Design of large signal set for DSCK modulations

Cabled computer networks have been installed in many applications as data transmission systems. Today, however, portable, handheld or vehicle-based data terminals are also required. The wireless local area network (WLAN) uses radio transmission to replace the cable connections in order to provide flexibility for the overall system. Because the Radiocommunications Agency (RA) has progressively exempted various high frequency ranges in the UK from licensing over the past few years, frequency bands where WLANs can be operated without registration are now available. In order to avoid interference, the transmitted power or power spectral density is limited in these frequency bands. The multipath propagation problem which causes serious performance degradation in mobile and/or indoor radio applications can be also avoided if the information signal to be transmitted is spread for transmission. The conventional solution to this problem is to use spread spectrum (SS) techniques. These, however, require relatively complex circuitry and have relatively high power consumption. In chaos communications the digital signal to be transmitted is mapped to a wideband chaotic signal. These systems can be implemented with extremely simple circuitry and offer an alternative solution to licence-exempt radio applications. The differential chaos shift keying (DCSK) technique is a robust chaotic modulation scheme, where the demodulation can be performed without synchronization. This paper shows how the multilevel modulation technique can be used to increase the data rate of the DCSK modulation scheme.