CN105284079B

CN105284079B - A kind of system and method for CSMA-CA half-window scheme

Info

Publication number: CN105284079B
Application number: CN201480033251.8A
Authority: CN
Inventors: 孙晟; 徐正勳
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2013-06-19
Filing date: 2014-06-19
Publication date: 2019-07-09
Anticipated expiration: 2034-06-19
Also published as: CN105284079A

Abstract

The present embodiment is for realizing the CSMA-CA half-window scheme in 802.11 networks or other suitable wireless networks that can be benefited from it.The half-window scheme improves the calculation method of back off time by the addition probabilistic forecasting factor.The back off time is a part of the delay time of website (STA) access wireless transmission medium.The probabilistic forecasting factor is used to adjust the competition window (CW) of back off time described in the medium access probability calculation based on the STA.The CW is divided at least two half-window by the STA, then selects one of half-window to carry out probabilistic forecasting according to the information gain of window.Selected window is used to select random number for the back off time.After the calculation method of back off time obtains improvement, reduce the competition that the medium is accessed between STA.

Description

System and method for CSMA-CA half-window scheme

The present application claims priority of prior applications of united states provisional application entitled "a System and Method for CSMA-CA Half Window Scheme" (application number 61/836,942 filed by Sheng Sun et al on 19.6.2013, and priority of prior applications of united states non-provisional application entitled "a System and Method for a CSMA-CA Half Window Scheme" (application number 14/309,521 filed on 19.6.2014., and content of which is incorporated herein by reference).

Technical Field

The present invention relates to wireless communications, and in some particular embodiments, to a system and method of a carrier sense multiple access/collision avoidance (CSMA-CA) half-window scheme.

Background

In the current CSMA-CA scheme for IEEE 802.11(WiFi) communication, a Station (STA) accesses a medium for transmitting data after delaying a certain back-off time, e.g., several microseconds (μ sec). The back-off time is calculated by selecting a random number from a predetermined contention window size. Markov chain analysis of throughput using the back-off time calculation formula shows that under normal network conditions (STA or transmission density meets requirements), peak throughput can be kept around 70% of the total throughput. Increasing or decreasing the size of the contention window in accordance with detecting whether the STA collides with other STA transmissions and based on previous success or failure. After the scheme for determining the back-off time is improved, collisions between STAs are reduced, and the overall throughput is increased, for example, for the case where STAs or transmissions are more concentrated.

Disclosure of Invention

According to an embodiment, a method for carrier sense multiple access with collision avoidance (CSMA-CA) by a station in a wireless communication network comprises: information related to a previous attempt to delay access to a medium for transmitting data is collected. The delay comprises a back-off time determined in accordance with a contention window. The method further comprises the following steps: determining a probability value of successful access to the media for each of a plurality of window regions of the contention window according to the information; selecting the window region from the plurality of window regions based on the success probability value determined for the selected window region.

For example, the selecting step includes selecting the window region having the highest probability value of success.

For example, it also includes:

performing a Clear Channel Assessment (CCA) procedure to access the medium, wherein the CCA procedure comprises: waiting for an interframe space (IFS) time and the back-off time before transmitting the data on the medium;

incrementing a value of a counter for which a CCA step has been completed, each time the CCA procedure is performed;

a respective sample of the information is collected.

For example, it also includes:

repeating the CCA process, increasing the value of the counter, and collecting respective samples of the information until the value of the counter reaches a predefined maximum value;

initiating the determining of success probability values for each of the plurality of window regions when the value of the counter reaches the predefined maximum value.

According to another embodiment, a method for CSMA-CA by a station in a wireless communication network comprises: a data set relating to a previous attempt to delay access to the data transmission medium is collected based on a value of a previous back-off time, wherein the value of the back-off time is determined based on a contention window. The method further comprises the following steps: dividing the contention window into a first half-window and a second half-window; a first probability value of successful access to the medium is calculated for the first half-window from the set of data. Further calculating a second probability value of successful access to the medium for the second half-window according to the data set. Then, according to one of a first success probability value of the selected first half-window and a second success probability value of the selected second half-window, one of the first half-window and the second half-window is selected to be used for generating a random number for determining the back-off time.

