[opendtv] DTV Receiver Performance Standards Recommended
- From: Tom Barry <trbarry@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 14 Mar 2005 08:32:31 -0500
I just saw this article today in TV Technology about DTV performance
standards. Can anyone who understands the numbers tell me if there is
any meat on this spec for multi-path handling (Recommended Practice A/74)?
See:
http://www.tvtechnology.com/features/atsc/F_Whitaker-03.09.05.shtml
- Tom
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ATSC Update: Jerry Whitaker
DTV Receiver Performance Standards Recommended
A concerted, cross-industry effort has led the ATSC to publish DTV
receiver performance guidelines. A/74, "Recommended Practice: Receiver
Performance Guidelines," is the result of a collaboration of
broadcasters, consumer electronics manufacturers, semiconductor
manufacturers and other ATSC members.
This recommended practice provides performance guidelines for receiver
sensitivity, multiple signal overload, phase noise, selectivity and
multipath. The document also suggests the use of the antenna-control
interface CEA-909 developed by the Consumer Electronics Association,
which facilitates automatic control of antenna parameters.
Recommended Practice A/74 addresses the front-end portion of a DTV
receiver. The performance guidelines in the document are intended to
ensure reliable reception. Guidelines for interference rejection are
based on the FCC planning factors that were used to analyze coverage and
interference for the initial DTV channel allotments. Guidelines for
sensitivity and multipath handling reflect field-testing undertaken by
ATTC, MSTV, NAB and receiver manufacturers.
As covered within A/74, the front-end includes all circuitry from the
antenna through the process of forward error correction (FEC) that is
associated with recovery and demodulation of the 8-VSB signal (see Fig.
1). The output of the receiver front-end is the input to the transport
layer decoder.
Fig 1.
The circuits contributing to meeting the A/74 guidelines include:
Antenna and antenna control interface (CEA-909);
Tuner, including RF amplifiers, associated filtering, and the local
oscillator (or pair of local oscillators in the case of double
conversion tuners), as well as mixers required to bring the incoming
RF-channel frequency down to that of the intermediate frequency (IF)
amplifier/filter;
IF amplification (with automatic gain control) and filtering, including
the major portion of pre-decoding gain, channel selectivity and at least
a portion of the desired-channel band-shaping;
Digital demodulation, including in-band interference rejection,
multipath cancellation and signal recovery;
¥ FEC, wherein errors in the demodulated digital stream caused by
transmission impairments are detected and corrected for incoming signals
with signal-to-impairment ratios above a threshold. Packets with
uncorrectable errors are flagged for possible mitigation in the video
and audio decoders.
A/74 does not discuss optional means by which receivers might attempt to
conceal or otherwise mitigate the visible or audible consequences of
uncorrected bitstream errors. Although most receivers include circuits
that accomplish some degree of error concealment, the results are
subjective and not quantified as easily as the performance of the other
circuits listed above.
The recommended performance guidelines are divided into four general
categories:
Sensitivity
Selectivity
Interference rejection
Multipath handling
The various industry segments that comprise the broadcast-to-reception
chain have positively responded to publication of A/74 and supporting
bitstreams have been distributed to various organizations for testing
and study. In addition, the ATSC Specialist Group on Receivers, T3/S10,
continues to look for and document unique and interesting reception
sites that may be useful in designing new receiving devices.
FOR MORE INFORMATION
Document A/74, as all ATSC Standards, Recommended Practices, and
informational documents, can be downloaded free from the ATSC Web site
at http://www.atsc.org
Jerry Whitaker is vice president of standards development for the ATSC.
You can reach him via TV Technology.
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