Roaming on Public Networks Is Problematical
08.06.2010 by Mel Samples
I assert that the decision to split the D Block, made at a macro level, can have devastating consequences at the micro level.
Mel A. Samples, Guest Contributor
Mel has been involved with public safety for more than 30 years. First as a certified practicing Paramedic, and then in the industry including the company that developed the first paramedic voice and EKG field unit. During his career at Motorola, he held a number of positions working in both the public safety and commercial cellular infrastructure markets. Today he is a consultant to several public safety entities in the Southern California area.
I attended a conference a few years ago where a noted economist was the keynote speaker. His presentation had to do with predicting the U.S. economy over the next few years. He started with a statement that applies here as much as it does in economics. “All economists’ predictions are wrong; the question is which are least wrong.”
For economics and finance, investments win and lose based on predictions. But cash is a liquid asset, and losses (or gains) can be quickly reversed. Our radio spectrum is not a tradable asset and mistakes cannot be quickly or easily corrected.
I assert that the decision to split the D Block, made at a macro level, can have devastating consequences at the micro level. Since there is a high probability that any decision will be at least partly flawed, I believe that it is the FCC’s duty to err on the side of caution. To that end, the anticipated $3 billion raised at auction should be nothing more than a tiebreaker because it is of the least value in the entire discussion.
If you will allow me some latitude and follow my logic, I will try to clarify what I think are some points that are not being given due consideration. This is not an engineering exercise. We all know that engineers, given enough paper, can prove that “Heaven is Hotter than Hell” (by the way, it took seven years to refute that argument).
As I see it, the argument here is not whether there is enough spectrum to go around—we all know there isn’t. The FCC even says in its discussion of this pending decision that by keeping the spectrum in its split form, public safety should have enough capacity to meet only its routine requirements. This is instead an argument of who will be blocked and under what circumstances.
Before I continue, I must ask the FCC, with no disrespect intended, exactly whom are you trying to serve? I always thought it was your job to create policy that is in the best interest of ALL stakeholders. At the table now, you have federal taxpayers, airwaves, yourselves, private (cellular) network operators, electronics manufacturers (hardware and software), public safety, and local taxpayers. But your deliberations and recommendations appear to be in conflict.
You told Congress that for broadband to work we need wide swaths of contiguous bandwidth. You allocated the D Block after rigorous debate and input from a myriad of sources. Even during those debates, everyone seemed to agree that from a usage standpoint, allocation of the full 20 MHz (2×10 MHz) is the most efficient. Now you want to keep the block split into smaller pieces in order to raise money? You posed this new plan without thoroughly examining the potential consequences, i.e., now you want to find out whether a guard band might be needed. Am I missing something? We have a $trillion deficit and you think you can balance the budget by auctioning $3 billion worth of spectrum that might not even be equitably divided (see below)?
Sorry, I got sidetracked. Really FCC, what is the driver for this sudden change of position? I thought government finance was the purview of the IRS and FTC. I see no logic other than this keeps a lot of very smart FCC engineers busy justifying a (new) FCC position. It’s not an industry or constituent position, and it is not in concert with accepted best practices or other FCC positions.
As with most problems, there appear to be different ways to handle this:
- Give (auction) the entire block (20 MHz) to commercial network operators and let market forces determine how much access public safety will enjoy.
- Assume that the commercial network operators should control half of the spectrum, public safety gets the other half, and public safety will have “priority” roaming into commercial spectrum when the need arises.
- Allow public safety to control the entire block and allow commercial users to roam into that portion on a non-priority basis.
The first option has already been taken off the table. Item #2 is the focus today; however, I believe #3 should be considered much more seriously.
What Is an Emergency?
Getting to the heart of the question, who needs capacity and when? Well, that seems to revolve around the definition of an “emergency.” So we are all on the same page, I personally like the definition that says, “anything that cannot be handled by the person on the scene is an emergency.” The federal government has an emergency when some disaster affects thousands of people, over a wide area, and typically extends over a long period of time, usually weeks or more. For some reason, the focus seems to be on the data-passing needs of this type of emergency.
Local public safety, in every city in the nation, has an emergency when it needs to send ten fire trucks and ten police cars to a high-rise fire in downtown, or there’s a water main break that closes streets, or there’s a chase on the freeway.
What’s the difference? Widespread disasters happen perhaps a dozen times a month but in different areas of the country. The “smaller” emergencies happen every day, in every city, and “big emergencies” are made up of a cluster of smaller emergencies. The NIMS Incident Command system is in fact based on the concept that “all incidents begin and end locally.”
I submit that capacity at the local cell site/sector level is the most critical component of the communications network. If access is limited or denied at this point, all the priority routing in the world is of no value to the personnel dealing with the problem. Additionally, these local incidents cannot be predicted or planned with respect to location, time, size, or potential to grow into large emergencies.
We all agree that neither commercial nor public safety communication systems have the capacity to serve all users all the time. Blocking and “hot spots” exist on a daily basis in nearly every system, public and private, across the country.
The Fiction of Priority
When I read the National Broadband Plan submitted to Congress by the FCC only three months ago, I did not find anything that said, “public safety only needs enough bandwidth (capacity) to serve its routine requirements, and should beg for additional capacity during an emergency.”