For example, the selecting step comprises selecting one of the first and second half-windows having a greater probability of success.

For example, the data set is acquired at a timing phase prior to a half-window scheme phase, wherein the first probability value and the second probability value are calculated at the half-window scheme phase.

For example, during the timing phase, further comprising:

initializing a counter;

performing multiple instances of a Clear Channel Assessment (CCA) procedure to access the data transmission medium, wherein the CCA procedure comprises: waiting for an interframe space (IFS) time and a previously determined back-off time before transmitting data on the medium;

incrementing a value of the counter upon completion of each of the instances of the CCA procedure;

adding a pair of values to the data set each time one of the instances of the CCA procedure is completed;

starting the half-window scheme phase when the counter reaches a predefined maximum value.

According to still another embodiment, a communication apparatus supporting CSMA-CA includes: at least one processor, and a non-transitory computer readable storage medium storing a program for execution by the at least one processor. The program includes instructions for: information is collected relating to a previous attempt to delay access to a medium for transmitting data, wherein the delay comprises a back-off time determined in accordance with a contention window. The program further includes instructions for: determining a probability value of successful access to the media for each of a plurality of window regions of the contention window according to the information; selecting the window region from the plurality of window regions based on the success probability value determined for the selected window region. The device is further configured to determine a new back-off time based on the selected window region.

The foregoing has outlined rather broadly the features of an embodiment of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of embodiments of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

Drawings

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

figure 1 shows a Clear Channel Assessment (CCA) scheme;

FIG. 2 illustrates a carrier sense multiple access with collision avoidance (CSMA-CA) scheme;

FIG. 3 illustrates a half-window scheme decision tree provided by an embodiment of the present invention;

FIG. 4 illustrates a half-window scheme provided by an embodiment of the present invention;

FIG. 5 is a diagram of a processing system that can be used to implement various embodiments.

Corresponding reference numerals and symbols in the various drawings generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.

Detailed Description

The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the invention.

Fig. 1 shows a current IEEE 802.11 Clear Channel Assessment (CCA) scheme, for example, for STAs to access a medium. A STA herein may be any user wireless device or Access Point (AP). For example, STAs include smartphones, tablets, laptops, and desktops. An AP is any device that allows other STAs to access a wireless network, such as WiFi. The STA (or AP) waits an inter-frame space (IFS) time before accessing the medium to transmit data. After waiting the IFS time, the STA further delays its data transmission by a back-off time (e.g., in μ sec) to ensure that the delay time is sufficient to avoid collisions with other transmissions (from other STAs). The STA may also wait for an IFS time to re-receive an acknowledgement (Ack) signal after data transmission.

In the current IEEE 802.11CSMA-CA scheme, the back-off time required to access the medium is calculated by (STA) randomly selecting a number (integer) between 0 and a predetermined Contention Window (CW) size, and multiplying the number by a predefined (minimum) time slot (e.g., in μ sec). The size of the CW is limited between a predefined minimum CW (cwmin) and a predefined maximum CW (cwmax). Further, according to the CSMA-CA scheme, the size of the CW is increased or decreased based on collision detection when accessing the medium. For example, in case of a previous access failure to the medium, the size of the CW is doubled; or, in case no collision occurs, resetting the size of the CW to a minimum value CWmin. Fig. 2 shows the CSMA-CA algorithm.

The 802.11 Station (STA) calculates the back-off time using the following standard equation: back-ofttime ═ Random (0, CW) x Slot time, where CW is limited between CWmin and CWmax; random () is a Random function generator; the Slot time is a predefined Slot. The algorithm may be expressed as follows:

selecting a random wait time between [ CWMin, CWMax ];

CCA:

if(Idle)

Back-offTime＝Back-offTime-1；

if(Back-offTime＝0),send；

if(collision)

CW＝2x CW；

else Back-offTime＝0and send；

else Back-offTime＝Back-offTime-1；

else

CW＝CW.

