Basestation methods and apparatus for supporting timing synchronization

• US 7,974,261 B2
• Filed: 07/18/2005
• Issued: 07/05/2011
• Est. Priority Date: 06/13/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Laroia, Rajiv, Li, Junyi, Lane, Frank A.
• Primary Examiner(s): Appiah; Charles N
• Assistant Examiner(s): HOLLIDAY, JAIME MICHELE
• Application Number:
  US11/184,741
• Publication Number:
  US 20060280200A1
• Time in Patent Office: 2,178 Days
• Field of Search: 370/328
• US Class Current: 370/350
• CPC Class Codes: H04B 7/2125 Synchronisation
• CPC Class Codes: H04W 56/0045 compensating for timing error by altering transmission time

Abstract

A wireless terminal using OFDM signaling supporting both terrestrial and satellite base station connectivity operates using conventional access probe signaling in a first mode of operation to establish a timing synchronized wireless link with a terrestrial base station. In a second mode of operation, used to establish a timing synchronized wireless link with a satellite base station, a slightly modified access protocol is employed. The round trip signaling time and timing ambiguity between a wireless terminal and a satellite base station is substantially greater than with a terrestrial base station. The modified access protocol uses coding of access probe signals to uniquely identify a superslot index within a beaconslot. The modified protocol uses multiple access probes with different timing offsets to further resolve timing ambiguity and allows the satellite base station access monitoring interval to remain small in duration. Terrestrial base station location/connection information is used to estimate initial timing.

Claims

1. A method of operating a base station having a periodic downlink timing structure in which beacon slots occur on a periodic basis in the downlink, the method comprising:

monitoring, during a beacon slot, to detect the receipt of an access probe signal, the beacon slot including a plurality of superslots, the superslots within a beacon slot being identifiable through the use of a superslot index, each superslot including a plurality of symbol transmission time periods;

transmitting a response to the access probe signal, the response including information indicating at least one of;

i) a main superslot timing offset correction, the main superslot timing offset correction being an integer multiple of a superslot time period and being one of a plurality of possible main superslot timing offset correction values and ii) a superslot identifier indicating the position of a downlink superslot within the beacon slot during which the base station received the access probe signal to which the received response corresponds.

2. The method of claim 1, wherein the transmitted response includes said main superslot timing offset correction.

3. The method of claim 2, wherein said monitoring is performed for said portion during each access interval which occurs in an uplink timing structure.

6. The method of claim 1, further comprising:

transmitting at least one beacon signal during each beacon slot.

7. The method of claim 6, wherein said beacon signal is a single tone signal.

8. The method of claim 7, wherein said beacon signal has a duration of less than three OFDM symbol transmission time periods.

9. The method of claim 6, wherein said access probe signal is an OFDM signal.

10. The method of claim 9, wherein transmitting a response to a received access probe signal includes encoding a downlink superslot identifier indicating the position of the superslot within a downlink beacon slot during which the base station received the access probe signal.

11. The method of claim 10, wherein the received access probe includes an encoded downlink superslot identifier, the method further comprising:

decoding the encoded downlink superslot identifier;

determining said main superslot timing offset correction from a difference between the decoded downlink superslot identifier and a superslot index within a downlink beacon slot of the downlink superslot during which the access probe was received.

12. The method of claim 9, wherein said main superslot timing offset correction is an integer value and wherein transmitting a response to a received access probe signal further includes:

encoding the determined main superslot uplink timing offset correction in said response.

13. The method of claim 12, wherein transmitting a response to a received access probe signal further includes:

encoding sub-superslot uplink timing correction information in said response, said super-slot uplink timing correction information indicating a timing adjustment smaller than the duration of a superslot.

14. The method of claim 13, wherein said main superslot timing offset correction and said sub-superslot uplink timing correction information are encoded as part of a single coded value.

15. The method of claim 13, wherein said main superslot timing offset correction and said sub-superslot uplink timing correction information are encoded as two separate values.

16. The method of claim 1, wherein transmitting a response to a received access probe signal includes:

transmitting said main superslot timing correction as part of said response; and

transmitting sub-superslot uplink timing correction information as part of said response, said sub-superslot uplink timing correction information indicating a timing adjustment smaller than the duration of a superslot.

17. The method of claim 1, wherein said base station is a satellite base station and wherein said access probe signal and said transmitted response are OFDM signals.

18. The method of claim 1 wherein said response to the access probe signal includes an indicated main superslot timing offset correction which is a non-zero value.

19. The method of claim 1, wherein said beacon slot includes a superslot which includes a beacon signal and also includes a superslot which does not include a beacon signal.

20. The method of claim 19 wherein said beacon slot includes more superslots which do not include a beacon signal than superslots which include a beacon signal.

21. The method of claim 1, wherein each beacon slot includes a fixed number of indexed superslots.

22. The method of claim 21, wherein each superslot includes an access interval.

4. The method of 1, wherein said step of transmitting a response to the access probe signal includes transmitting the response in a downlink superslot having a predetermined superslot time offset from the time the access probe was received.

5. The method of claim 4, wherein said step of transmitting a response includes transmitting a device identifier identifying the device which transmitted the access probe being responded to and a sub-superslot timing correction indicator value.

