With the change from DVB-S to DVBS2, a more efficient method was created that permits more channels to be carried over one and the same transponder. This increase in efficiency is due in large part to the significant improvement in error correction so that fewer error correction bits need to be transmitted. From a mathematical point of view the increase in efficiency compared to DVB-S is roughly 30%, a value that in reality isn’t quite reached, but it is definitely showing potential.
There are a variety of ways that programming can be transmitted. With DVB-S and for the moment also with DVB-S2, it’s mostly CCM (Constant Coding and Modulation) that is used. In this process the programming organizer selects a fixed error correction and modulation process with which every receiver within a satellite’s footprint can receive a usable signal with a reasonable amount of effort. If the programming organizer wants to also be able to reach as many viewers as possible at the edge of a satellite’s footprint, he chooses an all around correction process so that these users can also obtain an acceptable signal. If the provider is looking to reach only those viewers in the heart of the footprint, he’d choose a less costly error correction.
The operator has to make some decisions. But how? It would be much more efficient and the operator could avoid having to make these technical decisions if the signal was transmitted in exactly the same way that it would be needed by the receiver.
This is precisely the strategy behind VCM (Variable Coding and Modulation) as well as ACM (Adaptive Coding and Modulation): the entire bandwidth of a transponder is split into multiple segments and through the use of various modulations and error correction processes, these bandwidth segments would be filled with different programming content corresponding to the available bandwidth. For receivers in the heart of the satellite’s footprint, a very small error correction and highly efficient modulation process could be used so that a relatively high data rate could be achieved. At the same time, the lower the signal level along the edge of the footprint, the better the error correction and more reliable modulation that could be used.
This all takes place within one transponder, that is, one and the same transponder transmits through VCM different modulation and error correction processes! We’re referring in this case here to MIS (Multi Input Streams). With MIS a satellite receiver can receive multiple transponder streams from one transponder that are transmitted completely independent from each other with differing modulations and error correction. The idea behind all of this is that depending on the reception location, not every transponder stream from a transponder can be received. The end user can only receive signals that are strong enough at his location. This means that the receiver would automatically measure the signal and use these values to determine which transponder streams it could process and use.
A VCM target area could look something like this: in the heart of the satellite’s footprint the available TV channels would be receivable in HD or 3D while on the outer edge of the footprint these channels would only be available in SD; all of this would occur over one single transponder. The TV viewers in the center of the footprint would profit from the higher data transmission rates while the viewers on the footprint’s edge could still receive the signal with smaller antennas thanks to the more complex error correction and the more reliable modulation that would be used, it just wouldn’t be HD or 3D. It’s important to note that no return channel from the receiver is necessary with VCM while ACM is geared more towards studio transmissions (feeds) since here the reception quality of the return channel has to be taken into consideration and the modulation and error correction are matched from the transmitting end.
This transmission technology is so new that VCM or ACM transponders cannot be received by most DVB-S2 receivers. Once more PayTV providers have switched over to this new VCM method or have begun some intensive testing, we can assume that more and more receivers will support this clever system that optimizes a satellite’s bandwidth use. There’s already an exciting opportunity to receive this new transmission technology: the PC card manufacturer Tenow has already integrated this technology in its professional PC card TBS6925. An initial test report on the TBS6925 was presented in the 10-11/2011 edition of TELE satellite. Now we can actually take a closer look at the MIS capabilities of this PC card.
If you try to look for ACM/VCM transponders in your favorite Internet satellite list, you won’t have much luck. Most providers of this kind of information have not included this data in their lists simply because there’s hardly any reception hardware available that can receive these transponders. So the first you would do is to search for ACM/VCM transponder using blindscan tools such as CrazyScan and TBS Blindscan.
Once you know transponders available with your reception setup, you have to start the TBS6925 TS recorder. This program, that we also introduced to you in the 10-11/2011 issue of TELEsatellite, can be used as an aid in selecting the desired transport streams. After entering the parameters of the MIS transponder (frequency, polarization and symbol rate), you then simply need to click on the “Lock TP” button after which the software reads the desired transponder.
In the lower most lines of Tools, one or more numbers appear in the field”Input Stream Identify “that highlights the available transponder streams in the transponder. Here you simply make a choice and click on one of the entries. You can now stop the TBS6925 TS recorder and start any of the popular TBS6925 compatible TV viewers. For our tests we opted to use DVBViewer. Simply start a scan on the frequency of the MIS transponder, the software will then read in the available channels and store them. With that you’ve read in the first of multiple transponder streams on that transponder. Now you would repeat these steps as often as necessary until all the streams in the„Input Stream Identify“ field have been selected and read in. You’ll be amazed! With each newly selected stream the TV software will recognize an entirely new set of channels, all on the same frequency!
For our tests we used the 12718 MHz transponder on ATLANTIC BIRD 1 at 12.5° west on which are four fully independent transponder streams that each carry their own set of programming. The bandwidth is enough for 11 channels in SD resolution or up to three in HD or 3D. Naturally, all of the typical features, such as EPG or language selection, are available with MIS reception. The only difference with CCM is the number of available transponder streams per transponder.
The abbreviation MIS is something we’ll all have to start getting used to seeing more often. Gradually, more and more programming providers will begin taking advantage of this new technology and once this happens the need for compatible satellite receivers will naturally grow.
Next article: TBS6925 Test Report DVB-S2 MIS Reception