Method and system for blind detection of modulation

• US 6,400,928 B1
• Filed: 11/19/1999
• Issued: 06/04/2002
• Est. Priority Date: 11/19/1999
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Khullar, Anders, Stenström, Niklas
• Primary Examiner(s): Hunter, Daniel
• Assistant Examiner(s): Tran, Pablo N
• Application Number:
  US09/443,932
• Time in Patent Office: 928 Days
• Field of Search: 455/67.1, 455/67.3, 455/67.4, 455/68, 455/71, 455/73, 455/39, 455/142, 455/143, 455/101, 455/102, 455/144, 455/110, 455/108, 375/224, 375/231, 375/237, 375/238-243
• US Class Current: 455/67.11
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0025 Transmission of mode-switching indication
• CPC Class Codes: H04L 1/0038 Blind format detection for detection of modulation format H04L27/0012
• CPC Class Codes: H04L 1/0059 Convolutional codes
• CPC Class Codes: H04L 1/18 Automatic repetition systems, e.g. Van Duuren systems
• CPC Class Codes: H04L 27/0012 arrangements for identifying the type of modulation
• CPC Class Codes: H04L 27/2017 in which the phase changes are non-linear, e.g. generalized and Gaussian minimum shift keying, tamed frequency modulation H04L27/201 takes precedence
• CPC Class Codes: H04L 27/2067 with more than two phase states H04L27/2064 takes precedence

Abstract

A method and system for blind detection of modulation in a wireless telecommunications network. In accordance with the method and system, a plurality of bursts are transmitted over an air interface to a receiving station using a first modulation scheme. Modulation detection statistics for the plurality of received bursts are calculated at the receiving station. Based on the modulation statistics, however, it is determined that at least one of the plurality of received bursts has been transmitted using a second modulation scheme. As a result, the modulation detection statistics are analyzed to identify a single modulation scheme that was most likely used in modulating the plurality of bursts. Any faulty received bursts, for which a detected modulation scheme differs from the identified single modulation scheme, are then processed to reduce the effect of the faulty bursts.

Claims

1. A method for blind detection of modulation in a wireless telecommunication system, comprising the steps of:

transmitting a plurality of bursts over a radio interface using a first modulation scheme;

receiving the plurality of bursts;

calculating modulation detection statistics for each of the plurality of received bursts;

detecting a modulation scheme for each of the plurality of received bursts based on an evaluation of the modulation detection statistics;

determining that the modulation scheme detected for at least one of the plurality of received bursts comprises a second modulation scheme and that the modulation scheme detected for at least one other of the plurality of received bursts comprises the first modulation scheme;

identifying a single modulation scheme that was most likely used in modulating the plurality of bursts; and

decoding the plurality of received bursts, wherein said decoding includes processing at least one of the plurality of received bursts for which the detected modulation scheme differs from the identified single modulation scheme to adjust the effect of said at least one received burst having a different detected modulation scheme.

2. The method of claim 1, wherein the identified single modulation scheme comprises the first modulation scheme.

3. The method of claim 1, wherein the transmission of the plurality of bursts is conducted in accordance with Enhanced Data rates for Global Evolution (EDGE) technology.

4. The method of claim 1, wherein the first modulation scheme comprises gaussian minimum shift keying (GMSK).

5. The method of claim 1, wherein the first modulation scheme comprises eight phase shift keying (8-PSK).

6. The method of claim 1, wherein the first modulation scheme comprises quadrature phase shift keying (QPSK).

7. The method of claim 1, wherein the modulation detection statistics for each received burst comprise a correlation quality measure between a training sequence in the received burst and a known training sequence.

8. The method of claim 7, further comprising the step of de-rotating the training sequence in each received burst prior to calculating the correlation quality measure for the received burst.

9. The method of claim 1, wherein the step of identifying a single modulation scheme further comprises identifying a modulation scheme detected for a majority of the plurality of bursts.

10. The method of claim 9, wherein the plurality of bursts consists of four bursts, the detected modulation scheme for three of the bursts comprising the first modulation scheme.

11. The method of claim 1, wherein the step of identifying a single modulation scheme further comprises the steps of:

determining that no single modulation scheme was detected for a majority of the bursts;

evaluating additional modulation detection information to identify a single modulation scheme.

12. The method of claim 11, wherein the plurality of bursts consists of four bursts, the detected modulation scheme for two of the bursts comprising the first modulation scheme and the detected modulation scheme for the other two of the bursts comprising the second modulation scheme.

13. The method of claim 11, wherein the additional modulation detection information comprises a correlation quality measure for each burst, each said correlation quality measure indicating a degree of correlation between a training sequence in the received burst and a known training sequence.

14. The method of claim 11, wherein the additional modulation detection information comprises historical data relating to modulation schemes detected for at least one burst preceding said plurality of bursts.

