WO2012008927A1 - Probabilistically scheduled cognitive ieee 802.11 mac - Google Patents

Abstract

A method, system, and computer program product for media access control in a wireless network with a plurality of stations, comprising: receiving, at a station in the plurality of stations, a request for information from the access point and a transmit range; selecting a transmit position at random within the transmit range; identifying a start time to begin initiating a CSMA/CA protocol of transmitting the information based on the transmit position of the station and a bin interval time of other stations with earlier transmit positions than the transmit position of the station; and initiating the CSMA/CA process of transmitting the information after its identified start time.

Description

PROBABILISTICALLY SCHEDULED COGNITIVE IEEE 802.11 MAC

The present application claims the benefit of the Singapore patent application no.

201005048-2 filed on 13 July 2010, the entire contents of which are incorporated herein by reference for all purposes.

Technical Field

[0001] Various embodiments relate generally to communications systems, such as wireless communication systems, for example. In particular, the various embodiments relate to a probabilistically scheduled cognitive IEEE 802.1 1 media access control.

Background

[0002] A wireless local area network (WLAN) links two or more devices through a wireless medium. Access to the wireless medium is controlled by coordination functions. IEEE 802.11 is a set of standards for implementing WLAN networks. IEEE 802.11 distributed coordination function (DCF) uses a carrier sense multiple access with collision avoidance (CSMA/CA). It has two access methods. One of them is the basic access method with two- way handshaking, while the other is the request-to-send/clear- to-send (RTS/CTS) access method with four-way handshaking. In the basic access method, a data packet is sent from the source station to the destination station and the destination station replies with an acknowledgement (ACK) frame if the data packet is correctly received.

[0003] As part of the collision avoidance built into the 802.11 MAC, stations delay transmission until the medium becomes idle. Varying interframe spacings create different priority levels for different types of traffic.

[0004] After frame transmission has completed, stations may attempt to transmit congestion- based data. A period called the contention window or backoff window follows the frame transmission. This window is divided into slots. Within each 802.1 la/b/g/n standard, the slot time is fixed. For example, the slot time for IEEE 802.1 lb is 20 /xs, the slot time for 802.1 la is 9 /is, the slot times for IEEE 802.1 In is 20 μβ (long preamble) and 9 (short preamble) for 2.4 GHz operation, and the slot time for IEEE 802.1 In is 9 xs for 5 GHz operation.. When a station has a data packet for transmission, it picks a random number uniformly from zero to the minimum contention window size as the value for the backoff counter and waits for this value to count down to zero before attempting to access the medium; all values of the numbers are equally likely selections.

[0005] When the channel is busy subjected to the necessary interframe spaces like DCF interframe space (DIFS) and short interframe space (SIFS), the value in the backoff counter of the station is frozen. Only when the channel is idle excluding the necessary interframe spaces will the value of the backoff counter continue to count down by one for each time slot that the channel is idle. When several stations are attempting to transmit, the station that picks the lowest value for the random number wins. A new value for the backoff counter is selected from a larger range from zero to the next current contention window size each time a transmission fails. If the maximum contention window size is not reached, the next current contention window size is doubled with one added. In other words, if the initial contention window size is 15, the next contention window size is 31. If the current contention window size is 31, the next contention window size is 63 and so on; {15, 31, 63, 127, 255, 511, 1023, 1023}. The maximum contention window size is set at 1023 and the number of backoff stages retry limit is 7; backoff stages 0-7, where once it is at 1023 at backoff stage 6, it remains at 1023 at backoff stage 7 as the maximum contention window size has been reached. When the contention window reaches its maximum size, it remains there until it can be reset. It will be reset if the number of retry limit for the number of backoff stages is reached. Allowing long contention windows when several competing stations are attempting to gain access to the medium keeps the MAC algorithms stable even under maximum load. The contention window is reset to its minimum size when frames are transmitted

successfully, or the associated retry limit is reached, and the frame is discarded.

[0006] The more stations competing to transmit during a data transmission period, the more likely a collision will occur. Since the contention window has a set of values for the range of numbers, the likelihood of multiple stations selecting the same value increases as the number of stations increase. If stations select the same random number, then those stations will be on the same backoff progression for the initial backoff stage. Thus, these stations will collide in the initial backoff stage. However, they will not be in the same backoff progression in the next backoff stage if they each select a different value for their backoff counter with a large range of selection based on the next current contention window size.

