U.S. patent application number 13/900096 was filed with the patent office on 2014-01-09 for terminal transmit power control with link adaptation.
This patent application is currently assigned to Telcordia Technologies Inc.. The applicant listed for this patent is Telcordia Technologies Inc., Toshiba America Research, Inc.. Invention is credited to David Famolari, Toshikazu KODAMA, Ryoko MATSUO, Shuichi OBAYASHI.
Application Number | 20140010174 13/900096 |
Document ID | / |
Family ID | 36001465 |
Filed Date | 2014-01-09 |
United States Patent
Application |
20140010174 |
Kind Code |
A1 |
MATSUO; Ryoko ; et
al. |
January 9, 2014 |
Terminal Transmit Power Control with Link Adaptation
Abstract
Methods for coordinating power usage and link adaptation in
wireless communications are described. Terminals and/or access
points (APs) may attempt to modify terminals' transmit power in
relation to a desired communication data transfer rate. Link
adoption may also be used in conjunction with the described
methods.
Inventors: |
MATSUO; Ryoko; (Tokyo,
JP) ; OBAYASHI; Shuichi; (Yokohama, JP) ;
KODAMA; Toshikazu; (Yokohama, JP) ; Famolari;
David; (Stewartsville, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Telcordia Technologies Inc.
Toshiba America Research, Inc. |
Piscataway
Piscataway |
NJ
NJ |
US
US |
|
|
Assignee: |
Telcordia Technologies Inc.
Piscataway
NJ
Toshiba America Research, Inc.
Piscataway
NJ
|
Family ID: |
36001465 |
Appl. No.: |
13/900096 |
Filed: |
May 22, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10968244 |
Oct 20, 2004 |
8463308 |
|
|
13900096 |
|
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 52/24 20130101;
H04W 52/46 20130101; H04W 24/00 20130101; H04W 28/22 20130101; H04W
52/146 20130101; H04W 52/267 20130101; H04W 52/22 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 52/24 20060101
H04W052/24 |
Claims
1. A method for controlling power comprising the steps of:
determining whether a change has occurred in antenna parameters of
an access point; determining if a transmit power of a mobile
terminal should be modified based on said change in said antenna
parameters; and modifying said transit power of said mobile
terminal in accordance with said determining steps.
2. The method according to claim 1, wherein said antenna parameters
are transmitted in a beacon to said mobile terminal and wherein
said modifying step is performed for every change in antenna
parameters in said beacon.
3. The method according to claim 1, wherein said antenna parameters
are transmitted in a beacon to said mobile terminal and wherein
said modifying step is performed once per multiple beacons.
4. The method according to claim 1, wherein said determining steps
are performed in said access point.
5. The method according to claim 1, wherein said determining steps
are performed in said mobile terminal.
6. The method according to claim 1, further comprising the step of:
modifying said transit power of said mobile terminal when a change
in data rate has occurred.
7. The method according to claim 1, further comprising the step of:
determining if a network is at or near capacity, wherein said
modifying step is at least partially based on an outcome of said
network determining step.
8. A system for modifying transmit power for a mobile terminal
transmitting data to an access point comprising: a processor that
determines whether antenna parameters of said access point have
changed, determines if said transit power from said mobile terminal
to said access point should be modified based on the change in said
antenna parameters, and adjusts said transit power of said mobile
terminal.
9. The system according to claim 8, wherein said processor is in
said mobile terminal.
10. The system according to claim 8, wherein said processor is in
said access point.
11. The system according to claim 8, further comprising: an antenna
that transmits said data at an adjusted transit power level.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/968,244, filed Oct. 20, 2004, whose contents are expressly
incorporated by reference.
TECHNICAL FIELD
[0002] Aspects of the present invention relate to wireless
communications. More particularly, aspects of the present invention
relate to controlling power used to transmit wireless signals.
RELATED ART
[0003] The growth of wireless communications and integration with
the internet continues to influence the growth of local area
networks. Since the expansion of IEEE 802.11-based communication
protocols and related devices, wireless local area networks (WLANs)
are appearing with regular frequency. WLANs provide high speed
wireless connectivity between PCs, PDAs and other equipment in
corporate, public and home environments. WLAN users have come to
expect access to WLANs and wanting larger coverage areas and higher
throughputs. For portable users power consumption concerns are also
an issue.
[0004] Currently, IEEE 802.11-series protocols are the leading WLAN
standards. Some standards (ex: IEEE 802.11a/b/g) have finished
standardization. Some of these standards include the ability to
modify power on a link to a unit.
[0005] At the same time, wireless providers are experimenting with
adaptive antenna arrays (also referred to as smart array antennas).
Current approaches to adaptive antenna arrays do not address power
control issues. Rather, adaptive arrays concentrate on beam
steering techniques.
SUMMARY
[0006] Aspects of the present invention address one or more of the
issues identified above, thereby providing an improved power
control system for use with wireless communications.
BRIEF DESCRIPTION OF DRAWINGS
[0007] Aspects of the present invention are described in relation
to the following drawings.
[0008] FIG. 1 shows transmit power control in accordance with
aspects of the present invention.
[0009] FIGS. 2A and 2B show changing array patterns based on load
equalization in accordance with aspects of the present
invention.
[0010] FIGS. 3A and 3B show changing array patterns based on packet
steering in accordance with aspects of the present invention.
[0011] FIG. 4 shows a process for reducing power in accordance with
aspects of the present invention.
[0012] FIG. 5 shows a conventional link adaptation method.
[0013] FIGS. 6 and 7 show link adaptation in accordance with
aspects of the present invention.
[0014] FIGS. 8A and 8B show modifications of antenna parameters in
accordance with aspects of the present invention.
[0015] FIGS. 9-18 show link adaptation in accordance with aspects
of the present invention.
[0016] FIG. 19 shows an illustrative example of a base station in
accordance with aspects of the present invention.
[0017] FIGS. 20-21 show additional illustrative examples of access
points in accordance with aspects of the present invention.
[0018] FIG. 22 shows a process for determining premium gain in
accordance with aspects of the present invention.
