Fiber can be used to carry significant amounts of information and is a great solution for communication to substations, downline devices, and in some cases customers. But it’s unrealistic to believe that fiber can be a solution for all communication services. Wireless communications are still needed to enable utility grid modernization efforts in addition to traditional field worker communication such as land mobile radio (LMR), Supervisory Control and Data Acquisition (SCADA), and Field Area Network (FAN). Microwave communication may also still be needed in areas where fiber construction is too costly or impractical due to terrain or geographical factors.
Wireless communication requires radio frequency (RF) spectrum, which is becoming increasingly more challenging for utilities to acquire. Spectrum typically must be purchased or leased from a secondary owner versus being leased from the Federal Communication Commission (FCC) as was the case in the past, and at considerable cost. In some cases, the spectrum required for the desired technology may not be available in the area the utility operates.
Wireless communications vary in frequency bands, channel sizes, technology application, and licensing abilities. This results in certain frequency bands being better suited for certain use cases, geographies, and technologies. One of the industry challenges this brings is that utilities are not able to standardize on wireless deployments industry wide.
Selecting the right communication network is critical to a utility’s success. Spectrum comes in different forms that utilities should consider based on their current and future needs.
Unlicensed spectrum can be an attractive solution because there is typically no cost. It can be a solution for applications that are not mission-critical or in rural areas that are less susceptible to interference. The downside is that it’s shared, is subject to interference from other users, and not protected from interference by the FCC. It’s important to note that even if interference is not present when a system or site is installed, it can occur at any time and there is not a way to dispute the interference. With unlicensed spectrum, interference needs to be accepted and the interference mitigation is the utility’s responsibility. Commonly used unlicensed spectrum bands in the U.S. are 902-928 MHz, 2.4 GHz, and 5.8 GHz.
Lightly licensed or managed spectrum is shared with other users but can be managed either through a fixed data base where users input their information or through a spectrum manager on a real-time basis. There is spectrum in the 700 MHz band (frequently referred to as TV white spaces) and the General Authorized Access (GAA) of the 3.5 GHz Citizens Broadband Radio Service (CBRS) band that fall into this spectrum category.
Utilities typically build, operate, and maintain their own private networks for mission-critical communication applications. Using licensed spectrum allows the utility to provide the high level of availability, reliability, security, and low latency required for these applications. However, acquiring spectrum can be a significant challenge for utilities in building their own networks. As utility data needs have increased, the amount of spectrum utilities have access to has decreased. For the past several years, the FCC has moving to shared spectrum models (unlicensed or managed) for spectrum that is not sold at auction.
Private, licensed spectrum is difficult to acquire. Narrow channel spectrum is easier to get than broadband spectrum and some spectrum that was previously auctioned off by the FCC is available on secondary markets for lease or purchase. Spectrum and technology go hand in hand when determining a telecommunications network. However, it is important to be mindful that spectrum needs to be acquired or at least “locked in” before purchasing equipment as spectrum acquisition is challenging and time consuming. In some cases, an attorney that specializes in spectrum purchases and FCC transactions may be required to assist with spectrum purchases or leases.
Lower spectrum bands propagate farther and are typically better for rural areas that have a less dense distribution of devices. Higher spectrum bands do not propagate as far and are typically more line of site. In more populated environments, higher spectrum bands allow for deployment of smaller cells which allows for networks that have a denser distribution of devices.
Spectrum bands will typically dictate the technology that can be used. LTE, in particular, needs a minimum channel size of 1.4 MHz. 5G requires a minimum channel size of 5 MHz. These mainstream technologies have spectrum requirements that are difficult, expensive, or impossible to get. Other spectrum bands have limited technologies due to their smaller channel sizes. IEEE 802.16s and IEEE 802.16t (in process), land mobile radio (LMR) technologies, or proprietary solutions create a different set of challenges utilities need to be aware of.
This is not an exhaustive list of spectrum available to utilities but a list of commonly used utility spectrum bands.