Summary

[0007] A method, system, and computer program product for media access control in a wireless network with a plurality of stations, comprising: receiving, at a station in the plurality of stations, a request for information from the station and an indication a total number of stations of the plurality of stations; selecting a transmit position at random within the transmit range; identifying a start time to begin initiating a CSMA/CA protocol of transmitting the information based on the transmit position of the station and an bin interval time of other stations with earlier transmit positions than the transmit position of the station; and initiating the CSMA/CA process of transmitting the information after the identified start time.

Brief Description of the Drawings

[0008] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the invention are described with reference to the following drawings, in which:

[0009] FIGURE 1 is a communication system in accordance with an illustrative

embodiment;

[0010] FIGURE 2 is a beacon interval in accordance with an illustrative embodiment;

[0011] FIGURE 3 is an example of bin intervals in a probabilistically scheduled cognitive IEEE 802.11 MAC protocol;

[0012] FIGURES 4-5 are charts showing the delay versus number of smart meters using a cognitive CSMA/CA DCF IEEE 802.11 MAC;

[0013] FIGURES 6-7 are charts showing the delay versus number of smart meters using a probabilistically scheduled cognitive CSMA/CA DCF IEEE 802.11 MAC;

[0014] FIGURE 8 is a flowchart of the probabilistically scheduled cognitive IEEE 802.11 MAC in accordance with an illustrative embodiment; and

[0015] FIGURE 9 is a flowchart of the probabilistically scheduled cognitive IEEE 802.11 MAC in accordance with an illustrative embodiment.

Detailed Description

[0016] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. The word "exemplary" is used herein to mean "serving as an example, instance, or illustration". Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

[0017] Note that in this Specification, references to various features (e.g., elements, structures, modules, components, steps, operations, characteristics, etc.) included in "one embodiment", "example embodiment", "an embodiment", "another embodiment", "some embodiments", "various embodiments", "other embodiments", "alternative embodiment", and the like are intended to mean that any such features are included in one or more embodiments of the present disclosure, but may or may not necessarily be combined in the same embodiments.

[0018] The different illustrative embodiments described herein relate to a cognitive IEEE 802.11 MAC which is scheduled probabilistically for a large number of stations attempting to access the channel. Sensing of other network signals is done in a quiet period by an access point (AP). The different illustrative embodiments recognize and take into account a number of different considerations. For example, due to high collisions of data packets when there are many stations transmitting at the same time, the overall delay of using the carrier sense multiple access with collision avoidance (CSMA/CA) in distributed

coordination function (DCF) of IEEE 802.11 MAC can be very long. The method and systems of the different illustrative embodiments reduce the overall delay of the information from the stations. Additionally, the number of stations that can be supported is increased. One example use of the method and system of the different illustrative embodiments is in the area of smart metering using TV bands. A broadcast command frame is transmitted to obtain the smart meter readings in the downlink and the stations (smart meters) respond by transmitting the meter readings in the uplink under the constraint of an overall delay.

[0019] The most prominent WLAN under deployment today is the IEEE 802.11 wireless local area network (WLAN). The IEEE 802.11 standard has further been evolved into at least the following six types: IEEE 802.11b, 802.11a, 802.1 lg, 802.11η, 802.11s and 802.11 ad. The IEEE 802.1 In provides high throughput, while the upcoming IEEE 802.11 s supports mesh networking. Other types of IEEE 802.11 standards are also under

consideration. [0020] IEEE 802.1 lb can operate up to 11 Mbps, while IEEE 802.1 la can operate up to 54 Mbps. Both standards were published in 1999. The former operates in the 2.4 GHz unlicensed band, while the latter, which operates in the 5 GHz band, has not yet become widely used. IEEE 802.1 lb uses direct sequence spread spectrum (DSSS), while IEEE 802.1 la uses orthogonal frequency division multiplexing (OFDM) as the multiple access technology. The IEEE 802.1 lg standard, released in 2003, which operates in the 2.4 GHz band and uses OFDM as multiple access technology to achieve a data rate of up to 54 Mbps, has been gaining popularity.

[0021] The IEEE 802.1 In standard, published in 2009, uses a combination of OFDM and multiple-input multiple-output (MIMO) techniques to enhance diversity gain, aims to achieve a data rate of up to 600 Mbps. The goal is to design a media access control (MAC) protocol that can deliver a user throughput of more than 100 Mbps at the MAC layer.

