Note: Descriptions are shown in the official language in which they were submitted.
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Description
Title of Invention: APPARATUS AND METHOD FOR POWER
SAVE MODE IN WIRELESS LOCAL AREA NETWORK
Technical Field
[11 The present invention relates to a wireless local area network (WLAN),
and more
specifically to an apparatus and method for managing power save mode in a WLAN
system.
Background Art
[2] Advances in a wireless local access network (WLAN) make mobile phone
users,
such as Laptop computer users, easy to perform their works due to an improved
mobility. For example, users can carry with their laptop computers to a
meeting room
in order to attend a conference, and can get on a local network through WLAN.
[31 For a system based on Institute of Electrical and Electronics
Engineers (IEEE)
802.11 standards, Basic Service Set (BSS) refers to a station assembly that is
suc-
cessfully synchronized. And a Basic Service Area (BSA) refers to an area
including
members that consist of BSS. BSA may be changed according to characteristics
of
radio wave in a wireless media. BSS may be basically classified into two
config-
urations, an independent BSS and an infrastructured BSS (IBSS). The former
implies
BSS that establishes a self-contained network and cannot access to a
Distribution
System (DS), and the latter implies BSS that includes one or more a Access
Point
(AP), the Distribution System (DS), and the like and generally use AP in all
of the
communication processes including the communications between the stations.
[4] According to IEEE 802.11e standard "Part 11: Wireless LAN Medium
Access
Control (MAC) and Physical Layer (PHY) specifications / Amendment 8: Medium
Access Control (MAC) Quality of Service Enhancements" published at November
11,
2005, it was not allow to directly transmit data between non-AP STAs in the
IBSS, but
it surely required through a AP in order to the data transmissions. It means
that the
station in BSS cannot directly transmit data to other STA, and pass through AP
in
order to frame transmission.
[51 Further, since IEEE 802.11e standard, a Direct link Setup (DLS)
between non-AP
STAs is having supported. The station can directly transmit the frame to other
station
through DLS Direct link.
[6] The station is operated in two power management modes, such as one of
an Active
Mode (AM) and a Power Save Mode (PSM). The station in the AM keeps in the
awake
state, and the station in the PSM transitions between the wakeup state and a
doze state.
The station is awake at the beginning of the wakeup state and stays awake
during a
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wake window. The station in the wakeup state can transmit and/or receive
frames. The station
in the doze state cannot transmit and/or receive frames.
[7] Generally, the station belongs to user as a portable device, so that
supporting
PSM is essential to effectively manage a power. In the IEEE 802.11e standard,
the
management of the power is called an Automatic Power Save Deliver (APSD). APSD
has two
mechanisms: an unscheduled APSD (U-APSD) and a scheduled APSD (S-APSD).
[8] The management of the power is needed for the direct link. According to
IEEE
802.11e, after DLS Direct link is setup, the station in AM or PSM transmits a
DATA Frame
and/or a Management Frame to other station through DLS Direct link.
[9] In order to establishing DLS direct link, a DLS Request Frame and a DLS
Response Frame between two non-AP STAs are exchanged through AP. It means that
AP
supporting IEEE 802.11e is required in order for the setup of the DLS direct
link. However,
since WLAN system that has been used widely is based only on the IEEE
802.11a/b/g
standards, the AP supporting the IEEE 802.11a/b/g cannot support DLS.
Therefore, even
though non-AP STAs supports IEEE 802.11e, non-AP STAs cannot setup DLS direct
link
through the AP, so that DLS service cannot be utilized.
[10] A Tunneled Direct link Setup (TDLS) has been introduced in order to
establish
a direct link between non-AP STAs even if the AP cannot support IEEE 802.11e.
In the
TDLS, TDLS direct link is set up through encapsulated data frames.
Summary
[11] There is a need for a technique for effectively managing the PSM under
the
TDLS direct link.
[12] Embodiments of the present invention may provide a method and
apparatus for
a power save mode through a TDLS direct link in a WLAN system.
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[12a] In an aspect, there is provided a method for a power save mode
(PSM) in a
wireless local area network, the method comprising: establishing, by a
station, a Tunneled
Direct link Setup (TDLS) direct link with a peer station via an access point
(AP); entering, by
the station, the power save mode (PSM); transmitting, by the station after
waking up to enter a
wakeup state, a power save mode (PSM) request frame to the peer station, the
PSM request
frame including a wakeup schedule for the PSM, the wakeup schedule including a
wakeup
window duration and a wakeup interval, the wakeup window duration indicating a
duration of
a wakeup window, the wakeup interval indicating a time interval between
consecutive wakeup
windows; and receiving, by the station, a PSM response frame from the peer
station through
the TDLS direct link directly in response to the PSM request frame, wherein
the wakeup state
is maintained until the PSM response frame is received, and wherein the PSM
request frame is
not directly transmitted to the peer station but the PSM request frame is
transmitted to the peer
station though the AP.
