Raising capacity

How OSN boosted its satellite capacity by more than 20% at no extra cost
Mohamed Said Zerari, technology specialist at Dubai-based Pay-TV broadcaster OSN.
Mohamed Said Zerari, technology specialist at Dubai-based Pay-TV broadcaster OSN.

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With demand for HD soaring and data capacity at a premium, Mohamed Said Zerari, technology specialist at Dubai-based Pay-TV broadcaster OSN was keen to explore ways of maximising the potential of the company’s existing data resources.

However, as Zerari explained, the key challenge was to find and implement a technique that would expand capacity without compromising quality and without having to replace the current set top-boxes.

“OSN is a company where the capacity demand is increasing every day and we are looking for the best ever video quality, and if you have an OSN set top box, the quality is clear with perfect HD,” he said.

“We needed larger bandwidth for SD and HD channels, especially as most of the channels are now converting to HD and we are also looking to 4K in 2016. For these reasons I started looking at how to optimise the resources and get more bandwidth within the same transponder or space capacity at no cost.”

Zerari was aware of new techniques to increase capacity at the modulation stage. OSN invested in a Newtec M6100 Modulator in 2014 and Zerari was aware that, with a software release from Newtec later that year, it would be theoretically possible to increase the data rate on OSN’s satellite capacity by about 20%.

However, the process, called Automated Equalink was released in October 2014, and so Zerari was excited to test it on satellite. After gaining the required licence, Newtec support loaded the software into OSN’s M6100 modulator.

The first step of the project was to assess OSN’s existing STBs with their different chipsets, as the Equalink software from Newtec would have to be tested on the existing STBs and across OSN’s footprint in the MENA region.

“The idea first of all was to calculate our link budget to see where we are: the satellites’ downlink power, the performance of the dishes, coaxial cables and the different type of LNBs. We buy from vendors who give us exactly the specification we need because most of our channels are HD and we are on the higher modulation index, which is 8PSK modulation. This requires higher carrier-to-noise ratio and of course less data errors,” he said.

The second step was to start looking to optimise the capacity by increasing the data rate on a single transponder and test the results across OSN’s footprint. “Our network is not only on one single satellite, it is on three different satellites: Nilesat, Eutelsat 7 West A and Eutelsat 8 West C.”

In terms of installing the Automated Equalink software, Zerari said that it took a couple of weeks to do the necessary preparations, and for the Automated Equalink SW to be released to perform the indoor tests. He then used a transponder on one of the satellites, which was free for use for a couple of weeks, to run real tests.

“Because we had that transponder for a couple of weeks, we took the chance to transmit test carrier fully loaded and then we measured its downlink performances within the footprint of MENA where we have customers. We received good feedback from North Africa and the GCC.

The feedback was even good from the satellite downlink footprint spill over, such as southern Spain, Southern Italy and Cyprus. In fact, the tests revealed a 22% increase in capacity on a single transponder, from 53 megabits to 65 megabits,” Zerari said.

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Another important part of the tests was to ensure that the increased data rate, which requires greater signal quality, would not affect the existing customers that are located at the edge of the footprint. Tests revealed that existing customers were unaffected by the change. Zerari also stressed that another advantage of the Automated Equalink system was that there was no need for OSN to change the current set top boxes.

“We keep our existing set top boxes, existing antennas, cabling and so on. We have a higher data rate and it doesn’t cost us anything,” Zerari added.

Zerari worked with other members of OSN’s technical team in offices around the region on the tests, and also with engineers at Du teleport in Dubai and with the satellite operator Nilesat.

“In coordination with the satellite provider, Du teleport and Newtec support, we started the line-up tests to determine the optimum gain step setting on the transponder that would provide the best carrier-to-noise margin on the ground.

It was necessary to reload the Automated Equalink SW after each adjustment of the transponder’s gain step, which requires about 20 minutes to be completed. In this way we were able to determine the optimum transponder’s gain step adjustment and the best Automated Equalink setting on the modulator for the best carrier-to-noise margin. Then we had to move on and do a survey within the whole MENA region, and this is what took a long time,” Zerari said.

With 22% additional data rate added to a single transponder, OSN is effectively able to broadcast an additional two HD channels from each transponder at no extra cost.

“Before we could broadcast seven HD channels from each transponder, now we can broadcast nine. This means that OSN will end up having about 12 transponders and then you add 22% capacity and you have about 120 megabits at no additional cost, which is more than one and a half transponders. This means a big saving,” Zerari said.

“The DEMO licence from Newtec that was loaded into our M6100 modulator did help me to increase the current data rate by 22.70% within the 33 MHZ transponder bandwidth,” Zerari said.

“Initially I was interested to know more about the DVB S2X modulation scheme, but with the Automated Equalink, the roll-off of 10% and the transponder gain step adjustment that was done in coordination with the satellite operator, it was possible to achieve the 22.70% additional data rate within same transponder at zero cost to OSN.

“I can say that OSN is the first ever DTH Pay-Tv broadcaster in the region who has used the Automated Equalink technology on one of its DTH transport streams.”

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Equalink explained
Equalink 3 is a linear and non-linear pre-distortion technology implemented in Newtec DVB-S and DVB-S2 modulators, designed to compensate for the effects of imperfections in the filters and amplifiers of the satellite.

This pre-correction improves the performance of the end-to-end satellite communication channel by a typical 2 dB and allows the use of higher modulation schemes such as DVB-S2 16APSK or 32APSK on carriers occupying a full transponder.

For Direct-to-Home broadcasting applications, Internet backbones and other high speed satellite applications, this performance improvement represents up to an additional 15% of data traffic in the same satellite capacity.
Equalink 3 is a set of advanced digital filters and algorithms implemented in the modulator.

The linear filter compensates for group delay and frequency response imperfections of the satellite input multiplexer (IMUX), while the non-linear pre-correction compensates for the combined effect of matched filters and transponder TWTA nonlinearities (AM/AM and AM/PM conversions)

Equalink 3 can be used in conjunction with any standard satellite receiver and is very easy to operate

 

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