U.S. patent application number 14/258762 was filed with the patent office on 2014-08-14 for method and apparatus for reducing power consumption in a wireless communication device.
This patent application is currently assigned to Qualcomm Incorporated. The applicant listed for this patent is Qualcomm Incorporated. Invention is credited to Akbar Rashid Ahmed Attar, Donna Ghosh, Linhai He, Christopher Gerard Lott.
Application Number | 20140226550 14/258762 |
Document ID | / |
Family ID | 47604274 |
Filed Date | 2014-08-14 |
United States Patent
Application |
20140226550 |
Kind Code |
A1 |
He; Linhai ; et al. |
August 14, 2014 |
METHOD AND APPARATUS FOR REDUCING POWER CONSUMPTION IN A WIRELESS
COMMUNICATION DEVICE
Abstract
A wireless communications power saving method and apparatus is
provided. The method includes establishing a circular buffer
configured to maintain a number of most recently encountered frame
delay times and waiting a frame delay time after receiving a
further frame before the station enters a power save state. Frame
delay time is a period equal to a largest most recently encountered
frame delay period in the circular buffer. The method further
determines, at a station, a dormancy time based on a number of data
frames received since the station transitioned from an inactive
mode to an active mode, a packet transmission rate, and a data
frame time interval representing time between data frames received
at the station, and causes the station to switch to a further
inactive mode if a next packet is not received within the dormancy
time after receipt of a previous packet.
Inventors: |
He; Linhai; (San Diego,
CA) ; Attar; Akbar Rashid Ahmed; (San Diego, CA)
; Lott; Christopher Gerard; (San Diego, CA) ;
Ghosh; Donna; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Qualcomm Incorporated |
San Diego |
CA |
US |
|
|
Assignee: |
Qualcomm Incorporated
San Diego
CA
|
Family ID: |
47604274 |
Appl. No.: |
14/258762 |
Filed: |
April 22, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13401143 |
Feb 21, 2012 |
|
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14258762 |
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Current U.S.
Class: |
370/311 |
Current CPC
Class: |
Y02D 70/1242 20180101;
Y02D 70/1224 20180101; H04W 52/0232 20130101; H04W 88/08 20130101;
Y02D 30/70 20200801; Y02D 70/142 20180101; H04W 52/0258 20130101;
H04W 52/0241 20130101 |
Class at
Publication: |
370/311 |
International
Class: |
H04W 52/02 20060101
H04W052/02 |
Claims
1. A method for saving power in a station in a wireless
communication system, comprising: determining, at the station, a
dormancy time based on a number of data frames received since the
station transitioned from an inactive mode to an active mode, a
packet transmission rate, and a data frame time interval
representing time between data frames received at the station; and
causing the station to switch to a further inactive mode if a next
packet is not received within the dormancy time after receipt of a
previous packet.
2. The method of claim 1, wherein the packet transmission rate
represents a rate at which data packets are received at the
station, wherein the packet transmission rate is determined based
on the number of data frames received since the station
transitioned from the inactive mode to the active mode.
3. The method of claim 1, further comprising transitioning from the
further inactive state to a further active state when reverse link
traffic to be transmitted by the station is available at the
station.
4. The method of claim 3, further comprising causing the terminal
to transition to an additional inactive mode after waiting no
longer than the dormancy time.
5. The method of claim 1, wherein the dormancy time is determined
based further on a previous maximum dormancy time.
6. The method of claim 5, wherein the dormancy time is determined
based further on a configured constant.
7. A station configured for use in a wireless communication system,
comprising: a processor configured to determine a dormancy time
based on a number of data frames received since the station
transitioned from an inactive mode to an active mode, a packet
transmission rate, and a data frame time interval representing time
between data frames received at the station; and a transmitter
configured to transmit data from the station to an access point;
wherein the processor is further configured to cause the station to
switch to a further inactive mode if a next packet is not received
within the dormancy time after receipt of a previous packet.
8. The station of claim 7, wherein the packet transmission rate
represents a rate at which data packets are received at the
station, wherein the packet transmission rate is determined based
on the number of data frames received since the station
transitioned from the inactive mode to the active mode.
9. The station of claim 7, wherein the station is further
configured to transition from the further inactive state to a
further active state when reverse link traffic to be transmitted by
the station is available at the station.
