METHOD AND APPARATUS FOR FRAME DETECTION IN A COMMUNICATIONS SYSTEM

• US 20090316611A1
• Filed: 06/24/2008
• Published: 12/24/2009
• Est. Priority Date: 06/24/2008
• Status: Active Grant

• Current Assignee: CommScope Technologies, LLC (CommScope Holding Company, Inc.)
• Original Assignee: LGC Wireless Incorporated (TE Connectivity Limited)
• Inventors: STRATFORD, SCOTT, VUCICH, DAVID
• Granted Patent: US 8,385,373 B2
• Time in Patent Office: Days
• US Class Current: 370/294
• CPC Class Codes: H04J 3/0608 Detectors therefor, e.g. correlators, state machines
• CPC Class Codes: H04L 27/2656 Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
• CPC Class Codes: H04L 5/1469 using time-sharing
• CPC Class Codes: H04W 56/008 detecting arrival of signal based on received raw signal

Abstract

A method of determining a boundary of a subframe in a time division duplexing (TDD) system is provided. The method detects a power level of a signal on at least one radio frequency, the signal comprising at least one subframe. A time-domain correlation is done on the detected signal with a first reference signal, wherein the first reference signal represents at least one subframe. The location in time of a boundary of the at least one subframe of the detected signal is determined based on the correlation of the detected signal and the first reference signal.

Claims

1. A method of determining a boundary of a transmission structure in a time division duplexing (TDD) system comprising:

detecting a power level of a signal on at least one radio frequency, the signal comprising at least one subframe;

time-domain correlating the detected signal with a first reference signal, wherein the first reference signal represents at least one subframe; and

determining a location in time of a boundary of the at least one subframe of the detected signal based on the correlation of the detected signal and the first reference signal.

2. The method of claim 1, further comprising:

correlating the detected signal with a second reference signal, wherein the first reference signal is a maximum subframe length expected to be detected and the second reference signal is a minimum subframe length expected to be detected; and

wherein determining the location in time of a boundary of a subframe determines the location in time of a boundary of the subframe based on the correlation of the detected signal with the first reference signal and the second reference signal.

3. The method of claim 2, further comprising:

summing the correlation of the first reference signal with the correlation of the second reference signal; and

wherein determining the location in time of a boundary of a subframe determines the location in time of a boundary of a subframe based on the summation of the first reference signal and the second reference signal.

4. The method of claim 2, wherein determining the location in time of a boundary of a subframe further comprises:

correlating the first reference signal and the detected signal at a first point in time to calculate a minimum subframe overlap;

correlating the second reference signal and the detected signal at the first point in time to calculate a maximum subframe overlap;

summing the minimum subframe overlap and the maximum subframe overlap to calculate a correlation result for the first point in time of the detected signal;

time shifting the reference signal relative to the detected signal; and

repeating the steps of;

correlating to calculate a minimum subframe overlap, correlating to calculate a maximum subframe overlap, summing the minimum subframe overlap and the maximum subframe overlap, and time shifting, to obtain time varied correlations between the reference signal and the detected samples.

5. The method of claim 1, further comprising:

summing a signal comprising a maximum subframe length expected to be detected and a signal comprising a minimum subframe length expected to be detected to form the first reference signal.

6. The method of claim 1, wherein detecting a signal further comprises:

detecting a signal comprising a plurality of subframes across a plurality of frames, each subframe having the same position within its respective frame;

wherein correlating the detected signal with a first reference signal further comprises correlating each subframe with the first reference signal; and

determining a frame boundary based on the correlation of each subframe.

7. The method of claim 6, wherein determining the location in time of a boundary of a subframe further comprises:

extracting a time value from a peak of a correlation result for each of the plurality of subframes;

sorting the time values; and

determining the location in time of a boundary of a subframe based on a median of the time values.

8. The method of claim 6, wherein determining the location in time of a boundary of a subframe further comprises:

summing correlation results for each of the plurality of subframes to produce composite correlation results having a length of one frame; and

determining the location in time of a boundary of a subframe based on the composite correlation results.

9. The method of claim 8, further comprising:

extracting a time value from a peak of a correlation result for each of the plurality of subframes;

sorting the time values; and

shifting correlation results such that a median of the time values is centered in each frame prior to summing correlation results for each of the plurality of subframes.

10. A method of switching in a time division duplexing (TDD) system comprising:

detecting a power level of a signal on at least one radio frequency, the signal comprising at least one subframe;

time-domain correlating the detected signal with a first reference signal, wherein the first reference signal represents at least one subframe;

determining a location in time of a boundary of the at least one subframe of the detected signal based on the correlation of the detected signal and the first reference signal; and

switching between an uplink communication path and a downlink communication path based on the determination of the location in time of the boundary of a subframe.

11. The method of claim 10, wherein switching between an uplink communication path and a downlink communication path is based on the determination of the location in time of the boundary of a subframe and a frame duration.

12. The method of claim 10, further comprising:

determining a location in time of a subframe boundary of another subframe detected subsequent in time to the at least one subframe;

determining a first time offset based on a reference and the subframe boundary of the at least one frame;

determining a second time offset based on a reference and the subframe boundary of the another subframe;

determining a difference between the first offset and the second offset;

determine a number of frames between the at least one subframe and the another frame;

divide the difference by the number of frames to determine a drift measurement; and

adjusting a timing of switching between an uplink communication path and a downlink communication path based on the drift measurement.

