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Handoff between overlay and underlay cells

  • US 5,557,657 A
  • Filed: 09/09/1993
  • Issued: 09/17/1996
  • Est. Priority Date: 09/09/1993
  • Status: Expired due to Term
First Claim
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1. A method of handing off an on-going communication of a mobile unit between an overlay cell having a first coverage area and an underlay cell having a second coverage area common with and less than the first coverage area, the method comprising:

  • establishing a threshold level by establishing a predefined nominal threshold level; and

    adjusting the predefined nominal threshold level in accordance with the current transmit attenuation level of the mobile unit;

    handing off the on-going communication of the mobile unit to the underlay cell at times when RF signal strength of the serving cell is greater than the established threshold level and to the overlay cell at times when the RF signal strength of the serving cell is equal to or less than the established threshold level; and

    wherein in the step of establishing the threshold level the substep of establishing a predefined nominal threshold level comprisespredefining a nominal threshold level in accordance with the RF signal strength of a traffic channel of the serving cell and the minimum attenuation level of the mobile unit permitted by the underlay cell at times when a mobile unit is in the overlay cell.

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