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>
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My opinions are my own no matter | Robert W. McGwier, N4HY
who I work for! ;-) | CCR, AMSAT, etc.
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