System and method for adaptive modulation

• US 20050195908A1
• Filed: 03/04/2005
• Published: 09/08/2005
• Est. Priority Date: 03/05/2004
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: NextNet Wireless, Inc. (Motorola Solutions, Inc.)
• Inventors: Dunn, J. Eric, Grindahl, Mervin L., Barnes, Keith W.
• Granted Patent: US 7,702,031 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 1/0025 Transmission of mode-switching indication
• CPC Class Codes: H04L 27/0012 arrangements for identifying the type of modulation
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/26134 Pilot insertion in the transmitter chain, e.g. pilot overlapping with data, insertion in time or frequency domain
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

A wireless communication system is configured for adaptive modulation of a transmitted symbol. The specific modulation and/or coding is uniquely identified and data related thereto is embedded within the transmitted symbol. A receiver extracts pilot signals form the transmitted symbol and performs a correlation analysis to identify the particular modulation/coding used for that particular transmitted symbol. This permits adaptive modulation on a symbol-by-symbol basis. A base station communicating with a plurality of peripheral subscribers may utilize different modulation/coding for each subscriber depending on channel conditions.

Claims

1. An orthogonal frequency division multiplexing (OFDM) modulation method comprising:

generating a symbol using a selected one of a plurality of modulation techniques;

embedding a plurality of pilot tones distributed throughout the symbol at predetermined intervals; and

encoding the pilot tones such that a combination of pilot tones uniquely identifies the selected one of the plurality of modulation techniques.

2. The method of claim 1 wherein a pilot tone is embedded at every sixth interval throughout the symbol.

3. The method of claim 1 wherein each of the embedded pilot tones has an associated phase assigned in a deterministic manner wherein the associated phases of the pilot tones uniquely identify the selected one of the plurality of modulation techniques.

4. The method of claim 1 wherein each of the embedded pilot tones has an associated phase assigned using a pseudorandom number (PN) sequence wherein the associated phases of the pilot tones uniquely identify the selected one of the plurality of modulation techniques.

5. The method of claim 4 wherein the associated phases assigned to the embedded pilot tones has a phase of 0°

or 180°

based on the PN sequence.

6. The method of claim 1 wherein generating the symbol further comprises coding the symbol using a selected one of a plurality of coding techniques and the combination of pilot tones uniquely identifies the selected one of the plurality of modulation techniques and the selected one of the plurality of coding techniques.

7. The method of claim 1 wherein the modulated symbol is transmitted, the method further comprising:

receiving the symbol;

detecting at least a portion of the pilot signals embedded within the symbol; and

determining the selected one of the plurality of modulation techniques used based on the detected pilot signals.

8. The method of claim 7 wherein the location of the detected pilot signals embedded within the symbol provide a coarse frequency synchronization.

9. The method of claim 7, further comprising determining an average phase shift from pilot signal to pilot signal and using the average phase shift to estimate a time synchronization error.

10. The method of claim 7, further comprising using an amplitude and phase of a selected pilot signal to determine a channel signal level plus noise at the location of the selected pilot signal.

11. A method for identifying a modulation type for a received symbol, comprising:

analyzing the symbol to identify a plurality of pilot tones embedded within the symbol;

analyzing the pilot tones; and

on the basis of the pilot tone analysis, uniquely identifying the modulation type for the received symbol.

12. The method of claim 11 wherein each of the embedded pilot tones has an associated phase assigned in a deterministic manner wherein analyzing the pilot tones comprises analyzing the associated phases of the pilot tones to uniquely identify the modulation type.

13. The method of claim 11 wherein each of the embedded pilot tones has an associated phase assigned using a pseudorandom number (PN) sequence wherein analyzing the pilot tones comprises analyzing the associated phases of the pilot tones to uniquely identify the modulation type.

14. The method of claim 13 wherein the associated phases assigned to the embedded pilot tones has a phase of 0°

or 180°

based on the PN sequence.

15. The method of claim 11 wherein a pilot tone is embedded at every sixth interval throughout the symbol.

16. The method of claim 11 wherein analyzing the symbol comprises performing a correlation analysis of the received symbol.

17. The method of claim 16 wherein the correlation analysis of the received symbol comprises a correlation analysis using patterns corresponding to the modulation types.

18. The method of claim 11 wherein the symbol is encoded using a selected one of a plurality of coding techniques and analyzing the pilot tones uniquely identifying the selected one of the plurality of modulation techniques and the selected one of the plurality of coding techniques.

