Forward Error Correction – What It’s All About

One thing Mainstream Data has always specialized in is transferring data via satellite. We use a 2-way VSAT satellite network to deliver movies every week to hundreds of movie theaters around the world.

Transmitting large data files through satellite can save huge amounts of time (see our experiment with 20+ gigapixel pictures); however, there are some inherent snags that can come from transferring data via satellite. Sometimes signals can be confused or weather can interfere with a transmission resulting in an incomplete message.

To fix this problem, Mainstream (and just about anyone transmitting data through satellite) uses a technique called forward error correction (FEC). Essentially, this is a method of error control and is used to compensate for missed signals when information is being translated through satellites. The process is quite complicated, but we’ll break it down for you.

When transmitting a file over satellite, we will first add some data to the files. As the sender, we do what’s called redundant coding using algorithms (aren’t we thankful for people who like math? Apparently the math is “fairly deep” when you get into it, but “pretty cool” in its own right according to our CTO). That means we have multiple sets of the code on the information. The next step comes with the receiver.

satellite-uplinkLet’s say that the sender put three sets of the code on the data being sent. That means the receiver gets the message three times. If the code matches up for all three of those, then the receiver knows there was not an error. If one of the three is off, then the receiver uses “majority rules” and takes whichever number there are two of. Remember that computers use 0’s and 1’s, so there will always be a majority. For example, if the sender sent 111, and the receiver received 101, then the receiver would know that 1 was the intended code. Check out this chart for more examples.

Only having three sets is a really poor example, since most likely there would be several dozen, or even several hundred, bits of code to go through. But we hope that it can give you a fairly high-level understanding of how FEC can work. Once the receiver gets the data, the FEC allows them to see if the file was damaged. If it wasn’t damaged too badly, they can fix it. But if its too badly damaged then the file either needs to be retransmitted via satellite, or it may need another means of transportation if the interference is too much. For example, satellite transmission wouldn’t work too well to areas currently getting pounded by the massive rains from Hurricane Isaac.

Mainstream Data’s VSAT program uses this top-of-the-line technology in combination with our own software. FEC is used mostly when sending a large file to multiple people. If you ever need to transfer a large file to mutliple parties, you can do it all from just one platform. Interested? Feel free to get in touch with us.