Broadband: Be All, End All Spectrum?

Of grave concern to me is that the FCC, as well as many within the Executive Branch and in Congress, believe that broadband is the only spectrum we will need going forward and, therefore, spectrum currently used for narrowband communications or Land Mobile Radio (LMR) and other services should be made available for broadband service.

In its Broadband Plan, the Federal Communications Commission has pledged to find 500 MHz of additional broadband spectrum within the next ten years. Of that, the first 300 MHz will be identified and available before year five of the Plan and the balance by the end of the ten-year period.

This spectrum is needed because of the increasing demand for wireless broadband services from the general public and businesses. An FCC report that supports this need states that by the year 2012, the United States will be short 95 MHz of broadband spectrum and that shortage will have grown to 250 MHz by 2015, in spite of the fact that new fourth-generation technologies are the most spectrum-efficient yet and later releases of LTE and WiMAX will be even more efficient. The demand for wireless broadband services is growing fast, and with companies such as Netflix and others offering streaming video movies, YouTube, and other video providers, demand will continue to grow.

Added to this is the growth in smartphone usage and the wide array of tablets coming onto the market in record numbers, all of which have at least one form of wireless broadband capability, and many of which have built in wide-area and local-area services. Tablets are selling well with Apple, of course, taking the lead, but there are many other products already in the market and I have seen predictions that there will be between 75 and 100 different tablets available by the end of this year. This means prices will come down quickly, making tablets even more affordable, thus further increasing sales.

So the stage is set. We need more broadband spectrum, but where, exactly, will it come from? The FCC and NTIA control all of the available wireless spectrum, with the NTIA controlling more for government use than is available via the FCC for commercial use un the United States, so some will come from the government side. The FCC is considering incentive auctions that will, it is thought, persuade TV broadcasters to move off of some of the upper TV channels and make them available for broadband use, and the FCC and Congress are studying overall spectrum usage to identify what might be repurposed for broadband services.

Of grave concern to me is that the FCC, as well as many within the Executive Branch and in Congress, believe that broadband is the only spectrum we will need going forward and, therefore, spectrum currently used for narrowband communications or Land Mobile Radio (LMR) and other services should be made available for broadband service. There is a major fallacy with this reasoning, which I will discuss below. They also believe that spectrum is spectrum and it really doesn’t matter where it is located. This, too, is false.

Broadband Is the Only Way Forward

As mentioned, there are many in D.C. who believe broadband is the only technology that will be important in the future. This is partly due to the fact that most of those in a position to determine the direction forward have only been exposed to cellular and now broadband systems and have no working knowledge of the value of narrowband or channelized communications systems (although cellular 1G and 2G services are narrowband in nature), and so they assume that because of the demand for wireless broadband we will be able to duplicate everything we now do and more over broadband spectrum.

CIOs and those familiar with wired broadband access have seen broadband used for both voice and data, so broadband is the logical choice for all wireless communications going forward. When you point out that there is still a need for push-to-talk (PTT) services and one-to-many communications, they say this can be done with broadband systems and point to Nextel, Sprint, Verizon, and AT&T, all of which offer PTT services with multiple group capabilities.

What they don’t seem to understand is that cellular phones and wireless broadband services ONLY work when within range of a cell site. If you are out of range, your device might as well be a paperweight. They seem to think the solution lies in wireless broadband coverage that is very good and getting better, and the government has pledged to bring broadband services to 95% of the U.S. population within the next few years.

They also seem to believe that, over time, broadband systems will add voice capabilities that will provide all of the services that are available over narrowband systems today. I believe this too is a faulty assumption. The ability to talk unit-to-unit or one unit to many might be called peer-to-peer communications. This is a vital element of many narrowband radio systems, more so for public safety mission-critical voice services than other services, but also important within conference centers, warehouses, and inside structures where today’s wireless cellular and broadband services do not provide coverage.

It is a fact of life that wireless networks become congested from time to time. Wireless broadband is a shared resource and when the number of people within a given cell sector is too great, some within that area may not have access to the system or have only very limited access. The answer from the broadband folks is that within the fourth-generation broadband technology is the ability to provide Quality of Service (QoS) and to some extent priority service assignments. However, even using these new tools, at some point there will be people who cannot access the system.

As for the features that are available today in the narrowband world and not in the broadband world, it is important to keep in mind that the standards bodies have a list of future requirements that are driven by the network operators and frankly, most of the network operators I have discussed this type of voice communications with have no desire, nor do they see a market for, device-to-device or peer-to-peer communications. They want all traffic to be routed via their network so they can charge for it, or at least count it toward our buckets of minutes. The chance of the voice requirements for narrowband finding their way into broadband technologies is slim to none.

