U.S. patent application number 12/620167 was filed with the patent office on 2010-03-18 for method and apparatus for clear channel assessment optimization in wireless communication.
This patent application is currently assigned to INTERDIGITAL TECHNOLOGY CORPORATION. Invention is credited to Christopher Cave, Angelo Cuffaro, Paul Marinier, Vincent Roy.
Application Number | 20100067473 12/620167 |
Document ID | / |
Family ID | 34657355 |
Filed Date | 2010-03-18 |
United States Patent
Application |
20100067473 |
Kind Code |
A1 |
Cave; Christopher ; et
al. |
March 18, 2010 |
METHOD AND APPARATUS FOR CLEAR CHANNEL ASSESSMENT OPTIMIZATION IN
WIRELESS COMMUNICATION
Abstract
A method and apparatus are directed toward optimizing clear
channel assessment (CCA) parameters in wireless communications. A
CCA parameter request is received from an optimizing station. A
current CCA parameter is read and transmitted to the optimizing
station. A notification is received from the optimizing station of
an optimized CCA parameter to be used by the optimizing
station.
Inventors: |
Cave; Christopher;
(Montreal, CA) ; Roy; Vincent; (Longueuil, CA)
; Marinier; Paul; (Brossard, CA) ; Cuffaro;
Angelo; (Laval, CA) |
Correspondence
Address: |
VOLPE AND KOENIG, P.C.;DEPT. ICC
UNITED PLAZA, SUITE 1600, 30 SOUTH 17TH STREET
PHILADELPHIA
PA
19103
US
|
Assignee: |
INTERDIGITAL TECHNOLOGY
CORPORATION
Wilmington
DE
|
Family ID: |
34657355 |
Appl. No.: |
12/620167 |
Filed: |
November 17, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12209692 |
Sep 12, 2008 |
7620063 |
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12620167 |
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10937123 |
Sep 9, 2004 |
7443821 |
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12209692 |
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60535021 |
Jan 8, 2004 |
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 28/18 20130101;
H04W 74/08 20130101; H04L 1/203 20130101; H04W 84/12 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 40/00 20090101
H04W040/00 |
Claims
1. A method for optimizing clear channel assessment (CCA)
parameters in wireless communications, comprising: receiving a CCA
parameter request from an optimizing station; reading a current CCA
parameter; transmitting the current CCA parameter to the optimizing
station; and receiving from the optimizing station a notification
of an optimized CCA parameter to be used by the optimizing
station.
2. The method according to claim 1, wherein the optimizing station
is an access point (AP).
3. The method according to claim 1, wherein the optimizing station
is a station (STA).
4. The method according to claim 1, wherein the receiving a
parameter request, the reading, the transmitting, and the receiving
a notification all occur at an access point (AP).
5. The method according to claim 1, wherein the receiving a
parameter request, the reading, the transmitting and the receiving
a notification all occur at a station (STA).
6. A method for optimizing clear channel assessment (CCA)
parameters in wireless communications, comprising: receiving a
calculated optimal CCA parameter from an optimizing station;
receiving a request to change a current CCA parameter to the
optimal parameter; determining whether the change can be made;
changing the current CCA parameter to the optimal parameter on a
condition that the change can be made; and transmitting a message
reporting whether or not the change has occurred.
7. The method of claim 6, wherein the optimizing station is an
access point (AP).
8. The method according to claim 6, wherein the optimizing station
is a station (STA).
9. The method according to claim 6, wherein the receiving a
calculated optimal CCA parameter, the receiving a request to change
a current CCA parameter, the determining, the changing, and the
sending all occur at an access point (AP).
10. The method according to claim 6, wherein the receiving a
calculated optimal CCA parameter, the receiving a request to change
a current CCA parameter, the determining, the changing, and the
sending all occur at a station (STA).
11. A wireless communications station, comprising: a receiver
configured to receive a clear channel assessment (CCA) parameter
from an optimizing station; reading circuitry configured to read a
current CCA parameter; and a transmitter configured to transmit the
current CCA parameter to the optimizing station; the receiver
further configured to receive from the optimizing station a
notification of an optimized CCA parameter to be used by the
optimizing station.
