FCC Adopts New Radio Broadcasting Rules—Is Your Machine Control System Compliant?

A 906Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

A large percentage of machine control installations rely on GNSS real-time technology. Often, radio solutions are used as the communication link between a GNSS base station and its rovers. On January 1, 2013, the Federal Communications Commission (FCC) established new guidelines for many of these radios. If you are in the United States and operating a base station using UHF radio broadcasts in the 421 to 512 MHz frequency band, read further. If your system uses spread-spectrum radios, frequencies outside this range or some other technology such as cellular or WiFi, then you likely are not affected. These changes only affect United States users; the rest of the world is not impacted by the new laws.

The radio spectrum is very competitive. As technology has exploded, so has the need for various types of telecommunications. In an effort to meet the growing demand for bandwidth, the FCC announced that radio broadcasts operating in various ranges of the spectrum would have to adapt in order to make room for more users. In the case of many machine control systems, the existing radios being used are now capable of broadcasting illegally. Some of the radios in use can adapt to the new rules with virtually no degradation in performance. Other systems may be able to adapt, but be subjected to degraded performances in terms of range, battery life or other metrics. Some radio systems will not be able to meet the new guidelines and should be replaced with compliant radios.

It is unclear about fees and penalties associated with violation of the new guidelines, but end users' in violation of FCC rules could be subjected to daily fines in the thousands of dollars all the way down to merely receiving a warning and a requirement to prove that appropriate changes were made within a specified amount of time. According to a leading supplier of UHF radios in the industry, there is no lower end transmission exception1. Regardless of the power outputs, broadcasters (UHF GNSS base stations) operating within this range of frequencies must be licensed and must adhere to certain requirements related to their broadcasts. Many users believe that as long as their transmission is less than 1 or 2 Watts, they do not need to worry about licensure or compliance. This is not the case.

Most of the requirements have not changed. Operators must still be licensed with the FCC. If you are not currently licensed, consider using a licensing company that specializes in the process since FCC forms can be lengthy and complex with terminology that is not familiar to non-radio experts. Licensed operators must periodically broadcast their call sign over the air. The broadcasting radios in use must have a CSMA monitor and it must be turned on. This monitor can detect the difference between voice traffic and data traffic. If the CSMA monitor detects voice on the frequency it is using for its broadcast, it must squelch the data transmission until the voice transmission has stopped. The FCC typically deems data transmissions to be subservient to voice transmissions within this frequency range. To learn more about the licensing requirements from the FCC, visit: http://wireless.fcc.gov/index.htm?job=rules_and_regulations.

The changes in FCC guidelines that are the most problematic to GNSS UHF systems are Over the Air (OTA) baud rate and channel spacing. Over the Air baud rate is also sometimes called the Link Rate.

Let us assume that most of the radios inside this affected frequency band have been using an OTA baud rate of 9600 with 25 KHz spaced channels. This has been a standard configuration in many systems but has become non-compliant with FCC rules as of January 1, 2013. The new rules generally state that an end user can broadcast at any link rate on 12.5 KHz spaced channels or if they wish to continue to use the 25 KHz spaced channels, the link rate must be 19200 or greater. If 25 KHz channels are used with the higher OTA baud rates, then the end user will need to specify this when their FCC license comes up for renewal.

What do these changes actually mean?
Let's first examine the channel spacing issue. Within the domain of FCC licenses for these types of radios, the allowable range is from 450 MHz up to 470 MHz. Therefore, there are a total of 20 MHz available for users to consume. With 25 KHz spaced channels, this allows 800 unique channels. With 12.5 KHz spaced channels, it will allow twice as many channels. This brings an immediate benefit because it will take time to grow the user base to twice as many broadcasters within the same spectrum; there will be twice as many frequency slots available and yet the number of users will probably not double for many years. Frequencies in use will be more likely to have clear reception due to less competition or interferences. So the first question a user must ask is: Can my current radios (base and rovers) be configured with 12.5 KHz channel spacing? As stated above, 25 KHz spaced channels will still be allowed, but OTA requirements will be in effect and this in turn affects the broadcasting protocol that must be used. If all of your radios can be configured to 12.5 KHz, nothing more needs to be done except to program them.

The link rate is a bit more complex. The protocols of broadcasting vary depending upon the link rate and type of equipment being used. For instance, a popular configuration in the past used a link rate of 9600 baud. This link rate would be supported by the protocol of GMSK. If a user wants to continue to use a 25 KHz spaced channel, they must now broadcast OTA at no less than 19200 baud. The GMSK protocol is not available at this rate. Some other protocol that is compatible with the existing radio systems must be deployed such as 4FSK. This change in protocol can in turn affect other performance factors that might be important such as range (base station to rover) or battery life.

The link rate also impacts the amount of data that can be streamed. Higher link rates support more data being sent and received. In most instances, an OTA of 9600 is sufficient to stream all of the necessary data. But as these data streams gain more quantity due to the increasing number of satellites signals that are available or the augmentation messages that many systems can provide, 9600 baud or the contents of the correction streams themselves may have to be considered as part of this whole equation. The day is not so far away when an end user will be able to customize the contents of the data stream, the rates of this stream and even the coordinate system against which the corrections are based. And yet there will still remain a limit as to how much data can be sent through the pipe which is directly related to this issue about OTA baud rates. Generally speaking, a higher OTA baud rate increases the capacity inside the data stream but can also significantly reduce the effective range between a base and its rovers.

Unfortunately, there is no cookiecutter answer that will fit all configurations. Most machine control sites have combinations of requirements, new and old equipment, varying brands and different configurations within specific models. All of the parameters that must be considered cannot be laid out in a simple graph. If possible or necessary, this topic should be taken up with the local support arm that goes along with most machine control contracts. Obviously, the answer for your own particular situation may cost money. But, the alternative to doing nothing could also cost money. Are you licensed with the FCC to use your radios? Are you compliant with the new regulations?

Most machine control support and installation organizations do a good job of conveying these requirements to their customers and ensuring compliance at the time of installation. But these changes in the law may have gone unnoticed. Consider taking a look at your system and performing your own research as to whether the systems in your organization meet the new guidelines. Work with your local supplier or support people and determine what, if anything needs to be done. It might be a simple matter of re-programming radios and testing the configuration. Or the solution could involve purchasing new hardware. In most instances, it should be sufficient to replace the radios only, but with embedded sub-systems, it could also mean that actual GNSS hardware may need to be modified.

This article is not intended to provide specific advice; there are too many variables and exceptions. As suggested above, perform your own investigations. This article is intended to be a prod for you to consider this topic as it relates to your own situation and then you can make your own determinations. Compliance or non-compliance is each user's responsibility. This author's advice is based on years of experience combined with information that is readily available on the internet. MachineControlOnline is committed to providing its readers with information that is timely and useful. It is our hope that you have found this information to be both and that you will come back next time for another perspective on geo-positioning ideas and innovations.

1 Pacific Crest Technical Bulletin: http://pacificcrest.com/library/040713_Bull.pdf

Joe Sass has more than 15 years experience in GNSS. He currently works as a Field Applications Engineers for Spectra Precision with a mission to bridge the gaps between customers, marketing and engineering.

A 906Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

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