Profile: Gregory Hellbourg

Greg Hellbourg, Ph.D., is a staff scientist and spectrum manager at California Institute of Technology in Pasadena, California. His academic background and current work centers on the field of radio astronomy.

In this conversation, we chatted with Dr. Hellbourg about his experiences with spectrum management for radio astronomers, the role of academia in presenting career opportunities in the field, and the process of updating international telecommunications regulations.

iNARTE: Please tell us about your career as a radio astronomer and how you began working on issues around spectrum management.

GREG HELLBOURG: I obtained an engineering degree in France back in 2010 with a focus on signal processing and later earned my Ph.D. in radio astronomy and signal processing. My thesis was on mitigating radio astronomy interference to allow modern radio telescopes to more clearly receive signals. It’s always been a topic of interest to me.

Radio astronomy is a passive service, by which I mean that we listen only. We also share the radio spectrum, in a sense, although there were always frequencies allocated to passive services such as radio astronomy. In the past that worked just fine, but nowadays, because of technological advances leading to higher sensitivity in radio telescopes, we have a need for much larger bandwidths. To get it, we take advantage of underutilized frequency bands.

We put radio astronomy sites as far as possible from metropolitan centers to minimize cellular or satellite emission “interference.” I use the term interference, but that’s not technically correct—those people are transmitting legally, but the communications are still disruptive to our receivers. However, these are transmitters that you can’t really avoid.

I therefore work a lot with signal processing to try to find ways to estimate the interference waveforms as much as possible and subtract that from signals originating in deep space. There are different ways to do that, including digital and spatial filtering techniques, but a certain residual of signal remains after processing, and it’s dominant compared to the sensitivity that’s required to detect astronomical emissions.

So, the general conclusion that those of us in the field slowly came to is that we need to find other ways to coexist, and in my opinion the best way is spectrum management. That means suppressing the interference— not blindly, but with the help of the transmitter itself. One of the projects I’m currently working on is exploring collaborations with, for example, cellular transmitters so that we can have prior information on what specific signal is being transmitted. We can transmit that information to the telescope in real time, which allows us to filter that signal much more clearly. If you have prior knowledge of the actual waveform, the subtraction process becomes much easier.

I: How does your work apply to spectrum management as a discipline, regardless of whether it occurs in the context of radio telescopes, electronics, defense, or other sectors?

GH: Radio communication, in its most basic form, involves a transmitter and a receiver. Those receivers are usually quite sensitive to interference from, for example, emissions from neighboring bands. That creates a need to suppress that interference to recover the signal that’s being transmitted with the best signal-to-noise ratio possible.

For instance, someone managing the spectrum might encounter interference from power lines at very low frequencies across a very wide band that overlaps with many frequencies. Fortunately, for the frequencies at which we see those wideband emissions, there are also very strong transmitters. The receivers are therefore receiving that transmitted signal at a high enough signal-to-noise ratio to continue to operate. But that might not be necessarily true if a new service comes in and tries to utilize a secondary allocation with lower power.

So, as you can see, one key aspect of this work is trying to make receivers more resilient. That applies to radio astronomy and is translatable to pretty much any other service, because we have such stringent requirements in terms of sensitivity. Few if any other transmitters on earth, commercial or governmental, work at the sensitivity levels we do.

I: You are a researcher at CalTech. Although you don’t teach, in your view, what role do high-level academic institutions play in helping prepare students to enter technical fields such spectrum management, electromagnetic compatibility, electrostatic discharge, or other telecommunications disciplines that fall within the iNARTE sphere?

GH: We have an excellent electrical engineering department here which has a very visible presence on campus. I would really like to interact more with those students because there are so many commonalities between what we do and where their expertise lays. We do have some outstanding program coordinators who can play a big part in exposing them to the work I do.

I’m the only spectrum manager here in the CalTech astronomy department, which might be surprising given how new spectrum management schemes affect our work. I’m sure we will have additional positions like mine in the future, but at this stage it’s just me.

A project that I’m working on now is trying to invite some radio astronomy colleagues to campus this summer to teach them the basics of spectrum management, electromagnetism, and other areas of study that touch the iNARTE community.  I don’t want to reduce spectrum management just to those areas that affect radio astronomy, because I think people need to have a bigger and better picture of what spectrum management is and what it can mean to a wide range of industries.

I: You recently went to Geneva to attend a meeting of the International Telecommunications Union. Can you tell us a little bit about the ITU and what you experienced at this gathering?

GH: Every six months there is a meeting for all the ITU study groups. I’m part of Study Group 7 and specifically a member of Working Party 7D, which focuses on the scientific use of the spectrum as it applies to radio astronomy. That was the Geneva meeting that I attended earlier this year.

Every four years the ITU offers a World Radiocommunication Conference. Following that conference, all the various delegations work on studies and reports to establish recommendations for new radio regulations to be presented at the forthcoming WRC. Old regulations can also be recommended for removal. So, that’s part of what we do in my working party for our area of interest.

We meet online every few weeks and discuss these recommendations for the radio astronomy space. Stakeholders like the National Telecommunications and Information Administration, the Federal Communications Commission, and the Cellular Telecommunications Industry Association here in the United States, along with some commercial partners, are involved, too.

To give you an example of how we might discuss potential recommendations, from the perspective of radio astronomy, I might say, “I made observations of out-of-band emissions at frequencies that are not allocated to radio astronomy.” Someone else might say, “How is that relevant?” And it’s relevant because since emissions at that bandwidth are not normally seen in the radio astronomy field, we need to find ways to improve the existing regulations to account for these findings.

I: And how are these suggestions then presented to the ITU?

GH: For those of us in the U.S. delegation, our recommendations go to State Department for approval. Once we know which documents are approved, we return to Geneva, where those resolutions are introduced by the chairperson of Working Party 7D. We present the results of our findings, explain methodologies, and describe what we are trying to achieve through these suggestions. And, of course, we answer questions from other delegates in other countries and/or sector members from the industry.

The chairperson then issues a report containing all the documents that will go up to the next level, Study Group 7. Eventually, these will be presented at the WRC a few years hence.

I: It seems like your expertise is very helpful within the framework of this pyramidal structure.

GH: Yes, I’m kind of at the base of that pyramid right now! I’m doing a lot of these studies with a focus on areas in which I have expertise: making measurements with radio telescopes and spectrum management equipment, simulations, programming, and things like that. I try to contribute as much as possible where I can.

At this most recent meeting, I feel that we were rather successful with our presentations. We’ll be back in Geneva this September and returning in March and September next year ahead of the next WRC in 2027.

I: It would seem that, like most development bodies, moving ahead with international standardization is all about consensus and buy-in from various segments of industry, including academia, manufacturers, national regulatory bodies, etc. There’s lots of room for everyone to get involved, and those in the iNARTE community might wish to explore having their voices heard as well.

GH: It happens rather slowly, but it does happen. Yes, there are a lot of people involved in the process, which helps validate the suggestions from different viewpoints. The more people who contribute, the better.

One other thing I should mention is that, although there are indeed many of these international regulations as we’ve discussed, there are still some countries that operate according to their own sets of rules. For instance, the radio astronomy bands are not necessarily recognized worldwide. They are defined by the radio regulations, but some countries might overrule that as long as there is protection for neighboring countries. Here in the United States, we are in a great position, because this is a big country and local regulation will not impede with neighboring countries like Mexico and Canada. That means that there’s a certain degree of freedom of operation here in the United States that you might not find in Europe because the countries are so small. You can’t really shift the rules as easily there.

All that is quite interesting, because it gives us some leverage to try new things and experiment with spectrum management.