What Are These Requirements?

I have listed these requirements below, and while I have divided them into groups, within each group there is a need for some of these voice capabilities to be treated as mission-critical, not only for public safety, but for other services as well. I am sure you are familiar with the needs of the public safety community, which needs voice communications when it needs it to save lives and property. An incident that could have been contained can grow in size and become a major incident if mission-critical voice capabilities are not available ALL of the time. And there are other situations that require mission-critical voice communications, for example, an electric utility truck in the field responding to a power pole down, or a high-voltage line over a car at an accident. Though it may not seem to be mission-critical, two-way radio service used by cement mixers certainly is. If the motor that turns the barrel full of concrete freezes or stops working for any reason, there is only a very short period of time in which to contact the plant for another truck. If the concrete in the barrel hardens before they can remove it, the barrel is ruined and it will cost the company thousands of dollars to replace it. Some of you may try to tell me that all of these communications can be handled via commercial networks, but I will argue that this is not true. Mission-critical voice communications means no dropped calls, not being out of coverage, and never being unable to talk to someone and request additional help.

Voice Requirements:

1. One-to many communications. It is important in many cases for everyone on a given channel to hear what is being said between the dispatcher and another unit or two units. This is most important in public safety dispatch because it enables other units to start moving toward an incident in case they are needed or it enables a Battalion Chief to know which units are assigned to an incident and what is left available for other emergencies within the area. But is it is also important for many other types of voice communications users, including utility companies and others who need to know what is happening within their coverage area.
2. Fast access to voice communications. Push-to-talk over land mobile radio is fast. You push the PTT button and within a fraction of a second you are able to communicate on the channel. This is vital for many types of land mobile radio services but again, especially for the public safety community.
3. Unit-to-unit and unit-to-multi-unit OFF NETWORK communications. This is a critical piece of narrowband communications for many different land mobile radio services that enables communications between and among units when they are out of the range of the base radio (cell site), when deep inside buildings, or if they want to move their voice traffic off the dispatch channel so it can be used by others.
4. Hands-free communications—not the type using a Bluetooth handset as we are accustomed to in cellular, but rather using a loud speaker and a PTT handset. In this type of LMR communications, the radio is mounted in a vehicle or on a belt with a speaker and microphone. The users are listening to traffic on the channel without having to use a phone, and when they need to talk, they pick-up the mic, press the PTT button, and can talk. The speaker phone feature in a typical commercial handset today is not capable of the volume needed for this type of communications in noisy surroundings, and in many cases, users are wearing gloves required for their work and need to be able to grasp the mic and press the PTT switch without having to remove the gloves.
5. Moving to a different channel. Two-way radios have multiple channels and changing from one channel to another is simple—merely turn the rotating knob on the radio. In a vehicular radio, it might be as simple as a push button and on a handheld it is usually a knob on the top of the radio. Typically, the radio is worn on the belt and changing channels is a one-handed affair. The operator reaches down, finds the knob, and twists it through the appropriate number of clicks. So moving from channel one to channel three means advancing the knob two clicks. Users don’t have to look at the radio or do anything other than turn the knob to change channels.

There are more requirements, but the ones I have listed are the most difficult to accomplish in a cellular or broadband system and are required by those who use land mobile radio systems.

I have yet to find any broadband equipment vendor that understands these requirements and when they are explained, that says they can or will soon be provided for over broadband. Another requirement for public safety that can also be required for large fleet operators is the need for multiple dispatch channels in a given city. Broadband MAY at some point support what is known as multi-cast, which is one-to-many communications. However, it will be limited in how many different sessions can be overlaid within the same geographic area.

In public safety it is not unusual to have one dispatch channel for each precinct overlaid with a few citywide calling channels. For example, one city uses sixteen different dispatch channels and three citywide channels for a total of nineteen channels. This is not a current capability in fourth-generation broadband systems nor is it planned. As an aside, third-generation systems already have multicasting capabilities, but to my knowledge, they have not been implemented in a single network because network operators do not see any demand for this type of service.

You cannot simply look at the technical requirements for voice services when comparing narrowband and broadband systems. In order to implement push-to-talk over LTE, for example, the network operator needs to also install what is called MMBS or Mobile Multi-Media Broadcast Services, which ads a great deal of expense to a network build-out. Again, while it is in the standard, there is no indication from network operators that they intend to include MMBS in their networks. This is an important point. Because something may be included in the standard does not mean it will be included in commercial networks. The operators will pick and chose which feature sets they want and install them while excluding others for which they see no demand.

