Application of LMDS Broadband wireless access Technology

This paper first introduces the general situation, system composition and network structure of LMDS technology, then discusses several typical applications of LMDS system in the field of access, and finally, combining the experience of constructing LMDS test or commercial system at home and abroad, some problems needing attention in constructing LMDS system in our country are put forward.
Application of LMDS system LMDS of key word access network

5g millimeter wave speed
With the development of communication and computer technology, information industry is becoming more and more important in national economy, so it is imperative to carry out broadband telecommunication service. It has become an urgent task for the construction and Development of telecommunication network in China to speed up the digital, wideband and intelligent construction of access network. In recent years, the broadband access technology has high speed digital loop (XDSL), Optical fiber access (FTTH), fiber coaxial mixed access (HFC) and broadband wireless access (LMDS and MMDS).
1 LMDS Broadband Wireless access Technology
*LMDS, the local multicast distribution service, is a broadband point-to-point access system that can access voice, data and video services. LMDS system using millimeter wave transmission, working in the 20-40ghz band, can provide up to 155.52Mbps user access rate, known as a "Wireless optical fiber" access system. In addition, the LMDS system supports all major voice and data transmission standards, such as ATM, TCP/IP, and MPEG-2.

Millimeter wave 5g speed
The *LMDS system adopts a kind of honeycomb structure configuration, by which one or more rational distributions can cover the base station of the required region, and the transceiver of the base station communicates with the fixed users of the service area via point to multicast Wireless link. Each base station can support 4 to 24 separate sectors and is connected to a public switched platform via a high-speed backbone link.

5g millimeter wave frequency
The LMDS system is divided into four parts of user's remote station, base station, backbone network and network Management Center, which can be regarded as the combination of access layer, edge layer and center layer. The access layer is the user station Access service, the hardware refers to the client device, including the outdoor Unit, network Interface Unit and modulation and Demodulation module. The edge layer realizes the conversion between the backbone network and the wireless transmission, and provides the corresponding QoS and COS, mainly including the node send/receive wireless unit and the basic Channel group connected to the ATM or l2/l3 edge switch. The central layer optimizes costs through efficient transfer, exchange and allocation of bandwidth, and is a switching platform using SDH transmission technology, ATM or IP or ATM+IP switching technology, which provides interconnection interfaces with PSTN, Internet and other private networks.

5g and millimeter wave
2 typical applications of LMDS systems

Millimeter wave health risks
* Application in the Data communication network: The LMDS system as the access part of the data Communication network, which plays the role of connecting the Service node interface and the user network interface. This application is the traditional telecom operators on the basis of existing networks, as a complementary means of optical fiber access, in the short term to meet user demand for broadband services effective way. Shanghai Telecom has conducted experiments on related technologies. Based on the running Shanghai ATM broadband platform, the test network transmits the data between the base station and the user station based on the ATM signal multiplexing continuous carrier. The test results show that the LMDS system can be used as a flexible access mode for broadband ATM network, which provides a good service for broadband users.

