Patent Publication Number: US-2016227563-A1

Title: Traffic indication map association mechanism for low-energy devices

Description:
TECHNICAL FIELD 
     The present disclosure relates, in general, to wireless communications, and, more particularly, to a traffic indication map association mechanism for low-energy devices. 
     BACKGROUND 
     Wireless local area network (WLAN) systems based on IEEE 802.11, used for example in Industrial, Scientific and Medical (ISM) bands, access the wireless medium via contention based protocols complying with different regulatory domains. Some WLAN systems may be designed to support a large number of devices with low traffic profiles. An example of such a WLAN system is the IEEE 802.11ah Standard Draft (IEEE 802.11ah). A contention based protocol allows multiple devices to share the same spectrum by defining events that occur when two or more transmitters attempt to simultaneously access the same channel, and by establishing rules by which a transmitter provides reasonable opportunities for other transmitters to operate on the same channel. In IEEE 802.11, a radio capable device may be referred to as a wireless device or station (STA) and access point (AP). 
     Based on “IEEE 802.11ah: The Wi-Fi Approach for M2M Communications”, the MAC Layer of IEEE 802.11ah is designed to maximize the number of stations supported by the network while ensuring minimum energy consumption. IEEE 802.11ah defines two different types of stations: traffic indication map (TIM) stations and non-TIM stations, each with different procedures and time periods to access the common channel. 
     TIM stations need to listen to AP beacons to send or receive data within the associated TIM interval. Data transmissions of TIM stations may be performed within a restricted access window (RAW) period as well. 
     Non-TIM stations do not need to listen to any beacons to transmit data. During the association process, non-TIM devices directly negotiate with the AP to obtain a transmission time allocated in a periodic RAW (PRAW). The following transmissions can be either periodically defined or renegotiated, depending on the requirements set by the station. 
     Although non-TIM stations can transmit data periodically, it is advisable to deploy TIM stations for high-volume data applications to achieve better management of channel resources, and benefit from all the improvements developed by IEEE 802.11ah, especially for those requiring high reachability. For instance, when a large group of devices are triggered simultaneously for data access, TIM deployment becomes essential. 
     SUMMARY 
     To address the foregoing problems with existing solutions, disclosed is a method in an access point. The method comprises determining an energy status of a wireless device, the energy status comprising one of a low-energy device and a high-energy device, and determining an access group of a plurality of access groups to which to allocate the wireless device. The method also comprises allocating the wireless device to a first access group upon determining that the wireless device is a low-energy device, the first access group for wireless devices that are to receive beacon information in a low-energy consumption format, and communicating the beacon information to the first access group in the low-energy consumption format. 
     In certain embodiments, a low-energy device may include one or more of a battery-powered device that has a battery life below a battery life threshold, a device with a battery capacity below a battery capacity threshold, and a device that is not plugged in. The method may comprise receiving one of an indication of the energy status of the wireless device in a field of an association signaling message and an indication of the energy status of the wireless device using dedicated signaling. The dedicated signaling may be performed after the wireless device associates with the access point. The plurality of access groups may comprise at least one of traffic indication map groups, periodic restricted access window groups, and restricted access window groups. In certain embodiments, the first access group may be a first traffic indication map group, and the beacon information may comprise a delivery traffic indication map information element and a first traffic indication map information element used by the wireless device to send or receive data. The first traffic indication map information element may be associated with the first traffic indication map group. Determining the access group of a plurality access groups to which to allocate the wireless device may comprise determining whether a load of the first access group is below a load threshold. 
     In certain embodiments, communicating the beacon information to the first traffic indication map group in the low-energy consumption may comprise communicating both a delivery traffic indication map information element and a first traffic indication map information element to the first traffic indication map group at the same time, the first traffic indication map information element contained within the delivery traffic indication map information element and associated with the first traffic indication map group. In certain embodiments, communicating the beacon information to the first traffic indication map group in the low-energy consumption format may comprise communicating both a delivery traffic indication map information element and a first traffic indication map information element to the first traffic indication map group within a defined time interval. The first traffic indication map information element may be associated with the first traffic indication map group, and the defined time interval may have a duration such that the wireless device allocated to the first traffic indication map group only wakes up once to receive both the delivery traffic indication map information element and the first traffic indication map information element. 
     Also disclosed is a method in a wireless device. The method comprises communicating an energy status of the wireless device to an access point, the energy status of the wireless device comprising one of a low-energy device and a high-energy device, the energy status for use in allocating the wireless device to an access group of a plurality of access groups, wherein wireless devices having a low-energy device energy status are allocated to a first access group of the plurality of access groups, the first access group for wireless devices that are to receive beacon information in a low-energy consumption format. The method further comprises receiving the beacon information in the low-energy consumption format when the wireless device is allocated to the first access group. 
     In certain embodiments, a low-energy device may be one or more of a battery-powered device that has a battery life below a battery life threshold, a device with a battery capacity below a battery capacity threshold, and a device that is not plugged in. The method may comprise communicating an indication of the energy status of the wireless device in a field of an association signaling message. The method may comprise communicating an indication of the energy status of the wireless device using dedicated signaling. The dedicated signaling may be performed after the wireless device associates with the access point. The plurality of access groups may comprise at least one of traffic indication map groups, periodic restricted access window groups, and restricted access window groups. In certain embodiments, the first access group may be a first traffic indication map group, and the beacon information may comprise a delivery traffic indication map information element and a first traffic indication map information element used by the wireless device to send or receive data. The first traffic indication map information element may be associated with the first traffic indication map group. 