[0022] The goal of the upcoming IEEE 802.1 lad draft standard is to provide very high throughput (VHT). Its call for proposals was in March 2010.

[0023] IEEE 802.11 distributed coordination function (DCF) uses a carrier sense multiple access with collision avoidance (CSMA/CA). It has two access methods. One of them is the basic access method with two-way handshaking, while the other is the request-to-send/clear- to-send (RTS/CTS) access method with four-way handshaking. In the basic access method, a data packet is sent from the source station to the destination station and the destination station replies with an acknowledgement (ACK) frame if the data packet is correctly received.

[0024] The different illustrative embodiments enable the stations to probabilistically schedule their packet transmissions using IEEE 802.11 MAC, after a broadcast command frame in the downlink, so that collisions of packets are minimized and the overall delay of all stations is reduced and the number of stations that can be supported is increased. [0025] The different illustrative embodiments provide that if other network transmissions are present as detected by the AP, the network under consideration will stop its transmission and the AP will decide to stay or move to another frequency band. Also, the different illustrative embodiments provide that if the other network transmissions are not present, the network under consideration will carry out its normal data transmission operations.

[0026] The foregoing has outlined rather broadly the features and technical advantages of the different illustrative embodiments in order that the detail description of the invention that follows may be better understood. Additional features and advantages of the different illustrative embodiments will be described hereinafter. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or redesigning other structures or processes for carrying out the same purposes of the different illustrative embodiments. It should also be realized by those skilled in the art that such equivalent constructions do not depart form the spirit and scope of the invention as set forth in the appended claims.

[0027] The various illustrative embodiments may be also embodied as a method of media access control that relates generally to data communications of stations in a secondary network in the presence of a primary network in order to spread out the data packet transmissions from the stations to the AP in the uplink after receiving a broadcast command frame from the AP in the downlink. Thus, data packet collisions are minimized, the overall delay is cut down and the number of stations that can be supported in such applications is increased.

[0028] The different illustrative embodiments can be used by a cognitive WLAN in the TV band whitespace. If the AP informs the smart meters that the current data transmission period (DTP) can be used and the meter also sense that there is no TV band signal, the CSMA/CA MAC protocol works in the DTP as follows. Upon receiving the command to send the meter readings, each smart meter will select a random bin number from zero to bin_jnax, where bin_max = twice the number of smart meters (stations), N, associated with the level 1 concentrator (AP). In general, the calculation of binjnax needs not be twice the number of smart meters; it can be any number that is greater than or equal to one time the number of smart meters. The smart meter will then scheduled its transmission to the bin interval that corresponds to the bin number, taking into account of the quiet period, the beacon period and the beacon interval. The bin interval is calculated as equal to 2*T_max, where T_max = T_packet + T_SIFS + T ACK + T_DIFS + CWmin*aSlotTime, T_packet is the data packet transmission time, T SIFS is the SIFS time, T_ACK is the acknowledgement frame time, T DIFS is the DIFS time, CWmin is the minimum contention window size and aSlotTime is a slot time. In general, the bin interval does not need to be twice of T_max, it can be any integer number that is greater than or equal to 2. Given the number of smart meters and the starting and ending times of the quiet period and sensing period and the beacon interval, the starting time of each bin can easily be computed. This information can be obtained by listening to the beacons. At its probabilistically scheduled time

corresponding to its bin interval, the basic IEEE 802.11 MAC is executed for each smart meter. The transmission are spread out from different smart meters to minimize collisions, achieve low overall delay, and increase the number of smart meters that can be supported.

[0029] FIGURE 1 is a communication system in accordance with an illustrative

embodiment. Communication system 10 is a system in which more than one device may communicate through networks 20. Networks 20 may be a direct connection and the transmitted airspace for access point 12 and plurality of stations 14.

[0030] In different illustrative embodiments, networks 20 represent a series of points or nodes of interconnected communication paths for receiving and transmitting packets of information that propagate through communication system 10. Networks 20 offer communicative interfaces between any of the components of FIGURE 1 and local and/or remote network nodes and other electronic devices, and may be any local area network (LAN), wireless local area network (WLAN), wide area network (WAN), wireless wide area network (WW AN), metropolitan area network (MAN), wireless metropolitan area network (WMAN), virtual private network (VPN), Intranet, Extranet, or any other appropriate architecture or system that facilitates communications in a network environment. Networks 20 may include any suitable communication link to access point 12 such as wireless technologies (e.g., IEEE 802.1 lx), satellite, cellular technologies (e.g., 3G, 4G, etc.), etc., or any combination thereof. Networks 20 may also include configurations capable of transmission control protocol/Internet protocol (TCP/IP) communications, user datagram protocol/IP (UDP/IP), or any other suitable protocol, where appropriate and based on particular needs.