[13] In another aspect, a method for a power save mode in a wireless local
area
network is provided. The method includes establishing a Tunneled Direct link
Setup (TDLS)
direct link with a peer station, transmitting, to the peer station via an
access point (AP) or via
the TDLS direct link, a power save mode (PSM) request frame including a wakeup
schedule
for the PSM, the wakeup schedule including a wakeup window duration and a
wakeup
interval, the wakeup window duration indicating a duration of a wakeup window,
the wakeup
interval indicating a time interval between consecutive wakeup windows, and
receiving, from
the peer station via the TDLS direct link, a PSM response frame in response to
the PSM
request frame.
[14] The method may further include waking up to enter a wakeup state
before
transmitting the PSM request frame, wherein the wakeup state is maintained
until the PSM
response frame is received.
[15] Establishing the TDLS direct link may includes transmitting a TDLS
setup
request frame to the peer station via the AP, receiving a TDSL setup response
frame in
response to the TDLS setup request frame from the peer Station via the AP, and
transmitting a
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TDSL setup confirm frame in response to the TDSL setup response frame to the
peer Station
via the AP.
[16] The PSM Request Frame may be an encapsulated data frame.
[17] The PSM response frame may include a status field indicating
acceptance or
rejection of the wakeup schedule.
[18] If the status field indicates the rejection, the PSM response frame
may include
an alternative wakeup schedule.
[19] The wakeup schedule further may include an idle count indicating the
number
of consecutive wakeup windows during no directed frame is received from the
peer station
before the peer station deletes the wakeup schedule.
[19a] There is also provided a wireless apparatus for a power save
mode (PSM) in a
wireless local area network, the wireless apparatus comprising: an interface
unit; and a
processor operatively couples with the interface unit and configured to:
establish a Tunneled
Direct link Setup (TDLS) direct link with a peer station via an access point
(AP); enter the
power save mode (PSM); after waking up to enter a wakeup state, transmit a
power save mode
(PSM) request frame to the peer station, the PSM request frame including a
wakeup schedule
for the PSM, the wakeup schedule including a wakeup window duration and a
wakeup
interval, the wakeup window duration indicating a duration of a wakeup window,
the wakeup
interval indicating a time interval between consecutive wakeup windows; and
receive a PSM
response frame from the peer station through the TDLS direct link directly in
response to the
PSM request frame, wherein the wakeup state is maintained until the PSM
response frame is
received, and wherein the PSM request frame is not directly transmitted to the
peer station but
the PSM request frame is transmitted to the peer station through the AP.
[20] In another aspect, a wireless apparatus for a power save mode in a
wireless
local area network is provided. The wireless apparatus include an interface
unit, and a
processor operatively couples with the interface unit and configured to
establish a Tunneled
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Direct link Setup (TDLS) direct link with a peer station, transmit, to the
peer station via an
access point (AP) or via the TDLS direct link, a power save mode (PSM) request
frame
including a wakeup schedule for the PSM, the wakeup schedule including a
wakeup window
duration and a wakeup interval, the wakeup window duration indicating a
duration of a
5 wakeup window, the wakeup interval indicating a time interval between
consecutive wakeup
windows, and receive, from the peer station via the TDLS direct link, a PSM
response frame
in response to the PSM request frame.
[21] To enter a power save mode after establishing a TDLS direct link, a
station can
acknowledge the timing of the periodic wakeup schedule. Power consumption for
setting up
the power save mode may be reduced.
Brief Description of Drawings
[22] FIG. 1 illustrates a wireless local area network (WLAN) system to
implement
an embodiment of the present invention.
[23] FIG. 2 illustrates a conventional procedure to setup a TDLS direct
link.
[24] FIG. 3 illustrates the format of a TDLS action frame.
[25] FIG. 4 illustrates a procedure to setup a peer PSM.
[26] FIG. 5 illustrates a method of PSM according to an embodiment of the
invention.
[27] FIG. 6 illustrates a format of a PSM response frame.
[28] FIG. 7 illustrates a wireless apparatus to implement an embodiment of
the
present invention.