12. The wireless communications station of claim 11 configured to
act as an access point (AP).
13. The wireless communications station of claim 11 configured to
act as a station (STA).
14. The wireless communications station of claim 11 configured to
function on a condition that the optimizing station is an access
point (AP).
15. The wireless communications station of claim 11 configured to
function on a condition that the optimizing station is a station
(STA).
16. A wireless communications station, comprising: a receiver
configured to receive a calculated optimal CCA parameter from an
optimizing station and to receive a request to change a current CCA
parameter to the optimal parameter; determining circuitry
configured to determine whether the change can be made; changing
circuitry configured to change the current CCA parameter to the
optimal parameter on a condition that the change can be made; and a
transmitter configured to transmit a message reporting whether or
not the change has occurred.
17. The wireless communications station of claim 16 configured to
act as an access point (AP).
18. The wireless communications station of claim 16 configured to
act as a station (STA).
19. The wireless communications station of claim 16 configured to
function on a condition that the optimizing station is an access
point (AP).
20. The wireless communications station of claim 16 configured to
function on a condition that the optimizing station is a station
(STA).
21. An integrated circuit for optimizing clear channel assessment
(CCA) parameters in wireless communications, comprising: a receiver
configured to receive a clear channel assessment (CCA) parameter
from an optimizing station; reading circuitry configured to read a
current CCA parameter; and a transmitter configured to transmit the
current CCA parameter to the optimizing station; the receiver
further configured to receive from the optimizing station a
notification of an optimized CCA parameter to be used by the
optimizing station.
22. An integrated circuit for optimizing clear channel assessment
(CCA) parameters in wireless communications, comprising: a receiver
configured to receive a calculated optimal CCA parameter from an
optimizing station and to receive a request to change a current CCA
parameter to the optimal parameter; determining circuitry
configured to determine whether the change can be made; changing
circuitry configured to change the current CCA parameter to the
optimal parameter on a condition that the change can be made; and a
transmitter configured to transmit a message reporting whether or
not the change has occurred.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/209,692, filed Sep. 12, 2008; which is a
continuation of application Ser. No. 10/937,123, filed Sep. 9,
2004, which issued on Oct. 28, 2008 as U.S. Pat. No. 7,443,821;
which claims the benefit of U.S. Provisional Application No.
60/535,021, filed Jan. 8, 2004, all of which are incorporated by
reference as if fully set forth herein.
FIELD OF THE INVENTION
[0002] The present invention relates generally to wireless local
area networks (WLANs), and more particularly, to a method for
optimizing clear channel assessment parameters in a WLAN.
BACKGROUND
[0003] In WLAN systems, the Distributed Coordination Function (DCF)
is the fundamental access method for asynchronous data transfer on
a best effort basis. The WLAN DCF mode is used to support
contention services promoting fair access to the channel for all
stations. The multiple access scheme used to achieve this is
Carrier Sense Multiple Access with Carrier Avoidance (CSMA/CA). One
way by which stations detect if the channel is busy is by analyzing
all detected packets that are sent from other WLAN users and by
detecting activity in the channel via relative signal strength from
other sources. The physical carrier sensing that is performed prior
to data transmission is referred to as Clear Channel Assessment
(CCA).
[0004] CCA is used for transmission and reception of packets in
802.11 devices. Prior to data transmission, the device must ensure
that the wireless medium is free, by using CCA. For data reception,
the device only senses packets that meet the CCA criterion for a
busy channel.
[0005] The 802.11 standards define different CCA modes. A commonly
used CCA mode requires carrier sense and energy above the Energy
Detect Threshold (EDT) before reporting that the medium is busy.
More specifically, CCA reports a busy medium upon detection of a
WLAN type of signal with energy above the EDT. Other CCA modes
require carrier sense only, or energy above the EDT only.
[0006] A single EDT parameter is typically used to tune CCA for
both transmission and reception of packets. CCA is well-tuned for
transmission when:
[0007] 1) The access point (AP) always senses the channel as busy
when a station (STA) from its basic service set (BSS) is
transmitting a packet.
