Method for preventing a dropped call during a handoff in a radiotelephone system

Claim 2

In a cellular radiotelephone communication system including at least one switch controller, a plurality of base stations including first and second base stations, and at least one mobile station, wherein a switch controller is coupled to the first and second base stations to provide radiotelephone communication throughout first and second coverage areas, respectively, wherein a mobile station is in an active call in the first coverage area with the first base station on a first traffic channel and substantially shadowed from transmissions from the second base station in the second coverage area, a method, performed by the mobile station, for preventing the active call from being dropped when the mobile station suddenly transitions from the first coverage area to the second coverage area, the method comprising the steps of: determining that the active call is in danger of being dropped responsive to the mobile station suddenly transitioning from the first coverage area to the second coverage area; notifying the first base station that the active call is in danger of being dropped responsive to the step of determining that the active call is in danger of being dropped; determining that the active call with the first base station is in the process of being dropped responsive to the step of notifying the first base station that the active call is in danger of being dropped; and establishing the active call with the second base station in the second coverage area before the active call with the first base station is dropped responsive to the step of determining that the active call with the first base station is in the process of being dropped.

Claim 3

A method for preventing the active call from being dropped according to claim 1 wherein the step of determining the active call is in danger of being dropped further comprises the step of: monitoring a total energy received by the mobile station; measuring a signal energy for the active call received by the mobile station; calculating a ratio of the signal energy to the total energy; and determining that the ratio is unfavorable to indicate that active call is in danger of being dropped.

Claim 4

A method for preventing the active call from being dropped according to claim 2 wherein the step of monitoring the total energy received by the mobile station further comprises the steps of: measuring the total energy received by the mobile station at selected points in time to produce samples of the total energy including at least one previous sample and a current sample of the total energy; determining that the current sample of the total energy is greater than the at least one previous sample of the total energy by a predetermined amount; integrating the current sample of total energy with the at least one previous sample of the total energy to produce an integrated total energy; and storing the integrated total energy to produce a stored total energy.

Claim 5

A method for preventing the active call from being dropped according to claim 1 wherein the step of notifying the first base station that the active call is in danger of being dropped further comprises the step of: sending a pilot signal strength message to the first base station indicative of signal strengths of a plurality of pilot signals transmitted by the plurality of base stations, respectively.

Claim 6

A method for preventing the active call from being dropped according to claim 1, wherein the active call includes a plurality of sequential frames, wherein the step of determining that the active call with the first base station is in the process of being dropped further comprises the step of: determining that a predetermined number of the plurality of sequential frames are unacceptable; and determining, within a predetermined amount of time, that no two sequential frames of the plurality of sequential frames are acceptable.

Claim 7

A method for preventing the active call from being dropped according to claim 1 wherein the step of establishing the active call with the second base station in the second coverage area further comprises the steps of: identifying the second base station; sending a reconnect request message to the second base station responsive to the step of identifying the second base station; receiving a reconnect grant message from the second base station within a predetermined amount of time responsive to the step of sending a reconnect request message to the second base station; and resuming the active call in the second coverage area with the second base station on a second traffic channel responsive to the step of receiving a reconnect grant message from the second base station.

Claim 8

A method for preventing the active call from being dropped according to claim 6 wherein the step of identifying the second base station further comprises the steps of: searching for a plurality of pilot signals transmitted by the plurality of base stations, respectively; and selecting a pilot signal having the strongest signal strength from among the plurality of pilot signals, wherein the pilot signal having the strongest signal strength corresponds to the pilot signal transmitted by the second base station.

Claim 9

A method for preventing the active call from being dropped according to claim 6 wherein the step of receiving a reconnect request message further comprises the step of: receiving the reconnect request message on a paging code channel.

Claim 10

In a code division multiple access (CDMA) cellular radiotelephone communication system including at least one switch controller, a plurality of base stations including first and second base stations, and at least one mobile station, wherein a switch controller is coupled to the first and second base stations to provide radiotelephone communication throughout first and second coverage areas, respectively, wherein a mobile station is in an active call in the first coverage area with the first base station on a first traffic channel and substantially shadowed from transmissions from the second base station in the second coverage area, a method, performed by the mobile station, for preventing the active call from being dropped when the mobile station suddenly transitions from the first coverage area to the second coverage area, the method comprising the steps of: monitoring a total energy received by the mobile station; measuring a signal energy for the active call received by the mobile station; calculating a ratio of the signal energy to the total energy; determining that the ratio is unfavorable to indicate that active call is in danger of being dropped; sending a pilot signal strength message to the first base station indicative of signal strengths of a plurality of pilot signals transmitted by the plurality of base stations, respectively, responsive to the step of determining that the ratio is unfavorable; determining that the active call with the first base station is in the process of being dropped responsive to the step of sending a pilot signal strength message to the first base station; and establishing the active call with the second base station in the second coverage area before the active call with the first base station is dropped responsive to the step of determining that the active call with the first base station is in the process of being dropped.

