System operable to transmit and receive messages

• US 20050026639A1
• Filed: 07/14/2004
• Published: 02/03/2005
• Est. Priority Date: 07/14/2003
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Infineon Technologies AG
• Inventors: Lewis, Michael
• Granted Patent: US 7,619,980 B2
• Time in Patent Office: Days
• US Class Current: 455/509
• 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 operable to transmit and receive messages via a wireless medium and/or a wired medium, minimising transmission delays and avoiding loss of synchronisation, 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 to said detection means connected control means operable inter alia to switch said transceiver means from receiving to transmitting or vice versa, wherein each transceiver means also comprises a to said control means connected backoff counter operable to decrement its count at the end of each time slot when performing a backoff procedure, wherein a transceiver means which wishes to transmit and is performing said backoff procedure for which said detection means detects that said medium is busy, said control means freezes said backoff counter and if this medium busy condition is subsequently determined to be a false alarm said control means resumes said backoff counter at the beginning of the next time slot after rejection of said false alarm, 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 defined 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 backoff 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 so called 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, i.e. a transmission, of said medium, said control means freezes said backoff counter and resumes said backoff counter at the beginning of the next time slot following said busy condition of said medium, i.e. transmission.

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 the 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 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.

10. A transceiver means operable to transmit and receive messages via a wireless medium and/or a wired medium, minimising transmission delays and avoiding loss of synchronisation, using a contention based multiple access protocol, which transceiver means comprises a detection means operable to detect the condition of said medium, a to said detection means connected control means operable inter alia to switch said transceiver means from receiving to transmitting or vice verse, a to said control means connected backoff counter operable to decrement its count at the end of each time slot when performing a backoff procedure, wherein a transceiver means which wishes to transmit and is performing said backoff procedure, for which said detection means detects that said medium is busy, said control means freezes said backoff counter, and if this medium busy condition is subsequently determined to be a false alarm, said control means resumes said backoff counter at the beginning of the next time slot after rejection of said false alarm, 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 backoff 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 so called 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, i.e. a transmission, of said medium, said control means freezes said backoff counter and resumes said backoff counter at the beginning of the next time slot following said busy condition of said medium, i.e. transmission.

16. The transceiver means according to claim 10, wherein said control means distinguish between a false alarm condition 18 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, minimising transmission delays and avoiding loss of synchronisation, 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 the steps of;

detecting the condition of said medium;

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

if medium busy is detected, freezing said backoff counter;

detecting if said medium busy was caused by a false alarm, and

resuming said backoff counter at the beginning of the next time slot after rejection of said false alarm.

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 backoff 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 so called 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, i.e. a transmission, is detected, freezing said backoff counter; and

resuming said backoff counter at the beginning of the next time slot following said busy condition of said medium, i.e. transmission.

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 802.11/802.11b 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.