Balanced tranversal I,Q filters for quadrature modulators
First Claim
1. A quadrature modulator for impressing a desired modulation on a radio signal, comprising:
- digital signal processing means for forming an I-signal and a Q-signal representative of a desired radio signal modulation, said I and Q signals each assuming only a single signal value or its complementary value at successive intervals of a sampling clock;
first (I) and second (Q) shift register means for clocking said I and Q signals respectively into a chain of register stages using said sampling clock and producing from each stage a delayed I or Q output and its logical inverse complementary output;
first weighting means connected to selected I-outputs or their complementary outputs of said first (I) shift register and a second, identical weighting means connected to the opposite outputs not selected by said first weighting means, said first and second weighting means producing first and second weighted output signals;
third weighting means connected to selected Q-outputs or their complementary outputs of said first (Q) shift register and a fourth, identical weighting means connected to the opposite outputs not selected by said third weighting means, said third and fourth weighting means producing third and fourth weighted output signals; and
quadrature modulating means having inputs for receiving said first through fourth weighted output signals for impressing said desired modulation on a radio frequency carrier signal.
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Abstract
Radio transmissions are spectrally contained to reduce adjacent channel interference by a method and apparatus for I,Q filtering of signals before quadrature modulation in digital cellular radio transmission systems such as communications systems following the GSM TDMA, IS-54 or IS-95 standards. The filtering is accomplished by multiple stage registers connected at their complementary outputs to identical resistor networks. The outputs of the resistor networks are summed to represent a smoothly transitioning analog representation of the digital voice or data transmission. The analog representation may be additionally low pass filtered to remove higher frequency components before quadrature modulation. Because rapid transmissions in the transmittal signal are avoided, adjacent channel interference is reduced.
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Citations
8 Claims
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1. A quadrature modulator for impressing a desired modulation on a radio signal, comprising:
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digital signal processing means for forming an I-signal and a Q-signal representative of a desired radio signal modulation, said I and Q signals each assuming only a single signal value or its complementary value at successive intervals of a sampling clock; first (I) and second (Q) shift register means for clocking said I and Q signals respectively into a chain of register stages using said sampling clock and producing from each stage a delayed I or Q output and its logical inverse complementary output; first weighting means connected to selected I-outputs or their complementary outputs of said first (I) shift register and a second, identical weighting means connected to the opposite outputs not selected by said first weighting means, said first and second weighting means producing first and second weighted output signals; third weighting means connected to selected Q-outputs or their complementary outputs of said first (Q) shift register and a fourth, identical weighting means connected to the opposite outputs not selected by said third weighting means, said third and fourth weighting means producing third and fourth weighted output signals; and quadrature modulating means having inputs for receiving said first through fourth weighted output signals for impressing said desired modulation on a radio frequency carrier signal. - View Dependent Claims (2)
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3. A code division multiple access spread-spectrum signal transmitter comprising:
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digital signal processing means for coding a speech or data signal for transmission into a digital signal; spread-spectrum coding means for converting said digital signal to an `I` chipstream and a `Q` chipstream at a given chiprate, said chipstreams comprising sequences of signal values or their complements; first (I) and second (Q) shift register means for clocking said I and Q chipstreams respectively into a chain of register stages using a sampling clock equal to said chiprate or a multiple thereof and producing from each stage a delayed I or Q output and its logical inverse complementary output; first weighting means connected to selected I-outputs or their complementary outputs of said first (I) shift register and a second, identical weighting means connected to the opposite outputs not selected by said first weighting means, said first and second weighting means producing first and second weighted output signals; third weighting means connected to selected Q-outputs or their complementary outputs of said first (Q) shift register and a fourth, identical weighting means connected to the opposite outputs not selected by said third weighting means, said third and fourth weighting means producing third and fourth weighted output signals; and quadrature modulating means having inputs for receiving said first through fourth weighted output signals for impressing said code division multiple access spread spectrum modulation on a radio frequency signal. - View Dependent Claims (4)
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5. A method of quadrature modulation for impressing a desired modulation on a radio signal, comprising the steps of:
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forming an I-signal and a Q-signal representative of a desired radio signal modulation, said I and Q signals each assuming only a single signal value or its complementary value at successive intervals of a sampling clock; clocking said I and Q signals respectively into a chain of register stages using said sampling clock and producing from each stage a delayed I or Q output and its logical inverse complementary output; weighting said delayed I output and its logical inverse complementary output to produce first and second weighted output signals; weighting said delayed Q output and its logical inverse complementary output to produce third and fourth weighted output signals; and impressing said desired modulation on a radio frequency carrier signal in a quadrature modulating means in response to said first through fourth weighted output signals. - View Dependent Claims (6)
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7. A method of code division multiple access spread-spectrum signal transmission, comprising the steps of:
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coding a speech or data signal for transmission into a digital signal; converting said digital signal to an `I` chipstream and a `Q` chipstream at a given chiprate, said chipstreams comprising sequences of signal values or their complements; clocking said I and Q chipstreams respectively into a chain of register stages using a sampling clock equal to said chiprate or a multiple thereof and producing from each stage a delayed I or Q output and its logical inverse complementary output; weighting said delayed I output and its logical inverse complementary output to produce first and second weighted output signals; weighting said delayed Q output and its logical inverse complementary output to produce third and fourth weighted output signals; and impressing said code division multiple access spread spectrum modulation on a radio frequency signal in a quadrature modulating means. - View Dependent Claims (8)
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Specification