Methods and apparatus for performing handoffs in a multi-carrier wireless communications system

• US 7,212,821 B2
• Filed: 10/14/2004
• Issued: 05/01/2007
• Est. Priority Date: 12/05/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Laroia, Rajiv, Li, Junyi, Lane, Frank A.
• Primary Examiner(s): Nguyen; Duc M.
• Assistant Examiner(s): Huynh; Chuck
• Application Number:
  US10/964,905
• Publication Number:
  US 20050124345A1
• Time in Patent Office: 929 Days
• Field of Search: 455/437, 455/436, 455/438, 455/439, 455/442, 455/450, 370/330, 370/331, 370/332, 370/333, 370/334
• US Class Current: 455/437
• CPC Class Codes: H04W 36/06 Reselecting a communication resource in the serving access point
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection

Abstract

A mobile communications device initiates a handoff from its current base station (BS) sector network attachment point to a new BS sector. The mobile sends a handoff request over its current wireless link to the current BS sector, which forwards the request to the new BS sector, e.g., via a network link. The new BS sector processes the request assigning dedicated resources, e.g., an identifier and dedicated uplink segments. Information identifying the allocated resources is conveyed from the new BS sector via the current BS sector to the mobile. The mobile determines the time of the allocated dedicated segments based upon a received beacon signal from the new BS sector with known timing relationships to dedicated segments. The mobile breaks the original wireless link just prior to the time of the first assigned dedicated segment. The mobile communicates information on the assigned dedicated segments to perform registration operations, e.g., timing synchronization and power control, establishing a new wireless link.

Claims

1. A method of operating a mobile communications device to implement a handoff of a mobile communications device between a first network attachment point and a second network attachment point, said mobile communications device having a first wireless communications link with the first network attachment point at the time said handoff is initiated, said first wireless communication link using signals in a first frequency band, the method comprising:

communicating to said second network attachment point, via a first signal communicated over said first wireless communications link, an intent to initiate a handoff to said second network attachment point, wherein said first communications link corresponds to a first frequency band and said second communications link corresponds to a second frequency band which does not use frequencies in said first communications band;

receiving, via said first wireless communications link, information indicating a dedicated air link resource assigned to said mobile device by said second network attachment point to be used in communicating with said second network attachment point over a second frequency band which is different from said first frequency band;

terminating said first wireless communications link;

using said dedicated communications resource to transmit a signal over the air in said second frequency band to establish a second wireless communications link with said second network attachment point;

determining second network attachment point timing information from a transmitter information signal transmitted by said second network attachment point into said first frequency band; and

wherein said terminating of said first communications link is performed at a time determined by said mobile communications device as a function of the time said transmitter information signal was received from said second network attachment point

determining from said beacon signal at least one of a cell identifier and a sector identifier; and

determining, from stored information corresponding to the determined cell or sector identifier information, information about the structure of a communications segment used for registration signaling at the second network attachment point, wherein said information about the structure of a communication segment includes information about tones in said segment which are to be used on a contention free basis for mobile device registration signaling, wherein said dedicated resource assigned to said mobile node is a set of tones in an uplink communications segment, said mobile communications device identifying the set of tones from information received from said second network point of attachment via said communications link and form said information about the structure of a communication segment.

2. The method of claim 1, wherein receiving information indicating a dedicated airlink resource assigned to said mobile communications device by said second network attachment point includes receiving information communicated by said second network attachment point to said first network attachment point in response to said first network attachment point acting as a proxy for said mobile communications device in interacting with said second network communications device.

3. The method of claim 1, wherein receiving information indicating a dedicated airlink resource assigned to said mobile communications device by said second network attachment point includes receiving a packet from said second network attachment point including resource assignment information which was routed through said first network attachment point prior to transmission over said first wireless communications link.

4. The method of claim 1, wherein said transmitter information signal is a beacon signal, the method further comprising:

determining from said beacon signal at least one of a cell identifier and a sector identifier; and

determining, from stored information corresponding to the determined cell or sector identifier information, timing of a communications segment used for registration signaling at the second network attachment point relative to said received beacon signal.

5. The method of claim 1, wherein using said dedicated communications resource to communicate via a second wireless communications link includes:

using said identified set of tones to transmit a signal in said second frequency band to said second point of network attachment, said signal including at least one of;

a registration signal, a timing control signal and a power control signal.

6. The method of claim 1, wherein communicating to said second network attachment point an intent to initiate a handoff includes transmitting OFDM symbols to said first network attachment point over said first wireless communication link.

7. The method of claim 1, wherein said step of terminating said first wireless communications link is performed prior to said step of using said dedicated communications resource.

8. The method of claim 7, wherein said dedicated resource includes at least one of:

an uplink segment dedicated to said mobile communication device and a device identifier to be used for determining an uplink communications segment dedicated to said mobile communications device by said second network point of attachment.

9. The method of claim 1, wherein if said mobile communications device is unsuccessful in establishing said second wireless communications link using said dedicated communications resource, the method further comprises the step of:

registering with said second network point of attachment using contention based signaling said registering including transmitting a registration signal in an uplink communications segment into which multiple devices are permitted to transmit signals at the same time.

10. The method of claim 7, wherein said first and second network attachment points are located in the same cell, the method further comprising:

transmitting to said second network attachment point user data including at least one of voice, text and image data, following termination of said first wireless communications link and prior to performing a symbol transmission timing adjustment in response to a signal transmitted over the air from said second network attachment point.

11. The method of claim 10,

wherein transmitting to said second network attachment point user data includes transmitting modulated symbols on a plurality of signal tones;

and

wherein transmitting to said second network attachment point user data is performed prior to receiving a power control signal from said second network point of attachment which is transmitted subsequent to termination of said first wireless communications link.

