MPEG-2 / DVB Digital Television System Integration

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In order to integrate complex systems, such as MPEG-2 digital  television delivery systems, the proper tools are required to isolate and solve problems quickly and easily in order to reduce integration time. These same tools can be applied to smaller subsets of integration, such as verification of the output of a MPEG-2 compression system. An important tool to have at hand is one that can analyze the transmitted data - and for MPEG-2 digital television, it is the MPEG-2 transport stream as defined in the ISO/IEC 13818-1 specification and additional DVB extensions as defined in various ETS and ETR specifications.

The MPEG-2/DVB Transport Stream Analyzer (Acterna DTS-A) from Wavetel Wandel Goltermann provides real-time continuous monitoring capabilities to help solve the system integration problems inherent in the deployment of digital television systems. The above figure illustrates a MPEG-2 system and where Acterna DTS-As could be utilized to help speed integration and isolate problems, possibly performing dual-analysis from a single instrument.

In the above figure, if the IRD is able to correctly receive and display the compressed digital television signals, then the system may appear to be working properly. However, the typical situation is that such systems do not work properly the first time, or even the second time. The problem area, or areas, in the system need to be identified and resolved quickly and the typical high level questions to be asked are:

1. Is the data coming out of the MPEG-2 Compression and Multiplexing System a valid MPEG-2 Transport Stream?

2. Is this data being transmitted properly by the modulator?

3. Is the IRD receiving the valid MPEG-2 transport stream that it expects and is it able to decode all DVB service information?

4. Is there any hidden performance issue, resulting from fine configuration of multi-vendor products or for optimal interworking along the broadcast chain?

The WG DTS-A can help answer these questions quickly and efficiently. The following table lists the desirable test equipment features that can help solve the spectrum of problems usually encountered during integration.

The Acterna DTS-A has been designed with the system integration problem in mind: it has all the capabilities listed above and provides a layered approach to extracting information regarding the transport stream under test. A typical approach to using the Acterna DTS-A in the system integration process is listed in the following steps:

1. Investigating top-level stream information

2. Verifying PIDs and ascertaining PID details

3. Examining MPEG-2 PSI and DVB SI tables and descriptors

4. Viewing any detected errors or events (ETR290 and conformance)

5. Analyzing timing and PCR jitter and spacing

6. Synthesizing all analysis results on a program basis

7. Tracking bandwith use per PID or per program

8. Locating source of errors and impact per program

9. Reporting and archiving measurement results

STEP 1: Investigating top-level stream information

From the Transport Summary display, the user can quickly establish the following information about the transport stream:

1. Overall transport stream data rate

2. Number of MPEG-2 synchronization errors detected

3. Valid MPEG-2 PSI and DVB SI data in stream

4. Number of PIDs in the stream for the different stream types and current data rates and percentage bandwidth

5. Number of Programs and number of Clock References (PCR)

STEP 2: Verifying PIDs and ascertaining PID details

From the PID Information display, the user can view information about each individual PID, including the following items:

1. Related Program Name

2. Packet count

3. Current, min. and max. bit rates and burst peaks

4. Table errors detected on PID if table PID

5. Continuity counter errors

6. Stream type(audio, video, data, table)

7. Unit starts per second (if access unit for video is a whole frame, this will indicate the frame rate for the video)

8. PTS and DTS values if available

9. Duration PID has been detected in the stream

10. PCR data (current, arrival rate, peak and average jitter) if available

STEP 3: Examining MPEG-2 PSI and DVB SI data

The PSI/SI display allows the user to navigate the MPEG-2 PSI and DVB SI table information through a tree display. This intuitive display, in the left panel above, shows the links between the tables in a hierarchy as defined by the MPEG-2/DVB network and transport stream structures. The panel on the right allows the user to view formatted information for the currently selected table or descriptor. The formatted view provides the following basic information for each table:

1. Table PID

2. Table version number

3. Section count

4. Packet count

5. Tables per second

6. Count of table received

7. Number of syntax errors detected

Certain tables such as the TDT do not follow the generic section syntax and so the table version and section count information is omitted for such tables.
The Acterna DTS-A extracts all other table specific information and displays the results in a different formatted view for each table type processed: PAT, CAT, PMT, NIT, BAT, SDT, EIT, RST, and TDT. The above example illustrates the output for an EIT descriptor.