DETAILED DESCRIPTION
[0019] Aspects of the present invention relate to controlling power
in access points for us with wireless local area networks. The
following has been divided into sections to assist the reader:
power control; transmit power control in IEEE 802.11h; transmit
power control in IEEE 802.11b, 802.11e, and other standards; link
adaptation methods; and transmit power control with link
adaptation.
[0020] It is noted that various connections are set forth between
elements in the following description. It is noted that these
connections in general and, unless specified otherwise, may be
direct or indirect and that this specification is not intended to
be limiting in this respect.
Power Control
[0021] Aspects of the present invention may be used with
non-reciprocal uplink and downlink systems in terms of link gain.
For instance, aspects of the present invention may be used with
WLAN systems using access points (APs) with smart antennas. Here,
aspects of the present invention address at least one of the
stations transmit rate but also the stations power consumption.
Transmit power control (TPC) capabilities and link adaptation may
be used with various environments or expectations. For example,
aspects of the present invention may be used in systems where
stations transmit with their highest data rate or where stations
transmit with their lowest power.
[0022] To realize the reduction in power consumption while
maintaining usefulness of the system, methods and systems that
function with TPC and compliant wireless LAN APs and stations may
be used.
[0023] Power reduction does not mean that all devices will always
be connected to an access point. Rather, hidden terminals exist
where every station's transmit power isn't enough to reach every
other station or back to an access point. In the 802.11b or 802.11e
specification, stations transmit with a constant power and have no
TPC functionality. The following describes various approaches to
allow TPC in 802.11 protocols.
Transmit Power Control in IEEE 802.11h
[0024] IEEE 802.11h is a specification for Europe in 5-GHz band.
This specification mainly deals with TPC and Dynamic Frequency
Selection (DFS). The primary reason for TPC in 802.11h is that TPC
(which means maximum regulatory transmit power setting in 802.11h)
is required for operation on a 5 GHz band in Europe. Concerning
TPC, 802.11h defines only the frame structure. It describes no
method to achieve TPC.
[0025] Aspects of the present invention relate to using IEEE
802.11h specification's Probe Request/Response or Action commands
to send some TPC information. These features may help other IEEE
802.11 specifications use TPC. These commands may or may not be
used to transmit control signals to help avoid any hidden
terminals. If control signals are used, they may be set to transmit
with normal power to avoid the hidden terminal problem. This may
include some modification of both AP and stations. However, aspects
of the present invention may use any slot or frame that is reserved
in 802.11b/e specification to allow for TPC based on a technique
similar to that used with 802.11h.
[0026] While both 802.11h and 802.11b have frame structures, they
are not identical. The following describes various observations in
802.111h and how to achieve TPC in non-802.11h protocols. [0027] a.
For a TPC report, 802.11h changes the Probe response for this
operation. While the response is changed, no change is made with
the Probe Request to initiate TPC. Rather, 802.11h uses an Action
frame for a TPC request. [0028] i. The same changes in Probe
response in 802.11b/e are possible, because an order number that is
used for TPC in 802.11h is currently reserved in 802.11b/e. [0029]
ii. In 802.11b, there is no regulation for an Action frame. Thus,
it is easier to modify Probe request in this protocol. [0030] iii.
In 802.11e, both an Action frame and a Probe request are defined.
[0031] b. In 802.11h, a station knows that an AP does TPC if a
Spectrum Management slot (inside Beacon or Probe response) is set
by 1. [0032] i. The same slot of a Spectrum Management slot is
reserved in 802.11b/11e. Aspects of the present invention may use
this slot to achieve TPC.
[0033] Considering this overview, in 802.11h, TPC may be
accomplished as shown in FIG. 1. FIG. 1 shows an access point 101
and a mobile station 102. Transmit power is included in TPC Report
from mobile station 102 to access point 101. The TPC Report may be
included as part of an Action Frame or part of a Probe Response.
This figure shows the situation where the access point 101 wants to
adjust a transmit power of mobile station 102. The TPC report is
generated in response to a TPC Request from access point 101 to
mobile station 102 using an access frame. If mobile station 102
wants to adjust access point 101's transmit power, it may by having
reciprocal requests and reports.
[0034] However, there is no availability for mobile station 102 to
adjust its own transmit power. The current transmit power
information for TPC is contained in the Probe response frame. This
means that any calculation must be done at a receiver.
[0035] Aspects of the present invention include the ability of a
mobile station 102 to adjust its own transmit power. The access
point 101 may calculate the difference between a current mobile
station 102's transmit power, update this information, and forward
this information to the mobile station 102.
Transmit Power Control in IEEE 802.11b, 802.11e, and Other
Standards
[0036] To achieve TPC in 802.11b/e, a minor modification of the
slot structure of 802.11h may be used. Various TPC approaches may
be constrained by the ability to modify 802.11b/e protocol's frame
structure. The access point 101 and mobile station 102 may also
need to be modified to allow for TPC. TPC may be realized as a
method of using Probe Request and Probe Response signals. Both
types of situations (fixed array and changing array) may be used
with TPC. This is shown with respect to FIGS. 2A, 2B, 3A, and
3B.
[0037] Referring to FIGS. 2A and 2B, TPC is described. Here,
station mobile stations know whether the access point 201 changes
the various array patterns. [0038] a. A station 207 sends an RTS
(Request to Send) signal 208 to access point 201. A Probe
request/response time may be added to a NAV setting timer in the
Duration field of the frame. The access point 201 receives the RTS
208 and replies with a CTS (Clear to Send) signal 209 to the mobile
station. [0039] b. The station 207 sends a Probe Request 210 and
requests access point 201 to use TPC (for instance, by setting a
TPC flag). [0040] c. The access point 201 detects the received
power from the station and determines the value difference between
a received power and a power needed to communicate with the access
point 201. [0041] d. The access point 201 sends a Probe Response
211 to the mobile station and informs the mobile station of the
value difference. [0042] e. The mobile station then reduces a
transmit power and continues operation as normal.
