![<?echo $_SERVER['SERVER_NAME'];?>](/template/twentyseventeen/skin/images/header.jpg)
With the rapid development of GSM mobile services, it is always the goal of network operators to maximize GSM network capacity while ensuring communication quality. The traditional method of GSM capacity expansion is cell division and frequency band expansion, but the possibility of obtaining new spectrum resources is not high at present. Due to interference restrictions in traffic-intensive areas, cell division is also difficult, so closer frequency reuse is adopted. Technology, establishment of micro-cells / pico-cells, construction of SM900 / 1800 dual-band network and network optimization have become important means of solving GSM network capacity.
1 Cell splitting technology
Cell splitting technology is the logical first choice for increasing network capacity. In the early days of GSM network construction, it was mainly to solve the coverage problem. In regions / periods with abundant spectrum resources, with the increase of users, the original cell can be split into more cells with a smaller coverage area or the carrier frequency of the original cell can be increased, so as to achieve the purpose of capacity expansion. Through cell division or new carrier frequencies, the number of base stations in the entire network increases, and the number of carrier frequencies, channels, traffic, and users of the entire network increases significantly. The key to improving the spectrum utilization rate by cell splitting is to reduce the area of ​​a unit cell.
The following principles should be followed when selecting the cell split and expansion method:
(1) Ensure that the built base station can continue to be used;
(2) The regularity and repeatability of the frequency reuse method should be maintained;
(3) Minimize or avoid the transition zone;
(4) Ensure that cell division can continue in the future.
The method of splitting an omnidirectional cell into an omnidirectional cell mainly includes the 1: 3 split method; the method of splitting an omnidirectional cell into an omnidirectional and moving cell is: 1: 7 splitting method; ; 3 & TImes; 4 splitting method and 1 & TImes; 6 & TImes; 3 splitting method; The method of splitting directional cells into directional cells is: hexagonal edge center splitting method and hexagonal vertex splitting method.
2. Frequency band extension and frequency close multiplexing technology
Frequency band expansion is of course an ideal means of capacity expansion, but in the current situation, it is unlikely that new spectrum will be obtained.
At present, Zhejiang Unicom has 6MHz resources in the 900MHz frequency band, except for some hot spots, it can basically meet the needs for the time being. After the fifth phase of Zhejiang Telecom ’s GSM capacity expansion, the frequency range of the GSM network is: 898.6-908.8MHz, a total of 10.2MHz. In principle, the current capacity expansion plans to extend the frequency band of network A to 885.0125MHz and the frequency band of GSM network downward to 14.4MHz, using frequency points 23-94.
At present, the base stations of Zhejiang Telecom's G network are very dense in many areas, especially in the cities of Hangzhou, Fu and Wen. The distance between some base stations is only four or five hundred meters. It is becoming more and more difficult to select a suitable site. The distance between the stations is too close, resulting in an increase in co-channel and adjacent-channel interference. In addition, the higher the antenna gain, the narrower the beam width in the vertical plane. If the stations are too close, the probability that the mobile station is outside the main beam of the antenna is greatly increased. In addition, there is not much room for frequency shifting in network A. Therefore, the space for spectrum spreading is very limited.
However, because GSM uses such methods as GMSK, equalization modulation, interleaved coding, etc., in particular, it also provides some other technologies aimed at improving spectral efficiency, such as frequency hopping, discontinuous transmission (DTX), power control, half rate channels Diversity reception and mobile assisted handover, etc., thereby reducing the network's requirements for co-frequency and adjacent source interference indicators, making it possible to closely reuse frequencies.
(1) Frequency hopping. Frequency hopping means that the carrier frequency hops according to a certain frequency sequence. It includes baseband frequency hopping and radio frequency hopping.
The function of frequency hopping is to provide frequency diversity and improve the anti-interference and anti-fading capabilities of the system.
(2) Discontinuous transmission (fDTX). Using DTX technology can reduce the total interference level of the system.
(3) Power control. This is also an effective means to reduce interference and increase capacity.
(4) Half-rate channel. This can double the system capacity.
(5) Diversity. There are many forms of diversity, and the use of diversity techniques can improve the system's ability to resist fading.
