Patent Publication Number: US-2021176705-A1

Title: Energy efficient network connectivity maximization

Description:
RELATED APPLICATION 
     This application is a divisional of and claims priority to U.S. patent application Ser. No. 13/407,181, filed on Feb. 28, 2012, the disclosure of which is incorporated by reference herein. 
    
    
     BACKGROUND 
     A networked electronic device typically includes a wireless transceiver that enables the electronic device to transmit data and receive data from other devices over a network. In many instances, the wireless transceiver may be a wireless network interface controller (NIC) that includes a Wireless Fidelity (Wi-Fi) IEEE 802.11 radio. The Wi-Fi radio may enable the electronic device to connect to the Internet via multiple wireless network access points, also known as hotspots, which may be distributed over a geographical area. However, the communication range of each wireless network access point is generally limited, which may pose a problem when the electronic device is a mobile device that is frequently carried to many different locations by a user. 
     For example, in order to maximize the time for which a mobile electronic device is connected to the network, the network interface controller and the main processor of the electronic device may remain powered on even when no data is being communicated over the network. The constant powering of the network interface controller and the main processor may enable the electronic device to conduct searches for new wireless access points as current wireless access points recede out of range. These searches for new wireless access points as the electronic device travels through different geographic areas may prematurely deplete the battery of the electronic device due to the constant power consumption by the network interface controller and the main processor. 
     Alternatively, the user of the electronic device may manually power off the network interface controller of the electronic device, and then periodically turn on the network interface controller to search for new wireless access points at each new geographical location. However, such efforts may be cumbersome and inefficient as the user may experience time delays associated with the initiation and performance of each new search. Further, applications on the electronic device that rely on push data, such as email programs and instant messaging programs, may not promptly receive new data due to the network interface controller being temporarily disabled. 
     SUMMARY 
     Described herein are techniques for maximizing the network connectivity of an electronic device while minimizing the amount of power consumed by the electronic device in acquiring or maintaining the communication connection. The electronic device may be a mobile electronic device. The electronic device may use a Wi-Fi transceiver to connect to a network, such as the Internet. The wireless transceiver may be a wireless network interface controller (NIC) that includes a Wi-Fi radio. The electronic device may use the network interface controller and the main processor of the electronic device to not only communicate data over the network, but also to search for new wireless access points as the mobile electronic device moves about different geographical regions. Accordingly, the network interface controller and the main processor of the electronic device may consume considerable power while acquiring or maintaining network connectivity to the network. 
     In a scenario in which the electronic device is attempting to acquire network connectivity with a wireless access point, power consumption may be minimized by powering off the main processor of the electronic device, and periodically powering on the network interface controller to search for one or more wireless access points that are pre-selected based on a usage context of the electronic device. Thus, since the network interface controller generally consume less power than the main processor of the electronic device, periodically powering on the network interface controller while the main processor is powered off may reduce overall energy consumption, 
     In such a scenario, the electronic device may select at least one wireless access point identifier for inclusion in a list of wireless access point identifiers and populate the network interface controller memory with the list. The at least one access point identifier may be selected based at least on contextual data related the electronic device using the main processors. The electronic device may then power off the main processor. The electronic device may further periodically cycle the network interface controller between a power on state and a power saving state, so that the network interface controller may perform a scan for wireless access points that match the wireless access point identifiers during the power on state. In some instances, such a scan for wireless access points that match the wireless access point identifiers in the list may consume less energy than a scan for any available wireless access point. The electronic device may additionally power on the main processor in response to the network interface controller detecting a wireless access point that matches a corresponding wireless access point identifier in the network interface controller memory. 
     In another scenario in which the electronic device is connected to a wireless access point, power consumption may be minimized by using different techniques. In at least one instance, the electronic device may cycle a network interface controller of the electronic device between a power on state and a power off state without terminating the communication connection. Accordingly, the electronic device may further power on a main processor of the electronic device when the network interface controller detects a beacon during the power on state that indicates the wireless access point has a buffered data frame for the electronic device. 
     In another instance, power consumption minimization may include powering of the main processor of the electronic device, and placing the network interface controller into a power saving state for time intervals that vary according to a robustness of the communication connection between the wireless access point and the electronic device. In such an instance, the electronic device may calculate an adaptive sleep interval for a network interface controller of the electronic device based on a robustness of the communication connection. The electronic device may then switch the network interface controller of the electronic device from a power saving state that lasts the adaptive sleep interval to a power on state. Accordingly, the electronic device may power on a main processor of the electronic device when the network interface controller detects a beacon during the power on state that indicates the wireless access point has a buffered data frame for the electronic device. 
     Thus, by minimizing the amount of power consumed by an electronic device in acquiring or maintaining network connectivity with a network, the duration of the overall network connectivity of the electronic device with the network may be increased. Further, the power consumption minimization may also increase the battery longevity of the electronic device, resulting in additional convenience and productivity for the user of the electronic device. 
     This Summary is provided to introduce a selection of concepts in a simplified form that is further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The use of the same reference number in different figures indicates similar or identical items. 
         FIG. 1  is a block diagram that illustrates an example scheme that implements energy efficient network connectivity maximization for an electronic device in a connected scenario and a disconnected scenario. 
         FIG. 2  is an illustrative diagram that shows example modules and components of the electronic device that minimizes power consumption during acquisition and maintenance of network connectivity with a wireless access point. 
         FIG. 3  is an illustrative diagram that shows search techniques employed by the electronic device that minimizes power consumption during a search for available wireless access points 
         FIG. 4  is a flow diagram that illustrates an example process for implementing a periodic power off mode that periodically cycles a network interface controller of the electronic device on and off to reduce power consumption. 
         FIG. 5  is a flow diagram that illustrates an example process for implementing an adaptive sleep mode that places the network interface controller of the electronic device into a power saving state for varying time intervals to reduce power consumption. 
         FIG. 6  is a flow diagram that illustrates an example process for determining whether to place the electronic device into the periodic power off mode or the adaptive sleep mode based on usage context of the electronic device. 
         FIG. 7  is a flow diagram that illustrates an example process for reducing power consumption by periodically powering on the network interface controller to search for one or more wireless access points that are pre-selected based on contextual data. 
     
    
    
