Recent talk about opening up the designated 4.9 GHz ‘public safety band’ for commercial use may be premature.
Recall that in 2002, the FCC allocated 50 megahertz (MHz) of spectrum in the 4940-4990 MHz band (4.9 GHz band) for fixed and mobile services, designated for public safety support. The FCC also allowed non-traditional public safety entities such as utilities and the Federal Government to negotiate 4.9 GHz band sharing agreements with eligible public safety entities. Restricting usage to public safety entities was intended to enhance 4.9 GHz transmission reliability and avoid potential interference experienced in other unlicensed and heavily-used bands, such as 5 GHz or 900 MHz.
First Responder Network Authority (FirstNet), with AT&T as its network builder and operator, promises first responders across the country with exclusive, interoperable wireless broadband communications (mobile voice, data and video) using 4G LTE in 10 MHz channels in Band 14. (D/L: 758-768 MHz; U/L: 788-798 MHz).
With AT&T now rolling out FirstNet, the FCC is revisiting whether it is still worthwhile to maintain the designation of such a large block of unlicensed spectrum for exclusive public safety use.
The ‘against-argument’ is that 4.9 GHz band usage has not developed as was originally envisaged and still is underutilized. More important, with growing demand for commercial mobile broadband services, service providers need more spectrum and could better use the 50 MHz of the 4.9 GHz band.
A ‘for-argument’ is that because of FirstNet, a designated band like 4.9 GHz is needed more than ever for complementary services that the Band 14 LTE network cannot, or should not, handle.
Three use cases make compelling points for retaining 4.9 GHz for exclusive public safety use albeit as a complement to FirstNet: point-to-multipoint (PMP) fixed, wide-area video surveillance; nomadic terminals; and, point-to-point (PTP) microwave for public safety backhaul.
Note that similar uses were identified when the FCC originally designated the 4.9 GHz band. These applications take on more significance with the rise of FirstNet. Here’s why.
Video surveillance is not a good use of LTE
Video surveillance is a low-volume, high-density fixed wireless application. With bullet-type and pan-tilt-zoom (PTZ) Internet protocol (IP) cameras, video surveillance involves lots of bandwidth in the upstream direction from a number of cameras throughout a coverage area to a monitoring center, but much less downstream bandwidth to the cameras. Low latency, measured in milliseconds (ms), is also important for high-quality video resolution. With 50 MHz of spectrum, the 4.9 GHz band is well-suited for high-bandwidth video transport. Several radio manufacturers have products that work in 4.9 GHz frequencies.
By contrast, LTE is a high-volume, low-density protocol. LTE is a mobility technology better suited to serve large numbers of active mobile user equipment (UE) such as smartphones, laptops and tablets. Typically, more traffic is downloaded than uploaded to low-bandwidth UEs. It is inadvisable download high-value 10 megahertz Band 14 LTE two-way channels with large chunks of fixed bandwidth for video surveillance.
“We’re Going to Need a Bigger Boat!”
Second, nomadic applications involve transportable terminals that can be deployed at an emergency scene on a temporary basis. AT&T refers to these terminals as cell sites-on-wheels (COWs) or cell sites-on-light trucks (COLTs). FirstNet COWs have a LTE eNodeB base station installed on an extendable tower with omnidirectional or sector antennas to serve first responders on scene. Since the COW is moveable and often is located at some distance from the FirstNet backbone network, an over-the-air connection is needed to connect the COW. A 4.9 GHz PTP microwave hop provides high-throughput, secure communications to make that connection no matter where the COW is located.
RF alignment is required, however, between the COW and the far-end radio on the backbone network. Making such a connection can be simplified by equipping the COW with a self-aligning radio. First responders simply position the COW at the scene, extend the tower and turn on the radios. Several types of RF alignment products on the market use either mechanical alignment gear or an electronic-only solution with no moving parts.
AT&T is supplying Band 14 COWs but that number is very low, less than 100 at last count, to serve the whole country. But with nearly 66,000 police, fire and emergency medical services (EMS) departments in the United States, you could expect large numbers of these agencies use a COW in many more situations than currently anticipated. To paraphrase that famous line from the movie ‘Jaws’: “We’re going to need a bigger fleet!” Meaning, a lot of 4.9 GHz PTP hops.
Every FirstNet eNodeB needs a 4.9 GHz backhaul link
Last, FirstNet should utilize a dedicated 4.9 GHz PTP link between each eNodeB on a tower and the FirstNet Evolved Packet Core (EPC) where fiber cable is not available. In practice, various licensed or unlicensed PTP systems could do the job. But radios operating in the designated 4.9 GHz band offer high data throughput, low latency and security that FirstNet needs for a high-performance, end-to-end public safety network.
Let’s not forget land mobile radio (LMR). Almost every first responder carries a LMR radio. A 4.9 GHz PTP system is a better choice for secure, exclusive connections from countless towers with LMR base stations to command centers. Even with the FirstNet, LMR with remain in service – it is entrenched as first responders’ primary communications. Many public safety jurisdictions have stated they will continue relying on LMR, especially in remote areas where FirstNet will not reach for some time.
In the end, combined Band 14 LTE/4.9 GHz solutions in specific applications can provide first responders with the highest quality, dedicated wireless broadband communications where Band 14 LTE-only deployments cannot do it all. More important, 4.9 GHz utilization likely will increase dramatically.
If the FCC removes the 4.9 GHz public safety designation now, there will be no going back.
John Celentano is an independent marketing and sales consultant with years of experience in telecommunications. He regularly writes and speaks on telecom issues and trends, and advises investor groups on telecom M&A. He assists suppliers in developing and executing custom print and digital marketing campaigns with customer-focused content. For short-term engagements, or temp-to-permanent positions, John can be reached at firstname.lastname@example.org