Methods and apparatus for antenna control in a wireless terminal

• US 20060205356A1
• Filed: 10/13/2005
• Published: 09/14/2006
• Est. Priority Date: 03/09/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Laroia, Rajiv, Li, Junyi, Lane, Frank A.
• Granted Patent: US 7,826,807 B2
• Time in Patent Office: Days
• US Class Current: 455/66.100
• CPC Class Codes: H04B 7/0811 during preamble or gap period
• CPC Class Codes: H04B 7/0848 Joint weighting
• CPC Class Codes: H04B 7/088 using beam selection

Abstract

Base stations transmit strip signals using strip signal segments and self supporting modulation scheme techniques facilitating rapid channel estimate. A strip segment occupies one OFDM symbol time interval and uses a set of downlink tones; some, e.g., half, of the tones are left unused facilitating SIR measurement. The strip segments are advantageously timed to correspond to uplink access intervals in which connected wireless terminals do not typically transmit uplink signals. Connected wireless terminals including: multiple antennas used in combination, an antenna duplex module, single RF receiver chain and single RF transmitter chain, switch antenna coefficient combinations based on strip signal segment timing. The wireless terminal determines an independent downlink channel quality measurement, e.g., SNR and/or SIR for each strip signal segment and for on-going non-strip signaling. The wireless terminal compares channel quality measurements and selects an antenna coefficient combination to be used during non-strip signaling intervals obtaining very good antenna gain.

Claims

1. A communications method, the method comprising:

during a first period of time;

i) receiving at a plurality of antenna elements, symbols transmitted using a first modulation method;

ii) using a first set of antenna gain coefficients to control individual gains applied to the signals received from different ones of said plurality of antenna elements to produce gain adjusted signals;

iii) combining the gain adjusted signals received from the different antenna elements to produce a first combined gain adjusted signal;

during a second period of time, following said first period of time;

iv) receiving at said plurality of antenna elements, a symbol transmitted using a second modulation method than the modulation method used during said first period of time; and

v) using a second set of antenna gain coefficients to control individual gains applied to the individual signals received from different ones of said plurality of antenna elements to produce gain adjusted signals.

2. The method of claim 1, further comprising:

during said second period of time;

iii) combining the gain adjusted signals received from the different antenna elements; and

iv) making a second signal quality measurement indicating the quality of the second combined gain adjusted signal.

3. The method of claim 2, further comprising:

prior to a third period of time following said first and second periods of time, selecting a set of gain coefficients to be used during said third period of time as a function of the second signal quality measurement.

4. The method of claim 3, further comprising:

prior to the second period of time, making a first signal quality measurement of a combined signal generated using the first set of antenna gain coefficients; and

wherein said step of selecting a set of gain coefficients to be used during said third period of time is performed as a function of the first and second signal quality measurements.

5. The method of claim 4, wherein said step of making a first signal quality measurement prior to the second period of time is performed during said first period of time.

6. The method of claim 4, wherein said first modulation method is a coherent modulation method which requires the use of a channel estimate to decode a symbol modulated using said coherent modulation;

and

wherein the second modulation method is a self supporting modulation scheme which does not require the use of said channel estimate derived in said first period of time to decode the signal in the second period of time.

7. The method of claim 6, wherein the self supporting modulation scheme is a non-coherent modulation scheme, which does not require channel estimation to decode the signal.

8. The method of claim 6, wherein the self supporting modulation scheme is a coherent modulation scheme, and pilot tones are received in the second period of time and used to derive a channel estimate to coherently decode the signal.

9. The method of claim 6, further comprising:

generating a first channel estimate indicative of the effect of a communications channel during said first period of time;

using said first channel estimate to decode at least one symbol included in said first combined gain adjusted signal; and

decoding a data included in the second combined gain adjusted signal during said second time period using a self supporting modulation decoding which does not use a channel estimate derived from signal in said first period of time as part of the decoding process.