Claim 11

In a code division multiple access (CDMA) cellular radiotelephone communication system including at least one switch controller, a plurality of base stations including first and second base stations, and at least one mobile station, wherein a switch controller is coupled to the first and second base stations to provide radiotelephone communication throughout first and second coverage areas, respectively, wherein a mobile station is in an active call in the first coverage area with the first base station on a first traffic channel and substantially shadowed from transmissions from the second base station in the second coverage area, a method, performed by the mobile station, for preventing the active call from being dropped when the mobile station suddenly transitions from the first coverage area to the second coverage area, the method comprising the steps of: monitoring a total energy received by the mobile station; measuring a signal energy for the active call received by the mobile station; calculating a ratio of the signal energy to the total energy; determining that the ratio is unfavorable to indicate that active call is in danger of being dropped; sending a pilot signal strength message to the first base station indicative of signal strengths of a plurality of pilot signals transmitted by the plurality of base stations, respectively, responsive to the step of determining that the ratio is unfavorable; determining that the active call with the first base station is in the process of being dropped responsive to the step of sending a pilot signal strength message to the first base station; and establishing the active call with the second base station in the second coverage area before the active call with the first base station is dropped responsive to the step of determining that the active call with the first base station is in the process of being dropped.

Claim 12

A method for preventing the active call from being dropped according to claim 9 wherein the step of monitoring the total energy received by the mobile station further comprises the steps of: measuring the total energy received by the mobile station at selected points in time to produce samples of the total energy including at least one previous sample and a current sample of the total energy; determining that the current sample of the total energy is greater than the at least one previous sample of the total energy by a predetermined amount; integrating the current sample of total energy with the at least one previous sample of the total energy to produce an integrated total energy; and storing the integrated total energy to produce a stored total energy.

Claim 13

A method for preventing the active call from being dropped according to claim 9 wherein the active call includes a plurality of sequential frames, wherein the step of determining that the active call with the first base station is in the process of being dropped further comprises the step of: determining that a predetermined number of the plurality of sequential frames are unacceptable; and determining, within a predetermined amount of time, that no two sequential frames of the plurality of sequential frames are acceptable.

Claim 14

A method for preventing the active call from being dropped according to claim 9 wherein the step of establishing the active call with the second base station in the second coverage area further comprises the steps of: identifying the second base station; sending a reconnect request message to the second base station responsive to the step of identifying the second base station; receiving a reconnect grant message from the second base station within a predetermined amount of time responsive to the step of sending a reconnect request message to the second base station; and resuming the active call in the second coverage area with the second base station on a second traffic channel responsive to the step of receiving a reconnect grant message from the second base station.

Claim 15

A method for preventing the active call from being dropped according to claim 12 wherein the step of identifying the second base station further comprises the steps of: searching for a plurality of pilot signals transmitted by the plurality of base stations, respectively; and selecting a pilot signal having the strongest signal strength from among the plurality of pilot signals, wherein the pilot signal having the strongest signal strength corresponds to the pilot signal transmitted by the second base station.

Claim 16

A method for preventing the active call from being dropped according to claim 12 wherein the step of receiving a reconnect request message further comprises the step of: receiving the reconnect request message on a paging code channel.