     DETAILED DESCRIPTION 
     Described herein are techniques for maximizing the network connectivity of an electronic device while minimizing the amount of power consumed by the electronic device in acquiring or maintaining the communication connection. The electronic device may be a mobile electronic device. The electronic device may use a Wi-Fi transceiver to connect to a network, such as the Internet. The wireless transceiver may be a wireless network interface controller (NIC) that includes a Wi-Fi radio. The electronic device may use the network interface controller and the main processor of the electronic device to not only communicate data over the network, but also to search for new wireless access points as the electronic device moves about a geographical region. Accordingly, the network interface controller and the main processor of the electronic device may consume considerable power while acquiring or maintaining network connectivity to the network. 
     In some embodiments, the techniques may reduce the power consumption of the network interface controller and the main processor of the electronic device while the electronic device is seeking to acquire network connectivity with a wireless access point. In such embodiments, the techniques may include selecting a list of wireless access points based on data related to a current usage context of the electronic device. Subsequently, the main processor of the electronic device may be powered off and the network interface controller may be placed in a power saving state. The network interface controller may then be periodically power on to search for one or more of the wireless access points in the list. The list may be periodically updated to adapt to changes in the usage context of the electronic device. 
     In other embodiments, the techniques may reduce the power consumption of the network interface controller and the main processor of the electronic device while the electronic device is engaged in an active communication connection with the network through a wireless access point. In some instances, the techniques may include powering off the main processor of the electronic device, and periodically cycling the network interface controller on and off. In such instances, a network stack of the electronic device may be configured to refrain from disconnecting the network connectivity with the wireless access point even during intervals in which the network interface controller is powered off. 
     In other instances, the techniques may include powering of the main processor of the electronic device, and placing the network interface controller into a power saving state for time intervals that vary according to a robustness of the communication connection between the ireless access point and the electronic device. In such instances, the robustness of the communication connection may be directly measured based on the signal strength of the communication signal emanating from the wireless access point that is acquired by the electronic device  106 . Alternatively, the robustness of the communication connection may be indirectly measured by the proportions of data beacons transmitted by the wireless access point that failed to reach the electronic device. 
     Accordingly, by minimizing the amount of power consumed by an electronic device in acquiring or maintaining network connectivity with a network, the duration of the overall network connectivity of the electronic device with the network may be increased. Further, the power consumption minimization may also increase the battery longevity of the electronic device, resulting in additional convenience and productivity for the user of the electronic device. Various examples of techniques for implementing energy efficient network connectivity maximization in accordance with the embodiments are described below with reference to  FIGS. 1-7 . 
     Example Scheme 
       FIG. 1  is a block diagram that illustrates an example scheme  100  that implements energy efficient network connectivity maximization for an electronic device in a connected scenario  102  and a disconnected scenario  104 . The electronic device  106  may be a general purpose computer, such as a tablet computer, a laptop computer, and so forth. However, in other embodiments, the electronic device  106  may be one of a smart phone, a game console, a personal digital assistant (PDA), or any other electronic device that is capable of interacting with a network via a network interface controller. 
     In various embodiments, the electronic device  106  may include at least one main processor  108  and a network interface controller  110 , among other components. The main processor  108  may process input data that is inputted into the electronic device  106  or generated by another component of the electronic device  106  to produce output data. In turn, the output data may be presented to a user of the electronic device  106  or processed by another component of the electronic device  106 . For example, in an instance in which the electronic device  106  is a smart phone, the main processor  108  may execute various applications that are stored in the smart phone so that the smart phone may perform communication and/or productivity functions. 
     The network interface controller  110  may enable the electronic device  106  to establish and carry out communication with other electronic devices over a network. In various embodiments, the network interface controller  110  may include a Wi-Fi radio  112  that provides the electronic device  106  with the ability to communicate with one or more wireless access points, such as a Wi-Fi wireless access point  114 . 
     The electronic device  106  may operate in several different states. In an active state, the electronic device  106  may be processing data and carrying out functionalities. For example, in the instance in which the electronic device  106  is a smart phone, the electronic device  106  may be in the active state when the user is using the electronic device  106  to make a phone call, check email, browse a web site, compose a text message, and/or so forth. 
     However, the electronic device  106  may also frequently operate in a standby state. In the standby state, the electronic device  106  may be configured to minimize energy consumption while keeping the electronic device  106  ready to resume the active state. Nevertheless, the electronic device  106  may be often configured to perform tasks even in the standby state. In various scenarios, the main processor  108  and the network interface controller  110  may remain powered on in order to constantly seek out and/or maintain network connectivity with one or more WI-FI wireless access points, such as the wireless access point  114 . In this way, communication data (e.g., emails, incoming VOIP call alerts, text messages) may be pushed to or pulled by applications on the electronic device  106  even when the electronic device  106  is in the standby state. However, such acquisition or maintenance of network connectivity in the standby state, especially when the electronic device  106  is a mobile device that moves between different Wi-Fi wireless access points, may dramatically decrease the battery life of the electronic device  106 . 
     For example, during an establishment of a communication connection  116  with the wireless access point  114 , the electronic device  106  may initially authenticate to the wireless access point  114 . During authentication, the network interface controller  110  may send an authentication request to the wireless access point  114 . The authentication request may include the station identifier of the electronic device  106  (e.g., MAC address of the network interface controller  110 ). In turn, the wireless access point  114  may answer with an authentication response message that indicates success or failure of the authentication. 
     In instances in which shared key authentication is implemented between the electronic device  106  and the wireless access point  114 , the authentication may also include the passing of the shared key to the wireless access point  114 . For example, such shared key may be a Wired Equivalent Privacy (WEP) key or a Wi-Fi Protected Access (WPA) key. 
     Once the authentication is completed, the network interface controller  110  may send an association request to the wireless access point  114  to gain access to the network. Upon receiving the association request, the wireless access point  114  may record the station identifier of the electronic device  106  (e.g., the MAC address of the network interface controller  110 ) so that data packets or frames may be delivered to the electronic device  106 . For instance, when the wireless access point  114  grants association to the electronic device  106 , the wireless access point  114  may respond to the electronic device  106  with a status code that indicates successful association, as well as an association ID (AID). Otherwise, the wireless access point  114  may respond to the electronic device  106  with an association failure status code. 
     Further during the association, the electronic device  106  and the wireless access point  114  may further establish a target beacon transmission time (TBTT) and/or a listen interval. In various embodiments, the wireless access point  114  may buffer data frames for the electronic device  106  so that the network interface controller  110  may cycle between a power saving state and a power on state to save energy without missing any buffered data frames from the wireless access point  114 . While in the power saving state, the network interface controller  110  is not completely powered off, but is in an inactive state to conserve power. Further, the main processor  108  of the electronic  102  may be powered off while the network interface controller  110  is cycling between the power saving state and the power on state to further save energy. 
     The TBTT may be the time at which the wireless access point  114  sends a beacon to the electronic device  106 . Each beacon may inform the electronic device  106  whether the wireless access point  114  has buffered a data frame for the electronic device  106 . For example, the beacon may be a frame of data that includes a buffer status indicator, in which the buffer status indicator may have a value of “0” when no data frame is buffered, and a value of “1” when a data frame is buffered. Accordingly, the time difference between two TBTTs may be known as the beacon interval. 
     In turn, the network interface controller  110  of the electronic device  106  may provide a listen interval to the wireless access point  114 . The listen interval may indicate to the wireless access point  114  the number of beacon intervals that the electronic device  106  desires to remain in the power saving state. Accordingly, the wireless access point  114  may be configured to hold a buffered data frame for at least the duration of the listen interval before discarding the data frame. In this way, the electronic device  106  may enter into the power saving state, and then periodically power on to check for beacons at regular intervals. Thus, if a received beacon does not indicate that a data frame is buffered, the network interface controller  110  may resume the power saving state until the next beacon check. However, if a received beacon does indicate that a data frame is buffered, the network interface controller  110  may remain powered on to receive the buffered data frame, and the network interface controller  110  may further trigger the main processor  108  to power on and process the received data frame. 
     Nevertheless, while the use of the TBTT and the listen intervals may provides some power saving benefits, additional power saving benefits may be realized from the use of a periodic power off mode  118  and/or an adaptive sleep mode  120  for the network interface controller  110  when the electronic device  106  is in the connected scenario  102 . In the connected scenario  102 , the electronic device  106  may have already established network connectivity with the wireless access point  114 . 
     The periodic power off mode  118  is implemented when the electronic device  106  is in a standby state. For example, the user may put the electronic device  106  into the standby state by activating a sleep key of a user interface of the electronic device  106 . During the periodic power off mode  118 , the main processor  108  of the electronic device  106  may be powered off. Further, rather than cycling between the power saving state and the power on state to save energy, the network interface controller  110  may be alternatively powered on and powered off at regular intervals. Each of the power off durations may be longer than the listen interval that the network interface controller  110  established with the wireless access point  114  at an association phase. 
