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

A mobile radio unit for communicating with a base station, comprising:

• means for selecting, randomly, a first time delay within a predetermined range;
• means for transmitting an access probe at a first power level after said first randomly selected time delay to said base station, said first power level being determined on the basis of amount of power at which a signal transmitted from said base station is received;
• means for detecting an acknowledgment signal from said base station;
• wherein said acknowledgment signal indicating reception of said access probe at said base station;
• if said access probe has not been received, said means for selecting further for selecting, randomly, a second time delay within said predetermined range;
• and
• means for commanding said means for transmitting to retransmit said access probe, after said second randomly selected time delay, at a power level greater than said first power level.

A communications system with minimized access channel interference, comprising:

• a plurality of mobile radio units, each mobile radio unit including:
• means for transmitting an access probe initially at a first power level and after a first randomly selected time delay within a predetermined range, and retransmitting said access probe at a power level greater than said first power level and after a second randomly selected time delay within said predetermined range until said access probe is received;
• means for determining whether said access probe has been received based on reception of an acknowledgment indicating reception of said access probe;
• at least one base station including:
• means for receiving transmissions of said access probe during any
• randomly selected time delays within said predetermined range;
• means for transmitting said acknowledgment message to the mobile
• radio unit from which at least one of said access probes is received;
• wherein said first power level is determined on the basis of amount of power at which a signal transmitted from said at least one base station is received.