Don’t fool yourself, “Priority Access” invoked due to capacity constraints on any system is a Hail Mary. Its existence is based on the presumption that a system was built with insufficient capacity in the first place. Priority access in any but the most exceptional cases has too many unintended consequences to be relied upon, especially during emergencies.
Let’s think about a few scenarios to get in the mood:
- Public Safety Answering Points (PSAPs) enjoy all kinds of priority service. But there are almost daily examples of calls being blocked due to incoming trunks being overloaded or being routed to a PSAP with an insufficient number of call takers. Calls do not get through, dispatch doesn’t know who needs help or where, and citizens are not served.
- Most government officials are familiar with GETS (Government Emergency Telecommunication Service). As the literature says, “once the system is accessed and a user is authenticated, their call receives priority routing” through the phone system when it is overloaded. What is not emphasized here is that if the user picks up a phone and there is no dial tone, the priority is of no value, and the call does not get through, period. The weakest link in the system is the end-point where capacity is least.
- Imagine what might happen if a local system (think at the cell site level) is built to handle “day-to-day” call loads. All local public safety and (for interoperability) all federal agencies have priority access. Something bad happens in front of a federal building that is basically served by one cell site. (I think the FCC would consider this a local emergency.) Is there a possibility that the “priority” responders could busy themselves out? Who will really have “priority,” and who needs it? Fire? EMS? Would your decision change if you were inside the building?
So can we agree that communication systems function best when they do not block calls?
How to Make It Worse
Undisputed is the fact that broadband gains efficiency (in terms of data speed and/or number of users served) as bandwidth increases. The D Block, as it is currently described, consists of two, 10-MHz slices of spectrum (aka, 2×10 MHz, or 20 MHz); one slice is for uplink and the other for downlink. What is being considered is to split each of these slices.
To make things simple, let’s talk about only one of the 10-MHz blocks. First, the LTE emission was designed to operate in 10-MHz, 5-MHz, 3-MHz, or 1.4-MHz bandwidths. It would seem as though splitting the 10 MHz into two each 5-MHz blocks would result in the same amount of capacity, right? Wrong.
I won’t even attempt to deal with the nuts and bolts of the question, “will a guard band be required, and how much?” that the FCC has most recently posed. I will simply say that if a guard band is needed, it automatically means that one or the other (or both?) of the 5-MHz pieces will in fact not be 5 MHz. Anything less than a full 5-MHz allocation means that only one 3-MHz, LTE channel can be used in that piece. Who will accept the lesser “half,” public safety or commercial network operators? It is a sure bet that the auction value will be reduced if the limitation is placed on the commercial side. So maybe it’s best to further limit public safety? After all, it can simply do a little more “priority roaming” on the commercial system. Right?
So we will ignore that little gem sitting in the middle of the room and deal with a couple more facts.
The single 10-MHz channel yields more usable capacity than two 5-MHz channels. First, channels cannot bump against each other where they meet in the middle. The usable emission is always less than the allowed bandwidth because there have to be “skirts” on the edges of each channel to reduce interference to the adjacent channel. So those two little pieces in the middle, between the 5-MHz slices, represent lost capacity as compared to a single, contiguous 10-MHz channel that can use that space.
Next, if you would like to ignore these other really inane spectrum issues, you need to know that there are all kinds of technical things that must happen to facilitate hand-offs between two different channels. So when you have multiple public safety responders in an area and some are in the public safety channel while others are “roaming” in the commercial part, there are potential prioritization and routing issues that can affect call completions (or dropped calls like we have all experienced).
Finally, can anyone prove that the true spectrum utilization is equal when you have two subscribers under the same cell site and sector receiving streaming video from the same source, but one is on the public safety block and the other has roamed to the commercial side? The logic of the FCC position on the D Block is therefore in question on this point alone since the D Block allocation is all about addressing a shortage of capacity.
Let’s face it, anything less than a single 10-MHz block allocation is bad policy, bad practice, and bad engineering. The FCC already said it needs an additional 500 MHz of spectrum for broadband over the next ten years. This spectrum is extremely valuable to public safety right now and in the future.
We know that public safety systems are expensive, complex, are not easily modified, and must stay in service for a long time in order to achieve value for the taxpayer. Artificial system constraints imposed by ill-conceived rules make these systems functionally inadequate, thus frustrating the national objectives of securing communities.
Therefore, I suggest that strong consideration be given to the concept that allocates the full 20 MHz (2×10 MHz) as a single block to public safety so the spectrum can yield its maximum potential capacity. In the interest of the public good, and to enable tighter integration with commercial network operators, condition the allocation on agreements and system architectures being implemented such that commercial users can roam into this spectrum on a non-priority basis.
This isn’t a question of who’s right about how much bandwidth is needed. It is about what public safety does every day—making a judgment decision that errs in favor of the best interest of all involved. This is an opportunity for the FCC to make a single allocation that by some measures “might be excessive” for public safety. Or it has the opportunity to continue down the path that says, “Well, if we’re wrong, we THINK we can find a way to fix it later.” (How does the FCC define “if,” “fix,” and “later”?)
Mel A. Samples
 Thermodynamic humor first published in Applied Optics (1972, 11 A14)