Claim 17

In a code division multiple access (CDMA) cellular radiotelephone communication system including at least one switch controller, a plurality of base stations including first and second base stations, and at least one mobile station, wherein a switch controller is coupled to the first and second base stations to provide radiotelephone communication throughout first and second coverage areas, respectively, wherein a mobile station is in an active call in the first coverage area with the first base station on a first traffic channel and substantially shadowed from transmissions from the second base station in the second coverage area, a method, performed by the mobile station, for preventing the active call from being dropped when the mobile station suddenly transitions from the first coverage area to the second coverage area, the method comprising the steps of: determining that the active call is in danger of being dropped responsive to the mobile station suddenly transitioning from the first coverage area to the second coverage area; notifying the first base station that the active call is in danger of being dropped responsive to the step of determining that the active call is in danger of being dropped; determining that the active call with the first base station is in the process of being dropped responsive to the step of notifying the first base station that the active call is in danger of being dropped; searching for a plurality of pilot signals transmitted by the plurality of base stations, respectively, responsive to the step of determining that the active call with the first base station is in the process of being dropped; selecting a pilot signal having the strongest signal strength from among the plurality of pilot signals, wherein the pilot signal having the strongest signal strength corresponds to the pilot signal transmitted by the second base station; sending a reconnect request message to the second base station responsive to the step of identifying the second base station responsive to the step of determining the pilot signal having the strongest signal strength from among the plurality of pilot signals; receiving a reconnect grant message from the second base station within a predetermined amount of time responsive to the step of sending a reconnect request message to the second base station; and resuming the active call in the second coverage area with the second base station on a second traffic channel responsive to the step of receiving a reconnect grant message from the second base station.

Claim 18

In a code division multiple access (CDMA) cellular radiotelephone communication system including at least one switch controller, a plurality of base stations including first and second base stations, and at least one mobile station, wherein a switch controller is coupled to the first and second base stations to provide radiotelephone communication throughout first and second coverage areas, respectively, wherein a mobile station is in an active call in the first coverage area with the first base station on a first traffic channel and substantially shadowed from transmissions from the second base station in the second coverage area, a method, performed by the mobile station, for preventing the active call from being dropped when the mobile station suddenly transitions from the first coverage area to the second coverage area, the method comprising the steps of: determining that the active call is in danger of being dropped responsive to the mobile station suddenly transitioning from the first coverage area to the second coverage area; notifying the first base station that the active call is in danger of being dropped responsive to the step of determining that the active call is in danger of being dropped; determining that the active call with the first base station is in the process of being dropped responsive to the step of notifying the first base station that the active call is in danger of being dropped; searching for a plurality of pilot signals transmitted by the plurality of base stations, respectively, responsive to the step of determining that the active call with the first base station is in the process of being dropped; selecting a pilot signal having the strongest signal strength from among the plurality of pilot signals, wherein the pilot signal having the strongest signal strength corresponds to the pilot signal transmitted by the second base station; sending a reconnect request message to the second base station responsive to the step of identifying the second base station responsive to the step of determining the pilot signal having the strongest signal strength from among the plurality of pilot signals; receiving a reconnect grant message from the second base station within a predetermined amount of time responsive to the step of sending a reconnect request message to the second base station; and resuming the active call in the second coverage area with the second base station on a second traffic channel responsive to the step of receiving a reconnect grant message from the second base station.

Claim 19

A method for preventing the active call from being dropped according to claim 15 wherein the step of determining the active call is in danger of being dropped further comprises the step of: monitoring a total energy received by the mobile station; measuring a signal energy for the active call received by the mobile station; calculating a ratio of the signal energy to the total energy; and determining that the ratio is unfavorable to indicate that active call is in danger of being dropped.

Claim 20

A method for preventing the active call from being dropped according to claim 16 wherein the step of monitoring the total energy received by the mobile station further comprises the steps of: measuring the total energy received by the mobile station at selected points in time to produce samples of the total energy including at least one previous sample and a current sample of the total energy; determining that the current sample of the total energy is greater than the at least one previous sample of the total energy by a predetermined amount; integrating the current sample of total energy with the at least one previous sample of the total energy to produce an integrated total energy; and storing the integrated total energy to produce a stored total energy.

Claim 21

A method for preventing the active call from being dropped according to claim 15 wherein the step of notifying the first base station that the active call is in danger of being dropped further comprises the step of: sending a pilot signal strength message to the first base station indicative of signal strengths of a plurality of pilot signals transmitted by the plurality of base stations, respectively.

Claim 22

A method for preventing the active call from being dropped according to claim 15 wherein the active call includes a plurality of sequential frames, wherein the step of determining that the active call with the first base station is in the process of being dropped further comprises the step of: determining that a predetermined number of the plurality of sequential frames are unacceptable; and determining, within a predetermined amount of time, that no two sequential frames of the plurality of sequential frames are acceptable.

