Soft handoff algorithm and wireless communication system for third generation CDMA systems

Abstract

A method and apparatus for providing an improved soft handoff algorithm in a wireless communication system for third generation code division multiple access (“CDMA”) systems. The method comprises establishing communication between the wireless communication device and the at least one serving base station, the at least one serving base station having a list of at least one neighboring base station which neighbors the respective serving base station, monitoring the reverse channel signal strength at the wireless communication device from at least one neighboring base station, transmitting to a base station controller the wireless communication device signal strength detected at each neighboring base station, compiling at the base station controller a list of effective neighboring base stations from the at least one neighboring base station based on the monitored wireless communication device signal strength, transmitting the list of effective neighboring base stations to each at least one serving base station, periodically transmitting a neighboring base station list update message to the wireless communication device, the neighboring base station list update message including the effective neighboring base station list, storing the effective neighboring base station list as a neighbor set in the wireless communication device, performing forward channel signal strength searching of the neighbor set in the wireless communication device after storing the effective neighbor list as the neighbor set, and monitoring the signals from the effective neighboring base stations to accomplish a handoff between the at least one service base station and the receiving neighboring base station.

1 . A method of handing off a wireless communication device between at least one serving base station and a receiving base station in a wireless communication system comprising: 
 establishing a call between the wireless communication device and the at least one serving base station;    monitoring a signal from the wireless communication device from at least one base station neighboring the serving base station;    compiling a list of effective neighboring base stations from the at least one neighboring base station based on the monitored wireless communication device signal; and    monitoring the signals from the effective neighboring base stations to accomplish a handoff between the at least one serving base station and the receiving base station.    
     
     
         2 . The method of  claim 1 , wherein monitoring the signal from the wireless communication device from the at least one neighboring base station includes monitoring the reverse pilot channel signal strength from the wireless communication device.  
     
     
         3 . The method of  claim 2 , wherein compiling the list of effective neighboring base stations is further based on the monitored wireless communication device reverse pilot channel signal strength.  
     
     
         4 . The method of  claim 3 , wherein the list of effective neighboring base stations includes base stations neighboring the at least one serving base station which receive the wireless communication device signal at a predetermined strength.  
     
     
         5 . The method of  claim 4 , further comprising transmitting an extended handoff direction message from the base station controller to the wireless communication device autonomously.  
     
     
         6 . The method of  claim 5 , wherein transmitting the extended handoff direction message is based on the base station controller analysis of the wireless communication device signal strength detected by each neighboring base station and independent of the pilot strength measurement message generated by the wireless communication device.  
     
     
         7 . The method of  claim 1  wherein each neighboring base station to the at least one serving base station constantly monitors the reverse channel signal strength.  
     
     
         8 . The method of  claim 1 , further comprising transmitting an extended handoff direction message independent of a pilot strength measurement message generated by the wireless communication device.  
     
     
         9 . A method of optimizing a neighbor list comprising: 
 establishing a call between a wireless communication device and at least one serving base station;    storing at each at least one serving base station a list of neighboring base stations;    monitoring a reverse channel signal strength at each neighboring base station and reporting the respective reverse channel signal strength to a base station controller;    compiling a list of effective neighbor base stations based on the reported reverse channel signal strength;    transmitting the list of effective neighbors to each at least one serving base station;    transmitting a neighbor list update message containing the list of effective neighbors to the wireless communication device; and    storing the effective neighbor list as a neighbor set in the wireless communication device.    
     
     
         10 . The method of  claim 9 , wherein the base station controller directs each neighboring base station to monitor the reverse channel signal strength of the wireless communication device.  
     
     
         11 . The method of  claim 10 , wherein compiling the effective neighbor list comprises processing the reverse channel signal strength from the neighboring base stations and comparing the respective reverse channel signal strength with a predetermined threshold.  
     
     
         12 . The method of  claim 11 , wherein the effective neighbor list comprises neighboring base stations that have a reverse channel signal strength of at least a predetermined value.  
     
     
         13 . The method of  claim 9 ,wherein the neighbor list contains at most six neighboring base stations.  
     
     
         14 . The method of  claim 9 , wherein the neighbor list contains at most three neighboring base stations.  
     
     
         15 . The method of  claim 9 , wherein transmitting the list of effective neighboring base stations to each at least one serving base station is performed by the base station controller which updates the neighbor set using a neighbor list update message including the list of effective neighboring base stations to each at least one serving base station.  
     
     
         16 . The method of  claim 15 , further comprising transmitting the neighbor list update message from the at least one serving base station to the wireless communication device.  
     
     
         17 . A method of handing off a wireless communication device between a plurality of serving base stations and at least one receiving base station in a wireless communication system comprising: 
 establishing a call between the wireless communication device and the plurality of serving base stations;    monitoring the reverse channel signal strength from at least one neighboring base station to each of the plurality of serving base stations;    compiling a list of effective neighboring base stations corresponding to each of the plurality of serving base stations; and    monitoring the signals from the effective neighboring base stations to accomplish a handoff between the plurality of serving base stations and the at least one receiving base station.    
     
     
         18 . The method of  claim 17 , wherein the signal from the wireless communication device is monitored from at least one neighboring base station to each of the plurality of serving base stations, and the lists of effective neighboring base stations includes respective base stations neighboring each of the plurality of serving base stations which receive the wireless communication device signal at a predetermined strength.  
     
     
         19 . A wireless communication system comprising: 
 a wireless communication device which communicates with a serving base station;    at least one base station neighboring the serving base station which monitors a reverse channel signal strength from the wireless communication device; and    a base station controller which compiles a list of effective neighboring base stations from the at least one base station neighboring the serving base station based on the monitored reverse channel signal strength from the wireless communication device, the base station controller communicating the list of effective neighboring base stations to the wireless communication device.    
     
     
         20 . The wireless communication system of  claim 19 , wherein the serving base station periodically sends a neighbor list update message containing the list of effective neighboring base stations to the wireless communication device, and the wireless communication device stores the list of effective neighboring base stations as a neighbor set and performs forward channel searches based on the updated neighbor set.  
     
     
         21 . A wireless communication system comprising: 
 a wireless communication device which communicates with a serving base station;    a plurality of base stations neighboring the serving base station, each of the plurality of base stations monitoring a reverse channel signal strength from the wireless communication device;    a base station controller, the plurality of neighboring base stations transmitting each of the monitored reverse channel signals to the base station controller, which compiles a list of effective neighboring base stations from the plurality of neighboring base station based on the monitored reverse channel signal strength from the wireless communication device; and    the base station controller transmitting the effective neighboring list to the base station, and the base station transmitting a neighbor list update message to the wireless communication device, the neighbor list update message containing the effective neighboring list.    
     
     
         22 . The wireless communication system of  claim 21 , wherein the serving base station periodically sends a neighbor list update message containing the list of effective neighboring base stations to the wireless communication device, and the wireless communication device stores the list of effective neighboring base stations as a neighbor set and performs forward channel searches based on the updated neighbor set.