Seamless handoff for radio telephone systems

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, 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.

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:

• 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.