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Mode for the Invention
[29] FIG. 1 illustrates a wireless local area network (WLAN) system to
implement
an embodiment of the present invention. The WLAN system includes at least one
Basic
Service Set (BSS). A BSS is a set of stations (STAs) that are successfully
synchronized in
order to communicate each other. The BSS may be classified into an independent
BSS and an
infrastructured BSS (IBSS).
[30] The BSS1 and BSS2 in FIG. 1 are the IBSS including AP1 20 and AP2 50,
respectively. The BSS1 includes STA1 10, STA2 20, and AP1 20. The BSS2
includes STA3
30, STA4 40 and AP2 50. An access point (AP) is a STA that provides a
distribution service.
The independent BSS is operated as an ad-hoc mode, and does not include any
AP. A
plurality of IBSSs are connected by means of a distribution system (DS) 80. An
extended
service set (ESS) is a plurality of BSSs connected through the DS 80. In the
same ESS, a non-
AP STA can be moved from a BSS to other BSS while performing a seamless
communication.
[31] A STA is any functional medium including a medium access control (MAC)
layer and a physical (PHY) layer that are satisfied with the IEEE 802.11
standard. The STA
may be an AP or a non-AP STA, but in the absence of any different indication
hereinafter, a
STA refers to a non-AP STA. The STA can be called any other name, such as a
user
equipment (UE), a mobile station (MS), a mobile terminal, a portable device,
an interface
card, and the like. An AP is a functional medium that provides the connection
through a
wireless medium. The AP can be called any other name, such as a centralized
controller, a
base station (BS), a scheduler, and the like.
[32] A tunneled direct link setup (TDLS) is a protocol that uses
encapsulated frames
via an AP in order to setup a direct link. An encapsulation frame is
transferred as a data frame
in view of the AP but is processed as a management frame between non-AP STAs.
A sender
sends the encapsulation frame to a recipient via the AP transparently.
Hereinafter, a direct link
or a TDLS direct link refers to a direct link that is set up through TDLS.
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[33] FIG. 2 illustrates a conventional procedure to setup a TDLS direct
link. This
can refer the section 11.20 of IEEE 802.11z/D3.0 "Draft Amendment for Direct
link Setup"
published at November 2008. The IEEE 802.11z standard supports the TDLS direct
link
between non-AP STAs supporting IEEE 802.11e via a AP supporting IEEE
802.11a/b/g.
Dotted lines in FIG. 2 illustrate transmissions of encapsulated DATA frames.
[34] Referring to FIG. 2, in step S200, A STA1 transmits a TDLS setup
request
frame to a STA2 via an AP. The TDLS Setup Request Frame is a TDLS action frame
for
requesting the setup of the direct link.
[34a] In step S210, the STA2 transmits a TDLS setup response frame
to the STA1
1 0 via the AP in response to the TDLS setup request frame.
[35] In step S220, the STA1 transmits a TDSL setup confirm frame to the
STA2 via
the AP in order to confirm that the TDSL setup response Frame is received.
[36] In the TDLS setup process, there is high possibility to miss some TDLS
action
frame because the TDLS action frame is encapsulated and transmitted as a data
frame via the
AP. Therefore, an initiating STA (i.e., STA1) transmits the TDLS setup confirm
frame in
response to the TDLS setup response frame from a peer STA (i.e., STA2).
[37] The initiating STA (i.e., STA2) may be called a TDLS initiator and is
a STA
that transmits a TDLS setup request frame. The Peer STA may be called a TDLS
responder
and is a STA that receives the TDLS setup request frame. In FIG. 2, the
initiating STA is the
STA1 and the peer STA is the STA2.
[38] A TDLS action frame is a frame associated with configuration of TDLS
and
release of TDLS, and is encapsulated as a data frame. The AP regards the TDLS
action frame
as the data frame. Therefore, although the AP does not support IEEE 802.11e,
the TDLS
action frame may be transmitted to the peer STA via the AP.
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[39] FIG. 3 illustrates the format of a TDLS action frame. The format of
the TDLS
action frame is just an example, so that additional field may be added or some
field can be
omitted.
[40] A TDLS action frame 300 includes a MAC header 310, a frame body 320,
and
a frame check sequence (FCS) 330. The MAC header 310 may include a frame
control field, a
Duration/ID field, a plurality of Addresses, such as Address 1, Address 2,
Address 3, and
Address 4, a sequence control field, a Quality of Service (QoS) control field,
and the like. The
FCS 330 includes a cyclic redundancy check (CRC) for the MAC header 310 and
the frame
body 320.
