US 2003/0193365 A1 · QPSK and 16 QAM self-generating synchronous direct downconversion demodulator

Abstract

A system for recovering and demodulating a carrier includes a carrier recovery loop and a data detector. The carrier recovery loop receives the carrier as an input and produces a recovered carrier at a frequency approximately equal to that of the carrier. The carrier recovery loop includes a downconverting mixer, a ×5 multiplier, a ×4 multiplier, and a phase locked loop. The downconverting mixer receives the carrier input, and the phase locked loop provides a VCO reference frequency through the ×5 multiplier to the downconverting mixer, which provides a frequency shifted signal. The frequency shifted signal is passed through the ×4 multiplier as input to the phase locked loop. The data detector receives the carrier and the recovered carrier as inputs and uses the recovered carrier to demodulate the carrier and detect I channel data and Q channel data.

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Claims34

Dependent claims

A system for recovering and demodulating a carrier, comprising:

a carrier recovery loop receiving the carrier as an input, said carrier recovery loop producing a recovered carrier at a frequency approximately equal to that of the carrier;
and
a data detector, said data detector receiving the carrier and said recovered carrier as inputs and using said recovered carrier to demodulate the carrier and detect I channel data and Q channel data.

A system for recovering and demodulating a carrier, comprising:

a carrier recovery loop receiving the carrier as an input, said carrier recovery loop producing a recovered carrier at a frequency approximately equal to that of the carrier;
wherein said carrier recovery loop comprises a downconverting mixer, a ×5 multiplier, a ×4 multiplier, and a phase locked loop, and wherein said downconverting mixer receives the carrier as an input, said phase locked loop provides a VCO reference frequency through said ×5 multiplier to said downconverting mixer, said downconverting mixer provides a frequency shifted signal, and said frequency shifted signal is passed through said ×4 multiplier to said phase locked loop;
and
a data detector, said data detector receiving the carrier and said recovered carrier as inputs and using said recovered carrier to demodulate the carrier and detect I channel data and Q channel data.

1 more element

A system for recovering and demodulating a carrier, comprising:

a carrier recovery loop receiving the carrier as an input, said carrier recovery loop producing a recovered carrier at a frequency approximately equal to that of the carrier;
wherein said carrier recovery loop comprises a downconverting mixer, a ×5 multiplier, a first ×4 multiplier, and a phase locked loop, and wherein said downconverting mixer receives the carrier as an input, said phase locked loop provides a VCO reference frequency through said ×5 multiplier to said downconverting mixer, said downconverting mixer provides a frequency shifted signal, and said frequency shifted signal is passed through said first ×4 multiplier to said phase locked loop,
wherein said phase locked loop comprises a phase detector, a loop filter, a VCO, and a second ×4 multiplier, and wherein said VCO provides said VCO reference frequency to said second ×4 multiplier, said second ×4 multiplier produces an upconverted VCO reference frequency to provide said recovered carrier, said phase detector compares an upconverted frequency shifted signal to said upconverted VCO reference frequency and drives said loop filter, and said loop filter provides a control voltage to said VCO, and
wherein the carrier has a carrier frequency and said frequency shifted signal has a frequency, said frequency of said frequency shifted signal is approximately one quarter said carrier frequency, and said first ×4 multiplier upconverts said frequency shifted signal by a factor of four;
and said VCO reference frequency is approximately one quarter said carrier frequency, and said ×5 multiplier upconverts said VCO reference frequency by a factor of five;
a phase adjuster, wherein said recovered carrier is passed through said phase adjuster to provide a phase adjusted recovered carrier, and wherein the carrier and said phase adjusted recovered carrier each have a phase and said phase adjuster matches the phase of said phase adjusted recovered carrier to the phase of the carrier;
and
a data detector, said data detector receiving the carrier and said phase adjusted recovered carrier as inputs and using said phase adjusted recovered carrier to demodulate the carrier and detect I channel data and Q channel data,
wherein said data detector comprises a first mixer, said first mixer using the carrier and said phase adjusted recovered carrier to detect said I channel data, said data detector comprises a second mixer and a phase shifter, said phase adjusted recovered carrier feeding to said second mixer via said phase shifter, and said second mixer using the carrier and said phase adjusted recovered carrier to detect said Q channel data, said data detector comprises a first post detection filter, an output of said first mixer being passed through said first post detection filter to reproduce said I channel data, and said data detector comprises a second post detection filter, an output of said second mixer being passed through said second post detection filter to reproduce said Q channel data.

