The 2023 NAB Show exhibits and sessions demonstrated the future of ATSC 3.0 can extend beyond traditional over-the-air TV broadcasting. I’ll focus on three ATSC 3.0 innovations: Use of ATSC 3.0 to provide precision time and positioning services; efficient data transmission for radio over ATSC 3.0; and sharing an ATSC 3.0 channel with a 5G signal.
Broadcast Positioning System
The topic of using ATSC 3.0 as a backup for GPS was discussed in the session “Delivering Traceable Reference Time for ATSC 3.0-based Broadcast Positioning System (BPS),” by Patrick Diamond of Diamond Consulting and co-authored with Tariq Mondal and Robert Weller from NAB and Andrew Hansen at Volpe Center.
During the session they listed some of the critical services that depend on precise timing from GPS, including mobile wireless networks, equity trading systems and power grid synchronization as well as multiple services requiring precise position information. Loss of GPS timing, whether due to failure or intentional disruption, will have a significant impact on the systems we depend on—indeed, high-precision position, navigation and timing (PNT) has been recognized as a national security concern.
The concept of using ATSC 3.0 to provide precision time and positioning is not new. One of the questions I had about precision timing was how the differences in timing in the transmission chain were accounted for. For example, the length of the transmission line on a 2,000-foot tower will change with temperature, and timing in the path from where ATSC 3.0 time is generated to the transmitter site may also change.
The system presented uses data from an Avateq receiver to compare the received signal timing with a precision reference—GPS if available, a local cesium or rubidium clock, or another ATSC 3.0 station with a precision reference are possible options—and send that information to the Triveni Digital Broadcast Gateway, which adjusts ATSC 3.0 clocks to within 200-nanosecond accuracy required by critical applications. By placing the timing data on a robust physical layer pipe (PLP), reception should be possible at signal-to-noise ratios below zero dB, allowing the BPS to work indoors where GPS signals aren’t available.
This presentation and another one with details on the system used, “BPS ATSC 3.0 Broadcast Emission Time Stabilization System Proof-of-Concept” by Mark Coril of Triveni, Vladimir Anishchenko from Avateq and Tariq Mondal, are available in the NAB BEIT Conference Proceedings. The presentation, “Broadcast Positioning System (BPS) Using ATSC 3.0,” by NAB's Tariq Mondal, Robert D. Weller and Sam Matheny featured at a recent meeting of the National Space-Based Positioning, Navigation, and Timing Advisory Board, is available online at gps.gov. Fig. 1 from the presentation shows the system configuration.
Radio Over ATSC 3.0
At first, the idea of sending audio broadcasts (radio) over ATSC 3.0 sounds simple. The ATSC 3.0 standard includes options for Dolby AC-4 and MPEG-H multichannel audio.
However, as Liam Power from ONE Media pointed out in the paper “Audio Services Over ATSC 3.0: A Proof of Concept,” transmitting audio to receivers in vehicles in a bandwidth-efficient manner is not that simple. Designing an efficient ATSC 3.0 radio system requires selecting an audio codec compatible with a wide range of clients that delivers sufficient quality using the least amount of bandwidth, finding a method for transmitting the audio in the ATSC 3.0 signal with the least amount of overhead and complexity on the receiver side, and selecting physical layer parameters that provide a reliable signal in a mobile environment.
Designing an efficient ATSC 3.0 radio system requires selecting an audio codec compatible with a wide range of clients that delivers sufficient quality using the least amount of bandwidth"
ONE Media found the xHE-AAC codec met audio requirements at bit rates as low as 24 kbps. Dolby AC-4 performed well at 48 kbps but due to encoder restrictions could not be tested at less than 48 kbps. Support for Dolby AC-4 is also limited in client devices, particularly on computers and mobile devices, compared to the HE-AAC family of codecs. For the proof-of-concept, HE-AACv2 was used as it currently has wider support than xHE-AAC.
