This last circuit is known as a "symetric binary channel" with error probability of 1/4.
Try to experiment by sending each signal twice: for example if you want to send an A, you should send AA; discuss what happens in this case.
Discuss also the case of sending three times each symbol. Is it possible to detect some errors, sending more symbols? And what about being able to correct errors??
AuthorAndrea Valente - Aalborg University in Esbjerg - DK
C-cards projecthomepage: http://c-cardsdev.sf.net