WO2014013430A1

WO2014013430A1 - Method, apparatus and computer program for low-power operation of a device in a wireless network

Info

Publication number: WO2014013430A1
Application number: PCT/IB2013/055836
Authority: WO
Inventors: Anna Pantelidou; Timo K. Koskela; Sami-Jukka Hakola; Samuli Turtinen
Original assignee: Renesas Mobile Corporation
Priority date: 2012-07-16
Filing date: 2013-07-16
Publication date: 2014-01-23
Also published as: GB201212647D0; GB2504088A

Abstract

A wireless device receives an indication that a second device has a data message intended for the first device (615, 620). Low-power timing information is determined for the first device (630). A data request message is sent to the second device (640), wherein the data request message comprises the low-power timing information. It is determined that a response to the data request message has been received (650). A low- power state or mode corresponding to the low-power timing information is entered (600).

Description

METHOD, APPARATUS AND COMPUTER PROGRAM FOR

LOW-POWER OPERATION OF A DEVICE IN A WIRELESS NETWORK

Cross Reference to Related Application

This application claims the benefit under 35 U.S.C. § 119 and 37 CFR § 1.55 to

UK patent application no. 1212647.0, filed on July 16, 2012, the entire content of which is incorporated herein by reference.

Technical Field

The present invention relates to methods, apparatus and computer programs for low-power operation of a device in a wireless network.

The disclosure herein relates generally to the field of wireless local-area communications, and particular examples relate to methods for improving the efficiency of data communication among low-power wireless devices by providing earlier indication of when such devices will be powered on and able to receive transmissions.

Background

The 802 LAN/MAN Standards Committee of the Institute of Electrical and

Electronic Engineers (IEEE) develops and maintains networking standards and recommends practices for local, metropolitan and other area networks. The IEEE 802 Standards Committee comprises a number of working groups (WGs), each focused on developing standards related to a particular area of networking. IEEE 802.11 is the working group dedicated to developing standards for wireless local-area networks (WLANs).

Generally speaking, the output of IEEE 802.11 comprises a collection of standards specifying the physical (PHY) and medium access control (MAC) layers for wireless, local-area network operation in unlicensed frequency bands including, for example, around 2.4, 3.6 and 5 GHz. IEEE 802.11 standards are published as official versions along with interim amendments, which are incorporated into subsequent official releases. For example, version IEEE 802.11-2007 incorporated IEEE 802.11- 1999 plus amendments 802.1 la (OFDM PHY at 5 GHz), 802.1 lb (higher-speed PHY at 2.4 GHz), 802.1 le (quality-of-service), 802.1 lg (OFDM PHY at 2.4 GHz), 802.1 lh (spectrum and transmit power management), 802.1 li (security mechanisms), and 802.1 lj (Japan-specific operation). In addition, version IEEE 802.11-2012 incorporated IEEE 802.11-2007 and amendments such as 802.11k (radio resource management), 802.1 lr (fast secure handoffs), 802.1 ly (3.6-GHz operation), 802.11η (increased throughput using MIMO and frame aggregation), 802. l ip (vehicular operation), 802. l lv (network management), and other amendments. Typically, an amendment is developed as a project by a task group (TG) that is dedicated to the particular subject area. One of the current projects, known as 802.11 ah, relates to extension of IEEE 802.11 for low-power operation at frequencies below 1 GHz for applications such as sensor networks, smart metering, healthcare, surveillance, intelligent transport systems (ITS), etc.

Fig. 1A is a block diagram showing the most fundamental architecture of an 802.11 network. The addressable unit in an IEEE 802.11 network is referred to as a station (STA), while the basic service set (BSS) is the basic building block. Fig. 1 shows two BSSs - BSS1 and BSS2 - each of which comprises two member STAs - STA1 and STA2 in BSS1, STA3 and STA4 in BSS2. Generally speaking, a BSS is a coverage area and member STAs may communicate directly with each other so long as they remain within it. Because the topology of Fig. 1A is often formed without preplanning, and retained for only as long as needed by the member STAs, this type of operation is often referred to as an ad hoc network, and each of the BSSs is referred to as an independent BSS (IBSS).

Fig. IB is a block diagram showing a more complex 802.11 topology in which BSS1 and BSS2 of Fig. 1A are connected into an extended network by a distribution system (DS) comprising a distribution system medium (DSM). The DS enables STAs to be mobile between multiple BSSs by providing the logical services necessary to handle address to destination mapping and seamless BSS integration. STAs access the DS over the wireless medium via an access point (AP), which is an entity that has STA functionality (e.g. it is addressable) and provides access to the DS. Instead of communicating directly with each other as in Fig. 1A, the STAs in Fig. IB communicate with each other via the AP of the BSS that they are associated with. Accordingly, the BSS topology of Fig. IB is commonly referred to as infrastructure BSS.

The basic medium access protocol of the 802.11 MAC layer is a distributed coordination function (DCF) that allows STAs with compatible PHY layers to automatically share the wireless channel using carrier sense multiple access/collision avoidance (CSMA/CA) techniques with a random back-off time following a busy medium condition. The CSMA/CA protocol is designed to reduce the collision probability between multiple STAs accessing a medium, at the time when collisions are most likely occur, such as just after the medium becomes idle following a busy medium, since multiple STAs may have been waiting for the medium to become available again. The random backoff procedure, which causes STAs to randomly delay their medium access attempts, helps to reduce such conflicts. The state of the medium is indicated by the carrier sense (CS) function of the 802.11 MAC layer. The CS function distributes reservation information announcing the impending use of the medium, such as by STAs exchanging clear-to-send/request-to-send (CTS/RTS) prior to exchanging data frames, or by various other means specified in the 802.11 standard and amendments.

Summary

According to a first aspect of the present invention, there is provided a method for low-power operation of a first device in a wireless communication network, the method comprising: receiving an indication that a second device has a data message intended for the first device; determining low-power timing information for the first device; sending a data request message to the second device, wherein the data request message comprises the low-power timing information; determining that a response to the data request message has been received; and entering a low-power state or mode corresponding to the low-power timing information.

According to a second aspect of the present invention, there is provided a method for selectively transmitting a data message based on the power mode of a target wireless communication device, the method comprising: transmitting a message comprising an indicator that a data message is available for the target device; receiving a data request message from the target device; determining that the data request message comprises low-power timing information for the target device; and transmitting the data message to the target device based on low-power timing information for the target device.

According to a third aspect of the present invention, there is provided apparatus comprising a processing system for a wireless communication device constructed and arranged to cause the wireless communication device to, upon receipt of an indication that a second device has a data message intended for the device: determine low-power timing information; send a data request message to the second device, wherein the data request message comprises the low-power timing information; determine that a response to the data request message has been received; and enter a low-power state or mode corresponding to the low-power timing information.

According to a fourth aspect of the present invention, there is provided apparatus comprising a processing system for a wireless communication device constructed and arranged to cause the wireless communication device to: transmit a message comprising an indicator that a data message is available for a target device; determine that a data request message received from the target device comprises low- power timing information for the target device; and transmit the data message to the target device based on low-power timing information for the target device. According to a fifth aspect of the present invention, there is provided a computer program comprising program code that, when executed by a wireless communication device, causes the wireless communication device to, upon receipt of an indication that a second device has a data message intended for the device: determine low-power timing information for the device; send a data request message to the second device, wherein the data request message comprises the low-power timing information; determine that a response to the data request message has been received; and enter a low-power state or mode corresponding to the low-power timing information.