[0043] FIGS. 2A and 2B show transition of coverage areas of an
array 201 changing automatically to load equalize each beam.
[0044] FIGS. 3A and 3B show transition of coverage areas of an
array 301 changing automatically by packet steering.
[0045] FIG. 4 shows a signal flow chart between a mobile station
401, an access point 402, and other mobile stations 403. An access
point 402 sends a beacon or probe response 404 to announce, for
instance, that the antenna beam array associated with access point
402 is going to change. Next, mobile station 401 sends an RTS 405
at high power to access point 402. This may be picked up by other
mobile stations 403 as signal 406. Of course, the other mobile
stations 403 may or may not be in range to be able to pick up
signal 406. Next, access point 402 transmits a CTS signal 407 to
mobile station 401. The CTS signal 407 may or may not be received
by other mobile stations 403.
[0046] Access point 402 may then send a Probe Request or Action
signal 408 to access point 402. The same signal may or may not be
received by other mobile stations 403 (shown here as broken signal
409. The access point 402 next determines in step 410 the power to
be reduced with respect to mobile station 401.
[0047] Access point 402 then sends a Probe Response 411 to mobile
station 401 that includes the new power setting or the amount by
which mobile station 401 may reduce power. Using the new low power
setting, mobile station 401 transmits data at signal 412 to access
point 402. The access point 402 then acknowledges (ACK signal 413)
the receipt of the data. The transmission of signal 413 may be
performed at high power to ensure that mobile station 401 knows
that the access point 402 has received the data signal 412.
Alternatively, ACK signal 413 may be transmitted at low power to
save energy at access point 402.
[0048] One benefit of transmitting ACK signal 413 at high power is
that other stations 403 may then recognize that mobile station 401
has completed transmitting data and now other mobile stations 403
may start the process of transmitting data with access point
402.
[0049] Two navigation setting intervals may occur. A first 414 may
occur from RTS signal 405 through acknowledgement signal 413. A
second 415 may occur from CTS signal 406. through acknowledgement
signal 413.
Link Adaptation Methods
[0050] The following describes various link adaptation methods in
accordance with aspects of the present invention. Here, each
station may check a received power and change a data rate according
to a received power from an access point. These methods may
minimize or eliminate the need to send any control information
from/to AP.
[0051] A practical method for link adaptation is not defined in
current IEEE 802.11 specifications. Nonetheless, most of the
current IEEE 802.11 chipsets or relate equipment perform a type of
link adaptation with traditional approaches. Considerations include
setting a transfer rate at a highest rate first then decrease it
according to channel condition, setting a transfer rate at a lowest
rate then increasing it, how often should link adaptation be
performed, should a received power and an error detection result be
used for link adaptation, and the like. FIG. 5 illustrates a
conventional link adaptation method. Each station 502 receives a
beacon or control signal 503 from access point 501. The stations
502 may use the beacon or other control signal to determine whether
changing power according to the power of the received signal as
shown in step 504.
[0052] As shown in FIG. 5, these link adaptation methods assume
that uplinks and downlinks between access point 501 and stations
502 are reciprocal in terms of link gain. This suggests current
approaches to not use smart antennas. This is because, when a
system uses an access point with a smart antenna, uplinks and
downlinks are not always reciprocal. This is because antenna
patterns for receiving is not always the same as that for
transmission, especially in packet steering systems as shown in
FIG. 3. In addition, link adaptation is currently performed on the
supposition that all access points 501 have a constant transmit
power in current wireless LAN. However, in the future, access
points may not be able to change transmit power using an adaptive
array or similar devices to reduce interference. While the link
adaptation methods of FIG. 5 may be used with a smart antenna, they
will likely be error prone and not provide quality service to
users.
[0053] FIGS. 6 and 7 show various link adaptation methods that may
be used with a smart antenna in accordance with aspects of the
present invention. Referring to FIG. 6, access point 601 determines
if it antenna parameters are going to be changed in step 603. If
yes from step 603, then the parameters of the new antenna pattern
and/or the access point 601's transmit power are inserted into a
beacon (or other control signal) 605. If no from step 603, then
step 604 is skipped.
[0054] Next, the beacon or other control signal 605 is sent to
station 602. The station 602 then changes in step 606 its
transmission rate up or down according to the information in the
beacon (or other signal) 605. The modifications may occur once per
beacon or once per multiple beacons. The access point 601 and
station 602 then wait (paths 607 and 608, respectively) for a next
transmission of the beacon or other signal 605. Also link
adaptation may be performed with the transmission of every beacon
signal, may be done periodically, or may only be performed when the
antenna parameters change.
[0055] Antenna parameters may be, for example, the gain difference
between transmit beam and receive beam. This may be applicable in a
system that uses packet steering as the transmit beams are wide to
cover a larger area.
[0056] FIG. 7 shows an approach in which an access point 601 only
sends only sends change antenna parameter information or change
AP's transmit power information (inserted in step 604) in the
beacon 605. The station may then change the rate up or down per
information in the beacon (occurring once per beacon or once per
multiple beacons). Each station 602, which receives beacon 605 with
any change information, sends a Probe request or Action frame 701
to request power control information from access point 601. The
access point 601 then calculates in step 702 the margin or gain
difference between a transmit beam and a received beam. Next,
access point 601 sends the gain difference or margin in a Probe
Response or Action frame 703 to station 602. Alternatively or
additionally, access point 601 may send its transmit power using
the Probe Response or Action Frame 703 to station 602.
[0057] FIGS. 8A and 8B show examples of antenna parameters used in
packet steering. In general, for both wide beam 802 (G.sub.A,
G.sub.B, G.sub.C) and sharp beams 803-805 (G.sub.A', G.sub.B',
G.sub.C') from access point 801, antenna parameters are different
according to the azimuth (G.sub.A.noteq.G.sub.B.noteq.G.sub.C,
G.sub.A'.noteq.G.sub.B'.noteq.G.sub.C') for stations A-C. However,
access point 801 may be limited as not being able to accommodate
all these differences when it sends antenna parameters to all
stations (as represented in FIGS. 6 and 7. Two approaches are
described that address the situation where less than all antenna
parameters are forwarded (including but not limited to no antenna
parameters) to all stations with Beacon 605.