10. The method of claim 6, further comprising:

generating a first channel estimate during said first period of time, said channel estimate being indicative of an effect of a communications channel on received signals.

11. The method of claim 10, further comprising:

using the first channel estimate generated during said first period of time during the third period of time if the set of coefficients selected to be used during said third period of time is the same as said first set of coefficients.

12. The method of claim 11, further comprising:

using a different channel estimate during said third period of time than the channel estimate generated during said first period of time, when the set of coefficients selected to be used during said third period of time is different from said first set of coefficients.

13. The method of claim 12, wherein using a different channel estimate during said third period of time includes resetting said first channel estimate to a predetermined channel estimate value and using said reset channel estimate at the start of said third time period.

14. The method of claim 12, further comprising

generating a second channel estimate during said second period of time, said channel estimate being indicative of an effect of a communications channel on received signals;

15. The method of claim 14, wherein using a different channel estimate during said third period of time includes resetting said first channel estimate to said second channel estimate value and using said reset channel estimate at the start of said third time period, when the set of coefficients selected to be used during said third period of time is the same as said second set of coefficients.

16. The method of claim 3, wherein said communications method is for use in a frequency division multiplexed system which includes a base station that transmits signals to said wireless terminal using, in parallel, a plurality of tones, and where no signal is transmitted on at least one tone during said second time period;

and wherein the step of measuring a second signal quality measurement includes;

measuring signal interference power on a tone on which no signal is transmitted during said second time period;

measuring signal power on another tone in which signal is transmitted during said second time period; and

generating at least one signal to interference ratio value from the ratio of measured signal power and measured interference power.

17. The method of claim 16, wherein a plurality of tones are used during said second time period and wherein the percentage of tones on which no signals are transmitted during said second time period is between 30% and 70% of the total number of tones used during the first time period.

18. The method of claim of claim 16, wherein said second time period includes a single OFDM symbol transmission time period and said first time period includes at least 50 OFDM symbol transmission time periods.

19. The method of claim of claim 16, wherein said second time period is at most one fortieth said first time period.

20. The method of claim 12, further comprising:

maintaining a plurality of different channel estimates for different sets of channel coefficients; and

using a channel estimate corresponding to the set of coefficients selected to be used during said third period of time, during said third period of time.

21. The method of claim 20, wherein coherent modulation is used during said first, and third time periods, self supporting modulation scheme is used in said second time period, and wherein coherent modulation is used in at least some additional periods of time, the method further comprising:

updating the channel estimate in said plurality of different channel estimates corresponding to a particular one of the sets of coefficients, during additional time periods in which the particular one of the sets of coefficients is used and coherent modulation is used.

22. The method of claim 4, wherein said first, second and third time periods recur according to a predetermined downlink transmission schedule, the steps performed in each of said first, second and third time periods being repeated as the time periods repeat.

23. The method of claim 20, wherein the first period of time includes multiple consecutive OFDM symbol transmission time periods;

and

wherein the second period of time includes at most three consecutive OFDM symbol transmission time periods.

24. The method of claim 3, wherein said received symbols are transmitted by a base station which transmits OFDM signals, and wherein said second period of time corresponds to an access interval during which wireless terminals already timing synchronized with the base station are not required to transmit uplink signals, said first and third periods of time being data transmission periods of time during which user data is transmitted using OFDM signals to said wireless terminal.

25. The method of claim 3, wherein said received symbols are transmitted by a base station which transmits OFDM signals, and wherein said second period of time corresponds to an access interval during which wireless terminals already timing synchronized with the base station are prohibited from transmitting uplink signals, said first and third periods of time being data transmission periods of time during which user data is transmitted using OFDM signals to said wireless terminal.

26. The method of claim 3, further comprising:

using the selected set of gain coefficients transmit signals to a base station.

