Guest Blog: TV’s Evolution Depends on Smart Use of Spectrum
As broadcast television changes in fundamental ways with the next generation of over-the-air technology, we’ll need an extremely robust content distribution platform reaching into places contemporary broadcast TV doesn’t. We will also need nearly ubiquitous return communications to facilitate interactive and individualized consumer experiences.
TV's next generation is far less about upgrading technology for prettier pictures than it is about building a broadcast delivery platform that greatly out performs the present ATSC and any other competing platforms. Anything less and broadcast TV becomes less viable. To get there, as an industry we are obligated to pursue a platform that is more about good public policy than any legacy business, technology or tenure of spectrum concerns.
As unglamorous as modulation schemes might seem, it is the technical details of the modulation scheme--the way we use the spectrum--that is the foundation determining what kind of future broadcast business we will have. It is the piece that is subject to spectrum scarcity and, thus, regulation. It is the piece that determines if a service can be mobile, and if it will work in buildings, vehicles and mass transit. Modulation defines how many services at what quality and coverage there can be. As we approach ATSC-3.0, all the other pieces (compression, interactivity, converged and divergent media) are relatively easy to change, especially in this software-defined world. Transmission, however, follows the laws of physics and requires investment in expensive hardware with (hopefully) long life cycles.
Back when legacy UHF was a vast wilderness of spectrum that was given to almost anyone willing and able to build a station and pay the power bill. Today, UHF is the beachfront property of the wireless world. As broadcasting's birthright of bargain spectrum ends, the laws of economics and physics don't align well with our legacy of numerous big towers, low frequency reuse, mostly high-power services and adjacent protections. All of that has created canyons of inefficient spectrum use and spotty penetration in the spaces where people now watch TV.
Physics dictates that the most efficient situation is co-locating one single all-encompassing unbroken multiplex per market. If we were to break the UHF spectrum into four blocks and reuse the blocks market to market (just as the four blocks of a cellular network plan are reused) we put broadcast into 25% of the UHF spectrum and leave nearly 75% of the spectrum for other uses. Replacing multiple sites and legacy allocations with a cellular-style plan dramatically reduces interference issues and spacing concerns that waste spectrum. Most important, what interference and wasted spectrum there is, inherently lands outside of the densely populated metropolitan areas.
There are now advanced modulation schemes in which, within that singular broadcast multiplex, we can adjust the robust-versus-throughput relationship service by service. Likewise, we can select parameters that allow either single frequency networks (SFNs) or a single high-power (boomer) system … or a combination of both. The receivers remain the same—universal and fully useful—however, the modulation is dynamically optimized for the location and current programming. The receivers should be able to display any program that they can pick up, low-res services should be seeable on a big screen, and high-res services should display on a mobile device.
New York might use their spectrum as an SFN with distributed antenna systems (DAS) in subways and buildings. Rapid City, South Dakota might have one big boomer reaching out to antennas mounted on houses and silos on the distant horizon. Denver might be a combination of a boomer, SFNs and a few simulcast repeaters in mountain communities using different spectrum blocks than urban Denver. Each DMA designed to best achieve the optimum coverage, cost and other goals. SFNs require expensive distribution systems, usually fiber, but can approach the 20 to 40 dB extra signal level needed for in building reception.
There are other benefits to the single big multiplex approach. Everyone shares the same program guide and control table. The viewer experience is better as they see all of the channel guides, not just one station at a time. Emergency alerting need not be duplicated or delayed, or for that matter, interrupt the broadcast services. Alerting can be location aware and user defined. It also makes DAS distribution into venues, subways and high value areas much more economical, especially if the combined broadcasters can leverage existing DAS systems.
There are some game-changers in this scheme. Incumbents are no longer separated into coverage haves and have-nots. Everybody has to share the same tower(s), transmitter(s), multiplexer, etc. How the bandwidth is split up by the incumbents and any new services (think emergency communications, push content, in-band software upgrades and text services) takes some thought. Even so, today’s codecs and modulation schemes make the number of services this approach supports comparable to the current setting. The full service legacy station may have more of a claim to bandwidth than a narrowcasting fringe station. Likewise, how the cooperative transmission entities operate and are financed might vary community to community.
There is a certain overriding logic to the approach. Broadcasters reach the big, high bit rate (someday soon to be 4K) TVs, mostly via the retransmission paying MVPDs. Broadcasters reach the tiny antenna, secondary TVs and portable and mobile devices via a robust RF distribution system.
Equally important is that solid, bi-directional, wireless services enabled by the spectrum that this approach frees up, empowers broadcasters to expand interactive and advanced services; especially in the increasingly essential mobile environment. Expanding wireless connectivity is a major plus.
I have no doubt that broadcasting will survive and thrive and that it is a virtuous use of significant spectrum. Without discussing how selling off the wireless spectrum could pay for the transition to ATSC 3.0. Without debating how the VHF spectrum can be part of a transition plan for ATSC 1.0/2.0 DTV (and maybe even revitalize the AM broadcasters). Without consideration of what codecs will be used today or tomorrow, the one thing that needs to be settled is how the spectrum is apportioned and thus what modulation is used. Everything else in the future of TV follows this critical, foundational decision.
The 2009 DTV transition was markedly more difficult than ATSC 3.0 should be. Technology refresh cycles are both shorter and less expensive than the ones before. We’re no longer waiting for affordable flat screens, cheap memory, or $20 coupons. In 2009, broadcasters used every bit of spectrum and largely funded the transition. Any new merged broadcast distribution platform should be considerably more affordable to build and far less expensive to operate than building or operating the contemporary parallel and duplicative DTV transmission system. Some of the revenue from reallocating 75% of the broadcast UHF spectrum could pay for it.
In the end, only one approach allows for the most efficient, nimble, economical, and robust use of the UHF spectrum: a single-multiplex-per-market, cellular-style spectrum reuse plan, with a flexible, upgradeable modulation suite. American broadcasting has a lot to recommend it, but “big stick” decentralized transmission locked into inefficient compression is no longer one of them. If we take the path of refarming spectrum, consolidating stations, and individual “owners” sell off broadcast spectrum slot by slot, it might move half of the UHF spectrum to wireless use, but it reduces broadcasting’s already insufficient reach, utility and relevance. TV stations aren’t about how much bandwidth they occupy, they are about the eyeballs they can put their message in front of. Given a good transition plan and self-funding, why wouldn’t embracing the laws of physics and economics be the ultimate public policy win-win?
Fred Baumgartner is a broadcast engineer who has worked on a variety of broadcast technologies ranging from emergency alerting to mobile television.
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By Jens Koerner