Key point of DAS and LTE-PIM

Key point of DAS and LTE-PIM



What is PIM

Passive intermodulation (PIM) is a kind of signal interference in wireless systems. PIM is a common problem in almost all wireless networks, but for distributed antenna system (DAS) networks and LTE networks, it is a major problem that can cause great damage. DAS network is used to spread cellular and Wi Fi signals in a building or area, while LTE network supports high-speed wireless access of mobile phones, tablets and other wireless mobile devices. As these two technologies increasingly support wireless devices, how to detect PIM and reduce the impact of PIM becomes more and more important.

Measuring method of PIM

PIM is expressed in decibels (dBc) or decibels milliwatts (dBm) relative to carrier power. Generally, a PIM not exceeding - 100dBm is considered an acceptable PIM level, and the lower the better. However, the test results show that even though - 105dBm is considered an acceptable PIM level, when the PIM level increases from - 125dBm to - 105dBm, the download speed can still be reduced by 18%.

How to protect your network

PIM test is usually carried out for each component in the design and production process to ensure that it will not produce serious PIM after installation. For DAS system, in addition to various components, sometimes the PIM of the whole system will be tested. In addition, installation is also an important part. This is because whether the connection mode of components is correct is also a necessary condition to minimize the PIM level.

PIM evaluation is also required during cellular site setup. Ideally, this type of assessment needs to be carried out before and during the siting and installation of cellular base stations and antennas.

At present, not only more and more testing companies can provide special equipment to detect, locate and solve PIM sources, but also there are low PIM products on the market that can solve PIM problems.

In addition, PIM certified devices are becoming more common. For example, antennas below - 140 dBm can now obtain PIM certification, and this requirement is becoming increasingly stringent.

Because so many devices rely on powerful wireless signals, PIM will inevitably bring problems to the system. Fortunately, however, the adverse effects of PIM can be identified and prevented by following a series of existing measures step by step.

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