RELATED APPLICATION
[0001] This patent application is divided out of Indian Patent Application No.
4964/DELNP/2005 filed on 28 October 2005 and related to India Patent Application
No. 517/DELNP/2010, filed January 22, 2010, entitled "Method And Apparatus For
Network Management Using Periodic Measurements Of Indicators"
[0002]
[0003]
FIELD OF INVENTION
This invention relates to beacon measurement request signals used
in wireless slotted communications and network management. More
particularly, the invention relates to network management using periodic
measurements of parameters such as new beacon received power level or signal
quality.
[0004]
[0005]
BACKGROUND
The IEEE 802.11 communications protocol allows a client to roam
among multiple access points that may be operating on the same or separate
channels. IEEE 802.11 communications are generally effected through wireless
LAN access points (APs), which are typically single standalone units, but can
include networks with multiple APs which provide a roaming function. To
support the roaming function, each access point typically transmits a beacon
signal every lOOms. A roaming station (STA) uses the beacon to gauge the
strength of its existing access point connection. If the STA senses a weak signal,
the roaming STA can implement the reassociation service to connect to an access
point emitting a stronger signal.
[0006] IEEE 802.11 supports two power modes; active and power-saving
(PS). The protocols for infrastructure networks and ad hoc networks are
different. Under an infrastructure network, there is an AP to monitor the mode
of each mobile station. A station in the active mode is fully powered and thus
may transmit and receive at any time. On the contrary, a station in the PS mode
only wakes up periodically to check for possible incoming packets from the AP. A
station always notifies its AP when changing modes. Periodically, the AP
transmits beacon frames spaced by a fixed beacon interval. A PS station should
monitor these frames. In each beacon frame, a traffic indication map (TIM) are
delivered, which contains IDs of those PS stations with buffered unicast packets
in the AP. A PS station, on hearing its ID, should stay awake for the remaining
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beacon interval. Under the contention period (i.e., DCF), an awake PS station
can issue a PS-POLL to the AP to retrieve the buffered packets. While under the
contention-free period (i.e., PCF), a PS station waits for the AP to poll it. The AP
sends delivery TIMs (DTIMs) within beacon frames to indicate that there are
buffered broadcast packets. The delivery TIMs are spaced by a fixed number of
beacon intervals. Immediately after DTIMs, the buffered broadcast packets are
sent.
[0007] Since IEEE 802.11 presumes that mobile stations are fully
connected, the transmission of a beacon frame can be used to synchronize all
stations' beacon intervals. In addition to the use in IEEE 802.11, beacon signals
are useful in other WLAN communications and wireless communications in
general. Periodic measurements are performed in systems implementing the
third generation partnership program (3GPP) wideband code division multiple
access (W-CDMA) system. Such systems use a time division duplex mode. To
support higher layer functions in IEEE 802.11 standards for efficient network
management, several physical parameters relating to different aspects of
network management are desirable.
[0008] One such parameter is the perceived signal to noise indicator
(PSNI), the measurement of which provides a quantized, comparative measure of
received signal quality for all channels/rates and among aJ.l physical channels
and between all stations. Another parameter is the received channel power
indicator (RCPI) indicator, which is a measure of the received RF power in the
selected channel, measured at the antenna connector. The RCPI parameter may
be a measure by the PRY sub layer of the received RF power in the channel
measured over the PLOP preamble and over the entire received frame. RCPI is a
monotonically increasing, logarithmic function ofthe received power level defined
in dBm. The exemplary allowed values for the RCPI parameter may be an 8-bit
value in the range from 0 through 220.
[0009] In known approaches, the measurement of the parameters RCPI
and PSNI is done as a single measurement, which approach has certain
disadvantages. It is desirable to provide an improved method of making
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measurements of the parameters, e.g., RCPI and PSNI, to result in specific
advantages resulting in more efficient network management.
