ATSC 3.0 / NextGen TV Solutions

DTV Power Amplifier De-rating with ATSC 3.0
In addition to the IP networked capabilities that ATSC 3.0 will bring to the broadcast industry, impacts to your DTV transmitter plant need to be considered. The table to the right provides a quick overview of the estimated RF output power difference when converting a DTV transmitter from ATSC 1.0 (8VSB) to ATSC 3.0 (OFDM). Why do amplifiers need to be de-rated? The answer lies in the fact that VSB and OFDM have different peak-to-average power ratios. And since DTV output power is always measured in average watts, the amplifier’s peak power capability limits the average. So when converting a DTV transmitter from 8VSB (6dB peak-to-average) to ODFM (8 to 10dB peak to average), the peak power must be taken into account.

RF Plant Considerations with ATSC 3.0
Beyond the DTV transmitter that you operate (or plan to replace) other factors should be considered when migrating to ATSC 3.0. These factors are primarily geared towards the transmission line, antenna, and tower structure. However, it could also impact filters and combiners. To take full advantage of ATSC 3.0, DTV stations should consider transmit antennas that use either Circular Polarization (50% H-Pol with 50% V-Pol) or Elliptical Polarization (70% H-Pol with 30% V-Pol or something similar). Adding a vertical component to your transmit antenna has proven to aid mobile services and deep indoor signal penetration. Remember that ERP is based only on the H-Pol power, therefore a higher power transmitter may be required (2x in the case of Circular Pol) should you decide to add a vertical component for ATSC 3.0.

Most important with ATSC 3.0 is the power handling capability of the mask filter ®, transmission line ®, and transmit antenna. Remember that ATSC 3.0 will have peak power levels 10dB (x10) above the average power of the transmitter output. ATSC 3.0 will also have a wider bandwidth than ATSC 1.0 using 97% of the allocated spectrum compared to 90% for ATSC 1.0. A standard bandpass filter that is tuned for the correct channel should be capable of either format. However, an ATSC 1.0 sharp tuned filter or channel combiner may have problems with ATSC 3.0. And while reviewing the power handling of the hardware that runs up and is mounted on the top of the tower; remember that the tower should be reviewed for wind loading and compliance with the most recent issues of EIA/TIA engineering standards.

Single Frequency Network with ATSC 3.0
ATSC 3.0 supports both high power – high tower deployments as well as Single Frequency Network (SFN) deployments. We begin by asking the simple question, “What is an SFN?” A Single Frequency Network (SFN) is made up of two or more transmitters simultaneously broadcasting the same time-synchronized signal over the same frequency to achieve greater signal coverage and reception. “Why would a Broadcaster want to implement an SFN system?” SFN’s allow broadcasters to more completely “blanket” RF coverage to their target market. Adding second, third, and fourth transmitters in SFN mode in conjunction with a main transmitter can significantly increase signal reception in targeted areas. Consider SFN design parameters including “sparse” SFN transmitter placement and their associated antenna patterns.

Time vs. Layer Division Multiplexing
ATSC 3.0 can be setup to deliver data in either Time Division Multiplexing (TDM) or Layer Division Multiplexing (LDM). The broadcast gateway in conjunction with the exciter is configured for either TDM or LDM at the launch of the ATSC 3.0 service. An ATSC 3.0 system that uses TDM concatenates, in time, multiple PLP’s within a subframe by using non-dispersed PLP’s. An ATSC 3.0 system that uses LDM multiplexes multiple RF signals that are layered on top of one another. A 2 layer LDM system has Core layer (more robust ModCod) and an Enhanced layer (less robust ModCod). The Enhanced layer is “injected” between -3 and -10dB relative to the Core layer. For additional info on the tradeoffs of LDM, see the Solution Datasheet.