10. The station of claim 9, further comprising causing the station
to transition to an additional inactive mode after waiting no
longer than the dormancy time.
11. The station of claim 7, wherein the dormancy time is determined
based further on a previous maximum dormancy time.
12. The station of claim 11, wherein the dormancy time is
determined based further on a configured constant.
13. The station of claim 7, wherein the processor is further
configured to alter the inactivity period based on a physical layer
rate of the transmitting station.
14. A non-transitory computer readable storage medium comprising
instructions that, when executed by a processor, performs the
following method: determining a dormancy time based on a number of
data frames received since a station transitioned from an inactive
mode to an active mode, a packet transmission rate, and a data
frame time interval representing time between data frames received
at the station; and causing the station to switch to a further
inactive mode if a next packet is not received within the dormancy
time after receipt of a previous packet.
15. The non-transitory computer readable storage medium of claim
14, wherein the packet transmission rate represents a rate at which
data packets are received at the station, wherein the packet
transmission rate is determined based on the number of data frames
received since the station transitioned from the inactive mode to
the active mode.
16. The non-transitory computer readable storage medium of claim
14, wherein the method further comprises transitioning from the
further inactive state to a further active state when reverse link
traffic to be transmitted by the station is available at the
station.
17. The non-transitory computer readable storage medium of claim
16, wherein the method further comprises causing the terminal to
transition to an additional inactive mode after waiting no longer
than the dormancy time.
18. The non-transitory computer readable storage medium of claim
14, wherein the dormancy time is determined based further on a
previous maximum dormancy time.
19. The non-transitory computer readable storage medium of claim
28, wherein the dormancy time is determined based further on a
configured constant.
Description
[0001] The present Application for Patent is a divisional of U.S.
patent application Ser. No. 13/401,143, filed Feb. 21, 2012,
entitled "Method and Apparatus for Reducing Power Consumption in a
Wireless Communication Device," which is related to co-pending U.S.
patent application Ser. No. 13/401,122, filed Feb. 21, 2012,
entitled "Wireless Communication Device Power Reduction Method and
Apparatus", both assigned to the assignee hereof, and expressly
incorporated in their entireties by reference herein.
BACKGROUND
[0002] I. Field
[0003] The present invention relates generally to
telecommunications, and, more specifically, to power savings for
wireless devices employed in wireless communication systems and
cellular communication systems.
[0004] II. Background
[0005] A modem communication system provides data transmission for
a variety of applications, including voice and data applications.
In point-to-multipoint communications, modem communication systems
have been based on frequency division multiple access (FDMA), time
division multiple access (TDMA), code division multiple access
(CDMA), and other multiple access communication schemes.
[0006] A CDMA communications system is typically designed to
support one or more CDMA standards, such as (1) the "TIA/EIA-95
Mobile Station-Base Station Compatibility Standard for Dual-Mode
Wideband Spread Spectrum Cellular System" (this standard with its
enhanced revisions A and B may be referred to as the "IS-95
standard"), (2) the "TIA/EIA-98-C Recommended Minimum Standard for
Dual-Mode Wideband Spread Spectrum Cellular Mobile Station" (the
"IS-98 standard"), (3) the standard sponsored by a consortium named
"3rd Generation Partnership Project" (3GPP) and embodied in a set
of documents known as the "W-CDMA standard," (4) the standard
sponsored by a consortium named "3rd Generation Partnership Project
2" (3GPP2) and embodied in a set of documents including "TR-45.5
Physical Layer Standard for cdma2000 Spread Spectrum Systems," the
"C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000
Spread Spectrum Systems," and the "TIA/EIA/IS-856 cdma2000 High
Rate Packet Data Air Interface Specification" (the "cdma2000
standard" collectively), (5) the 1xEV-DO standard, and (6) certain
other applicable standards. The standards expressly listed above
are incorporated by reference as if fully set forth herein,
including annexes, appendices, and other attachments.
[0007] Generally, a wireless local area network (WLAN) Access Point
provides data on the downlink to a user's wireless device, also
called a station, or STA. The downlink transmission of large
quantities of data from an Access Point to a STA can sometimes
result in the STA remaining fully powered for extended periods of
time due to uncertainty as to whether all data has been received
from the upstream devices. As a result, such devices do not
efficiently conserve power in the device.
