Information security aspects of spread spectrum systems

Abstract

Recently spread spectrum systems have been intensively studied and developed for new commercial applications in cellular mobile communication networks and wireless personal communication networks. This is because they have some advantages such as robustness against interference and noise, low probability of intercept, anti-jamming property, high communication capacity per frequency and so on. Some of these features have given spread spectrum systems reputation that they have high information security. A purpose of this paper is to examine this reputation. It is often claimed that in some spread spectrum communication systems, noise and interference have much higher power than the desired signal so that any opponent who does not know the spreading mechanism cannot detect the signal. It is shown, however, that the knowledge of the spreading mechanism gives legitimate users at most about 5 dB advantage of signal to noise ratio over opponents. Therefore, in order to protect privacy, it is recommended to encrypt transmitting data. From the viewpoint of privacy, untraceablity is also important. We propose a registration protocol for cellular systems to keep users unidentified by opponents. From the aspects of information security, the most significant feature peculiar to spread spectrum systems is anti-jamming property. We discuss some designing methodology for spreading mechanisms to strengthen this property.