Apparatus and method for reducing message collision between mobile stations simultaneously accessing a base station in a CDMA cellular communications system

Abstract

Collisions between messages simultaneously transmitted by multiple spread-spectrum transmitters are reduced by distributing the transmissions over the available resources of the receiver. Each mobile station in a CDMA system uses one or more randomization methods to distribute its transmissions. In the first randomization, the mobile station time-delays its transmissions by a number of chips of the PN code with which it spreads the transmitted signal. In a second randomization, the mobile station randomly selects the PN code. In a third randomization, the mobile station inserts a random delay between successive message transmissions or probes if it does not receive an acknowledgement after a predetermined timeout period. A predetermined number of such transmissions is called a probe sequence. In a fourth randomization, the mobile station inserts a relatively long random delay between successive probe sequences if it does not receive an acknowledgement of any probe in the sequence.

1 . A method for an access request attempt of a communication station in a communication network, comprising: 
 sending a plurality of probe sequences to said communication station;    including in each of said probe sequences a plurality of probes; and    terminating said access request attempt if after said sending of any of said probes in any of said probe sequences an acknowledge message is received from said communication station.    
     
     
         2 . The method as in  claim 1  further including providing said plurality of probes with increasing power levels in each of said probe sequences.  
     
     
         3 . The method as in  claim 1  further including separating said probe sequences by random delays.  
     
     
         4 . The method as in  claim 1  further including separating said plurality of probes by random delays.  
     
     
         5 . The method as in  claim 1  further including sending said plurality of probe sequences through different access channels.  
     
     
         6 . The method as in  claim 1  further including abandoning said request for initial access request if after said sending of a predetermined number of said probe sequences no acknowledgement message is received from said communication station.  
     
     
         7 . An apparatus in a communication network, comprising: 
 means for sending a plurality of probe sequences for an access request attempt to a communication station;    means for including in each of said probe sequences a plurality of probes having increasing power levels; and    means for terminating said access request attempt if after any of said probes in any of said probe sequences an acknowledge message is received from said communication station.    
     
     
         8 . The apparatus as in  claim 7  further including means for providing said plurality of probes with increasing power levels in each of said probe sequences.  
     
     
         9 . The apparatus as in  claim 7  further including means for separating said probe sequences by random delays.  
     
     
         10 . The apparatus as in  claim 7  further including means for separating said plurality of probes by random delays.  
     
     
         11 . The apparatus as in  claim 7  further including means for sending said plurality of probe sequences through different access channels.  
     
     
         12 . The apparatus as in  claim 7  further including means for abandoning said access request attempt if after a predetermined number of said probe sequences no acknowledgement message is received from said communication station.  
     
     
         13 . Electrical signals transmitted via a carrier wave to a communication station in a communication system, said electrical signals comprising computer-readable instructions for: 
 sending a plurality of probe sequences for an access request attempt to said communication station;    including in each of said probe sequences a plurality of probes having increasing power levels; and    terminating said access request attempt if after said sending of any of said probes in any of said probe sequences an acknowledge message is received from said communication station.