One final point with PTT over commercial networks. Since the bandwidth is shared on a sector by sector basis, most of the units you need to communicate with are within a single sector (each cell sector is 120 degrees), thus using PTT to communicate with multiple units could mean there is not enough bandwidth in that sector to enable this type of communication. This is yet another reason public safety normally switches to simplex or peer-to-peer communications when working at an incident. Most incidents occur in a confined area and thus the number of users on a single channel could cause communications problems. Moving to peer-to-peer takes them off of the main dispatch channel and enables them to communicate among themselves without tying up a network.

Spectrum Issues

The second issue has to do with where, within the spectrum, broadband systems will be deployed. Today, commercial broadband is on 700, 800, 1900, and 2100 MHz in the United States. Of these, the 700 MHz and 800 MHz spectrum has the most coverage per cell site, but the others are usable. Typically, a wireless device will accommodate most of these bands plus Wi-Fi, GPS, and Bluetooth. This means that in each handset or tablet there are multiple antennas, filters, and what are known a duplexers, which permit transmitting and receiving at the same time using the same antenna for full two-way operation. It is amazing that design engineers have been able to build all of this into single devices. You might recall that the iPhone 4 uses the metal bands around the device for antennas and that there are issues with touching the sides of the phone and shorting out two antennas so that the range of the phone is greatly diminished.

The length of each antenna has to be calculated to cover a specific band. You cannot simply hook all of these different radios up to the same antenna and have anything work. The antenna is THE most critical part of any radio; the better it is, the better the device works. To give you an idea of the differences in length, the following are the lengths for what is called a quarter-wave antenna at each of the above frequencies. A quarter-wave means that the antenna is exactly one quarter of the length of the wavelength at that particular part of the spectrum.

For those who want to work the math for themselves, the formula used to derive the results is:

λf = c = 2.998*10⁸m/s (speed of light)
λ = wavelength in meters
f = frequency in Hz

700 MHz                                 4.0114″
800 MHz                                 3.51″
1900 MHz                                1.478″
2100 MHz                                1.33″

2.4 GHz Wi-Fi                          1.17″

As you can see, the length of the antenna is shorter as you go up in frequency. Also note that there is no correlation between any two of the bands, so using one antenna to cover two bands is difficult (it is done but it degrades the performance of the radio). There are ways to shorten this type of antenna but for our purposes I will use the quarter-wavelength size.

Now suppose new broadband spectrum is made available at 450 MHz. A quarter-wave antenna has to be 6.24″ long and if we go lower, say to 150 MHz, the length needs to be 18.72″. At some point then, it is no longer feasible to make use of lower spectrum for handheld broadband devices. This is a point that is missed by many of those in D. C. who are not engineers and do not understand the differences in antenna and other component sizes.

In addition to differences in length, each antenna also requires a duplexer and a series of filters. As with the antenna, at some point when moving lower in the spectrum, the components become too small to be useful in handheld devices or even in tablets or notebooks.

In talking with several device engineers, the consensus seems to be that today’s practical limits for broadband spectrum that could be used in conjunction with existing broadband spectrum would include spectrum above 500 MHz an below 2500 MHz (2.5 GHz). Therefore, some of the spectrum the FCC and NTIA are looking at for broadband is not suitable for handheld broadband devices. It might be applicable for point-to-multipoint broadband for backhaul or for rural or other fixed deployments, but not for inclusion in handheld products.

This indicates, to me, that the way to increase the amount of broadband spectrum is to move TV stations to spectrum below 500 MHz or below TV channel 20 (506-512 MHz). This would open up 190 MHz of ideal spectrum for broadband services and would account for almost 50% of the FCC’s five-year goal. Of course the NAB will fight this and it has a lot of clout, but this would be the most logical move.

Meanwhile, narrowband communications today is in the 900, 800, 700 and below 470 MHz areas and there are some LMR and public safety radio systems in the 470-512 MHz band on a city-by-city basis on unused TV channels. These systems should be left as they are so voice communications within fleets and for public safety should not be considered as spectrum to be repurposed for broadband communications.

Conclusions

All spectrum was not created equal and not all spectrum is suitable for mobile broadband usage. Further, broadband systems today and well into the future cannot provide the type of voice communications needed by those currently making use of narrowband spectrum for their land mobile radio systems.

Those in the federal government who are to decide which spectrum to repurpose for broadband services need to understand both the advantages and the downsides of the specific spectrum they are considering and understand the technical limitations of specific spectrum.

They also need to understand voice communications systems requirements and the fact that broadband cannot be all things to all people. Narrowband voice communications systems play an important part in our wireless ecosystem and will continue to be needed for many years to come.

Andrew M. Seybold