2. Wireless LAN access technology CDMA access technology CDMA is the abbreviation of code-divisionmulTIpleaccess, translated as "code division multiple access packet data transmission technology", and is called the 2.5th generation mobile communication technology. CDMA mobile phones have the characteristics of clear voice, not easy to drop calls, low transmission power and strong confidentiality. The transmission power is only 1-60 of the GSM mobile phone transmission power, which is called "green mobile phone". 4. Wireless LAN access technology CDPD access technology The biggest feature of CDPD access technology is fast transmission speed, the highest communication speed can reach 19.2kbps. In addition, in terms of data security, due to the use of RC4 encryption technology, the security is relatively high; the forward and reverse channel keys are asymmetric, the key is controlled by the switching center, the mobile terminal logs in once, and the switching center automatically checks the old password The key is replaced with a new key once, and dynamic management is implemented. 6. Wireless LAN access technology DBS satellite access technology DBS technology is also called digital direct broadcast satellite access technology. This technology uses communication satellites located in geosynchronous orbits to send high-speed broadcast data to users' receiving antennas, so it is also generally called High-orbit satellite communications. It is characterized by long communication distance, cost independent of distance, large coverage area and not limited by geographical conditions, frequency bandwidth, large capacity, suitable for multi-service transmission, can provide global users with a large span, large range, long-distance roaming and Mobile and flexible mobile communication services, etc. 8. Wireless LAN access technology HomeRF technology HomeRF is mainly designed for home networks and aims to reduce the cost of voice data. In order to achieve efficient transmission of data packets, HomeRF adopts the CSMA? CA mode in the IEEE802.11 standard, which is similar to CSMA? CD, and obtains control of the channel in a competitive manner. An access point transmits data on the network. 10. Wireless LAN access technology 3G communication technology This technology is also known as International Mobile Phone 2000. This technology stipulates that when the mobile terminal moves at the speed of the vehicle, its transfer data rate is 144kbps, when the outdoor is still or walking, the rate is 384kbps, and indoor It is 2Mbps. But these requirements do not mean that the user's available rate can reach 2Mbps, because the indoor rate will also depend on the detailed frequency planning in the building and how closely the organization cooperates with the operator. However, since the rate of high-speed services such as wireless LAN has reached 54Mbps, it is difficult to predict the market demand for 2Mbps services when the 3G network is fully rolled out. 5V Desktop Power supply Product Features: 5V Desktop Switching Power Supply 5V Power Adapter,5V Dc Adapter,5V Dc Desktop Adapter,5V Adapter Shenzhen Juyuanhai Electronic Co., Ltd. , https://www.powersupplycn.com
â—† Wireless access does not require the laying of pipeline lines, which provides the possibility of business access for areas where optical cables or cables cannot be laid, shortens the time of engineering projects, and saves investment in pipeline lines.
â—† With the development of access technology, wireless access equipment can simultaneously solve the access of multiple services such as data and voice.
â—† The bandwidth can be flexibly adjusted according to the increase and decrease of the regional business volume.
â—† It is very convenient for business migration and expansion. The advantage is more obvious in the application of temporary business establishment.
Commonly used wireless access can be roughly divided into two types in structure, one is that the central office equipment is interconnected by wireless means, which is equivalent to a repeater. The other is that the user terminal uses wireless access to access the central office equipment.
1. Wireless LAN access technology GSM access technology GSM is a mobile communication technology standard originated in Europe, and is the second generation mobile communication technology. This technology is a common technical representative of personal communication. It uses narrow-band TDMA, allowing 8 simultaneous calls on one radio frequency, or 'cellular'. GSM was put into use in 1991. By the end of 1997, it had operated in more than 100 countries and became the de facto standard in Europe and Asia. GSM digital network has strong confidentiality and anti-interference, clear sound quality, stable call, and has the advantages of large capacity, high frequency resource utilization rate, open interface, powerful functions and so on. China introduced and adopted this technical standard in the early 1990s. Previously, it has been using cellular analog mobile technology, that is, the first generation of GSM technology (China closed its analog mobile network on December 31, 2001). At present, China Mobile and China Unicom each have a GSM network, and the total number of GSM mobile phone users is over 140 million, making it the world's largest mobile communication network.
More importantly, CDMA based on broadband technology makes video applications in mobile communications possible. Like GSM, CDMA is also a relatively mature wireless communication technology. Unlike GSM, which uses TIme-DivisionMulTIplexing technology, CDMA does not allocate a certain frequency to each caller, but allows each channel to use all the available spectrum.
