Method for hard handoff in a CDMA cellular environment
First Claim
1. In a CDMA cellular network overlaid on an AMPS cellular network, a method for performing a handoff of a call from a mobile unit in a CDMA cell site of the CDMA cellular network wherein the CDMA cell site is co-located with an AMPS cell site of the AMPS cellular network, the method comprising the steps of:
- measuring a round trip delay ("RLTD") value representing a distance from the mobile unit to the CDMA cell site;
comparing the RTD value with a first predetermined value;
if the RTD value exceeds the first predetermined value, determining whether any other CDMA cell site is available for handoff;
comparing the RTD value with a second predetermined value;
if the RTD value exceeds the second predetermined value, handing off the call to a second CDMA cell site if one is available; and
if no other CDMA cell site is available for handoff, handing off the call to the AMPS cell site.
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Accused Products
Abstract
A method for performing a hard handoff of a call from a first cell site of a CDMA cellular network to a target cell site of a second cellular network, such as an AMPS network or a second CDMA network. As a mobile unit operating in the first CDMA network moves toward the second cellular network, the first cell site uses two separate RTD thresholds for comparison with a measured RTD distance between the mobile unit and the first cell site. Handoff is initiated when the RTD distance exceeds the first RTD threshold and is completed when the RTD distance exceeds the second RTD threshold. If the first cell site is not co-located with a cell site of the second network, the first cell site utilizes receivers placed in the target cell site for handoff. If the first cell site is co-located with a second cell site of the second network, the second cell site of the second network is always the target cell site.
142 Citations
21 Claims
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1. In a CDMA cellular network overlaid on an AMPS cellular network, a method for performing a handoff of a call from a mobile unit in a CDMA cell site of the CDMA cellular network wherein the CDMA cell site is co-located with an AMPS cell site of the AMPS cellular network, the method comprising the steps of:
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measuring a round trip delay ("RLTD") value representing a distance from the mobile unit to the CDMA cell site; comparing the RTD value with a first predetermined value; if the RTD value exceeds the first predetermined value, determining whether any other CDMA cell site is available for handoff; comparing the RTD value with a second predetermined value; if the RTD value exceeds the second predetermined value, handing off the call to a second CDMA cell site if one is available; and if no other CDMA cell site is available for handoff, handing off the call to the AMPS cell site. - View Dependent Claims (2, 3, 4, 5)
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6. In a first cellular network bordering an second cellular network, a method for handing off a call from a mobile unit being served by a first cell site and approaching a second cell site, where the first cell site is a border cell site of the first cellular network and the first cell site is co-located with a third cell site of the second cellular network, the method comprising the steps of:
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repeatedly measuring a round trip delay ("RTD") value representing a distance from the unit to the first cell site of the call; comparing the RTD value with a first predetermined value; if the RTD value exceeds the first predetermined value, determining if the second cell site is in the first network; comparing the RTD value with a second predetermined value; and if the RTD value exceeds the second predetermined value and the second cell site is not in the first network, performing a handoff to the third cell site so that the third cell site may perform a handoff to the second cell site. - View Dependent Claims (7, 8, 9)
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10. In a first cellular network bordering a second cellular network, a method for handing off a call from a first cell site to a second cell site, wherein the first cell site serves a border cell of the first cellular network and the second cell site serves a border cell of the second network, the method comprising the steps of:
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repeatedly measuring a round trip delay ("RTD") value representing a distance from a mobile unit making the call to the first cell site of the call; comparing the RTD value with a first predetermined value; if the RTD value exceeds the first predetermined value, providing a code identifying the call to a receiver at the second cell site; comparing the RTD value with a second predetermined value; and if the RTD value exceeds the second predetermined value, polling the receiver to determine if the receiver has detected the call and if so, performing a handoff to the second cell site. - View Dependent Claims (11, 12, 13, 14)
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15. In a CDMA cellular network overlaid on an AMPS cellular network, an apparatus for performing a handoff of a call from a mobile unit in a CDMA cell site of the CDMA cellular network wherein the CDMA cell site is co-located with an AMPS cell site of the AMPS cellular network, the apparatus comprising:
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means for measuring a round trip delay ("RTD") value representing a distance from the mobile unit to the CDMA cell site of the call; means for comparing the RTD value with a first predetermined value; means responsive to when the RTD value exceeds the first predetermined value, for handing off the call to a second CDMA cell site if one is available and if no other CDMA cell site is available for handoff, for handing off the call to the AMPS cell site. means for comparing the RTD value with a second predetermined value before comparing the RTD value with the first predetermined value; and means responsive to the RTD value exceeding the second predetermined value for determining whether any other CDMA cell site is available for handoff. - View Dependent Claims (16, 17, 18, 19)
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20. In a first cellular network bordering a second cellular network, a first cell site for serving a call and supporting a handoff of the call, wherein the first cell site is co-located with a cell site of the second cellular network, the first cell site comprising:
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a round trip delay ("RTD") measurement device for determining a RTD distance from a mobile unit making the call to the first cell site; a first comparator for comparing the RTD with a first predetermined value; selector logic, responsive to when the RTD distance exceeds the first predetermined value, for determining if a second cell site in the first cellular network is a potential cell site for handoff; a second comparator for comparing the RTD distance with a second predetermined value; and handoff logic for handing off the call in response to the RTD exceeding the second predetermined value, wherein the handoff logic performs a handoff to the second cell site if the selector logic determined that the second cell site is a potential cell site for handoff and the handoff logic performs a handoff to the cell site of the second cellular network if the selector logic determined that the second cell site is not a potential cell site for handoff. - View Dependent Claims (21)
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Specification