     In certain embodiments, the method comprises receiving both a delivery traffic indication map information element and a first traffic indication map information element at the same time. The first traffic indication map information element may be contained in the delivery traffic indication map information element and associated with the first traffic indication map group. The method may comprise receiving both a delivery traffic indication map information element and a first traffic indication map information element within a defined time interval, the first traffic indication map information element associated with the first traffic indication map group. The defined time interval may have a duration such that the wireless device only wakes up once to receive both the delivery traffic indication map information element and the first traffic indication map information element. The defined time interval may be selected to prevent the wireless device from falling asleep between receiving the delivery traffic indication map information element and the first traffic indication map information element. 
     Certain embodiments of the present disclosure may provide one or more technical advantages. For example, some embodiments may enable reduced energy consumption by low-energy devices by communicating beacon information in a low-energy consumption format. As another example, certain embodiments may allow wireless devices to have a longer sleep time, potentially allowing the wireless devices to switch off more components, which may result in energy savings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the disclosed embodiments and their features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a WLAN system having an access point and a plurality of stations, in accordance with certain embodiments; 
         FIG. 2  illustrates a comparison of energy consumption by devices allocated to TIM groups when each TIM group includes the same number of devices, in accordance with certain embodiments; 
         FIG. 3  illustrates a comparison of energy consumption by devices allocated to TIM groups, when each TIM group does not include the same number of devices, in accordance with certain embodiments; 
         FIG. 4  illustrates a flow diagram for a TIM prioritization method, in accordance with certain embodiments; 
         FIG. 5A  is a signal flow diagram illustrating signaling of a wireless device&#39;s TIM preference to an access point, in accordance with certain embodiments; 
         FIG. 5B  is a signal flow diagram illustrating signaling of a wireless device&#39;s energy status to an access point; 
         FIG. 6  illustrates a method in an access point, according to an embodiment; 
         FIG. 7  illustrates a method in a wireless device, according to an embodiment; 
         FIG. 8  is a block diagram illustrating a wireless device  110 , according to certain embodiments; and 
         FIG. 9  is a block diagram illustrating a network node  120 , according to certain embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     As described above, certain wireless devices, such as TIM stations, may need to receive certain beacons in order to send or receive data. For a variety of reasons, certain TIM stations, such as low-energy devices, may benefit from receiving beacon information in a low-energy consumption format. The present disclosure contemplates various embodiments that may provide access mechanisms that may allow low-energy wireless devices, such as TIM stations, to receive beacon information in a low-energy consumption format. 
       FIG. 1  illustrates a wireless communications network  100 , in accordance with certain embodiments. Network  100  includes a plurality of wireless devices  110 A,  110 B,  110 C, network node  120 , and other network  130 . Wireless communications network  100  may operate based on any suitable radio access technology. For example, in certain embodiments network  100  may be a wireless local area network (WLAN) governed by IEEE 802.11 technology, such as IEEE 802.11ah. Wireless communications network  100  may operate over any suitable range. For example, network  100  may have a fairly limited range, such as an office building or a building block. 
     Wireless devices  110  may also be referred to as stations (STA) or user equipment (UE). Wireless devices  110  may communicate with network node  120  over a wireless interface. For example, wireless devices  110  may transmit wireless signals to network node  120 , and/or receive wireless signals from network node  120 . The wireless signals may contain voice traffic, data traffic, control signals, and/or any other suitable information. Network  100  may include any suitable number of wireless devices  110 . 
     Network node  120  may also be referred to as access point (AP)  120 . AP  120  is a network node that allows wireless devices, such as wireless devices  110 A,  1108 , and  110 C to communicate wirelessly and to connect to another network  130 . The other network  130  may be any suitable network, such as an organization&#39;s wired infrastructure or the Internet. AP  120  may have an associated coverage area. Wireless devices  110 A-C located within a coverage area of AP  120  may be able to communicate with AP  120 . Network  100  may include a plurality of APs  120 . Example embodiments of wireless device  110  and access point  115  are described below with respect to  FIGS. 8 and 9 , respectively. 
     In certain embodiments, network  100  may be a WLAN operating according to IEEE 802.11ah. As described above, there are two types of stations in such a network: TIM stations and non-TIM stations. Wireless devices  110 A,  110 B, and  110 C may be any suitable type of station. For example, wireless devices  110 A-C may all be TIM stations, wireless devices  110 A-C may all be non-TIM stations, or wireless devices  110 A-C may be a mixture of TIM and non-TIM stations. 
     Each wireless device  110  of network  100  may have an energy status. The energy status of a wireless device may be one of low-energy device and high-energy device. Low-energy devices may be devices that suffer from one or more of high energy-consumption, limited battery lifetime, small battery capacity, and devices that are not connected to an energy source. For example, a device may be a low-energy device if it is a battery-powered device that does not have sufficient battery lifetime, or a device with a small battery capacity, or a device that is not plugged in. High-energy devices may be those devices that do not suffer from one or more of the above discussed characteristics of low-energy devices. For example, a device may be a high-energy device it is a battery-powered device that has a long battery lifetime, or a device with a large battery capacity, or a device that is plugged in. 
