On broadband wireless access technology

Access network refers to the "user interface and Business node interface between the implementation of the host function of the entity." Access network basically includes transmission system, multiplexing equipment, user/network interface, digital crossover equipment, etc., usually access network transmission system according to the transmission medium into wired access and wireless access. Wireless access technology has a variety of classification methods, according to the transmission rate, the narrowband  data rate is less than 64kb/s, the broadband  data rate is 64kb/s-2mb/s and broadband  data rate ≥2mb/s.
Narrowband and Medium-wideband wireless access is based on circuit switching, and broadband wireless access is based on packet switching, which can be point-to-point topology or point-to-point topological mode. At present, the practical broadband wireless access technology has digital microwave, MVDS, MMDS, LMDS, satellite access, wireless LAN and so on. Broadband wireless access technologies are being developed or are about to be put into practice with wireless optical fiber, mobile satellite systems and 3G.
A practical broadband wireless access technology
Digital microwave
Microwave technology is the first technology used in wireless access network. The first generation of wireless access technology in the the 1970s is microwave technology. Today, the microwave technology to digital, high frequency, broadband direction, very suitable for broadband access, a bit of the structure, but also a bit of the multiple point structure. Point-to-Point bandwidth is the highest 51~622mb/s, and point-to-point structure is composed of Central station  connected with local switch, peripheral station  user station and repeater.
Mvds
MVDS (Microwave video distribution system consists of interface network adapter, front-end transceiver system, microwave transmission line, network interface Unit, user transceiver, MPEG-2 encoder, Internet server, telephone gateway, telephone server, video-on-demand (VOD) server. The interface network adapter consists of a CPU module, a receiver module and a transmitter module. The network interface Unit consists of a front-end disk, a processor disk, and a telephone disk.
Signal after the interface network adapter processing, sent to the front-end transceiver system, and then sent by the microwave transmission line to the user transceiver, receiving signal in the network interface unit after processing to the user terminal  set-top box, PC, telephone and so on. This is the downlink operation, and the client information sent out, through the uplink line, its operation is the opposite.
Mmds
Multi-channel microwave distribution System (MMDS) is also called multi-channel multiple distribution system, wireless cable or aerial cable. Mmds use of the band, the International 21-23ghz, 2. 3-2. 5GHz, 2. 5-2. 7GHz, the more commonly used is 2. 5-2. 7GHz. There are also jobs in 2g-4g (and even 1g-10ghz products).
Early MMDS was used in television distribution, and later developed to transmission television, FM stereo, data and so on. After the advent of digital MMDS, MMDS is also used for broadband access, such as Internet access.
The MMDS is composed of MMDS transmitting system and client RF system. A signal sent by the front end of the CATV, or receive satellite signal, video camera sent live broadcast program  audio and video signal, the signal sent by the VCR and other foreign signals, sent to the MMDS launch system, after processing feed to the launch tower, and then by the antenna launch, the antenna can be a fully-shaped 360°), heart-shaped 180°, Fan 45°,80°,110°. Within certain coverage, the client's RF system receives the MMDS signal and is processed to the user terminal.
The signal transmitted by the digital MMDS is based on the MPEG-2/DVB standard. The digital MMDS has the transmission program many  in a 8MHz frequency point transmission 5-7 sets of programs, the transmission quality is high, realizes the digital encryption, the coverage scope is wider, may transmit the TCP/IP, the VDP/IP data, realizes the high speed Internet access and so on the characteristic, deeply favored. Digital MMDS can not only transmit TV, but also provide Internet access, video-on-demand, IP telephony, online shopping, information inquiry, karaoke on-demand value-added services.
LMDs
The LMDS, known as "Wireless optical fiber", is a local multicast distribution system. The LMDS works in millimeter wave, with a frequency of 10GHz, 24GHz, 26GHz, 28GHz, 31GHz, 38GHz, and 40GHz. About 80% per cent of the countries assigned to the LMDS band were 275-295ghz.
