With the rapid development of communication technology and the continuous improvement of social living standards, traditional and pure voice services can no longer meet people's needs. Especially with the rapid development of the Internet, people prefer to enjoy multimedia, diversification and personality. The telecommunications business, the surge in data traffic has led to an increasing demand for communication bandwidth. Although fiber access represents the direction of broadband access in the future, its huge engineering volume and huge capital investment make it difficult to achieve it in the near future. The broadband wireless access technology that emerged at the historic time has received extensive attention due to its rapid flexibility and economic characteristics. Both new and old operators have shown strong interest in it. Although the current growth of broadband wireless access users is not so fast compared with wired broadband access, the number of Internet users in China has been in a period of rapid growth in recent years, and there is still much room for growth. Compared with wired access technology, the proportion of wireless access is still relatively small, far from meeting the needs of end users. However, the broadband wireless access technology under the new technology has a very strong transmission capability, and the mobility is gradually improving. The perfect technical standards and mature operation mode will promote the rapid growth of the broadband wireless access industry, so broadband wireless access Technology will certainly have a good application prospect in the future. The 802.11 series is temporarily in the leading position in the field of broadband wireless access, but other technologies are also emerging, it is difficult to say which technology will dominate the future market. But what is certain is that the complete industrial chain will lead to a win-win situation for equipment manufacturers, operators and users. Whether or not to build a complete industrial chain is the key to future development.
At the present stage, in the process of informationization of radio management in China, data transmission relies on star-shaped cable networks that are hierarchically interconnected by the state, province, and city. Data resources and business systems have been transplanted into the network environment one after another, which has increased the dependence of radio managers on the network. Due to the limitations of wired networks, as mobile monitoring and out-of-office workers use data and systems in the network, there is currently no data. Very well solved. How to combine broadband wireless access technology, solve remote access, and improve the extension of existing networks is the work that should be considered in the next step of information construction.
Analysis of current application status of wireless access technology in China(1) 400 MHz band (TDD)
In order to support the development of communication in rural and remote areas and alleviate access difficulties, the country has planned the frequency band 406.5 MHz to 409.5 MHz for the use of time-division multiple access (TDD) wireless access systems for wireless access to local public communication networks. Communication. It is also stipulated that in this frequency band, the radio astronomy service, the fixed service and the mobile service are all major services, but the radio astronomy service must be protected. Two carrier spacings, 250 kHz and 500 kHz, are also specified.
(2) Band of 450 MHz (Rural Wireless Access System FDD)
According to the earliest regulations, the band 450 MHz to 470 MHz is used for dual-frequency network telephones. In 1998, the frequency band used for the 450 MHz walkie-talkie was adjusted to increase the rural wireless access service, and the 450 MHz frequency was mainly used for wireless walkie-talkies in areas where urban and wireline communications were more popular. In rural areas where people were sparsely populated, The 450 MHz frequency can be used for rural wireless access systems.
(3) 1800 MHz band (SCDMA)
In order to adapt to the needs of local wireless access services, promote the development of wireless access technologies, improve spectrum utilization, and work on the 1800 MHz time division duplex (TDD) wireless access system according to China's radio frequency allocation regulations and spectrum usage. The frequency bandwidth is extended from the original planned 5 MHz to 20 MHz. The operating frequency band of a time division duplex (TDD) wireless access system is extended from 1800 MHz to 1805 MHz to 1785 MHz to 1805 MHz. This band is mainly used for wireless access in the local public network, and can also be used for wireless access to the local private network that is really needed. In principle, frequency assignments start from the high-end, and the frequency bandwidth assigned to the same public network operator or private network unit with wireless service management rights in the same area generally does not exceed 5 MHz. At present, this frequency is mainly used for SCDMA wireless access systems.
(4) 1900 MHz band (public or private network wireless access system)
The 1900 MHz to 1920 MHz band is used for the TDD mode of the radio access system, and the 1880 MHz to 1900 MHz and 1960 MHz to 1980 MHz bands are used for the FDD mode of the radio access system (this band belongs to the 3G frequency, and the radio access system is not yet used). The current frequency band of 1900 MHz to 1920 MHz is mainly PHS wireless access technology.
(5) 2.4 GHz band (802.11b/g)
2400 MHz ~ 2483.5 MHz is the ISM (Technology) frequency band, which is used as a shared frequency band for various radio stations such as wireless LAN, wireless access system, Bluetooth system, point-to-point or point-to-multipoint spread spectrum communication system, but set 2.4 Radio stations in the GHz band must be managed in accordance with the Interim Provisions for Micropower (Short Range) Radio Equipment issued by the Ministry of Information Industry.
(6) 3.5 GHz band (MMDS)
The FDD (Frequency Division Duplex) operating frequency used in the 3.5 GHz fixed wireless access system is 3400 MHz to 3430 MHz and 3500 MHz to 3530 MHz, of which the terminal station transmits the frequency band from 3400 MHz to 3430 MHz, and the central station transmits the frequency band to 3500. MHz ~ 3530 MHz with a duplex interval of 100 MHz.
(7) 5.8 GHz band (802.11a)
In 2002, the country allocated the frequency band 5725 MHz to 5850 MHz, allowing radio stations such as point-to-point or point-to-multipoint spread spectrum communication systems, broadband wireless access systems, high-speed wireless local area networks, Bluetooth technology equipment, and vehicle wireless automatic identification systems. This band is shared. To set up a radio station using a 5.8 GHz band point-to-point or point-to-multipoint spread spectrum communication system, wireless local area network, and broadband wireless access system, in principle, for public network wireless access communication, the operating enterprise must obtain the corresponding basic telecommunication service operation. license.
(8) 26 GHz band (LMDS)
According to the Ministry of Information, there is no document [2001] 652. In 2001, the country used part of the frequency band of 24.45 GHz to 27 GHz as the frequency of FDD local multipoint distribution service (LMDS). The remote station frequency is 25757 MHz ~ 26765 MHz, the central station frequency is 24507 MHz ~ 25515 MHz, the duplex interval is 1250 MHz, the basic channel bandwidth is 3.5 MHz, 7 MHz, 14 MHz, 28 MHz, which can be based on specific business needs. The basic channels are combined for use.
Broadband wireless access technology2.1 Problems facing the development of broadband wireless access applications
At present, the broadband wireless access system is mainly a fixed access method, but the fixed access method is far from meeting the needs of people. Although broadband wireless access has been developed in China, the development speed is not very fast. Faced with various problems.
(1) Spectrum issues. Wireless access is accomplished by wireless means, and electromagnetic waves are required to carry, that is, frequency resources are required. However, frequency resources are very limited resources and are uniformly allocated and coordinated by the Radio Authority in accordance with relevant regulations and policies. Therefore, the application of broadband wireless access technology is affected by relevant national policies and regulations. Although the 2.4 GHz band and the 5.8 GHz band are unlicensed, the services in this band are unprotected and the interference problem cannot be solved without good quality of service; the 3.5 GHz band is the licensed band and the interference problem can be used in the network. The planning method is solved, but the 3.5 GHz frequency band is small and the bandwidth is small, which cannot meet the needs of telecom operators for large-scale networking and providing users with high-bandwidth access and transmission services; the 26 GHz band is licensed, and the bandwidth is It is wide enough, but the frequency band is too high, the rain attenuation is poor, the coverage is small, and the equipment cost is still not well utilized. Therefore, solving the spectrum problem is an important factor in developing broadband wireless access technology.
(2) Standard questions. The unification of air interface standards and the unification of equipment platform interfaces will greatly reduce costs. 3.5 GHz radio access technology: There is no uniform air interface standard, and the types of device interfaces are also different. LMDS: There are differences in the implementation of the air interface, and the platform of the device is consistent with the type of interface provided. The above two technologies, because they do not support any mobility, are not as open to air interface technology as other mobile access technologies. However, if a standard protocol is adopted, it will promote the decline of product cost and promote the further development of fixed wireless access technology. WLAN technology: The air interface protocol is based on the IEEE 802.11 series of standards, and the degree of standardization is high. There is currently no interoperability problem. However, the network standards involved in WLAN operations are relatively scarce.