27. A wireless terminal comprising:

a plurality of antenna elements for receiving signals;

a plurality of controllable gain elements each controllable gain element being coupled to a different one of the plurality of antenna elements;

a combining circuit coupled to each of the gain elements for combining the output of each gain control element into a combined signal, the gain of each gain control element being controlled by a gain control coefficient;

a signal quality measurement module coupled to said combining circuit for making signal quality measurements on the combined signal output by said combining circuit during different periods of time; and

a gain control module coupled to said signal measurement module for controlling the wireless terminal to use different sets of gain control coefficients during different periods of time, said gain control module including a coefficient selection module for selecting the set of gain coefficients to be used during a subsequent period of time based on signal measurements made during at least two different periods of time during which different sets of gain control coefficients were used.

28. The wireless terminal of claim 27, further comprising:

a coherent decoder module coupled to said combining circuit for performing coherent decoding to recover information communicated using coherent modulation during a time period of a first type during which information is communicated to the wireless terminal using coherent modulation; and

a self supporting modulation decoder module coupled to said combining circuit for performing self supporting modulation decoding to recover information communicated using self supporting modulation scheme during a time period of a second type during which information is communicated to the wireless terminal without using a channel estimation derived from the signal in a previous time period.

29. The wireless terminal of claim 28, wherein said coefficient selection module selects the set of gain coefficients to be used based on signal quality measurements during multiple time periods, said coefficient selection module selecting the set of gain control coefficients which resulted in the higher received signal quality.

30. The wireless terminal of claim 29, further comprising:

a channel estimation module for generating a channel estimate during periods of time in which coherent modulation is used.

31. The wireless terminal of claim 30, further comprising:

a channel estimation control module for controlling the use of channel estimates, said channel estimation control module changing the channel estimate from a first time period in which coherent demodulation is used to the next time period in which coherent channel estimation is used, when the next time period uses a different set of gain coefficients than said first time period.

32. The wireless terminal of claim 31, further comprising:

memory for storing a plurality of channel estimates, each channel estimate corresponding to a different set of gain control coefficients, said channel estimation module maintaining different channel estimates in memory which are generated while decoding received signals using different gain control coefficients.

33. The wireless terminal of claim 31, wherein said channel estimation control module resets to a predetermined value, a channel estimate being used for coherent demodulation, when the set of gain control coefficients changes from one period in which coherent demodulation is used the next period in which coherent demodulation is used.

34. The wireless terminal of claim 31, wherein said gain control module includes means for changing the set of gain control coefficients used from one time period of the second type to the next time period of the second type according to a predetermined sequence.

35. The wireless terminal of claim 34, wherein said predetermined sequence is a sequence used to test different gain coefficient sets to determine their effect on signal quality.

36. The wireless terminal of claim 27, wherein during time periods of a second type, an OFDM symbol is received which includes at least one null tone and a plurality of additional tones on which information is communicated using self supporting modulation scheme;

and

wherein said signal quality measurement module includes;

a signal to interference measurement module for computing a signal to interference measurement as a function of a measurement of said at least one null tone and one of said additional tones used to communicate information in the said OFDM symbol.

37. A communications method for use by a wireless terminal including a plurality of antenna elements, a plurality of controllable gain elements and a combining circuit, each gain element controlling a gain applied to at least one signal communicated between the corresponding antenna element and the combining circuit, the method comprising:

operating the wireless terminal to receive data signals during a first time period using a first set of gain values, each gain value in the first set being used to control a different one of the gain control elements;

operating the wireless terminal to measure the signal quality of the signals received during the first time period; and

operating the wireless terminal during a second time period, immediately following said first time period, said step of operating the wireless terminal during a second period of time including;

i) setting the gains of the gain control elements to a second set of gain control values which is different from the first set of gain control values used during said first time period.

38. The method of claim 37, wherein operating the wireless terminal during said second period of time further includes:

ii) receiving signals during said second time period, said signals including data; and

iii) applying gain to the received signals using the second set of gain values to control the gain applied to individual received signals.

39. The method of claim 37, wherein operating the wireless terminal during said second period of time further includes:

iv) recovering data from the signals received during the second time period by performing a self supporting modulation decoding operation which does not use communications channel information from a previous time period; and

v) measuring the quality of at least one signal received during the second time period.

