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

• US 20030199252A1
• Filed: 06/10/2003
• Published: 10/23/2003
• Est. Priority Date: 03/05/1992
• Status: Active Grant

• Current Assignee: Edward G. Tiedemann Jr, Lindsay A. Weaver Jr, Roberto Padovani
• Original Assignee: Edward G. Tiedemann Jr, Lindsay A. Weaver Jr, Roberto Padovani
• Inventors: Tiedemann, Edward G. Jr., Padovani, Roberto, Weaver, Lindsay A. Jr.
• Granted Patent: US 6,985,728 B2
• Time in Patent Office: Days
• US Class Current: 455/69
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/7103 the interference being multiple access interference
• CPC Class Codes: H04B 2201/709709 Methods of preventing interference
• CPC Class Codes: H04B 7/2628 using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA] H04B7/2618 takes precedence
• CPC Class Codes: H04J 13/0022 PN, e.g. Kronecker
• CPC Class Codes: H04J 13/10 Code generation
• CPC Class Codes: H04J 13/16 Code allocation
• CPC Class Codes: H04L 1/188 Time-out mechanisms
• CPC Class Codes: H04L 1/1887 Scheduling and prioritising arrangements
• CPC Class Codes: H04W 52/48 during retransmission after error or non-acknowledgment
• CPC Class Codes: H04W 52/50 at the moment of starting communication in a multiple access environment
• CPC Class Codes: H04W 74/002 Transmission of channel access control information
• CPC Class Codes: H04W 74/08 Non-scheduled access, e.g. ALOHA hybrid access H04W74/02
• CPC Class Codes: H04W 74/0833 Random access procedures, e.g. with 4-step access
• CPC Class Codes: H04W 74/0841 with collision treatment
• CPC Class Codes: H04W 74/0866 using a dedicated channel for access

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.

Claims

1. A method of reducing message collisions between transmitted messages in a communication network, the method comprising:

determining whether an access attempt is an access channel request;

performing a persistence test for an access channel slot if the access attempt is an access channel request; and

transmitting a first access probe of an access probe sequence in the slot if the persistence test passes.

2. The method of claim 1, wherein the step of performing the persistence test comprises:

generating a random probability;

comparing the random probability to a predetermined parameter representing a probability that a subsequent access probe sequence will be performed;

determining that the persistence test passes if the random probability is less than the predetermined parameter; and

determining that the persistence test fails if the random probability is not less than the predetermined parameter.

3. The method of claim 1, further comprising:

if the persistence test fails, repeating the persistence test until the persistence test passes.

4. The method of claim 1, further comprising:

generating a random number for channel randomization; and

selecting an access channel for transmitting the first access probe based on the random number.

5. A mobile station apparatus, comprising:

means for determining whether an access attempt is an access channel request;

means for performing a persistence test for an access channel slot if the access attempt is an access channel request; and

means for transmitting a first access probe of an access probe sequence in the slot if the persistence test passes.

6. The apparatus of claim 5, wherein the means for performing the persistence test comprises:

means for generating a random probability;

means for comparing the random probability to a predetermined parameter representing a probability that a subsequent access probe sequence will be performed;

means for determining that the persistence test passes if the random probability is less than the predetermined parameter; and

means for determining that the persistence test fails if the random probability is not less than the predetermined parameter.

7. The apparatus of claim 5, further comprising:

means for repeating the persistence test until the persistence test passes.

8. The apparatus of claim 5, further comprising:

means for generating a random number for channel randomization; and

means for selecting an access channel for transmitting the first access probe based on the random number.

9. A computer readable medium embodying a method of reducing message collisions between transmitted messages in a communication network, the method comprising:

determining whether an access attempt is an access channel request;

performing a persistence test for an access channel slot if the access attempt is an access channel request; and

transmitting a first access probe of an access probe sequence in the slot if the persistence test passes.

10. The computer readable medium of claim 9, wherein the step of performing the persistence test comprises:

generating a random probability;

comparing the random probability to a predetermined parameter representing a probability that a subsequent access probe sequence will be performed;

determining that the persistence test passes if the random probability is less than the predetermined parameter; and

determining that the persistence test fails if the random probability is not less than the predetermined parameter.

11. The computer readable medium of claim 9, wherein the method further comprises:

if the persistence test fails, repeating the persistence test until the persistence test passes.

12. The computer readable medium of claim 9, wherein the method further comprises:

generating a random number for channel randomization; and

selecting an access channel for transmitting the first access probe based on the random number.