(3) The number of users. Compared with broadband cable access technology, the number of users of broadband wireless access technology is not enough. The number of Internet users in China has grown by leaps and bounds in recent years, and there is still much room for growth. The number of xDSL users represented by ADSL has reached 20 million before, and it has an absolute high proportion among broadband access users in China. Compared with wired access technology, wireless access accounts for a small proportion, far from meeting the needs of end users.
2.2 Status of broadband wireless access technology
Broadband wireless access refers to a technology that can provide users with high data rates (2 Mbit/s or more) to the Internet by wireless transmission. The IEEE divides broadband wireless access into PAN, WirelessLAN, WirelessMAN, and WAN according to coverage. The coverage ranges from 10m to less than 100m, and then covers the city and covers it to a large extent.
(1) 802.16 technology. The IEEE 802.16 standard, also known as the IEEE Wireless MAN Air Interface Standard (WiMAX), regulates the air interface of broadband wireless access systems operating in different frequency bands. 802.16 is designed for a wide range of broadband wireless access deployment scenarios, including long-distance (up to 50 km) deployments in outdoor line-of-sight (LOS) conditions up to urban environment non-line-of-sight (NLOS) short-range deployments.
(2) Mcwill (Datang Xinwei SCDMA). Xinwei's McWiLL is a broadband wireless access product developed on the basis of the original SCDMA technology by adding a series of key technologies.
(3) WiBro. WiBro (Wireless Broadband) is a broadband wireless access service proposed by Korea and is applied to the 2.3 GHz frequency. WiBro was derived from the HPI project launched by TTA in June 2003, after which the HPI project was fused in the IEEE 802.16 working group. The WiBro standard is fully compliant with the IEEE 802.16e standard and can be viewed as a subset of the IEEE 802.16e standard.
(4) HIPERMAN. HIPERMAN is based on IEEE802.16a, 16d to 16e, whether it is from the physical layer or the MAC layer. However, HIPERMAN has reduced some options according to the situation in Europe, which is more conducive to system implementation and interconnection. In terms of carrier bandwidth selection, the requirement is an integer multiple of 3.5 MHz, 7 MHz or 14 MHz. The desired result is that it can be integrated with 802.16, providing a globally unified OFDM standard and taking care of European interests.
(5) IEEE 802.20. A mobile broadband wireless access standard planned by the IEEE 802.20 standard working group can support a mobile target rate of approximately 250 km/h. Due to the high support for mobility, IEEE 802.20 has a lower transmission rate than IEEE 802.16e, and its service positioning is to provide high-speed Internet services in a mobile environment, which is similar in scope to 3G systems.
(6) IEEE 802.22. The task of the IEEE 802.22 working group is to develop a protocol standard for PHY and MAC called the air interface of the Wireless Regional Area Network (WRAN). The WRAN network uses the free frequency band between 54MHz and 862 MHz with the help of cognitive radio technology to provide users with broadband wireless access services. With the aid of cognitive radio technology, the allocated frequency bands that are actually idle are utilized. This is a valuable idea for developing broadband wireless services in the case of very tight radio frequency resources.
2.3 Trends in the development of broadband wireless access
Although broadband wireless access currently faces many problems, as a better access method, there will be good development prospects in the future. The IEEE 802.16 organization will gradually standardize the 802.16d and 802.16e unified standards. The unified air interface standard can ensure compatibility and interoperability between devices, base stations and terminals of different equipment manufacturers, and reduce the cost of products. At present, the terminal is mainly in the form of fixed access, and the support of simple nomadic low-speed mobile is its transition, and finally it can provide good service in the case of high-speed mobile. Broadband wireless access value-added applications will also have greater room for development, such as: location services, e-commerce, wireless office technology related wireless office / sales, wireless online games, wireless monitoring, etc., for business, home, entertainment, Provide wireless application services in various aspects such as office and travel.
summaryWith the gradual maturity of broadband wireless technology and its continuous enhancement in reliability, security and bandwidth, in the future of radio management informationization in China, we can consider the use of broadband wireless access technology on the basis of wired networks. Establish a wireless network to achieve the convergence of wired and wireless networks, and continuously expand the scope of the network, from a local network to a cross-regional, cross-city or even cross-country network, making full use of the internal resources of the network to improve the network availability, which may Will become the trend of network development in the future.
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