PIM Happens - Why, What, When?

For wireless cellular networks to achieve their full operating potential, each sector within the network must perform up to its design standard. When this does not occur, the economic impact to the service provider can be substantial:

• lost revenue at that site

• customer dissatisfaction and churn

• increased infrastructure cost

• reduction in cell site coverage area

To achieve the full operating potential of each node in the network, each radio frequency (RF) component and interconnection of the RF path components must be properly installed, verified and maintained to ensure optimum performance overtime.

Viewed from the RF perspective, to maximize performance it is essential that:

• the wireless carrier signals be efficiently propagated from the transmitter output through the RF path components with minimum loss and distortion

• upon receiving the RF signal from the mobile handset at the base-station antenna (BSA), the signal must be efficiently propagated back to the basestation receiver

• interference/noise at the base-station receiver within the frequency band of the handset uplink signals must be lower in magnitude than the system noise floor

There are more components than ever in the RF transmission path, including cables, connectors, amplifiers, antennas, and each additional component is another potential source of signal degradation. All of these components contribute to INCREASING system Insertion Loss and REDUCING the overall Return Loss value, which simply stated means “The system performance is getting worse”.

Wireless operators have invested and are investing a lot of money into 3G and 4G networks and will continue to do so for the next generation of technologies. These investments are often overlayed on the existing network, utilizing existing tower equipment such as coaxial feeder cable, filters and base station antennas. Steps need to be taken to avoid potential signal degradation that can result from overlays, especially when adding new frequency bands. Passive Intermodulation (PIM) is one of the causes of signal degradation, and the incidence and cost of PIM is no longer simply a nuisance—it is a critical threat to network efficiency, channel capacity, and bottom line profit.

Interested in learning more? The SP6160 PIM/VSWR Fundamentalstraining course is a self paced online course that details the key testing and troubleshooting techniques and is available from the CommScope Infrastructure Academy.