Adaptive Medium Access Control

• US 20120182867A1
• Filed: 09/12/2011
• Published: 07/19/2012
• Est. Priority Date: 09/10/2010
• Status: Active Grant

• Current Assignee: Johns Hopkins University
• Original Assignee: Johns Hopkins University
• Inventors: Farrag, Osama I., D'Amico, William P.
• Granted Patent: US 8,675,678 B2
• Time in Patent Office: Days
• US Class Current: 370/230
• CPC Class Codes: H04J 3/16 in which the time allocation to individual channels within a transmission cycle is variable, e.g. to accommodate varying complexity of signals, to vary number of channels transmitted H04J3/17, H04J3/24 take precedence
• CPC Class Codes: H04L 47/32 by discarding or delaying data units, e.g. packets or frames
• CPC Class Codes: H04W 28/0236 radio quality, e.g. interference, losses or delay
• CPC Class Codes: H04W 28/0284 detecting congestion or overload during communication monitoring arrangements H04L43/00
• CPC Class Codes: H04W 74/0816 with collision avoidance
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks

Abstract

Bandwidth allocation configuration and fully decentralized adaptive medium access control (AMAC) systems and methods with support for time critical applications, spectrum efficiency, scalability enhancements, and fair allocation of bandwidth among nodes sharing a common channel. The methods fully integrate TDMA and CSMA/CA channel access approaches and incorporate adaptive congestion and collisions avoidance scheme to reduce bandwidth wastage and diminish adverse cross layers interactions. AMAC improves support for multi-media traffic while allowing higher transmission incidents from large number of transmitting devices sharing a common channel, with fair distribution of the available bandwidth, to enable improved multi-level-security connectivity over a common multi-hop wireless network, provide end-to-end performance enhancement for constant bit rate traffic, variable bit rate traffic, and distribute bandwidth fairly amongst competing TCP traffic flows that traverse varying length paths in multi-hop ad-hoc wireless networks.

Claims

1. A method of adaptively avoiding collisions in an ad hoc wireless network, comprising:

synchronizing periodic epochs of time and a state of a schedule with other nodes of the network, wherein the schedule includes alternating contention periods and contention free periods within the epochs, and wherein each contention free period is allocated to one of the nodes;

initiating a transmission during a contention free period allocated to the node and completing the transmission during an immediately-subsequent contention period;

measuring busy times of contention periods and aggregating the measured busy times over durations of corresponding epochs;

maintaining an aggregate channel congestion factor, over the duration of the corresponding epochs, as a function of an elapsed time of the epoch and a corresponding aggregate of the measured busy times of contention periods within the epoch;

precluding broadcasting of a packet from the node during a contention period when the channel congestion factor is above a configurable congestion factor threshold;

maintaining a count of a number of times a unicast packet is re-transmitted from the node; and

precluding re-transmission of the unicast packet from the node during a contention period when the count reaches a first count threshold.

2. The method of claim 1, wherein the contention periods are at least equal to a sum of,

a maximum size packet permitted by a physical layer,

a deferral period;

a maximum random access back-off period,

a time to exchange request-to-send and clear-to-send control frames, and

a time to receive an acknowledgement control frame.

3. The method of claim 1, wherein the contention free periods includes a contention free period at least equal to a sum of,

a deferral period,

a time to exchange request-to-send and clear-to-send control frames, and

time to transmit at least a portion of a corresponding data packet.

4. The method of claim 1, wherein the contention free periods include a short-duration contention free period approximately equal to a sum of,

a deferral period, and

a time to exchange request-to-send and clear-to-send control frames.

5. The method of claim 4, further including;

reserving one of the short-duration contention free periods in each of multiple successive epochs to support a variable bit rate application of the node; and

reserving multiple ones of the short-duration contention free periods in each of multiple successive epochs to support a constant bit rate application of the node.

6. The method of claim 1, wherein the contention free periods include contention free periods of various durations.

7. The method of claim 1, further including:

precluding re-transmission of the unicast packet from the node during a contention free period allocated to the node when the count reaches a second count threshold.

8. The method of claim 1, wherein the precluding of the re-transmission of the unicast packet includes:

selectively operating the node in one of a static mode and a responsive mode,

applying a fixed value to the first count threshold when the node is in the static mode; and

selectively applying one of multiple values to the first count threshold when the node is in the responsive mode based a value of the channel congestion factor.

9. The method of claim 1, wherein the maintaining of the aggregate channel congestion factor includes, for each epoch, maintaining a ratio of,

TotalCSMACABusyDuration/TotalCSMACADuration, and wherein,

TotalCSMACADuration is the elapsed time of the epoch,

TotalCSMACABusyDuration=(TotalCSMACABusyDuration)+(CPi_BusyDuration),

CPi_BusyDuration is the measured busy time of a most recent contention period as of the elapsed time of the epoch, and

TotalCSMACABusyDuration is the aggregate busy time of preceding contention periods of the epoch.