     Thus, by using these longer durations and completely powering off the network interface controller  110  rather than putting the controller in the power saving state in each of the durations, the periodic power off mode  118  may achieve greater power conservation than is possible with the use of TBTT and the listen intervals. However, because the network interface controller  110  is intermittently powered off, the electronic device  106  may miss beacons that indicate that the wireless access point  114  has buffered data frames for the electronic device  106 . As a result, the wireless access point  114  may discard such buffered data frames that are intended for the electronic device  106 . 
     Nonetheless, the possibility that the wireless access point  114  may discard one or more data frames during an interval when the network interface controller  110  is powered off may be offset by the communication redundancy of an application that sends the data frames. For example, the application may be a VOIP communication program on a network server that is alerting the electronic device  106  of an incoming call. Accordingly, the VOIP communication program may continuously sent out multiple incoming call alert data frames that are intended for the electronic device  106 . The multiple incoming call alert data frames are buffered by the wireless access point  114 . The electronic device  106  may fail to receive one or more buffered incoming call alert data frames before they are discarded by the wireless access point  114  due to the network interface controller  110  being powered off. However, the network interface controller  110  may eventually detect a beacon from the wireless access point  114  that indicates an incoming call alert data frame is buffered during a power on interval. The network interface controller  110  may subsequently receive the data frame and trigger the main processor  108  to process the data frame. Other examples of delay tolerant applications that compensate for the possibility of missed buffered data frames when the electronic device  106  is operating in the periodic power off mode  118  may include text messaging programs, email programs, and/or so forth. Accordingly, the periodic power off mode  118  may provide a viable way for the electronic device  106  to conserve additional energy during the connected scenario  102 . 
     In other embodiments, the adaptive sleep mode  120  provides another way for the electronic device  106  to conserve additional energy during the connected scenario  102 . In the adaptive sleep mode  120 , the network interface controller  110  may establish, during an association with the wireless access point  114 , a standard TBTT and a standard beacon interval. The network interface controller  110  may also establish a buffer duration for the wireless access point  114  to buffer each data frame that is multiple times the length (e.g., 10 times) of the beacon interval during the association. 
     Subsequently, in order to save power while maintaining the network connectivity with the wireless access point  114  when the electronic device  106  is in a standby state, the network interface controller  110  may be placed in a power saving state for multiple adaptive sleep intervals. Each of the adaptive sleep intervals (e.g., adaptive sleep interval  122 ) is a time between two power ups of the network interface controller  110  to listen for beacons, and may be stipulated to never exceed the buffer duration established with the wireless access point  114 . Further, the network interface controller  110  may proportionally vary the length of each adaptive sleep interval based on the robustness of the communication connection  116  between the electronic device  106  and the wireless access point  114 . Thus, the stronger the communication connection  116 , the longer the adaptive sleep interval, while the weaker the communication connection  116 , the shorter the adaptive sleep interval. 
     The variation of each adaptive sleep interval may be based on the principle that when the communication connection  116  is strong, the likelihood that the network interface controller  110  may fail to detect a beacon is small, so that the network interface controller  110  is more likely to afford to ignore some of the beacons that are sent out by the wireless access point  114  without missing a buffered data frame. On the other hand, when the communication connection  116  is weak, the likelihood that the network interface controller  110  may fail to detect a beacon becomes greater, so that the network interface controller  110  is less likely to afford to ignore some the beacons. 
     Thus, by using adaptive sleep intervals rather than fixed length listen intervals, the adaptive sleep mode  120  may enable the main processor  108  to be powered off and the network interface controller  110  to be placed in the power saving state for longer durations during the connected scenario  102 . 
     While the periodic power off mode  118  and the adaptive sleep mode  120  may enable the electronic device  106  to obtain greater power savings during the connected scenario  102 , they do not afford the electronic device  106  any power conservation benefits during the disconnected scenario  104 . In the disconnected scenario  104 , the electronic device  106  may be unconnected to any wireless access points, and is actively searching for wireless access points to establish network connectivity. Accordingly, the main processor  108  and the network interface controller  110  may be powered on and searching for available wireless access points. 
     As shown with respect to the disconnected scenario  104 , the electronic device  106  may take advantage of Wi-Fi offloading to reduce energy consumption while searching for the available wireless access point  124 . Wi-Fi offload enables a Wi-Fi offloading capable network interface controller, such as the network interface controller  110 , to store selected wireless access point identifiers in an offload list  126  in the memory of the network interface controller. The wireless access point identifiers may be Wi-Fi Service Set Identifiers (SSIDs) or Wi-Fi Basic Service Set Identifier (BSSIDs). A SSID may be a public name of a wireless access point, while the BSSID may be a Media Access Control (MAC) address of a wireless access point. Accordingly, while a set of wireless access points may in some instances share a common SSID, each wireless access point generally has a unique BSSID. The wireless access point identifiers may be selected for storage in the offload list  126  by the main processor  108  of the electronic device  106 , and stored into the offload list  126  by a network interface controller processor of the network interface controller  110 . The wireless access point identifiers may be selected from master identifier data  128  based on the usage context of the electronic device  106 . In various embodiments, the usage context may include a current location of the electronic device  106 , a predicted location of the electronic device  106 , a time of the day, upcoming events or appointments of the user indicated by a task management application on the electronic device  106 , and/or so forth. The master identifier data  128  may include identifier information that is stored in the electronic device  106  and/or identifier information that is stored on an external server, such as a server at a data center that is in a computing cloud. 
     Once the selected wireless access point identifiers have been stored in the offload list  126 , the main processor  108  may be powered off and the network interface controller  110  may be placed in a power saving state. Subsequently, the network interface controller  110  may be periodically powered on to search for one or more wireless access points that match the wireless access point identifiers. Thus, if the network interface controller  110  is able to discover a matching wireless access point, the network interface controller  110  may then trigger the main processor  108  to power on in order to establish network connectivity with the discovered wireless access point. In some embodiments, once the network connectivity is established, the electronic device  106  may enter the periodic power off mode  118  or the adaptive sleep mode  120 . Otherwise, the network interface controller  110  may power off or go back into power saving state for a predetermined time interval until the next power on to search for one or more matching wireless access points. 
     Additionally, the main processor  108  may be periodically powered on to refresh the offload list  126  that is stored in the memory of the network interface controller  110 . Each of the refreshments of the list may take into consideration any changes in the usage context of the electronic device  106 . Thus, by taking advantage of an offloading capable network interface controller and using a network interface controller processor on the controller to discover available wireless access points, the electronic device  106  may further reduce power consumption by periodically powering off the main processor  108  of the electronic device  106  in the disconnected scenario  104 . 
     In some embodiments, the network interface controller  110  may use a probabilistic data structure scheme to increase the number of wireless access point identifiers that are monitored for discovering matching wireless access points. For example, the memory capacity of the memory  206  that stores the offload list  126  may be limited to the storage of 10 wireless access identifiers. In such an example, the network interface controller  110  may use a Bloom filter to tradeoff false positives in exchange for the ability to store more than 10 wireless access identifiers in the same amount of memory  206  for monitoring by the network interface controller  110 . As used herein, a false positive means that the network interface controller  110  may power on the main processor  108  even though a newly discovered identifier does not actually match one of the monitored wireless access identifiers stored in the memory  206 . Thus, the tradeoff is between minimizing a false positive rate and maximizing a number of monitored wireless access point identifiers. 
     In such embodiments, the network interface controller  110  may implement the probabilistic data structure by maintaining a bit vector, and hashing the wireless access identifiers to be monitored using a set of hash functions. For each hash implemented using a hash function, the network interface controller  110  may flip a corresponding bit in the bit vector. Further, when a wireless access point is newly discovered by the network interface controller  110  during a search, the network interface controller  110  may hash an identifier of the newly discovered wireless access point. Following the hash, the network interface controller  110  may check whether the resulting corresponding bits are all “1”s. In the event that the corresponding bits are all “1”s, the network interface controller  110  may power on the main processor  108 . It will be appreciated that having all the bits equal to “1” does not guarantee an exact match between the newly discovered wireless access point and a wireless access point identifier stored in the memory  206 . Instead, such a result may indicate that there is a high probability that the newly discovered wireless access point matches a wireless access point identifier stored in the memory  206 . 
     Electronic Device Components 
       FIG. 2  is an illustrative diagram that shows example modules and components of the electronic device  106  that minimizes power consumption during acquisition and maintenance of network connectivity with a wireless access point. The electronic device  106  may includes at least one main processor  108 , a network interface controller  110 , main memory  202 , and/or user controls that enable a user to interact with the electronic device. In turn, the network interface controller  110  may include a NIC processor  204 , a memory  206 , a periodic power off component  208 , an adaptive sleep component  210 , a trigger component  212 , a periodic search component  214 , and a probabilistic match component  216 . The memory  206  may store the offload list  126 , among other data. The components of the network interface controller  110  may use the NIC processor  204  to perform tasks and functionalities. 
