12 kinds of wireless access methods

Wireless development is inseparable from the progress of wireless technology. So what are our wireless access technologies now? Some of the technology we are still using, some have gradually faded out of our horizons. So let's take a summary of these wireless access technology types.

　　Wireless access technology Type 1 GSM access technology

GSM is a kind of mobile communication technology standard originated from Europe, it is the second generation mobile communication technology ｡ This technique is a kind of common technical representative of personal communication at present ｡ It uses narrow-band TDMA, allowing 8 groups of calls to be made at the same time as a radio frequency, "honeycomb" ｡ GSM is the ｡ that began to be put into use in 1991 By the end of 1997, it has operated in more than 100 countries, becoming the de facto standard ｡ in Europe and Asia. GSM Digital Network has a strong confidentiality and anti-jamming, sound quality, call stability, and have large capacity, high frequency resource utilization, interface open, powerful and other advantages ｡ The introduction of this technical standard in China in the early 1990s has been the use of cellular analog mobile technology, that is, the first generation of GSM technology (December 31, 2001 our country closed the analog mobile network) ｡ At present, China Mobile ､ Unicom has a GSM network, the total number of GSM mobile phone users in more than 140 million, the world's largest mobile communications network ｡

Wireless access technology Type 2 CDMA access technology

The acronym code-division Multiple access, translated as "CDMA packet data transmission technology", is called the 2.5-generation mobile communication technology ｡ CDMA mobile phone with clear voice ､ not easy to drop ､ low emission power and strong confidentiality characteristics, known as "Green mobile phone" ｡ More importantly, CDMA based on wideband technology makes it possible to use video in mobile communication ｡ CDMA, like GSM, is a kind of mature wireless communication technology ｡ Unlike GSM, which uses time-division multiplexing technology, CDMA does not assign a certain frequency to each caller, but lets each channel use all the spectrum it can provide ｡ Therefore, CDMA Digital Network has the following advantages: efficient bandwidth utilization and greater network capacity ､ Simplified network planning ､ call quality high ､ confidentiality and signal coverage, not easy to drop words and so on ｡ In addition, the CDMA system uses the coding technology, its code has 440 million kinds of digital arrangement, each handset's code also changes at any time, this makes the pilfer code only then becomes theoretically possible ｡

　　Wireless access technology Type 3 GPRS access technology

Compared with the original GSM dialing mode of the circuit Exchange data transmission mode, GPRS is packet switching technology ｡ Because of the use of the "group" technology, users can access the Internet to avoid the pain of disconnection  situation is probably the same as using the download software netants almost ｡ In addition, the use of GPRS Internet access and WAP and different, with WAP Internet, such as at home in the Internet, the first "dial-up connection", and the Internet can not use the phone line at the same time, but GPRS is more advantageous, download information and call can be carried out at the same time ｡ Technically speaking, if the pure voice call, it may be possible to continue to use GSM, but if there is data transmission requirements, it is best to use GPRS, it put the application of mobile phones to a higher level ｡ At the same time, the development of GPRS technology is also very "economic", because it only needs to upgrade the existing GSM network can be ｡ GPRS is widely used, including sending and receiving emails via mobile phones, browsing on the internet and so on ｡

GPRS's biggest advantage lies in: its data transmission speed is not WAP can compare ｡ The current GSM mobile communication network data transmission speed of 9.6K bytes per second, and GPRS reached 115kbps this speed is commonly used 56K modem ideal rate of twice times ｡ In addition to the advantages of speed, GPRS also has "forever online" characteristics, that is, users at any time to maintain contact with the network ｡

　　Wireless access technology Type 4 CDPD access technology

CDPD Access technology is the most important feature of high-speed transmission, the highest communication speed can reach 19.2kbps｡ In addition, in the data security, because of the use of RC4 encryption technology, so the security is relatively high, positive and negative channel key asymmetry, key by the Exchange Center Master, mobile terminal login, switching center automatically check the old key to replace the new key once, the implementation of dynamic management ｡ In addition, since the CDPD system is an open system based on TCP/IP, we can easily access the Internet, all applications based on TCP/IP protocol can be used without modification, and the application software development is simple; Mobile terminal communication number directly using IP address ｡ CDPD system also supports user handoff and full network roaming ､ broadcast and group call, and can interconnect with public wired data network ｡

