Noise Phase Shift Keying for Secure Multiuser Code Division Communication Systems

This paper shows that the noise signals can be used to carry users´ information in a code division multiple access (CDMA) system. The random sequences, which have the Gaussian distribution of their samples, can be efficiently used to spread and encode the users´ messages given in binary form. A mathematical model of this system, called the noise phase shift keying (NPSK), is presented and the expression for the probability of error is derived. It was shown that this probability depends on the number of users as well as on the spreading factor used in the system. Because the transmitted signal is a sum of the random signals the security of the communication system can be enormously increased. It is shown also that this kind of spreading can be used also in a single user spread spectrum communication system