TELL IT LIKE IT IS blog

Channelized Communications

I respectfully disagree with your assumption that the channelized portion of the 700-MHz spectrum would be of more value to the public safety community as broadband spectrum.

The Following is a copy of an email I sent to FCC Commissioner Robert M. McDowell. I have reprinted it below because it helps to explain why channelized communications systems are and will continue to be needed by first responder and other two-way radio (Land Mobile Radio) systems for years to come. This is one of the most difficult subjects to explain to someone whose only experience with wireless is the use of a cell phone for voice and other services. Today’s cell phone systems, and those being built out as next-generation systems are not capable of providing the types of services discussed below.

I read with interest your comments regarding the 24 MHz of public safety spectrum at 700 MHz and your belief that the spectrum set-aside for channelized communications should be converted to broadband spectrum. Apparently this is one of the reasons you seem to favor putting the D Block out to auction again.

I respectfully disagree with your assumption that the channelized portion of the 700-MHz spectrum would be of more value to the public safety community as broadband spectrum. Perhaps your staff and the FCC engineering staff have not properly conveyed to you the importance of channelized spectrum for first responders. If you will permit me, I would like to make several points that might help you understand the critical need for both broadband and channelized spectrum at 700 MHz.

Broadband systems require that each and every contact between two field units, or between a field unit and a fixed point, pass through a cell site. Channelized communications have unique capabilities that are not available with broadband systems today, nor will they be well into the future.

1)      Channelized communications for voice is one- to-many, which is a critical component of first responder communications. A dispatch that is verbally sent to units that are to respond is also received simultaneously by other units in the same area. It is vitally important for all units in a given area to hear what is happening so they can prepare to provide additional coverage or assistance. Think about your own cell phone. If you receive a call that affects you and your staff, you must, in some way, notify your staff. However, if the call had been sent over a channelized radio system being monitored by yourself and your staff, everyone would have received the message at the same time, reducing the time it takes to mobilize.

2)      One-to-many voice is also critical during each incident, no matter how small. The first unit on the scene normally provides a condition report that must be heard by the dispatcher, all of the responding units, and any other units in the area.

3)      Once on the scene of an incident, first responders switch to channels that do not interfere with the primary dispatch channels. During a bank robbery, for example, one channel is assigned to the swat team, one to the uniformed officers, another to EMS personnel, perhaps one or two more to the fire department, and still other channels to others on the scene. Control of the incident is handled by the Incident Commander who must listen to all of the channels and communicate with the dispatch center to coordinate all of the various groups on the scene. Once again, one-to-many communications is vital in these incidents and because the radio traffic is not on the main channel, it does not delay dispatch of other calls. This traffic does NOT go through a radio site—it is one radio directly to many radios. While the range is limited, these direct systems are necessary to provide all of the channels required during both normal and major incidents.

The fires in Southern California last year are a typical example of a major incident where channelized voice communications were used. The combination of first responder agencies on the scene and protecting areas just outside the fire area made use of 38 command radio channels and 172 individual radio channels. In many incidents such as this or a major fire in a high-rise building, for example, signals from radios carried by first responders cannot reach a radio tower (cell site) so they must be able to talk directly to other radios on the scene.

Broadband vs. Channelized Radio systems

No commercial wireless systems can provide the number of channels required during such incidents, and no commercial wireless systems can support communications on a direct one-to-many basis. Commercial systems and all generations of wireless require that every call be routed to and from a cell site. Further, because of their architecture, they cannot be re-engineered to provide direct communications. Moving first responder voice communications to commercial systems is not a solution.

Perhaps in ten years or more, if there is demand, channelized types of services can be designed into the next generation of devices and commercial networks, but it is doubtful that any commercial vendor would spend the time and money it would take to modify the commercial networks for a relatively few first responders. Today there are more than 290 million wireless customers using voice and data services on commercial networks and less than 4 million first responders. There is no financial incentive for commercial suppliers and operators to change their systems to provide the voice services needed by public safety agencies.

Other examples of one-to-many and direct voice communications can be found in Washington DC not far from your office. The Secret Service, for example, uses radio equipment that eliminates the need to go through a cell site and permits agents to talk among themselves in real time whether they are in the open or in the sub-basement of a building. Direct communications are critical and it is also critical that every member of the team be able to hear at the same time and know exactly what is occurring at any given moment. Today’s or tomorrow’s commercial networks cannot provide this level of communications, which is the same as what the first responder community requires.