Wireless access technology type 5 fixed broadband wireless access (MMDS/LMDS) technology

The broadband wireless access system can be divided into MMDS (multi-channel multi-point distribution service) and LMDS according to the frequency band (local multi-point distribution Service) Two series, the Chinese meaning is called the local multicast distribution business ｡ This is a microwave broadband technology, but also dubbed "Wireless Optical fiber" technology ｡ It can realize bidirectional transmission of voice ､ data image ､ video ､ Conference TV and other broadband services in the near distance, and support ATM､TCP/IP and MPEG2 standard ｡ Using a similar cellular service area structure, a need to provide business areas to be divided into a number of services, each of the base station, the base station equipment through point to multicast Wireless Link and the user-side communication ｡ Each service area covers a few kilometres to more than 10 km and can overlap ｡

Because Nmds/lmds has the characteristics of higher bandwidth and bidirectional data transmission, it can provide a variety of broadband interactive data and multimedia services, overcome the bottleneck of traditional local loops, meet the increasing demand of users for high-speed data and image communication, so it is a sharp weapon to solve the problem of communication network access ｡

　　Wireless access technology type 6 DBS star access Technology

DBS technology is also known as Digital live satellite access technology, which utilizes communications satellites located in geosynchronous orbit to send high speed broadcast data to the user's receiving antenna, so it is also known as high orbit satellite communications ｡ Its characteristic is the communication distance, the cost is independent from the distance, the coverage area is big and is not restricted by the geographical condition, the frequency band is wide, the capacity is big, is suitable for the multiple service transmission, may provide the global user with the large span ､ wide range ､ long-distance roaming and the mobile communication Service and so In the DBS system, a large number of data by frequency division or time modulation after the use of satellite main station of the high-speed uplink and satellite transponder broadcast, the user through satellite antennas and satellite receiving modem reception data, receiving antenna diameter is generally 0.45m or 0.53m｡

Because of the high reliability of digital satellite system, unlike the PSTN network, the use of twisted-pair analog telephones requires more signal error correction, so the download rate can reach 400kbps, and the actual DBS broadcast rate can reach the maximum 12mbps｡ At present, the United States has been able to provide DBS services, mainly for Internet access, of which the largest DBS network is the Hughes Network Systems Company's direct Pc｡ Direct PC data transmission is also asymmetric, when the Internet access, download rate of 400kbps, the uplink rate of 33.6kbps, this rate although more than normal dial-up modem, but with DSL and cable modem technology still can not compare ｡

　　Wireless access technology Type 7 Bluetooth technology

The English name for Bluetooth is "Bluetooth", which is actually a protocol to implement wireless connections between multiple devices ｡ This agreement enables the exchange of information between devices including cellular phone ､ handheld PCs ､ laptops ､ related peripherals and family hub, including home RF ｡ Bluetooth is applied to mobile phone and computer, can save the cost of mobile phone, realize data sharing ､ Internet access ､ Wireless hands-free ､ synchronous data ､ image transmission ｡

Although the Bluetooth in the multi-directional transmission aspect has the big superiority, but if the equipment is numerous, the recognition method and the speed also can have the problem; Blue toothbrush has a one-to-many data exchange capability, so it needs a security system to prevent unauthorized access; Bluetooth's basic communication speed is 750Kbps, but now with 4Mbps IR Port products are already very common, and the recent 16Mbps extension has been approved ｡

　Wireless access technology type 8 home RF technology

Home RF is designed primarily to reduce the cost of voice data ｡ In order to achieve efficient transmission of packets, home RF uses the CSMA/CA mode in the IEEE802.11 standard, which is similar to CSMA/CD to gain control over the channel in a competitive way, and only one access point can transmit data in a network at a point in time ｡ Unlike other protocols, the home RF provides a true sense of support for the convection business (Stream Media) ｡ Due to the high priority of the convection business and the use of a priority-prone mechanism, this ensures the bandwidth required for real-time streaming services and low interference ､ low error ｡