[0008] Different power saving schemes have been devised. Various
methods have been employed to address a wireless device
transitioning to a power save mode after receiving large blocks of
data on the downlink, i.e. from the Access Point. Such methods have
included using power save indications on certain transmitted
frames, and use of inactivity timers, wherein after a certain
amount of inactivity the STA transitions to a power save mode.
However, these designs either require additional bandwidth or
processing, or employ timers in accordance with assumptions that
may be invalid or unduly excessive.
[0009] In one available implementation, called PS-Polling, the STA
goes into a sleep mode or state. The Access Point indicates the
presence of data for the sleeping STA through the Traffic
Indication Map (TIM) transmitted using the beacon signal which can
be received by the sleeping STA. The STA, upon receiving the TIM
indicating the availability of data at the Access Point, exists the
sleep state and sends a Null frame with a Power Management
"transition to active mode" indication. When the Access Point
receives the Power Management transition event from the STA, such a
WLAN arrangement has in the past computed a "worst case" delay
time, wherein the STA waits for a relatively long amount of time,
i.e. more time than is necessary in a worst case scenario, before
again entering Power Save mode. Values considered include the
amount of time needed to transmit the frame, the amount of delay
resulting from channel interference and frame retries, and so
forth, resulting in a relatively large inactivity period, i.e. a
relatively large amount of time before Power Save again begins at
the STA.
[0010] Therefore, there is a need for methods and apparatus that
would reduce power consumption at the STA without excessively
compromising performance characteristics of the STAs and of the
radio networks with which the STAs communicate.
SUMMARY
[0011] The following presents a simplified summary in order to
provide a basic understanding of some aspects of the claimed
subject matter. This summary is not an extensive overview, and is
not intended to identify key/critical elements or to delineate the
scope of the claimed subject matter. Its sole purpose is to present
some concepts in a simplified form as a prelude to the more
detailed description that is presented later.
[0012] Systems and methods are provided for saving power in a
terminal operating in a wireless communications system. The method
includes establishing a circular buffer configured to maintain a
number of most recently encountered frame delay times and waiting
for a frame delay time after receiving a further frame before
causing the station to enter a power save state. The frame delay
time is a period of time equal to a largest most recently
encountered frame delay period of time contained in the circular
buffer. The method further includes determining, at a station, a
dormancy time based on a number of data frames received since the
station transitioned from an inactive mode to an active mode, a
packet transmission rate, and a data frame time interval
representing time between data frames received at the station; and
causing the station to switch to a further inactive mode if a next
packet is not received within the dormancy time after receipt of a
previous packet.
[0013] To the accomplishment of the foregoing and related ends,
certain illustrative aspects are described herein in connection
with the following description and the annexed drawings. These
aspects are indicative, however, of but a few of the various ways
in which the principles of the claimed subject matter may be
employed and the claimed subject matter is intended to include all
such aspects and their equivalents. Other advantages and novel
features may become apparent from the following detailed
description when considered in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a high level block diagram of a system that
employs power saving according to the present design.
[0015] FIG. 2 illustrates a timeline showing operation of the
present design and the First Frame Delay.
[0016] FIG. 3 shows a circular buffer.
[0017] FIG. 4 is a timeline including multiple frame transmission
and first frame delay and inactivity timer operation when multiple
frames are transmitted.
[0018] FIG. 5 illustrates a timeline showing use of the First Frame
Delay and inactivity timer adapting to a change in the Phy
rate.
[0019] FIG. 6 is a flowchart of operation of one embodiment of the
present design.
[0020] FIG. 7 is a flowchart showing an alternate embodiment of the
present design.
[0021] FIG. 8 illustrates an alternate embodiment including a
typical transmission waveform and associated beacon.
[0022] FIG. 9 shows operation according to the alternate embodiment
and the values employed in determining the inactivity time.
