DTMB SFN Adapter DTMB 4010

Features

• SFN time and frequency synchronization
• Serial ASI selectable inputs and outputs
• Bit rates adjusted with transmission mode
• Rear panel monitoring points for TS output and sync output

Overview

For the operation of digital terrestrial TV networks, DTMB, where several transmitters broadcast the same programs on the same channel frequencies - Single Frequency Networks - the transmitters require precise time and frequency synchronization. Both the frequency reference (10 MHz) and the time reference (1 pps) signals can easily be obtained from the GPS system at all transmitter sites. The UBS DTMB 4010 SFN Adapter fulfils the task of inserting “synchronization marks” in a DVB transport stream (MIP insertion) in full accordance with DTMB standards.

The basic functions performed by the DTMB 4010 SFN adapter are:

• Inserts a megaframe initialization packet (MIP) into an MPEG transport stream
• Adjusts the bitrate of the transport stream to be synchronous with an external reference and in accordance with the chosen COFDM transmission mode
• Provides signaling/mode data for the control of individual transmitter modulators

MIP insertion

The MIP insertion occurs once per megaframe, with a time interval dependent on the chosen guard band. The MIP indicates the start of the transmission of the first packet in a mega-frame (Synchronization Time Stamp, STS). The time reference is an external 1 pulse per second signal, easily available from a GPS.

Bitrate Adaptation

The DTMB 4010 is provided with two serial (ASI) inputs. The input circuits accept an MPEG transport stream according to the DTMB recommendations (188 byte packets). The output is also 188 byte packets. Note: the maximum bit rate has to include the inserted MIP, which means that the input net bit rate must be slightly lower than maximum. The SFN Adapter removes the null packets in the input signal and inserts the MIP packets. New null packets are then added, to produce an output bit rate, which is precisely the required bit rate for the chosen transmission mode i.e. dependent on code rate, constellation and guard band. The maximum net allowable bit rate is governed by the intended transmission mode, according to the DTMB standards. As the transport rate is modified, the SFN adaptor performs PCR re-stamping.

Control

The operation of the DTMB 4010 is controlled either locally, with a display and push-buttons, or remotely, using the serial RS232 and/or RS485 ports. All mandatory system parameters, as defined in the DTMB standards, may be set from the remote interface. An Ethernet (10/100 BaseT) interface is also available, for remote control and remote software upgrade.

Alarms

One alarm circuit is provided. It may be "armed" for a number of conditions important for correct operation. The Alarm output is via floating contacts on the rear panel and the alarm information is also available via the remote control.