Higher-Level Multi-Carrier Modulation
V. Aue, Gerhard Paul Fettweis · 1996
We introduce a CDMA system based on multi-carrier spread spectrum (MC-SS) with one iden- tical code for all users. If the signals are transmitted inside the coherence bandwidth, a pair of surface acous- tics wave (SAW) filters can be used for both spreading and despreading the signals at low cost. In general, the employment of a multi-carrier trans- mission technique increases the dynamic range of the correspondent lowpass time signal, and therefore would require a highly linear power amplifier. By carefully de- signing the code of a MC-SS signal a significant decrease of several orders of magnitude in dynamic range can be obtained. The spectral properties of the multi-carrier signal are not affected by the code. In some spread spectrum systems, it is desired to sup- port different data rates over the same modem. In the SAW filter approach, neither spreading code nor spread- ing gain can be altered. The reduced dynamic range of the unmodulated multi-carrier signal, however, can allow for a multi-level modulation of the narrowband signal for higher rate transmission if the signal-to-noise ratio (SNR) is sufficiently high. Different implementa- tions for MC-SS are shown in this paper.