Due to the limited isolation of the conventional wireless co-channel repeater, the signal received from the air by its donor antenna will inevitably contain some coverage signals from the retransmitting antenna and are fed back through various channels to form co-channel interference signals. These The signal causes interference to the repeater, affects its output waveform quality, and even easily causes the repeater to self-excite. Because these interference signals are the product of the repeater itself, the frequency is the working frequency of the repeater, so this interference problem It cannot be solved in the frequency domain by conventional passive RF filter technology.
In order to ensure the quality of the output waveform of the repeater and avoid the self-excitation of the repeater, a gain guard band (GM) must be set so that the gain of the repeater is less than 10 ~ 15 dB of the antenna isolation. Even in the case of limited isolation, the gain of the repeater needs to be strictly controlled. For every 6 dB reduction in the gain of the repeater, the coverage will be reduced to half of the original. It can be seen that the isolation is for conventional wireless repeaters Station use effect has a great impact.
ICS = InteRFerence CancellaTIon System is the interference cancellation system. For the interference signal in the working frequency band, the conventional RF filter has no good way to solve it in the frequency domain. With ICS, it is possible to eliminate interfering signals through digital processing techniques. The ICS system can meet all RF specifications, such as spurious emissions, at high gain and high output (20W, 40W). The elimination of multipath feedback signals by the ICS system can generally reach more than 30dB. Even if the feedback interference signal is larger than the base station signal, the ICS system can still maintain the coverage signal quality. The link margin provided by the ICS system can make the system work in a state of high gain (100dBmax), so even very weak signals can be amplified. The ICS system eliminates some problems caused by feedback interference from the retransmission antenna to the donor antenna, such as system self-excitation and signal quality deterioration, solves the problem of wireless repeater equipment self-excitation, and reduces the installation requirements of wireless repeater projects.
The problem with ordinary wireless repeater products is that the feedback between the retransmission antenna and the donor antenna is the most important interference. other signal feedback channels include signals reflected from some distant or near buildings, vehicles, trees, etc. These signals will also be the interference introduced from the end of the donor antenna. Gain Margin (GM, gain margin) = isolation-gain, when GM <0, the repeater is prone to self-excitation, when GM is less than the system's signal-to-noise ratio requirements, the repeater is just a noise generator under normal application conditions , Select GM = 15 for the repeater. Using ICS repeater can allow GM <0, the interference signal can be 15 dB larger than the base station signal. The isolation requirement of the antenna is reduced, which makes the engineering installation easier. Under the same antenna isolation conditions, greater gain and output can be achieved .
The ICS repeater uses software radio and digital signal processing technology to achieve a certain technical threshold. ICS technology mainly uses interference adaptive cancellation technology to achieve the purpose of eliminating interference. Adaptive filtering can effectively track the time-varying input signal in an unknown environment to optimize the output signal. The schematic diagram is shown in Figure 1.
Using the ICS repeater, the output waveform quality is better in terms of performance, and it can effectively prevent self-excitation. Under the same antenna isolation application conditions, the repeater gain can be increased by 30dB, which in turn provides greater power output. Extend the coverage area and improve the quality of coverage. Economically, due to the low installation, operation and maintenance costs caused by the reduction in antenna isolation requirements, it can also avoid the additional cost increase caused by site selection and make the repeater cheap. It is easy to use, can be applied to all-climate environments, has power access, can be applied to meet line-of-sight transmission, and has more relaxed requirements for antenna isolation. Compared with the optical fiber repeater station, it does not need to lay fiber; compared with the wireless repeater station, the requirement for isolation is lower; compared with the frequency shift repeater station, it does not need to introduce the near and far ends, and works at the same frequency.
ICS is one of the hotspot technologies of repeaters, and will soon become the main product of wireless repeaters. It will replace traditional analog wireless repeaters and will occupy a large market share in some economically developed regions. Due to the high gain, high power, high stability and easy maintenance of ICS repeaters, ICS repeaters will snatch the market share of some base stations.
Main application scenarios of ICS repeater:
After the ICS device is turned on, the ICS function is closed, and the EC / IO:
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