If part of the table structure is missing, the tables can be viewed separately in a list format. All information is updated in real time on a continuous basis, automatically notifying the user about new tables or new table versions.

STEP 4: Viewing any detected errors or events (ETR290)

The Acterna DTS-A tracks a defined set of events that can occur in the system.
For each event, the display provides the following information:

1. Index and type of event (Informational, Warning, or Error)

2. Time of day event occurred

3. Acterna DTS-A test time event occurred

4. PID for event

5. Event number, type and description

The event table listing can be sorted by any of the columns by clicking on the column header in the table. In addition to the events defined in the ETR 290, the analyzer detects:

• Transport Stream Synchronization and sync. byte errors,

• Continuity Counter errors,

• Packet structure and errors such as adaptation size field too large,

• PID detection and comparison with PID referenced in PAT and PMTs,

• PID bit rate over a user-defined max. bit rate, or below a user-defined min. bit rate,

• Invalid scrambling on PSI/SI table PIDs,

• PCR detection, synchronization, jitter, accuracy outside 500 ns and intervals above 100ms or user-specified value,

• PTS detection and intervals,

• Table detection and table version detection,

• Table and descriptor errors such as syntax, size, CRC, section number, no data,

• Table beginning/ending versus payload unit start and zero pointer field,

• Table content changes without version number changing,

• Detection and repetition rate for PAT, PMT, CAT, NIT (actual and other), BAT, SDT (actual and other), EIT P/F (actual and other), EIT Schedule (actual and other), TDT, TOT,

• Mega-frame Initialization Packets related events (MIP for DVB-T single frequency networks).

Whenever applicable, the event context is stored along with the event (e.g. expected value versus received value for continuity counters).

In addition to logging the events, the analyzer can automatically perform a capture on trigger. The capture is up to a few seconds of the transport stream, it is performed prior to and after the occurrence of selected types of events.

The Acterna DTS-A also provides a monitoring display based on the ETR 290 DVB Recommendation. The display provides green/red LEDs for current errors as well as error counters. In addition, the user has direct access to the event logger for each error type.

STEP 5: Analyzing timing and PCR jitter and spacing

The Acterna DTS-A provides the capability to compare the PTS values on two different PIDs to a selected PCR so that audio/video synchronization can be analyzed. From the Synchronization Analysis display, the user can view the instantaneous, average, standard deviation, maximum, and minimum differences between the PTS values and their arrival times based upon the recovered PCR clock selected. The user is also presented with the delta between the two PID’s PTS/PCR differences for instantaneous and average values. A flag indicates to the user that the Acterna DTS-A has locked to the reference PCR selected.
The same display provides statistics or graphing of PCR jitter and spacing for all PIDs, on a continuous basis.

STEP 6: Synthesizing all analysis results on a program basis

The Acterna DTS-A has the unique capability to combine all the information related to a program on a single display, down to the audio and video components.
The user can also directly access the abstract of the event logger related to a given program.

STEP 7: Tracking bandwith use per PID or per program

Bandwith min. and max. limits are user setable on a PID basis. The Acterna DTS-A will automatically log any infrigement and its duration

STEP 8: Locating source of errors and impact per program

For Broadcasters, event logging has to be tracked on either a PID basis or a Program basis. The Acterna DTS-A event logger provides the related program name whenever appropriate.

STEP 9: Reporting and archiving measurement results

All the information provided by the Acterna DTS-A can be re-used in a text file for reporting and archiving. Information can be added to the text file either on-demand or automatically (on-trigger or on-schedule), therefore facilitating acceptance testing or base lining avertime.

For more information or to request a free evaluation software, please send your query to mpeg@jdsu.com.