[0031] Access point 12 is a device that allows plurality of stations 14 to communicate with each other as well as gain access to other networks and devices connected to access point 12. For example, if access point 12 is connected to the internet, plurality of stations 14 may be able to access the internet through access point 12. Access point 12 may be a wireless router or any other device capable of connecting to plurality of stations 14.

[0032] Plurality of stations 14 are devices connected to access point 12 through networks 20. Plurality of stations 14 comprises total number of stations 16. Total number of stations 16 is the number of stations within plurality of stations 14. For example, there may be two hundred stations. When there are two hundred stations, total number of stations 16 is two hundred.

[0033] Each station 18 within plurality of station 14 may be the same or different types of devices. For example, station 18 may be smart meter 22. Smart meter 22 may be a meter that monitors activity for a utility. For example, smart meter 22 may monitor electrical consumption for a house or building. Smart meter 22 may also monitor other types of activity, such as water consumption and any other suitable activity.

[0034] Smart meter 22 can include one or more memory elements (e.g., memory element 24) for storing information to be used in achieving operations associated with applications management, as outlined herein. For example, a scheduling policy may be stored in memory element 24 for optimizing transmission in communication system 10. These devices may further keep information in any suitable memory element (e.g., random access memory (RAM), read only memory (ROM), field programmable gate array (FPGA), erasable programmable read only memory (EPROM), electrically erasable programmable ROM (EEPROM), etc.), software, hardware, or in any other suitable component, device, element, or object where appropriate and based on particular needs. Any of the memory or storage items discussed herein should be construed as being encompassed within the broad term 'memory element' as used herein in this Specification.

[0035] In different illustrative embodiments, the operations for managing communications outlined herein may be implemented by logic encoded in one or more tangible media, which may be inclusive of non-transitory media (e.g., embedded logic provided in an ASIC, digital signal processor (DSP) instructions, software potentially inclusive of object code and source code to be executed by a processor or other similar machine, etc.). In some of these instances, one or more memory elements (e.g., memory element 24) can store data used for the operations described herein. This includes the memory elements being able to store software, logic, code, or processor instructions that are executed to carry out the activities described in this Specification.

[0036] Additionally, smart meter 22 may include processing elements 26. A processor can execute any type of instructions associated with the data to achieve the operations detailed herein in this Specification. In one example, the processors (as shown in FIGURE 1) could transform an element or an article (e.g., data) from one state or thing to another state or thing. In another example, the activities outlined herein may be implemented with fixed logic or programmable logic (e.g., software/computer instructions executed by a processor) and the elements identified herein could be some type of a programmable processor, programmable digital logic (e.g., an FPGA, an EPROM, an EEPROM), or an ASIC that includes digital logic, software, code, electronic instructions, flash memory, optical disks, CD-ROMs, DVD ROMs, magnetic or optical cards, other types of machine-readable mediums suitable for storing electronic instructions, or any suitable combination thereof.

[0037] Additionally, smart meter 22 comprises communications unit 23 which provides for communications with access point 12. In these examples, communications unit 23 may be a network interface card. Communications unit 23 may provide communications through the use of either or both physical and wireless communications links.

[0038] Access point 12 may send request 28 for information 30 to smart meter 22. Request 28 may be a command frame which includes transmit range 17 in addition to a request for information 30. Information 30 may be readings of the activity which smart meter 22 is monitoring. For example, information 30 may be the current power usage for a building. In other illustrative embodiments, information 30 may be other suitable readings. Transmit range 17 may be between zero and total number of stations 16 multiplied by a factor such that the maximum number is an integer

[0039] In response to request 28 for information 30, smart meter 22 may use scheduling module 32 to identify start time 34 for smart meter 22 to begin transmitting information 30 to access point 12. Scheduling module 32 selects transmit position 36 (bin) at random. Transmit position is the bin that smart meter 22 will transmit in. The number of transmit positions may be within total number of stations 16. For example, if total number of stations 16 is two hundred, scheduling module will select transmit position 36 randomly from zero to two hundred. In different illustrative embodiments, total number of stations may be multiplied by an integer or non-integer number such that the total number of bins (bin max) is still an integer to decrease the chances that multiple smart meters select the same transmit position. For example, if total number of stations 16 is two hundred and that is multiplied by two, transmit position is then selected randomly from zero to three hundred ninety-nine.

