Apparatus and method for mobile/IP handoff between a plurality of access technologies

• US 6,993,335 B2
• Filed: 11/15/2002
• Issued: 01/31/2006
• Est. Priority Date: 11/15/2002
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Valdivia, Mary M., Singh, Ajoy K., Natarajan, Kadathur S., Arumugam, Karthikeyan, Reddy, Muddasani S.
• Primary Examiner(s): CRAVER, CHARLES R
• Application Number:
  US10/295,187
• Publication Number:
  US 20040097230A1
• Time in Patent Office: 1,173 Days
• Field of Search: 4534141-4143, 453436-441, 453/445, 453 6711- 6713, 453/561, 379/114.05, 379/114.1, 379/114.3, 455436-444
• US Class Current: 455/437
• CPC Class Codes: H04W 36/0011 for data sessions of end-to-end connection
• CPC Class Codes: H04W 36/14 Reselecting a network or an air interface
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data
• CPC Class Codes: H04W 36/36 by user or terminal equipment
• CPC Class Codes: H04W 8/06 Registration at serving network Location Register, VLR or user mobility server
• CPC Class Codes: H04W 8/085 involving hierarchical organized mobility servers, e.g. hierarchical mobile IP [HMIP]
• CPC Class Codes: H04W 80/04 Network layer protocols, e.g. mobile IP [Internet Protocol]
• CPC Class Codes: H04W 88/06 adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals
• CPC Class Codes: H04W 92/02 Inter-networking arrangements

Abstract

An apparatus and method for performing Mobile/IP handoff between different access technologies. Associated with each access technology are two thresholds, a Low Water Mark and a High Water Mark. The method uses these water marks to its access technology selection in a particular environment. Using the method, a mobile node 102 remains on its preferred network when the signal strength on the preferred network (interface) is above the low water mark. When the signal strength on the preferred network drops below the high water mark, the method calculates the low water mark for the network. When the signal strength on the preferred network drops below the low water mark (LWM), the method initiates handoff to the next available network that meets certain conditions. The method initiates handoff back to the preferred network when the signal strength measurement on the preferred network is again above the high water mark.

Claims

1. In a mobile communication device configured to support a plurality of interfaces, a method of handoff comprising:

sensing that a signal strength on a current interface of the plurality of interfaces is at or below a first threshold for the current interface;

determining whether a signal strength of an available interface of the plurality of interfaces is greater than a first threshold for the available interface;

when the signal strength of the available interface is greater than the first threshold, determining whether a foreign agent advertisement has recently been received on the available interface;

when a foreign agent advertisement has recently been received, identifying the available interface as a target interface;

calculating a second threshold; and

initiating a first handoff to the target interface when the signal strength on the current interface reaches the second threshold.

2. The method of claim 1 wherein the step of calculating a second threshold comprises:

determining a signal strength S_i of the current interface, wherein S_i is determined at time T_i;

determining a rate of change of signal strength RCSS_i, wherein RCSS_i is determined at time T_i;

determining a time at which a signal strength on the current interface will reach a level where layer 2 connectivity is lost;

determining a registration time of the target interface;

deducting the registration time from the time at which a signal strength on the current interface will reach a level where layer 2 connectivity is lost to produce T_LWM; and

determining that the second threshold is equal to S_i−

[(T_LWM−

T_i)x RCSS_i].

3. The method of claim 2 wherein determining a registration time of the target interface comprises:

transmitting a ping to a home agent;

determining a round trip time of the ping; and

adding the round trip time to a fixed time duration for performing a registration update at the home agent.

4. The method of claim 2 wherein determining a registration time of the target interface comprises:

transmitting a dummy registration request;

receiving a reply;

measuring a time difference between transmitting the dummy request and receiving the reply; and

using the time difference to determine the registration time.

5. The method of claim 2 wherein determining a registration time of the target interface comprises receiving the registration time from a foreign agent for the target interface.

6. The method of claim 2 wherein determining a rate of change of signal strength RCSS_i comprises solving RCSS_i+n+1=(S_i+1−

S_i+n+1)/(n*Δ

).

7. The method of claim 1 further comprising initiating a second handoff to a higher ranked interface when a signal strength on the higher ranked interface increases above the first threshold for the higher ranked interface.

8. The method of claim 1 further comprising initiating a second handoff to a preferred interface when a signal strength on the preferred interface increases above the first threshold for the preferred interface.

9. A mobile communication device configured to support a plurality of interfaces, each interface associated with an access network, the device comprising:

a receiver for receiving signals from an access network;

a processor coupled to the receiver, the processor sensing that a signal strength on the current interface is at or below a first threshold for the current interface;

determining whether a signal strength of an available interface of the plurality of interfaces is greater than a first threshold for the available interface;

when the signal strength of the available interface is greater than the first threshold, determining whether a foreign agent advertisement has recently been received on the available interface;

when a foreign agent advertisement has recently been received, identifying the available interface as a target interface; and

determining that the device should initiate handoff to the target interface when the signal strength on the current interface reaches the second threshold; and

a transmitter coupled to the processor for transmitting signals to an access network.