PATENT ABSTRACT
A method for synchronizing a mobile station includes exiting a low power state to provide a wireless network and obtaining an identity and a last known power state of the mobile station from a station list. The mobile station is polled based on the last known power state and noted as synchronized if the polling is acknowledged. If the polling is not acknowledged, the mobile station is polled a second time based on an alternate power state and noted as synchronized if the second polling is acknowledged. If the second polling is not acknowledged, the mobile station is disassociated from the wireless network.

PATENT DESCRIPTION
BACKGROUND  
       [0001]     In a conventional wireless infrastructure network, mobile stations (e.g., a laptop computer with a wireless connection) are associated with a wireless access point (AP) within a basic service set. There may be multiple mobile stations within range of an AP, and the AP generally remains in an active power state while servicing the one or more mobile stations.  
         [0002]     Mobile stations may use different power states to conserve power while still providing a high quality user experience. For instance, a mobile station may be in an active power state when the mobile station is in use and generating traffic on a wireless network. Alternately, the mobile station may implement a power saving protocol, such as power save polling (PSP), to enter a standby power state that conserves power when the mobile station is inactive or not generating traffic on a wireless network.  
         [0003]     Unlike mobile stations, APs must remain in an active power state at all times. Conventional APs do not use PSP or other power saving protocols to enter a power standby state. This results in an unnecessary waste of power when there is no traffic on a wireless network. For instance, if an AP is servicing mobile stations that have (1) entered a standby power state, or (2) are not generating traffic on the wireless network, then the AP does not have to remain in an active state. If power saving functionality is implemented in an AP, there will be concerns about performance losses and an overall poor user experience if the chosen power saving protocol does not enable fast synchronization with associated mobile stations when the AP wakes up from a standby power state.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]      FIG. 1  illustrates one implementation of a wireless network infrastructure.  
         [0005]      FIG. 2A  is a method for an AP to enter a power saving state in accordance with an implementation of the invention.  
         [0006]      FIG. 2B  is a station list in accordance with an implementation of the invention.  
         [0007]      FIG. 3  is a method for fast synchronization according to an implementation of the invention.  
         [0008]      FIG. 4  illustrates polling interactions between an access point and four mobile stations conducted in accordance with an implementation of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0009]     The following description, various aspects of the illustrative implementations will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. However, it will be apparent to those skilled in the art that the present invention may be practiced with only some of the described aspects. For purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the illustrative implementations. However, it will be apparent to one skilled in the art that the present invention may be practiced without the specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.  
         [0010]     References to “one implementation”, “an implementation”, “example implementation”, “various implementations”, etc., indicate that the implementation(s) of the invention so described may include a particular feature, structure, or characteristic, but not every implementation necessarily includes the particular feature, structure, or characteristic. Further, the different implementations described may have some, all, or none of the features described for other implementations.  
         [0011]     In the following description and claims, the terms “coupled” and “connected,” along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular implementations, “connected” may be used to indicate that two or more elements are in direct physical or electrical contact with each other. “Coupled” may mean that two or more elements co-operate or interact with each other, but they may or may not be in direct physical or electrical contact.  
         [0012]     The term “processor” may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory. A “computing platform” may comprise one or more processors.  
         [0013]     The term “wireless” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated electromagnetic radiation through a non-solid medium. The term does not imply that the associated devices do not contain any wires, although in some implementations they might not.  
         [0014]     As used herein, unless otherwise specified the use of the ordinal adjectives “first”, “second”, “third”, etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner. Various operations will be described as multiple discrete operations, in turn, in a manner that is most helpful in understanding the present invention, however, the order of description should not be construed to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation.  
         [0015]      FIG. 1  illustrates one implementation of a wireless network that includes a wireless access point (AP)  100  and multiple mobile stations  102 . The mobile stations  102  may include, but are not limited to, laptop computers, notebook computers, personal digital assistants (PDAs), pagers, and mobile telephones. The AP  100  establishes a wireless local area network (WLAN)  104 . The WLAN  104  may be a basic service set and it may form a portion of an expanded service set. Mobile stations  102  may connect to the AP  100  to join the WLAN  104 . Mobile stations  102  out of range of the AP  100  cannot join the WLAN  104 .  
         [0016]     The mobile stations  102  may be in any one of several power states. Some mobile stations  102  may be in an active power state, therefore these mobile stations  104  may be actively generating data traffic on the WLAN  104 . In  FIG. 1 , the mobile stations  102  in an active power state are labeled as “ACT”. Alternately, some mobile stations  102  may be in a power saving state, therefore these mobile stations  102  will be generating minimal or no data traffic on the WLAN  104 . In  FIG. 1 , the mobile stations  102  in a power saving state are labeled as “PS”. In some implementations, the mobile stations  102  may use power save polling (PSP) as part of their power saving state. In some implementations, alternate power saving protocols may be used by the mobile stations  102 .  
