Patent ID: 6044272
Filing Date: 2000-03-28
Classification: H04W

Abstract:
A method for mobile assisted handoff of a communication link between a mobile station and a base station in a digital cellular communications network, from a current base station to one of a number of candidate base stations within said network, said method comprising the steps of:generating a list of a plurality of candidate channels for possible acceptance of said communication handoff;transmitting a first measurement order from said current base station to said mobile station, said first measurement order containing said list of candidate channels;measuring a received signal strength and a bit error rate at said mobile station for said communication between said mobile station and said current base station;measuring received signal strength at said mobile station for each of said candidate channels listed in said first measurement order;transmitting said received signal strength measurements from said mobile station to said current base station;selecting a plurality of most favorable candidate channels from said received signal strength measurement results;transmitting a second measurement order from said current base station to said mobile station, said second measurement order containing a list of said most favorable candidate channels;tuning and synchronizing said mobile station to each of said candidate channels listed in said second measurement order, said step of tuning and synchronizing including:tuning into said candidate channel, reading data within a time window on said candidate channel;correlating said data from said candidate channel with a plurality of known synchronization words and identifying a most probable synchronization word within said data; andreturning back to said current base station channel;reading and decoding an identification code for each of said candidate channels, said step of reading and decoding including:storing said data from said candidate channel into a memory device located on said mobile station;processing said data by searching for said identification code at a first predetermined number of symbols after the appearance of said probable synchronization word and, if said identification code cannot be found at said first predetermined number of symbols after said probable synchronization word, then searching for said identification code at a second predetermined number of symbols ahead of said probable synchronization word; andidentifying said identification code, said identification code comprising a digital voice color code word in said candidate channel;transmitting said identification codes for each of said candidate channels from said mobile station to said current base station;monitoring threshold received signal strength values for said current channel and said candidate channel, said threshold values determining when selection and activation of said handoff should occur; andcorrelating said received signal strength measurements with said identification codes to identify an optimal candidate base station for effecting said handoff of said communication.