Public safety needs interoperability for both broadband data and voice services. Today, first responders’ radio channels are spread out over many different portions of the spectrum. When the FCC granted the public safety community the spectrum in the 700-MHz band, some for voice and some for data services, it provided an opportunity to, over time, solve both types of interoperability issues.

Today, the 700-MHz spectrum is lightly used, but in much of the United States it was only made available this year after the HD transition. In areas where it was available earlier, it is being used and those charged with allocating this spectrum have been working with the FCC and the public safety community to establish frequency coordination for local, state, and regional interoperable communications systems. Funding is now the limiting factor for these projects. If funding were available, many departments would move more quickly to the 700-MHz channelized spectrum rather than pay to narrowband their existing radios between now and January 1, 2013.

I would like to suggest that you and perhaps members of your staff spend a Friday or Saturday night riding with police officers in Washington DC or your hometown. Talk to them about how important voice communications and one-to-many communications are to their job and their safety. Listen to the voice radio traffic that is generated on these nights and observe the officer as he or she changes channels for different incidents and talks to others who might be responding to the same incident, and see how many times they talk to each other in the field on other than the main dispatch channel.

It is not possible to provide the level of voice communications required by public safety within the confines of commercial wireless systems or using commercial wireless technologies. The 700-MHz channelized public safety channels are digital, which is a vast improvement over the analog systems on other public safety spectrum, and they work the same and provide the same types of services as analog systems. It can be difficult to understand how different channelized devices are from cell phones. They must be able to communicate directly with each other no matter where they are, and with those around them so everyone knows what is happening. A delay of only a few seconds can mean the loss of life or property.

Taking spectrum from public safety’s channelized band to expand their broadband network is not only counterproductive; it will exacerbate the interoperability issues.

Respectfully submitted,

Andrew M. Seybold

3 Comments on “Channelized Communications”

  1. Bravo – excellent! I hope he reads it and understands it as well.

  2. willaz says:

    Andy, That is the most succinct analysis of the channelization argument that I have encountered. Maybe the Commissioner will finally understand the situation.

  3. Arclight says:

    Andy: Your enunciation of the issues here was a good one. What it doesn’t consider is possible radio system designs that are neither cellular-based nor high-site simulcast-based (e.g. DARPA’s WNaN). Those are still several years in the future, though.

    It’s too much to hope for, but possibly someone in the Commission has finally figured out that if the D block is built out as cellular broadband the narrowband, high-site, coverage-based systems may be subject to interference around the broadband sites that cannot be easily mitigated. Of course, nobody is working the math on this yet, but as we have long ago discussed, they will start to do so when the problems begin to show up. They will probably conclude that the “technical solutions” called for in 47 CFR 27.64 involve massive amounts of new spending on the narrowband systems (to raise the signal levels to be more comparable to those from the broadband networks). Of course, that money will have to come from somewhere, and there’s no budget for it. We won’t discuss where all that extra cash will flow to.

    A truly “grand plan” (but financially unrealizable) would finally admit that the laws of physics dictate that high-site, noise-limited, coverage-based systems simply cannot easily exist in close geographic and spectral proximity to low-site, interference-limited, capacity-based systems without very special (and expensive) subscriber unit design that may not be physically realizable. That “grand plan” would then go on to figure out how to make the necessary spectral and geographic changes to accomodate both designs.

    The FCC’s consideration of repurposing UHF TV broadcast spectrum would certainly set the stage to finally resolve this issue once and for all, by allowing the narrowband systems to be migrated from 700 and 800 MHz down to UHF (and well away from the commercial operators, so that interference could be positively mitigated as part of the initial design). The rest of 700 MHz and 800 MHz freed up by this move could be auctioned to cover (at least in part) the costs.

    As I said, it’s financially unrealizable, but from a technical standpoint it would be a winner. The coverage-based narrowband systems could operate very close to the noise floor, and the capacity-based systems could operate with very short-spaced cells with low antennas, and everyone would be very happy.

    It’s nice to dream…

You must be logged in to comment or reply.