Claim 23

In a code division multiple access (CDMA) cellular radiotelephone communication system including at least one switch controller, a plurality of base stations including first and second base stations, and at least one mobile station, wherein a switch controller is coupled to the first and second base stations to provide radiotelephone communication throughout first and second coverage areas, respectively, wherein a mobile station is in an active call in the first coverage area with the first base station on a first traffic channel and substantially shadowed from transmissions from the second base station in the second coverage area, a method, performed by the mobile station, for preventing the active call from being dropped when the mobile station suddenly transitions from the first coverage area to the second coverage area, the method comprising the steps of: monitoring a total energy received by the mobile station; measuring a signal energy for the active call received by the mobile station; calculating a ratio of the signal energy to the total energy; determining that the ratio is unfavorable to indicate that active call is in danger of being dropped; sending a pilot signal strength message to the first base station indicative of signal strengths of a plurality of pilot signals transmitted by the plurality of base stations, respectively, responsive to the step of determining that the ratio is unfavorable; determining that the active call with the first base station is in the process of being dropped responsive to the step of sending a pilot signal strength message to the first base station; searching for a plurality of pilot signals transmitted by the plurality of base stations, respectively, responsive to the step of determining that the active call with the first base station is in the process of being dropped; selecting a pilot signal having the strongest signal strength from among the plurality of pilot signals, wherein the pilot signal having the strongest signal strength corresponds to the pilot signal transmitted by the second base station; sending a reconnect request message to the second base station responsive to the step of identifying the second base station responsive to the step of selecting the pilot signal having the strongest signal strength from among the plurality of pilot signals; receiving a reconnect grant message from the second base station within a predetermined amount of time responsive to the step of sending a reconnect request message to the second base station; and resuming the active call in the second coverage area with the second base station on a second traffic channel responsive to the step of receiving a reconnect grant message from the second base station.

Claim 24

In a code division multiple access (CDMA) cellular radiotelephone communication system including at least one switch controller, a plurality of base stations including first and second base stations, and at least one mobile station, wherein a switch controller is coupled to the first and second base stations to provide radiotelephone communication throughout first and second coverage areas, respectively, wherein a mobile station is in an active call in the first coverage area with the first base station on a first traffic channel and substantially shadowed from transmissions from the second base station in the second coverage area, a method, performed by the mobile station, for preventing the active call from being dropped when the mobile station suddenly transitions from the first coverage area to the second coverage area, the method comprising the steps of: monitoring a total energy received by the mobile station; measuring a signal energy for the active call received by the mobile station; calculating a ratio of the signal energy to the total energy; determining that the ratio is unfavorable to indicate that active call is in danger of being dropped; sending a pilot signal strength message to the first base station indicative of signal strengths of a plurality of pilot signals transmitted by the plurality of base stations, respectively, responsive to the step of determining that the ratio is unfavorable; determining that the active call with the first base station is in the process of being dropped responsive to the step of sending a pilot signal strength message to the first base station; searching for a plurality of pilot signals transmitted by the plurality of base stations, respectively, responsive to the step of determining that the active call with the first base station is in the process of being dropped; selecting a pilot signal having the strongest signal strength from among the plurality of pilot signals, wherein the pilot signal having the strongest signal strength corresponds to the pilot signal transmitted by the second base station; sending a reconnect request message to the second base station responsive to the step of identifying the second base station responsive to the step of selecting the pilot signal having the strongest signal strength from among the plurality of pilot signals; receiving a reconnect grant message from the second base station within a predetermined amount of time responsive to the step of sending a reconnect request message to the second base station; and resuming the active call in the second coverage area with the second base station on a second traffic channel responsive to the step of receiving a reconnect grant message from the second base station.

Claim 25

A method for preventing the active call from being dropped according to claim 20 wherein the step of monitoring the total energy received by the mobile station further comprises the steps of: measuring the total energy received by the mobile station at selected points in time to produce samples of total energy including at least one previous sample and a current sample of the total energy; determining that the current sample of the total energy is greater than the at least one previous sample of the total energy by a predetermined amount; integrating the current sample of total energy with the at least one previous sample of the total energy to produce an integrated total energy; and storing the integrated total energy to produce a stored total energy.

Claim 26

A method for preventing the active call from being dropped according to claim 20 wherein the active call includes a plurality of sequential frames, wherein the step of determining that the active call with the first base station is in the process of being dropped further comprises the step of: determining that a predetermined number of the plurality of sequential frames are unacceptable; and determining, within a predetermined amount of time, that no two sequential frames of the plurality of sequential frames are acceptable.