Bavarian Broadcasting Corporation Performs DVB-T2 Field Tests in Munich

Comprehensive testing is required before a network can begin regular operation using new broadcasting standards. This was also true for the transition from the DVB-T to the DVB-T2 TV standard. In 2010, the Bavarian Broadcasting Corporation started field testing in Munich. Rohde & Schwarz provided the necessary transmitters and T&M equipment.

A Long Journey – From the Standard to a Comprehensively Tested Network

DVB-T2 network test area in Munich.

In the spring of 2007, the first technical details for the new DVB-T2 terrestrial broadcasting standard were made public. In late 2009, Rohde & Schwarz finished implementing the new standard in the R&S®SFU broadcast test system to enable testing of consumer receivers. The first test networks in 2010 were pure multifrequency networks (MFN). At that time there was no experience regarding DVB-T2 single-frequency networks (SFN) since these networks required T2 gateways that had yet to be developed.

In early 2010, the Bavarian Broadcasting Corporation (BR) launched an initiative for additional field testing with the goal of testing the operability of DVB-T2 SFNs and setting up an IP-based distribution network to supply transmitter sites with the DVB-T2 MI transport stream. The focus of testing was also on the distributed MISO method, which was to be compared with SISO, the traditional configuration for DVB-T. Experts selected three of the Bavarian Broadcasting Corporation’s transmitter sites that were well-suited for MISO tests, located about 10 km apart from each other and essentially covering the Munich metropolitan area.

MFN with Three Transmitters

Impact of additive overlay in the SFN for MISO and with SISO. There is no correlation between the signals from transmitter 1 and transmitter 2.

In September 2010, the Freimann site, with its 110 m high antenna and an ERP of approximately 5 kW as a pure omni-directional antenna, was the first to go into operation. At first, the installed air-cooled 800 W R&S®NV 8302 V medium-power transmitter worked with the following operating parameters: 16K normal, code rate = 2/3, g = 1/16, SISO, single PLP; later it was switched to 32K extended carrier. Initially, an MFN with a TS-ASI feed was planned, with the transport stream already embedded in an IP distribution network. In the fall of 2010, the test team mounted antenna arrays on the BR radio mast at a height of 210 m in Ismaning pointing toward Freimann, again with an ERP of approximately 5 kW. An air-cooled R&S®SCV 8302 R compact transmitter with an output power of 600 W was connected to the antennas. In March 2011, the same type of transmitter was installed for the BR broadcasting center located at Munich central station. Now all three sites were on air as MFNs in SISO mode. Drive tests in this DVB-T2 network revealed a net data rate of about 26 Mbit/s – twice that of a DVB-T network – and with the same robustness. Just as with DVB-T, there were destructive notches in the spectrum at approximately the same levels and delay differences of a few microseconds between two transmitter sites.

Single-Frequency Network in MISO Mode

The R&S®TSE 800 transmitter system extension was installed at each site in order to successively upgrade the network to MISO and full DVB-T2 functionality as well as to multi-PLP mode with a single PLP being used. This was followed by the configuration of the SFN. Tests for MISO mode began in the spring of 2012.

Using network planning software, the team determined which test locations would be most relevant for the planned drive tests. The software simplified the selection thanks to its comprehensive maps and diagrams that clearly show the calculated field strengths, impulse responses and locations with the same delay differences, etc.

Equipped with T&M equipment from Rohde & Schwarz, vehicles belonging to BR and the Munich Broadcast Technology Institute (Institut für Rundfunktechnik, IRT) completed numerous drive tests in the SFN. A pivotable, directional test antenna located on Rohde & Schwarz grounds provided supplemental field strength values. GPS time and frequency standards synchronized the SFN with the transmitter sites. The Rohde & Schwarz gateway was synchronized via an NTP server with GPS connection.

Using the R&S®ETL test receiver, the test team evaluated the receive situation with respect to level, constellation, MER, spectrum and impulse response at all measurement locations. The Bavarian Broadcasting Corporation test vehicle was equipped with a horizontally polarized omnidirectional antenna with a known antenna gain or k factor. A precision attenuator was attached to attenuate the input signal in precise increments. The R&S®ETL and other consumer receivers were connected alternatingly to the attenuator. On each receiver, the test team measured the maximum possible attenuation of the signal or fall-off-the-cliff point with a resolution of one tenth of a decibel – at each measurement location and with various network configurations (SISO, MISO, etc.). This attenuation value was determined based on manual visual and acoustic evaluation of the receiver’s video and audio signals. The higher this value, the better the particular receiver was able to handle the receive situation or the set network parameters.

Technical Parameters of the Field Test

  • Frequency: 706 MHz, channel 50
  • Transmitter sites in the SFN Freimann: 5 kW ERP, 800 W transmitter output power, 110 m omnidirectional antenna Ismaning: 5 kW ERP, 600 W transmitter output power, 210 m directional antenna SW BR broadcasting center: 5 kW ERP, 600 W transmitter output power, 90 m directional antenna NO
  • Ismaning playout center: with live content adjusted to the data rate (SD and HD programs from ARD (German Public Broadcaster) and the Bavarian Broadcasting Corporation), first with T&M components, then with standard headend components and finally with the new R&S®AVHE100 headend from Rohde & Schwarz
  • Transmitter operating parameters usually 32 K ext., coderate = 2/3, g = 1/16, MPLP with one PLP (T2 network parameters were varied)

Summary

The field tests delivered useful, practical information about numerous design parameters in DVB-T2 SFNs. This information can be used to optimize network coverage.

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