[0040] Additionally, in different illustrative embodiments, transmit position 36 is uniformly selected at random. In other words, the distribution of the selection of transmit positions is even across all possible numbers. However, some transmit position may have more smarter meters transmitting than other transmit positions.

[0041] In one or more illustrative embodiments, scheduling module 32 identifies interval time 38 (bin interval). Interval time 38 is calculated as a data packet transmission time plus a short inter frame space time plus a distributed inter frame space time plus an

acknowledgement frame time plus (a minimum contention window time multiplied by a slot time). In different illustrative embodiments, interval time 38 may also include clear to send time plus request to send time plus another short inter frame space time. In one or more illustrative embodiments, interval time 38 may be multiplied by a number and therefore lengthening the size of interval time 38 which would reduce the number of collisions between smart meters using the same transmit position.

[0042] In one or more illustrative embodiments, scheduling module 32 identifies start time 34 to begin initiating the CSMA/CA protocol for transmitting information 30. This start time 34 may be based on transmit position 36 of smart meter 22 and interval time 38 of other stations 40 with earlier transmit positions 42 than transmit position 36. Start time 34 is the beginning for initiation of the CSMA/CA process for the transmit position 36. Initiation for the CSMA/CA process may start at start time 34. In different illustrative embodiments, the CSMA/CA protocol may process just after start time 38 or any other suitable time after start time 38.

[0043] During a quiet period preceding transmit position 36, access point 12 monitors channel 44 of networks 20 for activity. Channel 44 is a range of frequencies on networks 20. If there is activity, access point 12 notifies smart meter 22 to withhold transmitting information 30. If there is no activity and channel 44 is clear, smart meter 44 may transmit information 30.

[0044] When start time 34 is reached, scheduling module 32 executes contention-based IEEE 802.11 media access control protocol to transmit information 30 to access point 12. If channel 44 is idle for more than a DCF inter- frame space time (DIFS), smart meter 22 can transmit immediately. If the channel 44 is busy, smart meter 22 generates a random backoff period. The random backoff period is uniformly selected from zero to the current contention window size. The backoff counter will decrement by one if the channel is idle for each time slot and will freeze if the channel is sensed busy or if the its DTP is not active. The backoff counter is re-activated to count down when the channel 44 is sensed idle for more than a DIFS time or when its data transmission period (DTP) is active. At the initial backoff stage, the current contention window size is set at the minimum contention window size.

[0045] If the backoff counter reaches zero, smart meter 22 attempts to transmit its frame if the remaining time to the end of its active DTP is greater than or equal to interval time 38. If the transmission is successful, the destination device will send an acknowledgement after a SIFS and the current contention window size is reset to the minimum contention window size. If the transmission is not successful, the current contention window size is increased by doubling it and adding one in the next backoff stage and a new random backoff period is selected as before. [0046] If the backoff counter reaches zero, smart meter 22 will not attempt to transmit its frame if the remaining time to the end of its current active DTP is less than interval time 38. Instead, smart meter 22 will increase the current contention window size by doubling it and adding one in the next backoff stage and a new random backoff period is selected as before and the countdown of the backoff counter will start after a DIFS after the next beacon period (BP). If the maximum retry limit is reached, the packet will be dropped and the next packet will start its backoff process with a minimum contention window size after a DIFS from the beginning of its next active DTP.

[0047] If a busy period ends within interval time 38, all the backoff counters will freeze until after a DIFS from the beginning of its next active DTP. This process repeats itself until information 30, also a frame, is successfully transmitted or until the maximum retry limit is reached. If information 30 is still not successfully transmitted, then information 30 is dropped.

[0048] If a station does not receive an acknowledgement within an acknowledgement timeout period after information 30 is transmitted, it will continue to attempt to re-transmit information 30 according to the backoff algorithm.

[0049] For each of the next backoff stages, the maximum contention window size is doubled that of the previous maximum contention window size and plus one. Then, the backoff counter value is uniformly chosen from zero to the maximum contention window size. This is equivalent to doubling the previous maximum contention window size and choosing the backoff counter value uniformly from zero to the maximum contention window size minus one.