6 more elements

Dependencies are inferred from the claim text.

Description5,166 words

Summary2,457 words

#The present invention generally relates to high frequency, high data rate communication systems and, more particularly, to demodulation for band efficient quadrature phase shift keying (QPSK) modulation and quadrature amplitude modulation (QAM) using monolithic microwave integrated circuits (MMIC).

#The present invention is applicable to bandwidth efficient modulation communication systems. The invention provides a non-wired approach for high data rate needs, for example, in satellite to satellite communication, satellite to ground communication, terrestrial relay links for line-of-sight, demod/remod systems, and space based demod/remod systems.

#The purpose of a demodulator is to perform waveform recovery. The best demodulator will recover the baseband pulse with the best signal to noise ratio (SNR). The error degradation in the signals can be caused by two most prominent sources. One most prominent source is inter-symbol interference (ISI). The filtering used to reject unwanted parts of the signal and noise can cause a non-ideal system transfer causing ISI. The ISI distorts the signal and will produce errors in the received signal. The other most prominent source of degradation is due to noise from electrical sources, atmospheric effects, thermal effects, and inter-modulation products, for example. The demodulator should undistort, or correct distortion of, the pulse to give the best possible received signal.

Brief description of the drawings7 figures

#FIG. 1 is a block diagram for a typical implementation of quadrature phase shift keying (QPSK) modulation;

#FIG. 2 is a phase diagram for a typical implementation of QPSK modulation;

#FIG. 3 is a block diagram for QPSK modulation as typically implemented using bi-phase shift keying (BPSK);

Detailed description2,589 words

#The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.

#The present invention provides, in communication systems, demodulation that reduces amplitude and phase error, and allows higher data rates relative to the carrier frequency. The present invention may use monolithic microwave integrated circuits (MMIC) or application specific integrated circuits (ASIC) to directly, i.e., without wideband down conversion to an intermediate frequency (IF), demodulate a microwave carrier modulated at high data rates in a quadrature phase shift keying (QPSK) format or a quadrature amplitude modulation (QAM) format. The method of direct demodulation in an embodiment of the present invention enables the use of increased data rate and provides a more bandwidth-efficient transmission and reception of data, rendering an economic advantage where spectrum allocations are limited. In one embodiment, the present invention may reduce required hardware and operating costs.

#The present invention also provides, in communication systems, demodulation that achieves low amplitude and phase error—or imbalance—over a wide bandwidth, and improves overall performance of the communication system exhibited by, for example, low inter-symbol interference and low bit error rate of the system. In one embodiment, a wireless telecommunication system using the demodulation of the present invention exhibits an amplitude and phase imbalance of less than plus or minus 0.3 dB and 2 degrees respectively over a 6 GHz bandwidth. In one embodiment, a communication system is capable of delivering approximately 5 Gbps of data using a 16 QAM modulation and demodulation. Unlike prior art QAM systems, which are unable to achieve comparable levels of performance, the 16 QAM modulation and demodulation may be achieved as a direct result of the benefits of a QPSK MMIC implemented to operate at high switching speeds with improved vector, i.e., amplitude and phase, performance.

QPSK and 16 QAM self-generating synchronous direct downconversion demodulator

Life of this patent

QPSK and 16 QAM self-generating synchronous direct downconversion demodulator

Life of this patent

Life of this patent

Abstract

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Claims34

Description5,166 words

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Classification2 codes

Life of this patent

Description5,166 words