[0058] In a first approach, access point 801 calculates and informs
the minimum gain difference ((.delta.G).sub.min) as antenna
parameters. Access point 801 next sends control information with
the wide beam (G.sub.A, G.sub.B, G.sub.C) 802 and receives each
station's signal with the sharp beam (G.sub.A', G.sub.B', G.sub.C')
803-805. (.delta.G).sub.min may be represented by the following
equations:
(.delta.G).sub.min=Min[(G.sub.A'-G.sub.A),(G.sub.B'-G.sub.B),(G.sub.C'-G-
.sub.C)] Eq. (1)
or
(.delta.G).sub.min=Min[G.sub.A',G.sub.B',G.sub.C']-Max[G.sub.A,G.sub.B,G-
.sub.C] Eq. (2)
[0059] This method is easy to implement. However, not every station
may achieve an individual optimum gain with this approach. The
process for the equations is shown in FIG. 22.
[0060] In a second approach, access point 801 knows a direction of
each station and sends this information to each station in advance.
Each station A-C memorizes or stores the direction information.
Next, when access point 801 changes its antenna radiation pattern,
access point 801 calculates the relationship between antenna
directivity and a radiation characteristic, and send this
information to stations as an estimated radiation characteristic of
antenna beam (or beam pattern). Stations A-C receive this
information and calculate a premium gain by using the new beam
using current condition and an estimated radiation characteristic
of antenna beam.
[0061] For example, as shown in FIGS. 8A and 8B, access point 801
decides a center direction G.sub.ct. Station B, for instance,
received information from access point 801 that an angular
direction between the center G.sub.ct and station B is +1/87.pi..
Next, access point 801 changes the antenna radiation pattern and
sends the stations A-C information relating to the current center
gain is G.sub.ct' dB. Transmitted with this information or
transmitted separately is an indication that a gain of direction
+1/87.pi. is .alpha. dB smaller than that of the center direction.
Station B receives and adjusts its antenna parameter as
(G.sub.d'-.alpha.) dB.
[0062] Generally, each station has some information about the
relationship between received power and affordable transmit rate to
be used for link adaptation. If a station complies with one of the
above link adaptation methods, it may modify a received power using
the following equation:
Received power=actual received power+antenna parameter Eq. (3)
[0063] Then, if the case that an access point 801 changes its
power, stations may need received power and transmit rates and the
transmit power of access point 801 to perform link adaptation as
described above.
[0064] Tables 1 and 2 show various relationships between transmit
power, received power, and data rates tables. Using information
similar to that shown in table 1, stations may adjust their power
to achieve a useful transfer rate.
TABLE-US-00001 TABLE (1) Transmit power Receive power Rate -15 -84
11 Mb/s -15 -87 7 Mb/s : : : : : :
TABLE-US-00002 TABLE (2) Power loss (=Transmit power - Receive
power) Rate : 11 Mb/s : 7 Mb/s : :
Transmit Power Control with Link Adaptation
[0065] TPC and link adaptation may be used together as a systematic
control, because both of them use a received power level of
station. Both methods may be combined based on different priorities
or adopted policies for TPC.
[0066] The following lists various possible policies for TPC
methods with combined link adaptation: [0067] a. A first policy
emphasizes data throughput [0068] i. Each station transmits with as
high rate as link adaptation permits. [0069] ii. Stations transmit
with a constant rate. For example, if an access point restricts an
acceptable rate as 11 Mb/s and station's current rate is not 11
Mb/s, then that station does not transmit or it changes its rate
into 11 Mb/s. [0070] b. A second policy emphasizes power
conservation [0071] i. If all stations emphasize only power,
sometimes some stations may transmit at a much lower data rate than
link adaptation permits. This may adversely affect other stations.
In this policy assumes that all stations are able to handle a
lowest data rate. [0072] c. A third policy emphasizes data rates
based on a networks condition [0073] i. When a network is not
crowded, each station emphasizes TPC. [0074] ii. When the network
is crowded, each station emphasizes throughput. [0075] 1. Each
station transmits with the maximum rate or [0076] 2. The access
point sets the minimum rate and prohibits any station from
transmitting with lower rate than the minimum rate.
[0077] Next, a TPC interval performed by a station is related to
system throughput as well as control complexity. The following
three situations are considered: [0078] a. TPC is performed at
every station's signal sending opportunity [0079] b. TPC messaging
is reduced using the following two considerations: [0080] i. TPC
level from access point is calculated with sufficient fading margin
to maintain a link during the TPC message interval. Alternatively,
TPC level is calculated with sufficient margin to maintain the link
even if the access point changes its array pattern. [0081] ii.
Access point informs a station that access point's antenna
directivity or other radiation characteristics are changed whenever
it is required by a station. When the change does not occur, TPC is
not required. [0082] c. TPC messaging is reduced using only the
following: [0083] i. TPC level from access point is calculated with
sufficient fading margin to maintain a link during the TPC message
interval. Alternatively, TPC level is calculated with sufficient
margin to maintain the link even if the access point changes its
array pattern.
[0084] The combinations of control policies and message frequency
for TPC are shown in the following table 3. Various examples are
shown in the following figures as well. The examples described
herein include examples 1-9. The number in the following table
shows the example number to which it corresponds.
TABLE-US-00003 TABLE (3) Reduce Frequency of TPC Message Method/
Required Rate is TPC on Every Sending Using i. and Using only
Policy calculated at . . . Opportunity ii. i. Emphasis on
Throughput 1 2 3 Emphasis on Transmit Station 4 Power Reduction
Access Point 5 Emphasis on WLAN Station 6 Resource Management
Access Point 7 and 9* 8 *where the access point restricts the
minimum required rate
Example 1
[0085] FIG. 4 shows this first example. Here, each station 401 or
403 performs link adaptation using one of the methods described
above. Then, when station 401 wants to send its data, station 401
performs TPC as shown in FIG. 4.