According to a sixth aspect of the present invention, there is provided a computer program comprising program code that, when executed by a wireless communication device, causes the wireless communication device to: transmit a message comprising an indicator that a data message is available for a target device; determine that a data request message received from the target device comprises low- power timing information for the target device; and transmit the data message to the target device based on low-power timing information for the target device.

The processing systems described above may comprise a processor and at least one memory including program code that, when executed by the processor, causes the wireless communication device to operate as described above. The wireless communication device may comprise a transmitter and a receiver.

Examples of embodiments of the present disclosure also include a method for a first wireless communication device, such as an 802.11 STA, to inform a second wireless communication device, such as an 802.11 AP, of one or more time periods when the first wireless device will be entering a low-power state or mode, such as an 802.11 PS mode or an 802.11 Doze state, by sending low-power timing information in a message. In some embodiments, the low-power timing information may comprise the time when the first device will enter a low-power state or mode. In some embodiments, the low-power timing information may comprise parameters indicating the device's discontinuous reception (DRX) pattern comprising periodic and/or aperiodic transitions between low-power and non-low-power states. In some embodiments, the method comprises providing low-power timing information in one or more fields of a message sent by the first device to request data from the second device, such as an 802.11 PS- Poll MAC frame or an enhanced version of a PS-Poll frame. Embodiments include a wireless communication device (e.g. an 802.11 station (STA)) and a computer-readable medium with program code embodying one or more of these methods.

Examples of embodiments of the present disclosure also include a method for a wireless communication device having data to transmit to a target device to selectively retransmit the data based on low-power timing information related to when the target device will be entering a low-power state or mode. In some embodiments, the wireless communication device receives such low-power timing information in a message from the target device requesting the data from the second device. In some embodiments, the message from the target device may be an 802.11 PS-Poll frame or an enhanced version of a PS-Poll frame, sent by the target device in response to a Beacon frame from the wireless communication device, the Beacon frame comprising an indicator that data is available for the target device. In some embodiments, the wireless communication device determines one or more time periods, based on the received low-power timing information, when the target device will be in a non-low-power state or mode, and transmits the data message during one of those time periods. Embodiments include wireless communication devices (e.g. 802.11 STAs and APs) and a computer-readable medium with program code embodying one or more of these methods.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings.

Brief Description of the Drawings

Fig. 1A shows a schematic high-level block diagram of an 802.11 network arranged in an independent BSS (IBSS) configuration; Fig. IB shows a schematic high-level block diagram of an 802.11 network arranged in an infrastructure BSS configuration; Fig. 2 A shows a schematic diagram of the format of a generic 802.11 MAC frame; Fig. 2B shows a schematic diagram of the Frame Control field of a generic

802.11 MAC frame;

Fig. 2C shows a schematic diagram of an 802.11 PS-Poll MAC frame; Fig. 3 A shows a schematic timing diagram of an exemplary periodic discontinuous reception (DRX) pattern for an 802.11 station (STA), according to one or more embodiments of the present disclosure;

Fig. 3B shows a schematic timing diagram of an exemplary aperiodic discontinuous reception (DRX) pattern for an 802.11 station (STA), according to one or more embodiments of the present disclosure;

Fig. 4A shows a table showing examples of the values of the Type and Subtype subfields of the Frame Control field of an 802.11 MAC frame, according to one or more embodiments of the present disclosure;

Fig. 4B shows a schematic diagram of an example of the Frame Control field of an 802.11 "PS-Poll with low-power timing" MAC frame, according to one or more embodiments of the present disclosure

Fig. 5A shows a schematic diagram of another example of the Frame Control field of an 802.1 1 "PS-Poll with low-power timing" MAC frame, according to one or more embodiments of the present disclosure; Fig. 5B shows a schematic diagram of an example of an 802.11 "PS-Poll with low-power timing" MAC frame, according to one or more embodiments of the present disclosure; Fig. 6 shows a flowchart of an exemplary method for transmitting information relating to when a wireless communication device will be entering a low-power state or mode, according to one or more embodiments of the present disclosure;

Fig. 7 shows a flowchart of an exemplary method for selectively transmitting data frames or messages based on timing information related to when the target device for the data frames or messages will be entering a low-power state, according to one or more embodiments of the present disclosure;

Fig. 8 shows a block diagram an exemplary wireless communication device, such as an 802.11 station (STA), according to one or more embodiments of the present disclosure; and

Fig. 9 shows a block diagram an exemplary wireless communication device, such as an 802.1 1 station (STA) or access point (AP), according to one or more embodiments of the present disclosure.

Detailed Description

Fig. 2 A shows a diagram of the format of a generic 802.11 MAC frame. The first three fields (Frame Control, Duration/ID, and Address 1) and the last field (frame check sequence or "FCS") constitute the minimal frame format and are present in all types of MAC frames, including reserved types and subtypes. The other fields, namely Address 2, Address 3, Sequence Control, Address 4, QoS Control, HT Control, and Frame Body, are present only in certain frame types and subtypes. Fig. 2B shows the composition of the Frame Control field. It consists of the subfields Protocol Version, Type, Subtype, To DS, From DS, More Fragments, Retry, Power Management, More Data, Protected Frame, and Order. The Type (two bits) and Subtype (four bits) fields together identify the function of the frame. There are three frame types, namely control, data, and management, each of which has several defined subtypes.

The 802.11 standard defines power management in terms of states and modes. A STA may be in either "Awake" state, in which it is fully powered, or "Doze" state in which it is unable to transmit or receive and consumes very little power. The way that a STA transitions between the Awake and Doze states is determined by its power management mode. In "Active" mode, the STA remains in the Awake state. In power- save ("PS") mode, the STA remains in Doze state and enters Awake state at predetermined times to receive selected messages ("Beacon frames" in 802.11 parlance) broadcast by the AP and certain other transmissions from the AP following Beacon frames. The Power Management subfield in the Frame Control field shown in Fig. 2B is used by STAs to inform an AP (or another STA, in an IBSS or ad hoc configuration) of a change in power management mode. A STA must remain in its current Power Management mode until it informs the AP of a mode change via a frame exchange that includes an acknowledgement ("ACK") frame received from the AP.

A STA in PS mode also enters Awake state to transmit a PS-Poll frame if the traffic indication map (TIM) field in the most recent Beacon frame it received indicates that the AP has buffered a data frame intended for the STA. Fig. 2C is a diagram showing the contents of an 802.11 PS-Poll MAC frame. The BSSID field contains the address of the AP, the AID field contains the value assigned to the STA during the association phase with the AP, the TA field contains the address of the STA transmitting the frame, and the Frame Control and FCS fields are described above with reference to Figs. 2 A and 2B.

A STA quits the Doze State and re-enters the Awake state by transmitting a PS- Poll frame to the AP requesting for data. If the AP does not respond within SIFS (the Short Interframe Space), the STA may re-enter the Doze state. In normal operation, the AP responds to the PS -Poll immediately with a data frame or with an ACK frame followed by the corresponding data frame at a later time. When the STA successfully receives the data frame from the AP, it sends an ACK frame in which it may indicate a change in power management mode, e.g. from Active to PS mode, by setting the Power Management subfield in the Frame Control field to "1". If the STA receives no response from the AP to the PS-Poll frame, it will retransmit the PS-Poll.