     Each of the main memory  202  and memory  206  may be implemented using computer readable media, such as computer storage media. Computer-readable media includes, at least, two types of computer-readable media, namely computer storage media and communication media. Computer storage media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules, or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information for access by an electronic device. In contrast, communication media may embody computer readable instructions, data structures, program modules, or other data in a modulated data signal, such as a carrier wave, or other transmission mechanism. As defined herein, computer storage media does not include communication media. 
     The main memory  202  may store a mode selection module  218 , a list selection module  220 , a network interface module  222 , a user interface module  224 , a power management module  226 , and one or more applications  228 . Each of the modules may include routines, programs instructions, objects, scripts, and/or data structures that are executable by the main processor  108  to perform particular tasks or implement particular abstract data types. 
     The network interface controller  110  may use the periodic power off component  208  to implement the periodic power off mode  118 . In various embodiments, the periodic power off component  208  may include hardware and/or software instructions that cycle the network interface controller  110  on and off at regular intervals in the connected scenario  104 . In some embodiments, the software instructions may be stored in the memory  206 . The network interface controller  110  may listen for beacons that indicate the presence or absence of buffered data frames from the wireless access point  114  during each power on interval of the network interface controller  110 . 
     Accordingly, when the network interface controller  110  detects a beacon that indicates a data frame is buffered for the electronic device  106 , the network interface controller  110  may receive the buffered data frame. Further, the trigger component  212  of the network interface controller  110  may also trigger the main processor  108  to power on and process the received data frame. 
     The proper operation of the periodic power off component  208  may be dependent on the configuration of the network interface module  222  in the main memory  202 . The network interface module  222  may implement a hierarchical abstraction of a network stack  234  that includes, from bottom to top, a link layer  236 , an Internet layer  238 , a transport layer  240 , and an application layer  242  that enables the electronic device  106  to receive and transmit data over a network. In at least one embodiment, the link layer  236  may be configured to prevent the rest of the network stack from disconnecting the electronic device  106  from the wireless access point  114 , when the network interface controller  110  in an underlying physical layer  244  periodically powers off during the periodic power off mode  118 . In other words, the link layer  236  may be configured to refrain from releasing an IP address that the network interface controller  110  has previously obtained from the wireless access point  114 , and/or perform any other network connectivity termination activities that the link layer  236  would normally perform when the network interface controller  110  powers off. 
     In other embodiments, the network interface module  222  may implement an additional filter layer  246  in the network stack  234  beneath the link layer  236 . The filter layer  246  may prevent the remaining layers in the network stack from becoming aware of the powering off of the network interface controller  110  during the periodic power off mode  118 . For example, the filter layer  246  may block a media disconnect message initiated by the physical layer  244  from reaching the rest of the network stack  234  when the network interface controller  110  powers off. In this way, the link layer  236  may be prevented from releasing an IP address and/or perform other network connectivity termination activities. 
     As described above, the possibility that the wireless access point  114  may discard one or more data frames during an interval when the network interface controller  110  is powered off may be offset by communication redundancy of applications, such as the application  248 , that send the data frames. The application  248  may reside on a service server  250 . For example, the application  248  may be a VOIP communication program that continuously sent out multiple incoming call alert data frames  252 ( 1 )- 252 (N) that are intended for the electronic device  106 . As such, the wireless access point  114  may discard one or more of the data frames  252 ( 1 )- 252 (N), such as the data frames  252 ( 1 )- 252 ( 2 ), because the network interface controller  110  was powered off. However, the network interface controller  110  may nevertheless receive the incoming call alert data frame  252 (N) during a power on interval so that the user of the electronic device  106  does not miss the corresponding VOIP call. 
     The network interface controller  110  may use the adaptive sleep component  210  to implement the adaptive sleep mode  120 . In various embodiments, the adaptive sleep component  210  may include hardware and/or software instructions that vary the adaptive sleep intervals of the network interface controller  110  during the adaptive sleep mode  120 . The sleep intervals may be varied based on the robustness of the communication connection  116  between the electronic device  106  and the wireless access point  114 . In some embodiments, the software instructions may be stored in the memory  206 . 
     The robustness of the communication connection  116  may be assessed based on signal strength of the communication signal. As such, the adaptive sleep component  210  may measure the strength of the communication signal transmitted by the wireless access point  114  during the adaptive sleep mode  120 . Accordingly, the stronger a strength of the communication signal, the longer the adaptive sleep interval that is implemented by the adaptive sleep component  210 . Conversely, the weaker the strength of the communication signal, the shorter the adaptive sleep interval that is implemented by the adaptive sleep component  210 . 
     In some embodiments, the duration of the adaptive sleep interval may be directly proportional to the strength of the communication signal transmitted by the wireless access point  114 . For example, given that the data frame buffer duration of the wireless access point  114  is one second and the beacon interval is 100 milliseconds, the wireless access point  114  may transmit 10 beacons per second. In such an example, when the signal strength of the communication signal transmitted by the wireless access point  114  is 90% strength, the adaptive sleep component  210  may adopt 900 milliseconds as the adaptive sleep interval for the network interface controller  110 . However, when the signal strength of the communication signal transmitted by the wireless access point  114  is 10% strength, the adaptive sleep component  210  may adopt 100 milliseconds as the adaptive sleep interval for the network interface controller  110 . 
     Alternatively, the robustness of the communication connection  116  may be measured based on a beacon loss rate detected by the adaptive sleep component  210 . The beacon loss rate may be a percentage of expected beacons that the network interface controller  110  failed to receive during a test interval. In one example, the adaptive sleep component  210  may have knowledge that the wireless access point  114  is configured to transmit four beacons  254 ( 1 )- 254 ( 4 ) in a test interval  256  of 400 milliseconds, i.e., a beacon every 100 milliseconds. However, the network interface controller  110  only received two beacons (e.g., beacons  254 ( 2 ) and  254 ( 4 )) during the test interval. Based on these figures, the adaptive sleep component  210  may determine that the beacon loss rate is 50%. 
     Subsequently, after each test interval, the adaptive sleep component  210  may adjust the adaptive sleep interval based on the beacon loss rate during the test interval. In various embodiments, a higher beacon loss rate may result in a shorter adaptive sleep interval, while a lower beacon loss rate may result in a longer adaptive sleep interval. In at least one embodiment, the adaptive sleep interval may be inversely proportional to the beacon loss rate. For example, when the beacon loss rate is 10%, the adaptive sleep component  210  may adopt 900 milliseconds as the adaptive sleep interval for the network interface controller  110 . However, when the signal strength of the communication signal transmitted by the wireless access point  114  is 90% on a standardized scale, the adaptive sleep component  210  may adopt 100 milliseconds as the adaptive sleep interval for the network interface controller  110 . 
     In at least one embodiment, the adaptive sleep component  210  may conduct a beacon loss rate test following a power saving interval to determine the length of the next adaptive sleep interval. In this way, the adaptive sleep component  210  may adjust to changes in the robustness of the network connectivity between the electronic device  106  and the wireless access point  114 . 
     However, when the network interface controller  110  detects a beacon that indicates a data frame is buffered for the electronic device  106 , the network interface controller  110  may receive the buffered data frame. Further, the trigger component  212  of the network interface controller  110  may also trigger the main processor  108  to power on and process the received data frame. 
     The mode selection module  218  may enable the electronic device  106  to select the periodic power off mode  118  or the adaptive sleep mode  120  to implement by the network interface controller  110 . Such a determination may be made when the electronic device  106  is to be placed in a standby state. The mode selection module  218  may make a determination as to which mode to implement based on the usage context of the electronic device  106 . In various embodiments, the mode selection module  218  may command the network interface controller  110  to apply the adaptive sleep mode  120  when there is a high likelihood (e.g., over 50% likelihood) that the electronic device  106  is to be used again, i.e., powered on, within a particular period of time in the future. On the other hand, the mode selection module  218  may apply the periodic power off mode  118  when there is a low likelihood (e.g., 50% or less likelihood) that the electronic device  106  is to be powered on within the particular period of time in the future. This selection practice may be based on an observation that while the periodic power off mode  118  conserves more energy than the adaptive sleep mode  120 , powering on the network interface controller  110  to resume network connectivity after powering off may take more time and processing overhead than power on the network interface controller  110  from a power saving state. 
     The mode selection module  218  may determine the likelihood that the electronic device  106  is to be powered on again within a particular period of time in the future based on usage context of the electronic device  106 . Such usage context may include factors such as a time of day, a location of the electronic device  106  (e.g., home or office), a predicted location of the electronic device  106 , the presence or absence of an appointment or an event noted in a task management application on the electronic device  106 , prior usage patterns of the electronic device  106 , and/or other relevant factors. In some embodiments, the mode selection module  218  may also have the ability to switch the electronic device  106  between the modes at a future time based on predicted usage context of the electronic device  106 . For example, the mode selection module  218  may place the network interface controller  110  in the adaptive sleep mode  120  for the first 10 minutes after the user puts the electronic device  106  in a standby state, then switch the network interface controller  110  to the periodic power off mode  118  after the elapse of the 10 minutes, or vice versa 