[0086] FIG. 4 shows the case which satisfies the Distributed
Coordination Function (DCF) operation of the IEEE 802.11
specification. However, it may also be used with a modification of
the Point Coordination Function (PCF) operation of IEEE 802.11,
Enhanced Distributed Channel Access (EDCA) operation and Hybrid
Coordination Function (HCF) operation of IEEE 802.11e
specification.
[0087] In the case of EDCA, the method is similar to that of DCF.
One difference for TPC between DCF and EDCA is that Block ACK mode
exists in EDCA. In the Block ACK mode, ADDBA request/ADDBA response
commands are used instead of RTS/CTS and they can replace RTS/CTS
in FIG. 4. Additionally, ADDBA request/ADDBA response have several
reserve bits, so one may enclose TPC request and response signals
to the reserve bits. In this alternative approach, one does not
need to use the Probe request/response or Action frame to transmit
the power to be reduced.
[0088] In cases of PCF or HCF, a Point Coordinator (PC) (Hybrid
Coordinator (HC) in 802.11e) controls these signals. The PC (HC)
may be located in an access point. The PCF scheme may be initiated
by stations requesting that the PC (HC) registers them on a polling
list, and the PC (HC) then regularly polls the stations for traffic
while also delivering traffic to the stations. Stations may be
controlled by the PC (HC) and allows transmitting one (or several)
frame(s) for each polling signal from PC (HC). (See IEEE 802.11
specification.)
[0089] Thus, in PCF (HCF), a station should enclose TPC requests in
DATA+CF ACK frames and PC (HC) should enclose TPC responses in
DATA+CF Poll frames. Currently, slots for address 4 are N/A in
802.11/802.11e (according the specification, this is for the case
of transmit between an access point and another access point). It
can be used for the TPC signals as described herein. Alternatively,
any other reserved slots can be used. One may also use RTS/CTS.
[0090] In future specifications, some or all of the modes will
generally be backwards compatible and interoperable with IEEE
802.11a/b/g. Thus, the TPC and link adaptation described herein may
likely suit every standard in the 802.11 family.
[0091] To enable TPC, the access point may use tables showing
transmission rate and required received power levels to maintain a
link with specified rate. Most stations have such tables to perform
link adaptation. Table 4-1 and 4-2 are the sample tables. "b" is a
variable that represents the required power for 11 Mb/s. Here for
example, a station sending a signal with 11 Mb/s and its received
power is (b+4) dBm. The access point checks and knows from the
table that the required rate 11 Mb/s needs b dBm power. Thus, the
access point tells the mobile station to reduce power by 4 dB. In
response, the station reduces its transmit power by 4 dB.
TABLE-US-00004 TABLE (4-1) Rate Required Received Power (dBm) 11 b
5 b - 3 2 b - 6 1 b - 9
TABLE-US-00005 TABLE (4-2) Rate (Mb/s) Required Received Power
(dBm) 11 b 5.5 b - 3 2 b - 4 1 b - 7
Example 2
[0092] Example 2 shows an example where the system attempts to
reduce the frequency of TPC message exchange. Two approaches are
described with respect.
[0093] In a first approach with an access point 601 and a station
602, the station 602 examines whether access point 601 has changed
its antenna radiation pattern or other characteristic at every
transit opportunity. When the access point 601 uses a smart antenna
(adaptive antenna) and changes its array width, for instance,
reception conditions of station 602 are also changed. Thus, station
602 inquires whether a change has occurred. If a change has
occurred, the station invokes TPC.
[0094] This approach also applies where access point 601 changes
its transmit power for other reasons. Stations 602 with antenna
parameter signals can respond where an access point 601 changes its
condition more precisely. If an access point 601 changes an array
width or transmits power on a large scale and, if link adaptation
is done only at every several control signals, for instance, the
rate which is changed by link adaptation may not be updated as well
as it should be. Thus, under this condition, having an antenna
parameter is useful.
[0095] In a second approach, TPC is described with an additional
control margin to reduce its frequency. This margin is set so that
a usual fading depth by typical multi-path and shadowing are
impacted by a little change of an antenna parameter. Here, when the
antenna parameters do not exceed the margin, the station does not
need TPC at every transmission time.
[0096] This second approach has two advantages. First, this
approach may reduce the transmission of additional signals being
transmitted only for TPC between a station and an access point. One
reason why decreasing the frequency of transmission of signals only
for TPC is because redundant signals waste bandwidth. This may also
be referred to as throughput degradation. This is noticeable in the
situations that use RTS/CTS. (See Table 5.) One may use reserved
slots in RTS/CTS for TPC. However, the maximum reserved slots are 3
bits only in RTS/CTS slots in the current 802.11 standard. These 3
bits may not be enough to inform the power value to be reduced with
a sufficient range and accuracy.
[0097] Second, this approach provides advantages for channel
conditions between access points and stations that are not changed
and where the station (or access point) wants to send signals
almost constantly (like voice etc). The reduction of unnecessary
processing for TPC can avoid dissipating signal processing
resources as well as consuming power.
[0098] FIG. 9 shows the flow chart of the latter example. When a
station 602 wants to send data, the station changes a rate in step
901 and checks to see if antenna parameters have changed in step
902. If an antenna parameter signal changes, then the station 602
determines if a TPC change is required. Here, the TPC change
includes RTS signals 904, CTS signals 905, a probe request 906, and
a determination if TPC is required (step 907). Here, the access
point 601 checks the received rate and power of the signal and
determines if TPC is needed.
[0099] If TPC is required then it is performed in step 908 and the
information transmitted between the station 602 and access point
601 using a probe response 909, data signals 910, and ACK 911. If
no TPC is required, then the process steps to probe response, data
and ACK signals 909-911. Finally the new rate is stored in step
912.
[0100] If there was no change in antenna parameters from step 902,
then the stations 602 determines if the difference of rate or/and
power between a current rate (rate.sub.c) and a previous rate
(rate.sub.p) is greater than 2 times the rate level in step 903. It
is noted that power information may be used in conjunction or in
place of the rate information.