LMDs belongs to a point multiple access fixed wireless system, its structure is similar to the cellular system, it divides a certain range of coverage area into a number of service areas, each of the base station, each base station through a point of multiple access Microwave Wireless link with the service area of fixed users, each service zone coverage of a few kilometers to more than 10 kilometers, and can overlap each other.
A perfect LMDS system consists of backbone network, base station, client equipment  remote station and network Operation Center  or management system. Backbone network can be composed of optical fiber or microwave transmission network, ATM or Ip or IPATM architecture of the core platform as well as with the Internet, Public telephone Network (PSCN/ISDN), Data network interconnection module. Base station signal into backbone network, complete voice exchange, ATM Exchange, IP Exchange, and into international export  such as Internet exports.
Satellite communication system
Currently, the commonly used satellite communication technologies are dbsdirect broadcasting satellite) or DTH (direct to Home) and VSAT (very small).
DBS or Direct home DTH is one of the unilateral to a point of multiple access, involving television, video multimedia broadcasting, digital television, with High-definition television, stereo and other broadcasting services. VSAT can be accessed in a single direction, or both sides to access, mainly for two-way access, for different applications, there are different structures. For Internet broadband access, there are four basic structures, the first one, is a one-way satellite system, working in the Ku band, uplink transmission, the user with a traditional modem connection ISP, downlink transmission, the satellite to the VSAT information  broadcast-type. The second type of structure is a two-way satellite system, which also works in Ku-band, with satellite links on both uplink and downlink lines. The third structure is also a two-way satellite system, which is only transmitted by point Beam, and the satellite works in Ka-band. The fourth structure is a hybrid satellite network based on a satellite network and a terrestrial network. The rapid development of Internet provides an application place for satellite access.
Wireless local Area Network
Wireless LAN WLAN is implemented in a variety of technologies. such as Opeair, HomeRF, Bluetooth, infrared, and the three main forums atm,ieet,bran introduced standards. Based on the standards introduced by IEEE, the Wireless LAN is 2mb/s to 54mb/s data rate. Bran introduced by the standard wireless LAN maximum data rate is 54mb/s, that is to say, the above constitute wireless LAN technology, in addition to Bluetooth, can be used for broadband wireless access.
Broadband wireless access technology under development
IMT-2000 (3G is now the hot topic, currently, about 3G as a broadband mobile access, there are many people discussed. However, 3G is used for broadband access, and there are some years. Because, currently only determine the five 3G wireless transmission standards, 3G Core network solution is not determined, 3G global roaming program is not determined. Now, the outside coverage of the 3G practical, but also only with 2G core network, 25G transmission technology  such as CDMA 2000-1x system, is the system's practical timetable is also postponed. That is, 3G as a broadband wireless access, will be implemented in the near future. Japan has developed a 4G standard, the probationary period in 2010, the data rate of 100mb/s.
5GHz Broadband Wireless access will also develop rapidly. The FCC announced in January 1997 that it allocates three 100MHz bands in the 5GHz band, as a "u-nii use band for national information Infrastructure without a license", usually 5. 725-5. 825GHz Broadband wireless access to the community. The distribution of u-nii frequency band, the new members of broadband wireless access, to provide "free creative space" for the development of a variety of programs have been published.
The iridium of mobile satellite communications has affected the progress of ICO and Globastar in some degree, but the problems will always be solved, especially the utility of the mobile satellite communication system such as Hughes's space Way and Microsoft's Teledesic, which provides the conditions for broadband wireless access. Based on the geostationary satellite broadband access technology, the new scheme will be proposed, for example, the communication routing function from the ground central equipment to the space satellite is a solution.
Broadband wireless access technology, there will be new technologies, such as integrated fiber-optic wireless hybrid system Hfw or called wireless fiber, free space optical system, ATM wireless access communication system AWACS, stratospheric high air boat platform haps, high-density fixed business hofs. In short, broadband wireless access technologies that are being developed or are about to be applied will surface.