     When a TIM wireless device, such as wireless device  110 A, attempts to associate with network  100 , AP  120  may allocate wireless device  110 A to one or more access groups. AP  120  may allocate wireless device  110 A to any suitable type of access group, such as, for example, traffic indication map groups, periodic restricted access window groups, or restricted access window groups. To illustrate, AP  120  may allocate wireless device  110 A to one or more TIM groups. TIM groups may define the time during which members of a particular TIM group may access network  100 . For example, assume that network  100  has five TIM groups A-E, and five hundred wireless devices  110  associated with it. Assume further that each TIM group contains one hundred wireless devices. The one hundred wireless devices in TIM group A will access the network during a time period A, the one hundred wireless devices in TIM group B will access the network during time period B, and so on. For example, wireless devices  110 A,  110 B, and  110 C may be allocated to TIM groups A, B, and C, respectively, and may each access the network at different times. 
     There may be any suitable number of TIM groups associated with AP  120 , and each TIM group may include any suitable number of wireless devices  110 . The number of wireless devices that may be included in a particular TIM group may have an upper limit. The upper limit may define a load threshold, above which the particular TIM group is unable to accommodate additional wireless devices without removing at least one wireless device from the overloaded TIM group. 
     As described above, TIM wireless devices in network  100  may need to receive beacon information in order to send or receive data. The beacon information may be sent by AP  120 . The beacon information may include a delivery traffic indication map (DTIM) and a traffic indication map (TIM). DTIM allows TIM devices to get system information, including synchronization clock, time to receive group beacon, and any other suitable information. The DTIM beacon may be communicated first in time, and is required for all TIM groups associated with AP  120 . There may, however, be a plurality of TIM beacons, each associated with a particular TIM group. Using the example of TIM groups A-E described above, AP  120  may communicate a first TIM beacon associated with TIM group A, a second TIM beacon associated with TIM group B, and so on. Thus, there may be a period of time between the point at which AP  120  communicates the DTIM beacon and the point at which AP  120  communicates a particular TIM beacon associated with a particular TIM group. As a result of this gap in time, wireless devices in the particular TIM group may fall asleep between receiving the DTIM beacon and the TIM beacon associated with the TIM group to which the wireless devices are allocated. Thus, wireless devices that fall asleep during this time period must wake up twice, once to receive the DTIM beacon and once to receive the TIM beacon associated with the particular TIM group to which the wireless device was allocated. 
     To illustrate, assume wireless devices  110 A,  110 B, and  110 C of  FIG. 1  are all TIM stations. Wireless device  110 A,  110 B, and  110 C may be allocated to TIM groups A, B, and C, respectively, by AP  120 . AP  120  may communicate the DTIM first, followed by a first TIM beacon associated with TIM group A, a second TIM beacon associated with TIM group B, and a third TIM beacon associated with TIM group C, each communicated by AP  120  at a different time and within a different period of time after communicating the DTIM beacon. Thus, because of the gap in time between receipt of the DTIM beacon and the TIM beacons associated with TIM groups A, B, and C, wireless devices  110 A,  110 B, and  110 C may have time to go to sleep between receiving the DTIM beacon and receiving the TIM beacon associated with their respective TIM groups. Thus, wireless devices  110 A,  110 B, and  110 C will have to wake up twice: once to receive the DTIM beacon, and once to receive the TIM beacon associated with their respective TIM groups. This may result in increased energy consumption by wireless devices  110 A-C, which may be undesirable, especially if one or more of wireless devices  110 A-C are of the low-energy device energy status described above. Various embodiments of the present disclosure may provide improvements to the energy consumption of low-energy devices receiving DTIM and TIM beacons. 
     In certain embodiments, wireless device  110 A may communicate an energy status of wireless device  110 A to AP  120 . AP  120  may determine the energy status of wireless device  110 A. AP  120  may determine a TIM group of a plurality of TIM groups to which to allocate wireless device  110 A. AP  120  may allocate wireless device  110 A to a first TIM group upon determining that wireless device  110 A is a low-energy device. The first TIM group may be for wireless devices that are to receive beacon information in a low-energy consumption format. AP  120  may communicate the beacon information to the first TIM group in the low-energy consumption format. Wireless device  110 A may receive the beacon information in the low-energy format when wireless device  110 A is allocated to the first TIM group. 
     AP  120  may determine the energy status of one or more wireless devices  110  in any suitable manner. For example, wireless device  110 A may communicate to AP  120  that it is a low-energy device, and wireless device  110 B may communicate to AP  120  that it is a high-energy device. In certain embodiments, the energy status of a wireless device may be communicated to AP  120  during the association procedure. As one example, wireless device  110 A may indicate its energy status to AP  120  by adding a field or subfield in one of the association signaling messages. As another example, wireless device  110 A may indicate its energy status using an existing field or subfield in one of the association signaling messages. In certain embodiments, the energy status of wireless device  110 A may be communicated to AP  120  via dedicated signaling after association. 
     AP  120  may determine a TIM group to which to allocate wireless devices  110 A and  1108 , and allocate wireless devices  110 A and  1108  to the determined TIM groups. In certain embodiments, this determination may be based on any suitable characteristic. For example, AP  120  may determine a TIM group to which to allocate wireless devices  110 A and  1108  based on the energy status of wireless devices  110 A and  1108 . In certain embodiments, one or more TIM groups may be particularly suited for low-energy devices, and AP  120  may preferably allocate low-energy devices to the particular TIM group. For example, AP  120  may determine that wireless device  110 A is a low-energy device, and may assign wireless device  110 A to a first TIM group. Low-energy devices may be preferably allocated to the first TIM group because the first TIM group may be designated to communicate beacon information, such as the DTIM beacon and the TIM beacon associated with the first TIM group, in a low-energy consumption format. For comparison, AP  120  may determine that wireless device  1108  is a high-energy device, and allocate wireless device  1108  to a second TIM group that does not communicate beacon information in a low-energy consumption format. 
