چكيده لاتين :
The potentialities of chaos to secure transmitted messages in digital
communications has been proved. This by use Direct Sequence Code Division Multiple
Access (DS- CDMA) system using chaotic spreading sequences. Two synchronization
methods for Chuaיs digital chaotic generator, are presented: the master-slave
synchronization and the impulsive synchronization. In the first method, the driving signal is
continuously transmitted from the driving to the driven system. In the second method,
impulses from the driving system are transmitted to the driven one, by means of a time
division scheme. A more robust digital chaotic codec is then developed to increase the
complexity ofthe chaotic digital signal. The later is based on the general structure Penaudיs
codec and Freyיs modified codec, associated with the technique of dead-beat chaos
synchronisation developed by Angeli. Contrary to the others, the proposed codec is suitable
to pass-band modulation. Comparison between these methods is achieved. The principle of
the secure communication systems and the general chaotic QAM modem are presented.
