Methods and apparatus for supporting uplinks with remote base stations

• US 20060280199A1
• 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 8,036,205 B2
• Time in Patent Office: Days
• US Class Current: 370/458
• CPC Class Codes: H04B 7/1851 Systems using a satellite or space-based relay H04B7/18508, H04B7/18521 take precedence; providing specific services H04B7/18523 - H04B7/18576
• CPC Class Codes: H04B 7/2125 Synchronisation
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 27/2614 Peak power aspects
• CPC Class Codes: H04W 56/00 Synchronisation arrangements

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 communications device for use in a communications system where beacon time slots occur on a periodic basis, a beacon signal being transmitted by a base station during each beacon time slot according to a periodic downlink timing structure, said downlink timing structure including a plurality of superslots within each beacon slot, the individual 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:

receiving at least one beacon signal;

processing the received beacon signal to determine a downlink timing reference point, superslots occurring within a beacon slot having a predetermined relationship to the determined downlink timing reference point;

coding information in a first access probe signal that identifies a first superslot index;

transmitting the first access probe signal that identifies a first superslot index;

monitoring to determine if a response to the first access probe signal was received from the base station; and

if it is determined that a response was received, performing a transmission timing adjustment as a function of information included in said response.

2. The method of claim 1, where the first access probe signal is transmitted at a first timing offset relative to the start of a first superslot having said first superslot index.

3. The method of claim 2, further comprising:

if it is determined that a response to the first access probe signal was not received;

coding information in a second access probe signal that identifies a second superslot index;

transmitting the second access probe signal that identifies the second superslot index at a second timing offset relative to the start of a second superslot having said second superslot index as determined by said communications device, the second timing offset being different from the first timing offset.

4. The method of claim 3, wherein the first and second access probe signals are transmitted in different downlink beacon slots;

and

wherein the second superslot index is the same, or different from, the first superslot index.

5. The method of claim 4, wherein the first and second access probe signals are transmitted in different beacon slots;

and

wherein the second superslot index is different from the first superslot index.

6. The method of claim 3, wherein the first and second access probes are transmitted in the same beacon slot, said second superslot index being different from said first superslot index.

7. The method of claim 6, wherein said response includes information identifying the one of the probe signals being responded to.

8. The method of claim 3, further comprising:

coding information in a third access probe signal that identifies a third superslot index;

transmitting the third access probe signal at a third timing offset relative to the start of a third superslot having said third superslot index, wherein the third timing offset is different from the first and second timing offsets.

9. The method of claim 8,

wherein the second timing offset is different from the first timing offset by an initial timing offset value plus a first integer multiple of a fixed step size timing offset;

and

wherein the third timing offset is different from the first timing offset by an initial timing offset value plus a second integer multiple of said fixed step size timing offset which is different from said first integer multiple of said fixed step size timing offset.

10. The method of claim 9,

wherein said base station is a satellite base station;

and

wherein the round trip time between said satellite base station and said communications device for signals traveling at the speed of light is greater than the duration of a superslot.

11. The method of claim 10, wherein said round trip time is greater than 0.2 seconds.

12. The method of claim 9, wherein the fixed step size is less than the duration of a base station access interval, the base station access interval being a period of time during which said base station is responsive access probe signals.

13. The method of claim 9, wherein the fixed step size is greater than the duration of a symbol transmission period.

14. The method of claim 9, wherein said first and second integer multipliers can be either positive or negative numbers.

15. The method of claim 1, further comprising:

determining a time at which to transmit said first access probe as a function of location information determined from a signal received from a terrestrial base station.

16. The method of claim 15, wherein determining a time at which to transmit said first access probe is further performed as a function of known information indicating the location of said terrestrial base station and the location of said satellite base station.

17. The method of claim 1,

wherein the first access probe is an OFDM signal.

18. The method of claim 17, wherein the received beacon signal is an OFDM signal corresponding to a single OFDM tone.

19. A communications device for use in a communications system where beacon time slots occur on a periodic basis, a beacon signal being transmitted by a base station during each beacon time slot according to a periodic downlink timing structure, said downlink timing structure including a plurality of superslots within each beacon slot, the individual 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 communications device comprising:

a receiver for receiving at least one beacon signal;

a received signal processing module for received signals including received beacon signals, the processing module operating to determine a downlink timing reference point from at least one received beacon signal, superslots occurring within a beacon slot having a predetermined relationship to the determined downlink timing reference point;

a coding module for coding information in a first access probe signal that identifies a first superslot index;

a transmitter for transmitting the first access probe signal that identifies a first superslot index;

a monitoring module used to determine if a response to the first access probe signal was received from the base station; and

a timing correction module, responsive to said monitoring module, for performing a transmission timing adjustment as a function of information included in a received access probe response.

20. The device of claim 19, where the transmitter module includes:

means for transmitting the first access probe signal at a first timing offset relative to the start of a first superslot having said first superslot index.

21. The device of claim 20,

wherein said coding module includes means for coding information in a second access probe signal that identifies a second superslot index if it is determined that a response to the first access probe signal was not received:

and

wherein said transmitter includes means for transmitting the second access probe signal that identifies the second superslot index at a second timing offset relative to the start of a second superslot having said second superslot index, the second timing offset being different from the first timing offset.

22. The device of claim 21, wherein said transmitter transmits the first and second access probe signals are transmitted in different beacon slots;

and

wherein the second superslot index is the same, or different from, the first superslot index.

23. The device of claim 22, wherein the first and second access probe signals are transmitted in different beacon slots;

and

wherein the second superslot index is different from the first superslot index.

24. The device of claim 21, wherein the first and second access probes are transmitted in the same beacon slot, said second superslot index being different from said first superslot index.

25. The device of claim 24, wherein said response includes information identifying the one of the probe signals being responded to, the device further including:

a decoder module for decoding the information in the response identifying the one of the probe signals.

26. The device of claim 21,

wherein said coding module further includes means for coding information in a third access probe signal that identifies a third superslot index;

and

and wherein said transmitting the third access probe signal at a third timing offset relative to the start of a third superslot having said third superslot index, wherein the third timing offset is different from the first and second timing offsets.

27. The device of claim 26, further comprising:

a storage device including stored fixed step size timing offset information; and

wherein the second timing offset is different from the first timing offset by a first integer multiple of said stored fixed step size timing offset; and

wherein the third timing offset is different from the first timing offset by a second integer multiple of said stored fixed step size, the second interfere multiple being different from said first integer multiple of said fixed step size timing offset.

28. The device of claim 27,

wherein said base station is a satellite base station;

and

wherein the round trip time between said satellite base station and said wireless terminal for signals traveling at the speed of light is greater than the duration of a superslot.

29. The device of claim 28, wherein said round trip time is greater than 0.2 seconds.

30. The device of claim 27, wherein the stored fixed step size is less than the duration of a base station access interval, the base station access interval being a period of time during which said base station is responsive access probe signals.

31. The device of claim 19, wherein said transmitter is an OFDM transmitter.

32. The device of claim 19, further comprising:

means for determining a time at which to transmit said first access probe as a function of location information determined from a signal received from a terrestrial base station.

33. The device of claim 32, wherein said device includes stored information indicating the location of said terrestrial base station and the location of said satellite base station.