Inter-system soft handoff

Abstract

A method and apparatus for operating a cellular telephone system that supports performing an inter-system soft handoff is described. A subscriber unit generates a pilot strength measurement report when the pilot channel from a base station is detected. When a base station controller receiving the pilot strength measurement report determines that the base station is part of a second cellular telephone system, a inter-system soft handoff request is generated. An admission control subsystem receives the inter-system soft handoff and either grants or denies the request base on the traffic level with the second cellular telephone system. In a preferred embodiment of the invention, the traffic level is determined based on link load messages received periodically by the admission control subsystem that are generated by an interface port coupled to an interconnect between the first cellular telephone system and the second cellular telephone system. The link load message include peak queue length and average frame rate information.

I (We) claim:  
     
         1 . A method for conducting an inter-system soft handoff of a call made by a subscriber unit between a first cellular system and a second cellular system comprising the steps of: 
 a) monitoring a traffic level exchanged between the first cellular system and the second cellular system; and    b) granting a soft handoff request based on said traffic level.    
     
     
         2 . The method as set forth in  claim 1  wherein step a) is comprised of the steps of: 
 a.1) monitoring a peak queue length at an interface between the first cellular system and the second cellular system; and  
 a.2) monitoring an average frame rate over said interface.  
 
     
     
         3 . The method as set forth in  claim 1  wherein step a) is comprised of the step of monitoring a peak queue length at an interface between the first cellular system and the second cellular system.  
     
     
         4 . The method as set forth in  claim 1  wherein step a) is comprised of the steps of monitoring an average frame rate over said interface.  
     
     
         5 . The method as set forth in  claim 2  wherein step b) is comprised of the steps of: 
 b.1) comparing said peak queue length with a queue length threshold; and  
 b.2) granting said soft handoff request when said peak queue length is less than said queue length threshold.  
 
     
     
         6 . A cellular telephone system capable of conducting an inter-system soft handoff with a second cellular telephone system comprising: 
 a cellular system interface port for monitoring a traffic level exchanged with the second cellular telephone system;    a selector for initiating an inter system soft handoff; and    an admission control subsystem for admitting said inter-system soft handoff and rejecting said inter-system soft handoff based on said traffic level.