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Turbo Codes Promise Better Wireless Transmission
captain igor writes "IEEE is running a story about two French professors that have created a new class of encoding, called 'Turbo Codes,' that will allow engineers to pass almost twice as much data through a given communications channel, or equivalently, the same amount of data at half the power. The new codes allow the Shannon Limit (the theoretical maximum capacity of a channel) to be approached to, currently, within .5 dB. Scientists hope that this breakthrough will revolutionize wireless communications, especially with the coming reclamation of large swaths of the EM spectrum." As the article points out, such codes are in use now, but seem poised for much wider implementation.
I knew about it, as did many other people. But you have to realize that coding theory is a pretty funny and insular field. Related techniques had been used in other fields for many years prior to that discovery. Most people who work in this general area of statistics simply don't think about coding and aren't interested in it. One of the obstacles is that people who build communications systems generally are engineers thinking about fast, low-level processing; their first reaction to anything non-trivial and new is that it's too slow to be implemented in practice.
Turbo coding is ultimately not much of a theoretical breakthrough, but a compromise and algorithmic hack that happens to work fairly well for real-world problems and is expressed in a language that people who work on communications systems understand. But that's nothing to be sneezed at, since it will ultimately mean that we will get higher data rates and other benefits in real-world products.
Just because a company's revenue continues to grow doesn't mean that company's profit margin is a constant percentage... A multi-billion dollar corporation could very easily be making only five-hundred thousand in profit. Despite the size of the comany, adding another five hundred grand to their profit is still twice what they were making.
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Right, Gallager worked out LDPC codes in 1963. Then they were forgotton for 20 years until people realized that Digital Fountain's "Tornado" codes were LDPC codes.
LDPC codes will be behind DVB-S2, the new transmission system for digital satellite video distribution. Since they approach the Shannon limit so closely, there will be no DVB-S3.
I should say that the IEEE article is a little over-hyped, in that these codes really only buy about 2-4 dB additional gain, concatenated RS and convolutional coding were pretty close to the Shannon limit in AWGN, but those last couple of dBs were nice, but the remaining 0.5-1 dB beyond LDPC & Turbo Codes isn't worth much.
Much more important now are ways to handle "fast fading" channels found in mobile environments, this is what is driving OFDM.
Also, both Turbo Codes and LDPC codes are really computationally intensive to decode. They are currently only decoded at speeds below 20 Mbps, generally implemented as (expensive) FPGAs. We won't see real cheap ASICs for another year or two.