DETAILED DESCRIPTION
[0023] In this document, the words "embodiment," "variant," and
similar expressions are used to refer to particular apparatus,
process, or article of manufacture, and not necessarily to the same
apparatus, process, or article of manufacture. Thus, "one
embodiment" (or a similar expression) used in one place or context
can refer to a particular apparatus, process, or article of
manufacture; the same or a similar expression in a different place
can refer to a different apparatus, process, or article of
manufacture. The expression "alternative embodiment" and similar
phrases are used to indicate one of a number of different possible
embodiments. The number of possible embodiments is not necessarily
limited to two or any other quantity.
[0024] The word "exemplary" is used herein to mean "serving as an
example, instance, or illustration." Any embodiment or variant
described herein as "exemplary" is not necessarily to be construed
as preferred or advantageous over other embodiments or variants.
All of the embodiments and variants described in this description
are exemplary embodiments and variants provided to enable persons
skilled in the art to make or use the invention, and not to limit
the scope of legal protection afforded the invention, which is
defined by the claims and their equivalents.
[0025] The word "traffic" generally refers to payload or user
traffic, such as data other than air interface control and
pilots.
[0026] A station, also referred to as STA, subscriber station, user
equipment, UE, mobile terminal, or MT, may be mobile or stationary,
and may communicate with one or more base transceiver stations. An
access terminal may be any of a number of types of devices,
including but not limited to PC card, external or internal modem,
wireless telephone, smartphone, and personal digital assistant
(PDA) with wireless communication capability. A station transmits
and receives data packets to or from a radio network controller
through one or more base transceiver stations.
[0027] Base transceiver stations and base station controllers are
parts of a network called radio network, RN, access network, and
AN. A radio network may be a UTRAN or UMTS Terrestrial Radio Access
Network. The radio network may transport data packets between
multiple access terminals. The radio network may be further
connected to additional networks outside the radio network, such as
a corporate intranet, the Internet, a conventional public switched
telephone network (PSTN), or another radio network, and may
transport data and voice packets between each access terminal and
such outside networks. Depending on conventions and on the specific
implementation variants, a base transceiver station may be referred
to by other names, such as Node-B, base station system (BSS), or
simply base station. Similarly, a base station controller may be
referred to by other names, such as radio network controller, RNC,
controller, mobile switching center, or serving GPRS support
node.
[0028] The scope of the invention extends to these and similar
wireless communication system components.
[0029] The present design seeks to enable the a station (STA) in a
wireless local area network (WLAN) communication system to obtain
all buffered traffic in an Access Point's queue before
transitioning to a Power Save mode, but not waiting for an
excessive amount of time before transitioning to Power Save mode.
The present design employs a circular buffer at the STA containing
the most recent transmission delay times encountered at the STA.
The design can, in certain embodiments, employ an inactivity timer
together with the circular buffer to decrease the amount of time
the STA operates at full power. Using the circular buffer alone or
with the inactivity timer, the STA enters Power Save mode more
rapidly and can decrease the amount of power used when receiving
data on the downlink.
[0030] FIG. 1 illustrates a typical WLAN arrangement including the
components of the present design. From FIG. 1, a wired network 101
may be connected to a switch or hub 102. The switch or hub 102 is
typically connected to a router 103 and a device such as a cable
modem or DSL modem 104, which connects to the internet. Wired
connections may be provided from the switch or hub 102 to a number
of Access Points, where three are shown in FIG. 1, Access Points
105a, 105b, and 105c. Each Access Point 105a, 105b, and 105c may be
accessed by a station or terminal, wherein three such stations or
terminals 106a, 106b, and 106c are shown connecting wirelessly to
Access Point 105c.
[0031] Circular Buffer with First Frame Delay
[0032] FIG. 2 illustrates the associated concept of a First Frame
Delay, namely the amount of time between acknowledgement of receipt
of the Null Frame at the Access Point and acknowledgement by the
STA that the first frame has been successfully received. At the end
of the First Frame Delay, the STA transitions to a Power Save mode.
In this configuration, the First Frame Delay differs from the
inactivity period. The First Frame Delay represents the amount of
time needed to transmit and successfully receive the first frame,
while the inactivity period represents the largest amount of time
incurred by the STA in fetching the first frame in the history of N
samples.
[0033] In FIG. 2, the upper line represents transmissions and
activities at the Access Point, while the lower line represents
transmissions and activities at the STA. TBTT is the Target Beacon
Transmission time, while point 201 represents transmission of the
beacon with a Transmission Indication Map (TIM) indication. The STA
at point 202 transmits a null frame with Power Management bit off.