         [0017]      FIG. 2A  is a method  200 , according to an implementation of the invention, that may be used by the AP  100  to enter a power saving state if there is minimal or no data traffic on the WLAN  104 . The AP  100  may continuously monitor traffic on the WLAN  104  to determine if the flow of data has reached a threshold minimum level or has stopped ( 202 ). While there is an active flow of data on the WLAN  104 , the AP  100  continues with its normal operation ( 204 ). If, however, the data traffic on the WLAN  104  has dropped to a threshold minimum level or has ceased completely, the AP  100  may take steps to enter a power saving state to conserve power. In an implementation of the invention, the AP  100  begins this process by defining a station list ( 206 ). The station list may be a data file, such as an Extensible Markup Language (XML) file or a text file (.txt), or the station list may be stored data residing in a memory of the AP  100 , such as a random access memory or a flash memory. The AP  100  determines which mobile stations  102  are currently being serviced by the AP  100  and records their identities to the station list ( 208 ). In addition, the AP  100  may also record the current power state, active or power saving, of each mobile station  102  that is added to the station list ( 210 ).  
         [0018]     When all of the mobile stations  102  that are associated with the AP  100  have been recorded on the station list with their respective power states, the AP  100  may enter a power saving state ( 212 ). In some implementations, the power saving state may be a sleep mode, a stand-by mode, a hibernation mode, or any other power saving protocol that is appropriate for the AP  100 .  
         [0019]      FIG. 2B  is an exemplary station list  250  that may be generated by the AP  100 . As shown, the station list  250  may include a unique identity  252  of each mobile station  102  that is associated with the AP  100  at the time the AP  100  enters a power saving state. The unique identity  252  of each mobile station  102  may have been previously created by a user of that particular mobile station  102 . The unique identity  252  is generally received from the mobile station  102  when the mobile station  102  first connects to the AP  100 . The station list  250  also includes the power state  254  of each mobile station  102  at the time the station list  250  was generated. In  FIG. 2B , the possible power states include an active power state (ACT) and a power saving state (PS).  
         [0020]      FIG. 3  is a method  300 , in accordance with an implementation of the invention, for the AP  100  to synchronize with one or more mobile stations  102 . The method  300  may be carried out when the AP  100  wakes up from or exits a power saving state ( 302 ). The AP  100  determines if one or more mobile stations  102  were recorded to the station list  250  when the AP  100  originally went into the power saving state ( 304 ). If the station list  250  contains no unique identities  252 , the AP  100  may resume normal operation ( 306 ).  
         [0021]     If, however, the station list  250  includes one or more recorded unique identities  252 , the AP  100  may attempt to synchronize the mobile stations  102  associated with the recorded unique identities  252 . To perform the synchronization, the AP  100  begins by selecting one mobile station  102  that has not been polled ( 308 ). Initially, all of the mobile stations  102  recorded on the station list  250  will not have been polled.  
         [0022]     The AP  100  may poll the selected mobile station  102  with a null packet based on the last known power state of that mobile station  102  ( 310 ). In an implementation, the last known power state of the selected mobile station  102  may be found on the station list  250 . Generally, the power state  254  recorded for the selected mobile station  102  when the AP  100  entered the power saving state is the last known power state of that mobile station  102 . Accordingly, if the station list  250  discloses that the power state of the selected mobile station  102  is an active power state, the AP  100  may send a null packet to the selected mobile station  102  based on an active power state. Alternately, if the station list  250  discloses that the power state of the selected mobile station  102  is a power saving state, the AP  100  may send a null packet to the selected mobile station  102  based on a power saving state.  
         [0023]     The AP  100  may wait for an acknowledgement from the selected mobile station  102  that it has received the null packet ( 312 ). In some implementations, the AP  100  may wait a predetermined amount of time for the selected mobile station  102  to acknowledge the null packet. If the mobile station  102  acknowledges the null packet, the AP  100  notes that the selected mobile station is synchronized ( 314 ). The AP  100  may then check the station list  250  to determine whether any mobile stations  102  remain that have not been polled by the AP  100  ( 316 ). If un-polled mobile stations  102  remain, the AP  100  may select another mobile station  102  to poll ( 308 ). If all of the mobile stations  102  recorded on the station list  250  have been polled, the AP  100  may resume normal operation ( 306 ).  
         [0024]     If the selected mobile station  102  does not acknowledge the null packet from the AP  100 , the AP  100  may poll the selected mobile station  102  with a second null packet that is based on an alternate power state ( 318 ). For instance, if the first null packet was based on an active power state, the second null packet may be based on a power saving state. Similarly, if the first null packet was based on a power saving state, the second null packet may be based on an active power state.  
