Radio Spectrum Pollution: Facing the Challenge of a Threatened Resource

On November 14, 2013, the Silicon Flatirons Center hosted the conference “Radio Spectrum Pollution: Facing the Challenge of a Threatened Resource” at the University of Colorado Law School. Intensive use of radio frequencies by wireless systems is crucial to our economic and social wellbeing and to national defense and homeland security. Successful operation is essential for a wide variety of wireless applications, ranging from simple keyless entry systems and garage door openers, to broadcasting networks, Wi-Fi and cellular networks, complex navigation systems like GPS and radar, and mobile radio systems relied upon by first responders. By analogy to other important economic inputs like coal, water, and know-how, one can think of radio frequencies - also known as spectrum - as a resource. The proliferation of wireless devices along with the increasing amount of frequency capacity consumed by each device (e.g. tablet computers used to upload or download video programming) puts intense pressure on the resource - a topic addressed at previous Silicon Flatirons events. The good news is that, unlike other important natural resources such as oil, coal, or natural gas, the spectrum resource is not destroyed by use - it is infinitely renewable. However, like air and water, the spectrum resource can be polluted. In spectrum, pollution takes the form of interference from other radio sources. Since the performance of a radio link depends upon the strength of the desired signal relative to the strength of undesired interfering signals, increased background radio noise can reduce the total carrying capacity of the resource. When severe, the noise pollution manifests itself, for example, in the form of hissing or popping on radio channels, picture loss on television or other video feeds, interrupted wireless voice conversations, slow or intermittent internet connections, and - in extreme cases - degradation of communication and navigation systems that are vital to national security and homeland defense. This conference focused on radio frequency noise rather than interference in general, of which noise is a subset. In general usage, “noise” means energy (electromagnetic or sonic) that some particular person finds unwelcome given their activities. However, the conference and this report use the following more circumscribed definition: noise is radio frequency interference that does not come from an identifiable, intentional radiator. Three broad sub-categories of noise are: (1) Natural (not man-made) environmental noise, e.g. from lightning and atmospheric processes (most important at lower frequencies). (2) Interference from unintentional radiators, e.g. switching power supplies in fluorescent and LED light fixtures (often called “man-made” noise to distinguish it from the first category). (3) Aggregate out-of-band interference from a “sea” of intentional radiators, e.g. out-of-band emissions (OOBE) from hundreds or thousands of nearby transmitters leaking into noise-limited services like satellite or radar receivers. While there are regulations at the international and national level aimed at controlling man-made sources of interference, they are becoming more important because of the increasing number of devices involved, the close proximity within which they must operate, and the increasing importance of wireless services. Since the level of aggregate radio noise from both natural and human sources tends to decrease as frequencies become higher, the intense interest in noise levels back in the days of short- and medium-wave radio has declined with the shift of critical wireless systems to higher frequencies. However, evidence is emerging that the radio noise floor is rising in higher-frequency bands that are especially important to both commercial and public safety applications. This conference brought together academics, policymakers, spectrum users, and advocates to examine the extent of, and trends in, radio noise pollution and to explore how the associated policies and regulations may need adjustment to reflect changes in radio noise levels.