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

• US 20060052108A1
• Filed: 11/03/2005
• Published: 03/09/2006
• Est. Priority Date: 10/16/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Laroia, Rajiv, Lane, Frank A.
• Granted Patent: US 7,720,479 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• 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.