Code-division multiple-access communication system providing enhanced capacity within limited bandwidth

A transmitter for a code-division multiple-access spread-spectrum communication system, comprising:

• a pair of spreaders for spreading symbol data by a first spreading code and for spreading identical symbol data by a second spreading code to generate two baseband transmit signals;
• a carrier generator for generating two mutually orthogonal carrier signals;
• a pair of product modulators, coupled to said carrier generator, to modulate said two mutually orthogonal carrier signals by respective baseband transmit signals, thereby generating two radio-frequency signals;
• a waveform combiner, coupled to said product modulators, to combine said two radio-frequency signals into a single radio-frequency signal;
• and
• a transmitting antenna, coupled to said waveform combiner, to transmit said single radio-frequency signal.

A receiver for a code-division multiple-access spread-spectrum communication system, comprising:

• a receiving antenna for receiving a radio-frequency signal;
• a carrier generator for generating two mutually orthogonal carrier signals;
• a product demodulator, coupled to said carrier generator, to demodulate said radio-frequency signal by multiplication with one of said two mutually orthogonal carrier signals, thereby generating a baseband receive signal;
• another product demodulator, coupled to said carrier generator, to demodulate said radio-frequency signal by multiplication with the other of said two mutually orthogonal carrier signals, thereby generating another baseband receive signal;
• a first correlator, coupled to one of said product demodulators, to correlate one of said baseband receive signals with a first spreading code, thereby producing a first correlated signal;
• a second correlator, coupled to the other of said product demodulators, to correlate the other of said baseband receive signals with a second spreading code, thereby producing a second correlated signal;
• and
• an adder, coupled to said first and second correlators, to add said first and second correlated signals, thereby generating an output data signal.

A transmitting method for use in a code-division multiple-access spread-spectrum communication system, comprising the steps of:

• generating first and second spread signals by spreading an input signal with a first spreading code to obtain the first spread signal and spreading the same input signal with a second spreading code to obtain the second spread signal;
• generating a first modulated signal from the first spread signal and a first carrier signal;
• generating a second modulated signal from the second spread signal and a second carrier signal, the second carrier signal being orthogonal to the first carrier signal;
• and
• combining the first modulated signal and the second modulated signal before transmission thereof.