The rapid development of mobile communications requires the establishment of a large number of base stations. In particular, in 2001, Unicom invested nearly 20 billion to build C-network and CDMA repeater systems. In order to reduce the cost of the coverage system, the best method is to establish a repeater system. Strictly speaking, the cost of the repeater is only about 20% of the base station. Therefore, the selection of the repeater is the best solution for mobile communication construction. South Korea is a good reference in this regard, the base station and repeater ratio is 1:10. Among them, outdoor repeaters account for 1:4. We are far from South Korea. The United States has built a 150-kilometer RF continuous coverage system in its western region.
When it comes to the type of repeater, everyone is very clear, and the article has also made a lot of introductions. There are mainly RF repeaters, fiber optic repeaters, frequency shift repeaters (two types), radio frequency and fiber optic hybrid repeaters. Several types of repeaters are considered to be the most economical and effective way to comprehensively consider cost, distribution, construction and maintenance. From Table 1, we can see that RF repeater equipment is the cheapest.
It can be seen that the front-to-back ratio and the pitch angle of the donor antenna are 90o, and the flap attenuation level is required to be large. At present, domestic corner reflector antennas and backfire antennas perform slightly better. The rest of the antennas are not easy to meet the requirements. If the US Peninsula Company's requirements for the donor antenna and the user antenna reach 38dB before and after the 38dB and 90o ± 10o side flap loss level, it is not easy to achieve. According to a large number of domestic diagonal reflector antennas and backfire antennas and related units of 65o and 90o plate antennas, the isolation is only 85 to 105dB when tested with a height difference of 22 meters.
High-performance, high-isolation antennas bring great advantages to RF repeatersAs mentioned earlier, in all repeaters, it should be said that RF repeaters have the greatest economic advantage. However, the difficulty is that the donor antenna and the user antenna need to provide a high front-to-back ratio to meet the isolation requirements of the amplifier under higher gain conditions. If the isolation is not met, the amplifier will be self-excited and cause serious interference. This kind of radio frequency interference has also become a major problem in the construction of CDMA repeater in the first phase.
In order to solve the interference problem, various measures are taken:
1) Improve the height of the transceiver antenna frame by more than 20 meters.
2) When installing horizontally, use a corner reflector antenna or a back-projection antenna to increase the distance and increase the barrier.
3) Use frequency shift repeater.
These measures may solve some problems, but the result is that the cost of the entire repeater system is greatly increased. Conservative estimates will increase the cost of equipment and equipment by 20,000 yuan.
According to the gain of the amplifier provided at home and abroad, it is generally 60-90dB, with a dynamic range of 30dB. To make the amplifier not self-excited, the isolation of the transmitting and receiving antenna is greater than the gain of the repeater by 10~15dB. In fact, when setting up the RF repeater, make a reasonable plan and set it based on the drive test level. According to the analysis of the large number of installation and debugging results of the repeater in 2001, the gain of the repeater is not easy to be too large. This mainly considers the repeater as a two-way operation, and the level balance of the uplink and the downlink. If it is unbalanced, it will interfere with the automatic power of the mobile phone. Control and coverage areas will cause dropped calls, affecting the connection rate and dropped call rate in the channel statistics. In fact, the coverage of the repeater is mainly reflected in the effect: 1). Index stability of equipment performance. 2). Does not affect the parameters of the network. Simply pursuing high power is meaningless. According to the national regulations, the downlink output power of the repeater does not exceed 30dBm±3dBm. According to this requirement, the repeater gain is turned on to 80dB, which is enough to meet the requirements. The amplifier input level is around -65dBm, which is the normal input level.
In order to meet the best requirements of RF repeaters, we have developed 30o, 40o high performance donor antennas and 65o, 90o high performance user panel antennas in mid-2001. We set up a 5-meter-high pole on a 30-meter-high roof. Simulated repeaters, a large number of tests on antenna isolation.
1). The 30o high performance donor antenna and the 65o user panel antenna are mounted on the poles at a distance of 1 meter, an angle range of 120o to 180o, and a test isolation of 95dB or more.
2). The 30o high performance donor antenna and the 90o user panel antenna are mounted on the poles at a distance of 1 meter, an angle range of 120o to 180o, and a test isolation of 90dB or more.
Generally, the isolation between the donor and the user antenna should be less than 15 meters if the above values ​​(90 to 95 dB) are to be achieved. If the spacing is 1 meter, the isolation is only 65 to 70 dB. Therefore, when the 30o and 65o antennas are installed at a distance of 1 meter, the high isolation results in the first application of the repeater application, which is the first in China.
In summary, the high isolation antenna brings the following advantages to the RF repeater:
1). It replaces the high-priced base station.
2). It replaces the frequency shift repeater and the high maintenance cost fiber optic repeater.
3).95dB isolation can reach 10Km long distance coverage, eliminating large areas of the upper shadow area.
4). The antenna can be installed on the pole of the building to make installation, commissioning and maintenance convenient, reducing the cost of the high-speed tower and long feeder cable. It is the lowest price for the repeater system and is the operator's preferred solution.
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