In some cases, even when the AP sends the data frame in response to a PS-Poll frame and the STA responds with an ACK frame, the AP may fail to receive the ACK from the STA. If so, the AP will retransmit the data frame until either it receives an ACK frame or until it reaches the maximum number of retransmission attempts. However, as discussed above, the STA may indicate in the Power Management subfield of the ACK frame that it will go into PS mode (i.e. Doze state) after sending the ACK. Unbeknownst to the AP, the STA is unable to receive the AP's retransmissions of the data frame, which results in unnecessary power consumption and interference on the shared wireless medium.

A key requirement for many of the applications targeted by 802.11 ah is that a large number of STAs (e.g. at least 6000) should be able to be associated with a single AP. By way of example, such devices may be battery-powered sensors that transmit and receive data very rarely and stay in a low-power state or mode of operation for relatively long periods of time. In order to support such large numbers of STAs, the AP may utilise additional techniques that further restrict access to the shared wireless medium so as to avoid collisions caused by simultaneous transmissions by multiple STAs. For example, the AP may group STAs into multiple groups and assign certain parameters for each group to indicate which group is allowed to access the shared wireless medium at a specific time. Such grouping information and operation parameters can be broadcast by the AP to all the STAs in the BSS, or may be delivered to individual STAs in various ways, e.g. broadcast in a Beacon frame or directed to an individual STA during the process of associating with the AP. However, 802.11 ah STAs may operate in Doze state for prolonged periods of time and therefore the grouping parameters provided by the AP may no longer be valid when the STA re-enters Awake state and resumes accessing the medium. Moreover, if a STA stays in Doze state for extended periods of time it may lose the synchronisation (e.g. due to drift in the STA clock, the AP clock, or both) and is unable to estimate when the next Beacon frame will be transmitted after it re-enters Awake state. Since Beacon frames may be transmitted relatively infrequently, this may cause the STA to stay in Awake state for a relatively long period of time trying to receive a beacon transmission. The resulting power consumption is very undesirable for low-power, battery-operated devices such as sensors and the like.

Low-power 802.11 ah ST As, such as sensors and the like, also will be subject to the lost ACK problem discussed above. In fact, the problem may be more pronounced for such STAs because their transmission output may be reduced (e.g. little or no power amplification) in order to reduce size and total power consumption. If so, the links between the AP and the STAs will become asymmetric, meaning that the signal level received by the AP will be much lower than the signal level received by the STA, even though both signals are sent over the same channel path (albeit in opposite directions). Without introducing other costly measures in the AP, such as higher-gain antennas or higher-sensitivity receivers, this asymmetry will effectively reduce the range between the STA and AP, which is extremely undesirable to end users. Furthermore, as discussed above, low-power 802.11 ah STAs also may spend a larger portion or percentage of the time in PS mode (i.e. Doze state) than conventional STAs. As such, an 802.11 ah STA is less likely to receive any of the AP's retransmissions of the data frame intended for the STA. Embodiments of the present disclosure solve these and other problems by providing a method for a first wireless communication device, such as an 802.11 STA, to inform a second wireless communication device, such as an 802.11 AP, of one or more time periods when the first wireless device will be entering a low-power state or mode, such as an 802.11 PS mode or an 802.11 Doze state, by sending low-power timing information in a message. In some embodiments, the low-power timing information may comprise the time when the first device will enter a low-power state. In some embodiments, the low-power timing information may comprise parameters indicating the device's discontinuous reception (DRX) pattern comprising periodic and/or aperiodic transitions between low-power and non-low-power states. In some embodiments, the method comprises providing low-power timing information in one or more fields of a message, such as an 802.11 PS-Poll MAC frame or an enhanced version of a PS-Poll frame, sent by the first device to request data from the second device. In some embodiments, the low-power timing information may be provided in one or more fields that are reserved or otherwise unused in the message but utilised for other purposes in other types of messages, thereby not increasing the size of the improved message.

Embodiments of the present disclosure also include a method for a wireless communication device having data to transmit to a target device to selectively retransmit the data based on low-power timing information related to when the target device will be entering a low-power state or mode. In some embodiments, the wireless communication device receives such low-power timing information in a message from the target device requesting the data from the second device. In some embodiments, the message from the target device may be an 802.11 PS-Poll MAC frame or an enhanced version of a PS-Poll frame, sent by the target device in response to a Beacon frame from the wireless communication device, the Beacon frame comprising an indicator that data is available for the target device. In some embodiments, the wireless communication device determines one or more time periods, based on the received low- power timing information, when the target device will be in a non-low-power state or mode, and transmits the data message during one of those time periods. Embodiments include wireless communication devices (e.g. 802.1 1 STAs and APs) and a computer- readable medium with program code embodying one or more of these methods.

Embodiments of the present disclosure also include a method for low-power operation of a first device in a wireless communication network, comprising receiving an indication that a second device has a data message intended for the first device; determining low-power timing information for the first device; sending a data request message to the second device, wherein the data request message comprises the low- power timing information; determining that a response to the data request message has been received by the first device; and entering a low-power state or mode corresponding to the low-power timing information. In some embodiments, the low-power timing information comprises the time at which the first device will enter a low-power state or mode. In some embodiments, the low-power timing information comprises one or more discontinuous reception (DRX) pattern parameters indicating one or more durations that the first device will spend in a low-power state or mode and a non-low-power state or mode. In some embodiments, the discontinuous reception (DRX) pattern is one of a periodic pattern and an aperiodic pattern. Embodiments include wireless communication devices (e.g. 802.11 STAs) and a computer-readable medium with program code embodying one or more of these methods.

Embodiments of the present disclosure also include a method for selectively transmitting a data message based on the power mode of a target wireless communication device, comprising transmitting a message comprising an indicator that a data message is available for the target device; receiving a data request message from the target device; determining that the data request message comprises low-power timing information for the target device; and transmitting the data message to the target device based on low-power timing information for the target device. In some embodiments, the low-power timing information comprises the time at which the target device will enter a low-power state or mode. In some embodiments, the low-power timing information comprises discontinuous reception (DRX) pattern parameters indicating one or more durations that the target device will spend in a low-power state or mode and a non-low-power state or mode. In some embodiments, the discontinuous reception (DRX) pattern is one of a periodic pattern and an aperiodic pattern. In some embodiments, transmitting the data message to the target device based on the low- power timing information comprises determining a period when the target device is expected to be in a non-low-power state or mode, and transmitting the data message to the target device during the period. In some embodiments, transmitting the data message to the target device further comprises transmitting an acknowledgement of low-power timing information for the target device. Embodiments include wireless communication devices (e.g. 802.11 STAs and APs) and a computer-readable medium with program code embodying one or more of these methods. In some exemplary embodiments, an 802.1 1 STA provides timing information related to when it will enter Doze state of PS mode in one or more fields or subfields of an enhanced version of an 802.11 PS-Poll MAC frame sent to an 802.11 AP (or another STA, in an IBSS or ad hoc configuration). In some embodiments, the timing information may also comprise an indicator that timing information is present in the enhanced PS-Poll frame. As described above with reference to Figs. 2B and 2C, the Type (two bits) and Subtype (four bits) subfields of the Frame Control field identify the function of the frame. There are three frame types, Management (Type = 00 binary), Control (01), and Data (10), each of which has several defined subtypes. In the 802.11 standard, the fourth Type value (11 binary) is reserved, as are several Subtype values associated with the Control subtype. In some embodiments of the present disclosure, one or more of the reserved Type and/or Subtype values comprise an indicator that low- power timing information is present in the frame. In some embodiments, one or more of the reserved Type and/or Subtype values comprise the low-power timing information.