3. Adopt tighter frequency reuse technology
In the case of limited frequency bands, the use of tighter frequency reuse is undoubtedly one of the most direct ways to increase system capacity. The frequency reuse methods that can be used in GSM are mainly: 7-cell multiplexing, 4 × 3 multiplexing, 3 × 3 multiplexing, 4 × 3 and 3 × 3 mixed multiplexing, 2 × 6 Use mode, 1 × 3 multiplexing mode, Concentric Cell (Concentric Cell) technology and multiple multiplexing MRP (Multiple frequency Pattern) mode, etc.
(1) Multiplexing method of 7 base station areas
This multiplexing method of seven base station areas as a multiplexing group is suitable for areas with low traffic volume or low user density. It is generally an omni-directional base station with a D / R = 4.58 and a long distance of multiplexing on the same frequency. .
(2) 4 × 3 multiplexing
This is the multiplexing method recommended by the "900MHz TDMA Digital Public Terrestrial Cellular Mobile Communication Network Technology System", and it is also the most common and typical multiplexing method in the GSM system. For the clover 60-degree antenna, its D / R = 6; for the 120-degree antenna, its D / R = 3.46 when using clover 60-degree wireless, the same frequency interference performance is better.
(3) 3 × 3 multiplexing method
This is also the multiplexing method recommended by the "900MHz TDMA Digital Public Land Cellular Mobile Communication Network Technology System". The 3 × 3 multiplexing method is used together with frequency hopping, DTX, and power control to achieve the same frequency interference requirements. But when the bandwidth is below 6MHz, it cannot provide sufficient frequency hopping gain, so the performance is not good.
(4) 2 × 6 multiplexing
This is a method proposed by Motrola to solve frequency reuse in high traffic areas. This method has different degrees of frequency reuse in different antenna directions, and its D / R is less than 3 × 3 multiplexing.
(5) 1 × 3 multiplexing method
This method is currently the most compact reuse method, and its main features are:
· Applicable to areas where the frequency band is narrow, the capacity is relatively concentrated, and many base stations are not required;
Can provide larger capacity with a smaller number of base stations;
· Partial loading method is needed, that is, the carrier frequency cannot be used up, and the number of transceivers is about half of the carrier frequency;
· Need to adopt radio frequency hopping, power control, discontinuous transmission, antenna diversity and other technologies to reduce interference;
· No need to change the existing network structure.
However, although this method has a high frequency utilization rate, the system interference increases greatly. If the anti-interference measures adopted are not effective, it may have a greater impact on the network quality, so it should be used with caution.
(6) Concentric circle technology
The concentric circle technology divides the usual cell into an outer layer (Overlay) and an inner layer (Underlay). The outer layer coverage is a traditional cell, while the inner layer coverage is mainly concentrated near the base station. In addition, the frequency reuse coefficients of the inner and outer layers are generally different. The outer layer generally uses a 4 × 3 multiplexing method, while the inner layer uses a more compact multiplexing method, such as 3 × 3, 2 × 3, or 1 × 3. .
According to the different implementation methods of concentric circles, it can be divided into two types: ordinary concentric circles and intelligent double-layer network (IUO). The main difference between the two is the transmission power of the inner layer and the switching algorithm of the inner and outer layers. The transmission power of the inner layer of a common concentric circle is generally lower than that of the outer layer, thereby reducing co-frequency interference. The switching of the inner and outer layers is generally based on power and distance. The transmission power of the inner and outer layers of IUO is exactly the same, and it is switched based on C / I.
The increase in capacity of ordinary concentric circles is about 10% -30%, and the increase is not large. The IUO method increases the capacity relatively, generally 20% -40%, and can guarantee the quality of the call on the basis of increasing capacity.
(7) MRP method
The MRP method is to divide all available carrier frequencies into several groups, and each group of carrier frequencies serves as an independent layer. The frequencies of different layers use different multiplexing methods, and the frequency reuse is tight layer by layer. To ensure the safety of BCCH, the number of carrier frequencies used for BCCH in MRP should be no less than 12. According to different TCH grouping methods, MRP can be divided into strict MRP and improved MRP.
Electronic motors applications.
Multiple Electronic Limits Tubular Motor,Motor Solutions,Intelligent Remote Control Motor Solutions,Electronic Limit Garage Door Motor
GUANGDONG A-OK TECHNOLOGY GRAND DEVELOPMENT CO.,LTD. , https://www.a-okmotor.com