November 18, 2015
Operators have spent billions of dollars acquiring RF spectrum to increase capacity of their networks to best deliver high-bandwidth 4G services. Unfortunately, the return on that sizeable investment can be put in jeopardy by the presence of interference that can degrade network operation and frustrate consumers.
To optimize performance, reduce customer churn, and maximize their network investment, operators need to eliminate (at best) or minimize (at least) interference. As field engineers and technicians know all too well, this is easier said than done, due to the presence of illegal or unlicensed signals that can be periodic or present at different frequencies over time. For these reasons, a spectrum monitoring system is a valuable investment.
There are a number of benefits associated with a spectrum monitoring system, which is specifically designed to facilitate the identification and removal of illegal or unlicensed interference signals. Most importantly, by monitoring spectrum on a continual basis, problem signals can be identified as they occur in real time. Patterns of unwanted signal activity can also be examined, providing an efficient way to characterize and locate the source of the interference problem.
Monitoring these frequencies with the best possible tools will give operators the information they need to optimize spectrum for maximum utilization. Spectrum monitoring systems can detect a wide variety of signals. In this post, we will discuss three main categories – intentional interference (including illegal or unlicensed broadcasts), accidental interference, and occupancy.
Illegal AM/FM and video broadcasts are found in many parts of the world. These signals can be generated by pirated broadcast equipment or by using over-powered CB radios. Figure 1 shows a table listing interference complaints per year registered by the UK government communications regulator. “Critical service” refers to interference reports affecting life services communications.
Additionally, jammers are sometimes used for applications such as preventing students from cheating on tests, stopping employees from taking phone calls on company time or to prevent inmates from making illicit calls from prisons. Jammer signals can often leak into the wider environment, interfering with other legitimate services. Mitigating these types of interference has become a high priority with government regulators.
A wide variety of accidental interference can be seen in the RF spectrum. A common problem is cable TV leakage, which exists both from cable signals seeping into the outside environment, as well as from external signals bleeding into the cable system. This problem has been enhanced with the transmission of cable signals into frequency bands used by broadcasters and cellular operations such as the 700 MHz LTE band.
DECT phones also cause interference problems, particularly when people bring their wireless devices along when moving across borders. DECT frequencies vary in different countries, providing the potential for interference when transported. Figure 2 shows spectrum used in the U.S. for certain cellular frequencies. DECT phones brought by travelers from other countries can often cause interference. Other sources of interference include cellular signals (due to antenna tilt or azimuth errors), repeaters oscillating, wireless microphone problems, and power equipment.
Figure 2 (click for full size)
With the rapid demand for available spectrum from both public and private sectors, new ways are being investigated to allow more efficient use of various frequency bands. Much of the spectrum is potentially underutilized, providing the opportunity to re-purpose existing spectrum with additional applications. Spectrum occupancy measurements quantify the amount of usage of frequency bands over a given period of time (figure 3). Remote spectrum probes are used to monitor a band of frequencies to record spectral histories as a function of time.
As you can see, interference can come from many different sources. Spectrum monitoring systems can be used to efficiently monitor all these signals and maintain optimal network performance. To learn more about remote spectrum monitoring tools, download this application brief.