Also, the More Fragments, Retry, More Data, Protected Frame, and Order subfields of the Frame Control field shown in Fig. 2B are reserved in a PS-Poll frame according to the 802.11 standard. Accordingly, these fields, five bits in total, may be used by the STA to inform the AP of the time when the STA will enter Doze state following the reception of the data frame sent by the AP in response to receiving the enhanced PS-Poll frame. Alternately, or in addition, these fields may be used by the STA to inform the AP of the DRX pattern comprising periodic or aperiodic transitions between low-power and non-low-power states, which the STA will enter following reception of the data frame sent by the AP in response to receiving the enhanced PS- Poll frame. By doing so, these exemplary embodiments achieve the desired advantage of maintaining the same size and field configuration of the PS-Poll frame currently specified in the 802.1 1 standard.

As discussed above, in the PS-Poll frame shown in Fig. 2C, the TA field contains the address of the STA transmitting the frame and the AID field contains the value assigned to the STA during the association phase with the AP. Since the BSSID information along with either of the TA or AID can be used to uniquely identify the STA, the combination comprises redundant identity information. Therefore, in some embodiments, the TA field can be used instead for the purpose of providing the STA's low-power timing information, such as described above with respect to the sub fields of the Frame Control field.

Fig. 3A is a diagram of an exemplary periodic DRX pattern comprising a duration, T_a, in the Active state followed by a duration, Td, in the Doze state. The STA may include values for T_a and Td in the data request message. In some embodiments, the message may be an enhanced version of the 802.1 1 PS-Poll frame, which is referred to herein as a "PS-Poll with low-power timing" frame. Persons of ordinary skill will recognise, however, that this nomenclature is used for purposes of illustration, and that other names may be given to the message comprising low-power timing information. For example, the currently defined 802.1 1 PS-Poll frame may be replaced by the enhanced version comprising low-power timing information, while retaining the current "PS-Poll" label. In some embodiments, the STA may include in the message a parameter indicating the number of repetitions, N, of the DRX pattern. In other embodiments, the number of repetitions of the DRX pattern may be implicitly understood by both the STA and the AP. For example, it may be understood that the STA will repeat the T_a, Td DRX pattern until it sends another message comprising parameters indicating a new DRX pattern.

Similarly, Fig. 3B shows an exemplary aperiodic DRX pattern comprising a duration, T_ai, in the Active state followed by a duration, Tdi, in the Doze state, followed by another duration, T_a2, in the Active state, followed by another duration, Td2, in the Doze state. The STA may include values for T_ai, Tdi, T_a2, and Td2 in the message, e.g. a "PS-Poll with low-power timing" frame. The person of ordinary skill will recognise that further aperiodic extensions (e.g. T_a3, ds) are within the scope of the present disclosure. In some embodiments, the STA may include in the frame a parameter indicating the number of repetitions, N, of the DRX pattern. In other embodiments, the number of repetitions of the DRX pattern may be implicitly understood by both the STA and the AP. For example, it may be understood that the STA will repeat the DRX pattern defined by T_ai, Tdi, T_a2, d2, etc. until it sends another message comprising a new DRX pattern. In some embodiments, the STA may include one or more indices indicating one or more of a set of predefined periodic or aperiodic patterns that are known both to the STA and the recipient of the frame.

In some embodiments, the currently-defined 802.11 PS-Poll MAC frame can be utilised as is (i.e. without modification) to implicitly communicate the sending STA's low-power timing information to the receiving AP. In such embodiments, both the STA and the AP implicitly understand that the PS-Poll frame is associated with a default set of low-power timing information including, but not limited to, exemplary periodic and aperiodic DRX pattern parameters as described above. Accordingly, when the AP receives a PS-Poll frame from the STA, it determines the STA's low-power timing information based on this implicit understanding.

Fig. 4A is a table showing the values of the Subtype subfields of the Frame Control field in a Control-type frame for another exemplary embodiment in which the currently-reserved four-bit value "01 10" for the Subtype field is used to indicate that low-power timing information is being communicated in the Control-type frame. In this embodiment, the low-power timing indicator is a new Control Subtype called "PS- Poll with low-power timing", although persons of ordinary skill will recognise that other Subtype (or Type) values and names may be used within the scope of the present disclosure. In some embodiments, the low-power timing information may be communicated implicitly by the sending STA to the receiving AP. In such embodiments, both the STA and the AP implicitly understand that the "PS-Poll with low-power timing" frame is associated with a default set of low-power timing information including, but not limited to, exemplary periodic and aperiodic DRX pattern parameters as described above. Accordingly, when the AP receives a "PS-Poll with low-power timing" frame from the STA, it determines the STA's low-power timing information based on this implicit understanding.

In other embodiments, the low-power timing information may be communicated explicitly in the "PS-Poll with low-power timing" frame. Fig. 4B is a diagram of the Frame Control field of a "PS-Poll with low-power timing" frame, with the Type and Subtype fields having values according to Fig. 4A. Note that the bit order in each subfield in the diagram of Fig. 4B is opposite the order for that subfield given in the table of Fig. 4A. In the embodiment of Fig. 4B, information indicating the STA's low-power timing information is contained in the shaded subfields labelled "Timing info" in Fig. 4B. For example, the five bits of the "Timing info" subfields could be used to encode various combinations of the time when the STA will enter Doze state following the reception of the Data frame sent by the AP in response to the "PS-Poll with low-power timing" frame, parameters of a periodic DRX pattern after entering Doze state, and parameters of an aperiodic DRX pattern after entering Doze state. Although Fig. 4B shows the "Timing info" field comprising five bits of the Frame Control field, persons of ordinary skill will recognise that the "Timing info" field may comprise less than five bits, and that the remainder of the five bits may be used for other purposes.

Fig. 5A is a diagram of another embodiment of the Frame Control field of a "PS-Poll with low-power timing" frame, with the Type and Subtype fields having values according to the table of Fig. 4A. Note that the bit order in each subfield in the diagram of Fig. 5 A is opposite the order for that subfield given in the table of Fig. 4A. Fig. 5B is a diagram of the entire "PS-Poll with low-power timing" frame of the same embodiment. In this embodiment, the low-power timing information is not contained in any of the subfields of the Frame Control field. Instead, the low-power timing information is included in another field of the "PS-Poll with low-power timing" frame; for example, as shown in Fig. 5B, the low-power timing information may be included in the shaded field labelled "Timing info". For example, the six octets (i.e. 48 bits) of the "Timing info" field could be used to encode various combinations of the time when the STA will enter Doze state following the reception of the data frame sent by the AP in response to the "PS-Poll with low-power timing" frame, parameters of a periodic DRX pattern after entering Doze state, and parameters of an aperiodic DRX pattern after entering Doze state. Although Fig. 5B shows the "Timing info" field comprising the entire six octets (i.e. the entire length of the TA field in the current PS-Poll frame), persons of ordinary skill will recognise that the "Timing info" field may comprise less than the full six octets, and that the remainder of the six octets may be used for other purposes.

The low-power timing information may be explicitly communicated in other ways according to various embodiments of the present disclosure. In one exemplary embodiment, the currently-defined 802.11 PS-Poll MAC frame can be modified such that it retains the Type and Subtype values shown in Fig. 4A (i.e. "01" and "1010" respectively) but the low-power timing information can be included in various fields or subfields of the frame, including the mappings shown in Figs. 4B and 5B. Persons of ordinary skill will recognise that various other combinations of the embodiments described above are also possible within the scope of the present disclosure.