embodiments provided herein are for implementing a CSMA-CA half-window scheme in an 802.11 network or other suitable wireless network that can benefit therefrom. The half-window scheme is used to improve the calculation method of the back-off time by adding a probability predictor. Adjusting the CW using a probability predictor based on a medium access probability of the STA. In the half-window scheme, the STA builds a decision tree based on the information gain (G) of the probability prediction. The decision tree divides the CW into 2 half-windows, the STA selects one half-window from the half-windows, and selects a random number therein as the back-off time. The specific description is as follows: the 2 half-windows are a left half-window (CWmin ≦ X ≦ CWhalf) and a right half-window (CWhalf ≦ X ≦ CWmax), where CWhalf ≦ CWmax-CWmin)/2, and X is the number selected from the 2 half-windows. The half-window scheme greatly improves overall throughput. In other embodiments, the CW is divided into more than 2 half-windows to select a random number as the back-off time.

The half-window scheme is based on adjusting or tuning the Random function generator Random () by selecting a suitable CW size with a greater probability of success (with less likelihood of collision) when selecting the back-off time. Adjusting the CW based on a probability function (p). The function p is calculated by the differential information gain (G) of the entropy (E) of each half-window. First, passing history information S { (r1, st 1); (r2, st 2); (r3, st3) …; (rn, stn) } training the STA, where r is a real number (between 0 and 1) randomly generated based on Random (), and st represents a boolean state (success or failure) of accessing the medium. After the training phase, the STA calculates the gain for each half-window and selects the appropriate half-window based on the gain. The STA may repeat the process, e.g., each time the medium is accessed.

The CSMA-CA half-window scheme utilizes the history information of collision-free access medium success/failure to predict the next access CW by tuning the random function generator to 2 half-windows. The training phase processes the historical information to find a probability of success for each half-window, and the next half-window phase adjusts the CW to select a random number as the back-off time based on the probability. The scheme utilizes entropy calculations and information gain equations and generates the decision tree for the 2 half-windows accordingly. The decision tree is the state of operation in the STA, which calculates the information gain and entropy based on the historical information and then determines which half-window to select.

In a training stage, the STA collects a history window information set S { (r, st) } of the STA, wherein r is a randomly generated real number; st represents a Boolean status of success (noted +) or failure (noted-). For example, S can be { (199, -); (83, +); (156, +); (136, -); (251, +); (177, +); (103, +); (206, -); (58, -); (130, +); (226, -); (62, +); (152, +); (242,+)}. There were 14 samples in the S, of which 9 prior attempts to access the medium were successful (+), 5 failed (-), noted (9+,5-), and therefore, calculating the entropy yields E (9+,5-) -9/14log₂(9/14)-5/14log₂(5/14) ═ 0.94. Except that the exponential function (log)₂) The entropy may also be calculated using any other suitable function, such as by any suitable hardware (chip) or software implementation. Suitable implementations may be determined based on cost, power requirements, computation speed, accuracy, or other system design conditions.

Then, in a half-window phase, the STA builds a decision tree based on the obtained information gain calculated based on the entropy obtained above. The information gain may be obtained by the following formula:in the above example where S is (9+,5-), the left half-window S (31. ltoreq. X.ltoreq.112) is [6+, 2-]The entropy is 0.811; right half-window S (112)<X≤255)＝[3+，3-]The entropy is obtained as E1, CWmin 31, CWhalf 112 and CWmax 225. Therefore, the gain of S (31 ≦ X ≦ 112) is 0.94- (8/14) 0.811; the gain of S (112 < X.ltoreq.255) is 0.94- (6/14)1 is 0.4286. As shown in fig. 3, the computation of these 2 sets forms 2 branches of the decision tree. Since the gain of S (31. ltoreq. X. ltoreq.112)>S (112 < X ≦ 255), so the STA selects Random (31 ≦ X ≦ 112) to obtain the Random number for the back-off time.

Fig. 4 shows an embodiment of a half-window algorithm comprising the timing phase and half-window phase described above. In the figure, the left half window (or half window) is noted as (< 0.5) and the right half window is noted as (> 0.5). A counter is used to determine the time at which the decision tree is generated. The counter time is set to ensure that enough historical samples of successful/failed results of accessing the medium are collected, so that the probability prediction has sufficient accuracy, thereby ensuring reasonable selection of half-windows.

