Mini fejállomás MMH-3000+ maxi teljesítménnyel

This article is complementary to the Modular Headend TERRA MMH-3000 item describing the basic features of the TERRA MMH-3000 headend.

The characteristics of the Terra MMH-3000+ headend

MMH-3000+ and modern TVs - why to choose DVB-T standard in hotel systems?

How to check the bitrate of a satellite channel/transponder?

Modernization of analog headends for distribution of satellite channels in DVB-T standard

Conversion of DVB-S/S2 signals to DVB-T multiplexes - a case study

The headend is intended for facilities and institutions requiring centralized management of the programming distributed in the SMATV system. No need for additional devices (satellite receivers) connected to the televisions makes this solution particularly attractive e.g. for hotels and hospitals.

A headend or head station is a set of professional satellite (and often DVB-T) receivers, decoders, modulators, remodulators, converters etc. The output signals are distributed over an RF network and can be received by every (suitable) TV set connected to any outlet. Such a system can be installed both in newly built facilities and in existing buildings equipped with typical RF distribution networks based on splitters and taps or done in pass-through arrangement.

MMH-3000+ is a very flexible solution. Depending on the requirements and needs of the investor, it can be used to implement one or more of the following projects:

Depending on the desired outcome, the headend has to be equipped with the appropriate set of modules. All modules are described in detail later in this article.

The base unit UC-380 R81700 houses the components of Terra MMH3000+ headend. It can be put in a 19" rack cabinet. The unit incorporates power supply and cooling system, RF amplifier, and intelligent data bus. It may hold up to 8 individual modules for reception/modulation/transmodulation of various kinds of signals.

Fig. 2a. Base unit UC-380 R81700

Fig. 2b. View of an MMH3000+ headend: the UC-380 R81700 base unit with a set of modules

Before a detailed analysis of the components of the MMH-3000+ headend it is worth paying attention to the fact that almost all the modules have a built-in MPEG2 TS interface (Fig. 3).

Fig. 3. The MPEG2 TS interface implemented in MMH-3000+modules

This interface enables the transmission of the received channels from a whole satellite transponder or DVB-T multiplex between the components of the headend, in the form of a digital MPEG2 stream. Then, each "output" module can be used for selecting a desired channel from the stream in order to provide a modulated RF channel with the required modulation (PAL, COFDM, QAM).

The first module receives all channels from one satellite transponder,

and feeds them as MPEG2 TS to the second module.

The RDC-313 R81712 module receives and converts one satellite channel into PAL channel in terrestrial TV band and provides MPEG-2 stream from the received transponder to other modules.

Fig. 5. The RDC-313 R81710 module

RDC-313 has CI slot enabling - after installing adequate CA module - reception of encrypted programs. If the headend is equipped only with RDC-313 modules, the investor must apply for cards decoding individual channels. The advantage of this solution is higher stability than in the case of multi-stream CA modules.
The built-in VSB modulator with adjustable output level allows for efficient use of RF channels in the distribution system.

DM-313 R81712 modules are used in MMH-3000+ headends that distribute analog RF channels. They are intended to cooperate with RDC-313 receivers. One module decompresses a desired channel from MPEG-2 transport stream provided by the RDC-313 receiver and converts one satellite channel into PAL channel in terrestrial TV band. DM-313 and RD-313 can cooperate with each other only within channels from the same transponder. The DM-313 module has been also equipped with VSB PAL modulator with adjustable output level, which allows for efficient use of RF channels in the distribution system. The use of DM-313 is especially recommended for distribution of satellite FTA channels located on the same transponder.

NOTICE: The range of products also includes RDC-316 R817101 and DM-316 R817121 modules. These modules can receive DVB-S/S2 MPEG-4 signals. The RDC-316 module equipped with a DSB modulator is widely used in the case of headends distributing DVB-T signals. Such a case is presented later in this article.

The MT-310 R81708 modulator allows for injection of external baseband audio/video signals coming from a CCTV camera, DVD player, computer or other device generating audio-video content. On a selected RF channel, the owner of the facility can introduce e.g. commercials.