[0101] If yes from step 903, then the system proceeds as above. If
no, the system begins a new cycle.
[0102] In step 907, the access point 601 calculates the value of a
difference based on the signal data and a margin information which
may be taken from the tables shown for instance as Tables 4-1 and
4-2. For example, using Table 4-1, when the received rate is 2 Mb/s
(required power is (b-6)), access point 601 calculates the
difference between received power and required power for
transmission at rate 5.5 Mb/s, which is one-level higher than
current rate, and required power at this rate is (b-3). In this
case, the value of difference is "received power--(b-3)". This 3 dB
is the margin. The margin level in this example is 1 level, but it
can be changed according to a control policy. Also, if Table 4-2 is
used, the power difference between rates 2 Mb/s and 5.5 Mb/s is
little and it is possible to group them together in such a
case.
TABLE-US-00006 TABLE (5) Signal Total Length (MAC header length)
RTS CTS/ACK 14 octets (10 octets) DATA 34 + 0~2312 octets (30
octets) Management frame (Beacon, Probe 28 + 0~2312 octets
Request/response) (24 octets)
Example 3
[0103] FIG. 10 a signal flow chart for example 3. The approach of
Example 3 is similar to that of Example 2. However, step 903 is
performed as step 1001 in place of step 902. Here, station 602 does
not check a change in antenna parameters. This is because, if
access point 601 array changes, the influence is reflected in the
received power and transmission rate using link adaptation. In this
example, the station 602 does not need to check for a change in
antenna parameters of access point 601 prior to performing TPC. One
advantage of the system of Example 3 is that is may be easier to
implement than that of Example 2.
[0104] Example 3 may be useful under one or more of the following
conditions:
Where access point 601 rarely changes its antenna radiation pattern
or other characteristics, or where these changes are too small to
effect stations 602. Station 602 performs link adaptation by
comparing its frequency of TPC with the frequency of access point's
601 frequency of the changing its antenna parameters, or station
602 performs link adaptation as soon as it receives a new antenna
parameter of access point 601.
[0105] The following examples are described with respect to one of
the above approaches. For the following examples, one may
substitute steps 902-903 with step 1001 as well as step 1001 with
steps 902-903 for the reasons specified above.
Example 4
[0106] FIG. 11 shows an approach used by Example 4. Example 4
represents an approach where a policy provides an emphasis on power
restriction. Here, each station 602 calculates a required rate
before transmission.
[0107] When station 602 wants to send a payload, it checks a
transmit payload category according to traffic or content and its
required rate using table like that shown in Table 6 below, for
instance. A margin may be set at an access point 601 as shown in
FIG. 11. FIG. 11 is similar to that of FIG. 9. However, if no from
step 902, then the process steps to point B 1101. Point B continues
at FIG. 12.
[0108] In step 1201, the station 602 checks the data transmit
category and its required rate. Various rates are shown in Table 6.
In step 1202, the station 602 checks to see if the required rate is
less than the current rate. If yes, then in step 1203, the system
sets the required rate as the current rate. If no from step 1202,
then the process continues with step 903 where station 602 checks
to see if TPC is needed with or without a margin.
[0109] For example, using Table 6, if the transmit data category is
"voice" (the required rate being 2 Mb/s according to this table)
and current rate is 7 Mb/s, station updates the rate to 2 Mb/s. The
advantage of this case is that each station can transmit with
sufficiently high rate for desired traffic or content and lower
power.
[0110] The values used shown in Table 6 are for example purposes
only. They may be altered based on system preferences.
[0111] Station 602 can use antenna parameter change information for
examination as shown in Example 2. The process at the access point
601 is the same as that of Examples 2 and 3.
TABLE-US-00007 TABLE (6) Traffic Category Rate (Mb/s) Video 11
Photo 5.5 Voice 2 Best Effort 1
Example 5
[0112] Example 5 is shown with respect to FIGS. 10 and 13. Example
5 is similar to that of Example 4 but where the required by the
access point 601. The calculation begins at point A 1002 in FIG. 10
and continues with FIG. 13. At step 1301, the system checks the
required rate and the current rate at access point 601. In step
1302, the access point 601 determines if the current rate is larger
than the required rate. If yes, then the process steps to 1303
where the current rate is set to the required rate. Next, the
access point 601 determines if TPC is required in step 907. If no
from step 1302, then the process continues with step 907.
[0113] One advantage is that station 602 does not need to have
Table 6. Also, station 602 is not required to set the appropriate
rate. This example may be beneficial where station 602 is desired
to have less processing functions so as to minimize power
consumption for the station 602. However, in this example, the
access point 601 needs to send not only a value difference but also
rate information. Current Probe response or similar signals can be
used to send both power and rate with a little modification.
[0114] Table 7 shows a sample of a table that may be used with
Example 6. "b" shows the required power for 2 Mb/s. In this case,
access point 601 has both traffic category-rate and rate-required
power information. Station 602 may or may not use an antenna
parameter for examination like that shown in Example 2. Because
this process is shown in FIG. 9, it is not shown in FIG. 11 (but is
considered within the scope of this example).
TABLE-US-00008 TABLE (7) Traffic Category Rate Required Terminal
Transmit Power (dB) Video 11 b + 8 Photo 5.5 b + 4 Voice 2 b Best
Effort 1 b - 3
Example 6
[0115] The policy for Example 6 is an emphasis on WLAN management.
Here "WLAN resource" means how much wireless resource of access
point 601 is occupied. It mainly depends on a number of stations
which have payload to transmit/receive in each AP or in each array,
a size of load from/to each station and so on. Note that AP sends a
binary signal as "WLAN resource management signal" in this figure
but any other signals can be also used. For example, "Station
Count" and "Channel Utilization" signals are defined as a Beacon by
IEEE 802.11e specification and we can use these signals as WLAN
resource management signal. Here, "Station Count" indicates a total
number of stations currently associated in each AP (or array), and
"Channel Utilization" indicates a percentage of time AP (or array)
senses the medium busy, as indicated by either physical or virtual
carrier sense mechanism. In these cases, AP or stations sets a
threshold. If the value of these signals becomes larger than the
threshold, AP or stations consider the WLAN resource to be full.
