Seamless handoff for radio telephone systems
First Claim
1. In a time-division duplex radio communication system comprising a plurality of base stations and portable radio units communicating on a plurality of alternating transmit and receive frames, a method for seamless transfer of a communication link from a first base station to a second base station comprising the steps of:
- at the first base station;
receiving a communication link request from a calling portable radio unit;
synchronizing with the calling portable radio unitdetermining whether the calling portable radio unit has handoff authorization;
connecting received data to a transceiver in the second base station to allow for bit level synchronization to the calling portable radio unit;
measuring a first RSSI level at the first base station for the calling portable radio unit;
determining whether the first RSSI level for the calling portable radio unit is below a first handoff threshold;
determining a second RSSI level for the calling portable radio unit, as measured at the second base station, if the first RSSI level for the calling portable radio unit is below the first handoff threshold,determining whether the second RSSI level for the calling portable radio unit is above a second handoff threshold;
if the first RSSI level is below the first handoff threshold and the second RSSI level is above the second handoff threshold, alerting the second base station to pick up the communication link;
at the second base station;
synchronizing with the calling portable radio unit;
receiving the alert to pick up the communication link from the first base station; and
commencing to transmit in a next transmit frame of the second base station following a last transmit frame of the first base station.
1 Assignment
0 Petitions
Accused Products
Abstract
A method for seamless transfer of a communication link from a first radio telephone base station to a second radio telephone base station comprises the following steps performed at the first base station: (100) receiving a communication link request from a calling portable radio unit; (102) synchronizing with the calling portable radio unit; (104) determining whether the calling radio has handoff authorization; (108) connecting received data to a second base to allow for synchronization to the calling radio; (112) measuring a first RSSI level at the first base station for the calling radio; (114) determining whether the first RSSI level for the calling radio is below a first handoff threshold; (116) determining a second RSSI level for the calling radio, as measured at the second base station, is above a second handoff threshold, if the first RSSI level for the calling portable radio unit is below the first handoff threshold, (118) determining whether the second RSSI level for the calling portable radio unit is above a second handoff threshold, and (120) alerting the second base station to pick up the communication link. The method further comprises the following step performed at a second base station: (122) commencing to transmit in the frame immediately following the last transmit frame of the first base.
59 Citations
9 Claims
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1. In a time-division duplex radio communication system comprising a plurality of base stations and portable radio units communicating on a plurality of alternating transmit and receive frames, a method for seamless transfer of a communication link from a first base station to a second base station comprising the steps of:
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at the first base station; receiving a communication link request from a calling portable radio unit; synchronizing with the calling portable radio unit determining whether the calling portable radio unit has handoff authorization; connecting received data to a transceiver in the second base station to allow for bit level synchronization to the calling portable radio unit; measuring a first RSSI level at the first base station for the calling portable radio unit; determining whether the first RSSI level for the calling portable radio unit is below a first handoff threshold; determining a second RSSI level for the calling portable radio unit, as measured at the second base station, if the first RSSI level for the calling portable radio unit is below the first handoff threshold, determining whether the second RSSI level for the calling portable radio unit is above a second handoff threshold; if the first RSSI level is below the first handoff threshold and the second RSSI level is above the second handoff threshold, alerting the second base station to pick up the communication link; at the second base station; synchronizing with the calling portable radio unit; receiving the alert to pick up the communication link from the first base station; and commencing to transmit in a next transmit frame of the second base station following a last transmit frame of the first base station. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A time-division duplex radio communication system comprising:
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a plurality of base stations and portable radio units communicating on a plurality of alternating transmit and receive frames, each of the plurality of base stations comprising; receiver means for receiving a communication link request from a calling portable radio unit; synchronization means, coupled to the receiver means, for synchronizing with the calling portable radio unit; means, coupled to the receiver means, for determining whether the calling portable radio unit has handoff authorization; means for connecting received data to a transceiver in another of the plurality of base stations to allow synchronization to the calling portable radio; means for measuring a first RSSI level for the calling portable radio unit; means for determining whether the first RSSI level for the calling portable radio unit is below a handoff threshold; means for determining a second RSSI level, as measured at the another of the plurality of base stations for the calling portable radio unit, if the first RSSI level for the calling portable radio unit is below the handoff threshold, means for determining whether the second RSSI level for the calling portable radio unit is above the handoff threshold; and means for commencing to transmit in a next transmit frame of the another of the plurality of base stations following a last transmit frame of one of the plurality of base stations that is handing off a communication link to the another of the plurality of base stations.
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9. In a time-division duplex radio communication system comprising a plurality of base stations and portable radio units communicating on a plurality of alternating transmit and receive frames, a method for seamless transfer of a communication link from a first base station to a second base station, the first base station comprising:
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receiver means for receiving a communication link request from a calling portable radio unit; synchronization means, coupled to the receiver means, for synchronizing with the calling portable radio unit; means, coupled to the receiver means, for determining whether the calling portable radio unit has handoff authorization; means for connecting received data to a transceiver in the second base station to allow synchronization to the calling portable radio; means for measuring a first RSSI level for the calling portable radio unit; means for determining whether the first RSSI level for the calling portable radio unit is below a handoff threshold; means for determining a second RSSI level, as measured at the second base station, for the calling portable radio unit, if the first RSSI level for the calling portable radio unit is below the handoff threshold, means for determining whether the second RSSI level for the calling portable radio unit is above the handoff threshold; and means for connecting to transmit in a next transmit frame of the second base station following a last transmit frame of the first station that is handing off the communication link.
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Specification