     In certain embodiments, wireless device  110 A may indicate a preferred TIM grouping to AP  120  using dedicated signaling. For example, wireless device  110  may use a dedicated subfield of the S1G Capabilities Info field in IEEE 802.11ah for indicating a preferred TIM grouping to AP  120 . The ability of a wireless device to indicate a preferred TIM grouping is discussed in more detail in  FIG. 5A  below. 
     As described above, AP  120  may allocate wireless device  110 A to a first TIM group upon determining that wireless device  110 A is a low-energy device, and may communicate the beacon information, including the DTIM beacon and the TIM beacon associated with the first TIM group, in a low-energy consumption format. The present disclosure contemplates that communicating beacon information in a low-energy format may be performed in any suitable manner. 
     For example, in certain embodiments AP  120  may communicate both the DTIM beacon and the TIM beacon associated with the first TIM group to the first TIM group at the same time. The TIM beacon associated with the first TIM group may be contained within the DTIM beacon, or may be transmitted with the DTIM beacon. Communicating the beacon information in this format may be advantageous to wireless device  110 A because wireless device  110 A is able to receive the beacon information at the same time, and therefore does not have to wake up twice. 
     To highlight the energy efficiency of such an approach, consider the case of wireless device  110 B allocated to the second TIM group. Wireless device  110 B may have to wake up to receive the DTIM beacon when it is communicated by AP  120 , and then may have to wait to receive the TIM beacon associated with the second TIM group. During the time between receiving the DTIM beacon and the TIM beacon associated with the second TIM group, wireless device  110 B may fall asleep, and thus will have to wake up a second time to receive the TIM beacon associated with the second TIM group. Receiving beacon information in this format, as compared to the low-energy consumption format of communication used with the first TIM group, requires wireless device  1108  to consume more energy than wireless device  110 A. 
     As another example, in certain embodiments AP  120  may communicate both the DTIM beacon and the TIM beacon associated with the first TIM group to the first TIM group within a defined time interval. The defined time interval may have a duration such that wireless device  110 A allocated to the first TIM group only wakes up once to receive both the DTIM beacon and the TIM beacon associated with the first TIM group. Put another way, the defined time interval may be selected to prevent wireless device  110 A from falling asleep between communication of both the DTIM beacon and the TIM beacon associated with the first TIM group. The energy savings that result from such an approach are similar to those described above. Assuming that wireless device  1108  is assigned to a second TIM group to which beacon information is not communicated in a low-energy format, wireless device  1108  may have to wake up twice to receive the beacon information. Wireless device  110 A, however, will only have to wake up once, and therefore will consume less energy than wireless device  1108 . 
     As described above, low-energy devices, such as wireless device  110 A, may be allocated to a first TIM group to which beacon information is communicated in a low-energy format, and high-energy devices, such as wireless device  1108  may be allocated to a second TIM group or other TIM group that does not communicate beacon information in a low-energy format. In certain embodiments, however, high-energy device  110 B may be allocated to the first TIM group along with low-energy device  110 B. High-energy devices allocated to the first TIM group, and therefore receiving beacon information in a low-energy consumption format, may subsequently be reallocated to a TIM group that does not communicate beacon information in a low-energy consumption format. 
     As described above, AP  120  may determine the TIM group to which to allocate a wireless device based on any suitable characteristic, such as energy status. In certain embodiments, AP  120  may also take into account the load of a particular TIM group in determining the TIM group to which to allocate a wireless device, and in allocating the wireless device to a TIM group. The load may be determined in any suitable manner. For example, AP  120  may be able to obtain load information by measuring flow in the network. The load of a particular TIM group may be measured based on how many packets arrive, or based on the number of packets or bytes per device multiplied by the number of devices in the particular TIM group. 
     For example, assume that AP  120  has allocated wireless device  110 A, a low-energy device, and wireless device  1108 , a high-energy device, to the first TIM group. Assume further that wireless device  110 C, a low-energy device, attempts to associate with AP  120 . AP  120 , in determining the TIM group to which to allocate wireless device  110 C, AP  120  may consider the load in the first TIM group. For example, AP  120  may consider whether the load of the first TIM group is below a load threshold. The load threshold may be the max number of wireless devices that the first TIM group is able to accommodate. If the load of the first TIM group is below the load threshold, then AP  120  may allocate wireless device  110 C to the first TIM group. AP  120  may allocate wireless device  110 C to the first TIM group based at least in part on its energy status. If the load of the first TIM group is equal to the load threshold, AP  120  may allocate wireless device  110 C to the second TIM group or another TIM group, even though wireless device  110 C is a low-energy device, and would therefore benefit from the low-energy consumption communication format of the first TIM group. Alternatively, if the load of the first TIM Group is equal to the load threshold, AP  120  may simultaneously reallocate wireless device  1108 , a high-energy device, to another TIM group, and allocate wireless device  110 C to the first TIM group. Thus, wireless device  110 C may receive beacon information in a low-energy consumption format, which may be beneficial because of its low-energy device energy status. 
