Improving Spectrum Sharing Interference Criteria: A Survey of a Critical Need for Measurements

As radio spectrum becomes more congested and more valuable, an increasing number of potential conflicts is occurring between or among disparate systems and services. Such potential conflicts can be related to systems sharing the same band or even the same channel. Because of unwanted emissions (which include out-of-band emissions and spurious emissions), potential conflicts can arise in immediately adjacent bands, and even bands that are far removed from the operating frequencies of the potentially interfering system. We refer to these issues as potential conflicts, because whether a conflict does or does not exist in reality is often far from clear. Such claims are typically based on paper studies that combine interference criteria for a particular service, propagation models, deployment models, usage assumptions, and other factors. The inputs, assumptions, and even the applicability of any or all of these specific factors are debatable, with the potential interferer relying on liberal interpretations, and the potential victim assuming conservative parameters. In the end, often the potential interfering operator concludes with certainty that no harmful interference will occur, and the potential victim operator concludes with certainty that harmful interference will occur. The regulator, which is often understaffed with appropriate resources to perform its own detailed technical analyses, must make a judgment call, which is usually based on a combination of policy goals, politics, and the “loudest voice.” Sometimes that judgment call results in overly restrictive requirements that causes inefficient spectrum use, or policies that may in fact lead to harmful interference in actual deployments. In this paper, we make an argument that the current situation could be significantly improved if one or more independent third-party “co-existence labs” were established that can help provide neutral input to regulators on the compatibility between various systems and services in the radio spectrum.