Rohde & Schwarz DVM 100/120 transport stream monitors

The monitoring system uses a concept of distributed signal processing
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Rohde & Schwarz’s DVM 100/120 monitoring GUI can display the status of several details for each input.

After transitioning to digital, many broadcasters are in the process of adding an active electronic programming guide by inserting full PSIP data into their transport stream. Or, they are upgrading an existing static EPG to dynamic with extended coverage into future programming schedules and data ingestion from traffic and automation systems. Different multiplex profiles during the day (several SD programs during off peak, and one HD or HD and one SD during peak hours) require diligent service announcements by PSIP metadata, as do the FCC-mandated closed-captioning services and the broadcast flag (more correctly called redistribution descriptor). Additional services, such as directed channel change or data broadcasting, are new ways to enhance the attractiveness of a single channel and to prevent viewers from zapping away. All of these factors contribute to an increasing complexity of broadcast MPEG-2 transport stream multiplex signals. A broadcaster wants to make sure that all media and metadata are sent out properly and can be decoded properly by the DTV receiver or set-top box for continued viewer satisfaction. Thus, the requirements placed on the real-time monitoring equipment keep increasing with the complexity of the stream.

One system does it all

The MPEG-2 monitoring system from Rohde & Schwarz, R&S DVM 100/120, is compact and offers a scalable number of transport streams, up to 20 signals. It is used at transmitter locations, playout centers, central or regional distribution hubs, or cable headends. The 1RU base unit features an integrated system controller and up to four transport stream inputs, which can be switched electronically from DVB-ASI to SMPTE 310 as needed. Expansion units offer up to eight additional inputs. The system controller provides a user interface and offers a detailed overview of all monitoring results for every signal. It includes access to optional drill-down analysis displays in case of trouble or questions. Monitoring options include service table (PSIP) decoding, PCR jitter analysis and record-on-trigger. The monitoring system uses a concept of distributed signal processing. Highly integrated analyzer boards perform the basic transport stream analysis, each serving up to four inputs simultaneously. They are based on FPGAs, allowing for transport stream analysis up to the maximum ASI data rate of 216Mb/s. Processing power is shared between the four signals and can be allocated to provide power to each of the four inputs as needed.

A 100BaseT local Ethernet interconnects all analyzer boards with the system controller. Updated data on errors detected for all transport streams, as well as for the actual transport stream content tree, are exchanged on a continuous basis. The fast system controller collects all preanalyzed data, compares measurement values against the given limits, provides data logging and SNMP traps, and displays the results on the GUI.

Tailoring monitoring details

To avoid unnecessary alarms, it is crucial for a monitoring system to be capable of adapting all tests to the individual signals by adjusting measurement limits and excluding specific test elements. An indefinite number of monitoring configurations can be stored on the controller’s hard disk.

Every input is assigned to one monitoring configuration stored on file. This allows different streams to use either the same or different configurations. These monitoring configurations also include the basic stream standard, which can be ATSC, DVB or SCTE (for U.S. cable systems). This way, the system is capable of checking ATSC-compliant streams and typical cable streams simultaneously.

The system includes the common set of tests — called first, second and third priority errors — as they are defined in ETSI measurement guideline TR101 290. Because some of the third priority tests verify service tables exclusive to the system, a modified version of those tests was used for the ATSC PSIP system. Besides the usual checks for tables, such as MGT, STT, TVCT and so forth, further tests are included that are beneficial for ATSC OTA TV.

Other checks include the verification of the transport stream ID against a given number. The transport stream ID is a unique ID that is assigned to every station by the FCC. Another test verifies that the bit rates of elementary streams (video/audio/data) are within given upper and lower boundaries. The monitoring system also checks when one of the services or multiplex elements disappears unexpectedly, a new one shows up or one changes its type (i.e. from video to audio or data), unless such modification is announced correctly. Verification checks include tables required for OTA supplementation, such as the DCC and LTST for directed channel change and the DET for data broadcasting to ATSC A/90.

Display guides the user through data zoo

The GUI provides instantaneous access to monitoring data of all stream inputs. It can be viewed and operated either locally or remotely through a LAN/ WAN connection. The default monitoring view offers three windows, of which the two left ones display hierarchical trees and remain on the screen at all times, with other in-depth windows. The upper window of the two (titled “Site”) displays a hierarchical tree of all streams currently under investigation systemwide. The user can give all streams unique and easily identifiable names and group them into custom-named folders (i.e. “satellite feeds,” “off-air,” etc.)

The left lower window (“Input”) shows details of the stream currently selected in the Site window above, with a hierarchical representation of all elements, such as video and audio elementary streams, service tables and other metadata. Both tree displays have a common coloring scheme used to indicate each element’s error status (red dot = failure; yellow dot = failed before, currently without error; green dot or not marked = no error). If within any of the two tree displays a group of elements is collapsed, the remaining folder icon carries the summarized status of all elements with its color identification. This is valid over several levels and also for groups of folders, so that uninteresting details can be removed from the screen without losing the capability of monitoring any errors within. A red indicator with any folder icon leads the user to the troubled item underneath by a subsequent opening of tree branches.

The main window on the right side during monitoring mode is titled “Statistics and Log” and displays all monitoring errors observed by the system on the selected stream. The upper portion shows the error seconds per each error type, while the lower one lists all errors by time in a continuous log.

To interpret the displayed data, a system of context-related menu options is used. Depending on which error-indicating element is highlighted, further menu options are offered via right-mouse click.

Monitoring made easier

The DVM 100/120 can verify multiple transport stream signals simultaneously. It offers a large number of detailed real-time checks that can be easily tailored to the individual characteristic of each signal. To keep a clear overview, a specialized user interface not only unveils all monitoring details but also their interrelationships.

Alexander Woerner is the manager of market development for Rohde & Schwarz.

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