When stations examine whether the value becomes larger than the
threshold, AP sends the value of threshold signal to station in
advance. For example, if the maximum number of VoIP stations in
each AP (or array) is x+2, AP sets the threshold x-1, and the
current number of VoIP stations is x, AP or station consider the
WLAN resource to be full.
[0116] FIGS. 14 and 15 show the flow chart for example 6. Points C
1402, E 1403, and G 1404 are shown in parallel to reflect the
various actions that may be taken with respect to Example 6 and
other examples described below.
[0117] When the process of FIG. 14 steps to point C 1402, the
process continues in FIG. 15. In step 1501, the system determines
if the WLAN resource is full. If yes, then the process returns to
FIG. 14 and continues with the RTS/CTS signals. If no from step
1501, the system checks the transmit traffic category and its
required rate in step 1502. Next, in step 1503, if the required
rate is less than the current rate then the process continues with
step 1504, where the required rate is set as the current rate.
Otherwise, from step 1503 the process continues with the RTS/CTS
signals of FIG. 14.
[0118] Here, each array in an access point sends resource
information to a master resource controller in the access point or
in a backbone network. Next. A master resource controller examines
the WLAN resource considering information from all arrays, and
sends this result to each array. It is also possible that each
array examines WLAN resource associated with itself. The same
scheme can be used even if AP is not a smart antenna and only has
one array.
[0119] The AP may send WLAN resource information with control
signals like the Beacon. Then, station considers modifying the rate
considering WLAN resource. If this WLAN resource is full, each
station sends signals at its maximum rate. However, if WLAN
resource is not full, each station is not needed to send with its
maximum power. In such case, station updates the rate into the
required rate shown in Table 7 shown above to reduce the power
consumption.
Example 7
[0120] Example 7 relates to where the AP calculates a transmit rate
for each station considering the WLAN resource. FIGS. 14 and 16
provide a flowchart for this example.
[0121] The process of FIG. 14 includes changing the rate in step
901 then processing the RTS/CTS signals. After probe request 906
and encountering point C 1406, the process continues with FIG. 16.
In FIG. 16, the AP determines if the WLAN resource is full. If no,
then the system checks a transmit traffic category and its required
rate in step 1602. In step 1603 the AP determines if the required
rate is less than the current rate. If yes from step 1603, then the
AP sets the required rate as the current rate in step 1604. Next,
the process continues with step 907. If yes from step 1601 or no
from step 1603, then the process continues with step 907 as
well.
[0122] Here, a station requires TPC at every transmission in these
figures but the station may function with only a sparser interval.
When the station requires TPC, the AP calculates the value of
difference. If WLAN resource is not full, it also calculates a
transmit rate for each station. The advantages of this approach
includes the station does not need to do WLAN load examination as
well as to calculate the transmit rate.
[0123] Here, the WLAN load information is used for control. Of
course, other relevant information may also be available to achieve
control with an emphasis on WLAN resource management.
[0124] Optionally, it is possible to combine the flow charts of
FIGS. 14, 15 and 16. In this optional combination, the WLAN
resource is examined by the station and the AP. In this
combinational approach, if a station misunderstands a WLAN and
sends data at a low rate even though the resource is at full power,
the AP also may examine the resource and modify the power
accordingly.
Example 8
[0125] Example 8 shows a process where a station reduces the
frequency of TPC using the margin shown in examples 2 and 3 above.
Here, FIGS. 14, 16, and 17 show the process of example 8. Here, at
point E 1403, the process continues with FIG. 17. In step 1701, a
station checks whether a WLAN resource has changed from full to not
full. If yes from step 1701, then the process continues with
exchanging the RTS/CTS signals of FIG. 14. If no from step 1701,
the system determines if there was a change in antenna parameters
in step 1702. If no, then in step 1703, the system checks if the
difference between a current rate and a previous rate is greater
than or equal to two times a rate level. If no from step 1703, the
process continues to point F 1407. If yes from any of steps 1702 or
1703, then the process continues with exchanging the RTS/CTS
signals of FIG. 14. The process may then continue with FIG. 16 at
point D 1406 as described above.
[0126] Here, in FIG. 17, the station requires TPC, because WLAN
resource management changes to full from not full and the AP asks
every station to send with its maximum power. If no from the
determination step, the station examines the necessity of TPC.
Alternatively, "Change antenna parameter" information can be used
either optionally or be a requirement.
Example 9
[0127] That process of example 9 is shown in FIGS. 14 and 18. From
point G 1404, a station then determines in step 1801 whether a WLAN
resource is full. If yes, then the station determines if a current
rate is greater than a minimum rate in step 1802. If no, then the
process returns to point H 1405 in FIG. 14. If yes, then the
process continues with the exchange of the RTS/CTS signals in FIG.
14. If no from step 1801, the transmit traffic category and its
require rate are examined in step 1803. Next, in step 1804, the
system determines if the required rate is less than a current rate.
If no, then the process continues with the exchange of the RTS/CTS
signals in FIG. 14. If yes, then the system sets the required rate
as the current rate in step 1805. Next, the process continues with
the exchange of the RTS/CTS signals in FIG. 14.
[0128] Here, the AP instructs all stations the minimum required
rate when WLAN resource is full or almost full. When a station
wants to send a payload, but the WLAN resource is full or almost
full, the AP sends a required rate. The station compares the
current rate with this AP's required rate. If the current rate is
higher than the required rate, this station can send. But if the
current rate is lower than the required rate, this station cannot
send any data.
[0129] Optionally, the AP requires the minimum rate not only when
the resource is full but also for other reasons. For example, even
if the resource is not full, if one station transmits large scale
of data with very low rate, it affects other stations and reduces
the number of VoIP stations.
