Measurement Functions
2–14
MTD200 MPEG Test Decoder User Manual
The DVB Measurement Guidelines also recommend additional monitoring of the
accuracy of the PCR values transmitted. Accuracy of PCR values may be
impaired by inaccurate calculation of the 42-bit PCR word width or by errors
during modification of PCR values in a remultiplex.
NOTE
. The term accuracy in this case does not refer to absolute frequency
accuracy of the 27 MHz system timing, but to the fluctuation width of the PCR
values of a program, which is caused by the above mentioned errors.
The MPEG-2 standard (ISO/IEC 13818–1) as well as the DVB Measurement
Guidelines (ETR 290) prescribe a maximum tolerance of
±
500 ns for PCR
values. The MPEG-2 standard (ISO/IEC 13818–4) also describes a method to be
used for testing the so-called timing accuracy, which serves to monitor the
compliance of these PCR tolerances. The description of this method contains an
inequation, which must be fulfilled for all PCR values of a program. This
inequation is as follows:
(i–i”–1)
PCR(i)–PCR(i”)
)
v
k
v
(i–i”
)
1)
PCR(i)–PCR(i”)–
i being
index of the byte in which the current PCR value was
transmitted
i’’ being
index of the byte in which the previous PCR value was
transmitted
d
being
27 + 810 * (PCR(i)–PCR(i’’)) / 27E6;
If the above inequation is not fulfilled for any consecutive two pairs of PCR
values, (maximum value of the left side and minimum values of the right side are
stored) the precondition for a PCR_accuracy_error is fulfilled.
PCR Accuracy ERROR is signaled if
the PCR tolerance within a program is >
±
500 ns
A PCR_error and a PCR_accuracy_error are indicated in a cumulative message
signaling several single errors by the LED labeled OTHER lighting (line of
LEDs at front panel). More detailed information on the type of PCR error as
listed in the above tables can be obtained from the monitoring report.
Summary of Contents for MTD200
Page 1: ...User Manual MTD200 MPEG Test Decoder 070 9951 00...
Page 4: ......
Page 15: ......
Page 29: ...Introduction to Digital TV Transmission Technique 1 14 MTD200 MPEG Test Decoder User Manual...
Page 30: ......
Page 51: ......
Page 62: ......
Page 97: ......
Page 167: ...Remote Control 5 70 MTD200 MPEG Test Decoder User Manual...
Page 168: ......
Page 174: ...Maintenance and Checking 6 6 MTD200 MPEG Test Decoder User Manual...
Page 175: ......
Page 194: ......
Page 204: ...Glossary Glossary 10 MTD200 MPEG Test Decoder User Manual...
Page 205: ......
Page 209: ...Index Index 4 MTD200 MPEG Test Decoder User Manual...
Page 210: ......
Page 211: ......