Method for collision avoidance in an asynchronous communication system

• US 6,608,821 B1
• Filed: 11/20/1998
• Issued: 08/19/2003
• Est. Priority Date: 11/20/1998
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments Israel Ltd. (Texas Instruments, Inc.)
• Inventors: Gendel, Alon
• Primary Examiner(s): Kizou, Hassan
• Assistant Examiner(s): LY, ANH VU H
• Application Number:
  US09/196,957
• Time in Patent Office: 1,733 Days
• Field of Search: 370/280, 370/281, 370/347, 370/295, 370/294, 370/301, 370/302, 370/326, 370/330, 370/336, 370/344, 370/345, 370/395.4, 370/436, 370/442, 370/461, 370/468, 370/498, 370/539, 370/458
• US Class Current: 370/280
• CPC Class Codes: H04B 1/715 Interference-related aspects
• CPC Class Codes: H04B 2001/7154 with means for preventing interference
• CPC Class Codes: H04L 1/0083 Formatting with frames or packets; Protocol or part of protocol for error control
• CPC Class Codes: H04L 1/08 by repeating transmission, e.g. Verdan system H04L1/1858 and H04L1/189 take precedence
• CPC Class Codes: H04W 74/085 collision avoidance

Abstract

A method of avoiding collisions among a plurality of transmitters that communicate asynchronously in relation to each other with a single receiver. The transmission scheme utilizes a randomization process to minimize the probability of collision among transmitted signals from different non synchronized transmitters, thus achieving improved overall link quality for each transmitter and improved system performance. The method has applications to many types of communications systems including frequency hopping spread spectrum communications systems. Transmitters send data in a burst of data packets, each sent during a time slot within the burst. Each time slot is divided into two or more sub time slots. During each time slot, one of the sub time slots is randomly chosen and the data packet is transmitted during that particular sub time slot. The larger the number of sub time slots used results in lower probability of complete transmission loss.

Claims

1. A method of transmitting a message in a communications system comprising a plurality of transmitters and at least one receiver, each said transmitter including means for initiating and transmitting a message to said at least one receiver, said method comprising the steps of:

transmitting said message a predetermined number of times N, each message transmission occurring during a time slot within a burst of N time slots;

dividing each time slot into a plurality of M sub time slots;

randomly selecting one of said M sub time slots in which to transmit said message such that the time delay between successive transmissions during each time slot is random;

transmitting said message during said randomly selected sub time slot;

wherein each transmitter transmits messages asynchronously with respect to and independently of transmissions from all other transmitters;

wherein burst time slot timing for each message is determined independently by each transmitter asynchronous to other transmitters and without the use of any system time slot synchronization; and

wherein N and M are positive integers and M is equal to or greater than 2.

2. The method according to claim 1, wherein N is equal to 25.

3. The method according to claim 1, wherein M is equal to 2.

4. The method according to claim 1, further comprising the step of appending a gap time to each time slot.

5. The method according to claim 1, wherein M is equal to 3.

6. The method according to claim 1, wherein said communications system comprises a frequency hopping spread spectrum communications system.

7. The method according to claim 1, wherein said transmitters transmit asynchronously with respect to each other.

8. A method of avoiding collisions between transmission signals in a frequency hopping spread spectrum communications system comprising a plurality of transmitters and at least one receiver, each said transmitter including means for initiating and transmitting a message to said at least one receiver, each transmitter utilizing the same pseudo random hop sequence of N frequencies, said method comprising the steps of:

transmitting each message N times, each message transmission occurring during a different time slot wherein transmissions during each time slot are assigned different frequencies;

dividing each time slot into a plurality of M sub time slots;

randomly selecting one and only one of said M sub time slots in which to transmit said message such that the time delay between successive transmissions during each time slot is random;

transmitting said message during said randomly selected sub time slot;

wherein each transmitter messages asynchronously with respect to and independently of transmissions from all other transmitters;

wherein burst time slot timing for each message is determined independently by each transmitter asynchronous to other transmitters and without the use of any system time slot synchronization; and

wherein N and M are positive integers and M is equal to or greater than 2.

9. The method according to claim 8, wherein N is equal to 25.

10. The method according to claim 8, wherein M is equal to 2.

11. The method according to claim 8, further comprising the step of appending a gap time to each time slot.

12. The method according to claim 8, wherein M is equal to 3.

13. The method according to claim 8, wherein said frequencies are assigned in accordance with a pseudo random sequence.

14. The method according to claim 8, wherein said transmitters transmit asynchronously with respect to each other.

15. A communications transmitter, comprising;

means for transmitting a message a predetermined number of times N, each message transmission occurring during a time slot within a burst of N time slots;

means for dividing each time slot into a plurality of M sub time slot;

means for randomly selecting one of said M sub time slots in which to transmit said message such that the time delay between successive transmissions during each time slot is random;

means for transmitting said message during said randomly selected sub time slot;

means for transmitting messages asynchronously with respect to and independently of transmissions from all other transmitters;

means for determining burst time slot timing for each message independently by each transmitter asynchronous to other transmitters and without the use of any system time slot synchronization; and

wherein N and M are positive integers and M is equal to or greater than 2.

16. The transmitter according to claim 15, wherein said communications transmitter comprises a frequency hopping spread spectrum transmitter.