Fig. 6 is a flowchart of an example of a method for transmitting information relating to when a wireless communication device, such as an 802.11 STA, will be entering a low-power state or mode, such as an 802.11 PS mode or an 802.11 Doze state, according to one or more embodiments of the present disclosure. Although the method is illustrated in Fig. 6 by blocks in a particular order, this order is merely exemplary and the steps of the method may be performed in a different order than shown by Fig. 6, and may be combined and/or divided into blocks having different functionality. In block 600, the device utilising the method of Fig. 6 (also referred to below as the "first device") begins in a low-power state or mode (e.g. 802.11 Doze state). In block 610, the first device transitions to a non- low-power state or mode (e.g. 802.11 Awake state) at a predetermined time to listen for information broadcast by a second device (e.g. an 802.11 AP). In block 615, the device receives information broadcast by the second device, such as a Beacon frame broadcast by an 802.11 AP. In block 620, the first device determines if the broadcast information comprises an indication that the second device has buffered data for the first device. For example, the device may read the TIM (in case the second device is an 802.11 AP) or ATIM (in case the second device is an 802.11 STA) field of the Beacon frame to see if it contains an identifier for the device. If not, the first device returns to block 600 where it enters the low-power state or mode. In some embodiments, the first device may transmit a message to the second device before entering the low-power state or mode in block 600. In some embodiments, the first device may transmit a message to the second device before or after receiving the information broadcast by the second device in block 610.

If the first device determines in block 620 that the second device has buffered data, then the first device proceeds to block 630 where it determines low-power timing information and encodes a message in preparation for transmitting the message to the second device, as discussed below with reference to block 640. Alternatively, as another example not shown in this figure, the first device may proceed directly to block 630 from block 610 without receiving broadcast information, such as an 802.11 Beacon frame. In other words, in such embodiments, the first device may send a data request message without receiving indication of available data from the second device. In some embodiments, the operation of block 630 may comprise reading default low-power timing information that is known to both the first and second devices. In some embodiments, the operation of block 630 may comprise computing the time, t, when the first device intends to enter the low-power state or mode. In some embodiments, t may be computed relative to the time the message (e.g. a PS-Poll with low-power timing frame as shown in and described above in reference to Figs. 4 and 5) will be transmitted in block 640. By way of illustration using an 802.1 1 example, a time t would indicate that an STA will enter Doze state t time units or, alternatively, Beacon intervals after transmitting the PS-Poll with low-power timing frame. In some embodiments, a scaling factor can be used to indicate longer periods of time such that the time duration t is scaled by a factor s such that the actual duration until entering Doze state corresponds to t*s time units or Beacon intervals. In other embodiments, the time duration t can be absolute and based on a common clock or time base that is available to and understood by all devices in a network. In some embodiments, this common clock or time base may be a global time base, such as the Universal Time Coordinate (UTC) distributed by the Global Positioning System (GPS). In some embodiments, a scaling factor may be used together with an absolute time duration, t.

In other embodiments, the operation of block 630 may comprise computing a periodic or aperiodic DRX pattern comprising transitions between low-power and non- low-power (e.g. "Active") states, as shown in and described above in reference to Figs. 3A and 3B, respectively. The periodic DRX pattern may comprise parameters T_a and Td representing, respectively, the time spent in Awake and Doze states. Each of T_a and Td may be expressed or encoded in various ways, including the methods described above for encoding the time, t, that the STA will enter Doze state. The aperiodic DRX pattern may comprise parameters {T_ai} , i=\ to N, and {Tdi} ,j = 1 to M, representing a plurality of consecutive time periods the STA will spend in Awake and Doze states, respectively. Each member of { T_ai) and {¾} may be expressed or encoded in various ways, including the methods described above for encoding the time, t, that the STA will enter Doze state. In some embodiments, the first device may include one or more indices indicating one or more of a set of predefined periodic or aperiodic patterns that are known to both the first and second devices.

In some embodiments, the operation in block 630 may comprise determining that the most recently computed low-power timing information, which is currently in use by the device, should remain unchanged. In any event, in block 630, after determining the low-power timing information, the first device then forms a message comprising the low-power timing information. In some embodiments, the operation of block 630 comprises inserting the low-power timing information into fields or sub fields of the message. In some embodiments, the operation of block 630 comprises inserting an indicator that the low-power timing information is present in other fields or subfields of the message. For example, the operation of block 630 may comprise forming the Frame Control field of the "PS-Poll with low-power timing" frame shown in Fig. 4B or the Frame Control and Timing info fields shown in Figs. 5 A and 5B. In some embodiments, the operation of block 630 may comprise inserting appropriate values into the Type and Subtype subfields of the Frame Control field to indicate a "PS-Poll with low-power timing information" frame, without inserting explicit low-power timing information in other fields or subfields. In such cases, the Type and Subtype subfield values indicate predetermined default low-power timing information. In block 640, the first device transmits the message comprising the low-power timing information to the second device. In some embodiments, the operation of block 640 may comprise transmitting a data request message to the second device. For example, the operation of block 640 may comprise transmitting a "PS-Poll with low- power timing" frame, as shown in Figs. 4 and 5, to an 802.11 AP.

In block 650, the first device determines if it has received a response from the second device to the message transmitted in block 640 and, if so, the type of response received. In some exemplary 802.11 embodiments, the operation of block 650 may comprise determining whether the STA has received a response to a "PS-Poll with low- power timing" frame from the AP and, if so, whether the response is an ACK frame or a data frame. If the first device determines it has not received a response, it returns to block 630. If the first device determines in block 650 that it correctly received a data message in response to the message transmitted in block 640, it proceeds to block 690 where it sends a message to the second device acknowledging the receipt of the data message. In some embodiments, the operation in block 660 may comprise sending an ACK frame to an 802.11 AP. The device then proceeds to block 695 where it determines whether the second device has more data intended for the first device. In some embodiments, this may comprise reading the More Data subfield of the Frame Control field of the MAC header of an 802.11 Data frame. If the first device determines that second device has no more data to send, it proceeds to block 685 where it exits low-power timing mode. The first device then returns to block 600 where it enters a low-power state or mode.

On the other hand, if the first device determines in block 695 that the second device has more data to send, it proceeds to block 655. By the same token, the first device proceeds to block 655 if it determines in block 650 that it received an acknowledgement (e.g. an ACK frame) from the second device. In block 655, the first device determines if the received message, whether ACK or data, includes an acknowledgement to the low-power timing information in the message sent in block 640. In some embodiments, the acknowledgement may comprise a value of "1" in the Power Management subfield of the Frame Control field of the received message, as shown and described above with reference to Figs. 4B and 5A.

If the received message includes an acknowledgement of the low-power timing information, the first device proceeds to block 660, where it updates its low-power timing mode schedule according to the acknowledged information, then to block 665. If the received message does not include an acknowledgement of the low-power timing information, the first device proceeds directly to block 665, utilising either a previously- determined or default low-power timing mode schedule. Regardless, in block 665, the first device enters low-power timing mode operation according to its current schedule. For example, the operation in block 665 may comprise entering a low-power state or mode for a duration Td of a periodic DRX pattern, as described above with reference to Fig. 3A, or for a duration Tdj of an aperiodic DRX pattern, as described above with reference to Fig. 3B.