This band historically has been used for Land Mobile Radio (LMR) but has been vacated in some areas in the past few years. 12.5 kHz licenses are available from the FCC and availability is geographically dependent. Technology is either proprietary or IEEE 802.16t (currently under development).
Portions of the band are available in different channel sizes by multiple spectrum holders on the secondary market. Channel sizes and availability are geographically dependent. Technology is either proprietary or IEEE 802.16s or IEEE 802.16t (currently under development).
Lightly used spectrum by the federal government through NTIA. They have expressed an interest in partnerships. This may be an area of exploration. Spectrum is generally available nationwide, however because it is federal government spectrum, specific geographic availability is not known. Technologies that could be used in this band include PLTE, IEEE 802.16s/t, or proprietary.
This band was typically used for Land Mobile Radio (LMR). 12.5 kHz licenses are available from the FCC and availability is geographically dependent. Technology is either proprietary or IEEE 802.16t.
This spectrum is owned and used by Aclara for Aclara AMI systems. It is not available for purchase.
This spectrum was auctioned in 2017. Many channels were purchased by T-Mobile, but some channels were purchased by spectrum speculators. Spectrum availability and license holders vary by region. 10 MHz channels are available which can be used for PLTE or 5G.
Two x one MHz channels are available for purchase or lease in many parts of the U.S. from Access Spectrum or Select Spectrum. Technology is either proprietary or IEEE 802.16s/t.
Anterix owns spectrum in this band that was recently rebanded by the FCC to allow for 1.4 MHz channels initially and eventually 3 MHz channels that can be used to build out PLTE networks. This spectrum is not available for purchase but can be leased on a long-term basis from Anterix. There are incumbent users in the band that need to be cleared before the band can be utilized. Technology that can be used in this band is PLTE.
Multiple Address System (MAS) spectrum is typically in 12.5 kHz channels from the FCC and availability is geographically dependent. Technology is either proprietary or IEEE 802.16t.
There is spectrum in the 900 MHz band used by Sensus for Sensus AMI & DA systems. This spectrum is not available for purchase.
There is 2.5 MHz of spectrum available in the 1.4 GHz band from the FCC. Spectrum availability is geographically dependent and medical telemetry devices have priority. 50 kHz channels can be aggregated to form larger channel sizes. Technology is either proprietary or IEEE 802.16s/t.
AT&T previously had partnerships to allow utilities to build PLTE on this spectrum, but this has fallen apart twice. This spectrum is no longer a viable option for utility telecommunications.
Citizen Band Radio Service (CBRS) Spectrum has three levels:
Licenses are available from the FCC in 10 MHz channels. PAL licenses were auctioned in 2020 and are no longer available. GAA licenses are on a shared basis using a Spectrum Access System (SAS) database. The SAS database is a real time database, there can be times up to 24 hours where spectrum may not be available which can be challenging for building critical utility networks. There are no spectrum guarantees with GAA licenses. Technology can be PLTE or 5G.
This spectrum has been exclusively used by public safety in the past but has not been widely used. The FCC has made this spectrum available to utilities on a limited basis. Previously it was used for point-to-point technology, but the FCC is also expanding its use to point to multipoint. Channels are available as 10 x 1 MHz channels and 8 x 5 MHz channels. Technologies available are point to point, proprietary, PLTE (potentially), IEEE 802.16s.
6 GHz has been widely used by utilities for microwave backhaul. Recently the FCC has authorized unlicensed users in the 6 GHz band which is expected to cause interference issues in some instances. Spectrum is available in 10 MHz channels. Technologies available are point-to-point.
Additional spectrum is available for point-to-point microwave links in these bands. They are 10 MHz channels. With these higher frequencies, they become more susceptible to rain fades. Spectrum is available in 10 MHz channels. Technologies available are point-to-point.
Because acquisition of wireless spectrum can be challenging and, in many cases, quite expensive, utilities need to have a strategy for accessing spectrum in order to build communication networks to support their mission critical applications. Careful thought and analysis into how much spectrum is needed now and in the future needs to be considered. Negotiating, acquiring, and in some cases clearing spectrum can take time and needs to be considered in the timelines of any project requiring spectrum.