April 24, 2018
As demand for spectrum for commercial use continues to grow, policymakers are exploring spectrum sharing as a way to expand capacity while still fulfilling the needs of federal agencies. This model can work only if rules are designed to maximize the value of spectrum resources without compromising the quality and reliability of telecommunications.
Telecommunications systems must be able to deliver clear signals. If receiving systems experience enough interference, their performance can significantly degrade, potentially resulting in lost information and failed telecommunication. To minimize the probability of interference, spectrum managers separate systems in distance and frequency. The amount of separation is determined by IPC, which specify the allowed interference power at a specific center frequency offset.
IPC can be estimated through analysis, measurement, and computer simulation. Although the analytic method is fast it can also be highly inaccurate for pulsed interference. This is a significant problem in an era when it is important to know the effects of pulsed radars on WiFi and LTE personal communications networks. Spectrum engineers often turn to measurement when they need IPC estimates more precise than those available from analysis.
However, IPC measurements are often hindered by restrictions on equipment availability. In some cases, spectrum managers need estimates for systems that have not even been built yet, so measurements are not possible. In other cases, the systems can only be tested for a brief period of time to avoid service interruptions. These and other factors can make accurate and repeatable measurements difficult to obtain.
To overcome the limitations of measurement, the ITS and OSM have invested significantly in computer simulation capabilities. These investments are timely not only because radio system simulation software capabilities are very advanced but also because the number of IPC needed to address future spectrum sharing analysis are too numerous to obtain through the slower measurement method.
At the 2018 IEEE Radar Conference in Oklahoma City in April 2018, Robert Achatz presented a paper describing ground-breaking work performed at ITS to emulate IPC measurements through computer simulation. The research paper, “Interference Protection Criteria Simulation,” describes work jointly funded by ITS and OSM to improve existing and develop new methods for estimating IPC. The findings demonstrate that simulations can provide much needed verification of measurement results, and could potentially provide more accurate and timely IPC estimates in the future.
The simulation approach is based on emulating the same systems and equipment used in a traditional measurement test fixture, including the victim transmitter and receiver, interfering transmitter, and the various laboratory instruments. The software is capable of emulating most of the radio systems involved in today’s spectrum sharing options, such as radars, satellite communications, global navigation satellites, tactical mobile communications, Wi-Fi, and LTE cellular systems.
The research is part of a multitude of on ongoing efforts at ITS to enable data-driven regulatory innovations to increase spectrum utilization, making more spectrum available for commercial use and emerging technologies.