The AP acknowledges the null frame at point 203, and sends a
downlink frame at point 204. In this example, the downlink frame
fails, as the AP receives no acknowledgement from the STA. At point
205, the AP retries transmitting the downlink frame, whereupon the
STA transmits an acknowledgement at point 206. The First Frame
Delay represents the time between acknowledgement transmission 203
by the AP and acknowledgement transmission by the STA.
[0034] One embodiment of the present design collects all of the
First Frame Delays in a circular buffer maintained in firmware at
the Access Point. The Access Point and STA then uses the largest
First Frame Delay previously encountered, with an additional buffer
period, as the inactivity period. FIG. 3 illustrates the circular
buffer arrangement of this embodiment. From FIG. 3, the AP firmware
maintains the circular buffer 301 with N samples of First Frame
Delay.
[0035] FIG. 4 illustrates an alternate embodiment of the present
design, using the circular buffer concept in a different manner.
From FIG. 4, once the STA receives the TIM indication, the STA
sends a NULL frame with the Power Management bit clear. Upon
receiving the acknowledgement indication from the Access Point of
receipt of the NULL frame, the STA determines the time that elapses
in receiving the first downlink data frame from the Access Point.
The elapsed time represents the First Frame Delay for this
iteration of downlink data fetched from the Access Point. This
First Frame Delay is recorded as the latest (most recent) entry
into the circular buffer. The system selects the largest First
Frame Delay in the circular buffer (Tmsec) and uses this value as
the inactivity timer for subsequent frames.
[0036] As shown in FIG. 4, the firmware in the Access Point
initiates a timer of Tmsec upon reception of Frame 0 (the first
data frame) and resets the timer every time a frame is received
before the expiration of the timer. When the STA receives all the
buffered frames from the Access Point, the inactivity timer expires
and the STA sends the Null Frame with the Power Management bit set
to the Access Point to indicate the station is entering Power Save
mode. Thus the embodiment of FIG. 4 uses the circular buffer and an
inactivity timer, with the inactivity timer expiring at the time of
the largest First Frame Delay in the circular buffer.
[0037] FIG. 4 illustrates the TIM indication received by the STA
followed by the transmission of the null frame, with Power
Management set to zero, at point 401. The Access Point transmits an
acknowledgement at point 402, followed by a series of frames 403a,
403b, and 403c representing Frame0, Frame1, and Frame2,
respectively. The STA transmits acknowledgements 404a, 404b, 404c
after each frame 403a, 403b, and 403c is received. Each of the
three frames shown is received at the STA within the T millisecond
inactivity timer window, and thus the inactivity timer is reset
each time a frame is received. The inactivity timer T milliseconds
is set based on the greatest value in the circular buffer. When the
inactivity timer expires without having received a packet, the null
frame is sent by the STA and the power management bit is set high
at point 405. The AP sends an acknowledgement of receiving the null
frame at point 406.
[0038] One additional factor to be considered for power saving is
delays in transmission from the STA to the access point. FIG. 5
illustrates the adaptation of the inactivity timer to the physical
layer (Phy) rate of the AP, where the Phy rate is the speed at
which the STA communicates with the AP. The system monitors the Phy
rate for the Access Point and corresponding frame size, and when
the Phy rate on the Access Point drops to a low rate due to
interference, the system increases the First Frame Delay to
accommodate the Phy rate decrease. If the frame size is relatively
large and the Phy rate is relatively low, the system increases the
First Frame Delay. The values may vary, but for example, if the Phy
rate decreases by X per cent, the system may increase the First
Frame Delay to X per cent above the largest First Frame Delay in
the circular buffer. As a result, the inactivity timer period
(Tmsec) increases, seeking to ensure that the STA waits for
sufficient time to receive all the buffered frames from the AP even
in the presence of interference and low Phy rate.
