DIRECT SEQUENCE SPREAD SPECTRUM (DSS) COMMUNICATIONS SYSTEM WITH FREQUENCY MODULATION UTILIZED TO ACHIEVE SPECTRAL SPREADING

摘要

Hardware complexity of transmitting and receiving equipment in a CDMA (Code Division Multiple Access) cellular radio transmission system is reduced by the use of frequency modulation (FM) techniques to achieve spectral spreading in combination with signal modulation. The spectral spreading technique of a CDMA cellular radio telephone communications system is generalized by extending the range of values allotted to the spreading waveform code signal to include complex numbers of unity magnitude. This permits the addition (in 307) of a baseband version (at 301) of the information signal and spreading waveforms (from 303,305) instead of the conventional multiplication of the two signals in existing DSSS (Direct Sequence Spread Spectrum) communications systems. The resultant summed signal is used to control a Voltage Controlled Oscillator (309) to produce (at 312) a frequency modulated spread spectrum signal to be transmitted. This arrangement permits improved and more efficient implementations of the transmitting and receiving equipment.