After a duration in a low-power state or mode (e.g. 802.11 Doze state), the first device enters a non- low-power state or mode (e.g. 802.11 Active state) and proceeds to block 670 where it receives a data message from the second device (e.g. an 802.11 Data frame). Next, in block 675, the first device sends a message to the second device acknowledging the receipt of the data message. In some embodiments, the operation in block 675 may comprise sending an ACK frame to an 802.11 AP. The first device then proceeds to block 680 where it determines whether the second device has more data intended for the first device. In some embodiments, this may comprise reading the More Data subfield of the Frame Control field of the MAC header of an 802.11 Data frame. If the first device determines that second device has no more data to send, it proceeds to block 685 where it exits low-power timing mode. The first device then returns to block 600 where it enters a low-power state or mode. On the other hand, if the first device determines in block 695 that the second device has more data to send, it returns to block 665 where it continues operating according to the current low-power timing schedule determined earlier.

Fig. 7 is a flowchart of an example of a method for selectively transmitting data frames or messages based on timing information related to when the target device for the data frames or messages will be entering a low-power state or mode, such as an 802.11 Doze state or an 802.11 PS mode, according to one or more embodiments of the present disclosure. Although the method is illustrated in Fig. 7 by blocks in a particular order, this order is merely exemplary and the steps of the method may be performed in a different order than shown by Fig. 7, and may be combined and/or divided into blocks having different functionality. In block 700, the source device (which also is referred as the "second device") waits until a predetermined time to transmit a broadcast message. In some embodiments, the second device may be an 802.11 AP or an 802.11 STA, the broadcast message may be an 802.11 Beacon frame and the predetermined time may be an 802.11 Beacon interval.

In block 710, the second device transmits a broadcast message comprising a traffic indicator that further comprises information indicating that the second device is buffering one or more data messages for one or more other devices in communication with the second device, including data messages for a first device. In some embodiments, the traffic indicator may comprise an 802.11 Traffic Indication Map (TIM) field if the second device is an AP operating in infrastructure BSS mode, or an 802.11 Announcement Traffic Indication Map (ATIM) field if the second device is a STA operating in IBSS or ad hoc mode. In block 720, the second device determines if it received a message, such as a data request message, from the first device during an expected time period. If the second device determines that it did not receive a message from the first device during the expected time period, it returns to block 700 where it waits until time to transmit the next broadcast message.

On the other hand, if the second device determines that it received a message from the first device during the expected time period, it proceeds to block 730 where it reads the low-power timing information sent by the first device in the message. In some embodiments, the message comprising the low-power timing information may be a data request message, such as a "PS-Poll with low-power timing" frame shown in and discussed above with reference to Figs. 4 and 5. In some embodiments, the low-power timing information may comprise an indicator that low-power timing information is present in other fields or subfields of the data request message. In some embodiments, the low-power timing information may comprise one or more of the various forms of low-power timing information computed in block 630 of Fig. 6, as described above with reference to that block. Regardless of the form of the low-power timing information, the device in block 730 reads it from the message and stores it in a form that can be used to indicate the schedule at which the first device will transition between a low-power state (e.g. 802.11 Doze state or PS mode) and a non-low-power state (e.g. 802.11 Awake state or Active mode). Additionally, in block 730, the second device initialises the retransmission counter (RTX) to zero.

In block 740, the second device transmits a message to the first device, with the message comprising an acknowledgement of the low-power timing information included in the message received from the first device. In some embodiments, the message transmitted in block 740 may comprise both the buffered data message targeted to the first device and the acknowledgement of the low-power timing information. In some embodiments, the message transmitted in block 740 may be an 802.11 Data frame and the acknowledgement may be the Power Management subfield of the Frame Control field of the Data frame set to "1". In some embodiments, the message may comprise only the acknowledgement of the low-power timing information. In some embodiments, the message transmitted in block 740 may be an 802.11 ACK frame.

In block 750, the second device determines whether it received a response from the first device to the data message transmitted in block 740, during a time period consistent with the first device's low-power timing schedule information read in block 730. In some embodiments, the response may comprise an 802.1 1 ACK frame. If the second device determines that it received a response, it returns to block 700 where it waits until time to transmit the next broadcast message.

On the other hand, if the second device determines that it did not receive a response during the time period, it proceeds to block 760 where it increments the retransmission counter, RTX, and then to block 770 where it compares RTX to the maximum number of retransmissions allowed, RTX_max. If RTX is greater than or equal to RTXmax, then the second device proceeds to block 780 where it discards the data message, then returns to block 700 where it waits until time to transmit the next broadcast message. If RTX is less than RTX_max, the second device proceeds to block 765 where it waits until the data message recipient (i.e. the first device) is in a non-low- power state according to the first device's low-power timing schedule information read in block 730. At that time, the second device proceeds to block 740 where it retransmits the data message, including the low-power timing acknowledgement.

Fig. 8 is a block diagram of an exemplary wireless communication device or apparatus, such as an 802.11 STA, utilising certain embodiments of the present disclosure, including one or more of the methods described above with reference to other figures. Device 800 comprises processor 810 which is operably connected to program memory 820 and data memory 830 via bus 870, which may comprise parallel address and data buses, serial ports, or other methods and/or structures known to those of ordinary skill in the art. Program memory 820 comprises software code executed by processor 810 that enables device 800 to communicate with one or more other devices using protocols according to various embodiments of the present disclosure, including the 802.11 PHY and MAC protocol layer and improvements thereto, including those described above with reference to other figures. In some embodiments, program memory 820 may also comprise software code executed by processor 810 that enables device 800 to communicate with one or more other devices using protocols other than 802.11 , such as LTE; UMTS, HSPA, GSM, GPRS, and EDGE protocols standardised by 3 GPP; CDMA2000 protocols standardised by 3GPP2; Internet protocols such as IP, TCP, UDP, or others known to persons of ordinary skill in the art; or any other protocols utilised in conjunction with radio transceiver 840, user interface 850, and/or host interface 860. Program memory 820 further comprises software code executed by processor 810 to control the functions of device 800, including configuring and controlling various components such as radio transceiver 840, user interface 850, and/or host interface 860. Such software code may be specified or written using any known or future developed programming language, such as e.g. Java, C++, C, and Assembler, as long as the desired functionality, e.g. as defined by the implemented method steps, is preserved.

Data memory 830 may comprise memory area for processor 810 to store variables used in protocols, configuration, control, and other functions of device 800. As such, program memory 820 and data memory 830 may comprise non-volatile memory (e.g. flash memory), volatile memory (e.g. static or dynamic RAM), or a combination thereof. Persons of ordinary skill in the art will recognise that processor 810 may comprise multiple individual processors (not shown), each of which implements a portion of the functionality described above. In such case, multiple individual processors may be commonly connected to program memory 820 and data memory 830 or individually connected to multiple individual program memories and or data memories. More generally, persons of ordinary skill in the art will recognise that various protocols and other functions of device 800 may be implemented in many different combinations of hardware and software including, but not limited to, application processors, signal processors, general-purpose processors, multi-core processors, ASICs, fixed digital circuitry, programmable digital circuitry, analog baseband circuitry, radio -frequency circuitry, software, firmware, and middleware. Radio transceiver 840 may comprise radio-frequency transmitter and/or receiver functionality that enables device 800 to communicate with other equipment supporting like wireless communication standards. In an exemplary embodiment, radio transceiver 840 includes a transmitter and receiver compatible with the 802.11 standard that enable device 800 to communicate with various other devices according to the 802.11 standard. In some embodiments, radio transceiver 840 includes circuitry, firmware, etc. necessary for device 800 to communicate with other devices, such as 802.11 STAs and APs, using the PHY protocol layer methods and improvements thereto such as those described above with reference to other figures. In some embodiments, radio transceiver 840 is capable of communicating on one or more unlicensed frequency bands including, for example, frequency bands in the regions of 900 MHz, 2.4 GHz, 3.6 GHz and 5 GHz. The person of ordinary skill will understand that other bands, licensed or unlicensed, may be supported in radio transceiver 840 by adding appropriate circuitry. The radio functionality particular to each of these embodiments may be coupled with or controlled by other circuitry in device 800, such as processor 810 executing protocol program code stored in program memory 820.

