mac@idacrd.UUCP (Robert McGwier) (07/18/90)
RE: DSP Mania and books on the subject Howdy: Many people send me notes asking what DSP texts should be considered for an introduction. They always want the impossible however. One that is trivial to understand, does not require mathematics, and tells them how to write V.32 full duplex echo cancelling modems with the fastest Viterbi trellis decoder on the planet or does all the ham radio modes without operator intervention ;-). It should be clear that all these goals are contradictory (I don't want to say mutually exclusive even if I do personally believe this). I have two favorites, which show my bias towards modems. Theory and Practice of Modem Design by John A.C. Bingham, Wiley-Interscience and Digital Communication by Edward Lee and ??? Messerschmidt. (I can never remember Messerschmidt's first name or initial). I've forgotten the publisher and I left the book at home. All the other applications that I need to do code for (speech encoders, FFT code, etc.) can be sewn together from the code given away by the chip/board manufacturers. There are no real practical `how to' books that give code examples to aid you in putting together modems that I know of with the single exception of a booklet put out by TI. The individual chip manufacturers run BBS's, have PD libraries with loads of source,etc. and TI has put out a booklet for a 300/1200 bps telephone modem. This booklet has source, little aid in putting it together as a working system, and almost no information on the criteria which went into the modem design. It also uses 1st generation DSP chip technology from TI and a major translation job is required. Motorola has given away source for a V.32 trellis Viterbi decoder for the DSP56001. Not included is the rest of the modem which includes the difficult equalization, near-far echo cancellation, and data aided carrier recovery for the `non-round' constellation. The technical discussion given with the V.32 trellis decoder is appallingly bad. Don't hope to understand what is being done on the basis of what is in this booklet. Having written these decoders for a number of projects (always before in a high level language) I became so confused that I decided to start from scratch, but it is there for the taking. I am certain that I am being thick and just didn't like the exposition. Maybe for you it will all be crystal clear. It can be gotten from any Motorola Semiconductor division outlet from their tech manual/ reference works library. Just walk in grab a plastic bag (paper sack if you are environmentally conscious) and walk out with more books than you can carry. I am sure that TI does the same, I just haven't had the opportunity to do this yet. TAPR and AMSAT are working on DSP hardware for amateur radio modem use and will consist of a TMS320C25 plug in card with 85C30 for protocol work. There is code available from the TAPR AMSAT project available for anonymous ftp on tomcat.gsfc.nasa.gov. This code was written for the Delanco Spry TMS320C10 boards we were using at the time. I am sure it will be translated to the 320C25. I hope this helps some. Bob McGwier <N4HY> -- ____________________________________________________________________________ My opinions are my own no matter | Robert W. McGwier, N4HY who I work for! ;-) | CCR, AMSAT, etc. ----------------------------------------------------------------------------