Method and system for management of inter-frequency handoff

• US 8,804,670 B1
• Filed: 02/17/2011
• Issued: 08/12/2014
• Est. Priority Date: 02/17/2011
• Status: Active Grant

• Current Assignee: Sprint Spectrum LP (Deutsche Telekom AG)
• Original Assignee: Sprint Spectrum LP (Deutsche Telekom AG)
• Inventors: Talley, Ryan S., Malreddy, Muralidhar, Narendran, Rajveen, Srivinas, Shilpa Kowdley
• Primary Examiner(s): Hailu, Kibrom T
• Application Number:
  US13/029,610
• Time in Patent Office: 1,272 Days
• Field of Search: None
• US Class Current: 370/332
• CPC Class Codes: H04W 36/0085 Hand-off measurements
• CPC Class Codes: H04W 36/14 Reselecting a network or an air interface
• CPC Class Codes: H04W 4/00 Services specially adapted for wireless communication networks; Facilities therefor
• CPC Class Codes: H04W 84/045 using private Base Stations, e.g. femto Base Stations, home Node B
• CPC Class Codes: H04W 92/00 Interfaces specially adapted for wireless communication networks

Abstract

Disclosed is a method and corresponding system to help improve inter-frequency handoff. While a radio access network (RAN) is serving one or more devices, the RAN will receive from the device(s) one or more reports of air interface quality on each of a plurality of potential target frequency channels. Dynamically based on the reported air interface quality information, the RAN will then select a given one of the potential target frequency channels to be a preferred target frequency channel. When a given device is fading from coverage, the RAN will then direct the device to scan for coverage on the preferred target frequency channel that was selected based on the earlier reported measures of air interface quality, so as to facilitate inter-frequency handoff.

Claims

1. A method comprising:

while a radio access network (RAN) is serving one or more mobile stations on a first frequency channel, the RAN collecting from the one or more mobile stations measurements of air interface quality of a plurality of second frequency channels;

the RAN using the collected measurements as a basis to select a preferred second frequency channel to use as a handoff target;

the RAN detecting that a particular mobile station is fading from coverage on the first frequency channel; and

responsive to the detecting, (i) the RAN requesting the particular mobile station to determine and report to the RAN measurements of sector quality on the selected second frequency channel, (ii) the RAN receiving in response from the particular mobile station the requested measurements of sector quality on the selected second frequency channel, (iii) the RAN selecting a target sector based on the received measurements of sector quality, and (iv) the RAN directing the particular mobile station to hand off to the selected target sector on the selected second frequency channel.

2. The method of claim 1, wherein the collecting of measurements of air interface quality of the plurality of second frequency channels occurs before the detecting that the particular mobile station is fading, and wherein the using of the collected measurements as a basis to select the preferred second frequency channel occurs before the detecting that the particular mobile station is fading.

3. A method comprising:

a radio access network (RAN) serving one or more mobile stations through air interface communication on a first frequency channel;

while serving the one or more mobile stations through air interface communication on the first frequency channel, the RAN applying a pre-selection process to dynamically pre-select a preferred second frequency channel to be used as a handoff target, wherein the pre-selection process comprises (i) receiving from the one or more mobile stations reports of air interface quality measured by the one or more mobile stations on second frequency channels and (ii) using the received reports as a basis to select one of the second carrier frequency channels as the preferred second frequency channel; and

subsequent to applying the pre-selection process, the RAN detecting that a particular one of the one or more mobile stations is fading from coverage on the first frequency channel, and in response to the detecting, (a) the RAN requesting the particular mobile station to determine and report to the RAN measurements of sector quality on the dynamically pre-selected second frequency channel, (b) the RAN receiving in response from the particular mobile station the requested measurements of sector quality on the dynamically pre-selected second frequency channel, (c) based on the received measurements of sector quality on the dynamically pre-selected second frequency channel, the RAN selecting a target sector on the dynamically pre-selected second frequency channel, and (d) the RAN directing the particular mobile station to hand off to the selected target sector on the dynamically pre-selected second frequency channel.

4. The method of claim 3, carried out by a base station of the RAN.

5. The method of claim 4, wherein the base station is a femtocell, the first frequency channel is a femtocell frequency channel, and the second frequency channels are macro network frequency channels.

6. The method of claim 3, wherein receiving from the one or more mobile stations reports of air interface quality measured by the one or more mobile stations on second frequency channels comprises receiving the reports as responses to one or more Carrier Frequency Search Request Messages (CFSRQMs) that the RAN sends to the one or more mobile stations.

7. The method of claim 6, further comprising the RAN sending the CFSRQMs to the one or more mobile stations while the one or more mobile stations are active and being served by the RAN and not fading from coverage of the first frequency channel.

