A brief analysis of mobile communication jamming

Interference in the net

Generation of interference in the net

The ratio of interference in the network is the largest in the interference of mobile communication, and it is mainly the same frequency and adjacent frequency interference. For GSM network, in the case of expanding the scale of the network, due to the limitation of frequency resources, frequency multiplexing is bound to increase, for example, Unicom uses 2/2/2 frequency planning, in some high traffic density areas using 2/2/3 or even 2/3/3 frequency planning; for China Mobile, more use 6/6/6 even 8 /8/8 frequency planning, due to the narrowing of frequency multiplexing interval, the occurrence probability of the same and pro frequency interference increases greatly. At the same time, because of the division of the base station to further reduce the distance, in the dense urban area reached 500M, so that the frequency of multiplexing space to shrink, the same mobile users received from different base stations of the same frequency point of the possibility of increase, resulting in the same frequency interference.

For CDMA networks, because the system uses Code division multiple access technology, all users use the same frequency band, mutual use of unrelated PN code as a spread code to differentiate, because of this feature, the existence of the same frequency interference is inevitable; at the same time, the amount of interference depends on the number of telephone users, the system capacity also changes (that is, soft capacity).

From the subjective aspect, the main reasons for the same frequency interference are the unreasonable plot planning, improper frequency setting, the selection of antenna parameters and improper adjustment of the parameters of the adjacent cell. When the user receives the same, the pro frequency in the same place, once the same frequency load dry ratio is less than 9dB or the pro frequency load dry ratio is less than -12db, will form the interference, affects the call quality. (Computer science)

How to reduce the interference of mobile network

(1) According to the existing frequency point quantity, chooses the reasonable frequency multiplex method and the scientific frequency plan. For Unicom GSM900 Mobile network, the occupancy bandwidth of 6M, a total of 29 frequency points, according to 3 sectors per base station set, the standard frequency multiplexing mode for 2/2/2. For some of the high density of traffic, according to the environment and the surrounding base station, individual use of 2/2/3 frequency settings, a better way to solve the problem is the use of dual-frequency network, the use of DCS1800 base station to absorb traffic;

(2) Reasonable planning base station position, station height, antenna angle and so on;

(3) Reasonable setting of cell parameters;

(4) Adoption of new technical means. At present, it has been widely used: dual-frequency network technology, frequency hopping technology, DTX (discontinuous launch), automatic frequency planning and so on.

NET outside interference

For mobile networks, the interference from outside the network can not be ignored, at the same time, compared to the interference in the network, the external interference is more difficult to find and solve. The main external interference is: microwave communication, paging transmitter frequency interference, broadband repeater, CDMA downlink on the uplink of the interference, TV frequency multiplier on the uplink interference, PHS to GSM interference, electromagnetic interference and so on. There are a wide range of interference in the network, and it is difficult to analyze and locate.

Classification of disturbances

According to the frequency division characteristics of mobile networks, the following conditions are more than net interference: 1 interference signal bandwidth is very wide, affecting the entire use of frequency bands, 2 unknown mode of interference signal, 3, the emergence of IOI alarm. Initially, we can classify the jamming signal according to the characteristic and the spectrum characteristic.

Analysis and location of jamming

There are many reasons for the interference from the net, and the jamming source is not easy to find. In the process of finding the source of interference, you can first pass various test methods (such as road tester, base station tester, etc. to the interference signal testing and analysis, is the uplink or downlink interference, is a single frequency point interference or the entire frequency band interference, interference signal whether there is intermittent, interference intensity, interference source approximate distance, Interference signal may be the standard, test methods and network interference test methods have a similar place, and not the same, the network of interference to find more rely on the site repeated testing and practical work experience to complete. The following are some specific examples of interference analysis and positioning to make some useful discussion:

Case one: Interference of microwave communication to GSM1800 frequency band

W City A communications company's GSM1800 Network has a large area of strong interference, is the use of Base station tester for testing and search. First boarded a high-rise in the city center, will test equipment preset GSM1800 frequency band, the directional antenna horizontal rotation 360 degrees, found in a certain angle GSM1800 uplink and downlink respectively appear a pair of interference signal spectrum, respectively uplink 522, 671 channel, downlink 653, 786 channel, interference surface is very big, As an unknown interference source, the direction of downlink jamming signal is determined by directional antenna, and the initial judgment is that the interference comes from microwave communication. Near the power station building, after the directional antenna to the microwave antenna, found that the interference signal is very strong, bandwidth of 8M, further determine the source of the microwave antenna, and then through a similar way to find the upstream interference source of a substation 15 kilometers away. After the coordination with the Power Bureau, the frequency of microwave communication has been replaced, the interference disappears.

Case TWO: C-Net broadband repeater interference

A certain region CDMA base station appears uplink interference alarm, using the tester to scan its surrounding area, the north direction interference signal is the strongest, uplink band 283 channel is 16M bandwidth signal coverage. To the base station north facing the base station direction to test, combined with two tests to get the source of the general direction of the interference (cash test direction of the intersection), proved that the interference signal from the base station directly opposite a factory, and finally found an illegal C-net in the plant's top repeater, interference signal 16M bandwidth, power to reach -62dbm. After removal, the disturbance disappears.

The cause of mobile communication jamming is very complicated, a wide variety of the search for interference is not fixed mode or automatic equipment can be completed, only in-depth analysis of the mechanism of mobile communications, and gradually strengthen the understanding and analysis of interference, the right remedy, can effectively reduce the interference of mobile networks, for the vast number of mobile users to provide a high-quality network.