December 13, 2016
Cellular operators have spent billions of dollars purchasing rights to use allocated frequency spectrum. Carriers and other spectrum users – such as public safety organizations, military branches, and broadcasters – all need to protect their investments and quality of service from interference.
The importance of keeping networks free of interference will only become more imperative. Bandwidth usage is exploding, evident by reports that global demand for wireless capacity will increase six-fold by 2019 (figure 1). This will raise the stakes on carriers and the like to identify and repurpose under-utilized spectrum. It will also mean that mitigating interference is not only currently a top priority for optimizing network performance and maximizing revenue, it will be for years to come. To maintain spectrum integrity and optimize network performance, field engineers and technicians will need to utilize various tools.
Keeping a virtual eye on the spectrum 24/7/365 is a necessity in today’s wireless world. Spectrum monitoring tools discover and facilitate the removal of interference sources by alerting operators of patterns of unwanted signal activity, characterizing unwanted signal behavior, and locating the interference source. Systems such as the one shown in figure 2 generate a greater return on the spectrum investment; maximize network capacity; automate methods of surveillance, interference detection, and policy enforcement; and deliver greater flexibilities and cost efficiencies to network management.
There are other benefits realized with spectrum monitoring. It can be used to characterize spectrum occupancy so operators can determine usage rate for targeted frequency bands, as well as to identify under-utilized spectrum for potential sharing or repurposing.
Spectrum monitoring is an invaluable tool for satellite operators, government regulators and mobile carriers. For example, satellite operators may have to pay a penalty if customer service is jeopardized. This is particularly true for satellite farms home to TV/radio stations, corporate networks, maritime and in-flight systems, and mobile communications providers. Spectrum monitoring tools can monitor modulation error ratio (MER) and trigger alarms when there is a threshold violation to help maintain specified performance.
Government regulators can use spectrum monitors to identify unlicensed use of spectrum, interference from adjacent frequency bands, and spectrum occupancy. Other applications also include illegal transmissions (i.e. prisons, military installments, borders) as well as to detect drones and their location.
Spectrum monitoring may have the biggest payback for cellular operators for spectrum assurance. In the recent AWS-3 auctions for 65 MHz of spectrum in the U.S., $44.9 billion was raised. As gaudy a number as this is, it falls short of similar auctions in the U.K. and Germany, which generated $50 billion and $98 billion, respectively. Spectrum monitoring tools help prevent interference from lowering the return on this sizeable investment.
Spectrum monitoring can deliver the biggest benefits if dedicated software is part of the overall solution. A standard software tool will allow for remote control of multiple spectrum monitors and automated measurements, as well as provide valuable insights such as spectrum history and geo-location. Advanced tools build off the standard model by adding demodulation capabilities for signal analysis and identification. Metrics such as C/N, EVM, MER and identification codes can also be established by these higher-end software tools.
Mobile Interference Hunting
In cases when field engineers and technicians need to be deployed, they have the benefit of advanced interference hunting tools. Traditionally, a spectrum analyzer and a Yagi antenna are the equipment taken into the field. Directional antennas have trouble differentiating between the direct signal and reflections, and can lead even the most experienced user astray. They also have issues with RF shadows caused by buildings or terrain. Multi-path affects them as well, leading to somewhat erratic power measurements as the antenna is moved around.
Mobile interference hunting tools such as the one in figure 3 change the entire process. It takes many measurements per minute, averages them, and plots the result – all while the user is driving. There is no need to stop the car, get out and take a bearing, drive to a new location and repeat the process. Because so many power measurements are taken and averaged, multi-path does not affect the results. Reflections tend to be eliminated, because the reflected signal travels a longer path and so has more path loss, as well as loss when reflected. RF shadowing becomes apparent, since areas of low signal power can quickly be spotted, and either allowed for or ignored. Also, since the better mobile interference hunter tools use channel power to conduct measurements, they can locate signals that wander in frequency, such as oscillating cell phone boosters.
Tools such as the ones outlined in this post can help safeguard against interference that can lower the return on the massive spectrum investment. To learn more about these tools, visit our spectrum monitoring and mobile interference hunting pages.