     The list selection module  220  may configure the network interface controller  110  to efficiently search for wireless access points  124  during the disconnected scenario  104 . In operation, the list selection module  220  may select wireless access point identifiers for offloading to the network interface controller  110  from the master identifier data  128 . The master identifier data  128  may include the identifiers of wireless access points that are available in various geographical regions. The identifiers of the master identifier data  128  may include SSIDs and/or BSSIDs. The master identifier data  128  may be stored on an access point data server  258  and/or in the data store  230  of the electronic device  106 . The access point data server  258  may be a server that is a part of a computing cloud. 
     In various embodiments, the list selection module  220  may select identifiers from the master identifier data  128  based on contextual data  232  related to the electronic device  106 . The contextual data  232  may include global positioning system (GPS) data that is supplied by a GPS component of the electronic device  106 . The electronic device  106  may prompt the user for consent via the user interface module  224  prior to collecting the GPS data. The GPS data may provide information on a current location, direction of travel, speed of travel, road of travel, and/or so forth. Alternatively or concurrently, the contextual data  232  may also include historical data on wireless access points that the electronic device  106  connecting to, including the geographical locations of such wireless access points, durations of connectivity, and/or so forth. 
     In some embodiments, the contextual data  232  may also include information that is supplied by the applications  228  that are on the electronic device  106 . Such information may include appointments or booked events of the user of the electronic device  106 , travel plans of the user, and/or other scheduling information of the user that may be useful in projecting one or more future locations of the user. 
     Accordingly, the list selection module  220  may process the contextual data  232  to select identifiers for placement in the offload list  126 . In some embodiments, the list selection module  220  may use a conditional probability algorithm to predict expected directions of travel, and in turn, expected locations of the electronic device  106 , based on previously connected wireless access points of the electronic device  106 . 
     In other embodiments, the list selection module  220  may use other machine learning and/or classification algorithms to predict locations of the electronic device  106  based on the contextual data  232 . The machine learning algorithms may include supervised learning algorithms, unsupervised learning algorithms, semi-supervised learning algorithms, and/or so forth. The classification algorithms may include support vector machines, neural networks, expert systems, Bayesian belief networks, fuzzy logic, data fusion engine, and/or so forth. In additional embodiments, the list selection module  220  may employ one or more of directed and undirected model classification approaches, such as naïve Bayes. Bayesian networks, decision trees, neural networks, fuzzy logic models, and/or other probabilistic classification models. 
     Once the list selection module  220  has predicted a location for the electronic device  106 , the list selection module  220  may select identifiers of wireless access points that correspond to the predicted location from the master identifier data  128 . The list selection module  220  may further populate the offload list  126  with the identifiers of the corresponding wireless access points. The selection of the identifiers of wireless access points that correspond to a predicted location is illustrated in  FIG. 3 . 
       FIG. 3  is an illustrative diagram that shows techniques employed by the electronic device  106  during a search for available wireless access points that correspond to a predicted location of the electronic device  106 . In some embodiments, the list selection module  220  may use a nearest distance search  302  to select a predetermined number of identifiers from the master identifier data  128 . The selected identifiers may belong to wireless access points that are closest to a predicted location  304  of the electronic device  106 . For example, the list selection module  220  may select identifiers that belong to the wireless access points  306 ( 1 )- 306 (N) from identifiers of multiple wireless access points, as the wireless access points  306 ( 1 )- 306 (N) are closest to the predicted location  304 . 
     In other embodiments, the list selection module  220  may use a sector-based search  308  to select a predetermined number of identifiers from the master identifier data  128 . In the sector-based search  308 , the list selection module  314  may divided a geographical region that surrounds the predicted location  304  of the electronic device  106  into multiple sectors, such as the sectors  310 ( 1 )- 310 (N). Accordingly, the list selection module  314  may select the identifiers of one or more wireless access points from each sector that is closest to the predicted location  304  of the electronic device  106 . For example, the list selection module  220  may select identifiers that belong to the wireless access points  312 ( 1 )- 312 (N) from identifiers of multiple wireless access points. By selecting the identifiers of one or more wireless access points from each sector, the list selection module  220  may prevent the selection of identifiers of wireless access points that are clustered in a particular area. Instead, the list selection module  220  may distribute the selection across different compass directions. Such distribution may compensate for any errors with respect to the predicted location  304  of the electronic device  106  and/or a predicted direction of travel of the electronic device  106 . 
     Return to  FIG. 2 , while in some embodiments every slot in the offload list  126  may be populated with identifiers of wireless access points that correspond to the predicted location of the electronic device  106 , the slots in the offload list  126  may be populated differently in other embodiments. In such embodiments, while a number of the slots in the offload list  126  are populated with identifiers of wireless access points that correspond to a predicted location, the other slots may be populated with identifiers of popular wireless access points and/or identifiers of wireless access points that previously connected with the electronic device  106 . The popular wireless access points may be selected by the access point data server  258  based on historical usage data collected from the wireless access point usage patterns of a plurality of users. In various embodiments, a popular wireless access point may be a wireless access point whose usage rate is greater than an average usage rate for a group of wireless access points, whose usage rate is greater than a threshold value, and/or whose usage rate is in a predetermined highest range of usage rates. 
     Further, the number of slots in the memory  206  may be constrained by the capacity of the memory  206 . For example, when there are 32 slots in the offload list  126 , the list selection module  220  may populate  22  of the slots with the identifiers of wireless access points that correspond to the predicted location, 5 of the slots with the identifiers of popular wireless access points, and 5 of the slots with the identifiers of wireless access points that previously connected with the electronic device  106 . 
     Once the selected wireless access point identifiers have been stored in the offload list  126 , the main processor  108  may be powered off and the network interface controller  110  may be placed in a power saving state. Subsequently, the periodic search component  214  may periodically powered on the network interface controller  110  so that the network interface controller  110  may search for one or more wireless access points that match the wireless access point identifiers in the offload list  126 . In various embodiments, the periodic search component  214  may include hardware and/or software instructions that cycle the network interface controller  110  between a power on state and the power saving state in the disconnected scenario  104 . In some embodiments, the software instructions may be stored in the memory  206 . 
     Thus, if the network interface controller  110  is able to discover a matching wireless access point (e.g., wireless access point  114 ), the network interface controller  110  may then use the trigger component  212  to trigger the main processor  108  to power on in order to establish network connectivity with the discovered wireless access point. In instances in which multiple matching wireless access points are simultaneously detected, the electronic device  106  may select one of the multiple matching wireless access points based on one or more criteria. The one or more criteria may include strongest signal strength, histories of reliability, identities of the providers of the multiple wireless access points, and/or so forth. In some embodiments, once the network connectivity is established, the electronic device  106  may enter the periodic power off mode  118  or the adaptive sleep mode  120 . Otherwise, if no matching wireless access point is discovered, the network interface controller  110  may go back into the power saving state for a predetermined time interval until the next power on to search for one or more matching wireless access points. 
     However, in alternative embodiments, rather than using the trigger component  212  to power on the main processor  108  to establish the network communication, the network interface controller  110  may have the ability to establish the communication connection with the detected wireless access point without the involvement of the main processor  108 . Thus, in such embodiments, the network interface controller  110  may use the trigger component  212  to power on the main processor  108  after the communication connection with the detected wireless access point has been established. 
     In various embodiments, the network interface controller  110  may periodically cycle between the power saving state and actively searching for matching wireless identifiers in the power on state. The network interface controller  110  may do so until a number of failed scans, that is, failures to detect a matching wireless access point at each active search, reach a predetermined threshold value. The periodic search component  214  may track the number of such failed scans. At the point that the number of failed scans reaches the predetermined threshold value, the periodic search component  214  may power on the main processor  108  so that the list selection module  220  may select new identifiers from the master identifier data  128  based on contextual data  232  related to the electronic device  106 . In this way, the identifiers in the offload list  126  may be refreshed based on the contextual data  232 . 
     In some embodiments, the network interface controller  110  may use a probabilistic data structure scheme to increase the number of wireless access point identifiers that are stored in the memory  206  and monitored by the network interface controller  110 . For example, the memory capacity of memory  206  that stores the offload list  126  may be limited to the storage of 10 wireless access identifiers. In such an example, the network interface controller  110  may use a Bloom filter to tradeoff false positives in exchange for the ability to storing more than 10 wireless access identifiers in the same amount of memory  206  for monitoring by the network interface controller  110 . 
     In such embodiments, the probabilistic match component  216  may insert a set of SSIDs or BSSIDs into the memory  206  according to a Bloom filter. The set of SSIDs or BSSIDs may be selected by the list selection module  220 . The insertion may be performed by maintaining a bit vector, and hashing the wireless access identifiers to be monitored using a set of hash functions. The probabilistic match component  216  may have the ability to implement hash functions using the NIC processor  204 . In various embodiments, each of the hash functions may be a cryptographically-secure hash function or a hash function that is not cryptographically secure. For each hash implemented using a particular hash function, the probabilistic match component  216  may flip a corresponding bit in the bit vector. This insertion procedure may be illustrated by the following pseudocode: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 initialize bitvector to 0 
               