[0010] SUMMARY
[0011] According to the present invention, periodic measurements of the
new beacon request are used in order to support roaming and dynamic data rate
adjustment, and related functions. The concepts for periodic measurements are
performed in a manner analogous to periodic measurements in systems
implementing third generation partnership program (3GPP) wideband code
division multiple access (W -CDMA) system utilizing the time division duplex
mode.
(0012] BRIEF DESCRIPTION OF THE DRAWINGS
[00 13] Figure 1 is a schematic diagram of a network configuration in which
WLAN s communicate with a wireless transmit/receive unit (WTRU) through one
or more access points.
[0014] Figure 2 is a chart showing types of measurements or reports.
[0015] Figure 3 is a graph showing the effects of absolute threshold on data
rate selection.
[0016] Figure 4 is a graph showing a relative threshold which uses the
serving AP for a handoff.
[0017] Figure 5 is a graph showing the effect of a reporting offset.
[0018] Figure 6 is a graph showing the received channel power indicator
(RCPI) level of a serving AP.
[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] Hereafter, a wireless transmit/receive unit (WTRU) includes but is
not limited to a user equipment, mobile station, fixed or mobile subscriber unit,
pager, or any other type of device capable of operating in a wireless environment.
When referred to hereafter, an access point includes but is not limited to a
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Node B, site controller, access point or any other type of interfacing device in a
wireless environment.
[0021] An "access point" (AP) in a typical IEEE 802.11 implementation is a
station or device which provides wireless access for devices to establish a wireless
connection with a LAN, and establishes a part of a wireless LAN (WLAN). If the
AP is a fixed device on a WLAN, the AP is a station which transmits and receives
data. The AP permits connection of a WTRU to a network, provided that the
WLAN itself has a connection to the network.
[0022] Network management by making measurements of parameters, e.g.,
ROPI and PSNI, is performed periodically rather than in the manner of a
one-time measurement. The impact of making periodic measurements on the
network performance and the attendant benefits are addressed in the description
of the preferred embodiment. More specifically, the beneficial effect of making
periodic measurements on the beacon request extensions to support roaming and
dynamic data rate are addressed. Even though the invention is described in the
specific context of the standard IEEE 802.11 as an example, the invention is
envisaged to be applicable to other scenarios also.
[0023] Periodic beacon requests are made during connection between a
WTRU and an AP on a WLAN. A Measurement Request field corresponding to a
beacon request contains a measurement duration value and channel number for
which the request applies. The beacon request permits a scan mode which
includes "Active Scan" mode, "Passive Scan" mode and ••Beacon Table•• mode. In
Active Scan mode, the measuring station (STA) transmits a probe request with a
broadcast service station identifier (SSID). The measuring STA's beacon report
contains one information element for each STA from which it detects a beacon or
probe response, regardless of whether the probe response was triggered by the
measuring STA's own probe request. In Passive Scan mode, the measuring STA
passively receives on the specified channel and returns a beacon report
containing one information element for each STA from which it detects a beacon
or probe response. If the measuring channel is also the serving channel, the STA
concurrently carries out its normal data traffic operation. In Beacon Table mode,
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the measuring STA returns a Beacon Report containing the current contents of
its beacon table without performing additional measurements. The
Measurement Duration field is set equal to the duration of the requested
measurement, expressed in time units (TUs).
[0024] The following are some potential advantages of periodic
measurements as compared with the single measurement approach:
[0025] Periodic measurements reduce management traffic: single
measurement request produces multiple reports but only when relevant.
[0026] Absolute Threshold crossings on PSNI measures are ideal to trigger
data rate changes.
[0027] Absolute Threshold crossings on RCPI are ideal for proximity
detectors for location.
[0028] Relative Threshold with respect to serving AP detects conditions for
han doff.
[0029] The beacon request also contains periodic extensions (information
fields) which specify periodic beacon measurements. The extensions fields are
used to provide parameters for the periodic measurement and conditional
reporting of measurement results. These provide periodic measurements which
reduce management traffic, such that a single measurement request produces
multiple reports. The multiple reports are provided only when deemed relevant.