     In certain embodiments, there may be subgroups within the one or more TIM groups. For example, Restricted Access Window (RAW), page and page slicing subgroups may exist within a TIM group. Thus, in addition allocating a wireless device to a TIM group, AP  120  may further allocate the wireless device to a subgroup within the TIM group. Furthermore, in addition to taking into account the load of a TIM group in determining and allocating a wireless device to a TIM group, as described above, AP  120  may also take into account the load of a TIM subgroup. 
     Although the various embodiments may be described in the context allocating a TIM station to one of a plurality of TIM groups, this is for purposes of example only and is not intended to limit the scope of the disclosure. The present disclosure contemplates that the various embodiments may be applied to a variety of scenarios. 
       FIG. 2  illustrates the energy savings that may be achieved when the same number of devices are allocated to each TIM group, in accordance with certain embodiments. More particularly,  FIG. 2  depicts the energy consumption for each of four TIM groups ( 1 - 4 ) over the course of a simulation. Average energy consumption of each TIM group was measured for transmit  205 , receive  210 , backoff  215 , listening channel idle  220 , listening channel busy  225 , and virtual carrier sensing  230 . The simulation assumes an hour of data communication between forty Non-AP devices, such as wireless devices  110 A-C described above, and an AP, such as AP  120  described above. Packet arrival in each station follows Poisson Process, and has an average inter-arrival time of one second. Uplink is of the main interest. Each TIM group includes the same number of wireless devices, i.e., ten wireless devices per TIM group. 
     As shown in  FIG. 2 , the first TIM group (TIM group  1 ) consumes much less energy in receiving  210  than other TIM groups, while energy consumption in other states (transmit  205 , back-off  215 , listening channel idle  220 , listening channel busy  225 , and virtual carrier sensing  230 ) remains the same for all the groups. 
     As described above, TIM devices receive three kinds of information in total. Firstly, all TIM stations have to wake up to receive DTIM beacon. The DTIM beacon provides system information, including synchronization clock, time to receive group beacon, and other suitable information. Secondly, TIM devices have to wake up to receive their group TIM beacon. Lastly, after a device transmit its packet, it needs to receive ACK from AP to know whether the transmission is successful or not. Low-energy devices may benefit from placement in a TIM group to which beacon information is communicated in a low-energy consumption format. 
     As described above, in certain embodiments, the DTIM beacon may already contain the TIM beacon information for the first TIM group, the first TIM group devices only need to wake up once to receive the DTIM beacon and the TIM beacon associated with the first TIM group. Devices in the other TIM groups (groups  2 - 4 ) have to wake up twice to receive the DTIM beacon and TIM beacon each time. Thus, the first TIM group consumes less power because they receive the TIM beacon information for the first TIM group with the DTIM, and therefore spend less time on receiving and have more time to sleep. Overall, energy consumption was 13% for the first TIM group devices as compared to TIM groups  2 - 4 . 
     Furthermore, since the data traffic model and number of devices for each group are the same, each group will transmit almost the same number of packets, and experience the same collision probability and retransmission. Thus, it is not surprising that they consume expectedly the same energy in transmitting  205 , back-off  215 , and listening channel idle  220 . 
     In certain embodiments, the DTIM beacon may not include the TIM beacon for the first TIM group, but the DTIM beacon and the TIM beacon for the first TIM group may be consecutively broadcast by the AP. In such an embodiment, the wireless device could get a similar energy saving benefit from the wake up procedures, as it does not have to wake up for the DTIM and TIM beacons separately. This way, the wireless device may have a longer sleep time, and also may potentially switch off more components, potentially resulting in energy savings. 
       FIG. 3  illustrates the energy savings that may be achieved when each of the TIM groups do not have the same number of devices, in accordance with certain embodiments. More particularly,  FIG. 3  depicts the energy consumption for each of four TIM groups ( 1 - 4 ) over the course of a simulation. Average energy consumption of each TIM group was measured for transmit  305 , receive  310 , backoff  315 , listening channel idle  320 , listening channel busy  325 , and virtual carrier sensing  330 . The simulation assumes an hour of data communication between forty Non-AP devices, such as wireless devices  110 A-C described above, and an AP, such as AP  120  described above. Packet arrival in each station follows Poisson Process, and has an average inter-arrival time of one second. Uplink is of the main interest. Unlike  FIG. 2  described above, the TIM groups do not include the same number of wireless devices. The first TIM group (TIM group  1 ) contains  15  wireless devices, the second TIM group (TIM group  2 ) contains  5  devices, and TIM groups  3  and  4  contain  10  devices. 
     In the scenario illustrated in  FIG. 3 , the first TIM group, which contains the most wireless devices, consumes more energy on transmit  305 , back-off  315 , listening channel idle  320 , listening channel busy  325 , and virtual carrier sensing  330  since they have transmitted more packets under a higher collision probability channel with more retransmission. The first TIM group, however, still consumes much less energy on receiving  310 , even though its consumption in transmit and idle is significantly larger than the second TIM group. Thus, it can be concluded that receiving the TIM beacon in a manner that causes the wireless device to have to wake up twice may cost a large amount of energy in the TIM groups other than the first one (independently from the number of devices). On the other hand, the impact of device distribution among TIM groups should not be neglected, as the energy consumption figures largely depend on the number of devices, even for the first TIM group. 