[0039] FIG. 5 illustrates the Phy rate situation. From FIG. 5, the
STA provides the TIM indication and null frame 501, and the AP
acknowledges at point 502. The AP transmits frame zero 503a, with a
1 Mbps Phy rate in this example, larger than the standard frame
size. The STA acknowledges at point 504a. After the First Frame
Delay, the inactivity timer commences using the biggest First Frame
Delay available in the circular buffer. The AP then transmits frame
one 503b, the STA acknowledges at point 504b, and this sequence
causes a reset of the inactivity timer. Once no more packets are
received from the AP, the inactivity timer expires, and the STA
transmits the Null frame 505 with power management bit set high.
The AP acknowledges at point 506.
[0040] An alternate embodiment to reduce the latency in fetching
downlink frames, such as in the case of a local server requiring
minimal latency, uses the uplink frame to transition the STA from
the Power Save state to the active state. In this embodiment, the
system uses both uplink and downlink frames to transition to the
Power Save State. The STA uses the largest First Frame Delay from
its history (but not the circular buffer) as the inactivity period
for both uplink and downlink. In other words, the system resets the
inactivity timer on every uplink frame in addition to every
downlink frame. The First Frame Delay is not recorded into the
circular buffer because the system transitions from Power Save
state to Active state based on the uplink frame time rather than
based on receipt of the TIM indication from the Access Point.
[0041] The circular buffer is not employed in this embodiment
because the first frame received after state transition may not be
an appropriate frame, e.g. a buffered frame. As a result, the First
Frame Delay may be a misleading or incorrect indicator. The system
thus does not store the First Frame Delay in the circular buffer
and does not employ the circular buffer.
[0042] FIG. 6 is a flowchart summarizing the first (circular buffer
only) embodiment. In FIG. 6, the circular buffer is either unset
(empty) or may include one or more delay time set points, as
previous transmissions may have resulted in the circular buffer
containing certain time values. In either case, the circular buffer
has a current state at point 601. At point 602, the STA sends the
Null Frame with Power Management set to 0, or unset. The Access
Point at point 603 sends an acknowledgement to the STA of having
received the Null Frame. Point 604 indicates the Access Point sends
a data frame and the STA acknowledges the data frame. The First
Frame Delay, measuring the time from acknowledgement by the Access
Point of receipt of the Null Frame, to acknowledgment of the first
frame being received at the STA, is determined and provided to the
circular buffer at point 605. In this embodiment, point 606
indicates that the largest value available in the circular buffer
is employed with an additional time buffer as the inactivity time.
After the inactivity time expires, the STA sends the Null Frame
with Power Management set to 1, indicating entry into Power Save
mode.
[0043] FIG. 7 is a flowchart summarizing the circular buffer use
with an independent inactivity timer. As with FIG. 6, the circular
buffer may initially be unset or empty, or may include one or more
inactivity timer set points, and previous transmissions may have
resulted in the circular buffer containing certain time values. In
any of these situations, the circular buffer has a current state at
point 701. At point 702, the STA sends the Null Frame with Power
Management set to 0, or unset. The Access Point at point 703 sends
an acknowledgement of having received the Null Frame. Point 704
indicates the Access Point sends a data frame to the STA and the
STA acknowledges the data frame. The system determines the First
Frame Delay, representing the time from acknowledgement by the
Access Point of receipt of the Null Frame to acknowledgment of the
first frame being received at the STA, and provides this First
Frame Delay to the circular buffer at point 705.
[0044] Once the STA receives the first frame and acknowledgement
sent by the STA, the inactivity timer at the STA starts as shown by
point 706. At point 707 the system determines whether another frame
has been received at the STA from the Access Point while the
inactivity timer is still operating. If another frame has been
received, the system resets the inactivity timer to zero at point
708 and processing returns to point 707. If no other frame is
received, operation progresses to point 709, wherein the system
determines whether the inactivity timer has expired. If so, the STA
sends a Null Frame with Power Management set, i.e. equal to 1, at
point 710, indicating entry into Power Save mode. If the inactivity
timer has not expired and no other frame received, processing loops
back to await either receipt of an additional message and/or
expiration of the timer.
[0045] Thus according to the present design, there is provided a
method for saving power in a wireless communication system
comprising a station and an access point. The method comprises
establishing a circular buffer at the station, the circular buffer
configured to maintain a number of most recently encountered frame
delay times representing times between the access point
transmitting one frame of data and the station receiving the one
frame of data, and waiting for a frame delay time after receiving a
further frame, and if no additional frame of data is received
within the frame delay time, causing the station to enter a power
save state. In this embodiment, the frame delay time is a period of
time equal to a largest most recently encountered frame delay
period of time contained in the circular buffer.