[0008] 2) The AP always senses the channel as busy when the STA to
which it has a packet to send also senses the channel as busy due
to a packet transmission from a device in a neighboring BSS. By
satisfying this condition, the AP defers to external packets that
would cause transmission errors.
[0009] 3) The AP always senses the channel as free when the STA to
which it has a packet to send senses the channel as free, even if a
device from a neighboring BSS is using the channel. By satisfying
this condition, unnecessary deferrals are avoided.
[0010] On the other hand, CCA is well-tuned for reception when:
[0011] 1) The AP is capable of receiving packets from all STAs
within the coverage area of its BSS. If the EDT parameter is set
too high, the AP might not receive packets that are transmitted by
a STA located at the cell edge.
[0012] 2) The AP does not sense packets from devices in neighboring
BSSs. If the EDT parameter is set too low, the AP might "carrier
lock" onto packets that are transmitted by STAs that are located
outside of its BSS or transmitted by other APs. By "locking" on
external transmissions, the AP will miss any transmission from a
STA in its own BSS. Such a scenario would result in a packet error,
as the packet from the STA in its own BSS would collide with the
external packet that the AP is receiving.
[0013] Determining the ideal EDT setting involves a trade-off
between optimizing for packet transmission and optimizing for
packet reception. Moreover, a dynamic method for adjusting the EDT
parameter is required in order to adapt to varying network
conditions (e.g., a change in the BSS size).
SUMMARY
[0014] Three methods for optimizing CCA parameters in a WLAN having
an access point (AP) and at least one non-AP station (STA) are
described. The term "CCA parameters" is used herein to designate
collectively the CCA mode and the value of the EDT parameter.
[0015] The first method does not require any specific signaling
between STAs, or between a STA and an AP. In this method, each STA
or AP attempts to independently find the optimal setting for its
own CCA parameters based on certain statistics. There is no sharing
of information between the STAs and AP regarding the setting of the
CCA parameters. This method begins by receiving a trigger
condition. An upper bound and a lower bound for the EDT parameter
are determined. A value of the EDT parameter is calculated and is
bound by the upper bound and the lower bound. Lastly, the EDT
parameter is updated. The method can be performed at any one STA,
all STAs, or at the AP.
[0016] The second method requires signaling between STAs or between
a STA and an AP, to communicate the values of CCA parameters used
by the STAs or the AP. In this method, each node (STA or AP) has
the possibility of learning about the values of the CCA parameters
used by other STAs or the AP, but a node can only modify its own
CCA parameters. This second method begins with a STA or the AP
requesting from other STAs and/or the AP to report the values of
the CCA parameters currently used. The requested STAs and/or the AP
report these values to the requesting STA or AP. The requesting STA
or AP then computes the optimal values to use for its own CCA
parameters. Following this computation, the requesting STA or AP
may change the values of its own CCA parameters and, optionally,
signal the new values to the other STAs or the AP.
[0017] The third method requires signaling between STAs or between
a STA and an AP, that enables one STA or the AP to modify the
values of the CCA parameters used by other STAs or the AP. In this
third method, a node may determine the optimum settings of the CCA
parameters for itself as well as for other nodes in the system, and
may request that the other nodes use their respective optimum CCA
parameters as determined by the requesting node. In an
infrastructure BSS comprising one AP and one or several STAs, the
requesting node should preferably be the AP. This method begins
with the AP calculating the optimal CCA parameters for one or
multiple STAs associated to the AP. This calculation may (or may
not) be the same as the calculation used in the first method.
Following the determination of the optimal CCA parameters for each
STA, the AP signals the respective values of the optimal CCA
parameters to each STA. The STAs determine if the requested change
of parameters is possible and indicates the success or failure of
the change in a response message to the AP.
[0018] An access point for optimizing CCA parameters in a wireless
local area network having at least one station comprises a
receiver, an energy detector, a channel availability determination
device, and a CCA calculation device which receives input
parameters from the access point and calculates the CCA
parameters.
[0019] A station for optimizing CCA parameters in a wireless local
area network having an access point comprises a receiver, an energy
detector, a channel availability determination device, and a CCA
calculation device which receives input parameters from the station
and calculates the CCA parameters.
