Basestation methods and apparatus for supporting timing synchronization

• US 20060280200A1
• Filed: 07/18/2005
• Published: 12/14/2006
• 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.
• Granted Patent: US 7,974,261 B2
• Time in Patent Office: Days
• US Class Current: 370/458
• 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 time slots occur on a periodic basis in the downlink, each beacon time 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, the method comprising:

monitoring to detect the receipt of an access probe signal;

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

i) an amount of an indicated main superslot timing offset correction, the amount of the main superslot timing offset correction being an integer multiple of a superslot time period;

ii) a superslot identifier indicating the position of a downlink superslot within a beacon slot during which the base station received the access probe signal to which the received response corresponds;

iii) an identifier that identifiers the communications device which transmitted the access probe signal to which the received response corresponds, and iv) an identifier that identifies the access probe to which the response being responding to.

2. The method of claim 1, 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.

5. 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 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.

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

decoding the encoded superslot identifier;

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

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

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

14. The method of claim 13, 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.

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

16. The method of claim 14, wherein said main superslot timing offset and said sub-superslot time offset are encoded as two separate values.

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.

3. 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 at a predetermined superslot time offset from the time the response was received.

4. The method of claim 3, 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 indictor value.

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

a receiver module for receiving and detecting an access probe signal from a wireless terminal;

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

i) an amount of an indicated main superslot timing offset correction, the amount of the main superslot timing offset correction being an integer multiple of a superslot time period;

ii) a superslot identifier indicating the position of a superslot within a beacon slot during which the base station received the access probe signal to which the received response corresponds;

iii) an identifier that identifiers the communications device which transmitted the access probe signal to which the received response corresponds, and iv) an identifier that identifies the access probe to which the response being responding to.

19. The base station of claim 18, 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.

20. The base station of claim 18, further comprising:

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

21. The base station of claim 20, wherein said beacon signal is a single tone signal.

22. The base station of claim 21, wherein said beacon signal has a duration of less than three OFDM symbol transmission time periods.

23. The base station of claim 18, 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.

24. The base station of claim 18, 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.

25. The base station of claim 24,

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.

26. The base station of claim 18, 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 a main superslot timing offset correction which is an integer multiple of the duration of a superslot from the difference between the decoded superslot identifier and the downlink superslot index within a beacon slot of the superslot in which the access probe was received.