23. A base station using a periodic downlink timing structure in which beacon slots occur on a periodic basis, the base station comprising:

a receiver module for receiving and detecting, during a beacon slot, an access probe signal from a wireless terminal, the beacon slot including a plurality of superslots, the superslots within a beacon slot being identifiable through the use of a superslot index, each superslot including a plurality of symbol transmission time periods;

a transmitter module for transmitting, in response to the access probe signal, a response including information indicating at least one of;

i) a main superslot timing offset correction, the main superslot timing offset correction being an integer multiple of a superslot time period and being one of a plurality of possible main superslot timing offset correction values and ii) a superslot identifier indicating the position of a superslot within the beacon slot during which the base station received the access probe signal to which the received response corresponds.

24. The base station of claim 23, wherein said receiver module includes means for detecting the receipt of an access probe during predetermined periodic time periods, at least one of said predetermined periodic time periods occurring during a portion of at least one superslot time period in each beacon slot, said portion being less than one half the duration of a superslot.

25. The base station of claim 23, further comprising:

means for transmitting at least one beacon signal during each beacon slot.

26. The base station of claim 25, wherein said beacon signal is a single tone signal.

27. The base station of claim 26, wherein said beacon signal has a duration of less than three OFDM symbol transmission time periods.

28. The base station of claim 23, further comprising:

an encoder module for including in the transmitted response signal, a superslot identifier indicating the position of the superslot within a beacon slot during which the base station received the access probe signal.

29. The base station of claim 23, further comprising:

an encoder module for encoding sub-superslot uplink timing correction information in said response, said super-slot uplink timing correction information indicating a timing adjustment smaller than the duration of a superslot.

30. The base station of claim 29,

wherein the received access probe includes a communications device identifier and

wherein the base station further comprises:

a decoding module for decoding the received access probe to recover the encoded communications device identifier.

31. The base station of claim 23, wherein the received access probe includes an encoded superslot identifier, the base station further comprising:

a decoding module for decoding the received access probe to recover the encoded superslot identifier;

a timing correction determination module for determining said main superslot timing offset correction from a difference between the decoded superslot identifier and a downlink superslot index within a beacon slot of the superslot in which the access probe was received.

32. A base station using a periodic downlink timing structure in which beacon slots occur on a periodic basis, the base station comprising:

receiver means for receiving and detecting, during a beacon slot, an access probe signal from a wireless terminal, the beacon slot including a plurality of superslots, the superslots within a beacon slot being identifiable through the use of a superslot index, each superslot including a plurality of symbol transmission time periods;

transmitter means for transmitting, in response to the access probe signal, a response including information indicating at least one of;

i) a main superslot timing offset correction, the main superslot timing offset correction being an integer multiple of a superslot time period and being one of a plurality of possible main superslot timing offset correction values and ii) a superslot identifier indicating the position of a superslot within the beacon slot during which the base station received the access probe signal to which the received response corresponds.

33. The base station of claim 32, further comprising:

encoding means for including in the transmitted response signal, a superslot identifier indicating the position of the superslot within a beacon slot during which the base station received the access probe signal.

34. The base station of claim 32, further comprising:

encoding means for encoding sub-superslot uplink timing correction information in said response, said super-slot uplink timing correction information indicating a timing adjustment smaller than the duration of a superslot.

35. A computer readable medium including machine executable instruction for use in a base station, said base station using a periodic downlink timing structure in which beacon slots occur on a periodic basis, the computer readable medium comprising:

instructions for causing said base station to monitor, during a beacon slot to detect the receipt of an access probe signal, the beacon slot including a plurality of superslots, the superslots within a beacon slot being identifiable through the use of a superslot index, each superslot including a plurality of symbol transmission time periods;

instructions for causing said base station to transmit, in response to the access probe signal, a response including information indicating at least one of;

i) a main superslot timing offset correction, the main superslot timing offset correction being an integer multiple of a superslot time period and being one of a plurality of possible main superslot timing offset correction values and ii) a superslot identifier indicating the position of a superslot within the beacon slot during which the base station received the access probe signal to which the received response corresponds.

36. The computer readable medium of claim 35, wherein said monitoring to detect the receipt of an access probe is performed on a predetermined periodic basis according to the occurrence of access intervals in an uplink timing structure, each access interval being shorter than a downlink superslot time period.

37. The computer readable medium of claim 35, further comprising:

instructions for causing said base station to transmit at least one beacon signal during each beacon slot.

38. A communications device which uses a periodic downlink timing structure in which beacon slots occur on a periodic basis, the communications device comprising:

a processor configured to;

receive and detect, during a beacon slot, an access probe signal from a wireless terminal, the beacon slot including a plurality of superslots, the superslots within a beacon slot being identifiable through the use of a superslot index, each superslot including a plurality of symbol transmission time periods;

transmit, in response to the access probe signal, a response including information indicating at least one of;

i) a main superslot timing offset correction, the main superslot timing offset correction being an integer multiple of a superslot time period and being one of a plurality of possible main superslot timing offset correction values and ii) a superslot identifier indicating the position of a superslot within the beacon slot during which the base station received the access probe signal to which the received response corresponds.