       FIG. 4  illustrates a flow diagram for a TIM prioritization method, in accordance with certain embodiments. The flow diagram begins at decision point  404 , when the AP, such as AP  120  described above, determines whether a wireless device requesting access to the network is a low-energy device. If the AP determines that the wireless device is not a low-energy device, then the method proceeds to step  408 . At step  408 , the AP assigns the wireless device to a TIM group in which beacon information is not communicated in a low-energy consumption format. 
     If the AP determines that the wireless device is a low-energy device, then the method proceeds to step  412 . At step  412 , the AP determines whether the load in the TIM group of which the beacon information is communicated in a low-energy consumption format (i.e., TIM beacon transmitted within the DTIM beacon information, or together with the DTIM beacon information, or within a minimal time difference to the DTIM beacon information) exceeds a load threshold (Lmax). If the load of the first TIM group (Ltim 1 ) is below a parameter (e.g., Lmax), the method proceeds to step  416  and the AP allocates the new wireless device to the first TIM group to which TIM beacon information may be transmitted within the DTIM beacon information. Lmax may refer to the maximal load that can be allocated in the first TIM group. The Lmax parameter may be set as an absolute or relative value. For example, Lmax may be set with respect to the load in other TIM groups or non-TIM groups. If, at step  412 , the AP determines that the load of the first TIM group is equal or above Lmax, the method proceeds to step  420 , and the AP may assign the device to a TIM group or non-TIM group other than the first TIM group. In certain embodiments, this may be a TIM or non-TIM group that has the lowest load (i.e., the lowest traffic (Lmin)). 
     In certain embodiments, the new wireless device requesting access to the system may be allocated into one or more subgroups of a TIM group, such as a page subgroup or page slice subgroup. The AP may also take into account the load of the various subgroups in allocating the wireless device to a TIM group. For example, subgroups within non-TIM groups, namely PRAW, may also be considered while calculating Lmax. Thus, Lmax may be defined as an absolute or relative value (with respect to the load in other TIM groups or RAW groups within TIM groups or page within TIM groups or page slicing within TIM groups or non-TIM groups or PRAW groups within non-TIM groups). 
       FIG. 5A  is a signal flow diagram illustrating signaling of a wireless device  110 &#39;s TIM preference to an access point  120 , in accordance with certain embodiments. As described above, a wireless device  110  may be a low-energy device. Wireless device  110  may indicate a preferred TIM grouping to AP  120  using dedicated signaling. For example, and as illustrated in  FIG. 5A , in certain embodiments, wireless device  110  may use a dedicated subfield of the SIG Capabilities Info field in IEEE 802.11ah for indicating a TIM preference to AP  120 . In response to the TIM preference communicated by wireless device  110 , AP  120  may communicate a TIM Association/Assignment. 
       FIG. 5B  is a signal flow diagram illustrating signaling of a wireless device  110 &#39;s energy status to an access point  120 . As described above, wireless device  110  may communicate its energy status to AP  120 . For example, wireless device  110  may communicate its energy status during the association procedure. This may occur in any suitable manner. In the example illustrated in  FIG. 5B , wireless device  110  may indicate its energy status to AP  120  by including a low-energy device or high-energy device indication in SIG Capabilities information. In certain embodiments, wireless device  110  may indicate its energy status to AP  120  by adding a field or subfield in one of the association signaling messages. As another example, wireless device  110  may indicate its energy status using an existing field or subfield in one of the association signaling messages. In certain embodiments, the energy status of wireless device  110  may be communicated to AP  120  via dedicated signaling after association. In response to wireless device  110 &#39;s indication of energy status, AP  120  may respond with a TIM association/assignment. 
       FIG. 6  illustrates a method in an access point, according to an embodiment. The method begins at step  604 , when an energy status of a wireless device is determined. The energy status may include one of a low-energy device and a high-energy device. In certain embodiments, the access point may receive one of an indication of the energy status of the wireless device in a field of an association signaling message and an indication of the energy status of the wireless device using dedicated signaling. The dedicated signaling may be performed after the wireless device associates with the access point. A low-energy device may be one or more of a battery-powered device that has a battery life below a battery life threshold, a device with a battery capacity below a battery capacity threshold, and a device that is not plugged in. 
     At step  608 , the access point determines an access group of a plurality of access groups to which to allocate the wireless device. In certain embodiments, the access point may determine whether a load of the first access group is below a load threshold. The plurality of access groups may comprise at least one of traffic indication map groups, periodic restricted access window groups, and restricted access window groups. 
     At step  612 , the access point allocates the wireless device to a first access group upon determining that the wireless device is a low-energy device. The first access group is for wireless devices that are to receive beacon information in a low-energy consumption format. In certain embodiments, the first access group may be a first traffic indication map group, and the beacon information may include a delivery traffic indication map information element and a first traffic indication map information element used by the wireless device to send or receive data. The first traffic indication map information element may be associated with the first traffic indication map group. 
     At step  616 , the access point communicates the beacon information to the first access group in the low-energy consumption format. In certain embodiments, the access point communicates both a delivery traffic indication map information element and a first traffic indication map information element to the first traffic indication map group at the same time. The first traffic indication map information element may be contained within the delivery traffic indication map information element and associated with the first traffic indication map group. In certain embodiments, the access point may communicate both a delivery traffic indication map information element and a first traffic indication map information element to the first traffic indication map group within a defined time interval. The first traffic indication map information element may be associated with the first traffic indication map group, and the defined time interval may have a duration such that the wireless device allocated to the first traffic indication map group only wakes up once to receive both the delivery traffic indication map information element and the first traffic indication map information element. The defined time interval may be selected to prevent the wireless device from falling asleep between communication of both the delivery traffic indication map information element and the first traffic indication map information element to the first traffic indication map group. 