Millimeter wave spectrum 5g
* Application in Mobile communication network: In GSM mobile network, Base station controller (BSC) is connected by optical fiber and base station transceiver Signal (BTS), although the optical fiber has the characteristic of bandwidth, but it is difficult to lay the construction, which is unfavorable to the change of network topology structure. The interconnection between BSc and BTS is realized by using LMDS system, which not only retains the advantages of optical fiber connection bandwidth, but also shortens the cycle of system construction, realizes the "soft connection" between BSc and BTS, and facilitates the further optimization of network topology structure.
* Build Local Information loop: Based on the backbone of LMDS system, use reasonable networking technology to build high-speed exchange platform, enrich local information service through own construction, website mirroring or introducing information from outside, and rent the Telecom department's export line to realize the interconnection of local loop and Internet. Considering that the local information exchange platform needs to provide users with a variety of services, and the future of the network will be the main business from IP, so the use of IP core network, at the same time with the ATM Exchange layer, that is, the LMDS system to achieve the air ATM interface, and effectively support various types of business (such as DDN, FRN, etc.).
The application is often referred to as the "unique skills" of emerging telecom operators. Faced with a large number of infrastructure and users of the old operators, the emerging operators adopt LMDS technology, can achieve a one-time investment, open fast, networking flexibility and easy expansion and other advantages, LMDS system broadband and Low-cost also meet the current user demand for broadband services. Xi ' An mobile communications branch has carried out a series of planning and testing, the goal is to build XI ' an public network exchange platform and a variety of local information platform, the first phase of the project using four LMDS base stations covering the entire XI ' an, the backbone of the network using LMDS high-speed switching technology to solve the IP over ATM The adoption of LMDS core is in line with the trend of IP mainstreaming in the future, and it can provide the DDN service, Frame Relay service and various ATM-specific services that are widely used at present. According to the budget, the first phase of the project investment of 2 million U.S. dollars, and user demand survey shows that in the short term can access enterprise users 500, 50,000 individual users, local ISP Web site 20, with good economic benefits.
* Applications in radio and television networks: Celluar Vision has built a 28GHZ LMDS broadcast video system in New York. The system is currently the world's most mature lmds system, mainly for users to provide multi-channel television programs, the price is lower than their competitors 30%, by the end of 1997 has a user of 12,000. This system can provide 48Mbps downlink data rate, because of the early opening, the system itself is one-way, users need to achieve uplink through the PSTN connection. There are no technical problems in building a local interactive TV distribution network using LMDS system.
* Build integrated Service access network: Build integrated service access network, which integrates voice, data and vision, conforms to the trend of "three nets in one" and satisfies the demand of users for multimedia business. It is generally considered that the realization of all-optical (FTTH) of access network is the best solution for constructing integrated service access network. However, there are still many difficulties in the use of all-optical access network, such as the construction and operation of optical fiber is expensive, the laying of optical fiber is related to municipal, transportation and environment and so on. In the United States, the current 4.6 million commercial buildings in the implementation of fiber-optic to the building accounted for only 1%. There is still a long way to go to achieve FTTH. The maximum access rate supported by the LMDS system is up to 155Mbps, to meet the user's increasing demand for communication bandwidth, and it has less start-up funds, opening speed and flexibility to expand the advantages of the operators do not have the ability to access optical fiber, is undoubtedly and short-term expansion of broadband services to meet market demand, a powerful means.
3 problems needing attention in construction of LMDS system in China
User Demand Analysis: China's current telephone and internet penetration rate is low, users need more telephone and video business, so operators should target their clients to provide basic voice and data access for residential users and Internet access. The survey results in XI ' an city show that the user groups of LMDS system are individual users, enterprise users and broadband multimedia users. The individual user is the main body, the network purpose is to access the Internet, the rate requirements for more than 100kbps, more sensitive to tariffs, whether to provide them with cheap and fast internet access is the operator in this market can be the key to success. The needs of enterprise users are concentrated on the Enterprise Virtual Private Network (VPN) and Internet access. They require very high bandwidth, typically over 5Mbps, and require the use of ATM technology to guarantee the required QoS. Multimedia users are currently a small group, in terms of bandwidth and latency are demanding, access mode is pure ATM, this part of the number of users, although a few, but for the entire network of other users have a good demonstration role. (☆ Introduction to Programming Network ☆)
Equipment Selection Analysis: Here the United States P-com Company and Canada Newbridge Company's products do a comparison. P-com Company's LMDS equipment features in wireless transmission, such as higher transmission power and modulation order, direct support ATM protocol: Simultaneously provide FDMA and TDMA access mode, provide automatic transmission power control, etc. But p-com company's products in the network interface to do not enough, a variety of business modules to be developed. Relatively Newbridge company's product characteristics are embodied in the network, such as the base station itself has the Exchange function, providing end-to-end of a variety of business transport and a variety of access modes as well as Cross-platform network management system, based on ATM transport protocol, support dynamic bandwidth consumption. Business Access module directly to the user, if the operator can not provide the user required interface, will lose users in the competition, so we tend to Newbridge the company's LMDS equipment.
Investment risk Analysis: The LMDS system's investment risk mainly manifests in the technology and the operation. The technical risk is the frequency point of the LMDS system which has not been stipulated by the Radio Frequency Committee in our country at present. The operational risks are expressed in two aspects: (1) The commercial operation time of the LMDS system is very short, no exact operation data and experience can be found; (2) The LMDS system adopts the higher frequency microwave, the transmission quality is susceptible to the rain and snow weather, the whole base station and the user station can only carry on the line-of-sight transmission. According to the study of the conditions of the LMDS system in California, it is found that nearly 35% of the users in a community are in shaded areas, and it is difficult to receive signals. At present, China is in the rapid development of urban construction, it is difficult to ensure that the base station and the user station between the Line-of-sight transmission, the network operation brought great pressure.
4 Conclusion
With the advantages of less investment, fast opening, flexible networking and convenient expansion, LMDS system has become a new hotspot in the field of communication research and promotion in recent years. Due to technical superiority and commercial potential value, the LMDS system is likely to rise rapidly in the coming years. As a new technology, to promote and popularize worldwide, there is still a long way to go, we need to do further work in the following areas:
(1) The organization has the strength communication equipment provider to carry on the research of the LMDS System key technology, specially the millimeter wave transceiver technology and the millimeter wave integrated circuit based on the GaAs technology, provides the foundation for the development low cost LMDS transceiver station.
(2) Telecommunication operators and research institutions shall, on the basis of existing experimental and commercial networks, increase the hardware of the LMDS system's communication environment and transmission conditions, and accumulate the operational data and experience of the LMDS network.
(3) The National standard Establishment Department should launch the LMDS system and the MPLS technology national standard as soon as possible.
(4) The National Radio Frequency Committee should determine the allowable working frequency of China's LMDS system as soon as possible.