               
                   
                 foreach s in SSID(BSSID)_List do 
               
            
           
           
               
               
            
               
                   
                 foreach k in list_of_hash_functions do 
               
            
           
           
               
               
            
               
                   
                 index = hash k (s) 
               
               
                   
                 bitvector[index] = 1 
               
            
           
           
               
               
            
               
                   
                 endfor 
               
            
           
           
               
               
            
               
                   
                 endfor 
               
               
                   
                   
               
            
           
         
       
     
     Further, when a wireless access point is newly discovered by the network interface controller  110  during a search, the probabilistic matching component  214  may hash an identifier of the newly discovered wireless access point. Following the hash, the probabilistic matching component  214  may check whether the resulting corresponding bits are all “1”s. In the event that the corresponding bits are all “1”s, the probabilistic matching component  214  may use the trigger component  212  to power on the main processor  108 . This matching procedure may be illustrated by the following pseudocode: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 foreach k in list_of_hash_functions do 
               
            
           
           
               
               
            
               
                   
                  index = hash k (newSSID) 
               
               
                   
                 if(0 == bitvector[i]) 
               
            
           
           
               
               
            
               
                   
                 return false; 
               
            
           
           
               
               
            
               
                   
                 endfor 
               
               
                   
                 return true; 
               
               
                   
                   
               
            
           
         
       
     
     As illustrated by the pseudocode, having all of the bits of the hash result equal to “1” does not guarantee an exact match between the newly discovered wireless access point and a wireless access point identifier stored in the memory  206 . Instead, such a result may indicate that there is a high probability that the newly discovered wireless access point matches a wireless access point identifier stored in the memory  206 . 
     The number of hash functions implemented by the probabilistic match component  216  to perform the insertion procedure and the matching procedure described above may be set to minimize the rate of false positives in the Bloom filter. For example, assuming that m is the size of the memory  206  in the network interface controller  110  (in bits) n is the number of SSIDs or BSSIDs to be monitored, and k is the number of hash functions utilized by the Bloom filter, the probability of a false positive may be expressed as: 
     
       
         
           
             
               
                 
                   
                     ( 
                     
                       1 
                       - 
                       
                         
                           [ 
                           
                             1 
                             - 
                             
                               1 
                               m 
                             
                           
                           ] 
                         
                         kn 
                       
                     
                     ) 
                   
                    
                   k 
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     which may be approximated as: 
       (1−e −kn/m )k  (2)
 
     Accordingly, in order to minimize the probability of a false positive, k may be set to: 
     
       
         
           
             
               m 
               n 
             
              
             ln 
              
             
                 
             
              
             2. 
           
