Method of differential-phase/absolute-amplitude QAM

• US 20040247052A1
• Filed: 06/04/2003
• Published: 12/09/2004
• Est. Priority Date: 06/04/2003
• Status: Active Grant

• Current Assignee: Honeywell Federal Manufacturing & Technologies, LLC (Honeywell International Inc.)
• Original Assignee: Honeywell Federal Manufacturing & Technologies, LLC (Honeywell International Inc.)
• Inventors: Dimsdle, Jeffrey William
• Granted Patent: US 7,239,676 B2
• Time in Patent Office: Days
• US Class Current: 375/340
• CPC Class Codes: H04L 27/3405 Modifications of the signal space to increase the efficiency of transmission, e.g. reduction of the bit error rate, bandwidth, or average power
• CPC Class Codes: H04L 27/361 Modulation using a single or unspecified number of carriers, e.g. with separate stages of phase and amplitude modulation

Abstract

A method of quadrature amplitude modulation involving encoding phase differentially and amplitude absolutely, allowing for a high data rate and spectral efficiency in data transmission and other communication applications, and allowing for amplitude scaling to facilitate data recovery; amplitude scale tracking to track-out rapid and severe scale variations and facilitate successful demodulation and data retrieval; 2^N power carrier recovery; incoherent demodulation where coherent carrier recovery is not possible or practical due to signal degradation; coherent demodulation; multipath equalization to equalize frequency dependent multipath; and demodulation filtering.

Claims

1. A method of amplitude scale tracking to substantially reduce scale variations in a received quadrature amplitude modulated signal, the method comprising the steps of:

(a) determining an amplitude ratio of two or more consecutive sampled amplitude values;

(b) determining whether the amplitude ratio represents a valid transition;

(c) identifying, for a determined valid transition, one or more of the two or more consecutive sampled amplitude values with ideal amplitude levels;

(d) determining a scale factor value based upon the identified consecutive sampled amplitude value; and

(e) using the scaling factor value to scale and compensate for any changes in strength of the received quadrature amplitude modulated signal.

2. The method as set forth in claim 1, wherein each sampled amplitude value of the two consecutive sampled amplitude values is approximately equal to {square root}((I value)²+(Q value)²).

3. The method as set forth in claim 1, wherein the valid transition is determined as being within a pre-established tolerance of a nominal amplitude ratio.

4. The method as set forth in claim 3, wherein the nominal amplitude ratio 25 is of one or more higher amplitude values to one or more lower amplitude values.

5. The method as set forth in claim 3, wherein the nominal amplitude ratio is of one or more lower amplitude value to one or more higher amplitude values.

6. The method as set forth in claim 1, wherein the valid transition is determined as being within a pre-established tolerance of either a first nominal amplitude ratio or a second amplitude nominal ratio of any of the multiple possible pairs of amplitude levels, wherein the first nominal amplitude ratio is of a higher amplitude value to a lower amplitude value and the second nominal amplitude ratio is of the lower amplitude value to the higher amplitude value.

7. The method as set forth in claim 1, wherein the average is a windowed/weighted average weighted in favor of the identified amplitude values closer to each received amplitude to be scaled.

8. The method as set forth in claim 1, wherein step (e) includes—

(e₁) determining an I value and an Q value corresponding to each of the-two consecutive sampled amplitude values; and

(e₂) multiplying the I value and the Q value by the scaling factor value.

9. A method of amplitude scale tracking to substantially reduce scale variations in a received quadrature amplitude modulated signal, the method comprising the steps of:

(a) determining an amplitude ratio of two consecutive sampled amplitude values, wherein each of the two consecutive sampled amplitude values is approximately equal to {square root}((I value)²+(Q value)²);

(b) determining whether the amplitude ratio represents a valid transition as being within a pre-established tolerance of a nominal amplitude ratio;

(c) identifying, for a determined valid transition, one or more of the two consecutive sampled amplitude values with ideal amplitude levels;

(d) determining a scale factor value based upon the identified consecutive sampled amplitude value;

(e) determining an I value and a Q value corresponding to the identified consecutive sampled amplitude values; and

(f) multiplying the I value and the Q value by the scaling factor value to compensate for any changes in strength of the received quadrature amplitude modulated signal.

10. The method as set forth in claim 9, wherein the nominal amplitude ratio is of one or more higher amplitude values to one or more lower amplitude values.

11. The method as set forth in claim 9, wherein the nominal amplitude ratio is of one or more lower amplitude values to one or more higher amplitude values.

12. The method as set forth in claim 9, wherein the nominal amplitude ratio is either a first unique nominal amplitude ratio or a second unique nominal amplitude ratio, wherein the first unique nominal amplitude ratio is of an upper amplitude value to a lower amplitude value and the second unique nominal amplitude ratio is of the lower amplitude value to the higher amplitude value.

13. A method of amplitude scaling that also allows for scale tracking to substantially reduce scale variations in a received quadrature amplitude modulated signal, the method comprising the steps of:

(a) determining an ideal constellation amplitude magnitude;

(b) determining, for a signal segment of the received quadrature amplitude modulated signal, a maximum amplitude magnitude over the segment, with the maximum amplitude magnitude being an outer level amplitude magnitude;

(c) determining an ideal ratio of the ideal amplitude magnitude to the outer level amplitude magnitude;

(d) determining an upper limit and a lower limit around the ideal ratio;

(e) determining, for a symbol sample within the signal segment, with the symbol sample having a symbol sample magnitude, a ratio of the symbol sample magnitude to the maximum amplitude magnitude of step (b), and, if the ratio is between the upper limit and the lower limit of step (d), dividing the ideal amplitude magnitude by the symbol sample magnitude to obtain a scale factor;

(f) repeating step (e) for any other symbol samples within the signal segment, thereby generating a plurality of scale factors;

(g) averaging the plurality of scale factors to determine an amplitude scale factor for the signal segment; and

(h) multiplying all of the symbol sample magnitudes of the symbol samples within the signal segment by the amplitude scale factor to scale and also to compensate for any changes in strength of the received quadrature amplitude modulated signal.

14. The method as set forth in claim 13, wherein the upper limit and the lower limit around the ideal ratio do not overlap other upper limits and other lower limits around other ideal ratios.