[41] The frame body 320 includes an action field 321, a TDLS type field
322, and a
body Field 325. The action field 321 indicates that the encapsulated data
frame is the TDLS
action frame. The TDLS type field 322 indicates a type of the TDLS action
frame 300. The
body field 325 includes information according to the type of the TDLS action
frame 300.
[42] According to the section 7.4 of IEEE 802.11z/D3.0, the types of TDLS
Action
Frames are defined as following:
[43] Table 1
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[Table 1]
Field Value Type
0 TDLS Setup Request
1 TDLS Setup Response
2 TDLS Setup Confirm
3 TDLS Teardown
4 TDLS Peer Traffic Indication
TDLS Channel Switch Request
6 TDLS Channel Switch Response
7 TDLS Peer PSM Request
8 TDLS Peer PSM Response
9 TDLS AP PHY Rate Request
TDLS AP PHY Rate Response
11 ¨ 255 Reserved
[44] The TDLS setup request frame, the TDLS setup response frame and the
setup
confirm frame are used to set up the direct link as described above.
[45] The TDLS peer PSM request frame and the TDLS peer PSM response frame
are used
to set up a power save mode (PSM).
[46] In section 11 of the IEEE 802.11z/D3.0, there are two types of PSM.
One is a peer
PSM, and another is a peer unscheduled-automatic power save delivery (U-APSD).
The peer PSM is a power management mechanism on the basis of a periodic wakeup
schedule. The peer U-APSD is a non-scheduled power management mode.
[47] In the peer U-APSD, two STAs are in a doze state after the direct link
is established.
A STA (called a buffer STA) transmits a TDLS peer traffic indication frame to
a peer
STA (called a sleep STA) in the doze state via an AP. The TDLS peer traffic
indication
frame is an encapsulated data frame. The sleep STA received the TDLS peer
traffic in-
dication frame enters into a wakeup state, and receives data frames via the
direct link.
According to the peer U-APSD, the buffer STA does not know when the sleep STA
triggers a service period. Therefore, the buffer STA needs to remain in the
wakeup
state after transmitting the TDLS peer traffic indication frame.
[48] FIG. 4 illustrates a procedure to setup a peer PSM.
[49] In step S410, a TDLS direct link is established between a STA1 and a
STA2. In step
S420, the STA1 transmits a TDLS peer PSM request frame to the STA2 via an AP.
In
step S430, the STA2 transmits a TDLS peer PSM response frame to the STA1 via
the
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AP.
[501 The TDLS peer PSM request frame (shortly, a PSM request frame) and the
TDLS
peer PSM response frame (shortly, a PSM response frame) are transmitted as en-
capsulated data frames via the AP. Since the AP can arbitrarily forwards the
data
frames to the peer STA, a STA which transmits a frame does not know when the
AP
forwards he frame to the peer STA. For example, if the peer STA is in the doze
state,
the AP does not forward the frame to the peer STA before the peer ST enters
the
wakeup state.
[511 Synchronization is one of key issues to perform a scheduled power
management ef-
ficiently. Synchronization means that a wakeup schedule of a STA matched with
a
wakeup schedule of a peer STA. But it is not easy to acquire the
synchronization of the
two STAs if the encapsulated data frames are used.
[521 Therefore, the proposed method facilitates the synchronization in the
scheduled
power management.
[531 FIG. 5 illustrates a method of PSM according to an embodiment of the
invention.
[541 In step S510, a TDLS direct link is established between a STA1 and a
STA2. The
TDLS direct link can be established according to a procedure shown in FIG. 2.
[551 In step S520, a STA1 transmits a PSM request frame to the STA2 via an
AP or via
the TDDLS direct link. The PSM request frame is transmitted as an encapsulated
data
frame via the AP.
[561 The PSM request frame includes a wakeup schedule. The wakeup schedule
includes
a wakeup window duration, a wakeup interval and/or an idle count.
[571 The wakeup window duration indicates a duration in which a STA remains
in the
wakeup state (or in the doze state). The wakeup window duration may indicate a
duration of a wakeup window. The STA stays awake for the duration of the
wakeup
window.
[581 The wakeup interval indicates a time interval between two consecutive
wakeup
windows.