[0020] An integrated circuit for optimizing CCA parameters in a
wireless local area network comprises a receiver, an energy
detector, a channel availability determination device, and a CCA
calculation device which receives input parameters and calculates
the CCA parameters.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] A more detailed understanding of the invention may be had
from the following description of a preferred embodiment, given by
way of example, and to be understood in conjunction with the
accompanying drawings wherein:
[0022] FIG. 1 is a flowchart of an energy detection threshold
optimization process in accordance with a first method of the
present invention;
[0023] FIG. 2 is a block diagram of an apparatus embodying the
process shown in FIG. 1;
[0024] FIG. 3 is a diagram showing the signaling between an AP or
STA and another AP or STA to implement a second method in
accordance with the present invention; and
[0025] FIG. 4 is a diagram showing the signaling between an AP and
a STA to implement a third method in accordance with the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] The present invention describes methods to dynamically
optimize the EDT parameter that is used for CCA in WLAN
systems.
TABLE-US-00001 TABLE 1 Parameter Definitions Symbol/Name
Description T.sub.Periodic The basic triggering time period
P.sub.AP AP transmission power P.sub.STA Station transmission power
RS.sub.AP AP receiver sensitivity RNG.sub.base Baseline Range of
the AP. The baseline range specifies the coverage area that is
serviced by the AP. The baseline range can either be manually
configured or dynamically determined by the AP during system
operation. N.sub.Tx Number of packets over which the transmitted
packet error rate is calculated. N.sub.Rx Number of packets over
which the received packet error rate is calculated.
PER.sub.Tx.sup.MAX The target maximum transmitted packet error
rate. PER.sub.Rx.sup.MAX The target maximum received packet error
rate. DR.sup.MAX The target maximum deferral rate .alpha. Weighting
factor for received packet error rate. .beta. Weighting factor for
transmitted packet error rate. .gamma. Weighting factor for
deferral rate. .DELTA. EDT basic step size.
TABLE-US-00002 TABLE 2 Measurement Definitions Symbol/Name
Description PER.sub.Tx The transmitted packet error rate. This
measurement is calculated using a sliding window of N.sub.Tx last
transmitted packets. PER.sub.Rx The received packet error rate.
This measurement is calculated using a sliding window of N.sub.Rx
last received packets. DR Deferral rate. This is a measurement that
represents the percentage of time that the AP is carrier locked by
an out-of-BSS packet and has at least one packet to transmit.
[0027] A flowchart of a CCA optimization process 100 using a first
method in accordance with the present invention is shown in FIG. 1.
The process 100 can be applied both at the AP and at individual
STAs. This CCA optimization process addresses the determination of
the proper level of the EDT. The CCA mode is preferably set so that
it indicates busy if the received signal is above EDT and a WLAN
signal is sensed. Alternatively, the CCA mode may be set so that it
indicates busy if the received signal is above EDT only.
[0028] Triggering
[0029] The EDT optimization process 100 is triggered on any of the
following conditions:
[0030] 1. PER.sub.Tx>PER.sub.Tx.sup.MAX and at least N.sub.Tx
packets have been transmitted since the last EDT update.
[0031] 2. PER.sub.Rx>PER.sub.Rx.sup.MAX and at least N.sub.Rx
packets have been received since the last EDT update.
[0032] 3. Expiration of a periodic triggering timer, i.e.,
T.sub.Elapsed>T.sub.periodic, and at least N.sub.Tx packets have
been transmitted and at least N.sub.Rx packets have been received
since the last EDT update. T.sub.Elapsed is the elapsed time since
the last EDT update.
[0033] When triggered according to condition 1, the optimization
process 100 attempts to solve the insufficient deferral problem.
One cause for excessive packet errors in the downlink (DL) is an
overly high EDT setting; the AP does not sense the channel as busy
while STAs are carrier-locked on neighboring BSS transmissions. A
minimum number of transmitted packets are imposed to ensure that a
problem really exists.
[0034] When triggered according to condition 2, the optimization
process 100 attempts to solve the exceedingly sensitive AP problem.