12. The method of claim 10, further comprising:

after transmitting user data to said second network attachment point, receiving a transmission timing correction signal and a transmission power control signal from said second point of network attachment;

performing a symbol transmission timing adjustment in response to said received transmission timing correction signal; and

performing a transmission power adjustment in response to said received transmission power control signal.

13. The method of claim 12, wherein said first and second network attachment points are different sectors within a cell.

14. The method of claim 12, wherein said first and second network attachment points are modules within the same sector corresponding to different carrier transmission frequencies.

15. The method of claim 7, wherein said first and second network attachment points are sectors in different cells, the method further comprising:

performing at least a transmission timing adjustment in response to a signal received from said network attachment point following termination of said first communications link and prior to transmitting user data to said second network attachment point.

16. The method of claim 15, wherein using said dedicated communications resource includes transmitting a signal used for at least one of power control and timing control to said second network access point.

17. A mobile node for use in a communication system including a first network point of attachment which uses a first frequency band to receive user data and a second network attachment point which uses a second frequency band which is different from said first frequency band to receive user data, said mobile node comprising:

means for initiating a handoff from said first network attachment point to said second network attachment point by communicating a signal indicating an intent to handoff to the second network attachment point transmitted in the first frequency band over a wireless communications link with said first network attachment point;

means for receiving from said second network attachment point, via a second signal communicated via said first link information indicating a resource dedicated to said mobile device by said second network attachment point to be used in communicating with said second network attachment point, wherein said indicated dedicated resource is an uplink channel segment dedicated to said mobile node for use in performing at least one of registration signaling, timing control signaling and power control signaling;

means for terminating said first communications link;

means for transmitting a signal in said second frequency band using said dedicated communications resource to establish a second wireless communications link with said second network attachment point;

means for detecting a beacon signal used to communicate transmitter information from said second network access point;

stored information about the structure of uplink communications channels for a plurality of different base station sectors, said stored information including information about the timing between beacon signals transmitted from said base station sectors and access segments to be used for registration in said base station sectors; and

means for performing contention based registration signaling with said second network access point if the second communications link is not successfully established through the use of said dedicated resource, wherein said stored information further includes information about tones assigned to devices identified by different wireless terminal identifiers that are assigned by said second network access point.

18. The mobile node of claim 17, wherein said means for terminating said first link includes control logic for ceasing communications over said first link prior to transmitting a signal in said second frequency band.

19. The mobile node of claim 17, wherein said first network attachment point is a sector of a first base station and wherein said second network attachment point is a sector of a second base station;

and

wherein said means for transmitting in said second frequency band using said dedicated communication resource includes;

a timing synchronization module which uses said dedicated resource to perform a timing synchronization operation as part of initiating a second communications link, said second communications link being with said second base station.

20. The mobile node of claim 17, wherein said means for transmitting in said second frequency band using said dedicated communication resource includes:

a transmission power control module for communicating transmission power control signals between said mobile node and second base station using said dedicated resource.

21. A method of implementing a mobile node handoff between a first wireless communications link with a first base station sector, said first wireless communications link using a first carrier, and a second wireless communications link with a second base station sector said second wireless communications link using a second carrier, at least the first sector being different from the second sector or the first carrier being different from the second carrier, the method comprising:

operating said mobile node to receive a timing correction signal over said first wireless communications link;

operating said mobile node to make a transmission timing adjustment to adjusting the timing of signals transmitted by said mobile node over the first wireless communications link;

operating the mobile node to send a signal over said first wireless communications link indicating an intent to handoff to said second wireless communications link;

operating the mobile node to receive over said first wireless communications link information indicating a dedicated resource to be used by said mobile when communicating over said second wireless communications link, wherein said dedicated resource is a dedicated airlink communications segment to be used in establishing communications with said second base station sector when transmitting signals over the air to said second base station sector using said second carrier frequency to establish said second wireless communications link, wherein said first and second base station sectors are different sectors within the same cell;

operating the mobile node to terminate said first wireless communications link;

operating the mobile node to transmit at least one of user data and a non-timing control signal over said second wireless communications link prior to making a transmission timing control adjustment based on a timing control signal received over said second wireless communications link;

operating a second sector control module to;

allocate said dedicated resource; and

communicate information about said dedicated resource to said first sector for transmission to said mobile node; and

operating said first sector to transmit an IP routing update signal to trigger redirection of IP packets directed to said mobile node, to said second sector prior to said mobile node being able to receive or transmit user data over said second wireless communications link.

22. The method of claim 21, wherein said transmission timing adjustment adjusts the time at which symbols are transmitted over said first wireless communications link so that they arrive in a synchronized manner at the base station with symbols transmitted by other mobile nodes.

23. The method of claim 21, wherein said dedicated resource is an identifier specific to said second sector and said second carrier.

24. The method of claim 23, wherein said identifier is a device identifier to be used by said mobile node when communicating over said second wireless communications link.

25. The method of claim 21, wherein said mobile node uses dedicated air link resources for communications during a time interval extending from a point in time when the mobile node terminates said first communications link to a point in time where the mobile node transmits user data over said second wireless communications link, said mobile node avoiding the use of shared communications resources for uplink signaling which other mobile nodes can access at the same time as said mobile node during said time interval.

26. The method of claim 21, where said step of operating the mobile node to transmit at least one of user data and a non-timing control signal over said second wireless communications link prior to receiving a timing control signal mobile node transmits user data including one of speech and text prior to making a symbol transmission timing adjustment.