An improved CSMA-CA half-window scheme can be obtained by modifying said 802.11CSMA-CA procedure to include the following formula for calculating said back-off time:

back-oftimereg ═ Rand (0, CW) × Slot time was used for typical back-off time calculations (not modified); for the case of selecting the left half-window (half-window), back-off timehwl ═ Random (CWmin, CWhalf) × Slot time is used; for the case where the right half window (half window) is selected, back-off timehwh is used.

In the above embodiment, the contention window is divided into 2 half-windows to build a decision tree with 2 branches. In other embodiments, the contention window may be divided into any suitable number of smaller windows to build a decision tree with more than 2 branches. For example, the contention window may be divided into 4 windows: (CWmin ≦ X ≦ CW (1/4), CW (1/4) < X ≦ CW (1/2), CW (1/2) < X ≦ CW (3/4), CW (3/4) < X ≦ CWmax), where CW (1/4) ═ CWmax-CWmin)/4, CW (1/2) ═ CWmax-CWmin)/2, and CW (3/4) ≦ CWmax-CWmin) X3/4. Other numbers of windows are also possible, such as 3, 5, 6, 7, 8 or other numbers. In still other embodiments, the windows may be divided into unequal time slots, where some windows may be larger or smaller than others. In any of these embodiments, the entropy and information gain are calculated according to the number of windows and their sizes.

Fig. 5 is a block diagram of a processing system 500 that can be used to implement various embodiments. The processing system 500 may be part of a STA or other network device. A particular device may utilize all of the components shown or only a subset of the components, and the degree of integration between devices may vary. Further, a device may include multiple instances of a component, such as multiple processing units, processors, memories, transmitters, receivers, etc. Processing system 500 may include a processing unit 501 equipped with one or more input/output devices, such as speakers, microphones, mice, touch screens, keys, keyboards, printers, displays, etc. The processing unit 501 may include a Central Processing Unit (CPU)510, a memory 520, a mass storage device 530, a video adapter 540, and an I/O interface 560 connected to the bus. The bus may be one or more of any type of several bus architectures including a memory bus or memory controller, a peripheral bus, and the like.

The CPU510 may comprise any type of electronic data processor. Memory 520 may include any type of system memory such as Static Random Access Memory (SRAM), Dynamic Random Access Memory (DRAM), synchronous DRAM (sdram), Read Only Memory (ROM), combinations thereof, and the like. In an embodiment, memory 520 may include ROM for use at boot-up and DRAM for program and data storage for use during program execution. In an embodiment, memory 520 is non-transitory. The mass storage device 530 may include any type of storage device for storing data, programs, and other information and for enabling the data, programs, and other information to be accessed via the bus. The mass storage device 530 may include one or more of the following: solid state drives, hard disk drives, magnetic disk drives, optical disk drives, and the like.

The video adapter 540 and the I/O interface 560 provide interfaces to couple external input and output devices to the processing unit. As shown, examples of input-output devices include any combination of a display 590 coupled to the video adapter 540 and a mouse/keyboard/printer 560 coupled to the I/O interface 570. Other devices may be coupled to the processing unit 501, and additional or fewer interface cards may be utilized. For example, a serial interface card (not shown) may be used to provide a serial interface for a printer.

The processing unit 501 also includes one or more network interfaces 550, and the network interfaces 550 may include wired links such as ethernet cables, and/or wireless links to access nodes or one or more networks 580. The network interface 550 allows the processing unit 501 to communicate with remote units over a network 580. For example, the network interface 550 may provide wireless communication via one or more transmitters/transmit antennas and one or more receivers/receive antennas. In one embodiment, the processing unit 501 is coupled to a local or wide area network for data processing and communication with remote devices, such as other processing units, the internet, remote storage facilities, or the like.

While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein. For example, various elements or components may be combined or combined in another system, or certain features may be omitted, or not implemented.

Furthermore, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may also be indirectly coupled or communicating through some interface, device, or intermediate component, whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.