One cause for excessive packet errors in the uplink (UL) is an
overly low EDT setting; the AP locks onto neighboring BSS packets,
causing it to miss packets from its own STAs. An UL packet error
generally occurs when a STA transmits a packet while the AP is
already carrier-locked on a neighboring BSS transmission. A minimum
number of received packets are imposed to ensure that a problem
really exists.
[0035] Condition 3 is for general optimization purposes. The
optimization process 100 is triggered periodically, once enough
packets have been transmitted and received to have collected
significant statistics.
[0036] The triggering parameters should be selected so that the
optimization process 100 reacts quickly to an excessive packet
error situation. For example, the optimization process 100 could
trigger periodically once per second, once sufficient statistics
have been collected. If a minimum of 100 packets is required for
triggering, a 10% error rate results in 10 errors.
[0037] Determining EDT Bounds
[0038] The optimization process 100 begins by determining upper and
lower bounds for the EDT parameter (step 102). An upper bound on
the EDT parameter, EDT.sub.MAX, is determined as follows:
EDT.sub.MAX=P.sub.STA(RNG.sub.base+RNG.sub.adj) Equation (1)
[0039] where RNG.sub.adj is a range adjustment value determined by
the Power Control algorithm. The EDT parameter should be set so
that the AP can at least sense all packets originating from its own
BSS. EDT.sub.MAX corresponds to the signal level at which a
transmission from a STA located at the cell edge is received.
[0040] The calculated value of EDT.sub.MAX is compared to the
maximum value allowed by the 802.11 standards, and the lower of the
two values is taken. The maximum EDT value allowed by the standard
is based on the AP's transmission power, P.sub.AP. EDT.sub.MAX is
dynamically calculated as RNG.sub.base, RNG.sub.adj, and P.sub.STA
can be modified by the Power Control algorithm at any time, and is
updated whenever there is a change to RNG.sub.base, RNG.sub.adj, or
P.sub.STA.
[0041] The lower bound on the EDT parameter, EDT.sub.MIN, is set to
the AP receiver sensitivity level, RS.sub.AP.
[0042] EDT Update
[0043] Next, the EDT parameter is calculated based on its current
value, the received and transmitted packet error rates, and the
deferral rate (step 104):
EDT = EDT + ( .alpha. PER Rx PER Rx MAX - .beta. PER Tx PER Tx MAX
+ .gamma. DR DR MAX ) .DELTA. Equation ( 2 ) ##EQU00001##
[0044] The default values for the weighting factors is 1, and can
be optimized based on the deployment of the system (i.e., the
layout of the APs and the STAs).
[0045] The EDT parameter is adjusted between the lower and upper
bounds (step 106):
EDT=max(EDT.sub.MIN,min(EDT.sub.MAX,EDT)) Equation (3)
[0046] The EDT value is updated (step 108) and the process
terminates (step 110). It is noted that if a channel change
occurred since the last invocation of the EDT optimization process
100, the EDT parameter is automatically set to EDT.sub.MIN.
[0047] Alternatively, it is possible use different EDT parameter
settings for transmission and reception. EDT.sub.Tx is optimized
for packet transmission, whereas EDT.sub.Rx is optimized for packet
reception. Immediately before sending a packet, the AP sets the CCA
EDT parameter to EDT.sub.Tx, and sets it back to EDT.sub.Rx once
the data transmission is complete.
[0048] EDT.sub.Tx is determined using a procedure similar to that
shown in FIG. 1, except using the following equation:
EDT Tx = EDT Tx + ( .gamma. DR DR MAX - .beta. PER Tx PER Tx MAX )
.DELTA. Equation ( 4 ) ##EQU00002##
[0049] EDT.sub.Tx is then adjusted between the upper and lower
bounds, as shown in Equation (3).
