System operable to transmit and receive messages

• US 7,619,980 B2
• Filed: 07/14/2004
• Issued: 11/17/2009
• Est. Priority Date: 07/14/2003
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: Infineon Technologies AG
• Inventors: Lewis, Michael
• Primary Examiner(s): Rao; Seema S
• Assistant Examiner(s): WONG, XAVIER S
• Application Number:
  US10/890,709
• Publication Number:
  US 20050026639A1
• Time in Patent Office: 1,952 Days
• Field of Search: 370445-448, 370/241, 370/242, 370/243, 370/244, 370/245, 370/246, 370/250, 370/251
• US Class Current: 370/242
• CPC Class Codes: H04W 74/085 collision avoidance
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A system, minimising transmission delays and avoiding loss of synchronisation, using a contention based multiple access protocol comprises n transceivers each comprising a detector for detecting the condition of the medium and connected to a controller for switching the transceiver from receiving to transmitting or vice versa. Each transceiver also comprises a to the controller connected backoff counter operable to decrement its count at the end of each time slot when performing a backoff procedure. A transceiver which wishes to transmit and is performing the backoff procedure for which the detector detects that the medium is busy, the controller freezes the backoff counter and if this medium busy condition is subsequently determined to be a false alarm the controller resumes the backoff counter at the beginning of the next time slot after rejection of the false alarm, using the time slot timings in force prior to the false alarm event.

Claims

1. A system configured to transmit and receive messages via a wireless medium and/or a wire medium, minimizing transmission delays and avoiding loss of synchronization, using a contention based multiple access protocol, which system comprises n transceiver means, wherein n is an integer and n≧

2, wherein each transceiver means comprises a detection means operable to detect the condition of said medium, wherein each transceiver means also comprises a control means connected to said detection means operable to switch said transceiver means from receiving to transmitting or vice versa, wherein each transceiver means also comprises a back-off counter connected to said control means operable to decrement its count at the end of each time slot in a sequence of time slots when performing a back-off procedure, wherein a transceiver means which wishes to transmit and is performing said back-off procedure for which said detection means detects that said medium is busy, said control means freezes said back-off counter and if this medium busy condition is subsequently determined to be a false alarm said control means resumes said back-off counter at the beginning of the immediate next time slot in the sequence of time slots after the time slot in which rejection of said false alarm occurs, using the time slot timings in force prior to said false alarm event.

2. The system according to claim 1, wherein a time slot is define as a detection time followed by a switch time for said transceiver means.

3. The system according to claim 1, wherein said control means starts said back-off counter after the duration of a fixed inter-frame spacing following the end of the last transmission on said medium.

4. The system according to claim 2, wherein said detection time of a time slot is the Clear Channel Assessment period during which period each transceiver means is receiving.

5. The system according to claim 1, wherein said condition of said medium detected by said detection means is either busy, free or a false alarm.

6. The system according to claim 5, wherein if said detection means detects a busy condition, of said medium said control means freezes said back-off counter and resumes said back-off counter at the beginning of the next time slot following said busy condition of said medium.

7. The system according to claim 1, wherein said control means distinguish between a false alarm condition and a busy condition by the use of a duration of the by said detection means detected event.

8. The system according to claim 1, wherein, if a modulation format IEEE 802.11a/802.11g is used, said control means distinguish a false alarm condition when said detection means detects an absence of a long preamble symbol.

9. The system according to claim 4, wherein, if the DSSS modulation format defined in IEEE 802.11/802.11b and the short time defined in IEEE 802.1g is used, said control means distinguish between a false alarm condition and a busy condition by making use of a longer CCA period for detection of DSSS modulated signals.

10. A transceiver means configured to transmit and receive messages via a wireless medium and/or a wired medium, minimizing transmission delays and avoiding loss of synchronization, using a contention based multiple access protocol, which transceiver means comprises a detection means operable to detect the condition of said medium, a control means connected to said detection means operable to switch said transceiver means from receiving to transmitting or vice versa, a back-off counter connected to said control means operable to decrement its count at the end of each time slot in a sequence of time slots when performing a back-off procedure, wherein a transceiver means which wishes to transmit and is performing said back-off procedure, for which said detection means detects that said medium is busy, said control means freezes said back-off counter, and if this medium busy condition is subsequently determined to be a false alarm, said control means resumes said back-off counter at the beginning of the immediate next time slot in the sequence of time slots after the time slot in which rejection of said false alarm occurs, using the time slot timings in force prior to said false alarm event.

