cell phones.
At present, the two main GSM systems in China are GSM 900 and GSM 1800, which are applicable to different cell phones due to their different frequencies. However, most of the current cell phones are basically dual-frequency phones, which can be freely switched between these two frequency bands. European countries commonly used system in addition to GSM900 and GSM1800 in addition to the addition of GSM1900, cell phones for the tri-band cell phone. In our country with the further development of the cell phone market, has also appeared in the tri-frequency cell phone, can be in the GSM900 \ GSM1800 \ GSM1900 three bands within the free switching of cell phones, a cell phone can be done to swim in the world.
Early to see, GSM900 development time is earlier, the use of more, on the contrary, GSM1800 development time is later. Physical characteristics, the former spectrum is lower, the wavelength is longer, the penetration is worse, but the transmission distance is farther, and the cell phone transmit power is stronger, the power consumption is larger, so the standby time is shorter; and the latter spectrum is higher, the wavelength is shorter, the penetration is good, but the transmission distance is shorter, and the cell phone's transmit power is smaller, the standby time is correspondingly longer
"Bluetooth Bluetooth technology is a wireless network technology jointly launched by Ericsson, IBM and five other companies in 1998. Subsequently, the Bluetooth Special Interest Group (SIG) was established to be responsible for the development of the technology and the formulation of technical agreements, and now there are more than 1,800 companies around the world that have joined the organization, and recently Microsoft has officially joined and become one of the leading members of the SIG organization.
Bluetooth is an open standard for wireless data and voice transmission that connects a variety of communication devices, computers and their terminals, digital data systems, and even home appliances wirelessly. Its transmission distance is 10cm to 10m, and if the power is increased or some peripherals are added, the transmission distance can reach 100m. It adopts 2.4GHz ISM band and FM, frequency hopping technology, using right-to-error correction coding, ARQ, TDD and baseband protocols.TDMA is 0.625μs per time slot, and the baseband conformity rate is 1Mb/s. Bluetooth supports real-time voice and data transmission at 64kb/s, with voice coding as CVSD, and the transmitting powers of 1mW, 2.5mW, and 100mW, respectively, and uses a globally standardized 48-bit device identification code. Because Bluetooth uses a wireless interface to replace the wired cable connection, it has strong portability and is suitable for a wide range of occasions, coupled with the technology's low power consumption, low harm to the human body, and the application is simple and easy to implement, so it is easy to promote.
Bluetooth technology
SIG organization in July 26, 1999 launched the Bluetooth technical specifications 1.0 version. The system structure of Bluetooth technology is divided into three main parts: the bottom hardware module, the intermediate protocol layer and the high-level application. The underlying hardware part includes radio frequency hopping (RF), baseband (BB) and link management (LM). The RF layer filters and transmits data bit streams through microwaves in the 2.4GHz unauthorized ISM band. The protocol of this layer mainly defines the conditions that Bluetooth transceivers need to satisfy for normal operation in this band. Baseband is responsible for frequency hopping and the transmission of Bluetooth data and information frames. Link management is responsible for connecting, establishing and dismantling links and performing security controls.
Bluetooth technology combines circuit-switched and packet-switched features to enable asynchronous data communications, support for up to three simultaneous synchronous voice channels, and the ability to use a single channel to transmit both asynchronous data and synchronous voice. Each voice channel supports a synchronous voice link of 64 kb/sec. Asynchronous channels can support asymmetric links with a maximum rate of 721kb/sec at one end and 57.6kb/sec at the other, as well as symmetric links with a rate of 43.2kb/sec.
The intermediate protocol layer includes the logical link control and adaptation protocol, the service discovery protocol, the serial emulation protocol, and the telephony communication protocol. The logical link control and adaptation protocol has the function of completing data disassembly, controlling the quality of service and multiplexing protocols, and this layer of protocols is the basis for the realization of the other layers of protocols. The Service Discovery Protocol layer provides a mechanism for upper layer applications to discover the services available in the network and their characteristics. The serial port emulation protocol layer has the capability to emulate a 9-pin RS232 serial port. The telephony communication protocol layer provides call control commands for voice and data between Bluetooth devices.
The Host Control Interface (HCI) layer is the interface between hardware and software in the Bluetooth protocol, and provides a unified command interface for calling hardware such as baseband, link management, status, and control registers. When communicating between Bluetooth devices, the protocol software entities above the HCI run on the host computer, while the functions below the HCI are performed by the Bluetooth device, and the two interact through a transport layer that is transparent to both ends.
At the top of the Bluetooth stack are various high-level application frameworks. The more typical ones are dial-up networking, headset, LAN access, file transfer, etc., which correspond to an application mode. Various applications can realize wireless communication through their corresponding application modes. Dial-up network applications can access the Piconet through the emulated serial port, and data devices can also access the traditional LAN; users can realize wireless transmission of audio streams in cell phones and earbuds through the Audio layer in the protocol stack; multiple PCs or laptops can quickly and flexibly transfer files and **** enjoy information without any wires, and multiple devices can also realize synchronous operation. This means that you can also synchronize the operation of your PCs with other devices.
In summary, the entire Bluetooth protocol is simple, using a retransmission mechanism to ensure link reliability, in the baseband, link management and application layer can also be implemented in a graded variety of security mechanisms, and through the frequency hopping technology can be eliminated in the network environment from the interference of other wireless devices