User interface 850 may take various forms depending on the particular embodiment of device 800. In some embodiments, device 800 is a mobile phone, in which case user interface 850 may comprise a microphone, a loudspeaker, slidable buttons, depressable buttons, a keypad, a keyboard, a display, a touch screen display, and/or any other user-interface features commonly found on mobile phones. In other embodiments, device 800 is a data modem capable of being utilised with a host computing device, such as a data card or data modem contained within a host computing device, such as a laptop computer or tablet. In some embodiments, device 800 is capable of being plugged into a USB port of the host computing device. In embodiments such as these, user interface 850 may be very simple or may utilise features of the host computing device, such as the host's display and/or keyboard. Host interface 860 of device 800 also may take various forms depending on the particular embodiment of device 800. In embodiments where device 800 is a mobile phone, host interface 860 may comprise for example a USB interface, an HDMI interface or the like. In the embodiments where device 800 is a data modem capable of being utilised with a host computing device, host interface may be for example a USB or PCMCIA interface.

In some embodiments, device 800 may comprise more functionality than is shown in Fig. 8. In some embodiments, device 800 may also comprise functionality such as a video and/or still- image camera, media player, etc., and radio transceiver 840 may include circuitry necessary to communicate using radio-frequency communication standards other than 802.11, including GSM, GPRS, EDGE, UMTS, HSPA, CDMA2000, LTE, Bluetooth, GPS, and/or others. Persons of ordinary skill in the art will recognise the above list of features and radio -frequency communication standards is merely exemplary and not limiting to the scope of the present disclosure. Accordingly, processor 810 may execute software code stored in program memory 820 to control such additional functionality.

Fig. 9 is a block diagram of an exemplary wireless communication device 900, such as an 802.1 1 AP, utilising certain embodiments of the present disclosure, including those described above with reference to other figures. Device 900 comprises processor 910 which is operably connected to program memory 920 and data memory 930 via bus 970, which may comprise parallel address and data buses, serial ports, or other methods and/or structures known to those of ordinary skill in the art. Program memory 920 comprises software code executed by processor 910 that enables device 900 to communicate with one or more other devices using protocols according to various embodiments of the present disclosure, such as the 802.11 PHY and MAC protocol layer and improvements thereto, including those described above with reference to other figures. Program memory 920 also comprises software code executed by processor 910 that enables device 900 to communicate with one or more other devices using other protocols or protocol layers, including any other higher-layer protocols utilised in conjunction with radio network interface 940 and distribution network interface 950. By way of example and without limitation, distribution network interface 950 may comprise an IEEE 802.3 wired LAN ("Ethernet") interface that is commonly known to persons of ordinary skill in the art. Program memory 920 further comprises software code executed by processor 910 to control the functions of device 900, including configuring and controlling various components such as radio network interface 940, distribution network interface 950, and OA&M (operations, administration and management) interface 960.

Data memory 930 may comprise memory area for processor 910 to store variables used in protocols, configuration, control, and other functions of device 900. As such, program memory 920 and data memory 930 may comprise non- volatile memory (e.g. flash memory, hard disk, etc.), volatile memory (e.g. static or dynamic RAM), network-based (e.g. "cloud") storage, or a combination thereof. Persons of ordinary skill in the art will recognise that processor 910 may comprise multiple individual processors (not shown), each of which implements a portion of the functionality described above. In such case, multiple individual processors may be commonly connected to program memory 920 and data memory 930 or individually connected to multiple individual program memories and/or data memories. More generally, persons of ordinary skill in the art will recognise that various protocols and other functions of device 900 may be implemented in many different combinations of hardware and software including, but not limited to, application processors, signal processors, general-purpose processors, multi-core processors, ASICs, fixed digital circuitry, programmable digital circuitry, analog baseband circuitry, radio -frequency circuitry, software, firmware, and middleware.

Radio network interface 940 may comprise transmitters, receivers, signal processors, ASICs, antennas, beamforming units, and other circuitry that enables device 900 to communicate with other equipment such as, in some embodiments, a plurality of compatible STAs. In some embodiments, radio network interface may comprise various protocols or protocol layers, such as the 802.11 PHY and MAC layer protocols standardised by IEEE, improvements thereto such as described herein with reference to one of more of the figures, or any other higher-layer protocols utilised in conjunction with radio network interface 940. In some embodiments, the radio network interface 940 may comprise a PHY layer based on orthogonal frequency division multiplexing (OFDM) or orthogonal frequency division multiple access (OFDMA) technologies.

Distribution network interface 950 may comprise transmitters, receivers and other circuitry that enable device 900 to communicate with other equipment in a distribution network such as, in some embodiments, a wired network based on the IEEE 802.3 wired LAN standard. OA&M interface 960 may comprise transmitters, receivers and other circuitry that enable device 900 to communicate with external networks, computers, databases, and the like for purposes of operations, administration, and maintenance of device 900 or other network equipment operably connected thereto. Lower layers of OA&M interface 960 may be compatible with one or more of the IEEE 802.3 wired LAN and IEEE 802.11 wireless LAN standards. In some embodiments, one or more of radio network interface 940, distribution network interface 950, and OA&M interface 960 may be multiplexed together on a single physical interface, such as the examples listed above. As described herein, a device or apparatus may be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset. This, however, does not exclude the possibility that a functionality of a device or apparatus, instead of being hardware implemented, may be implemented as a software module such as a computer program or a computer program product comprising executable software code portions for execution or being run on a processor. A device or apparatus may be regarded as a device or apparatus, or as an assembly of multiple devices and/or apparatuses, whether functionally in cooperation with or independently of each other. Moreover, devices and apparatuses may be implemented in a distributed fashion throughout a system, so long as the functionality of the device or apparatus is preserved. Such and similar principles are considered as known to a skilled person. The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

1. A method for low-power operation of a first device in a wireless communication network, the method comprising:

receiving an indication that a second device has a data message intended for the first device;

determining low-power timing information for the first device;

sending a data request message to the second device, wherein the data request message comprises the low-power timing information;

determining that a response to the data request message has been received; and entering a low-power state or mode corresponding to the low-power timing information.

2. A method according to claim 1 , wherein the low-power timing information comprises the time at which the first device will enter a low-power state or mode.

3. A method according to claim 2, wherein the time at which the first device will enter a low-power state or mode is relative to the time when the data request message is sent.

4. A method according to claim 2, wherein the time at which the first device will enter a low-power state or mode is an absolute time.

5. A method according to any of claims 1 to 4, wherein the low-power timing information comprises discontinuous reception (DRX) pattern parameters indicating one or more durations that the first device will spend in a low-power state or mode and a non-low-power state or mode.

6. A method according to claim 5, wherein the discontinuous reception (DRX) pattern is at least one of a periodic pattern and an aperiodic pattern.

7. A method according to any of claims 1 to 6, comprising:

determining that the second device has no more data messages intended for the first device; and

entering the low-power state or mode independent of the low-power timing information.

8. A method according to any of claims 1 to 7, wherein the low-power timing information comprises a message type indicator.

