March 27, 2017
A recent report published by Ericsson highlighted how much data was transmitted throughout the 2016 Summer Olympic Games held in Rio de Janeiro. The numbers are record-breaking. Over 1.4 million fans attended the world’s biggest sporting event, sharing their feelings and opinions from 144 venues and related sites.
Ericsson reported about 303 TB data was consumed and 1.1 million Erlangs were carried at the event, with LTE accounting for 45% of the data traffic. On average, consumers spent more than two hours a day streaming live broadcasts or video clips on their smartphones. This represented an increase in network traffic of 72% compared to a normal day in Rio. Figure 1 is an infographic from Ericsson that highlights all mobile data-related statistics from the event, which are staggering.
These record-setting statistics included 4x more consumption of mobile data compared to the 2012 Olympic Games in London. One could reasonably assume that future Olympic Games and similar major sporting events, such as the World Cup and Super Bowl, will have significant mobile data usage, as well.
PIM Testing for High-speed Networks
To satisfy these large crowds accessing high-bandwidth services in a confined area, such as arenas and stadiums, network operators need to mitigate interference so they meet ever-demanding KPIs. In such network environments, minimizing passive intermodulation (PIM) remains one of the key factors to maintain optimal network performance. PIM is a serious issue for operators seeking to maximize their network’s reliability, data rate, capacity, and return on investment. In multi-operator DAS environments, which are common in large cities such as Rio and sports complexes like those at the Olympics, PIM issues are more severe due to the increased probability of low order products falling in one or more operator’s uplink band.
High-speed digital data communications, such as those at the 2016 Rio Olympics, make PIM testing critical. As cell usage and throughput grows, the peak power produced by digital modulations increases dramatically, contributing heavily to PIM problems. On-site experiments have shown significant decreases in download speeds linked to slight increases in PIM. Drive tests have revealed an approximate 18% drop in download speed when residual PIM level was increased from –125 dBm to –105 dBm. The latter figure is hardly considered poor. If PIM had been a problem in Rio, it is unlikely that there would have been such a high satisfactory rate of 53% from users.
There are several best practices to follow when working with precision RF cables and connectors to prevent PIM. By following these tips, you can help improve network performance.
Inspection – When the connectors are apart, inspect them for physical damage. The center connector should not be loose, and should have no visible dents or scratches. Any damage or contamination may allow micro arcing or the diode effect to occur, causing some level of PIM. This inspection will also help spot sources of VSWR problems.
Cleaning – To keep connectors clean, follow this simple three-step procedure:
- Remove loose particles by using low-pressure compressed air, which is available in spray cans. A toothpick can be used to remove any small particles that the air does not dislodge.
- Use Isopropyl alcohol on cotton swabs to clean the rest of the surface. Use only enough to do the job because it may melt any plastic parts, if too much is applied.
- Use the low-pressure air again to remove any remaining small particles and dry the surface.
Be careful not to twist connectors when reassembling or mating them. If they are twisted, small scratches will form on the center pin, which can destroy its precision. The small scratches can generate both excessive VSWR and PIM.
Torque – Proper torque on the connector is required and will help minimize PIM. Low torque will allow gaps and PIM from the center connector. High torque will damage the center connector, again causing PIM. If you must connect and disconnect the same joints several times, mating cycles may be an issue. Manufacturers specify the number of mating cycles they can guarantee.
Some devices cannot handle more than a few complete torque cycles and care must be exercised so the device is not technically “worn out” before it is even installed. A good example is the connector on an antenna panel. Very few designs appear to be able to handle any more than a couple of cycles before the connector base loosens from the chassis. This generally causes the antenna to fail PIM and will most likely show a questionable line sweep.
For 7/16 DIN connectors, 20 foot-pounds is an accepted value, and for Type N connectors, 12 inch-pounds is common. If the manufacture specifies slightly lower values, use them. Make sure to tighten connectors with the proper torque wrench.
PIM Testing Solutions
PIM testing is the only sure way to understand how an antenna system responds to multiple high-powered RF signals. The Anritsu PIM Master™ B-series (figure 2) is well suited for any PIM testing application. A 40 Watt, battery-operated PIM analyzer featuring Site Master™ line sweep capability, the PIM Master is able to fully certify cable and antenna system performance, measuring PIM, Distance-to-PIM, Return Loss, VSWR, Cable Loss and Distance-to-Fault with a single test instrument.
To learn more about PIM testing, visit a special technology webpage devoted to PIM and how to keep it out of your network. An application note, Understanding IBW, is also a valuable resource when designing and installing DAS and other in-building wireless networks.