13. The method of claim 12, wherein re-determining a location in time of a subframe boundary is done periodically.

14. The method of claim 10, further comprising:

time-domain correlating the detected signal with a second reference signal, wherein the first reference signal is a maximum subframe length expected to be detected and the second reference signal is a minimum subframe length expected to be detected; and

wherein determining the location in time of a boundary of a subframe determines the location in time of a boundary of the subframe based on the correlation of the detected signal with the first reference signal and the second reference signal.

15. An apparatus for switching in a time division duplexing (TDD) system comprising:

a switch having a first port coupled to an uplink communication path, and a second port coupled to a downlink communication path;

a power level detector configured to measure a power level of radio frequency signals propagating through the switch;

a processing device configured to time-domain correlate a signal detected by the power level detector and comprising at least one subframe, with a first reference signal representing at least one subframe, the processing device configured to control the switch based on the correlation between the detected signal and the reference signal.

16. The apparatus of claim 15, wherein the processing device is further configured to determine a location in time of a boundary of the at least one subframe of the detected signal based on the correlation, and to control the switch based on the determination of the location in time of the boundary.

17. The apparatus of claim 16, wherein the processing device is further configured to correlate the detected signal with a second reference signal, wherein the first reference signal is a maximum subframe length expected to be detected and the second reference signal is a minimum subframe length expected to be detected;

and

wherein the processing device is further configured to determine the location in time of a boundary of the subframe based on the correlation of the detected signal with the first reference signal and the second reference signal.

18. The apparatus of claim 17, wherein the processing device is further configured to sum the correlation of the first reference signal with the correlation of the second reference signal;

and

wherein the processing device is further configured to determine the location in time of a boundary of the subframe based on the summation of the first reference signal and the second reference signal.

19. The apparatus of claim 16, wherein the processing device is further configured to set the switch to one of an uplink mode or a downlink mode in time for the start of an upcoming subframe by predicting the start of the upcoming subframe based on the duration of frame and the determined time of the boundary of a subframe.

20. The apparatus of claim 15, wherein the first reference signal is a summation of a signal comprising a maximum subframe length expected to be detected and a signal comprising a minimum subframe length expected to be detected.

21. The apparatus of claim 15, wherein the power level detector is further configured to detect a signal comprising at plurality of subframes across a plurality of frames, each subframe having the same position within its respective frame;

and

wherein the processing device is configured to correlate each subframe with the first reference signal.

22. The apparatus of claim 15, wherein the processing device is further configured to periodically re-determine the location in time of a subframe boundary and determine a difference between a predicted frame boundary and the re-determined frame boundary;

and

wherein the processing device is further configured to adjust a timing of setting the switch to one of an uplink mode or a downlink mode based on the determined difference between an predicted frame boundary and the re-determined frame boundary.

23. A communication system comprising:

at least one hub that is configured to communicate with a base station;

a plurality of remote antenna units communicatively coupled to the at least one hub and configured to communicatively couple signals between the at least one hub and a plurality of wireless terminals;

wherein the at least one hub further comprises;

a switch having a first port coupled to an uplink communication path, and a second port coupled to a downlink communication path;

a power level detector configured to measure a power level of a radio frequency signal propagating through the switch;

a processing device configured to time-domain correlate a detected signal comprising at least one subframe with a first reference signal representing at least one subframe, the processing device configured to control the switch based on the correlation between the detected signal and the reference signal.

24. The system of claim 23, wherein the processing device is further configured to determine a location in time of a boundary of the at least one subframe of the detected signal based on the correlation, and to control the switch based on the determination of the location in time of the boundary.

25. The system of claim 24, wherein the processing device is further configured to correlate the detected signal with a second reference signal, wherein the first reference signal is a maximum subframe length expected to be detected and the second reference signal is a minimum subframe length expected to be detected;

and

wherein the processing device is further configured to determine the location in time of a boundary of the subframe based on the correlation of the detected signal with the first reference signal and the second reference signal.

26. The system of claim 25, wherein the processing device is further configured to sum the correlation of the first reference signal with the correlation of the second reference signal;

and

wherein the processing device is further configured to determine the location in time of a boundary of the subframe based on the summation of the first reference signal and the second reference signal.

27. The system of claim 24, wherein the processing device is further configured to set the switch to one of an uplink mode or a downlink mode in time for the start of an upcoming subframe by predicting the start of the upcoming subframe based on the duration of frame and the determined time of the boundary of a subframe.

28. The system of claim 23, wherein the first reference signal is a summation of a signal comprising a maximum subframe length expected to be detected and a signal comprising a minimum subframe length expected to be detected.

29. The apparatus of claim 23, wherein the power level detector is further configured to detect a signal comprising at plurality of subframes across a plurality of frames, each subframe having the same position within its respective frame;

and

wherein the processing device is configured to correlate each subframe with the first reference signal.

30. The apparatus of claim 23, wherein the processing device is further configured to periodically re-determine the location in time of a subframe boundary and determine a difference between a predicted frame boundary and the re-determined frame boundary;

and

wherein the processing device is further configured to adjust a timing of setting the switch to one of an uplink mode or a downlink mode based on the determined difference between an predicted frame boundary and the re-determined frame boundary.