       FIG. 7  illustrates a method in a wireless device, according to an embodiment. The method begins at step  704  when the wireless device communicates an energy status of the wireless device to an access point. The energy status of the wireless device is one of a low-energy device and a high-energy device, and may be used in allocating the wireless device to an access group of a plurality of access groups. Wireless devices having a low-energy device energy status are allocated to a first access group of the plurality of access groups, and the first access group is for wireless devices that are to receive beacon information in a low-energy consumption format. The wireless device may communicate an energy status of the wireless device in any suitable manner. For example, the wireless device may communicate an indication of the energy status of the wireless device in a field of an association signaling message. As another example, the wireless device may communicate an indication of the energy status of the wireless device using dedicated signaling. The dedicated signaling may be performed after the wireless device associates with the access point. In certain embodiments, a low-energy device is one or more of a battery-powered device that has a battery life below a battery life threshold, a device with a battery capacity below a battery capacity threshold, and a device that is not plugged in. 
     At step  708 , the wireless device receives the beacon information in the low-energy consumption format when the wireless device is allocated to the first access group. The plurality of access groups may comprise at least one of traffic indication map groups, periodic restricted access window groups, and restricted access window groups. In certain embodiments, the first access group may be a first traffic indication map group, and the beacon information may comprise a delivery traffic indication map information element and a first traffic indication map information element used by the wireless device to send or receive data. The first traffic indication map information element may be associated with the first traffic indication map group. 
     In certain embodiments, the wireless device may receive both a delivery traffic indication map information element and a first traffic indication map information element at the same time. The first traffic indication map information element may be contained in the delivery traffic indication map information element and associated with the first traffic indication map group. In certain embodiments, the wireless device receives both a delivery traffic indication map information element and a first traffic indication map information element within a defined time interval. The first traffic indication map information element may be associated with the first traffic indication map group, and the defined time interval may have a duration such that the wireless device only wakes up once to receive both the delivery traffic indication map information element and the first traffic indication map information element. The defined time interval may be selected to prevent the wireless device from falling asleep between receiving the delivery traffic indication map information element and the first traffic indication map information element. 
       FIG. 8  is a block diagram illustrating a wireless device  110 , according to certain embodiments. Examples of wireless device  110  include a mobile phone, a smart phone, a PDA (Personal Digital Assistant), a portable computer (e.g., laptop, tablet), a sensor, a modem, a machine type (MTC) device/machine to machine (M2M) device, laptop embedded equipment (LEE), laptop mounted equipment (LME), USB dongles, other wireless device capable of D2D operation, or other device that can provide wireless communication. Wireless device  110  may also be referred to as a user equipment, a station, or a terminal in some embodiments. Wireless device  110  includes transceiver  810 , processor  820 , and memory  830 . In some embodiments, transceiver  810  facilitates transmitting wireless signals to and receiving wireless signals from an access node (e.g., via an antenna), processor  820  executes instructions to provide some or all of the functionality described above as being provided by wireless devices, and memory  830  stores the instructions executed by processor  820 . 
     Processor  820  may include any suitable combination of hardware and software implemented in one or more modules to execute instructions and manipulate data to perform some or all of the described functions of wireless device  110 . In some embodiments, processor  820  may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more applications, and/or other logic. Processor  820  may include analog and/or digital circuitry configured to perform some or all of the described functions of mobile device  110 . For example, processor  820  may include resistors, capacitors, inductors, transistors, diodes, and/or any other suitable circuit components. 
     Memory  830  is generally operable to store instructions, such as a computer program, software, an application including one or more of logic, rules, algorithms, code, tables, etc. and/or other instructions capable of being executed by a processor. Examples of memory  830  include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or or any other volatile or non-volatile, non-transitory computer-readable and/or computer-executable memory devices that store information. 
     Other embodiments of wireless device  110  may include additional components beyond those shown in  FIG. 8  that may be responsible for providing certain aspects of the wireless device&#39;s functionality, including any of the stronger interferer detection functionality described above and/or any additional functionality (including any functionality necessary to support the solution described above). 
     In certain embodiments, wireless device  110  may include one or more modules. For example, wireless device  110  may include a determining module, a communication module, a receiver module, an input module, a display module, and any other suitable modules. The determining module may perform the processing functions of wireless device  110 . For example, the determining module may determine an energy status for the wireless device. The determining module may include or be included in processor  820 . The determining module may include analog and/or digital circuitry configured to perform any of the functions of the determining module and/or processor  820 . The functions of the determining module described above may, in certain embodiments, be performed in one or more distinct modules. 
     The communication module may perform the transmission functions of wireless device  110 . The communication module may transmit messages to one or more access points  120  of network  100 . For example, the communication module may communicate an energy status of the wireless device to an access point. The communication module may include a transmitter and/or a transceiver, such as transceiver  810 . The communication module may include circuitry configured to wirelessly transmit messages and/or signals. In particular embodiments, the communication module may receive messages and/or signals for transmission from the determining module. 
     The receiving module may perform the receiving functions of wireless device  110 . For example, the receiving module may receive beacon information in a low-energy consumption format. The receiving module may include a receiver and/or a transceiver. The receiving module may include circuitry configured to wirelessly receive messages and/or signals. In particular embodiments, the receiving module may communicate received messages and/or signals to the determining module. 