         [0025]     The AP  100  may wait for an acknowledgement from the selected mobile station  102  that it has received the second null packet ( 320 ). In some implementations, the AP  100  may wait a predetermined amount of time for the selected mobile station  102  to acknowledge the second null packet. If the mobile station  102  acknowledges the second null packet, the AP  100  notes that the selected mobile station is synchronized ( 314 ). As described previously, the AP  100  may then check the station list  250  to determine whether any un-polled mobile stations  102  remain ( 316 ), and if so, the AP  100  may select another mobile station  102  to poll ( 308 ). Alternately, if all of the mobile stations  102  recorded on the station list  250  have been polled, the AP  100  may resume normal operation ( 306 ).  
         [0026]     If the selected mobile station  102  does not acknowledge the second null packet, the AP  100  may determine that the mobile station  102  is unavailable and may disassociate the selected mobile station  102  from the WLAN ( 322 ). The mobile station  102  may be unavailable for many reasons. For instance, the mobile station  102  may have moved to a location that is out of range of the AP  100 . Alternately, the mobile station  102  may have turned off its wireless functionality or it may have shut down.  
         [0027]     After the AP  100  disassociates the selected mobile station  102 , the AP  100  may check the station list  250  to determine whether any un-polled mobile stations  102  remain ( 316 ), and if so, the AP  100  may select another mobile station  102  to poll ( 308 ). Alternately, if all of the mobile stations  102  recorded on the station list  250  have been polled, the AP  100  may resume normal operation ( 306 ).  
         [0028]      FIG. 4  illustrates an example of polling transactions that may occur between the AP  100  and four mobile stations  102  according to an implementation of the invention. In the example of  FIG. 4 , mobile station # 1  was in an active power state when the AP  100  went into standby and is in an active power state when the AP  100  wakes up. Mobile station # 2  was in a power saving state when the AP  100  went into standby and is in a power saving state when the AP  100  wakes up. Mobile station # 3  was in an active power state when the AP  100  went into standby and is in a power saving state when the AP  100  wakes up. And mobile station # 4  was in an active power state when the AP  100  went into standby and is currently out of range of the AP  100 .  
         [0029]     As shown in  FIG. 4 , the AP  100  polls each of the four mobile stations  102  based on the last known power state of each mobile station. The last known power state may be found on the station list  250 . For mobile stations # 1 , # 3 , and # 4 , the last known power state is active, and the AP  100  polls each of these mobile stations with a null packet based on an active power state (ACT). For mobile station # 2 , the last known power state is power saving, and the AP  100  polls mobile station # 2  with a null packet based on a power saving state (PS).  
         [0030]     In  FIG. 4 , mobile station # 1  receives the null packet based on an active power state and transmits an acknowledgement (ACK) back to the AP  100 . Similarly, mobile station # 2  receives the null packet based on a power saving state and transmits an acknowledgement (ACK) back to the AP  100 . The AP  100  may note mobile stations # 1  and # 2  as synchronized. Mobile station # 3 , which received a null packet based on an active power state, cannot acknowledge the null packet because it is now in a power saving state. Mobile station # 4 , which has moved out of range of the AP  100 , does not receive the null packet and therefore cannot respond.  
         [0031]     The AP  100  may wait a predetermined amount of time for an acknowledgement from mobile stations # 3  and # 4 . When no acknowledgement is received during the predetermined time, the AP  100  may transmit a second null packet to mobile stations # 3  and # 4  based on an alternate power state. Since the first null packets to both mobile stations # 3  and # 4  were based on an active power state, the second null packets to both may be based on a power saving state. In  FIG. 4 , the AP  100  transmits null packets based on a power saving state to mobile stations # 3  and # 4 . Mobile station # 3 , because it is in a power saving state, may finally acknowledge the null packet, and the AP  100  may note mobile station # 3  as synchronized. Mobile station # 4 , which cannot receive the second null packet since it is out of range, again does not respond. The AP  100  may then disassociate mobile station # 4  from the WLAN.  
         [0032]     Implementations of the invention enable the AP  100  to screen out all mobile stations  102  that have moved out of range or have changed power state during the time when the AP  100  was in a power standby state. Implementations of the invention allow the AP  100  to go into power standby state when there is no active traffic being detected, and allow the AP  100  to wake up as soon as any traffic from mobile stations  102  is detected. The AP  100  may then perform the methods of the invention to synchronize mobile stations  102  with improved performance loss.  
         [0033]     The invention may be implemented in one or a combination of hardware, firmware, and software. The invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by a processing platform to perform the operations described herein. A machine-readable medium may include any mechanism for storing, transmitting, or receiving information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM), such as dynamic random access memory (DRAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, the interfaces that transmit and/or receive those signals, etc.), and others.  
         [0034]     The above description of illustrated implementations of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific implementations of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.  
         [0035]     These modifications may be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific implementations disclosed in the specification and the claims. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.