Claims

1. A method for carrier sense multiple access with collision avoidance (CSMA-CA) by a station in a wireless communication network, the method comprising:

collecting information related to a previous attempt to delay access to a medium for transmitting data, wherein the delay comprises a back-off time determined according to a contention window;

determining a probability value of successful access to the medium for each of a plurality of window regions of the contention window according to the acquired information;

selecting window regions meeting conditions from the plurality of window regions according to the success probability value determined for each window region;

wherein the method further comprises: determining a new back-off time according to the selected window region with the higher success probability value, specifically comprising: generating, by a random function generator, a value of the new back-off time from the selected window region.

2. The method of claim 1, wherein the selecting step comprises selecting the window region having the highest probability value of success.

3. The method of claim 1, further comprising:

a respective sample of the information is collected.

4. The method of claim 3, further comprising:

5. The method of claim 1, wherein determining, from the information, a probability value for successful access to the media for each of a plurality of window regions of the contention window comprises:

determining an entropy for each of the window regions based on the information;

and determining information gain for each window region according to the entropy.

6. The method of claim 1, wherein the contention window is limited in size between a predefined minimum contention window and a predefined maximum contention window.

7. The method of claim 6, wherein the window region is two half-window regions comprising a left half-window and a right half-window, wherein the size of the left half-window is limited to between the predefined minimum contention window and half of the contention window size; the size of the right half-window is limited between half the contention window size and the predefined maximum contention window.

8. The method of claim 1, wherein the information is arranged in a set comprising a plurality of value pairs, wherein each of the value pairs comprises a Boolean status indicating success or failure of a corresponding previous attempt to access the medium without collision, and a random number generated between 0 and 1 for determining a back-off time of the corresponding previous attempt.

9. A method for carrier sense multiple access with collision avoidance (CSMA-CA) by a station in a wireless communication network, the method comprising:

collecting a data set relating to a previous attempt to delay access to a data transmission medium based on a value of a previous back-off time, wherein the value of the back-off time is determined based on a contention window;

dividing the contention window into a first half-window and a second half-window;

calculating a first probability value of successful access to the medium for the first half-window in accordance with the set of data;

calculating a second probability value of successful access to the medium for the second half-window according to the data set;

selecting one of the first half-window and the second half-window according to one of a first success probability value of the selected first half-window and a second success probability value of the selected second half-window;

and generating a random number for determining the back-off time from the selected one of the first half-window and the second half-window.

10. The method of claim 9, wherein the selecting step comprises selecting the one of the first half-window and the second half-window having the greater probability value of success.

11. The method of claim 9, wherein the data set is acquired at a timing phase prior to a half-window scheme phase, wherein the first probability value and the second probability value are calculated at the half-window scheme phase.

12. The method of claim 11, further comprising, during the timing phase:

initializing a counter;

13. The method of claim 11, wherein calculating the first probability value comprises calculating entropy and corresponding information gain for the first half-window from the set of data; calculating the second probability value comprises calculating entropy and corresponding information gain for the second half-window from the data set.

14. The method of claim 13, further comprising, during the half-window scheme stage:

computing entropy for the set of data, wherein the entropy and information gain of each of the first half-window and the second half-window is consistent with the entropy of the set of data;

establishing a decision tree, wherein a root node comprises the data set and the entropy of the data set, a left leaf node comprises the entropy and the information gain of the first half-window, and a right leaf node comprises the entropy and the information gain of the second half-window.

15. The method of claim 9, wherein the wireless communication network is an IEEE 802.11 network and the station is a WiFi device or an Access Point (AP) in the IEEE 802.11 network.

16. A communication device supporting carrier sense multiple access with collision avoidance (CSMA-CA), the communication device comprising:

at least one processor;

a non-transitory computer-readable storage medium storing a program for execution by the at least one processor, the program comprising instructions to:

determining a probability value of successful access to the media for each of a plurality of window regions of the contention window according to the information;

selecting the window region from the plurality of window regions in accordance with the success probability value determined for the selected window region;

determining a new back-off time according to the selected window area;

wherein the instructions to determine the new back-off time based on the selected window region comprise instructions to generate a value for the new back-off time from the selected window region via a random function generator.

17. The communications device of claim 16, wherein the instructions for selecting the window region include instructions for selecting a window region having a maximum probability value of success.

18. The communications device of claim 16, wherein the programming further comprises instructions for:

a respective sample of the information is collected.