[0050] The illustration of communication system 10 in FIGURE 1 is not meant to imply physical or architectural limitations to the manner in which different illustrative

embodiments may be implemented. Other components in addition and/or in place of the ones illustrated may be used. Some components may be unnecessary in some illustrative embodiments. Also, the blocks are presented to illustrate some functional components. One or more of these blocks may be combined and/or divided into different blocks when implemented in different advantageous embodiments.

[0051] FIGURE 2 is a beacon interval in accordance with an illustrative embodiment.

Beacon interval 50 is as specified in the IEEE 802.11 Standard "Part 11 : Wireless LAN Media Access Control (MAC) and Physical Layer (PHY) Specifications," June 2007. Each beacon interval consists of three parts: beacon period 51 (BP), data transmission period 52 (DTP), and quiet period 53 (QP). There is a period before the end of each DTP that does not allow a packet transmission to be successful as it is insufficiently long to transmit the packet, short inter-frame space (SIFS) time and AC frame. Beacon period 51 may be defined as a period of time declared by a device during which it sends or listens for beacons. A beacon may refer to information regarding the reservation of time slots in the following data period. In t quiet period 53, only the AP monitors the channel for activity. For example, the AP may sense the TV band whitespaces for any TV signal.

[0052] FIGURE 3 is an example of bin intervals in a probabilistically scheduled cognitive IEEE 802.11 MAC protocol. Bin intervals 55 are each an example of an illustrative embodiment of interval time 38 as shown in FIGURE 1. Between before and after each bin interval 56 and 57 is beacon periods 58 and quiet periods 59. After the broadcast command frame is sent in the downlink to obtain data packets from the stations, each station chooses a value uniformly between one and 2*N (bin_max), where N is the number of stations associated with the AP. This information is contained in the broadcast command frame. In different illustrative embodiments, the calculation of bin_max needs not be twice the number of smart meters, bin max can be any number that is greater than or equal to one time the number of stations. Each bin value is associated with a bin interval. The time duration of the bin interval is calculated as twice the sum of a data packet transmission time, a short interframe space (SIFS), an acknowledgement (ACK) frame time, a distributed coordination function interframe space (DIFS) and the product of the minimum contention window size (CWmin) and a slot time (aSlotTime). This is for basic access method. If RTS/CTS access method is used, additional corresponding RTS and CTS frame times and two SIFS time must be added in the calculation. The starting time to initiate the CSMA/CA protocol

corresponding to each bin can be calculated, given the beacon period, the quiet period, and the beacon interval which can be obtained by listening to the beacons. When the starting time of the bin interval that a station is associated with is reached, the basic cognitive CSMA/CA DCF IEEE 802.11 MAC is executed.

[0053] FIGURE 4 is a chart showing the delay versus number of smart meters using a cognitive CSMA/CA DCF IEEE 802.11 MAC for data rates of 1.5 Mbps. Only about 75 and 150 smart meters can be supported for a constraint of 5 seconds and 10 seconds, respectively, using the cognitive IEEE 802.11 MAC. There are 100 runs in each simulation point. The minimum, average and maximum delays are presented.

[0054] FIGURE 5 is a chart showing the delay versus number of smart meters using a cognitive CSMA/CA DCF IEEE 802.11 MAC for data rates of 13.5 Mbps. Only about 75 and 150 smart meters can be supported for a constraint of 5 seconds and 10 seconds, respectively, using the cognitive IEEE 802.11 MAC. There are 100 runs in each simulation point. The minimum, average and maximum delays are presented.

[0055] FIGURE 6 is a chart showing the delay versus number of smart meters using a probabilistically scheduled cognitive CSMA/CA DCF IEEE 802.11 MAC for data rates of 1.5 Mbps in accordance with the different illustrative embodiments. About 600 and 1000 smart meters can be supported for a constraint of 5 seconds using the probabilistically scheduled cognitive IEEE 802.11 MAC. There are 100 runs in each simulation point. More than 1250 smart meters can be supported at data rates of 1.5 Mbps using the probabilistically scheduled cognitive IEEE 802.11 MAC for a 10 s delay constraint. The minimum, average and maximum delays are presented.

[0056] FIGURE 7 is a chart showing the delay versus number of smart meters using a probabilistically scheduled cognitive CSMA/CA DCF IEEE 802.11 MAC for data rates of 13.5 Mbps in accordance with the different illustrative embodiments. About 600 and 1000 smart meters can be supported for a constraint of 5 seconds using a probabilistically scheduled cognitive IEEE 802.11 MAC. There are 100 runs in each simulation point. More than 2000 smart meters can be supported at data rates of 13.5 Mbps using the

probabilistically scheduled cognitive IEEE 802.11 MAC for a 10 seconds delay constraint. The minimum, average and maximum delays are presented.

