Resource utilization efficiency during hand-off in mobile communication systems

Abstract

An improved method of maintaining data throughput during handoff in a wireless communication link operating with the Mobile IP protocol is described. A first base station initially servicing a mobile subscriber unit is associated with a first Mobile IP foreign agent that is registered with the Mobile IP home agent as a first mobility binding between the subscriber unit and the home agent. When the subscriber unit issues a request to be handed off from the first base station to a second base station, a second foreign agent associated with the second base station is registered with the home agent as a simultaneous binding with the first mobility binding between the subscriber unit and the home agent. This permits both foreign agents to simultaneously receive a sequence of data packets from the home agent. Before handoff is executed, the data packet sequence routed to the second foreign agent is stored at the second base station. After handoff is complete, such stored packets are forwarded to the subscriber unit starting with a predetermined numbered packet in the stored sequence, and the first foreign agent is de-registered with the home agent.

Description

RELATED APPLICATION [0001] This application is a continuation of application Ser. No. 09 / 802,128, filed on Mar. 8, 2001. The entire teachings of the above application are incorporated herein by reference.BACKGROUND OF THE INVENTION [0002] This invention relates to wireless communication systems, such as cellular packet networks, and more particularly to methods of and apparatus for improving efficiency in such systems during handoff. [0003] In wireless communication systems for the transmission of data packets from a sending machine such as an Internet server, the switching or “handoff” of a mobile subscriber unit from one cellular base station to another is implemented as the subscriber unit moves between areas of different signal strength. Any discontinuities in the wireless data path as a result of a handoff can cause data packet loss, which results in missing or delayed acknowledgment signals between the end user machine and the server. This is true whether packets are destined ...

AI Technical Summary

Benefits of technology

[0006] The present invention preserves the advantage of store-and-forward buffer systems in maintaining data throughput during a handoff while avoiding the disadvantages resulting from multicasting data packets to all of the base stations of the system. Rather than multicasting to all base stations within the vicinity of the subscriber, the invention makes use of the simultaneous bindings capability of the Mobile IP protocol to simultaneously send packets to only the two base stations involved in the handoff.

Problems solved by technology

Any discontinuities in the wireless data path as a result of a handoff can cause data packet loss, which results in missing or delayed acknowledgment signals between the end user machine and the server.

This increases the likelihood that the applicable TCP protocols at either end of the network connection will invoke congestion avoidance / slow start modes at the server, leading to a drop in data throughput in the system.

While multicasting arrangements of this type can decrease the probability of lost packets to help maintain throughput in the system during handoff, they do not use the resources of the cellular system in an efficient way.

The expensive facilities of all the other base stations in the group that are pressed into service in expectation of this particular handoff are unavailable for productive use elsewhere.

In addition, by multicasting identical packets to so many different base stations, the load on the network infrastructure is unnecessarily increased.

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