Sinclair View on 8VSB

Guest Commentary

The 8VSB - COFDM - Sinclair Issue

By Mark A. Aitken
Advanced Technology Group
(a part of the Sinclair Broadcast Group)

In an attempt to get everyone "on the same page", I will try to "demystify" the issues being raised by some.

"Why is Sinclair asking the FCC to 'abandon' 8VSB?"

This IS NOT what Sinclair has requested in its filing. The following list details Sinclair's primary position with respect to the filing:

What is Sinclair Asking the FCC to do?

1. Modify the digital modulation standard so broadcasters can transmit their digital signals using Coded Orthogonal Frequency Division Multiplexing (COFDM).

2. Appoint a COFDM Task Force that would be assigned two responsibilities:

Conduct a study and issue recommendations to the Commission regarding the integration of COFDM digital modulation technology into the DTV standard; and
Conduct a rigorous scientific analysis to determine the interference ratios for COFDM transmissions into existing NTSC and 8-VSB DTV signals.

3. Adopt rules implementing the recommendations of the Task Force.

What Sinclair is Not Asking the FCC to do?

1. Abandon 8-VSB as a digital television modulation standard.

2. Delay any of the time deadlines for the DTV rollout.

Why Should the FCC Allow Broadcasters to Operate Using COFDM Technology?

1. Use of COFDM digital modulation technology will permit reliable and robust over-the-air reception by viewers using simple antennas in broadcasters' core business areas.

2. Use of COFDM would enable broadcasters to provide mobile and portable DTV video services.

3. By permitting COFDM operations, the Commission will allow the marketplace to play an appropriate role in the development of broadcast technology. Permitting use of COFDM would make the US DTV system compatible with the DTV technology adopted in the majority of countries around the world. A decision by the Commission to permit COFDM operations would accelerate the development of DTV in the United States and speed the recapture of NTSC spectrum.

What's Wrong With The 8-VSB Digital Modulation Standard?

1. The ATSC 8-VSB standard does not currently permit reliable over-the-air reception of DTV with simple antennas in broadcasters' core business areas, or permit portable or mobile services.

2. Given the reception problems, continued reliance on the 8-VSB standard would diminish viewing functionality and impose unnecessary costs on US consumers, both during and after the DTV transition.

Are there Legitimate Technical or Economic Reasons To Preclude Broadcasters From Operating Using COFDM Technology?

1. There is no legitimate technical reason precluding the use of COFDM modulation technology.

COFDM signals can be used to provide HDTV over 6 MHz channels.
The greater coverage predicted for 8-VSB signals in a laboratory environment does not hold up under real-world conditions.
The Commission should not perpetuate exclusive reliance on the 8-VSB standard based on any speculated improvements in 8-VSB receiver technology.

2. Broadcasters, manufacturers, and consumers would incur only minor costs if the Commission decided to permit use of COFDM in the US.

Any additional costs for broadcasters would be borne voluntarily, and would likely be inconsequential.
Grant of the instant petition would not impose significant costs on DTV receiver manufacturers. The prior sale of 8-VSB receivers to a tiny fraction of consumers should not prevent the Commission from permitting broadcasters to use COFDM technology.

What about the extra power required by COFDM?

Some 8-VSB proponents have stated that a COFDM transmitter will need to operate at significantly higher peak and average powers to achieve the same coverage as an 8-VSB transmitter. Increases of up to 7 dB have been quoted; the implication being that the initial transmitter capital acquisition costs and the ongoing expenses associated with power consumption will be much higher for the COFDM transmitter. Ergo, a change to COFDM will cost the US Broadcaster huge sums of money. This is just not true and needs to be examined from both the peak and average power perspectives.

Peak power: COFDM does have a higher peak to average ratio than 8-VSB. However, the actual peaks occur for very short periods and both systems can tolerate a reduction of the peak to average ratio without significant distortion. Certain digital signal manipulation techniques currently being deployed take advantage of the inherent robustness of the multi-carrier COFDM format to provide a greater reduction in peak to average ratio than is possible for the single-carrier 8-VSB signal. The resultant peak to average ratio "penalty" of COFDM is reduced to about 1 dB. This may result in a slightly higher initial purchase cost for a solid-state transmitter due to a higher device count, but it is unlikely to have any impact on the cost of a high power vacuum tube transmitter.

Average Power: For equivalent data rates, 8-VSB would appear have a theoretical C/N "advantage" of about 4 dB over COFDM. This "advantage" is often used to justify the claim that 8-VSB will provide greater coverage than COFDM operating at the same average power. The theoretical advantage can, in fact, only be confirmed in a laboratory environment. When real world signal propagation and reception characteristics, such as static and dynamic multipath, are factored in, the "advantage" evaporates into the ether! Sinclair tested and demonstrated the ability to receive COFDM signals at the far fringe coverage areas with no meaningful differences when compared to 8VSB signals at the same average power. Given the realities of a typical fringe reception environment, any small difference is of little relevance when compared to:

Antenna downlead losses (6 dB)
Diurnal fade margins (6 dB)
Modern fringe antenna gains (+12 dB to +16 dB)
Low cost and effective "Low Noise Amps" (~2.5dB NF@13-20dB gain)

Under real-world conditions, there exists no meaningful or material difference in the receivability of 8VSB and COFDM signals. We see absolutely no reason why higher average power transmission would be required by COFDM.

Will COFDM have a Major (negative) Impact on the FCC Table of Allotments?

The FCC revealed in its recently released OET Report 99-2 that the most highly congested "Top 10" DTV markets were studied to determine the impact on the table of allotments and differences in service availability. In the FCC OET analysis they assumed COFDM to have an advantage in urban areas close to the transmission facility, and 8VSB to have an advantage in fringe area coverage. As well, they assumed (incorrectly) that COFDM would have to operate at an increased power level of +4dB (see above).

Under these conditions the FCC OET found that: The estimates indicate that the relative advantages/disadvantages of the systems have a "generally small" impact on the overall coverage, and vary by market. The interference to NTSC service, even when providing for an additional +4dB of power by COFDM, would be "generally small".

What is the cost impact to convert 8VSB transmission systems?

Clearly, the cost will vary from various system providers. In general, the conversion of an existing 8VSB transmitter at similar or equal power levels will typically be less than $50,000, the cost of integrating and setting up a new modulator. In many cases, where the equipment provider is also supplying COFDM equipment to the global market, the conversion may be significantly less than $20,000 (the cost of an exciter modulator card swap and setup). In the case of equipment such as encoders, there are similar variables. Many of the encoder manufacturers/providers are supplying exactly the same hardware for 8VSB and COFDM markets, with a simple requirement of software or firmware revisions.

We would like to thank you for the support that you have shown during most recent period. Your support and informed understanding of the issues at hand is shaping the course for the future of digital television broadcasting.

If you have questions, please visit our site: www.sbgi.net. You will find a link to DTV information, and may also address any your specific concerns to dtv@sbgi.net .