[591 The idle count indicates the number of consecutive wakeup windows
during no
directed frame is received from a peer STA before the peer STA deletes the
wakeup
schedule. If a service period is not started for wakeup windows indicated by
the idle
count, the peer STA can delete the wakeup schedule for this link. This means
that
related periodic wakeup no longer occurs. When traffics arrive at the peer STA
in PSM
for the link with no existing wakeup schedule, the STA may send a TDLS peer
PSM
request frame via a AP to activate a new wakeup schedule. The service period
is a
contiguous period of time during one or more unicast frames are transmitted
between
two peer STAs when at least one STA employs the peer PSM. The service period
may
be initiated during the wakeup window.
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[60] In step S430, STA2 transmits a PSM response frame as a response to the
PSM
request frame to the STA1 via the TDLS direct link.
[61] FIG. 6 illustrates a format of a PSM response frame. This is exemplary
purpose only,
and the order of each of the information element (IE) may be changed. Other IE
may
be added or some IE may be omitted.
[62] The PSM response frame includes a status field 610 and an alternative
wakeup
schedule 620. The status field 610 indicates acceptance or rejection of the
wakeup
schedule included in the PSM request frame. When the status field 610
indicates the
rejection, the alternative wakeup schedule 620 includes a proposed wakeup
schedule to
the peer STA. The wakeup window duration 621, the wakeup interval 622 and/or
the
idle count 623 included in the alternative wakeup schedule 620 have the same
meaning
as in the PSM request frame.
[63] After sending the PSM request frame, the STA1 may remain in the wakeup
state to
monitor the arrival of the PSM response frame via the TDLS direct link. The
STA1
may remain in the wakeup state until the PSM response frame is received.
[64] The PSM response frame is transmitted via the TDLS direct link. This
is for the syn-
chronization of the wakeup schedule between the two STAs and for reducing
power
consumption for monitoring the PSM response frame.
[65] It is assumed that the PSM response frame which indicates the
acceptance of the
wakeup schedule is transmitted as an encapsulated data frame via the AP. The
PSM
response frame can be dropped by the AP. The STA2 operates in the PSM but STA1
still keeps monitoring of the PSM response frame. In addition, it is not easy
that the
STA1 and STA2 determine when the wakeup schedule is initiated since the STA1
and
the STA2 cannot know when the PSM response frame is transmitted via the AP.
[66] Accordingly, the STA2 transmits the PSM response frame to the STA1 via
the TDLS
direct link.
[67] The wakeup schedule may be started from a time point that the PSM
response frame
is received. The STA1 can directly receive the PSM response frame since the
STA1
remains in the wakeup state after sending the PSM request frame. A start point
of the
first wakeup window can be set to a certain offset or Target Beacon
Transmission
Time (TBTT) after a time point that the PSM response frame is received. The
wakeup
schedule between the two STAs may be synchronized on the basis of a fixed time
point
or a transmitted frame (i.e., beacon frame) after receiving the PSM response
frame.
[68] FIG. 7 illustrates a wireless apparatus to implement an embodiment of
the present
invention.
[69] A wireless apparatus 700 includes a processor 710 and an interface
unit 720. The
interface unit 720 provides the processor 710 with an interface for other
devices. The
processor 710 implements a physical layer and a MAC layer. The embodiment of
FIG.
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may be implemented by the processor 720. The processor 720 may setup a
connection with other stations (i.e., AP or a peer station), and transmits
and/or receives
frames.
[70] The processor 710 may include an application-specific integrated
circuit (ASIC),
other chip sets, logic circuits and/or data processing devices. When the
embodiments
are implemented in software, the techniques described herein can be
implemented with
modules (e.g., procedures, functions, and so on) that perform the functions
described
herein.
[71] In view of the exemplary systems described herein, methodologies that
may be im-
plemented in accordance with the disclosed subject matter have been described
with
reference to several flow diagrams. While for purposed of simplicity, the
methodologies are shown and described as a series of steps or blocks, it is to
be un-
derstood and appreciated that the claimed subject matter is not limited by the
order of
the steps or blocks, as some steps may occur in different orders or
concurrently with
other steps from what is depicted and described herein. Moreover, one skilled
in the art
would understand that the steps illustrated in the flow diagram are not
exclusive and
other steps may be included or one or more of the steps in the example flow
diagram
may be deleted without affecting the scope and spirit of the present
disclosure.
[72] What has been described above includes examples of the various
aspects. It is, of
course, not possible to describe every conceivable combination of components
or
methodologies for purposes of describing the various aspects, but one of
ordinary skill
in the art may recognize that many further combinations and permutations are
possible.
Accordingly, the subject specification is intended to embrace all such
alternations,
modifications and variations that fall within the spirit and scope of the
appended
claims.
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