Therefore, the CDMA digital network has the following advantages: efficient frequency band utilization and greater network capacity, simplified network planning, high call quality, good confidentiality and good signal coverage, and not easy to drop calls. In addition, the CDMA system uses encoding technology, and its encoding has 440 million digital arrangements. The encoding of each mobile phone also changes at any time, which makes the theft of codes only theoretically possible.
3. Wireless LAN access technology GPRS access technology Compared with the original GSM dial-up circuit-switched data transmission method, GPRS is a packet-switched technology. Because of the use of "grouping" technology, users can avoid the pain of disconnecting the Internet? The situation is probably similar to using the download software NetAnts.
In addition, the method of using the wireless LAN access technology GPRS to access the Internet is not the same as WAP. Using WAP to access the Internet is like accessing the Internet at home. "Dial-up connection" is the first, and the phone line cannot be used at the same time after Internet access, but GPRS is superior. Download Data and calls can be conducted at the same time. Technically, if you simply make a voice call, you may wish to continue to use GSM, but if you have data transmission needs, it is best to use GPRS.
It takes the application of mobile phones to a higher level. At the same time, the development of GPRS technology is also very "economical" because it only needs to upgrade the existing GSM network. The use of GPRS is very extensive, including sending and receiving e-mails through mobile phones, browsing on the Internet, etc.
The biggest advantage of GPRS is that its data transmission speed is not comparable to WAP. The current data transmission speed of the GSM mobile communication network is 9.6K bytes per second, and GPRS has reached 115Kbps. This speed is twice the ideal rate of the commonly used 56Kmodem. In addition to the advantage in speed, GPRS also has the feature of 'always on', that is, users keep in touch with the network at any time.
In addition, because the CDPD system is an open system based on TCP? IP, so we can easily access the Internet, all application software based on TCP? IP protocol can be used directly without modification; application software development is simple; mobile terminal communication number directly Use IP address. The CDPD system also supports user handoffs and roaming, broadcasting, and group calls throughout the network. It supports data users with mobile speeds up to 100km? H, and can interconnect with public wired data networks.
5. Wireless LAN access technology Fixed broadband wireless access (MMDS / LMDS) technology Broadband wireless access system can be divided into MMDS (MulTI-channel Multi-point Distribution) according to different frequency bands used
Service) and LMDS (Local Multi-point Distribution Service), the Chinese meaning is called local multi-point distribution service. This is a microwave broadband technology, which is also known as "wireless fiber" technology. It can achieve two-way transmission of voice, data images, video, conference TV and other broadband services at a relatively short distance, and supports standards such as ATM, TCP IP, and MPEG2. Using a cellular-like service area structure, an area that needs to provide services is divided into several service areas. Each service area is provided with a base station, and the base station equipment communicates with users in the service area via a point-to-multipoint wireless link. Each service area covers a range of several kilometers to more than ten kilometers and can overlap each other.
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 the traditional local loop, and meet the increasing demand of users for high-speed data and image communication. It is a weapon to solve the problem of communication network access.
In the DBS system, a large amount of data is broadcast by using the high-speed uplink channel of the satellite master station and the satellite transponder after being modulated by frequency division or time division. The user receives the data through the satellite antenna and the satellite Modem. 0.53m. Due to the high reliability of digital satellite systems, unlike analog phones using twisted-pair wires in the PSTN network, which requires more signal error correction, the download rate can reach 400kbit / s, while the actual DBS broadcast rate can reach up to 12Mbit / s.
At present, the United States can already provide DBS services, mainly for Internet access. The largest DBS network is DirectPC from Hughes Network Systems. DirectPC data transmission is also asymmetric. When accessing the Internet, the download rate is 400kbit / s and the upstream rate is 33.6kbit / s. Although this rate is much higher than that of ordinary dial-up modems, it is still incompatible with DSL and CableModem technologies. compared to.
7. Wireless LAN access technology Bluetooth technology The English name of Bluetooth is "Bluetooth". In fact, it is a protocol that realizes wireless connection between multiple devices. Through this protocol, information can be exchanged between many devices including home RF, including cellular phones, PDAs, laptops, related peripherals and home Hubs. Bluetooth is used in the connection of mobile phones and computers, which can save mobile phone costs, realize data sharing, Internet access, wireless hands-free, synchronized data, image transmission, etc.
