Interference Hunting and Localization

Because of the latest developments in communications technology together with a drastic increase in the sheer volume of data that is to be transmitted wirelessly, there is heavy traffic in the occupied frequency bands, with the tendency being towards continuous growth. More and more wireless applications and devices have to share the available frequency ranges. This has been triggered by achievements such as the growing LTE/5Gwireless network and the Industrial Internet of Things (IIoT or IoT) industry 4.0, and Car to Car (C2C or C2x) or Machine to Machine communication (M2M), which also use a large part of the wireless network. Taken together with ever increasing data rates, this inevitably leads to higher signal densities and more complex modulation methods, wider signal bandwidths, and a  greater probability that interference will occur between signals.

Typically, when a site is affected by an interference, it usually triggers an alarm. The symptoms are bad throughput and interrupted calls. When the carriers’ technicians investigate the problem, they can see that the source of the problems lies in the spectrum: something or someone is interfering with the frequencies, which creates so much noise that the cell phones and the cell towers can no longer communicate with each other.

We specializes in hunting down and eliminating interference. The problem primarily occurs in the 800 MHz cellular reverse link (cell phone to cell site) bands, but we also see interference in the 700 MHz LTE bands and occasionally in the PCS and AWS bands. This interference comes from a variety of sources, including the following: 

• Booster amplifiers (sometimes called BDAs) that sometimes oscillate when there is inadequate isolation between input and output. Some of these are found in residences and inside vehicles and are designed to boost cell phone coverage for the user.
• Utility power transformers (occasionally)
• Florescent light ballasts (occasionally)
• Cable TV set top boxes, especially those used in hotel rooms
• Cordless phones and any devices operating in the 902-928 MHz license-free band
• Passive intermodulation (PIM) at the cell site, caused by unintentional non-linear mixing of transmit frequencies in corroded joints, loose connectors, etc. This is often the easiest to identify provided one has the proper test equipment.