US 6,549,780 B2 · Method and apparatus for adjacent service area handoff in communication systems

Abstract

A handoff technique in which system users detect transitions in service between a current service area and an adjacent service area, and request a forward link channel in the new service area when a detected signal strength for the new service area exceeds predetermined threshold levels. The forward communications link in the current service area is maintained until the strength of the new service area signal reaches a certain level and appropriate channel quality is confirmed, as based on various known criteria. Typically, service area transitions are detected using the signal strength of pilot or paging signals associated with service areas, which are used to determine a relative signal strength of new service area signals. Pilot signal level adjustments used to counter roll-off effects are detected and compensated for in comparing signal levels. To minimize the burden on system resources, new service area signals are not selectable until a minimum time has passed, or a minimum change in energy from a prior pilot signal is detected. In addition, communications using the previous service area can be dropped almost immediately upon engaging the new service area.

Claims25

Dependent claims

A method for performing handoff between adjacent service areas in a wireless communication system that transfers communication signals using at least one central communications station which establishes geographical service areas for user terminals operating within the system, comprising the steps of:

detecting a physical transition of a user terminal between a first service area and a second adjacent service area, each established by said one central communications station, by detecting signal strength for signals from said adjacent service areas;
detecting the presence of signal strength adjusted to compensate for signal roll-off in said signals from said adjacent service areas and applying a compensation value to signal strength for each adjusted signal to obtain a non-adjusted value;
requesting a forward link channel for use by said user terminal in said second service area, while said user terminal also communicates using said first service area for forward link communications, when a detected signal strength for the second adjacent service area at least equals that of said first service area;
confirming that said forward link channel for said second service area is operating according to a preselected minimum quality level;
and
disengaging use by said user terminal of the forward link for said first service area upon confirmation of said preselected minimum quality level.

3 more elements

Apparatus for performing handoff between adjacent service areas in a wireless communication system in which system users transfer communication signals using at least one central communications station which establishes geographical service areas for user terminals operating within the system, comprising:

means for detecting a physical transition of a user terminal between a first service area and a second adjacent service area, each established by said at least one central communications station, by detecting signal strength for signals from said adjacent service areas;
means for detecting the presence of signal strength adjusted to compensate for signal roll-off in said signals from said adjacent service areas;
means for applying a compensation value to signal strength for each adjusted signal to obtain a non-adjusted value;
means for requesting a forward link channel for use by said user terminal in said second service area, while said user terminal also communicates using said first service area for forward link communications, said request being made when a detected signal strength for the second adjacent service area at least equals that of said first service area;
and
means for disengaging use by said user terminal of the forward link for said first service area when said forward link channel for said second service area exceeds a preselected minimum quality level.

3 more elements

Dependencies are inferred from the claim text.

Method and apparatus for adjacent service area handoff in communication systems

Life of this patent

Method and apparatus for adjacent service area handoff in communication systems

Life of this patent

Abstract

Claims25