         
       
     
     Thus, in an example in which the memory  206  may hold up to 10 SSIDs of 32 bytes in length, then m may have a value of 10*32*8=2560 bits. Further, assuming that the probabilistic match component  216  is configured to monitor  100  SSIDs, then k may be set to (2560/100)*ln(2)≈17 to minimize the rate of false positives. 
     The user interface module  224  may enable a user to interact with the modules and component of the electronic device  106  using a user interface (not shown). The user interface may include a data output device (e.g., visual display, audio speakers), and one or more data input devices. The data input devices may include, but are not limited to, combinations of one or more of keypads, keyboards, mouse devices, touch screens, microphones, speech recognition packages, and any other suitable devices or other electronic/software selection methods. 
     In various embodiments, the user interface module  224  may enable the user to power on and off the electronic device  106 , place the electronic device  106  in the standby state, and reactivate the electronic device  106  from the standby state. Additionally, the user interface module  224  may also enable the user to interact with the applications  228  that are on the electronic device  106 . The user interface module  224  may further enable the user to switch the network interface controller  110  between the periodic power off mode  118  and the adaptive sleep mode  120 . 
     The power management module  226  may place the electronic device  106  in a standby state in response to an inactivation command. The inactivation command may be received from the user via the user interface module  224 . The placement of the electronic device  106  in a standby state may include powering off the main processor  108  and initiating the mode selection module  218  to place the network interface controller  110  in the periodic power off mode  118  or the adaptive sleep mode  120 . In other instances, the power management module  226  may place the electronic device  106  in the standby state when the main processor  108  is idle and the user interface module  224  and no input is received from the user for a predetermined amount of time. In additional instances, the power management module  226  may place the electronic device  106  in the standby state according to a pre-planned inactivation schedule. In some embodiments, the power management module  226  may also power off or place into power saving states other components of the electronic device  106 , such as hard drives, GPS chips, display screens, and/or so forth. 
     The applications  228  may include applications that provide contextual data  232  to the mode selection module  218  and/or the list selection module  220 . The applications  26  may include task management applications, email application, office productivity application, calendar applications, scheduling applications, travel planning applications, and/or so forth. 
     The data store  230  may store the inputs that are used by the modules and components of the electronic device  106 . In at least one embodiment, the data store  230  may store the master identifier data  128 , the contextual data  232 , and/or so forth. 
     Example Processes 
       FIGS. 4-7  describe various example processes for implementing energy efficient network connectivity maximization. The order in which the operations are described in each example process is not intended to be construed as a limitation, and any number of the described operations can be combined in any order and/or in parallel to implement each process. Moreover, the operations in each of the  FIGS. 4-7  may be implemented in hardware, software, and a combination thereof. In the context of software, the operations represent computer-executable instructions that, when executed by one or more processors, cause one or more processors to perform the recited operations. Generally, computer-executable instructions include routines, programs, objects, components, data structures, and so forth that cause the particular functions to be performed or particular abstract data types to be implemented. 
       FIG. 4  is a flow diagram that illustrates an example process  400  for implementing a periodic power off mode that periodically cycles a network interface controller of the electronic device on and off to reduce power consumption. 
     At block  402 , the electronic device  106  may establish a communication connection  116  with a wireless access point, such as the wireless access point  114 . During the establishment of the communication connection  116 , the electronic device  106  and the wireless access point  114  may further establish a TBTT and/or a listen interval. The communication connection  116  may be a Wi-Fi connection that is established with a Wi-Fi wireless access point. 
     At block  404 , the electronic device  106  may receive a command to become inactivated. In some embodiments, the user may use the user interface of the electronic device  106  to place the electronic device  106  in a standby state. In other embodiments, the electronic device  106  may place itself in the standby state when the main processor  108  is idle and there is a lack of input from the user for a predetermined amount of time, or according to a pre-planned inactivation schedule. 
     At block  406 , the power management module  226  may power off the main processor  108  in response to the inactivation command. The powering off of the main processor  108  may provide significant reduction in the amount of energy that is consumed by the electronic device  106 . 
     At block  408 , the periodic power off component  208  may power off the network interface controller  110  of the electronic device  106  for a predetermined time interval without terminating the communication connection  116  with the wireless access point  114 . In various embodiments, the power management module  226  may rely on a modified link layer  236  or an additional filter layer  246  of the network stack  234  to maintain the communication connection  116  during the predetermined time interval. 
     At block  410 , the periodic power off component  208  may power on the network interface controller  110  to listen for a beacon from the wireless access point  114 . The beacon may include a buffer status indicator that indicates whether the wireless access point  114  has buffered a data frame for the electronic device  106 . For example, the buffer status indicator may have a value of “0” when no data frame is buffered and a value of “1” when a data frame is buffered. 
     At decision block  412 , the network interface controller  110  may determine whether the beacon indicates that a data frame is buffered by the wireless access point  114 . Thus, if the beacon indicates that the wireless access point  114  has buffered a data frame for the electronic device  106  (“yes” at decision block  412 ), the process  400  may proceed to block  414 . 
     At block  414 , the network interface controller  110  may receive the buffered data frame from the wireless access point  114 . Further, the periodic power off component  208  may use the trigger component  212  to power on the main processor  108  to process the received data frame. However, if the beacon indicates that no data packet is buffered for the electronic device  106 , the process  400  may loop back to block  408 , so that the periodic power off component  208  may once again power off the network interface controller  110  for the predetermined time interval without terminating the communication connection  116  with the wireless access point  114 . 
     As described above, the possibility that the wireless access point  114  may discard one or more data frames during an interval when the network interface controller  110  is powered off may be offset by communication redundancy of a delay tolerant application  248 . The delay tolerant application  238  may send out redundant data frames that are eventually received by the network interface controller  110 . 
       FIG. 5  is a flow diagram that illustrates an example process  500  for implementing an adaptive sleep mode that places the network interface controller of the electronic device  106  into a power saving state for varying time intervals to reduce power consumption. 
     At block  502 , the electronic device  106  may establish a communication connection  116  with a wireless access point, such as the wireless access point  114 . During the establishment of the communication connection  116 , the electronic device  106  and the wireless access point  114  may further establish a target beacon transmission time (TBTT) and/or a listen interval. The communication connection  116  may be a Wi-Fi connection that is established with a Wi-Fi wireless access point. 
     At block  504 , the electronic device  106  may receive a command to become inactivated. In some embodiments, the user may use the user interface of the electronic device  106  to place the electronic device  106  in a standby state. In other embodiments, the electronic device  106  may place itself in the standby state when the main processor  108  is idle and there is a lack of input from the user for a predetermined amount of time, or according to a pre-planned inactivation schedule. 
     At block  506 , the power management module  226  may power off the main processor  108  in response to the inactivation command. The powering off of the main processor  108  may provide significant reduction in the amount of energy that is consumed by the electronic device  106 . 
     At block  508 , the adaptive sleep component  210  may calculate an adaptive sleep interval for the network interface controller  110  of the electronic device  106 . 
     The adaptive sleep interval may be calculated based on robustness of the communication connection  116  between the electronic device  106  and the wireless access point  114 . In various embodiments, the adaptive sleep interval is the time of the power saving state between two power ups of the network interface controller  110  to listen for beacons. The adaptive sleep interval may be calculated based on signal strength of the communication signal emanating from the wireless access point that is acquired by the electronic device  106 . Alternatively, the adaptive sleep interval may be calculated based on a beacon loss rate. 
