It is interesting to see the responses to my statement on the difficulty of machines copying CW better than humans. Although this is a little off-topic here, I hope we can have a short discussion of it anyway.
First, the success of negative SNR communications methods such as Olivia,JT65, and PSK31, are evidence that a well-designed computer algorithm should perform better than a human. But it is on codes that have been designed for machine decoding. Second, 'better' may mean many things: faster, many QSOs in parallel, or - what I imply - at lower SNR and under difficult conditions with fading and interference. There is no doubt that a computer has much more capacity for speed and parallel decoding than a human. The steps that a good algorithm needs to do are something like this: - real-time frequency analysis and filtering - detect morse signal and lock on to a particular frequency - adaptive estimation of datarate and adaptive matched filtering for optimal detection - decoding of dashes/dots/spaces into letters - decoding into words The first steps are signal processing such as filtering, detection and adaptivity. See e.g. http://www.journal.au.edu/ijcim/jan99/ijcim_ar1.html for some ideas on the adaptive estimation. As a side remark, Coherent CW, was a way of avoiding the adaptation to variable rate and ease machine decoding, but it does not seem to be a success. I believe that it takes an extraordinary algorithm to lock onto a very weak signal reliably, but even more so to do the last and maybe even the second last step, and that this is where the similarity with speech recognition is largest. As an example, say that my call is a weak DX-call and I'm sending CQ de LA3ZA LA3ZA LA3ZA. On the receiver end you hear DA---, LA3-T, L-3ZA due to fading and interference. This is where a good operator is able to use a priori information on the syntax of a callsign, similarities between morse codes for various letters, and the three partial calls to piece this together to LA3ZA. I'm not saying this is not doable, only that it may take more than a month for a good programmer to do this, and maybe much more also. -- Sverre 2008/2009: F/LA3ZA _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
