| In ordinary DS-CDMA communication systems all users transmit their information using their own basis signals, which are orthogonal to each other. These basis signals can be pseudo random sequences with good orthogonal characteristics, Walsh functions, wavelets or chaotic sequences. These sequences allow spread spectrum characteristics of the transmitted signals and enhance the security of the communication system as well as anti-jamming protection of the system. This paper shows that pure 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 expressed in binary form. The system is supposed to have the best possible masking property of the trans-mitted information contents and the best possible protection of the information contents.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 systems system. After Introduc-tion, the characteristics of the transmitter signal-processing blocks are explained in second Section. In par-ticular the characteristics of the noise signal generators, which are carrying users’ information, are analyzed. In the third Section the receiver structure and the its mathematical model are presented, and the expression for probability of error is derived. The simulator of the communication system and results of simulation are presented in Section four. The conclusions are in Section five. |
| Stevan Berber was born in Stanisic, Serbia in 1950. He completed his undergraduate studies in electrical engineering in Zagreb, master studies in Belgrade, and PhD studies in Auckland, New Zealand. Before coming to the academic world he was working nearly 20 years in research institutions and in telecommunication industry having research interests mobile communication systems and digital transmission systems ISDN networks. At present Stevan is with the University of Auckland in New Zealand. His research interests are in the field of digital communication systems (modulation and coding theory and applications), in particular CDMA systems and wireless computer and sensor networks. His teaching interests are in communication systems, information and coding theory, digital signal processing and computer networks. He is an author of more than 50 referred journal and international conference papers and 7 books. Stevan has been leading or working on a number of research and industry projects. |