APPARATUS AND METHOD FOR REDUCING MESSAGE COLLISION BETWEEN MOBILE STATIONS SIMULTANEOUSLY ACCESSING A BASE STATION IN A CDMA CELLULAR COMMUNICATIONS SYSTEM
First Claim
1. A method for reducing interference in a communication channel used by at least one of a plurality of first transceivers to initiate communication with a second transceiver, said method comprising the steps of:
- selecting, randomly, a first time delay within a predetermined range;
transmitting from said at least one first transceiver an access probe at a first power level after said first randomly selected time delay, said first power level being determined on the basis of amount of power at which a signal transmitted from said second transceiver is received;
determining whether said access probe has been received at said second transceiver based on reception of an acknowledgement from said second transceiver;
if said access probe has not been received, selecting, randomly, a second time delay within said predetermined range; and
retransmitting said access probe, after said second randomly selected time delay, from said at least one first transceiver at a power level greater than said first power level;
wherein said transmitting and said retransmitting are included in an access probe transmissions sequence to initiate communication with said second transceiver, wherein said access probe sequence begins only if a persistence test is passed in accordance with a persistence parameter.
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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.
74 Citations
18 Claims
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1. A method for reducing interference in a communication channel used by at least one of a plurality of first transceivers to initiate communication with a second transceiver, said method comprising the steps of:
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selecting, randomly, a first time delay within a predetermined range;
transmitting from said at least one first transceiver an access probe at a first power level after said first randomly selected time delay, said first power level being determined on the basis of amount of power at which a signal transmitted from said second transceiver is received;
determining whether said access probe has been received at said second transceiver based on reception of an acknowledgement from said second transceiver;
if said access probe has not been received, selecting, randomly, a second time delay within said predetermined range; and
retransmitting said access probe, after said second randomly selected time delay, from said at least one first transceiver at a power level greater than said first power level;
wherein said transmitting and said retransmitting are included in an access probe transmissions sequence to initiate communication with said second transceiver, wherein said access probe sequence begins only if a persistence test is passed in accordance with a persistence parameter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A mobile radio unit for communicating with a base station, comprising:
means for performing an access probe transmissions sequence to initiate communication with said base station, wherein said access probe transmissions sequence begins only if a persistence test is passed in accordance with a persistence parameter, said means for performing comprises;
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. - View Dependent Claims (10, 11, 12)
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13. A communications system with minimized access channel interference, comprising:
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a plurality of mobile radio units, each mobile radio unit including;
means for performing an access probe transmissions sequence to initiate communication with a base station, wherein said access probe transmissions sequence begins only if a persistence test is passed in accordance with a persistence parameter, said means for performing comprises;
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 of said base stations 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. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification