Public Safety Advocate: Interoperability

After publishing last week’s Advocate, I received some emails and questions about the whole interoperability issue and why it is a problem for public safety and not for commercial cellular customers. The public safety community has been providing answers about interoperability for years to all who would listen and some in Congress seemed to “get it” when the bill that contained authorization for FirstNet was approved, but a number of them still do not understand the need.

It has always been difficult for those whose only exposure to voice, text, and data communications has been through their use of a cell phone and/or tablet. Commercial networks function like their wired predecessors for voice. If you want to talk to someone, you dial a 10-digit number, the phone on the other end rings, and either the person you want to talk to answers the call or it goes to voice mail. If you want to talk to multiple people at once, you need to establish a conference call, which takes even longer to set up. The advent of 2G, 3G, and 4G wireless broadband systems saw the addition of text, data, and video services but here again, you text someone by typing in their phone number and the text you want to send. If you want to watch a video, you go to a website, select a file, and it starts streaming to your phone. If you want to send a picture or video, you can send it to one person at a time if you know their phone numbers.

If this is your starting point for understanding wireless communications systems, it is no wonder you are confused about public safety’s claim that they have been unable to communicate with neighboring agencies or even between fire and police in the same city. If you can simply dial anyone, anywhere, on any network, why should public safety have this problem? The answer is a combination of the effect of spectrum allocations by government and the fact that public safety systems are designed to cover specific geographic areas.

Spectrum Issues

Let’s tackle these issues first. Here again, it may be difficult to understand that public safety agencies are on many different portions of the spectrum since the phone you carry for your network is equipped with 10 or more different portions of the spectrum and works almost anywhere you are. Land Mobile Radio (LMR) systems were designed over the course of many years, starting in the late 1920s with one-way Amplitude Modulation (AM) radios in vehicles and then in the 1930s with two-way radio systems. The first use of Frequency Modulation (FM) two-way radios was during World War II, and the public safety community began using FM heavily in the late 1940s.

As two-way, broadcast, and TV systems were being built out, the Federal Communications Commission (FCC) began allocating segments of the radio spectrum for each type of use. LMR started with one radio band, TV another band, and AM and FM radio stations on other parts of the spectrum. In the early days, radio spectrum used for cellular/broadband systems was not even considered as usable for any type of radio or TV communications. Advances in all types of communications systems meant more and more demand for spectrum, thus engineers “found” ways to use spectrum they did not previously believe could be put into service effectively.

These advances opened up new portions of the spectrum, each one higher than the other. As they were opened for use, the demand for licenses for the new spectrum was overwhelming so the FCC sliced up each segment of new spectrum and assigned it for different users. The spectrum issued for use by public agencies was intermingled, in most cases with LMR spectrum licensed to school buses, business users, farmers, and others. The advances in identifying more usable spectrum continue today. 5G commercial systems will be using spectrum that a few years ago was considered suitable only for point-to-point microwave. Now it will be made available to increase speed and capacity on commercial networks. If you have a car that keeps you in your lane or stops before it hits another, you have radio sensors installed in your vehicle that are operating very high in the radio spectrum.


The result of all this was that public safety ended up with the LMR section in the low band (30-50 MHz), VHF at 150-170 MHz, with federal systems in the 162-174 MHz band. Then comes the UHF band including channels that were carved out in the 1970s for paramedic communications from the field to hospitals, the 800-MHz band, then 700-MHz LMR bands, 4.9 GHz, and 700-MHz LMR. These portions of public safety radio spectrum are spaced too far from each other to be engineered into a single radio that includes all the public safety bands at a reasonable price. There are several radios on the market from Motorola, Harris, and others that contain almost all the bands but they sell in the $4,500-$6,000 price range putting them out of reach for most public safety users. Compare these radios with four different portions of the spectrum in them for $5,000 to the smartphone you are carrying with ten or more portions of the spectrum for under $1,000.

One reason for the large price differences can be attributed to the relatively small market for public safety devices. Smartphones sell in the millions of units per device while LMR radios sell in the hundreds. The quantities are even smaller for LMR radios when you have to build a radio to operate on only one of the public safety spectrum bands. There have been some concerns expressed that since the bulk of the market is controlled by only a few vendors the prices are artificially high at this point. It is interesting to note that at the IWCE convention for the past few years there have been a number of Chinese companies showing inexpensive LMR handhelds and mobiles. However, none of these are what I would consider to be public safety grade devices, and none, so far, support the P25 digital standard and/or trunking systems. Still, I think these companies are smart enough and determined enough to move upscale with their products over time. Hopefully this will put some pressure on existing LMR radio vendors.

