Friday, December 21, 2012

Progression of Modulation

When satellites first became commercially available for television broadcasts, analog transmission was the standard way video was sent.  Analog uplinks require large bandwidth- typically no less than 18MHz but often a full 36MHz transponder was used.  Large bandwidth requires large antennas and power, meaning a small portable uplink was limited to only one, or sometimes two paths, or channels on the uplink.

In the late 1990s, DVB-S, or Digital Video Broadcasting for Satellite- became more common.  A DVB-S uplink is made up of two main parts- the encoding and modulation.  Encoding is the process of converting the analog or uncompressed digital video- known as baseband- into a compressed format more easily sent over the limited bandwidth of a satellite uplink.  Modulation takes these digital bits and sends them over a radio frequency.  The most simple form of digital modulation is Morse code, turning a signal on and off to spell out letters.  Modulation used for DVB is far more advanced, and always improving, finding better ways to transmit more data in less bandwidth.  A typical uplink in 1998 used QPSK- which stands for Quadrature Phase Shift Keying, where each "symbol" of the uplink signal can represent 4 states for two bits per symbol by adjusting the phase of the RF carrier.  DVB includes FEC, or Forward Error Correction, which allows a receiver to produce a error-free output despite noise or other interference.  The FEC is expressed as a ratio, from 1/2 to 9/10 being common ratios.  1/2 means 1 out of every 2 bits is a data bit, and 9/10 is 9 out of 10 are data bits, the rest is the error correction overhead.  A signal uplinked with 1/2 can be received at much lower levels than 9/10, but the trade off is there is much less usable data available in the channel. 
QPSK modulation constellation

DVB also includes several QAM modes, which changes the amplitude of a signal.  Uplinks that use QAM modulation can carry more information in the same bandwidth.  There is no free lunch, and the tradeoff of putting more data in less bandwidth is the signal gets harder to receive, and requires larger antennas to "pick up" more of the signal.  Just as its harder for your eye to differentiate between 16 shades of a color compared to 4 shades, the same holds true for satellite links.  It gets even worse with even higher levels that have more "shades", such as 64QAM. 

16-QAM modulation constellation



64 QAM modulation constellation.  More "states" per symbol makes it harder to "see" what is being sent. 



Published in 2003, the second generation improvement to the DVB standard, known as S2, was created.  DVB-S2 has many improvements over the older DVB-S (now sometimes known as S1).  More efficient error correction allows more data at lower signal levels, more FEC ratios to choose the most optimal error correction level, and more modulation constellations to pick from. 
8PSK modulation is very common in DVB-S2 uplinks, and allows about 61% more data to be transmitted compared to the same signal in QPSK.  However, because of the more efficient error correction, 8PSK requires about the same signal level as DVB-S QPSK!   If signal level is an issue, DVB-S2 QPSK works at almost half as strong signal levels as DVB-S QPSK. 
8PSK modulation constellation


DVB-S2 also adds more complex hybrid modulations, such as 32APSK, or 32 level Amplitude and Phase Shift Keying.  Unlike QAM, which is very susceptible to noise, APSK combines the better noise performance of PSK with the higher levels available in QAM.   Comparing two 16-level constellations- 16APSK and 16QAM, the APSK mode requires 2.6dB LOWER (almost half) power than the QAM signal, and still carries 7% more info. 




The 3rd generation standard, DVB-S3 promises to include even higher levels- up to 64APSK- with dozens of FEC choices and tighter "roll off", making a sharper-sided signal with more usable bandwidth.  This comes very close to the Shannon Limit, the maximum amount of data that can be transmitted through a channel. 

What does all this mean to you?  DCI's engineers UNDERSTAND modulation.  Unlike companies who simply use the same standards that have been around for 15 years, we know all the tricks and tweaks to make a difficult shot work, or optimize a good shot with incredible quality.  While most uplinkers will simply shrug their shoulders if a uplink is breaking up despite maximum power, DCI knows the right adjustments to make.  In fact, on a recent flyaway in Los Cabos, when 6Mhz 8PSK was not working, DCI knew the margins would work at QPSK with 12MHz.  We can also apply the same technology to save money on sat space.  No matter if its a flyaway, satellite uplink truck, or teleport service, let DCI put our extensive know-how and experience to work for you. 


Wednesday, December 12, 2012

To fly-away... or not?

If you're going to hire a flyaway to cover an event, how will it get there?  Checked baggage?  Unlikely, unless its a Diversified Communications ATA-compliant system!

When DCI brought the first commercially-viable redundant flyaway system to the market in 1988, sending the system to a location typically required specialized freight airlines.  If it was a breaking story, the only way in would be an expensive private charter.  While we still use charters for special circumstances (commercial airlines not operating to an area), and freight forwarders are excellent for dealing with customs, they often need two weeks to get a shipment from DCI to the location.  Freight is excellent when working a pre-planned event, but for breaking news it is not a good shipping solution.






DCI's first 1.5 meter flyaway. Engineer with short-shorts is included.   ->
<-Kalitta Air DC9 brings DCI's flyaway to Lima Peru in 1996.