     At block  510 , the adaptive sleep component  210  may place the network interface controller  110  into a power saving state for the adaptive sleep interval. The power saving state may further reduce the amount of energy that is consumed by the electronic device  106 . 
     At block  512 , the adaptive sleep component  210  may power on the network interface controller  110  to listen for a beacon from the wireless access point  114 . The beacon may include a buffer status indicator that indicates whether the wireless access point  114  has buffered a data frame for the electronic device  106 . For example, the buffer status indicator may have a value of “0” when no data frame is buffered and a value of “1” when a data frame is buffered. 
     At decision block  514 , the network interface controller  110  may determine whether the beacon indicates that a data frame is buffered by the wireless access point  114 . Thus, if the beacon indicates that the wireless access point  114  has buffered a data frame for the electronic device  106  (“yes” at decision block  514 ), the process  500  may proceed to block  514 . 
     At block  514 , the network interface controller  110  may receive the buffered data frame from the wireless access point  114 . Further, the adaptive sleep component  210  may use the trigger component  212  to power on the main processor  108  of the electronic device to process the received data frame. However, if the beacon indicates that no data packet is buffered for the electronic device  106 , the process  500  may loop back to block  508 , so that the adaptive sleep component  210  may calculate another adaptive sleep interval for the network interface controller  110  of the electronic device  106 . 
       FIG. 6  is a flow diagram that illustrates an example process  600  for determining whether to place the electronic device into the periodic power off mode or the adaptive sleep mode based on usage context of the electronic device. 
     At block  602 , the electronic device  106  may establish a communication connection  116  with a wireless access point, such as the wireless access point  114 . The communication connection  116  may be a Wi-Fi connection that is established with a Wi-Fi wireless access point. 
     At block  604 , the electronic device  106  may receive a command to become inactivated. In some embodiments, the user may use the user interface of the electronic device  106  to place the electronic device  106  in a standby state. In other embodiments, the electronic device  106  may place itself in the standby state when the main processor  108  is idle and there is a lack of input from the user for a predetermined amount of time, or according to a pre-planned inactivation schedule. 
     At block  606 , the mode selection module  218  may determine a usage context of the electronic device  106 . The usage context may indicate the likelihood that the electronic device  106  is to be powered on again within a particular period of time in the future. The usage context may include factors such as a time of day, a location of the electronic device  106  (e.g., home or office), a predicted location of the electronic device  106 , the presence or absence of an appointment or an event noted in a task management application stored in the main memory  202 , prior usage patterns of the electronic device  106 , and/or other relevant factors. 
     At block  608 , the mode selection module  218  may place the network interface controller  110  of the electronic device  106  into the periodic power off mode  118  or the adaptive sleep mode  120  based on the usage context. In various embodiments, the mode selection module  218  may command the network interface controller  110  to enter the adaptive sleep mode  120  when the usage context indicates that there is a high likelihood (e.g., over 50% likelihood) that the electronic device  106  is to be used again, i.e., powered on, within a particular period of time in the future. On the other hand, the mode selection module  218  may apply the periodic power off mode  118  to the network interface controller  110  when the usage context indicates that there is a low likelihood (e.g., 50% or less likelihood) that the electronic device  106  is to be powered on within the particular period of time in the future. 
       FIG. 7  is a flow diagram that illustrates an example process  700  for reducing power consumption by periodically powering on the network interface controller  110  to search for one or more wireless access points  124  that are pre-selected based on contextual data. 
     At block  702 , the list selection module  220  may select wireless access point identifiers from the master identifier data  128  based on contextual data  232  related to the electronic device  106 . The selection may be made by the main processor  108  of the electronic device  106 . In some embodiments, the list selection module  220  may use a conditional probability algorithm to predict the expected directions of travel, and in turn, the expected locations of the electronic device  106 , based on previously connected wireless access points of the electronic device  106 . In additional embodiments, the list selection module  220  may use other machine learning and/or classification algorithms to predict locations of the electronic device  106  based on the contextual data  232 . Once the list selection module  220  has predicted a location for the electronic device  106 , the list selection module  220  may select identifiers of wireless access points that correspond to the predicted location from the master identifier data  128 . 
     In further embodiments, in addition to selecting wireless access point identifiers based on contextual data  232 , the list selection module  220  may also select identifiers of popular wireless access points and/or identifiers of wireless access points that previously connected with the electronic device  106 . 
     At block  704 , the list selection module  220  may push the selected wireless access point identifiers to the memory  206 . The memory  206  is located in the network interface controller  110  of the electronic device  106 . In some embodiments, the selected wireless access point identifiers may be stored in the offload list  126 . In other embodiments, the selected wireless access point identifiers may be stored in a probabilistic data structure in the memory  206  (e.g., Bloom filter). 
     At block  706 , the power management module  226  may power off the main processor  108  in response to the inactivation command. The powering off of the main processor  108  may provide significant reduction in the amount of energy that is consumed by the electronic device  106 . 
     At block  708 , the periodic search component  214  may place the network interface controller  110  into a power saving state for a predetermined time period. The power saving state may further reduce the amount of energy that is consumed by the electronic device  106 . 
     At block  710 , the periodic search component  214  may power on the network interface controller  110  to scan for wireless access points that match wireless access point identifiers in the memory  206 . At decision block  712 , the network interface controller  110  may determine whether a matching access point is detected. In some embodiments, the match may be an absolute match in the instances in which the wireless access point identifiers are stored in the offload list  126 . In other embodiments, the match may be a high probability match rather than an absolute match in instances in which the wireless access identifiers are stored in the probabilistic data structure (e.g., Bloom filter). Thus, if a matching wireless access point is detected (“yes” at decision block  712 ), the process  700  may proceed to block  714 . 
     At block  714 , the network interface controller  110  may use the trigger component  212  to power on the main processor  108  of the electronic device  106  to establish connectivity with the detected wireless access point. In instances in which multiple matching wireless access points are simultaneously detected, the electronic device  106  may select one of the multiple matching wireless access points based on one or more criteria. The one or more criteria may include strongest signal strength, histories of reliability, identities of the providers of the multiple wireless access points, and/or so forth. 
     However, if at decision block  712  the network interface controller  110  determines that no matching wireless access is detected (“no” at decision block  712 ), the process  700  may proceed to decision block  716 . At decision block  716 , the periodic search component  214  may determine whether the number of failed scans has reached a threshold value. Thus, if the number of failed scans has not reached the threshold value (“no” at decision block  716 ), the process  700  may loop back to block  708  so that the network interface controller may once again placed into a power saving state for the predetermined time period. 
     However, if the periodic search component  214  determines that the number of failed scans has reached the threshold value (“yes” at decision block  716 ), the process  700  may continue to block  718 . At block  718 , the periodic search component  214  may use the trigger component  212  to power on the main processor  108  of the electronic device  106  and re-select the wireless access point identifiers. Subsequently, the process  700  may loop back to block  702  so that the list selection module  220  may once again select wireless access point identifiers from the master identifier data  128  based on contextual data  232  related to the electronic device  106 . 
     Thus, by minimizing the amount of power consumed by an electronic device in acquiring or maintaining network connectivity with a network, the duration of the overall network connectivity of the electronic device with the network may be increased. Further, the power consumption minimization may also increase the battery longevity of the electronic device, resulting in additional convenience and productivity for the user of the electronic device. 
     CONCLUSION 
     In closing, although the various embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended representations is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as exemplary forms of implementing the claimed subject matter.