Even with the FCC segmenting the spectrum and determining who can use which part of it for what, there will still be some problems and near misses. The biggest problem for the public safety community so far was Nextel’s operation in the 800-MHz spectrum. The FCC permitted Nextel to turn its LMR radio channels into a cellular system. As a result, there was interference with the public safety users who were also on the 800-MHz portion of the spectrum. This became a major issue at times when first responders were in danger and needed help while in close proximity to a Nextel site. Public safety personnel could not hear their own radio channels. Another situation occurred in Oakland, CA, where public safety radios lost their ability to hear when they came in close proximity to cell towers in the area.

The solution was to “reband” public safety and Nextel spectrum to minimize interference. This rebanding is taking many, many years and it is still not complete. When Sprint purchased Nextel, it took on the cost obligation of billions of dollars to reband the radios. Situations such as this can and will be created by the FCC when it does not consult its radio engineers and also require testing to find out if there are or could be interference issues.

There was a near miss when Dish wanted to re-purpose its satellite spectrum for use as a cellular network. This spectrum was so close to GPS-receive spectrum that tests proved doing so would wipe out any GPS receiver in the area including all of the GPS systems used by the military, public safety, and consumers. This was only averted because the military, FAA, and others spoke up and expressed their concerns. Otherwise, Dish might have built out its cellular system and our GPS system would have failed. This is another example of an FCC that has become less technical and more about attorneys and appointed personnel. If we are not careful, we will end up with radio pollution as bad as smog pollution on a summer day in Beijing!


Public Safety has been wrestling with a lack of interoperability for more than 40 years (my first article on interoperability was written in 1980). Some examples to help you understand the issues that were brought to the public’s attention after the Oklahoma bombing and again as a result of those who perished in the twin towers during 9/11 and during Hurricanes Katrina and Sandy. These events highlighted the interoperability issues in play when public safety agencies working together on a major incident cannot communicate with each other. Since then, there have been a number of positive steps taken to solve the interoperability problem in the LMR spectrum. There are now statewide public safety networks such as the one in Michigan, regional systems such as the one in Northern California known as BayRICS, and many others.

Examples of interoperability with communications between agencies are more prevalent still. In Santa Barbara County, for example, the Santa Barbara City and County Sheriff are both on the UHF band and their radios include channels assigned to each other but they cannot communicate with fire agencies. Meanwhile, the fire service up and down the coast is on VHF and has 320-channel mobiles and 160-channel portables. Each year all the fire agencies come together to update a common channel plan so fire personnel can communicate with each other during a major fire (or flood).

Enter FirstNet

The issues described above are what drove the public safety community to fight so hard to gain access to broadband spectrum for a nationwide broadband network. However, one cannot jump to the conclusion that as this network takes on public safety users it will be able to replace existing LMR networks. As advanced as the LTE broadband network is today, it cannot provide many of the voice capabilities the public safety community uses daily. The FirstNet network is designed first and foremost to add data and video services. However, today it will support just enough voice to bridge selected LMR radios systems to enable different agencies at the same incident to communicate with each other using voice as well as data and video. Some believe FirstNet will, in fact, be able to replace the LMR networks but this does not appear to be practical for many years to come.


FirstNet is an important addition to the public safety communications landscape. It is nationwide, fully compatible from coast-to-coast and border-to-border, and it will play a significant role going forward. It will add data and video and in certain cases, make voice more interoperable. It won’t solve all the voice interoperability issues but it will enable first responders arriving on the scene of an incident outside their prime coverage area to be able to communicate with agencies in charge of the incident.

It has been 33 years since the terrible bombing in Oklahoma and 17 years since 9/11. Public safety has been working diligently to obtain what it finally has now—a true nationwide network common to all public safety users who sign up for it. The work by a large number of people before FirstNet was created and since has provided a unique opportunity for the public safety community. It is a communications capability that will make it easier to communicate regardless of where they are. However, it is not a replacement for LMR today. Interoperability is and will continue to be an issue but now we have a new set of tools that will help minimize its effects during an incident.

Andrew M Seybold
©2018 Andrew Seybold, Inc.


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