[0046] Dynamic Inactivity Computation
[0047] In most scenarios, the rate an Access Point can serve
Stations is much higher than the rate of traffic arriving at the
Access Point. An alternate embodiment duty cycles a STA connection
with an Access Point as follows. The STA initially turns off its
modem. Once the STA turns off its modem, or enters the sleep or
power save state, the Access Point buffers the subsequent packets,
or holds the packets without transmitting the packets, until the
STA turns its modem back on.
[0048] The decision as to when to turn off the STA modem in the
midst of active traffic does not depend on a fixed parameter in
this embodiment. The present embodiment adapts to the estimated
inter-packet arrival time and the service interval, where the
service interval is the amount of time needed to process the
transmission. One implementation uses the ratio of time that the
STA stays active during the last interval, i.e. the time from the
last beacon transmission, to the number of data packets received
during that period of time.
[0049] The present algorithm runs only when the STA is in the
active mode. Upon entering the active mode, the STA initializes the
dormancy timer DT to a maximum value, DTmax. When in active mode,
the system operates as follows when a new frame is received. First,
the system determines k, the number of data frames received since
the STA switched to active mode. The system then calculates E, an
estimate of how rapidly packets arrive at an Access Point, also
called a source interval:
E=E.sub.k/k (1)
where E.sub.k is the time that has elapsed since the Station last
entered a power saving mode to the time the kth data frame is
received. The system initially sets a value M to zero, where M
represents an estimate of the fastest rate at which the Access
Point transmits packets.
[0050] The system updates M as follows:
M=max(M, tj) (2)
where tj is the interval between the (j-1)th and jth frames. The
system then sets:
DT=min(DTmax, (w*M+(1-w)*E)) (3)
where w is a configured constant.
[0051] The STA then switches to power save mode if the next packet
is not received within DT amount of time, where DT is as computed
in Equation (3). When reverse link transmissions from the Access
Point to the STA occur while the STA is in a sleep state, the STA
wakes up and transmits the packets as soon as possible. The STA
returns to sleep mode after a wait no longer than DT. The DT value
of Equation (3) is not be reset by reverse link transmissions.
[0052] FIG. 8 illustrates the general waveforms encountered and the
parameters determined at the STA. FIG. 8 illustrates preceding
waveform 801, followed by beacon 802 and packet 803. Packet 803
includes a base power level, constantly transmitted during the
packet, having a plurality of frames provided therewith, shown as
frames 804a, 804b, and 804c. Number of frames and power levels may
vary. As shown, the service interval t.sub.k represents the period
between frames. The time E.sub.k shown represents the time since
the STA last entered power save mode to the time the k.sup.th
packet is received.
[0053] FIG. 9 illustrates an example of operation of the present
embodiment. The values calculated above are illustrated generally
in FIG. 9. FIG. 9 includes two beacons 901 and 902 and shows the
typical transmission waveform discussed in further detail below. In
the example presented in FIG. 9, the two beacon signals 901 and 902
are transmitted 100 milliseconds apart and the waveform shown
arrives at the STA every 20 milliseconds. These values may vary
depending on circumstances. The transmitted packet, such as packet
903, includes a level of power that is constantly available during
the transmission, i.e. a floor power value for the transmission.
Each packet transmitted in this example includes five frames,
numbered 1-5 in packet 904. The service interval, t.sub.j in
Equation (2) above, is the period from the start of one pulse to
the start of the next pulse, i.e. pulse number 2 to pulse number 3
in packet 904, representing the rate at which the Access Point
transmits packets. If DT in the FIG. 9 configuration is X
milliseconds as determined by Equation (3) above, a failure to
receive another packet X milliseconds after the packet is expected
results in the STA entering sleep mode.
[0054] It should specifically be noted that while certain
relationships between timing schemes, numbers of pulses, pulse
amplitudes and durations, timing gaps, delays, and so forth are
reflected herein, the design is not so limiting. For example,
different timing and/or power schemes may be employed while still
within the scope of the present invention, and the design is not
intended to be limited with respect to timing sequences or other
variable values provided.
