Secure Communication in Asynchronous Noise Phase Shift Keying CDMA Systems

Abstract

Gaussian distributed random signals are analyzed for encoding and spreading users' message sequences in code division multiple access systems (CDMA). Using theoretical analysis and practical implementation in DSP technology it has been shown that the random sequences generated from the Gaussian distribution can be efficiently used in this CDMA system. In this way the security of the message transmission is enhanced due to the random nature of all signals generated and used for users' message signal spreading and coding in this communication system. The signal processing blocks of the system, including the transmitter, receiver and the channel, are theoretically described. The expressions for the probability of error are derived for the case when the additive white Gaussian noise and fading are present in the channel. The system, including the transceiver and the channel, is implemented in DSP technology and the theoretical results are confirmed by measurements on the designed system. Moreover the acquisition phase of a synchronization block using Gaussian distributed random signals is also theoretically analyzed and implemented in DSP technology.