Using Smartphones for Electromagnetic Spectrum Forensics
Posted: 24 Mar 2017
Date Written: March 23, 2017
Availability of and access to wireless spectrum have become increasingly important to the US and worldwide economy. As more wireless devices access spectrum and increase their bandwidth consumption, there is an increased density of spectrum use across time and location. Regulators, stakeholders, and consumers rely on spectrum and would benefit from increased situational awareness of spectrum use by band and location.
Determining spectrum activity and troubleshooting unauthorized spectrum access requires sensors, since spectrum is invisible to the naked eye. Establishing sensor networks or deploying spectrum enforcement staff to find unauthorized emitters can be expensive and measurements would be limited to a single geolocation’s perspective. For example, a high-quality sensor located on on top of a building can give good information about the spectrum activity around that building, but it provides little information about spectrum energy on the ground, around the corners, or inside of those buildings. The types and numbers of sensors deployed also limit data gathering. The more sensors used, the more information can be gleaned about spectrum energy and activity.
This paper posits a methodology for using smartphones as deployed sensors that can aid in spectrum forensics investigations. Using smartphones as sensors is inexpensive and smartphones are abundant and ubiquitous. Long Term Evolution (LTE) smartphones and their basestations (enhanced node B, or eNodeB) use measurements of spectrum conditions to manage their networks. The proposed methodology suggests that cell phones can measure spectrum conditions to detect the presence of an interfering source.
To research smart phones’ ability to detect interfering sources, different types of interfering sources would be injected into a smartphone, specifically – eNodeB link in a controlled RF environment. The resultant log files and the measurands recorded would be analyzed to identify changes as outside interferers are present over different power levels. If this methodology is scalable across a network of smartphones, information can be gathered and analyzed to determine the type and location of these unwanted interferers.
Using smartphones as sensors to identify spectrum interference benefits carriers, regulators, and smartphone users. Carriers benefit by exploiting an already-deployed means to troubleshoot their networks. Results can be used to create and maintain coverage maps, and find rogue transmitters on their licensed spectrum, and identify gaps in wireless network build-outs. Regulators benefit by having more real-time accounts of the spectrum usage in a band of interest. Regulators may also use this information to identify rogue transmitters to better enforce spectrum use. Smartphone users (customers) benefit from sharing their spectrum conditions when carriers are better able to manage and regulate spectrum to reduce interferers.
The fundamental question, then, that this research strives to answer is: can numerous low-quality sensors deliver spectrum mapping information that is close to the truth in order to improve both understanding by carriers and regulators of actual spectrum usage (including intended and unintended uses) and the consumer mobile quality of experience?
Keywords: spectrum forensics, spectrum enforcement, LTE, EMI, electromagnetic interference
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