Absolute threshold crossings on perceived signal to noise indicator (PSNI) may be
used as a condition to provide a measurement report. The measurements on
PSNI are suitable to trigger data rate changes. Absolute threshold crossings on
received channel power indicator (RCPI) may be used as a condition to provide a
measurement report.
[0030] The periodic extensions are additional fields in the beacon request
which are use for periodic beacon measurements. The capability to do periodic
measurements is an optional capability for the AP, and therefore APs which are
not capable of doing periodic beacon measurements will ignore the periodic
extensions. A beacon request is a request to perform a measurement. A beacon
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report is the response containing the result(s) of the requested beacon
measurement.
[0031] The absolute threshold crossings are suitable for proximity detectors
used to determine location and approximate position relative to an AP. A
relative threshold with respect to a serving AP is used to detect conditions for a
han doff.
[0032] The measurement request field corresponding to a beacon request is
shown in Table 1 and contains the measurement duration and channel number
for which the request applies. Also included in Table 1 are the extensions
(additional information fields) needed to specifY periodic measurements and
conditional reporting. Table 1 generally shows the measurement request field
format for a beacon request. The illustration for the current measurement shows
the number of octets for the channel number, channel band, measurement
duration and scan mode. Table 1 also shows for comparison, the octets for
periodic extensions, with respect to basic service set identifier (BSSID),
measurement period, reporting condition, threshold/offset, and hysteresis effect.
More particularly, the Measurement Request field corresponding to a beacon
request is shown in Table 1 and contains the measurement duration and channel
number for which the request applies. A response to a beacon request is a beacon
report.
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Table 1 - Beacon Request
Channel Channel Measurement Scan
Number Band Duration Mode
Octets: 1 1 2 1
BSSID Measurement Reporting Threshold Hysteresis
Period Condition /Offset
Octets 6 2 1 1 1
[0033] If the AP is not capable of performing periodic measurements and
thus does not recognize the extensions, then the AP ignores the extensions and
provides a single measurement and a single report.
[0034] In Table 1, channel number indicates the channel number on which
the requesting STA instructs the receiving STA to report detected beacons and
probe responses. In the beacon request, the Channel Number field indicates the
channel number on which the requesting STA instructs the receiving STA to
report detected beacons and probe responses. The Channel Band field indicates
the frequency band, taken from Table 1, in which the receiving STA conducts its
measurement. The Scan Mode field is set to the type of scan, according to
Table 2 (infra). The scanning behavior is as follows:
[0035] In Active Scan mode, the measuring STA transmits a probe
request with the broadcast SSID. The measuring STA's beacon report contains
one information element for each STA from which it detects a beacon or probe
response, regardless of whether the probe response was triggered by the
measuring STA's own probe request
[0036] In Passive Scan mode, the measuring STA passively receives
on the specified channel and return a beacon report containing one information
element for each STA from which it detects a beacon or probe response. If the
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measuring channel is also the serving channel, the STA concurrently carries out
its normal data traffic operation.
[0037] In Beacon Table mode, the measuring STA returns a beacon
report containing the current contents of its beacon table without performing
additional measurements.
[0038] The Measurement Duration field is set equal to the duration of the
requested measurement, expressed in TU s.
[0039] Tables 2 and 3 show channel band definitions for radio
measurement requests and Scan Mode definitions for beacon request elements.
[0040] Table 2 - Channel Band definitions for radio measurement requests
Name Channel Band
2.4-GHz Band 0
5-GHz Band 1
[0041] Table 3 - Scan Mode definitions for Beacon Request elements
Name Scan Mode
Passive Scan 0
Active Scan 1
Beacon Table 2
Reserved 3-255
[0042] BSSID indicates the BSSID of the particular AP for which this
measurement is requested. The BSSID specifies which AP to measure when
several APs are detectable on a given channel. The BSSID is set to the broadcast
BSSID when the measurement is performed on any AP(s) on this channel. A
broadcast BSSID is used when an AP BSSID is unknown.
