Devices using self-adapting medium access control protocol
In wireless communication networks with distributed medium access control, maximal network throughput is achieved as a compromise between medium contention duration and collision rate. Maximal throughput in self-adapting medium access protocol is achieved by stations maintaining backoff counter BC and freezing counter FC, which define the state in two-dimensional state space. Countdown process is comprised of decrementing BC in idle timeslots, and incrementing FC in busy timeslots. Countdown ends if the value of BC reaches zero, when the station starts to transmit data, or when FC is incremented to be greater than freezing limit FL. In both cases, the station has to randomly select new backoff counter, reset its freezing counter, and continue to count down with these new values of BC and FC. At the end of countdown, the station calculates contention measure CM=a*BC+b*FC, and based on set of CM thresholds CMi, activates one of available contention windows Wi that define the interval of available values for the random selection of new backoff counter [Wi min , Wi max ]. In loaded network, the station can increase the total amount of backoff time to be greater than the maximal upper limit of available contention windows by selecting new backoff counter multiple times, which is made possible by limiting countdown freezing. This manifests the self-adaptive nature of the described medium access control protocol. The self-adaptive nature is also manifested in selection of contention window based on contention measure of the previous countdown, which additionally regulates medium contention duration, achieving good network throughput in various network load scenarios.
1. A wireless computer using self-adapting medium access control protocol, characterized by:
set of contention windows (Wi), of which at least one starts from zero and at least one is shifted from zero;
detector of contention measure parameter (DCM) and contention window selector (CMi);
backoff counter (BC) and freezing counter (FC);
detectors of final values BC=0 and FC>freezing limit (FL);
selector of random backoff counter (RBC); and
further characterized by the detector of contention measure parameter (DCM) that calculates at the end of backoff counting the contention measure (CM) as the weighted sum CM=a*BC+b*FC, where a and b are weighting factors used to define the contribution of BC (weighting factor a) and FC (weighting factor b) values in calculation of weighted sum CM, and where the said weighted sum CM is used by contention window selector (CMi) for selecting one of available windows by comparing the calculated value CM with the predefined borders CMi, so that the contention window (Wi) is selected when CMi−1<=CM<CMi, regardless whether the previous backoff counting was ended by winning or losing the medium.
2. The wireless computer of claim 1 , further characterized by the backoff counter BC and the freezing counter FC that determine the state of the station in two-dimensional state space by decrementing of BC in idle timeslot and incrementing of FC in busy timeslot, and detectors of final values BC=0 and FC>FL detect the end of backoff counting by detecting the condition BC=0, when the station wins the medium access, or the condition FC>FL, when the station ends the backoff counting by losing the medium.
3. The wireless computer of claim 1 , further characterized by the freezing limit FL that can be constant or can be a function of backoff counter BC.
4. The wireless computer of claim 1 , further characterized by the selected contention window Wi that determines at the end of backoff counting the upper and lower limits Wi min and Wi max for selector of random backoff counter RBC, and the selected random value is used for initialization of backoff counter BC, while the freezing counter FC is reset to zero.
5. A communication network comprising two or more wireless computers of claim 1 using self-adapting medium access control protocol.