[0055] Thus with respect to the current embodiment, the design
includes determining, at the station, a dormancy time based on a
number of data frames received since the station transitioned from
an inactive mode to an active mode, a packet transmission rate, and
a data frame time interval representing time between data frames
received at the station, and causing the station to switch to a
further inactive mode if a next packet is not received within the
dormancy time after receipt of a previous packet.
[0056] Aspects of the claimed subject matter may be implemented as
a method, apparatus, or article of manufacture using standard
programming and/or engineering techniques to produce software,
firmware, hardware, or any combination thereof to control a
computer or computing components to implement various aspects of
the claimed subject matter. The term "article of manufacture" as
used herein is intended to encompass a computer program accessible
from any computer-readable device, carrier, or media. For example,
computer readable media can include but are not limited to magnetic
storage devices (e.g., hard disk, floppy disk, magnetic strips . .
. ), optical disks (e.g., compact disk (CD), digital versatile disk
(DVD) . . . ), smart cards, and flash memory devices (e.g., card,
stick, key drive . . . ). Additionally it should be appreciated
that a carrier wave can be employed to carry computer-readable
electronic data such as those used in transmitting and receiving
voice mail or in accessing a network such as a cellular network. Of
course, those skilled in the art will recognize many modifications
may be made to this configuration without departing from the scope
or spirit of what is described herein.
[0057] Those of skill in the art would understand that information
and signals may be represented using any of a variety of different
technologies and techniques. For example, data, instructions,
commands, information, signals, bits, symbols, and chips that may
be referenced throughout the above description may be represented
by voltages, currents, electromagnetic waves, magnetic fields or
particles, optical fields or particles, or any combination
thereof.
[0058] Those of skill would further appreciate that the various
illustrative logical blocks, modules, circuits, and algorithm steps
described in connection with the embodiments disclosed herein may
be implemented as electronic hardware, computer software, or
combinations of both. To clearly illustrate this interchangeability
of hardware and software, various illustrative components, blocks,
modules, circuits, and steps have been described above generally in
terms of their functionality. Whether such functionality is
implemented as hardware or software depends upon the particular
application and design constraints imposed on the overall system.
Skilled artisans may implement the described functionality in
varying ways for each particular application, but such
implementation decisions should not be interpreted as causing a
departure from the scope of the present disclosure.
[0059] The various illustrative logical blocks, modules, and
circuits described in connection with the embodiments disclosed
herein may be implemented or performed with a general purpose
processor, a digital signal processor (DSP), an application
specific integrated circuit (ASIC), a field programmable gate array
(FPGA) or other programmable logic device, discrete gate or
transistor logic, discrete hardware components, or any combination
thereof designed to perform the functions described herein. A
general purpose processor may be a microprocessor, but in the
alternative, the processor may be any conventional processor,
controller, microcontroller, or state machine. A processor may also
be implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0060] The steps of a method or algorithm described in connection
with the embodiments disclosed herein may be embodied directly in
hardware, in a software module executed by a processor, or in a
combination of the two. A software module may reside in RAM memory,
flash memory, ROM memory, EPROM memory, EEPROM memory, registers,
hard disk, a removable disk, a CD-ROM, or any other form of storage
medium known in the art. An exemplary storage medium is coupled to
the processor such the processor can read information from, and
write information to, the storage medium. In the alternative, the
storage medium may be integral to the processor. The processor and
the storage medium may reside in an ASIC. The ASIC may reside in a
user terminal. In the alternative, the processor and the storage
medium may reside as discrete components in a user terminal.
[0061] What has been described above includes examples of one or
more embodiments. It is, of course, not possible to describe every
conceivable combination of components or methodologies for purposes
of describing the aforementioned embodiments, but one of ordinary
skill in the art may recognize that many further combinations and
permutations of various embodiments are possible. Accordingly, the
described embodiments are intended to embrace all such alterations,
modifications and variations that fall within the spirit and scope
of the appended claims. Furthermore, to the extent that the term
"includes" is used in either the detailed description or the
claims, such term is intended to be inclusive in a manner similar
to the term "comprising" as "comprising" is interpreted when
employed as a transitional word in a claim.
* * * * *