Vislink Strata RX, Техническое справочное руководство

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Link Quality D-2
Strata RX
Technical Reference Manual
errors begin to pass through to the MPEG decoder. The impact
on the video and audio will usually be minor at first, with some
pixellation of the video typically appearing. The operator may or
may not realize how badly the signal has now degraded.
Finally, if the signal quality continues to deteriorate, the errors
reaching the MPEG decoder will disrupt the decoder so badly
that it cannot construct an image. The decoder algorithm will
stop working, and the video will then suddenly be lost. Operators
sometimes refer to this sudden loss of video, with little or no
apparent warning, as “falling off a cliff”.
See Figure D-1 on page D-3 for a graphical representation of this
“cliff”.
D.3 Understanding Link Quality
D.3.1 Description
Vislink has developed the
Link Quality
(LQ) indicator to give you
back that ‘early warning’ of an analog system.
Link Quality
monitors several key parameters and settings, and uses a
proprietary algorithm to derive one simple indication of digital
signal quality.
The monitored parameters include:
• Received Carrier Level (RCL).
• Bit Error Ratio (BER) before Forward Error Correction
(FEC) (also called “Pre-Viterbi BER”).
• Bit Error Ratio (BER) after Forward Error Correction
(FEC) (also called “Post-Viterbi BER”).
• Signal-to-Noise Ratio (SNR).
In addition, the LQ algorithm takes into account these settings:
• The modulation in use (QPSK, 16 QAM, or 64 QAM).
• The Forward Error Correction (FEC) setting (1/2, 2/3, 3/4,
5/6, or 7/8).
• The Guard Interval (GI) setting (1/32, 1/16, 1/8, or 1/4).
• The CODFDM Bandwidth (BW) in use (6, 7, or 8 MHz).
D.3.2 The LQ Scale
The
Link Quality
indicator is scaled from 0 to 9, with 9 the
highest and 0 the lowest. See Table D-1.
Table D-1: Link Quality Levels
LQ
Reading
LInk Quality Description
9 Excellent
Link Quality - COFDM link is very robust
with ample ability to correct for degradation.
8 Very Good
Link Quality - COFDM link is robust for
the given environment.
7 Standard
Link Quality - COFDM link is acceptable
for current environment.
6 Average
Link Quality - COFDM link is average -
might improve or worsen.
5 Below Average
Link Quality - COFDM link is
marginal, not dependable.
4 Poor
Link Quality - COFDM link is unstable -
quality is intermittent and unpredictable.
1 - 3 Unsatisfactory
Link Quality - COFDM link is not
locked.
0 No signal
detected.