8. The method of claim 3, wherein using the received reports of air interface quality measured by the one or more mobile stations on the second frequency channels as a basis to select one of the second frequency channels as the preferred second frequency channel comprises:

determining respectively for each particular second frequency channel an aggregate measure of air interface quality based on the received reports of air interface quality measured by the one or more mobile stations on the particular second frequency channel;

selecting as the preferred second frequency channel one of the second frequency channels whose determined aggregate measure of air interface quality is best among the second frequency channels.

9. The method of claim 8, wherein establishing the aggregate measure of air interface quality based on the received reports of air interface quality measured by the one or more mobile stations on the particular second frequency channel comprises averaging measures of air interface quality on the particular frequency channel.

10. The method of claim 3, further comprising the RAN correlating the received reports of air interface quality measured by the one or more mobile stations on the second frequency channels with respective times of day, and wherein using the received reports of air interface quality measured by the one or more mobile stations on the second frequency channels as a basis to select one of the second frequency channels as the preferred second frequency channel comprises:

using a current time of day as a basis to select relevant air interface quality data from the received reports of air interface quality; and

basing the selection of the second frequency channel particularly on the selected relevant air interface quality data.

11. The method of claim 3, wherein detecting that the particular mobile station is fading from coverage on the first frequency channel comprises receiving from the particular mobile station a report of forward link quality on the first frequency channel and determining that the reverse link quality in the received report is threshold low.

12. The method of claim 3, wherein detecting that the particular mobile station is fading from coverage on the first frequency channel comprises detecting that quality of reverse link communication from the particular mobile station is threshold low.

13. The method of claim 3, wherein requesting the particular mobile station to determine and report to the RAN measurements of sector quality on the dynamically pre-selected second frequency channel comprises sending to the particular mobile station a Carrier Frequency Search Request Message (CFSRQM) that specifies the dynamically pre-selected second frequency channel and that requests the particular mobile station to measure and report sector quality on the specified frequency channel.

14. The method of claim 13, wherein receiving in response from the particular mobile station the requested measurements of sector quality on the dynamically pre-selected second frequency channel comprises receiving from the particular mobile station a CFSRQM response that specifies the measurements of sector quality.

15. The method of claim 3, wherein selecting the target sector based on the received measurements of sector quality on the dynamically pre-selected second frequency channel comprises selecting as the target sector a sector having a strongest measurement of sector quality of the received measurements of sector quality.

16. The method of claim 3, wherein directing the particular mobile station to hand off to the selected target sector on the dynamically pre-selected second frequency channel comprises sending to the particular mobile station a universal handoff direction message (UHDM) that specifies at least the second frequency channel, the target sector.

17. The method of claim 3, further comprising:

after selecting the target sector and before directing the particular mobile station to hand off, the RAN reserving resources on the target sector to accommodate handoff of the particular mobile station to the target sector.

18. A radio access network (RAN) comprising:

base stations radiating to provide coverage for served mobile stations on a plurality of frequency channels, wherein a given base station serves one or more mobile stations on at least a first frequency channel;

pre-selection logic executable by the RAN, while the given base station is serving the one or more mobile stations on the first frequency channel, to dynamically pre-select a preferred second frequency channel to be used as a handoff target, by (i) receiving via the given base station, from the one or more mobile stations, reports of air interface quality measured by the one or more mobile stations on second frequency channels and (ii) using the received reports as a basis to select one of the second carrier frequency channels as the preferred second frequency channel; and

handoff logic executable by the RAN to detect that a particular one of the one or more mobile stations is fading from coverage on the first frequency channel, and in response to the detecting, (a) to request the particular mobile station to determine and report to the RAN measurements of sector quality on the dynamically pre-selected second frequency channel, (b) to receive in response from the particular mobile station the requested measurements of sector quality on the dynamically pre-selected second frequency channel, (c) based on the received measurements of sector quality on the dynamically pre-selected second frequency channel, to select a target sector on the dynamically pre-selected second frequency channel, and (d) to direct the particular mobile station to hand off to the selected target sector on the dynamically pre-selected second frequency channel.

19. The RAN of claim 18, wherein the given base station is arranged to execute the pre-selection logic and handoff logic.

20. A method comprising:

while a cellular radio access network (RAN) is serving one or more mobile stations in a first sector defined by the RAN, the RAN collecting from the one or more mobile stations measurements of air interface quality of a plurality of frequency channels of surrounding sectors;

the RAN using the collected measurements as a basis to select a preferred frequency channel to use as a handoff target;

the RAN detecting that a particular mobile station is fading from coverage of the first sector; and

responsive to the detecting, (i) the RAN requesting the particular mobile station to determine and report to the RAN measurements of sector quality on the selected frequency channel, (ii) the RAN receiving in response from the particular mobile station the requested measurements of sector quality on the selected frequency channel, (iv) the RAN selecting a target sector based on the received measurements of sector quality, and (v) the RAN directing the particular mobile station to hand off from the first sector to the selected target sector on the selected frequency channel.