I have just tested my MAP decoder in loopback mode with no noise for the first time. Needless to say, it doesn't work! I am getting a BER of about 0.06 with a PRBS sequence. I had to invert my output to get this BER (trust me to pick the wrong one!). It would have been great to have the decoder work the first time, but I am still very happy for the decoder to produce an output that the BER test set could at least synchronise to! There are 64 pages of schematics that data stream goes through, so I think this is a good first step. Now I'll have to haul out the logic anaylser to find what's causing the problem. I'll let you know when I get a dramatic reduction of errors.
All the best,
Steven S. Pietrobon, Satellite Communications Research Centre
University of South Australia, The Levels SA 5095, Australia.
steven@spri.levels.unisa.edu.au
http://www.itr.unisa.edu.au/~steven/