Although Bluetooth has great advantages in multi-directional transmission, if there are many devices, the identification method and speed will also have problems; Bluetooth has one-to-many data exchange capabilities, so it needs a security system to prevent unauthorized The basic communication speed of Bluetooth is 750kbits / s, but products with 4Mbits / sIR ports are now very common, and the recent expansion of 16Mbits? S has also been approved.
Unlike other protocols, HomeRF provides real support for streaming services (StreamMedia). Since the streaming service stipulates a high level of priority and adopts a retransmission mechanism with priority, this ensures the bandwidth and low interference and low bit error required by the real-time streaming service.
HomeRF works in the 2.4GHz band? It uses digital frequency hopping spread spectrum technology, the rate is 50 hops / s? There are 75 frequency hopping channels with a bandwidth of 1MHz. The modulation method is FSK modulation with constant envelope, which is divided into 2FSK and 4FSK. Using FM modulation can effectively suppress interference and fading in the wireless environment.
In 2FSK mode, the maximum data transmission rate is 1Mb / s; in 4FSK mode, the rate can reach 2Mb / s. In the latest version of HomeRF2.x, WBFH? Widebandfrequencyhopping? Technology is used to increase the frequency hopping bandwidth, from the original 1MHz to 3MHz, 5MHz, the frequency hopping rate is also increased to 75 hops, the data peak is also up to 10Mb / s 11Mb / s, which is close to the IEEE802.11b standard, can basically meet the future home broadband communication.
9. Wireless LAN access technology WCDMA access technology WCDMA technology can provide users with a data transmission rate of up to 2Mbit / s. Under such conditions, any media used in computers can now be easily transferred through the wireless network. The advantage of WCDMA is that the chip rate is high, which effectively utilizes frequency selective diversity and spatial reception and transmission diversity.
It can solve the multipath problem and fading problem. It uses Turbo channel coding and decoding to provide a higher data transmission rate. The FDD system can provide full coverage in a wide area. The unique cell search method is used for downlink base station differentiation without strict synchronization between base stations. Using continuous pilot technology, it can support high-speed mobile terminals.
Compared with the second-generation mobile communication technology, WCDMA has larger system capacity, better voice quality, higher spectrum efficiency, faster data rate, stronger anti-fading ability, and better anti-multipath 3. The technical advantages of mobile terminals that can be applied up to 500km / h.
Moreover, it can smoothly transition from the GSM system, ensure the operator's investment, and provide a good technical foundation for 3G operations. WCDMA can not only process sound and image data smoothly, but also quickly connect to the Internet through the effective use of wide frequency bands; in addition, the combination of WCDMA and MPEG-4 technology can also process real dynamic images.
11. Wireless LAN access technology Wireless LAN Wireless LAN? WirelessLAN, or WLAN for short, is a combination of computer network and wireless communication technology. It is not bound by cables and is mobile. It can solve problems caused by difficulties in wired network wiring, and has flexible networking, easy expansion, compatibility with multiple network standards, and wide application. WLAN can not only meet the network access requirements of all kinds of portable computers, but also realize multiple functions such as remote access to computer LAN, fax and e-mail.
12. Wireless LAN access technology, wireless optical access system (FSO)
The wireless infrared light transmission system is a combination of optical communication and wireless communication, and transmits optical signals through the atmosphere instead of optical fibers. This technology can provide fiber-like speeds without the need for scarce resources such as spectrum. The main features are: high transmission rate, high-speed data transmission from 2Mb / s to 622Mb / s; transmission distance is in the range of 200 meters to 6 kilometers; because it works in the infrared light band, it will not interfere with other transmission systems, safety Strong; signal transmission and reception through optical instruments, no antenna feeder system is required, and the equipment is small.
full power, anti-jamming performance, DC ripple small;
the power supply operating temperature is low, long service life;the input voltage range, 100-240V, in line with global standards;good insulation properties, high-frequency transformer 100% vacuum impregnation;the product has a short circuit, overload, over voltage protection;full load high temperature burner, product 100% aging test, low rate of bad;there are countries to choose the input plug ;with perfect overcurrent, over voltage, short circuit, over temperature, overload protection;with moisture, dustproof function.
With the increasingly open communication market, telecommunications services are developing rapidly in terms of data, broadband, integration and personalization, and competition among operators is becoming increasingly fierce. The basic point of competition lies in the competition of access resources. How to provide various services required by customers quickly, efficiently, flexibly and at low cost has become the primary consideration for operators. The wireless access method meets the needs of operators to a certain extent.