The proof-of-concept used the “UserDefined” table in the ATSC 3.0 standard to provide signaling information for the audio transmitted as a transport stream embedded in RTP UDP data.
The demonstration used 16.66% of the total ATSC 3.0 signal capacity to provide 15 radio services at 45 kbps each (675 kbps total). A QPSK 11/16 modcod physical layer pipe (PLP) with a calculated 6.3 dB SNR requirement was used for audio. Test drives showed reception comparable (or better) than local FM radio stations. Refer to the paper in the BEIT Proceedings for more detail on how the parameters were selected and potential improvement in future designs.
ATSC 3.0 and 5G MIMS
In my last column I expressed doubts about support for combining ATSC 3.0 and 5G in a TV channel. At this year’s NAB Show it was clear the technology for sharing a TV channel with ATSC 3.0 and a 5G-compatible signal was still in active development.
In the NAB Futures Park, Korea's ETRI showed an ATSC 3.0 and 5G-MBMS signal sharing a single 6 MHz TV channel in a time-division-multiplex (TDM). The ATSC 3.0 and 5G signals were generated at different power levels to allow the switching to be displayed on a spectrum analyzer, (Fig. 2).
The 5G signal used 50% of the transmission time. For the demonstration, a single stream was transmitted on each signal at 5.77 Mbps for ATSC 3.0 and 5.21 Mbps for 5G-MBMS. The ATSC 3.0 signal used a non-uniform 64-QAM constellation with 8K FFT while the 5G signal used 64-QAM and 12K FFT. The code rates were similar so I would expect both signals to be close in robustness, with the ATSC 3.0 stream having a slight advantage.
Rohde and Schwarz did not have a live demonstration of 5G/ATSC 3.0 channel sharing, but did show their work using TDM to share a TV channel with 5G. Rohde and Schwarz has experience in 5G transmission systems and at the 2022 NAB Show showed a high-power UHF 5G-MBMS transmitter.
(Also read: What Can Broadcasters Do with 5G?)
Why would broadcasters be interested in sharing their channel with a 5G-compatible signal? If broadcasters are able to convince cell phone manufacturers and the wireless companies to include ATSC 3.0 capability in their phones there would be little advantage in transmitting content twice.
However, the difficulty in getting FM radio enabled on cell phones—even when a device has the circuitry to receive it—shows broadcasters are likely to struggle to get ATSC 3.0 on mobile devices. Transmitting a signal in a compatible, physical layer format would make it easier for device manufacturers. Qualcomm, a major mobile device chip supplier, has indicated it will support 5G over UHF TV channels in its new modem chips.
Transmitting a 5G physical layer signal along with a compatible ATSC 3.0 signal may be allowed under current FCC rules, and from what I saw at the show, equipment to do that will be available if customers demand it. That won’t happen unless devices become available that support 5G on UHF TV channels and wireless companies allow it on their devices. Until the transition to ATSC 3.0 is complete, ATSC 3.0 capacity is likely to remain scarce. How many stations will be willing to give up channel capacity to add a 5G signal?
These technologies show ATSC 3.0 is ready to provide services beyond delivering TV to screens. Adding Broadcast Positioning Service capability requires little extra capacity, especially if LDM is used for the robust layer, and adding more than a dozen radio services over ATSC 3.0 can be done effectively in much less bandwidth than a 1080P HD signal as ONE Media demonstrated.
Other work not mentioned here is being done to optimize data delivery over ATSC 3.0. When considering the role these “beyond TV” services could play in the future of broadcast TV, notice how cable TV has evolved from a service providing TV to consumers who could not receive TV on an antenna to a service most customers depend on for broadband internet. l
In Part 2 of my 2023 NAB Show coverage I’ll look at some of the interesting products I saw for RF transmission, reception and measurement. I welcome your comments, question, and observations on the future of broadcast TV. Email me at dlung@transmitter.com.