[0050] In one embodiment, EDT.sub.Rx=RNG.sub.base. In another
embodiment, EDT.sub.Rx is set according to the following
equation:
EDT Rx = EDT MAX - .alpha. PER Rx PER Rx MAX Equation ( 5 )
##EQU00003##
[0051] FIG. 2 shows an AP or a STA 200 constructed in accordance
with the present invention. The AP or STA 200 includes a receiver
202 connected to an energy detector 204. A channel availability
determination device 206 is connected to the energy detector 204
and a CCA calculation device 208 is connected to the channel
availability determination device 206. The CCA calculation device
208 accepts parameters, such as DR and PER, as inputs and outputs
an EDT value to the channel availability determination device 206
which uses the EDT value to determine if the channel is busy. The
EDT value is also cycled back into the CCA calculation device 208,
and is used as shown in Equations 2 and 3.
[0052] A diagram of a CCA optimization process 300 using the second
method is shown in FIG. 3. This method can be used by any STA or
AP. The STA or AP using the method is referred to as the
"optimizing" station 302. The optimizing station 302 requests
information about the setting of the CCA parameters in other STAs
or AP 304 (step 310). There are several possibilities for
implementing this signaling.
[0053] The first possibility is for the optimizing station 302 to
send separate requests (unicast) to each surrounding STA or AP 304
("requested stations") whose addresses are known by the optimizing
station 302. The optimizing station 302 may know these addresses by
different means. For example, if the optimizing station 302 is an
AP, it necessarily knows the addresses of all STAs associated to
it. If the optimizing station 302 is a STA, it can learn about the
addresses of other STAs in the same basic service set (BSS) by
looking at the MAC addresses of received packets. However, the WLAN
protocol may not allow direct communication between STAs in an
infrastructure BSS. In that case, this method would be usable by
the AP only.
[0054] The request must contain the addresses of the optimizing
station 302 and the requested station 304. In an 802.11 WLAN, this
information would already be in the MAC header. Optionally, the
request may contain a time limit for the requested station 304 to
respond. The requested station 304 sends back an acknowledgment
just after correct reception of the packet containing the request
(just as any other packet directed to a specific station). In this
way, the optimizing station 302 knows that the requested station
304 has properly received the request, and can retransmit the
packet containing the request if it did not receive an
acknowledgment within a certain time.
[0055] A second possibility is for the optimizing station 302 to
send one general request directed to all surrounding stations 304.
This can be done by transmitting a broadcast message specifying
only the basic service set (BSS) identity, in which case only the
STAs belonging to the specified BSS would respond. This can also be
done by transmitting a multicast message specifying the addresses
of all STAs from which it is desired to have the CCA parameters
reported.
[0056] In a third possibility, a STA (non-AP) may request the AP to
which it is associated for the CCA parameters of one or more STA(s)
associated to this AP, instead of directly requesting the
parameters from the STA. This request would contain the address of
the STA(s) from which it is desired to have the CCA parameters
reported, or a special flag indicating that the CCA parameters from
all STAs in the BSS are requested. Following this request, the AP
may respond with the CCA parameters of the requested stations 304.
The AP may already have this information, or it may need to request
the information (using one of the mechanisms described above) from
the STAs prior to responding to the optimizing station 302.
[0057] For any STA that successfully receives a CCA parameters
request according to one of the mechanisms described above, that
STA reads the values of the CCA parameters it is currently using
(step 312). These values (CCA mode and EDT) can be normally found
in the management information base (MIB) of the requested station
304. After having read the CCA parameters, the requested station
304 (after gaining access to the medium according to the usual
802.11 protocol) transmits a CCA parameters report (step 314). This
report may be a broadcast to all STAs in the BSS (in which case no
acknowledgment is expected) or, preferably, may be a unicast
directed at the optimizing station 302. In the latter case, an
acknowledgment is expected from the optimizing station 302 and the
requested station 304 can re-transmit in case of failure. The
report contains the values of the CCA parameters.
[0058] Once the optimizing station 302 has received CCA parameters
reports from all requested stations 304 (or after a certain period
of time has elapsed since the transmission of the requests, at the
discretion of the optimizing station 302), the optimizing station
302 calculates the new CCA parameters it will use for itself (step
316).