[0130] Further, it is also possible in this case that AP does not
send the minimum required rate and AP examines the station's
transmit rate. In this way, station sends RTS at first, but when
the AP determines that a station's transmit rate is lower than the
required rate, the AP does not send the CTS.
[0131] However, in this way, other stations in the same AP or in
the same array must to set the NAV and may be prevented from
sending any data for a while.
Example 10
[0132] FIG. 19 shows an illustrative example of block diagram of a
station. FIGS. 20-21 show block diagrams of illustrative AP to
realize the above mentioned control schemes. These figures focus on
blocks related to TPC and the link adaptation process. It is also
possible the other configurations, for example, "TPC controller
logic" may be included in a MAC or connected directly to a MAC.
Further, the TPC controller logic may be included in a host CPU or
other locations.
[0133] FIG. 19 includes SW 1901 forwarding received signals to RF
transceiver 1902. In RF transceiver 1902, receive radio 1903
forwards received data to the BB physical layer 1905. The BB
physical layer 1905 includes receive variable gain control and LNA
GS 1906 and demodular 1908, both of which receive data from receive
radio 1903. Demodulator 1908 transmits signals to MAC 1911 and
clear channel assessment CCA 1907. CCA 1907 provide signals to VGC
and LNA GS 1906, which then controls receive radio 1903. CCA also
transmits signals to CCA 1912 in MAC 1911. Signals from CCA 1912
and demodulator 1908 are received by Rx MAC 1913 and transmitted to
PCI bus 1915. From PCI bus 1915, the system may exchange data with
any of host CPU 1916, host memory 1917, and TPC control logic 1918.
Tx MAC 1914 in MAC 1911 receives data from PCI bus 1915 CCA 1912,
and transmitted to modulator 1909 in BB physical layer 1905.
Information may be exchanged between modulator 1909 and CCA 1907.
Modulator 1909 that outputs data to transmit radio 1904 in RF
transceiver 1902. PA 1910 then receives control signals from TPC
control logic 1918 and signals from transmit radio 1904 and sends
them to SW 1901 for transmission.
[0134] Link adaptation may generally be performed by done by "Tx
MAC" using information from CCA (Clear Channel Assessment) 1917 or
1912. At first when the station wants to send a payload and, if the
TPC is required at every transmitting opportunity (see examples 1-3
above), Tx MAC 1914 sends a TPC request signal using a Probe
request or Action or any other frame. If TPC is required at every
several opportunities, Tx MAC 1914 or TPC controller logic 1918
examines the requirements for TPC using at least one of transmit
rate and received power information, which may be derived from link
adaptation unit in Tx MAC 1914 or CCA 1907 or 1912.
[0135] When a station receives a TPC response from an AP, the
station picks up a value of difference information at Rx MAC 1913
and sends this information to TPC controller logic 1918. TPC
controller logic 1918 controls PA 1910 to change the transmit
power. It is also possible that Rx MAC 1913 controls PA directly.
In the cases where station checks a transmit data category and its
required rate, the necessary tables are located in the memory,
which is in MAC or host memory. Then TPC controller logic 1918 or
Tx MAC 1914 accomplishes the control using information from both
link adaptation unit and memory.
[0136] FIGS. 20 and 21 show illustrative examples of access points.
Components similar to those of FIG. 19 are not described. The
access point shown in FIG. 20 includes a master resource controller
2001 that may include TPC logic controller 2002. As connected to
PCI bus 1915. Each access point may include a combiner and divider
2003 with antenna elements 2004 providing access to various
channels (channels 1-3 (2005-2007) shown here for example).
[0137] When each channel 2005-2007 in AP receives a signal, that
received power information may be noted and stored. When each
channel receives a signal which includes a TPC required slot,
receiver MAC 1913 sends a control signal to TPC controller logic
unit 2002 indicating it that should initiate a TPC calculation. In
FIGS. 20 and 21, PCI bus 1915 connects MAC 1911 and TPC controller
logic 2002, thereby allowing all channels use the same TPC
controller logic 2002. It is also possible that TPC controller
logic 2002 may be located within each MAC 1911 for each
channel.
[0138] Next, a value of difference information may be sent to Tx
MAC 1914 and conveyed in the transmit signal. Various tables may be
stored in memory, which is located in MAC 1911 or host memory
1917.
[0139] When AP controls link adaptation and TPC considering the
WLAN resource, Master resource controller 2001 controls the WLAN
resource. FIG. 20 shows the case that each AP has a master resource
controller 2001 and FIG. 19 shows the case that master resource
controller 2108 is located in the backbone network and it controls
resources for multiple APs.
[0140] FIG. 21 shows access points with multiple channels 2101-2103
communicating with PCI bus 1915. PCI bus may be connected with host
CPU 2104, host memory 2105, and TPC controller logic 2106. Host CPU
2104 and TPC controller logic 2106 may be connected to Ethernet
2109, which may be connected to other access points 2107 and master
resource controller 2108. It is also possible that each channel has
its own master resource controller 2108.
[0141] The following provides examples of various policies
described above. [0142] 1. AP always emphasizes throughput. [0143]
2. AP always emphasizes transmit power. [0144] 3. AP always leaves
it to each station which policy stations should select. [0145] 4.
Basically AP leaves it to each station and only if a network
becomes crowded, AP emphasizes throughput.
[0146] If AP selects 3 or 4 mentioned above and each station
decides how to select policy, the following examples may further be
considered: [0147] 1. Station always emphasizes throughput. [0148]
2. As far as AP doesn't indicates to emphasize throughput, station
always emphasizes transmit power. [0149] 3. If station is without
power supply (and/or the rest of power is low), it emphasizes
transmit power, if not it emphasizes throughput. [0150] 4. Station
selects throughput or transmit power according to an application.
(For example, station emphasizes throughput only if it
sends/receives video application)
[0151] The present invention has been described in terms of
preferred and exemplary embodiments thereof. Numerous other
embodiments, modifications and variations within the scope and
spirit of the appended claims will occur to persons of ordinary
skill in the art from a review of this disclosure.
* * * * *