Want better network performance? Prevent PIM

BANGALORE, INDIA: Passive Intermodulation, also known as PIM, has been recognized as an obstacle to network efficiency from quite some time. PIM is defined as two or more wireless signals mixing together to create additional, undesired frequencies that cause interference or degrade transmission of desired signals in wireless networks.

New technologies have further helped PIM to grow exponentially. The multitude of carriers in the wireless domain and the increasing size and complexity of their networks is making transmission interference a growing problem for operators as they evolve to next generation network technologies.

Whilst distortion caused solely by active components such as amplifiers can be reduced or eliminated by filtering, unfortunately operators are now seeing increased network performance issues due to PIM, which occurs in non-powered devices (such as cables or antennas).

The mechanics of PIM involves the production of new, unwanted signal frequency components in the passive, non-linear devices commonly found in and around base stations (e.g. connectors). PIM is usually the result of two (or more) high power tones mixing at device non-linearities such as junctions of dissimilar metals, corrosion or rust and even loose connectors.

PIM can be particularly troublesome because initial site inspections often find that the equipment is linear and should be unable to generate intermodulation interference - making the source of the problem very hard to pin down and solve. For this reason PIM, in particular, is a problem that operators are increasingly concerned of.

Regulators are squeezing spectrum capacity to its limit, shared base stations are becoming more common and the number of antennas used for transmit and receive functions are being reduced. Additionally, there are now more components than ever in the radio frequency (RF) transmission path - including cables, connectors and antennas - and each additional component is another potential source of PIM signal degradation.

The impact of PIM

If PIM causes a network to operate at less than full potential, operators risk loss of revenue and customer churn with substandard service quality as one of the greatest factors. On top of that, they face increased infrastructure costs to track down and resolve problems, as well as a reduction in base station coverage areas.

In older wireless networks, radio interference might slightly affect the quality of a voice call. However in modern mobile networks, a site experiencing severe interference will hand-off traffic to another base station, meaning that subscribers may never even receive a call at all and-in today's multimedia society-delivery of videos and other forms of data traffic will suffer.

Moreover, operators have invested a great deal of money in purchasing spectrum rights, the efficiency of which can be wasted by severe PIM.

Preventing PIM: Network planning

Interference problems can be greatly reduced by choosing one vendor, which reduces deployment risks, lowers costs, improves network reliability, simplifies the network and provides one point of contact for any issues that may arise. Buying solutions from trusted partners who can provide robust, problem-free solutions also means that operators do not have to waste money implementing solutions to solve performance problems further down the line.

It is far more cost-effective to purchase complete, system engineered, integrated solutions, rather than relying on equipment from many disparate vendors. It is careful network design and planning that results in long-term, optimal performance of networks.

Preventing PIM: Training

Given that PIM can be difficult to both detect and resolve, it is essential that operators employ certified, comprehensively trained installers. Many occurrences of PIM can only be solved by experienced personnel conducting a first-hand survey of the site.

In developed countries, operators should partner with equipment vendors that have robust business partner programmes and provide expert installation for their own product offerings. When this is combined with purchasing all of the site equipment from a single vendor, operators can expect higher quality installation work, expert on-site advice and rock-solid accountability for any problems.

Preventing PIM: High quality components

Telecoms networks are currently facing the problem of reduced network service quality due to substandard equipment, resulting from the lower quality components and subsystems that are being produced in some markets.

Due to this lower quality hardware, many networks over time are running well below the efficiency levels they could have maintained with higher quality components. In the long-term, this means that these components must be painstakingly identified and replaced, at a far higher cost to the operator.

As operators invest in upgrading to 4G networks, new infrastructure is often overlaid on existing passive components, such as coaxial feeder cable, filters and base station antennas. Steps need to be taken to avoid potential signal degradation that can result from such overlays, especially when adding new frequency bands.

For wireless networks to achieve their full operating potential, each sector within the network must perform up to its design standard. To achieve the optimum operating potential of each node in the network, each RF component and interconnection of the RF path components must be properly installed, verified and maintained to ensure optimum performance over time.

PIM is no longer simply a nuisance - it is a critical threat to network efficiency, channel capacity, and bottom line profit. With 4G on the horizon and new technologies like active antennas being introduced, service providers, would increasingly need networks to be as interference free as possible.

In this context, it will be the operators who have squeezed the highest possible level of performance from their networks that will not only survive the immediate crisis of falling revenues and increasing expenditures, but also thrive well into the future.

The author is director, Wireless Sales, India, CommScope India.