# US 9,048,980 B2 · RF carrier synchronization and phase alignment methods and systems

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- Number: US 9,048,980 B2
- Document ID: US9048980B2
- Status: Granted
- Kind: B2
- Application number: 14/043,794
- Filed: 2013-10-01
- Published: 2014-04-03
- Granted: 2015-06-02
- Earliest claimed: 2012-10-01
- Assignees: PhasorLab, Inc.
- Applicants: Joshua C. Park
- Inventors: Joshua C. Park
- Web page: https://patentgrep.com/patent/US9048980B2

## CPC

- H04W 56/006: {using known positions of transmitter and receiver}
- G01S 3/18: derived directly from separate directional antennas
- H04B 7/0413: MIMO systems
- H04L 7/0016: {correction of synchronization errors}
- H04L 25/02: Details {; arrangements for supplying electrical power along data transmission lines (systems for transmitting signals via power distribution lines H04B3/54)}
- H04L 27/0014: {Carrier regulation (of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657)}
- H04L 27/364: {Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels}
- H04W 56/0035: {detecting errors in frequency or phase}
- H04W 64/006: {with additional information processing, e.g. for direction or speed determination}
- H04L 2027/003: {at baseband only}
- H04L 2027/0046: {Open loops}
- H04L 2027/0053: {Closed loops}
- H04L 2027/0067: {Phase error detectors}
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- H04B: TRANSMISSION
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A method comprising generating a baseband information signal by mixing a received modulated carrier signal with a local oscillator (LO) signal having an LO frequency; obtaining baseband signal samples of the baseband information signal having a baseband signal magnitude and a baseband signal phase; determining a cumulative phase measurement associated with baseband signal samples having a baseband signal magnitude greater than a threshold; and, applying a correction signal to compensate for an LO frequency offset of the LO frequency based on the cumulative phase.

## Claims

### Claim 1

A blind frequency synchronization method comprising:
generating a baseband information signal by mixing a received modulated carrier signal with a local oscillator (LO) signal having an LO frequency;
obtaining baseband signal samples of the baseband information signal having a baseband signal magnitude and a baseband signal phase;
determining a cumulative phase measurement associated with baseband signal samples having a baseband signal magnitude greater than a threshold; and,
applying a correction signal to compensate for an LO frequency offset of the LO frequency based on the cumulative phase,
wherein the cumulative phase measurement is based on an instantaneous phase of a data signal within the received modulated carrier signal, and
wherein determining a cumulative phase measurement comprises accumulating a plurality of differential phases between successive complex signal points, each of the successive complex signal points having magnitude greater than the threshold.

### Claim 2 (depends on 1)

The method of claim 1 wherein the LO signal includes an in-phase carrier signal and a quadrature carrier signal, and the baseband signal samples are determined from an in-phase channel sample and a quadrature channel sample.

### Claim 3 (depends on 1)

The method of claim 1 wherein applying a correction signal comprises adjusting an LO control signal.

### Claim 4 (depends on 1)

The method of claim 1 wherein applying a correction signal comprises applying a complex rotation to the baseband signal samples.

### Claim 5 (depends on 1)

The method of claim 1, further comprising calculating an instantaneous derivative of a first baseband signal sample and of a second baseband signal sample, the first and second baseband signal samples each having a baseband signal magnitude greater than the threshold.

### Claim 6 (depends on 5)

The method of claim 5, further comprising accumulating the instantaneous derivatives of the first baseband signal sample and the second baseband signal sample, thereby accumulating cumulative phase measurements.

### Claim 7

An apparatus comprising:
a mixer and a local oscillator (LO) configured to generate a baseband information signal by mixing a received modulated carrier signal with an LO signal having an LO frequency;
an analog to digital converter configured to generate baseband signal samples of the baseband information signal;
a phase accumulator configured to receive the baseband signal samples and to determine a cumulative phase measurement associated with baseband signal samples having a baseband signal magnitude greater than a threshold; and,
an LO correction module configured to apply a correction signal to compensate for an LO frequency offset of the LO frequency based on the cumulative phase,
wherein the cumulative phase measurement is based on an instantaneous phase of a data signal within the received modulated carrier signal, and
wherein the phase accumulator is further configured to accumulate a plurality of differential phases between successive complex signal points, each of the successive complex signal points having magnitude.

### Claim 8 (depends on 7)

The apparatus of claim 7 wherein the LO includes an in-phase carrier signal generator and a quadrature carrier signal generator.

### Claim 9 (depends on 7)

The apparatus of claim 7 wherein the cumulative phase measurement is determined over either (i) a predetermined time interval or (ii) a predetermined number of samples.

### Claim 10 (depends on 7)

The apparatus of claim 7 wherein the LO correction module comprises an LO control module configured to generate a control signal.

### Claim 11

A method comprising:
generating a baseband information signal by mixing a received modulated carrier signal with a local oscillator (LO) signal having an LO frequency, the modulated carrier signal being an in-phase signal and quadrature signal uncorrelated with each other and derived from different input data sets;
obtaining baseband signal samples of the baseband information signal having an in-phase signal sample and a quadrature signal sample;
determining an offset frequency rotation based on an estimated correlation between the in-phase signal samples and the quadrature signal samples; and,
processing the baseband information signal using the offset frequency rotation,
wherein the received modulated carrier signal is a quadrature-modulated signal with arbitrary orthogonal in-phase and quadrature signal components.

### Claim 12 (depends on 11)

The method of claim 11 wherein processing the baseband information signal using the offset frequency rotation comprises adjusting the LO frequency using an LO control signal.

### Claim 13 (depends on 11)

The method of claim 11 further comprising:
determining an offset phase associated with the estimated correlation between the inphase signal samples and the quadrature signal samples; and,
processing the baseband information signal using the offset phase.

### Claim 14 (depends on 11)

The method of claim 11 wherein the estimated correlation between the in-phase signal samples and the quadrature signal samples is based on squared in-phase samples and squared quadrature samples.

### Claim 15 (depends on 11)

The method of claim 11 wherein the estimated correlation between the in-phase signal samples and the quadrature signal samples is based on absolute values of in-phase samples and absolute values of quadrature samples.

### Claim 16 (depends on 11)

The method of claim 11, wherein determining the offset frequency rotation further comprises time averaging and integrating a product of either squares of or absolute values of the in-phase signal and the quadrature signal.

### Claim 17 (depends on 11)

The method of claim 11, wherein determining the offset frequency rotation further comprises calculating:
Σk=1N{|IR,i(k)|·|QR,i(k)|},
where IR,i refers to an in-phase part of an ith error-corrected data set and QR,i refers to a quadrature part of the ith error-corrected data set.

### Claim 18 (depends on 11)

The method of claim 11, wherein determining the offset frequency rotation further comprises calculating:
Σk=1N{(IR,i(k))2(QR,i(k))2},
where IR,i refers to an in-phase part of an ith error-corrected data set and QR,i refers to a quadrature part of the ith error-corrected data set.