9. A method according to any of claims 1 to 8, wherein the first device is an 802.11 station (ST A).

10. A method according to claim 9, wherein:

the low-power timing information comprises a message type indicator field; and sending the data request message comprises inserting the message type indicator field in one of the Type subfield and the Subtype subfield of the Frame Control field in an 802.11 frame.

11. A method according to claim 9, wherein sending the data request message comprises inserting the low-power timing information in the Medium Access Control

(MAC) header of an 802.11 frame.

12. A method according to claim 11, wherein sending the data request message comprises inserting the low-power timing information in one or more subfields of the Frame Control field in an 802.11 frame.

13. A method for selectively transmitting a data message based on the power mode of a target wireless communication device, the method comprising:

transmitting a message comprising an indicator that a data message is available for the target device;

receiving a data request message from the target device; determining that the data request message comprises low-power timing information for the target device; and

transmitting the data message to the target device based on low-power timing information for the target device.

14. A method according to claim 13, wherein the low-power timing information comprises the time at which the target device will enter a low-power state or mode.

15. A method according to claim 14, wherein the time at which the target device will enter a low-power state or mode is relative to the time when target device sent the data request message.

16. A method according to claim 14, wherein the time at which the target device will enter a low-power state or mode is an absolute time.

17. A method according to any of claims 13 to 16, wherein the low-power timing information comprises discontinuous reception (DRX) pattern parameters indicating one or more durations that the target device will spend in a low-power state or mode and a non-low-power state or mode.

18. A method according to claim 17, wherein the discontinuous reception (DRX) pattern is at least one of a periodic pattern and an aperiodic pattern.

19. A method according to any of claims 13 to 18, wherein transmitting the data message to the target device based on the low-power timing information comprises: determining a period when the target device is expected to be in a non-low- power state or mode; and

transmitting the data message to the target device during the period.

20. A method according to any of claims 13 to 19, wherein transmitting the data message to the target device comprises transmitting an acknowledgement of low-power timing information for the target device.

21. A method according to any of claims 13 to 20, comprising determining the low- power timing information based on the message type indicator of the data request message.

22. A method according to any of claims 13 to 21, wherein the target device is an 802.11 station (ST A).

23. A method according to claim 22, wherein:

the low-power timing information comprises a message type indicator field; and determining that the data request message comprises low-power timing information for the target device comprises reading the message type indicator field from one of the Type subfield and the Subtype subfield of the Frame Control field in an 802.11 frame.

24. A method according to claim 22, wherein determining that the data request message comprises low-power timing information for the target device comprises reading the low-power timing information from the Medium Access Control (MAC) header of an 802.11 frame.

25. A method according to claim 22, wherein determining that the data request message comprises low-power timing information for the target device comprises reading the low-power timing information from one or more sub fields of the Frame Control field in an 802.11 frame.

26. Apparatus comprising a processing system for a wireless communication device constructed and arranged to cause the wireless communication device to, upon receipt of an indication that a second device has a data message intended for the device: determine low-power timing information;

send a data request message to the second device, wherein the data request message comprises the low-power timing information;

determine that a response to the data request message has been received; and enter a low-power state or mode corresponding to the low-power timing information.

27. Apparatus according to claim 26, wherein the low-power timing information comprises the time at which the device will enter a low-power state or mode.

28. Apparatus according to claim 27, wherein the time at which the device will enter a low-power state or mode is relative to the time when the data request message is sent.

29. Apparatus according to claim 27, wherein the time at which the device will enter a low-power state or mode is an absolute time.

30. Apparatus according to any of claims 26 to 29, wherein the low-power timing information comprises discontinuous reception (DRX) pattern parameters indicating one or more durations that the device will spend in a low-power state or mode and a non-low-power state or mode.

31. Apparatus according to claim 30, wherein the discontinuous reception (DRX) pattern is at least one of a periodic pattern and an aperiodic pattern.

32. Apparatus according to any of claims 26 to 31, arranged to cause the wireless communication device to enter the low-power state or mode independent of the low- power timing information if it is determined that the second device has no more data messages intended for the device.

33. Apparatus according to any of claims 26 to 32, wherein the low-power timing information comprises a message type indicator.

34. Apparatus according to any of claims 26 to 33, wherein the wireless communication device is an 802.11 station (STA).

35. Apparatus according to claim 34, arranged such that sending the data request message comprises inserting a message type indicator field in one of the Type subfield and the Subtype subfield of the Frame Control field in an 802.11 frame.

36. Apparatus according to claim 34, arranged such that sending the data request message comprises inserting the low-power timing information in the Medium Access

Control (MAC) header of an 802.11 frame.

37. Apparatus according to claim 36, arranged such that sending the data request message comprises inserting the low-power timing information in one or more subfields of the Frame Control field in the 802.11 frame.

38. Apparatus comprising a processing system for a wireless communication device constructed and arranged to cause the wireless communication device to:

transmit a message comprising an indicator that a data message is available for a target device;

determine that a data request message received from the target device comprises low-power timing information for the target device; and

transmit the data message to the target device based on low-power timing information for the target device.

39. Apparatus according to claim 38, wherein the low-power timing information comprises the time when the target device will enter a low-power state or mode.

40. Apparatus according to claim 39, wherein the time at which the target device will enter a low-power state or mode is relative to the time when the target device sent the data request message.

41. Apparatus according to claim 39, wherein the time at which the target device will enter a low-power state or mode is an absolute time.

42. Apparatus according to any of claims 38 to 40, wherein the low-power timing information comprises discontinuous reception (DRX) pattern parameters indicating one or more durations that the target device will spend in a low-power state or mode and a non-low-power state or mode.

43. Apparatus according to claim 42, wherein the discontinuous reception (DRX) pattern is at least one of a periodic pattern and an aperiodic pattern.

44. Apparatus according to any of claims 38 to 43, arranged such that transmitting the data message to the target device based on low-power timing information for the target device comprises causing the wireless communication device to:

determine a period when the target device is expected to be in a non-low-power state or mode; and

transmit the data message to the target device during the period.

45. Apparatus according to any of claims 38 to 44, arranged such that transmitting the data message to the target device based on low-power timing information for the target device comprises causing the wireless communication device to transmit an acknowledgement of the low-power timing information.

46. Apparatus according to any of claims 38 to 45, arranged such that the wireless communication device determines the low-power timing information based on the message type indicator of the data request message.

47. Apparatus according to any of claims 38 to 46, wherein the wireless communication device is one of an 802.11 access point (AP) and an 802.11 station (STA).

48. Apparatus according to claim 47, arranged such that determining that the data request message comprises low-power timing information for the target device comprises causing the wireless communication device to read a message type indicator field from one of the Type subfield and the Subtype subfield of the Frame Control field of an 802.11 frame.

49. Apparatus according to claim 47, arranged such that determining that the data request message comprises low-power timing information for the target device comprises causing the wireless communication device to read at least a portion of the low-power timing information from the Medium Access Control (MAC) header of an 802.11 frame.

50. Apparatus according to claim 49, arranged such that determining that the data request message comprises low-power timing information for the target device comprises causing the wireless communication device to read at least a portion of the low-power timing information from one or more sub fields of the Frame Control field in the 802.11 frame.

51. A computer program comprising program code that, when executed by a wireless communication device, causes the wireless communication device to, upon receipt of an indication that a second device has a data message intended for the device: determine low-power timing information for the device;

52. A computer program comprising program code that, when executed by a wireless communication device, causes the wireless communication device to: transmit a message comprising an indicator that a data message is available for a target device;