19. A modulation system comprising:

a modulation selection processor to select a modulation type selected from a plurality of modulation types; and

a modulator to modulate data and thereby generate a symbol for transmission, the modulator configured to embed a plurality of pilot tones throughout the symbol at predetermined intervals, wherein the pilot tones are encoded such that a combination of pilot tones uniquely identifies the selected one of the plurality of modulation techniques.

20. The system of claim 19 wherein a pilot tone is embedded at periodic intervals throughout the symbol.

21. The system of claim 19 wherein the modulator is further configured to assign a phase to each of the embedded pilot tones has in a deterministic manner wherein the assigned phases of the pilot tones uniquely identify the selected one of the plurality of modulation techniques.

22. The system of claim 19 wherein the modulator is further configured to assign a phase to each of the embedded pilot tones using a pseudorandom number (PN) sequence wherein the assigned phases of the pilot tones uniquely identify the selected one of the plurality of modulation types.

23. The system of claim 22 wherein the modulator is configured to assign a phase of 0°

or 180°

to the embedded pilot tones based on the PN sequence.

24. The system of claim 19, further comprising an encoder to encode the modulated symbol using a selected one of a plurality of coding types and the combination of pilot tones uniquely identifies the selected one of the plurality of modulation types and the selected one of the plurality of coding types.

25. The system of claim 19 wherein the modulated symbol is transmitted, the system further comprising:

a receiver to receive the symbol and to detect at least a portion of the pilot signals embedded within the symbol, the receiver configured to determine the selected one of the plurality of modulation types used based on the detected pilot signals.

26. The system of claim 25 wherein the receiver is configured to derive a coarse frequency synchronization based on a location of the detected pilot signals embedded within the symbol.

27. The system of claim 25 wherein the receiver is configured to derive an average phase shift from pilot signal to pilot signal and to estimate a time synchronization error based on the average phase shift.

28. The system of claim 25 wherein the receiver is further configured to determine a channel signal level plus noise at the location of the selected pilot signal using an amplitude and phase of a selected pilot signal.

29. A modulated symbol modulated using a selected one of a plurality of modulation types, comprising:

a plurality of tones indicative of data; and

a plurality of pilot signals distributed throughout the symbol at predetermined intervals, wherein the pilot signals are encoded such that a combination of pilot signals uniquely identifies the selected one of the plurality of modulation types.

30. The symbol of claim 29 wherein each of the pilot signals has an associated phase assigned in a deterministic manner, the associated phases of the pilot signals uniquely identifying the modulation type.

31. The symbol of claim 29 wherein each of the embedded pilot signals has an associated phase assigned using a pseudorandom number (PN) sequence, the associated phases of the pilot signals uniquely identifying the modulation type.

32. The symbol of claim 29 wherein the symbol is encoded using a selected one of a plurality of coding techniques and the pilot signals uniquely identify the selected one of the plurality of modulation types and the selected one of the plurality of coding types.

33. An apparatus for identifying a modulation type, comprising:

a receiver to receive a symbol; and

a pilot analysis circuit configured to analyze the symbol to identify a plurality of pilot signals embedded therein, to analyze the pilot signals, and to uniquely identify the modulation type for the received symbol on the basis of the pilot signal analysis.

34. The apparatus of claim 33 wherein each of the embedded pilot signals has an associated phase assigned in a deterministic manner wherein the pilot analysis circuit is further configured to analyze the associated phases of the pilot signals to uniquely identify the modulation type.

35. The apparatus of claim 33 wherein each of the embedded pilot signals has an associated phase assigned using a pseudorandom number (PN) sequence wherein the pilot analysis circuit is further configured to analyze the associated phases of the pilot signals assigned using the pseudorandom number (PN) sequence to uniquely identify the modulation type.

36. The apparatus of claim 33 wherein a pilot signals are embedded at periodic intervals throughout the symbol and the pilot analysis circuit is further configured to identify a plurality of pilot signals embedded therein

37. The apparatus of claim 33 wherein the pilot analysis circuit is further configured to perform a correlation analysis of the received symbol.

38. The apparatus of claim 37 wherein the pilot analysis circuit performs the correlation analysis using patterns corresponding to the modulation types.

39. The apparatus of claim 33 wherein the symbol is encoded using a selected one of a plurality of coding types and the pilot analysis circuit is further configured to analyze the pilot signals to uniquely identify the selected one of the plurality of modulation types and the selected one of the plurality of coding types.