[0059] A simple method for determining CCA parameters is to use
those of the most sensitive STA from which CCA parameters were
received (i.e., the STA with the lowest setting of the EDT
parameter). If path loss information is available, the EDT
parameter can be calculated to be as sensitive as the most
sensitive reporting STA. For example, an AP could set its EDT
parameter such that it is as sensitive to external transmissions as
its most sensitive STA is. The AP could achieve this by setting its
EDT parameter lower than the sensitive STA's EDT parameter by an
amount equal to the difference in path losses to the most dominant
external interferers.
[0060] After the optimizing station 302 has calculated the new CCA
parameters it should use, it can immediately apply the new setting.
Optionally, it may send a CCA parameters notification to other
requested stations 304 to inform them of the new setting now used
by the optimizing station 302 (step 318). This message may be
directed to specific STAs (unicast) or multiple STAs (multicast or
broadcast).
[0061] A diagram of a CCA optimization process 400 using the third
method is shown in FIG. 4. This method is preferably used by the AP
in an infrastructure BSS, although use by a non-AP station is not
precluded (e.g., in an independent BSS). The AP using the method is
referred to as "controlling" station 402. The controlling station
402 computes or estimates the optimal CCA parameters for itself and
other STAs in the same BSS ("controlled" stations 404; step 410).
This determination may or may not be performed using the method 100
disclosed above.
[0062] After having determined the optimal CCA parameters for every
STA (these may or may not be different from one controlled station
404 to another depending on the algorithm), the controlling station
402 requests the controlled stations 404 to modify their CCA
parameters ("CCA parameters control request"; step 412). If the CCA
parameters are the same for all controlled stations 404, the
controlling station 402 may transmit a broadcast message containing
the BSS identity along with the values of the CCA parameters, and
optionally a time limit for responding. It may also transmit a
multicast message containing the addresses of all controlled
stations 404 along with the values for the CCA parameters.
Preferably, the controlling station 402 transmits a unicast message
(with acknowledgment) separately to each controlled station 404
with its new CCA parameters. When the new CCA parameters are
different from one controlled station 404 to another, multicast or
unicast messages are mandatory.
[0063] Following successful reception of the CCA parameters control
request message, a controlled station 404 determines whether it is
possible to apply the new CCA parameters requested by the
controlling station 402 (step 414). Applying the new parameters may
not be possible, depending on the capabilities of the controlled
station 404 (e.g., radio sensitivity or the availability of the
requested CCA mode). If the modification is possible, the
controlled station 404 immediately modifies its CCA parameters
(step 416) and transmits a response ("CCA parameters control
response") as a unicast message to the controlling station 402
(preferred) or as a broadcast message to all STAs in the BSS (step
418). This message contains a flag indicating the success or
failure of the CCA parameters modification. In case of failure, the
message may optionally contain a "cause" field that specifies the
reason for the failure (such as unavailable CCA mode or requested
EDT value too low or too high). It may also contain the values of
the CCA parameters currently in use by the controlled station
404.
[0064] After receiving the responses from all controlled stations
404 (or after a certain period of time has elapsed since the
transmission of the requests, at the discretion of the controlling
station 402), the controlling station 402 may decide to do nothing
until the next scheduled activation of the optimization algorithm,
in a manner similar to that described in the method 100. The
controlling station 402 may also decide to repeat the transmission
of requests to the controlling stations 404 in case some of them
did not transmit back a response.
[0065] While the present invention is described herein in
connection with a WLAN, the principles of the present invention can
be applied to other types of wireless communication systems. In
such circumstances, the STA could include, but is not limited to,
devices such as a wireless transmit/receive unit (WTRU), a user
equipment, a fixed or mobile subscriber unit, a pager, or any other
type of device capable of operating in a wireless environment.
Similarly, the AP could include, but is not limited to, devices
such as a base station, a Node B, a site controller, or any other
type of interfacing device in a wireless environment.
[0066] Although the features and elements of the present invention
are described in the preferred embodiments in particular
combinations, each feature or element can be used alone (without
the other features and elements of the preferred embodiments) or in
various combinations with or without other features and elements of
the present invention. While specific embodiments of the present
invention have been shown and described, many modifications and
variations could be made by one skilled in the art without
departing from the scope of the invention. The above description
serves to illustrate and not limit the particular invention in any
way.
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