[0057] As shown in FIGURES 4-7, the different illustrative embodiments can increase the number of smart meters that can be supported within a defined time period. The different illustrative embodiments can also be used when there is no cognitive aspect of the MAC in the beacon interval. That is, when there no quiet period, the different illustrative

embodiments is a probabilistically scheduled IEEE 802.11 DCF MAC, but it still has the same advantages over a standard IEEE 802.11 DCF MAC.

[0058] The parameter values used for the probabilistically scheduled cognitive IEEE 802.11 MAC example cases are shown in Table 1 below:

[0059] The basic access method is assumed in the numerical results. The value bin max is calculated as twice the number of smart meters, and the bin interval is calculated as 2xT_max.

[0060] One or more illustrative embodiments provides a media access method that spread out simultaneous data packet transmissions from the stations to the AP in the uplink of a WLAN at probabilistically scheduled time so as to minimize data packet collision, cut down overall delays, and increase the number of stations that can be supported. While the present implementation involves the use of the CSMA/CA DCF MAC of IEEE 802.11 Standard, June 2007, the idea presented by our invention have applications in other types of networks operating in the TV band whitespace, including future versions of the IEEE 802.11, IEEE 802.15 and ECMA-387 standards. Therefore, the different illustrative embodiments should not be constructed as being limited solely to the application to present wireless local area networks and wireless personal area networks compliant to these standards.

[0061] One or more illustrative embodiments provide co-existence of a secondary network operating in the TV band whitespace. An AP in secondary network under consideration senses the TV band signals through a quiet period. If data packet transmissions are possible as indicated by the AP in the beacon, a broadcast command frame is sent in the downlink and the data packet at each station is probabilistically scheduled for transmission in the uplink, all in the data transmission period. The calculation of the starting time of each bin interval is associated with a bin number that is uniformly selected between one and two times of the number of stations that are associated with the AP. The basic cognitive CSMA/CA DCF IEEE 802.11 MAC is executed at the starting time for each station. The data packet transmissions are spread out in the uplink so as to minimize packet collisions, cut down overall delay and increase the number of stations that can be supported.

[0062] One or more illustrative embodiments enables the stations to probabilistically schedule their packet transmissions using IEEE 802.11 MAC, after a broadcast command frame in the downlink, so that collisions of packets are minimized and the overall delay is cut down and the number of stations that can be supported is increased.

[0063] FIGURE 8 is a flowchart of the probabilistically scheduled cognitive IEEE 802.11 MAC in accordance with an illustrative embodiment. Process 800 may be implemented in system 10 from FIGURE 1.

[0064] Process 800 begins with an access point transmitting a broadcast command frame in the downlink (step 802). Next, each station receiving the broadcast command frame randomly selects a number between zero and nxN which will correspond to a bin number for that station (step 804). The variable "n" is a number selected by a user and the variable "N" is the total number of stations.

[0065] Then, each station computes the bin time interval (step 806). The bin interval is calculated as equal to 2*T_max, where T_max = T_packet + T SIFS + T ACK + T DIFS + CWminxaSlotTime. In different illustrative embodiments, Tpacket, is a system parameter which is a prior-knowledge.

[0066] Next, each station calculates the starting time to schedule transmitting the uplink data packet using IEEE 802.11 MAC protocol (step 808). Finally, each station transmits the uplink data packet using IEEE 802.11 MAC protocol at the scheduled time until successful. Thereafter, the process terminates. [0067] FIGURE 9 is a flowchart of the probabilistically scheduled cognitive IEEE 802.11 MAC in accordance with an illustrative embodiment. Process 900 may be implemented in system 10 from FIGURE 1.

[0068] Process 900 begins by receiving, at a station in a plurality of stations, a request for information and an indication of a total number of stations of the plurality of stations (step 902). Next, the station selects a transmit position at random within the total number of stations (step 904). Then, the station identifies a start time to begin initiating the CSMA/CA protocol for transmitting the information based on the transmit position of the station and an interval time of other stations with earlier transmit positions than the transmit position of the station (step 906). In different illustrative embodiments, other suitable types of protocol may be used. Finally, the station transmits the information using the CSMA/CA protocol at the start time (step 908). Thereafter, the process terminates.