10. A computer program product comprising a computer readable storage medium having computer program logic stored thereon, the computer program logic comprising instructions that, when executed by a processor, cause the processor to:

synchronize periodic epochs of time and a state of a schedule amongst the nodes, wherein the schedule includes alternating contention periods and contention free periods within the epochs, and wherein each contention free period is allocated to one of the nodes;

initiate a transmission during a contention free period allocated to the node, and complete the transmission during an immediately-subsequent contention period;

measure busy times of contention periods, and aggregate the measured busy times over durations of corresponding epochs;

maintain an aggregate channel congestion factor, over the duration of the corresponding epochs, as a function of an elapsed time of the epoch and a corresponding aggregate of the measured busy times of contention periods within the epoch;

preclude broadcasting of a packet from the node during a contention period when the channel congestion factor is above a configurable congestion factor threshold;

maintain a count of a number of times a unicast packet is re-transmitted from the node; and

preclude re-transmission of the unicast packet from the node during a contention period when the count reaches a first count threshold.

11. The computer program product of claim 10, wherein the instructions that cause the processor to synchronize include instructions to cause the processor to synchronize with respect to contention periods that are at least equal to a sum of,

a maximum size packet permitted by a physical layer,

a deferral period;

a maximum random access back-off period,

a time to exchange request-to-send and clear-to-send control frames, and

a time to receive an acknowledgement control frame.

12. The computer program product of claim 10, wherein the instructions that cause the processor to synchronize include instructions to cause the processor to synchronize with respect to contention free periods that are at least equal to a sum of,

a deferral period,

a time to exchange request-to-send and clear-to-send control frames, and

time to transmit at least a portion of a corresponding data packet.

13. The computer program product of claim 10, wherein the instructions that cause the processor to synchronize include instructions to cause the processor to synchronize with respect to a short-duration contention free period that is approximately equal to a sum of,

a deferral period, and

a time to exchange request-to-send and clear-to-send control frames.

14. The computer program product of claim 13, wherein the instructions that cause the processor to synchronize, further include instructions to cause the processor to:

reserve one of the short-duration contention free periods in each of multiple successive epochs to support a variable bit rate application of the node; and

reserve multiple ones of the short-duration contention free periods in each of multiple successive epochs to support a constant bit rate application of the node.

15. The computer program product of claim 10, further including instructions to cause the processor to:

preclude re-transmission of the unicast packet from the node during a contention free period allocated to the node when the count reaches a second count threshold.

16. The computer program product of claim 10, wherein the instructions that cause the processor to preclude re-transmission of the unicast packet include instructions to cause the processor to:

selectively operate the node in one of a static mode and a responsive mode,

apply a fixed value to the first count threshold when the node is in the static mode; and

selectively apply one of multiple values to the first count threshold when the node is in the responsive mode based a value of the channel congestion factor.

17. An adaptive medium access control (AMAC) system to adaptively access a shared wireless channel of an ad hoc wireless network on behalf of a node of the network, comprising:

a synchronizer to synchronize periodic epochs of time and a state of a schedule amongst the nodes, wherein the schedule includes alternating contention periods and contention free periods within the epochs, and wherein each contention free period is allocated to one of the nodes;

a transmit control system to initiate a transmission during a contention free period allocated to the node, and complete the transmission during an immediately-subsequent contention period;

a measurement system to measure busy times of the contention periods, and aggregate the measured busy times over durations of corresponding epochs;

a congestion monitor to measure busy times of the contention periods, aggregate the measured busy times over durations of corresponding epochs, and maintain an aggregate channel congestion factor over the duration of the corresponding epochs as a function of an elapsed time of the epoch and a corresponding aggregate of the measured busy times of contention periods within the epoch;

a broadcast control system to preclude broadcasting of a packet from the node during a contention period when the channel congestion factor is above a configurable congestion factor threshold;

a counter to maintain a count of a number of times a unicast packet is re-transmitted from the node; and

a unicast control system to preclude re-transmission of the unicast packet from the node during a contention period when the count reaches a first count threshold.

18. The system of claim 17, wherein the synchronizer is implemented to synchronize with respect to contention periods that are at least equal to a sum of,

a maximum size packet permitted by a physical layer,

a deferral period;

a maximum random access back-off period,

a time to exchange request-to-send and clear-to-send control frames, and

a time to receive an acknowledgement control frame.

19. The system of claim 17, wherein the synchronizer is implemented to synchronize with respect to contention free periods that are at least equal to a sum of,

a deferral period,

a time to exchange request-to-send and clear-to-send control frames, and

time to transmit at least a portion of a corresponding data packet.

20. The system of claim 17, wherein the synchronizer is implemented to synchronize with respect to a short-duration contention free period that is approximately equal to a sum of,

a deferral period, and

a time to exchange request-to-send and clear-to-send control frames.

21. The system of claim 20, wherein the synchronizer is further implemented to,

reserve one of the short-duration contention free periods in each of multiple successive epochs to support a variable bit rate application of the node;

and

reserve multiple ones of the short-duration contention free periods in each of multiple successive epochs to support a constant bit rate application of the node.

22. The system of claim 17, wherein the unicast control system is implemented to preclude re-transmission of the unicast packet from the node during a contention free period allocated to the node when the count reaches a second count threshold.

23. The system of claim 17, wherein the unicast control system is implemented to,

selectively operate in one of a static mode and a responsive mode,

apply a fixed value to the first count threshold when in the static mode;

and

selectively apply one of multiple values to the first count threshold when in the responsive mode based a value of the channel congestion factor.