15. The method of claim 11, wherein the additional modulation detection information comprises data indicating a bias in favor of at least one particular modulation scheme.

16. The method of claim 1, wherein said processing includes the steps of:

calculating a plurality of soft values for each of the plurality of received bursts, each said soft value indicating a probability that a corresponding symbol in the received bursts has a particular value;

altering the plurality of soft values for the at least one of the plurality of received bursts for which the modulation detection statistics indicate transmission using the second modulation scheme; and

performing said decoding using the plurality of soft values, as altered during the step of altering.

17. The method of claim 16, wherein the step of altering includes altering each of the plurality of soft values for the at least one of the plurality of received bursts for which the detected modulation scheme comprises the second modulation scheme to indicate that all possible values for the corresponding symbol are equally probable.

18. The method of claim 16, wherein said processing includes the step of altering the number of bits in the at least one of the plurality of received bursts for which the detected modulation scheme differs from the identified single modulation scheme.

19. The method of claim 1, wherein said processing to adjust the effect of said at least one received burst having a different detected modulation scheme comprises reducing the effect of said at least one received burst having a different detected modulation scheme.

20. A wireless data communication system, comprising:

a receiving station for receiving a plurality of burst signals transmitted over an air interface and for implementing blind detection of modulation schemes used to. transmit said data signals, wherein the receiving station comprises;

at least one channel estimation device for calculating modulation detection statistics for each of the plurality of received burst signals;

a modulation detection unit for analyzing the modulation detection statistics for each received burst signal to identify a probable modulation scheme for each received burst signal; and

a modulation correction unit operating to determine whether all of the identified probable modulation schemes for the plurality of received burst signals match, wherein, if all of the identified probable modulation schemes do not match, the modulation correction unit further operates to identify a single modulation scheme most likely used in modulating the plurality of burst signals.

21. The system of claim 20, wherein the identification of the single modulation scheme comprises determining that a majority of the identified probable modulation schemes match and selecting the probable modulation scheme identified for a majority of the plurality of burst signals as the identified single modulation scheme.

22. The system of claim 20, wherein the identification of the single modulation scheme comprises evaluating additional modulation detection information to select the identified single modulation scheme.

23. The system of claim 22, wherein the receiving station further comprises:

a first de-rotation device for de-rotating a training sequence in each received burst signal according to a bit rotation used for gaussian minimum shift keying (GMSK) modulated transmissions;

a second de-rotation device for de-rotating a training sequence in each received burst signal according to a bit rotation used for eight phase shift keying (8-PSK) modulated transmissions; and

wherein the at least one channel estimation device includes;

a first channel estimation device for calculating first correlation quality measures between a known training sequence and the received training sequences as de-rotated by the first de-rotation device; and

a second channel estimation device for calculating second correlation quality measures between the known training sequence and the received training sequences as de-rotated by the second de-rotation device.

24. The system of claim 23, wherein the evaluation of the additional modulation detection information comprises evaluating the first and second correlation quality measures for the plurality of burst signals.

25. The system of claim 22, wherein the additional modulation detection information includes historical modulation detection statistics for at least one burst signal that precedes the plurality of burst signals.

26. The system of claim 22, wherein the additional modulation detection information includes data identifying a bias toward a particular modulation scheme.

27. The system of claim 20, further comprising:

an equalizer for analyzing the burst signals to generate a most probable symbol sequence for each burst signal and to generate a plurality of soft values for each burst signal, each soft value associated with a symbol in the most probable symbol sequence and identifying a probability that symbol has a particular value; and

wherein the modulation correction unit receives each most probable symbol sequence and each plurality of soft values, the modulation correction unit operating to adjust the plurality of soft values for at least one burst sequence for which the identified probable modulation scheme does not match the identified single modulation scheme.

28. The system of claim 27, further comprising a channel decoder for decoding the plurality of burst signals using each most probable symbol sequence and each plurality of soft values, as adjusted by the modulation correction unit.

29. The system of claim 20, further comprising a network side of the wireless data communication system, the network side comprising:

a modulator for modulating the plurality of burst signals prior to the transmission over the air interface, the plurality of burst signals modulated in accordance with a modulation scheme that corresponds to current channel conditions of a radio channel used for communicating the plurality of burst signals between the network side and the receiving station; and

a transmitter for transmitting the plurality of modulated burst signals over the air interface.

30. The system of claim 29, wherein the plurality of burst signals are modulated and transmitted in accordance with Enhance Data rates for Global Evolution (EDGE) technology.

31. The system of claim 29, wherein the identified single modulation scheme matches the modulation scheme used by the modulator.

32. The system of claim 20, further comprising a demodulator for demodulating each of the plurality of received burst signals in accordance with the corresponding identified probable modulation scheme.

33. The system of claim 20, wherein the modulation correction unit further operates to adjust the number of bits in at least one burst sequence for which the identified probable modulation scheme does not match the identified single modulation scheme.