Enhanced carrier sense multiple access (CSMA) protocols
Systems and methods for enhanced carrier sense multiple access (CSMA) protocols are described. In various implementations, these systems and methods may be applicable to Power Line Communications (PLC). For example, a method may include attempting to access a communications channel to transmit a frame after a backoff time proportional to a randomly generated number within a contention window (CW), the CW having an initial value carried over from a previous transmission of a different frame. Additionally or alternatively, some of techniques described herein may facilitate the spreading of the time over which devices attempt to transmit packets, thereby reducing the probability of collisions using, for example, Additive Decrease Multiplicative Increase (ADMI) mechanisms.
1. A method, comprising:
performing, by the communications device,
attempting to access a communications channel to transmit a frame after a backoff time proportional to a randomly generated number (K) within a contention window (CW), the CW having an initial value carried over from a previous transmission of a different frame;
in response to: (i) reaching a predetermined number of attempts without having obtained access to the communications channel, or (ii) having transmitted the frame over the communications channel upon the expiration of a backoff time without having received a corresponding acknowledgement,
increasing the CW by doubling the CW up to a value smaller than or equal to a maximum CW value, and
attempting to access the communications channel to transmit or re-transmit the frame after another backoff time proportional to another K within the increased CW; and
doubling the maximum CW value in response to an average CW over a predetermined number of previous attempts to access the communications channel being greater than a first threshold; or
halving the maximum CW value in response to the average CW over the predetermined number of previous attempts to access the communications channel being smaller than a second threshold different from the first threshold.
2. The method of claim 1 , wherein the first threshold is equal to the maximum CW value divided by 2, and wherein the second threshold is equal to the maximum CW value divided by 4.
3. A method, comprising:
performing, by the communications device,
attempting to access a communications channel to transmit a frame after a backoff time proportional to a randomly generated number (K) within a contention window (CW), the CW having an initial value carried over from a previous transmission of a different frame;
in response to: (i) reaching a predetermined number of attempts without having obtained access to the communications channel, or (ii) having transmitted the frame over the communications channel upon the expiration of a backoff time without having received a corresponding acknowledgement,
increasing the CW by doubling the CW up to a value smaller than or equal to a maximum CW value, and
attempting to access the communications channel to transmit or re-transmit the frame after another backoff time proportional to another K within the increased CW; and
doubling the maximum CW value in response to an average K over a predetermined number of previous attempts to access the communications channel being greater than a first threshold, or
halving the maximum CW value in response to the average K over the predetermined number of previous attempts to access the communications channel being smaller than a second threshold different from the first threshold.
4. A method, comprising:
performing, by the communications device,
attempting to access a communications channel to transmit a frame after a backoff time proportional to a randomly generated number (K) within a contention window (CW), the CW having an initial value carried over from a previous transmission of a different frame;
in response to: (i) reaching a predetermined number of attempts without having obtained access to the communications channel, or (ii) having transmitted the frame over the communications channel upon the expiration of a backoff time without having received a corresponding acknowledgement,
increasing the CW by, and
attempting to access the communications channel to transmit or re-transmit the frame after another backoff time proportional to another K within the increased CW; and
in response to the backoff time reaching a maximum backoff time value, resetting the CW to a minimum CW value.
5. A non-transitory electronic storage medium having program instructions stored thereon that, upon execution by a processor within a communications device, cause the communications device to:
attempt to access a communications channel to transmit a frame after a backoff time proportional to a randomly generated number within a contention window (CW), the CW having an initial value carried over from a previous transmission of a different frame;
perform at least one of (a) or (b):
(a) increase the CW to a value smaller than or equal to a maximum CW value and attempt to access the communications channel to transmit the frame after another backoff time proportional to another randomly generated number within the increased CW in response to (i) a determination that the communications channel is not available upon expiration of the backoff time or (ii) a transmission of the frame over the communications channel upon the expiration of the backoff time not being followed by a corresponding acknowledgement; or
(b) decrease the CW to a value greater than or equal to a minimum CW value and attempt to access the communications channel to transmit another frame after yet another backoff time proportional to yet another randomly generated number within the decreased CW in response to a transmission the frame over the communications channel upon the expiration of the backoff time being followed by the corresponding acknowledgement; and
double the maximum CW value in response to an average CW over a predetermined number of previous attempts to access the communications channel being greater than the maximum CW value divided by 2.
6. A non-transitory electronic storage medium having program instructions stored thereon that, upon execution by a processor within a communications device, cause the communications device to:
attempt to access a communications channel to transmit a frame after a backoff time proportional to a randomly generated number within a contention window (CW), the CW having an initial value carried over from a previous transmission of a different frame;
perform at least one of (a) or (b):
(a) increase the CW to a value smaller than or equal to a maximum CW value and attempt to access the communications channel to transmit the frame after another backoff time proportional to another randomly generated number within the increased CW in response to (i) a determination that the communications channel is not available upon expiration of the backoff time or (ii) a transmission of the frame over the communications channel upon the expiration of the backoff time not being followed by a corresponding acknowledgement; or
(b) decrease the CW to a value greater than or equal to a minimum CW value and attempt to access the communications channel to transmit another frame after yet another backoff time proportional to yet another randomly generated number within the decreased CW in response to a transmission the frame over the communications channel upon the expiration of the backoff time being followed by the corresponding acknowledgement; and
halve the maximum CW value in response to an average CW over the predetermined number of previous attempts to access the communications channel being smaller than the current maximum CW value divided by 4.
7. A non-transitory electronic storage medium having program instructions stored thereon that, upon execution by a processor within a communications device, cause the communications device to:
attempt to access a communications channel to transmit a frame after a backoff time proportional to a randomly generated number within a contention window (CW), the CW having an initial value carried over from a previous transmission of a different frame; and
perform at least one of (a) or (b):
(a) increase the CW and attempt to access the communications channel to transmit the frame after another backoff time proportional to another randomly generated number within the increased CW in response to (i) a determination that the communications channel is not available upon expiration of the backoff time or (ii) a transmission of the frame over the communications channel upon the expiration of the backoff time not being followed by a corresponding acknowledgement; or
(b) decrease the CW and attempt to access the communications channel to transmit another frame after yet another backoff time proportional to yet another randomly generated number within the decreased CW in response to a transmission the frame over the communications channel upon the expiration of the backoff time being followed by the corresponding acknowledgement
in response to the backoff time reaching a maximum backoff time value, reset the CW to a minimum CW value.