Method and apparatus for controlling access to a communication system

DETAILED DESCRIPTION Accordingly, it is an object of the present invention to provide an improved communication system.
It is another object of the present invention to provide a method for detecting subscriber units having duplicated ID codes.
It is a further object of the present invention to provide a method for denying access to communication services to subscriber units having duplicated ID codes.
Accordingly, these and other objects are achieved in the present method for controlling access to a communication system.
Briefly, according to the invention, selected subscribers are addressed and required to solve a "Puzzle" generated by a central device (controller) of a two-way communication system.
The "Puzzle" comprises one or more digital words and an operand, which provides instructions to the subscriber unit as to how to generate an answer.
The subscriber units cannot anticipate either the occurrence nor the content of any particular "Puzzle".
All subscribers (both authorized and unauthorized) must return an "Answer" to the "Puzzle" or they may be denied access to the two-way communication system.
Also, unauthorized subscriber units may be detected when the central device receives multiple answers to a "Puzzle".