     The input module may receive user input intended for wireless device  110 . For example, the input module may receive key presses, button presses, touches, swipes, audio signals, video signals, and/or any other appropriate signals. The input module may include one or more keys, buttons, levers, switches, touchscreens, microphones, and/or cameras. The input module may communicate received signals to the determining module. 
     The display module may present signals on a display of wireless device  110 . The display module may include the display and/or any appropriate circuitry and hardware configured to present signals on the display. The display module may receive signals to present on the display from the determining module. 
       FIG. 9  is a block diagram illustrating a network node  120 , according to certain embodiments. Examples of network node  120  include a wireless access point (e.g., a Wi-Fi access point, such as access point  120  described above), eNodeB, a node B, a base station, a low power node, a base station controller, a radio network controller, a relay, a donor node controlling relay, a base transceiver station (BTS), transmission points, transmission nodes, RRU, RRH, nodes in a distributed antenna system (DAS), a core network node, an MME, etc. Network node  120  may include one or more of transceiver  910 , processor  920 , memory  930 , and network interface  940 . In some embodiments, transceiver  910  facilitates transmitting wireless signals to and receiving wireless signals from a wireless device (e.g., via an antenna), processor  920  executes instructions to provide some or all of the functionality described above as being provided by an access node, memory  930  stores the instructions executed by processor  920 , and network interface  940  communicates signals to backend network components, such as a gateway, switch, router, Internet, Public Switched Telephone Network (PSTN), etc. 
     Processor  920  may include any suitable combination of hardware and software implemented in one or more modules to execute instructions and manipulate data to perform some or all of the described functions of network node  120 . In some embodiments, processor  920  may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more applications, and/or other logic. 
     Memory  930  is generally operable to store instructions, such as a computer program, software, an application including one or more of logic, rules, algorithms, code, tables, etc. and/or other instructions capable of being executed by a processor. Examples of memory  930  include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or or any other volatile or non-volatile, non-transitory computer-readable and/or computer-executable memory devices that store information. 
     In some embodiments, network interface  940  is communicatively coupled to processor  920  and may refer to any suitable device operable to receive input for network node  120 , send output from network node  120 , perform suitable processing of the input or output or both, communicate to other devices, or any combination of the preceding. Network interface  940  may include appropriate hardware (e.g., port, modem, network interface card, etc.) and software, including protocol conversion and data processing capabilities, to communicate through a network. 
     In certain embodiments, network node  120  may include a determining module, an access group allocation module, a communication module, a receiving module, and any other suitable modules. In some embodiments, one or more of the determining module, the access group allocation module, the communication module, the receiving module, and any other suitable modules may be implemented using one or more processors  920  of  FIG. 9 . 
     In general, the determining module may perform the processing function of network node  120 . For example, the determining module may determine an energy status of a wireless device. As another example, the determining module may determine an access group of a plurality of access groups to which to allocate the wireless device. As yet another example, the determining module may determine whether a load of the first access group is below a load threshold. In general, the access group allocation module may allocate a wireless device to a first access group upon determining that the wireless device is a low-energy device. In certain embodiments, the determining module and the access group allocation module may be combined into a single module. 
     The communication module may perform the transmission functions of network node  120 . The communication module may transmit messages to one or more of wireless devices  110  or to other network nodes. For example, the communication module may communicate beacon information to the first access group in the low energy consumption format. The communication module may include a transmitter and/or a transceiver, such as transceiver  1210 . The communication module may include circuitry configured to wirelessly transmit messages and/or signals. In particular embodiments, the communication module may receive messages and/or signals for transmission from the determining module or the access group allocation module. 
     The receiving module may perform the receiving functions of network node  120 . The receiving module may receive any suitable information from a wireless device or other network node. For example, the receiving module may receive a message including information about the energy status of the wireless device. The receiving module may include a receiver and/or a transceiver. The receiving module may include circuitry configured to wirelessly receive messages and/or signals. In particular embodiments, the receiving module may communicate received messages and/or signals to the determining module. 
     Other embodiments of network node  120  may include additional components beyond those shown in  FIG. 9  that may be responsible for providing certain aspects of the network node&#39;s functionality, including any of the interferer detection functionality described above and/or any additional functionality (including any functionality necessary to support the solution described above). The various different types of network nodes may include components having the same physical hardware but configured (e.g., via programming) to support different radio access technologies, or may represent partly or entirely different physical components. 
     Modifications, additions, or omissions may be made to the systems and apparatuses disclosed herein without departing from the scope of the disclosure. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. Additionally, operations of the systems and apparatuses may be performed using any suitable logic comprising software, hardware, and/or other logic. As used in this document, “each” refers to each member of a set or each member of a subset of a set. 
     Modifications, additions, or omissions may be made to the methods disclosed herein without departing from the scope of the disclosure. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. 
     Although this disclosure has been described in terms of certain embodiments, alterations and permutations of the embodiments will be apparent to those skilled in the art. Accordingly, the above description of the embodiments does not constrain this disclosure. Other changes, substitutions, and alterations are possible without departing from the spirit and scope of this disclosure, as defined by the following claims. 
     Abbreviations used in the preceding description include: 
     STA Station 
     AP Access Point 
     DL Downlink 
     DTIM Delivery Traffic Indication Map 
     STA Station 
     TIM Traffic Indication Map 
     UL Uplink 
     WLAN Wireless Local Area Network