40. The method of claim 39, further comprising:

prior to a third time period, which is subsequent said second period of time, operating the wireless terminal to select a second set of gain values to be used during the third time period as a function of the measured signal quality corresponding to said first and second sets of gain values.

41. The method of claim 40, further comprising:

repeating each of the steps performed during said first, second and third periods of time for new first, second and third periods of time so that the steps are performed on a recurring basis.

42. The method of claim 40, further comprising:

generating channel estimation information during said first period of time; and

resetting said channel estimation information if the selected set of gain values to be used during the third time period is different from the set of gain values used during the first time period.

43. The method of claim 42, wherein the channel estimation information includes information indicating the effect of the communications channel on the signals received by said antenna elements.

44. The method of claim 42, further comprising:

using channel estimation information generated during said first time period, for received signal compensation purposes, during said subsequent third time period, when the selected set of gain values selected prior to the subsequent third time period, to be used during the subsequent third time period, is the same as the set of gain values used during the first time period.

45. The method of claim 42, wherein said communications method is for use in a frequency division multiplexed system which includes a base station that transmits signals to said wireless terminal using a plurality of tones, and where no signal is transmitted on at least some tones during said second time period;

and wherein the step of measuring the quality of signals received during the second time period includes;

measuring signal interference power on a tone on which no signal is transmitted during said second time period;

measuring signal power on another tone in which signal is transmitted during said second time period; and

generating at least one signal to interference ratio value from the ratio of measured signal power and measured signal interference power during said second time period.

46. The method of claim 45, wherein a plurality of tones are used during said second time period and wherein the percentage of tones on which no signals are transmitted during said second time period is between 30% and 70% of the total number of tones used during the first time period.

47. The method of claim 45, wherein the second time period is less than one fortieth the first time period and wherein different types of information coding are used in said first and second time periods.

48. The method of claim 47, wherein coherent modulation is used for information coding during said first time period and self supporting modulation scheme is used for information coding during said second time period, information coded using coherent modulation requiring use of a channel estimate for decoding, information coded using self supporting modulation scheme being capable of decoding without use of a channel estimate derived from signal in a previous time period.

49. The method of claim 45, wherein the second time period is a single OFDM symbol transmission time period.

50. The method of claim 49, wherein a fourth time period occurs between said second and third time periods, said fourth time period being a period of time in which a third set of gain values is used and additional signal quality measurements are made before performing the selecting step, said third set of gain values being different from said first and second sets of gain values.

51. The method of claim 40, wherein said gain values in said first and second sets of gain values are complex values.

52. The method of claim 51, wherein at least some of the complex gain values are real values.

53. The method of claim 40, wherein said step of selecting a set of gain values selects only one antenna element at a time from said plurality of antenna elements and said selected set of gain values includes a non-zero value for the one gain value corresponding to the selected antenna element and a value of zero for all other antenna element gain values in the selected set.

54. The method of claim 40, wherein each of the sets of gain values from which a selected set is obtained includes one non-zero gain value corresponding to one antenna element and zero for the gain values in the set corresponding to each of the other antenna elements, different sets having the non-zero value associated with different antenna elements.

55. The method of claim 40, wherein during said second time period said wireless terminal already timing synchronized with the base station refrains from transmitting any signal.

56. The method of claim 40, wherein when the wireless terminal selects and changes the gain values used to control the gain of received signals, the wireless transmitter changes the gain of transmitted signals using the same set of gain values used to control the gain of received signals.

57. The method of claim 56, wherein multiple different sets of gain values are tested prior to each selection of a set of gain values providing a ratio of gain value tests to selections of sets of gain values which is at least 2 to one.

58. The method of claim 56, wherein said wireless terminal has a single radio frequency receiver processing chain.

59. The method of claim 56, wherein said wireless terminal has a single radio frequency transmitter chain.