Comparative analysis of broadband wireless access technology

The broadband wireless access technology represents a new and noticeable development trend of broadband access technology, not only the network opening fast, maintenance simple, the user is more dense when the cost is low, and changed the traditional concept of local telecommunications business, the most suitable for new telecom competitors to carry out effective competition, can also be a telecommunication company wired access to an important supplement. At present, there are several popular broadband wireless access technology.

--a MMDS system for 2.5ghz/5.7ghz. It uses advanced VOFDM technology to realize wireless communication, in the city of high-rise buildings using "multipath" to achieve a single carrier 6MHz bandwidth transmission rate up to 22mbit/s data access, high spectral efficiency, In the 2.5GHz band can reach 90% of the communication probability, in the 5.7GHz band can reach more than 80% of the communication probability.

-A microwave sdhip ring system working in a high frequency band. In the past, more microwave SDH devices were used in point-to-point microwave relay transmission circuits. Now with the progress of technology, some companies have introduced a microwave SDH two-way ring network, with self-healing function, and fiber ring self-healing characteristics of the same, integrated ADM, using a serialized modem, realize QPSK-256QAM programmable, there are a variety of interfaces (g.703, STM-1, E3/t3, E1, Ethernet 10base-t/100base-t). At the same time, the engineering installation of miniaturized structural equipment more convenient than the previous microwave equipment, and in the case of frequency tension, this equipment can work in 13GHz, 15GHz, 18GHz, 23GHz and other frequencies, in the construction of the metropolitan area Network can avoid the 3.5ghz/26ghz wireless access frequency of fierce competition, can support 8x155m bandwidth.

--local multi-point distribution business LMDs. It works in the 20ghz~40ghz band, the transmission capacity can be compared with the optical fiber, at the same time the wireless communication of the economy and easy to implement the advantages. LMDS is based on MPEG technology and is developed from the microwave video distribution system (MVDS). A complete LMDS system consists of four parts, namely, local fiber backbone network, network Operation Center (NOC), base station system and client equipment (CPE). LMDs is characterized by: bandwidth can be compared with optical fiber to achieve wireless "fiber" to the building, the available frequency band of at least 1GHz, compared with other access technology, LMDS is the last kilometer of flexible alternative technology, optical fiber transmission rate up to GB, and LMDS transmission rate of up to 155mbit/s, stable second LMDs can support all major voice and data transmission standards; LMDS work in the millimeter-band, 20ghz~40ghz frequency, the permitted frequency is 24GHz, 28GHz, 31GHz, 38GHz, which 28GHz more licenses, the band has a more relaxed spectrum range, The most potential to provide a wide range of business.

At present, the type of air interface used in fixed wireless access system is broadly divided into three categories: ip-based, ATM based, TDMA based time slot assignment. It has corresponding theoretical values and engineering achievable values for modulation, demodulation, error correction, receiving sensitivity and spectral efficiency. Different modulation methods generally corresponding to different error correction methods, in the wireless communication system error correction performance will directly affect the overall performance of the system, especially in the organization of multiple sectors should pay more attention to this. However, it is undeniable that the corresponding relationship between the modulation mode and the error-correcting mode in the actual network has a great deviation from the theoretical value. Why is there a big difference between the theory and the project? The main reason is that any equipment in the case of Out-of-band radiation, to achieve the desired spectral efficiency is not possible, because the bandwidth must be increased in addition to the roll down router to prevent the system to the adjacent frequency system interference. At present, there is a widespread problem of exaggerated publicity for spectrum utilization, and there is a problem of inconsistent definition, the value of different definitions can sometimes make a great difference, which should be paid more attention to when choosing a network device, lest the device you choose cannot meet the requirements.

On the business load, 3.5G system business can be divided into two main categories: mainly based on transparent transmission of TDM Circuit basic services (base station transmission link and leased line services) and IP services, wireless access devices generally support both business, so that operators to provide users with differentiated services.

With regard to network management, authentication and billing, most of the network management systems of wireless access devices use SNMP protocol platform, and the user authentication and billing are basically done by the third party equipment, the wireless access device itself can provide as many parameters as possible for the relevant equipment access and use.

Due to resource constraints and the transmission characteristics of the 3.5GHZ device itself, antenna technology, an operator in the 3.5GHz band is difficult to organize the same city-wide system, unless the base station has a greater choice of freedom, so in the planning of the network should be carefully considered, especially the choice of equipment must have a higher performance indicators.