Home RF Work in the 2.4GHz band ｡ It uses the digital frequency hopping spread spectrum technology, the rate is 50 jumps/s altogether 75 bandwidth is the 1MHz frequency hopping channel ｡ The modulation mode is a constant envelope of FSK modulation, divided into 2FSK and 4FSK two kinds of ｡ Using FM modulation can effectively restrain the interference and fading ｡ in wireless environment. In 2FSK mode, the maximum data transmission rate is 1Mbps; in 4FSK mode, the rate can reach 2mbps｡ The latest version of Home rf2.x, using the WBFH wide band frequency hopping technology to increase the frequency of hopping bandwidth, from the original 1MHz to the 3mhz､5mhz, the rate of hopping also increased to 75 jump/s, the peak data is also up to 10Mbps, Close to the IEEE802.11B standard of 11Mbps, basic to meet the future of home broadband communications ｡

　　Wireless access technology Type 9 WCDMA access technology

WCDMA technology can bring users a maximum of 2Mbps data transfer rate, under such conditions, now the computer application of any media can be easily passed through the wireless network ｡ The advantage of WCDMA is that the rate of the chip is high, the frequency selectivity diversity and the space receiving and transmitting diversity are used effectively, the multipath problem and the fading problem can be solved, and the Turbo Channel codec is used to provide a higher data transmission rate, and the FDD system can provide wide area full coverage, The downlink base station distinguishes using the unique cell search method, without the strict synchronization between base stations ｡ Using continuous pilot technology, can support high-speed mobile terminal ｡

Compared to the second generation of mobile communication technology, WCDMA has greater system capacity ､ better voice quality ､ higher spectral efficiency ､ faster data rate ､ stronger resistance to decay ､ better multipath ､ can be applied to the technical advantages of mobile terminals up to 500km/h, and can smooth transition from GSM system To ensure the operators ' investment and provide a good technical foundation for 3G Operation ｡ Through effective use of broadband, WCDMA can not only smooth the processing of sound ､ image data ､ with the Internet fast Connection, in addition, WCDMA and MPEG-4 technology can also be combined to deal with real dynamic image ｡

　Wireless access technology type 3G communication technology

The technology is also known as the International Mobile Phone 2000, which stipulates that when the mobile terminal is moving at a speed, it transmits a data rate of 144kbps, outdoor static or pedestrian speed of 384kbps, and indoor 2mbps｡ But these requirements do not mean that the user can reach 2Mbps, because the indoor rate will also depend on the detailed frequency planning in the building and the degree of collaboration between the organization and the operator ｡ However, due to the high-speed service speed of wireless LAN is up to 54Mbps, it is difficult to predict how the market demand of 2Mbps business will be ｡ when 3G network is fully rolled out.

Wireless access technology Type 11 Wireless LAN

Wireless LAN Wireless LAN, referred to as WLAN is the combination of computer network and wireless communication technology products ｡ It is not bound by cable, removable, can solve the problems caused by cable network wiring difficulties, and network flexible, easy expansion, compatible with a variety of network standards, widely used and other advantages ｡ WLAN can not only meet the requirements of all kinds of portable computers, but also can realize remote access to computer LAN ､ facsimile ､ e-mail and other functions ｡

　　Wireless access technology Type 12 Wireless Optical access System (FSO)

Wireless Infrared optical transmission system is the combination of optical communication and wireless communication, through the atmosphere rather than optical fiber to transmit optical signal ｡ This technology can provide the same rate as the optical fiber, and does not require rare resources such as Spectrum ｡ The main features are: High transmission rate, from 2Mbps to 622Mbps high-speed data transmission, transmission distance of 200 meters to 6 km range; Due to the work in the infrared wavelength, the other transmission system will not interfere with the security is strong; signal transmitting and receiving through optical instruments, no day feeder system, small equipment volume ｡