Comparison and analysis of other wireless access technologies for 3.5G wireless access Technology

As one of the most hot access technology, wireless access technology by the operators, especially the new operators generally optimistic, the national radio Regulatory agencies also issued a specific frequency planning, it is evident that everyone to this technology attention and optimistic degree.
　　
According to the frequency planning of the national Radio Regulatory Agency, our frequency division is basically based on European standards. Within the limited 30MHz bandwidth, if the 1.75MHz bandwidth is divided into units, can accommodate 17 bands; According to the 3.5MHz bandwidth for the unit, can accommodate 9 bands, clear the division of frequency to talk about the use of 3.5G wireless access technology for network construction and operation.
　　
At present, the type of air interface used in fixed wireless access system is broadly divided into three categories: based on IP, ATM-based, TDMA-based time slot allocation, for modulation and demodulation, error correction, receiving sensitivity and spectral efficiency, and the corresponding theoretical values and engineering achievable values. 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.
　　
The bandwidth used by different devices is more about access bandwidth and bandwidth consumption. We see, for 802.11 based wireless LAN and other products, only about 1.8M, from some manufacturers known as 23M of the single carrier access bandwidth has some access, mainly because in the calculation did not remove the protocol overhead, so the value is not the user can use the net rate. For some devices that lower the operating frequency to 3.5G from the 26GHz LMDS system, single carrier occupancy
Bandwidth is 3.5 MHz, providing a net rate of 8M; Datang Telecom's R2000airsun product list
Carrier Bandwidth 1.7 MHz, provides a net rate of 4M (2XE1), and is able to actually
This is because we use the 64QAM modulation method with convolution encoding.
　　
In the business load, basically can be divided into two broad categories: mainly based on transparent transmission of TDM
Basic circuit Business (base station transmission link and leased line business), also can carry IP services, wireless access devices generally support both business, so that operators to provide users with differentiated services.
Datang Telecom R2000airsun can host all of the above services simultaneously, but wireless access products based on Ethernet technology often only support the latter and cannot provide the first class of business services.
On network management, authentication and charge, most wireless access products network Management system using SNMP protocol platform, and the user authentication and charge basic needs of the third party equipment, wireless access device itself can provide as many parameters as possible for the relevant equipment access and use.
The typical network mode of Datang equipment is eight sectors, which can be realized by two pairs of carriers, that is, the different frequency of adjacent sectors, the same frequency multiplexing of the adjacent sectors, the frequency difference and different polarization mode to organize the multi sector Base station. In practice, how much frequency resources The operator can get is the most important prerequisite, and it is a key problem that is more crucial than the sector reuse technology itself. If all 30MHz bandwidth is available in a city, the available bandwidth per sector can be as high as MHz, which facilitates the organization of multiple sector systems with high access bandwidth. But this condition is more difficult to meet in the actual frequency distribution. If you obtain a 14MHz bandwidth license, you can organize multiple sector base stations by 2x7mhz. If you obtain a 7MHz bandwidth license, you can organize multiple sector base stations by 2x3.5mhz. If the access device has a single carrier bandwidth of 14MHz, only the 2x14mhz bandwidth license can be used to organize multiple sector base stations; some devices organize multiple sectors with three carrier frequencies and a wide bandwidth of 7MHz per carrier. This requirement for air radio frequency bandwidth is more difficult (because it is difficult for a particular operator to get more than 14MHz of bandwidth in a city). Datang Telecom's equipment single carrier bandwidth occupancy is 1. 7MHz, so it can fully meet the flexible needs of operators, the use of available spectrum resources to effectively organize multiple sector base station.
Due to resource constraints and the transmission characteristics of the 3.5GHZ device itself, as well as the antenna's technological reasons, an operator in the 3.5GHz band is difficult to organize the same city-wide multi-cell system, unless the base station for a greater choice of freedom, so in the network planning needs careful consideration, especially the choice of equipment must have better performance indicators. Datang's equipment can be used to organize multiple cells and achieve a 10E-9 BER requirement when the same frequency load ratio is not greater than 21DB, or the neighbor frequency load dry ratio is not greater than 15DB. And, for the base station position within the general designation, user remote station location, station and the coupling between stations and other complex factors, we have a set of advanced design software, the system can be detailed parameter calculation, to ensure the implementation of a multi-community scheme to maximize the operator's valuable frequency resources to make full use of.
Datang Telecom equipment in Guizhou Mobile successfully realized the interconnection of more than 70 base stations, the demand for the spectrum is 28MHz; even in the 3.5GHz band can not get 28MHz bandwidth, our equipment support 3.5GHz, 26GHz Hybrid network, can be a good solution to this problem.
The previous main description of the 3.5GHz wireless access system, the following for the main wireless access means
A simple comparison is made in a technical sense.
　　
Wireless access products in different frequency bands
　　
Wireless access products of different frequency bands, mainly include:
A: A MMDS system for 2.5ghz/5.7ghz. At present, Datang Telecom and the United States Cisco companies are cooperating, combined with Datang Wireless RF technology in the experience and strength, the introduction of two-way data access wireless router products. The use of advanced VOFDM technology to achieve no line-of-sight communication, in the buildings in the city using "multipath" to achieve a single carrier 6MHz bandwidth up to 22M p BS data access services, the spectrum efficiency is high, In the 2.5GHz band can reach 90% of the communication probability, in the 5.7GHz frequency point can reach more than 80% of the communication probability.
Since the current radio and television system basically realized the use of optical fiber transmission signals, radio and television systems to exit the 2.5GHz band can have the opportunity to obtain a 2.5GHz license.
B: Working in the high-frequency microwave SDH IP ring system. In the past in point-to-point microwave relay transmission circuit used more microwave SDH equipment, now with the progress of technology we have introduced a two-way microwave SDH network, with self-healing function, and fiber ring self-healing characteristics of the same, can go up and down the business, integrated ADM, using a serialized modem, to achieve 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 small structure of the IDU+ODU equipment engineering installation More convenient than the previous microwave equipment, and in the case of frequency tension, This equipment can work in 13, 15, 18, 23GHz and other frequency points, in the construction of the metropolitan area Network can be avoided for 3. 5/26 Wireless access frequency of fierce contention, can support 8*155m bandwidth.
Structure diagram of microwave SDH/IP ring net
As for the LMDS system that works in the 26GHz band, we've heard a lot lately, so I won't repeat any of the basic performance overviews, and I need to emphasize that:
In the modulation mode, the problem of using FDMA or TDMA. Because of the large capacity of the system, if the use of FDMA to make the bandwidth by a single user is not economical and unnecessary, so the current practical system used more TDMA way, and there is no one to use TDMA-64QAM modulation, so the actual implementation of the project access bandwidth is limited, Not as big as some propaganda.