MMH-3000+ allows for injection of of external baseband audio/video signals coming from a CCTV camera, DVD player, computer or other device generating audio-video content in the form of digital DVB-T multiplex. The operation is performed in two stages, by converting analog video/audio signals coming from the sources into MPEG-2 coded transport streams in the MPEG-2 encoder MD-330 R81713, and then feeding them to the TRX-360 R81709 DVB-T modulator (COFDM) that distributes them in an RF network as channels in the DVB-T multiplex.

Fig. 7. Application of MD-330 and TRX-360 modules for injection of external signals as a DVB-T multiplex

The MD-330 encoder allows for simultaneous conversion of three analog signals into three transport streams with bit rates from 0.5 Mbps to 15 Mbps (each channel). Depending on the kind of source signal, each stream can have variable (VBR) or constant (CBR) bit rate.

The mentioned above DVB-T modulator TRX-360 R81709 is a powerful tool allowing for creation and distribution of "private" digital DVB-T multiplexes. It can (re)multiplex up to 6 transport streams (MPEG-2 TS) from any modules of the TERRA MMH-3000+ headend and convert them into COFDM modulated DVB-T RF channel (mux). The multiplex may include selected DVB-S/S2 satellite channels (from different transponders or even satellites), DVB-T channels, and signals from CCTV cameras or media players (see the section above).

Fig. 9. Remultiplexer and DVB-T Modulator TRX-360 R81709 with 6 MPEG2 TS inputs

Distinguish features of the TRX-360 modulator:

Planning the set of channels in a DVB-T multiplex, the installer has to take into account the bit rates of the channels that are to be distributed in the network. This is mainly due to the limited capacity of digital multiplexes. As mentioned above, the maximum capacity of a DVB-T multiplex with the guard interval of 1/32 and FEC of 7/8 is 31.66 Mbps. The assumption that such multiplex can carry six SD channels or two HD channels is generally true, but there may be exceptions. So, how many SD or HD channels can be put in a single multiplex?
There are several ways to solve the problem. The simplest one is to visit services like www.digitalbitrate.com or www.linowsat.de. They offer a range of statistics for multiple channels and transponders from all popular satellites, especially Hotbird and Astra. The statistics for individual channels can be recalled even up to a year back.

Fig. 13. Historical data from the www.linowsat.de website - maximum bitrates of some SD channels broadcast from Hotbird satellite on Jan. 22, 2011.

Knowing the bit rates of the channels that are to be distributed, the installer can appropriately select the components of the headend and configure the system.

The TRX-360 R81709 module has been designed to enable easy and fast adaptation of working analog TERRA headends to digital DVB-T standard. There is no need to purchase a new base unit or new satellite receivers/transmodulators.

Fig. 15. Simple adaptation of analog MMH-3000 headend to DVB-T. So far, the headend redistributed 6 satellite channels in the form of analog PAL channels. After equipping the base unit with the TRX-360 R81709 DVB-T modulator, any selected channels can be placed on a DVB-T multiplex. Interestingly, there is no need to switch off the analog PAL channels. What's more interesting, it is possible to distribute two independent channel packages, the analog one and the digital, with completely different content.

The requirements for a modern headend include the ability to receive satellite SD and HD channels (also encrypted ones) and redistribute them in the DVB-T standard.
Below we present an example implementation of TERRA MMH-3000+ headend in a hotel. This example shows how to select the individual components of the headend that are to perform the required functions.

The programming capabilities of the presented headend:

Fig. 16. Application of MMH-3000+ headend for the distribution of selected SAT TV channels in digital DVB-T standard. The output signals include eight DVB-T multiplexes (5 from TDX-311R81711 modules and 3 from TRX-360 R81709 modulators). The encrypted satellite channels are received in DVB-S standard. If they were broadcast in DVB-S2 standard, it would be necessary to replace the RDC-313 R81710 modules with RDC-316 R817101 ones.