19. The communications device of claim 18, wherein the programming further comprises instructions for:

initiating said determining a probability value for each of said window regions when the value of said counter reaches said predefined maximum value.

20. The communications device of claim 16, wherein the communications device is a WiFi station.

21. The communications device of claim 16, wherein the communications device is an Access Point (AP) in an IEEE 802.11 network.

22. A method for carrier sense multiple access with collision avoidance (CSMA-CA) by a station in a wireless communication network, the method comprising:

wherein, still include:

a respective sample of the information is collected.

23. The method of claim 22, further comprising:

24. The method of claim 22, wherein determining, from the information, a probability value for successful access to the media for each of the plurality of window regions of the contention window comprises:

determining an entropy for each of the window regions based on the information;

25. The method of claim 22, wherein the contention window is limited in size between a predefined minimum contention window and a predefined maximum contention window.

26. The method of claim 25, wherein the window region is two half-window regions comprising a left half-window and a right half-window, wherein the size of the left half-window is limited to between the predefined minimum contention window and half of the contention window size; the size of the right half-window is limited between half the contention window size and the predefined maximum contention window.

27. The method of claim 22, wherein the information is arranged in a set comprising a plurality of value pairs, wherein each value pair comprises a boolean state indicating success or failure of a corresponding previous attempt to access the medium without collision and a random number generated between 0 and 1 for determining a back-off time of the corresponding previous attempt.

28. A method for carrier sense multiple access with collision avoidance (CSMA-CA) by a station in a wireless communication network, the method comprising:

wherein,

determining, for each of a plurality of window regions of the contention window, a probability value of successful access to the medium based on the information, including:

determining an entropy for each of the window regions based on the information;

29. The method of claim 28, wherein the contention window is limited in size between a predefined minimum contention window and a predefined maximum contention window.

30. The method of claim 29, wherein the window region is two half-window regions comprising a left half-window and a right half-window, wherein the size of the left half-window is limited to between the predefined minimum contention window and half of the contention window size; the size of the right half-window is limited between half the contention window size and the predefined maximum contention window.

31. The method of claim 28, wherein the information is arranged in a set comprising a plurality of value pairs, wherein each value pair comprises a boolean state indicating success or failure of a corresponding previous attempt to access the medium without collision and a random number generated between 0 and 1 for determining a back-off time of the corresponding previous attempt.

32. A method for carrier sense multiple access with collision avoidance (CSMA-CA) by a station in a wireless communication network, the method comprising:

wherein,

the size of the contention window is limited between a predefined minimum contention window and a predefined maximum contention window;

the window area is two half-window areas including a left half-window and a right half-window, wherein the size of the left half-window is limited between the predefined minimum contention window and half of the contention window size; the size of the right half-window is limited between half the contention window size and the predefined maximum contention window.

33. The method of claim 32, wherein the information is arranged in a set comprising a plurality of value pairs, wherein each of the value pairs comprises a boolean state indicating success or failure of a corresponding previous attempt to access the medium without collision and a random number generated between 0 and 1 for determining a back-off time of the corresponding previous attempt.

34. A method for carrier sense multiple access with collision avoidance (CSMA-CA) by a station in a wireless communication network, the method comprising:

wherein,

the information is arranged in a set comprising a plurality of value pairs, wherein each of the value pairs comprises a Boolean status indicating success or failure of a corresponding previous attempt to access the medium without collision and a random number generated between 0 and 1 for determining a back-off time of the corresponding previous attempt.

35. A communication device supporting carrier sense multiple access with collision avoidance (CSMA-CA), the communication device comprising:

at least one processor;

determining a new back-off time according to the selected window area;

wherein the program further comprises instructions for:

a respective sample of the information is collected.

36. The communications device of claim 35, wherein the programming further comprises instructions for:

37. A communication device supporting carrier sense multiple access with collision avoidance (CSMA-CA), the communication device comprising:

at least one processor;

determining a new back-off time according to the selected window area;

wherein the program further comprises instructions for:

repeating the CCA process, increasing the value of a counter, and collecting respective samples of the information until the value of the counter reaches a predefined maximum value;