[0069] The flowcharts and block diagrams in the different depicted embodiments illustrate the architecture, functionality, and operation of some possible implementations of apparatus, methods and computer program products. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of computer usable or readable program code, which comprises one or more executable instructions for implementing the specified function or functions. In some alternative implementations, the function or functions noted in the block may occur out of the order noted in the figures. For example, in some cases, two blocks shown in succession may be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved.

Claims

Claims What is claimed is:

1. A method for managing communications in a wireless network with a plurality of stations, the method comprising:

receiving, at a station in the plurality of stations, a request for information and a transmit range;

selecting a transmit position at random within the transmit range;

identifying a start time to begin initiating a CSMA/CA protocol for transmitting the information based on the transmit position of the station and a bin interval time of other stations with earlier transmit positions than the transmit position of the station; and

transmitting the information using the CSMA/CA protocol at the start time.

2. The method of claim 1, wherein the plurality of stations is a plurality of smart meters.

3. The method of claim 1, wherein the transmit range is between zero and a total number of stations multiplied by a factor minus one such that the maximum number is an integer.

4. The method of claim 1 , wherein the transmit range is between zero and a total number of stations multiplied by a factor such that the maximum number is an integer.

5. The method of claim 1 , wherein the request and the indication are sent from an access point.

6. The method of claim 1 , wherein the step of transmitting comprises: executing contention-based IEEE 802.11 media access control protocol at the start time to transmit the information to an access point.

7. The method of claim 1 further comprising:

identifying the bin interval time, wherein the bin interval time is the following multiplied by another factor: a data packet transmission time plus a short inter frame space time plus a distributed inter frame space time plus an acknowledgement frame time plus a result of a minimum contention window time multiplied by a slot time.

8. The method of claim 1 , wherein the transmit position of the station is uniformly selected at random.

9. The method of claim 5 further comprising:

determining whether a channel in the wireless network is available; and

responsive to determining that the channel is available, indicating to the station that the channel is available.

10. The method of claim 7, wherein the transmission time further comprises clear to send time plus request to send time plus another short inter frame space time.

11. A system for managing communications in a wireless network with a plurality of stations comprising:

a communications unit configured to:

receive a request for information of a station in the plurality of stations and a transmit range; transmit the information using a CSMA/CA protocol at the start time a scheduling module configured to:

select a transmit position at random within the transmit range; and

identify the start time to begin initiating the CSMA/CA protocol transmitting the information based on the transmit position of the station and a bin interval time of other stations with earlier transmit positions than the transmit position of the station.

12. The station of claim 11 further comprising:

an access point configured to send the request and the transmit range.

13. The station of claim 11 , wherein the scheduling module is further configured to execute contention-based IEEE 802.11 media access control protocol at the start time to transmit the information to an access point.

14. The station of claim 11 , wherein the scheduling module is further configured to identify the bin interval time, wherein the bin interval time is the following multiplied by another factor: a data packet transmission time plus a short inter frame space time plus a distributed inter frame space time plus an acknowledgement frame time plus (a minimum contention window time multiplied by a slot time).

15. The station of claim 11 comprising:

an access point configured to determine whether a channel in the wireless network is available; and responsive to determining that the channel is available, indicate to the station that the channel is available.

16. A computer program product comprising logic encoded on a tangible media, the logic comprising instructions for:

receiving, at a station in the plurality of stations, a request for information and a transmit range;

selecting a transmit position at random within the transmit range;

identifying a start time to begin initiating a CSMA/CA protocol for transmitting the information based on the transmit position of the station and a bin interval time of each other station with earlier transmit positions than the transmit position of the station; and

transmitting the information using the CSMA/CA protocol at the start time.

17. The computer program product of claim 1 , wherein the logic comprising the instructions for transmitting comprises instructions for:

executing contention-based IEEE 802.11 media access control protocol at the start time to transmit the information to an access point.

18. The computer program product of claim 16 further comprising instructions for:

identifying the bin interval time, wherein the bin interval time is: a data packet transmission time plus a short inter frame space time plus a distributed inter frame space time plus an acknowledgement frame time plus (a minimum contention window time multiplied by a slot time).

19. The computer program product of claim 16, wherein the transmit position of the station is uniformly selected at random.

The computer program product of claim 16 further comprising instructions for: determining whether a channel in the wireless network is available; and

responsive to determining that the channel is available, indicating to the station that the channel is available.