11. The transceiver means according to claim 10, wherein a time slot is defined as a detection time followed by a switch time.

12. The transceiver means according to claim 10, wherein said control means starts said back-off counter after the duration of a fixed inter-frame spacing following the end of the last transmission on said medium.

13. The transceiver means according to claim 11, wherein said detection time of a time slot is the Clear Channel Assessment period during which period said transceiver means is receiving.

14. The transceiver means according to claim 10, wherein said condition of said medium detected by said detection means is either busy, free or a false alarm.

15. The transceiver means according to claim 14, wherein, if said detection means detects a busy condition, of said medium, said control means freezes said back-off counter and resumes said back-off counter at the beginning of the next time slot following said busy condition of said medium.

16. The transceiver means according to claim 10, wherein said control means distinguish between a false alarm condition and a busy condition by the use of the by said detection means detected event.

17. The transceiver means according to claim 10, wherein, if a modulation format IEEE 802.11a/802.11g is used, said control means distinguish a false alarm condition when said detection means detects an absence of a long preamble symbol.

18. The transceiver means according to claim 10, wherein, if the DSSS modulation format defined in IEEE 802.11/802.11b and the short slot time defined in IEEE 802.11g is used, said control means distinguish between a false alarm condition and a busy condition by making use of a longer CCA period for detection of DSSS modulated signals.

19. A method for transmitting and receiving messages via a wireless medium and/or a wired medium, minimizing transmission delays and avoiding loss of synchronization, using a contention based multiple access protocol, which method makes use of a number, n, of transceiver means, wherein n is an integer and n≧

2, the method comprising;

detecting, in at least one transceiver means, the condition of said medium;

if a transceiver means wishes to transmit when said medium is detected busy, selecting, in the transceiver means, a random time slot in a sequence of time slots and setting its back-off counter to indicate the chosen time slot, which back-off counter is operable to decrement its count at the end of each time slot in the sequence of time slots;

if medium busy is detected, freezing, in the transceiver means, said back-off counter;

detecting, in the transceiver means, if said medium busy was caused by a false alarm; and

resuming, in the transceiver means, said back-off counter at the beginning of the immediate next time slot in the sequence of time slots after the time slot in which rejection of said false alarm occurs.

20. The method for transmitting and receiving messages according to claim 19, wherein a time slot is defined as a detection time followed by a switch time for said transceiver means.

21. The method for transmitting and receiving messages according to claim 19, wherein said method further comprises the step of:

starting said back-off counter after the duration of a fixed inter-frame spacing following the end of the last transmission on said medium.

22. The method for transmitting and receiving messages according to claim 20, wherein said detection time of a time slot is the Clear Channel Assessment period during which period each transceiver means is receiving.

23. The method for transmitting and receiving messages according to claim 19, wherein said detection step is performed by,

detecting a busy condition;

or

or detecting a free condition;

or

or detecting a false alarm condition.

24. The method for transmitting and receiving messages according to claim 23, wherein said method further comprises the steps of:

if a busy condition, is detected, freezing said back-off counter; and

resuming said back-off counter at the beginning of the next time slot following said busy condition of said medium.

25. The method for transmitting and receiving messages according to claim 19, wherein said method further comprises the step of:

distinguishing between a false alarm condition and a busy condition by the use of the duration of the detected event.

26. The method for transmitting and receiving messages according to claim 19, wherein, if a modulation format IEEE 802.11a/802.11g is used, said method further comprises the step of:

distinguishing a false alarm condition by detecting an absence of a long preamble symbol.

27. The method for transmitting and receiving messages according to claim 22, wherein, the DSSS modulation format defined in IEEE 802.1/802.11b and the short slot time defined in IEEE 802.11g is used, said method further comprises the step of:

distinguishing between a false alarm condition and a busy condition by making use of a longer CCA period for detection of DSSS modulated signals.

28. At least one computer program product directly loadable into the internal memory of at least one digital computer, comprising software code portions for performing the steps of claim 19, when said at least one product is/are run on said at least one computer.