Seamless handoff system and method

Abstract

A multicellular communications system where transmission between a roving subscriber and multiple base station transceivers is maintained throughout the territory. Each mobile subscriber unit has global code seeds for the entire communications system or an updated neighbor list and continuously searches to access available cell base stations while maintaining a communication link with one base station. Candidate cell base stations are interrogated and communicated with. The candidate base station that requires less transmitting energy from the mobile subscriber unit is closely monitored. When the mobile subscriber unit can successfully communicate with less transmit power than currently required by the present base station, the mobile subscriber unit is handed off to the candidate base station transceiver.

What is claimed is: 
     
         1 . A subscriber unit comprising:
 a receiver and a processor configured to receive at least one synchronization code transmitted from a base station;   a memory, associated with the processor, configured to store an association between the at least one synchronization code and at least one global pilot code sequence;   the processor configured to derive time synchronization information from the received at least one synchronization code;   the receiver and the processor further configured to receive a global pilot code sequence of the base station using the derived time synchronization information and to determine the global pilot code sequence using the stored association; and   the receiver and the processor further configured to receive a broadcast channel utilizing the determined global pilot code sequence.   
     
     
         2 . The subscriber unit of  claim 1 , wherein:
 the receiver and the processor are further configured to receive at least one synchronization code transmitted from another base station and to derive a global pilot code sequence of the another base station using the stored association.   
     
     
         3 . The subscriber unit of  claim 1 , further comprising:
 a transmitter and the processor configured to transmit an access signal to the base station.   
     
     
         4 . The subscriber unit of  claim 3 , wherein the access signal includes a short code. 
     
     
         5 . The subscriber unit of  claim 3 , wherein:
 the transmitter and the processor are further configured to ramp up a transmission power level of the access signal.   
     
     
         6 . A method comprising:
 receiving, by a subscriber unit, at least one synchronization code transmitted from a base station;   deriving, by the subscriber unit, time synchronization information from the received at least one synchronization code;   receiving, by the subscriber unit, a global pilot code sequence of the base station using the derived time synchronization information and determining the global pilot code sequence using a stored association between the at least one synchronization code and at least one global pilot code sequence; and   receiving, by the subscriber unit, a broadcast channel utilizing the determined global pilot code sequence.   
     
     
         7 . The method of  claim 6  further comprising:
 receiving, by the subscriber unit, at least one synchronization code transmitted from another base station; and 
 deriving, by the subscriber unit, a global pilot code sequence of the another base station using the stored association. 
 
     
     
         8 . The method of  claim 6 , further comprising:
 transmitting, by the subscriber unit, an access signal to the base station.   
     
     
         9 . The method of  claim 8 , wherein the access signal includes a short code. 
     
     
         10 . The method of  claim 8 , further comprising:
 ramping up a transmission power level of the access signal.