In the early days of satellite newsgathering, everything was done with analog transmission, and combined with the fact that flyaway jobs were often in areas with poor satellite coverage, flyaway dishes were very large to get the required signal level into space.  This typical 2.4 meter dish alone has a half-ton shipping weight, more than twice what our current package weighs for dish and electronics!  The 2.4 requires freight forwarders, and is beyond the capacity of all but heavy charter jets.  Despite all the size and weight, the 2.4 would be able to run one only single analog path.  Today, DCI has run as many as 8 paths off a 1.1 meter dish, and carried it as checked baggage!
1100-lb 2.4 meter flyaway antenna. You're gonna need a bigger plane!


The switch to digital has had the greatest effect on flyaway systems.  Digital signals require less power than their old analog counterparts, meaning smaller dishes can be used, which increases and simplifies shipping options.  MPEG-2 advanced into more efficient MPEG-4/H.264, meaning the same picture quality can be delivered with half the data, again lowering the required power.  Now we can use smaller dishes and lighter, lower-power transmitters.  The next encoding standard, MPEG-HE, for High Efficiency, is due out soon, further improving what our flyaway system can do.  Digital modulation has also greatly improved over the past 10 years.  For example using the old DVB-S (Digital Video Broadcasting-Satellite) standard of 4PSK, we could transmit around 7mbps of data in a 6MHz slot, and it required a Es/No (signal measurement level) of 7.0.  Using the newer DVB-S2 standard of QPSK, we can transmit slightly more data in the same bandwidth, 8mbps, but the major improvement is a much lower signal level is required, only 5.5.  If the signal is stronger, we can pack in more data.  Using the 8PSK modulation scheme fits in 59% more data with the same signal level required for DVB-S QPSK. And if conditions allow we can move up to more complex modulation, known as "higher order", such as 16 and 32APSK.  The standard for DVB-S3 is due out in January and we eagerly look forward to what new capabilities it will bring. The combination of digital encoding and better modulation as allowed DCI to deploy a full airline-checkable HD flyaway.  This greatly reduces shipping costs and logistics.  Its just "grab and go".
DCI 2-path HD flyaway fits nicely on a hotel cart, and was checked as baggage by one slightly-tired engineer who lugged it all through an airport and customs office.
No DC9 needed now- when we are in a hurry, a little Beech Jet gets us there.

But we can still spread out all over the plush seats of a big Challenger 601 and travel in style. 

Many of the flyaway systems available for hire today are the older, larger dishes that will cost a fortune to ship and require weeks of transit time.  And many of the newer ones that are smaller do not carry the advanced electronics that DCI does, allowing our system to do more with less weight and power.  This is an important consideration when hiring a flyaway company- shipping the system may cost more than the job quote!  We recently shipped a 2 path HD flyaway to Mexico for only $350 each way.  As fully credentialed media members, we can take advantage of special media pricing for equipment on some airlines. 


The Air Transport Association (ATA) defines the maximum dimensions and weight that can be checked as baggage on a commercial airliner.  DCI is proud to have an ATA-complient flyaway system that allows us to be in the air within a few hours of a call.  Combined with DCI's full teleport service, we can offer a turnkey transmission solution, from anywhere to anywhere. DCI's flyaway engineers are savvy world travelers who are as comfortable in the news hotspot of the day as they are in a resort hotel. (maybe more so!) So if you need to cover a natural disaster, humanitarian crisis, or just a medical conference on a tropical island, the choice is easy- DCI is the best company to call!



Friday, December 7, 2012

DCI Prepares for Presidential Inauguration


DCI Prepares for Presidential Inauguration

The tradition of a parade down Pennsylvania Ave. from the Capitol to the White House on Inauguration Day dates back to 1829, with Andrew Jackson being the first president to get sworn in on the Capitol steps.  The first broadcast of an inauguration was on radio in 1925, when Calvin Coolidge took the oath of office.  The first televised inauguration came in 1949 with Harry S. Truman.

In 2005, DCI staff monitor the multiple microwave feeds in our old MCR room.


            DCI also has a history of inauguration firsts, including the first in-motion high definition (HDTV) coverage of the parade route.  DCI has been involved in transmitting live in-motion coverage of the parade since 2005.  Our microwave receive point in the Clocktower of the Old Post Office Pavilion is central to this effort.  DCI also has a long history of custom-designing equipment for special events when there are no suitable commercial products, and in 2005 we built a COFDM microwave transmitter and amplifier system totally in-house to provide the network pool operator a perfectly clean feed from the moving “camera van”, which carried a rooftop camera platform and drove ahead of the parade route to broadcast live television images.  In 2005 we used receive antennas on the east and west faces of the Clocktower and a second microwave relay point on a rooftop across from the White House using DCI’s 45mbps ASI microwave links to achieve unbroken coverage of the parade from start to finish.  
Network "Flash Van" for coverage of the parade route


            In 2009 we used the same powerful in-house microwave system, although this time it was refined with a H.264 (MPEG-4) high definition television encoder for the first-ever HDTV in-motion broadcast of the parade route. 
 Lab-bench testing of our custom-built 15W micrwave transmitter.

            For the upcoming inauguration, DCI continues this tradition of transmitting the best coverage of the parade for viewers worldwide. 

To see how DCI Teleport can help you get the picture out with our state of the art microwave high definition transmission system, visit dciteleport.com



45 megabit ASI link from the White House relay back to the Clocktower





Temporary microwave relay for White House