Methods and apparatus of improving inter-sector and/or inter-cell handoffs in a multi-carrier wireless communications system

• US 20050085265A1
• Filed: 10/14/2004
• Published: 04/21/2005
• Est. Priority Date: 10/16/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm Flarion Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Laroia, Rajiv, Lane, Frank A.
• Granted Patent: US 6,993,333 B2
• Time in Patent Office: Days
• US Class Current: 455/560
• CPC Class Codes: H04L 27/2602 Signal structure
• CPC Class Codes: H04L 5/0042 intra-user or intra-terminal allocation
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04L 5/0053 Allocation of signaling, i.e. of overhead other than pilot signals
• CPC Class Codes: H04W 36/0072 of resource information of target access point
• CPC Class Codes: H04W 36/08 Reselecting an access point

Abstract

A wireless communications system, e.g., an OFDM system, uses a plurality of carrier frequencies each with an associated frequency band. A base station sector transmitter in the system transmits ordinary signaling, e.g., user data, in its own assigned band. In addition the sector base station transmitter periodically transmits beacon signals into its own frequency band and the frequency bands used by adjacent sector transmitters for their ordinary signaling. Beacon signals, being short duration high power signals with sector transmission power concentrated on one or a few tones, are easily detectable. Each beacon signal may be identified as to the source base station sector transmitter, e.g., based on tone. A mobile node, tuned to a single carrier band, receives a plurality of beacon signals, identifies the sources of the received beacons, compares the received strength of the beacons, and makes handoff decisions, without having to switch carrier band.

Claims

1. A method of operating a first base station transmitter, the method comprising:

i) operating the first base station transmitter to transmit into a first frequency band during a first period of time during which said first base station transmitter does not transmit into a second frequency band;

ii) operating the first base station transmitter to transmit into a second frequency band during a second period of time which is shorter than said first period of time, said first base station transmitting into said second frequency band for a period of time which is less than 1/N the period of time it transmits into said first frequency band, where N is a positive value greater than 2; and

iii) repeating steps i and ii.

2. The method of claim 1, wherein steps i and ii are repeated over time at periodic intervals such that the amount of time said first transmitter transmits into said first frequency band remains on average greater than the amount of time it transmits into said second frequency band.

3. The method of claim 1, wherein during said second period of time said first base station transmitter does not transmit into said first frequency band.

4. The method of claim 1, wherein said first transmitter transmits into said first frequency band at least 20 times as much, in terms of time, as the first transmitter transmits into said second frequency band.

5. The method of claim 1, wherein said first and second frequency bands are the same size.

6. The method of claim 5, wherein operating the first base station transmitter to transmit into a second frequency band during a second period of time includes concentrating at least 60 percent of the transmitted power on one or more tones occupying less than one fifth of the second frequency band.

7. The method of claim 5, wherein operating the first base station transmitter to transmit into a second frequency band during a second period of time includes transmitting a tone with at least 20 times the average per tone power used to transmit tones in a preceding 1 second time interval.

8. The method of claim 1, further comprising:

operating the first base station to transmitter to transmit into said first frequency band during said second period of time.

9. The method of claim 1, wherein step i of transmitting into a first frequency band includes transmitting user data into said first frequency band on a plurality of different tones.

10. The method of claim 9, wherein said user data includes at least one of voice, text, and user application data.

11. The method of claim 9, wherein step ii of transmitting into a second frequency band includes transmitting transmitter information but no user specific data.

12. The method of claim 11, wherein said transmitter information includes at least one of cell identification information and sector identification information.

13. The method of claim 11, wherein step ii of transmitting into a second frequency band involves transmitting information on fewer tones than the number of tones used to transmit information into said first frequency band.

14. The method of claim 11, wherein said number of tones used to transmit information into the second frequency band is less than 3.

15. The method of claim 11, wherein steps i and ii each include transmitting at least one OFDM signal including at least one complex symbol.

16. The method of claim 15, wherein step ii includes transmitting two OFDM symbols.

17. The method of claim 11, wherein said transmitter information is transmitted using at least one tone, said first transmitter transmitting at least M times the amount of power on said at least one tone than the transmitter transmits on any one tone used to transmit user data during said first period of time into said first frequency band, where M is a positive integer greater than 2.

18. The method of claim 11, wherein said transmitter information is transmitted using at least one tone, said first transmitter transmitting said at least one tone using at least 20 times the average per tone power used to transmit tones during a preceding 1 second time interval.

19. The method of claim 17, wherein M is at least 5.

20. The method of claim 15, wherein the first period of time includes a plurality of symbol transmission time periods and wherein the second period of time includes fewer symbol transmission time periods than said first period of time.

21. The method of claim 1, further comprising:

iii) operating a second base station transmitter to transmit into said second frequency band during a third period of time during which said second base station transmitter does not transmit into said first frequency band;

iv) operating the second base station transmitter to transmit into said first frequency band during a fourth period of time which is shorter than said third period of time, said second base station transmitter transmitting into said first frequency band for a period of time which is less than 1/N the period of time the second base station transmitter transmits into said second frequency band; and

v) repeating steps iii and iv.

22. The method of claim 21, wherein the repeating of steps iii and iv are performed multiple times at periodic intervals.

23. The method of claim 21, wherein during said fourth period of time said second base station transmitter does not transmit into said second frequency band.

24. The method of claim 21, wherein the second base station transmitter transmits user data including at least one of text and voice data during said third period of time.

25. The method of claim 24, wherein said second base station transmitter transmits base station information during said fourth period of time but no user data.

26. The method of claim 25, wherein the first and second base station transmitters are in different physically adjacent cells.

27. The method of claim 25, wherein the first and second base station transmitters are in the same cell.

28. The method of claim 27,

wherein said first and second transmitters are sector transmitters;

and

wherein there is a fixed time offset between performing step ii using the first base station transmitter and step iv using the second base station transmitter.

29. A communications system, comprising:

a first base station, said first base station including;

a first transmitter for transmitting signals into first and second frequency bands; and

first transmitter control means for controlling said first transmitter to;

i) transmit into a first frequency band during a first period of time during which said first base station transmitter does not transmit into a second frequency band;

ii) transmit into a second frequency band during a second period of time, said second period of time being at least less than one fifth said first period of time; and

iii) repeat the sequence of steps i and ii at periodic intervals.

30. The communication system of claim 29, wherein during said second period of time said first base station transmitter does not transmit into said first frequency band.

31. The communication system of claim 29, wherein said first transmitter control means controls said first transmitter to transmit into said first frequency band during said second time period.

32. The communications system of claim 29, wherein said first and second frequency bands are the same size.

33. The communications system of claim 29, wherein said first base station further includes:

a set of stored user data to transmit, said set of stored user data including at least one of voice, text and user application data; and

wherein controlling the first transmitter to transmit into said first frequency band during the first time period includes controlling the transmitter to transmit at least some of said stored user data into said first frequency band.

34. The communications system of claim 33, wherein said first base station further includes:

transmitter information; and

wherein controlling the first transmitter to transmit into said second frequency band includes controlling the transmitter to transmit at least some of said transmitter information without transmitting any user data into said second frequency band.

35. The communications system of claim 34, wherein said first transmitter control means controls said transmitter to transmit fewer signal tones into said second frequency band during said second time period than it transmits into said first frequency band during said first time period.

36. The communications system of claim 34, wherein less than 4 signal tones are transmitted into said second frequency band by said first transmitter during said second time period.

37. The communications system of claim 36, wherein the signal tones transmitted into said second frequency band are transmitted with at least twice the maximum power used to transmit user data into said first frequency band during said first time period.

38. The communication system of claim 29, further comprising:

a second transmitter for transmitting signals into said first and second frequency bands; and

second transmitter control means for controlling said second transmitter to;

iii) transmit into said second frequency band during a third period of time during which said second base station transmitter does not transmit into said first frequency band;

iv) transmit into said first frequency band during a fourth period of time which is shorter than said third period of time, said second transmitter transmitting into said first frequency band for a period of time which is less than 1/N the period of time the second transmitter transmits into said second frequency band; and

v) repeat steps iii and iv.

39. The system of claim 38, wherein the first and second transmitters are in different physically adjacent cells.

40. The system of claim 38, wherein the first and second transmitters are in different sectors of the same cell.

41. The system of claim 40,

wherein said first transmitter control means causes said first transmitter to transmit user data and transmitter information relating to said first transmitter into said first frequency band during said first time interval;

and

causes transmitter information relating to said first transmitter but no text or voice user data to be transmitted into said second frequency band.

42. The system of claim 41,

wherein said second transmitter control means causes said second transmitter to transmit user data and transmitter information relating to said second transmitter into said second frequency band;

and

causes transmitter information relating to said second transmitter but no text or voice user data to be transmitted into said first frequency band.

43. The method of claim 42, wherein said transmitter information relating to the first transmitter is a first transmitter identifier and wherein said transmitter information relating to the second transmitter is a second transmitter identifier.