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

• US 7,426,391 B2
• Filed: 01/11/2007
• Issued: 09/16/2008
• Est. Priority Date: 03/05/1992
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Tiedemann, Edward G. Jr., Padovani, Roberto, Weaver, Lindsay A. Jr.
• Primary Examiner(s): Vuong; Quochien B
• Application Number:
  US11/622,403
• Publication Number:
  US 20070274267A1
• Time in Patent Office: 614 Days
• Field of Search: 455/434, 455/450, 455/452.1, 455/453, 455/515, 455/516, 370/321, 370/345, 370/347, 370/442, 370/515, 375/130, 375/140, 375/145, 375/146, 375/147, 701/219
• US Class Current: 455/434
• 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 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.

2. The method of claim 1 further including the step of upon receiving said access probe, transmitting said acknowledgment signal from said second transceiver to said at least one first transceiver.

3. The method of claim 1 wherein said at least one first transceiver is a mobile radio telephone and said second transceiver is a base station.

4. The method of claim 1 wherein said access probe is transmitted using spread-spectrum signal coding.

5. The method of claim 1 wherein said step of transmitting further includes the step of generating said access probe using a spreading code selected from a predefined set of spreading codes.

6. The method of claim 5 wherein each code in said predefined set of codes corresponds to a different access channel.

7. The method of claim 1, wherein the predetermined range is a predetermined number of time slots.

8. The method of claim 7, wherein the first and second time delays are measured as a number of time slots within said predetermined number of time slots.

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.

10. The mobile radio unit of claim 9 wherein said means for transmitting includes means for selecting a spreading code corresponding to an access channel used to transmit said access probe.

11. The mobile radio unit of claim 10, wherein the predetermined range is a predetermined number of time slots.

12. The mobile radio unit of claim 11, wherein the first and second time delays are measured as a number of time slots within said predetermined number of time slots.

13. A communications system with minimized access channel interference, comprising:

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.

14. The system of claim 13 wherein each said mobile radio unit includes means for generating each said access probe using one of a set of access channel codes.

15. The system of claim 14 wherein said set of access channel codes correspond to a range of access channels.

16. The system of claim 14 wherein said mobile station includes means for selecting one of said access channel codes.

17. The system of claim 13, wherein the predetermined range is a predetermined number of time slots.

18. The system of claim 17, wherein the first and second time delays are measured as a number of time slots within said predetermined number of time slots.

19. An apparatus 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 comprising:

a processor for randomly selecting a first time delay within a predetermined range;

a transmitter for 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;

wherein the processor determines whether said access probe has been received at said second transceiver based on reception of an acknowledgement from said second transceiver, and if said access probe has not been received, randomly selecting a second time delay within said predetermined range; and

wherein the transmitter retransmits 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, 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.

20. The apparatus of claim 19 wherein said at least one first transceiver is a mobile radio telephone and said second transceiver is a base station.

21. The apparatus of claim 19 wherein said access probe is transmitted using spread-spectrum signal coding.

22. The apparatus of claim 19 wherein said transmitting further includes generating said access probe using a spreading code selected from a predefined set of spreading codes.

23. The apparatus of claim 22 wherein each code in said predefined set of codes corresponds to a different access channel.

24. The apparatus of claim 19, wherein the predetermined range is a predetermined number of time slots.

25. The apparatus of claim 24, wherein the first and second time delays are measured as a number of time slots within said predetermined number of time slots.