Methods and Apparatus for Mobility Influenced Handoff

• US 20080233958A1
• Filed: 03/21/2007
• Published: 09/25/2008
• Est. Priority Date: 03/21/2007
• Status: Active Grant

• Current Assignee: Cellular Transitions, LLC (Dominion Harbor Enterprises, LLC)
• Original Assignee: Nextwave Broadband Incorporated (AT&T, Inc.)
• Inventors: Sutton, Todd R., Robbins, Barry R.
• Granted Patent: US 8,855,637 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04W 16/14 Spectrum sharing arrangements between different networks
• CPC Class Codes: H04W 36/0094 Definition of hand-off measurement parameters
• CPC Class Codes: H04W 36/32 by location or mobility data, e.g. speed data
• CPC Class Codes: H04W 36/324 by mobility data, e.g. speed data
• CPC Class Codes: H04W 88/06 adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals

Abstract

In a wireless communication system, a mobility factor is used to influence handoff. If a subscriber station has been in a low mobility state for some period of time, the system may handoff operation from a first service type to a second service type. If the mobility factor indicates that the subscriber station is moving, the system may handoff operation from the second service type back to the first service type.

Claims

1. A method of handoff in a wireless system, the method comprising:

determining a first value of a mobility factor indicative of a relative motion of a subscriber station communicating using a first service type;

determining an availability of an alternative service type; and

transferring communications to the alternative service type if the first value indicates that the subscriber station has been in a low mobility state for at least a predetermined period of time.

2. The method of claim 1, wherein determining the availability of the alternate service type comprises sending a scan request message to a base station.

3. The method of claim 1, wherein determining the availability of the alternate service type comprises sending a command from a base station to the subscriber station commanding the subscriber station to provide information about an availability of the alternative service type.

4. The method of claim 1, further comprising:

determining a second value of the mobility factor after transferring communications to the alternative service type; and

transferring communications to the first service type if the second value indicates that the subscriber station is in motion.

5. The method of claim 4, wherein transferring communications to the first service type comprises scanning licensed spectrum for an availability of the first service type.

6. The method of claim 5, wherein determining the availability of alternative service type comprises scanning for license exempt service.

7. The method of claim 4 further comprising receiving at the subscriber station the second value from a base station.

8. The method of claim 1, wherein determining the availability of alternative service type comprises scanning for license exempt service.

9. A processor-readable storage medium containing one or more instructions for a processor, the processor executing the one or more instructions performing the method comprising:

determining a first value of a mobility factor indicative of a relative motion of a subscriber station communicating using a first service type;

determining an availability of an alternative service type; and

transferring communications to the alternative service type if the first value indicates that the subscriber station has been in a low mobility state for at least a predetermined period of time.

10. A subscriber station comprising:

means for determining a first value of a mobility factor indicative of a relative motion of the subscriber station communicating using a first service type;

means for determining an availability of an alternative service type; and

means for transferring communications to the alternative service type if the first value indicates that the subscriber station has been in a low mobility state for some period of time.

11. A base station comprising:

a monitoring module that determines a mobility factor of a subscriber station serviced over a first service type;

a timing module that generates a handoff indication based on the mobility factor when the subscriber station has been in a low mobility state for an extend period of time; and

a message generator coupled to the timing module that sends a command to the subscriber station commanding the subscriber station to report an availability of an alternative service type in response to the handoff indication.

12. A subscriber station comprising:

a monitoring module that determines a mobility factor indicative of subscriber station motion;

a timing module that generates a handoff indication based on the mobility factor when the subscriber station has been in a low mobility state for an extend period of time;

a scanner that searches for a second service type and determines the availability of the second service type; and

a message generator that requests a handoff to the second service type in response to the handoff indication.

13. The subscriber station of claim 12, wherein the monitoring module comprises a mobility metric module configured to generate a mobility metric based, at least in part, on a wireless signal received by the subscriber station.

14. The subscriber station of claim 12, wherein the monitoring module comprises a pilot signal correlator configured to correlate pilot signals of at least two distinct Orthogonal Frequency Division Multiplex (OFDM) symbols separated by a time offset.

15. The subscriber station of claim 12, wherein the monitoring module comprises a frequency offset based mobility module configured to determine a frequency offset mobility metric based on a change in a frequency offset relative to a desired receive frequency over a time period by determining a product of symbol samples from an Orthogonal Frequency Division Multiplex (OFDM) symbol with corresponding samples from a cyclic prefix from the OFDM symbol.

16. The subscriber station of claim 12, wherein the monitoring module comprises a power detector configured to determine a power based mobility metric based in part on a change in an average power of received Orthogonal Frequency Division Multiplex (OFDM) symbols.

17. The subscriber station of claim 12, wherein the monitoring module comprises:

a plurality of mobility metric modules to generate a plurality of distinct mobility metrics, each mobility metric module configured to generate one of the plurality of distinct mobility metrics based, at least in part, on a wireless signal received by the subscriber station;

a combiner configured to combine the plurality of mobility metrics to generate a composite mobility metric; and

a quantizer configured to quantize the composite mobility metric to generate the mobility factor.

18. The subscriber station of claim 12, wherein the monitoring module comprises:

a mobility metric module configured to generate a mobility metric based, at least in part, on a wireless signal received by the subscriber station;

a state machine configured to determine an operating state based at least in part on information carried on the wireless signal; and

a multiplexer configured to select as the mobility factor one of a value based on the mobility metric or a predetermined value based on the operating state.

19. A communication system comprising:

a base station that offers licensed service and license exempt service; and

a subscriber station capable of wirelessly communicating with the base station over both licensed service and license exempt service and that determines to handoff from the licensed service to the license exempt service based in part on a mobility factor.

20. The communication system of claim 19, wherein the mobility factor indicates one of a limited number of discrete mobility states.