Noise shaping technique for spread spectrum communications
First Claim
Patent Images
1. A transmitter for transmitting a spread spectrum code division multiple access (CDMA) signal at a system chip rate over a carrier frequency, comprising:
- a single-sideband modulator for shifting the signal spectrum to the edge of the spectrum bandwidth, including;
a first phase shift network for converting the signal into I and Q components;
a second phase shift network for producing a sinusoidal carrier signal and a cosinusoidal carrier signal;
a pair of balanced modulators for receiving sinusoidal and cosinusoidal carrier signals from the second phase shifter; and
an adder for combining the balanced modulator outputs; and
a reference signal input with constant frequency for setting the shifting by said modulator.
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Abstract
A spread spectrum noise shaper uses a modulation technique to achieve a greater signal-to-noise or signal-to-interference ratio (SNR or SIR). The technique doubles the system SIR, in principle. This doubling yields a doubling in system capacity. SNR is increased by receiving the spread spectrum signal in the presence of less noise near the edge of the spread spectrum bandwidth. The technique requires only small additions to a conventional spread spectrum system, in the form of an extra modulator at the transmitter, and an extra demodulator and filter at the receiver.
53 Citations
7 Claims
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1. A transmitter for transmitting a spread spectrum code division multiple access (CDMA) signal at a system chip rate over a carrier frequency, comprising:
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a single-sideband modulator for shifting the signal spectrum to the edge of the spectrum bandwidth, including; a first phase shift network for converting the signal into I and Q components; a second phase shift network for producing a sinusoidal carrier signal and a cosinusoidal carrier signal; a pair of balanced modulators for receiving sinusoidal and cosinusoidal carrier signals from the second phase shifter; and an adder for combining the balanced modulator outputs; and a reference signal input with constant frequency for setting the shifting by said modulator. - View Dependent Claims (2)
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3. A transmitter for transmitting a spread spectrum code division multiple access (CDMA) signal at a system chip rate over a carrier frequency, comprising:
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a single-sideband modulator for shifting the signal spectrum to the edge of the spectrum bandwidth, including; a first phase shift network for converting the signal into I and Q components; a second phase shift network for producing a sinusoidal carrier signal and a cosinusoidal carrier signal; a pair of balanced modulators for receiving sinusoidal and cosinusoidal carrier signals from the second phase shifter; and an adder for combining the balanced modulator outputs; a reference signal input with a constant frequency for setting the shifting by the modulator; a spread spectrum encoder for encoding the shifted signal into a spread signal; and a low-pass filter having a cutoff frequency corresponding to the reference signal input configured to filter the spread signal. - View Dependent Claims (4, 5)
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6. A method for transmitting a spread spectrum code division multiple access (CDMA) signal at a system chip rate over a carrier frequency, comprising:
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shifting the signal spectrum to the edge of the spectrum bandwidth at a single-sideband modulator, comprising; converting the signal into I and Q components at a first phase shifter; producing a sinusoidal carrier signal and a cosinusoidal carrier signal at a second phase shifter; receiving, at a pair of balanced modulators, sinusoidal and cosinusoidal carrier signals from the second phase shifter; and combining the balanced modulator outputs at an adder; shifting by the modulator by a reference signal input with a constant frequency to produce a shifted signal; and encoding the shifted signal into a spread signal; and filtering the spread signal with a cutoff frequency corresponding to the reference signal input. - View Dependent Claims (7)
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Specification