[0043] The Measurement Period indicates whether this measurement is a
single measurement event or is a periodic measurement which is repeated each
Measurement Period. The Measurement Period is divided into two subfields:
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Unit and Period. The Unit subfield defines the time unit for the Period subfield
and consists of the 2 MSBs with the following values:
[0044] The Period subfield consists of the 14 LSBs and is an unsigned
integer number representing the repeating time interval for this periodic
measurement. A Period subfield value ofO indicates that the measurement is not
periodic but is a single measurement. A period subfield value of 16383 (3FFF
Hex) indicates that the measurement is periodic with no requested measurement
period; in this case the measurement is performed on a best effort basis and as
frequently as conditions permit.
[0045] The Reporting Condition defines when the measured results are
reported to the requesting STA. The Reporting Condition values are defined in
Table 4.
[0046] Table 4 - Reporting Condition Definitions for Beacon Request
Element
Condition Descriptl.on Reporting
Condition
Report to be issued after each measurement. 0
Report to be issued when the RCPI level ofthe measuredAP crosses above an 1
absolute threshold with hysteresis.
Report to be issued when the RCPI level of the measured AP crosses below an 2
absolute threshold with hysteresis.
Report to be issued when the PSNI level of the measured AP crosses above an 3
absolute threshold with hysteresis.
Report to be issued when the PSNI level ofthe measured AP crosses below an 4
absolute threshold with hysteresis.
Report to be issued when the RCPI level of the measured AP crosses above a 5
threshold defined by an offset (with hysteresis) from the serving AP's RCPI.
Report to be issued when the RCPI level ofthe measured AP crosses below a 6
threshold defined by an offset (with hysteresis) from the serving AP's RCPI.
Report to be issued when the PSNI level of the measured AP crosses above a 7
threshold defined by an offset (with hysteresis) from the serving AP's PSNI.
Report to be issued when the PSNI level ofthe measured AP crosses below a 8
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threshold defined by an offset (with hysteresis) from the serving AP's PSNI.
Periodic reports (one per measurement) to begin when the RCPI level of the 9
measured AP enters and remains in a range bound by the serving AP's RCPI
and an offset (with hysteresis) from the serving AP's RCPI.
Periodic reports (one per measurement) to begin when the PSNI level of the 10
measured AP enters and remains in a range bound by the serving AP's PSNI
and an offset (with hysteresis) from the serving AP's PSNI.
Reserved !11- 255
[0047] Threshold/Offset provides either the threshold value or the offset
value to be used for conditional reporting. A threshold value is an unsigned 8 bit
integer having units which are equivalent to PSNI or RCPI. An offset value is a
signed 7 bit integer in the range of(-127, +127).
[0048] Hysteresis provides an unsigned 8 bit integer hysteresis value
having units equivalent to the units used in the Threshold/Offset field.
[0049] Figure 1 is a schematic diagram of a network configuration 11 in
which one or more WLANs 12, 13 communicate with a WTRU 15 through one or
more APs 17-19. In the example depicted the WLANs 12, 13 are able to
establish a network link 22, either directly or through a radio network controller
(RNC) 23.
[0050] Figure 2 is a chart showing types of measurements or reports,
showing how event detection triggers a report, or, triggers periodic reporting.
More specifically, Figure 2 illustrates for comparison, a single report scenario for
PSNI and RCPI, as compared to similar periodic conditional reports for absolute
threshold, serving AP threshold, serving AP periodic range. Also illustrated is
the periodic reporting for each trigger event for comparison. The broadest
category is a measurement 26. As used here, 11measurement11 can be a
measurement or report. The measurement 26 may be a single 27 or periodic 28
measurement. A single measurement generates a single report 29, which
includes a single report PSNI 30 and a single report RCPI 31. The periodic
measurement 28 can generate a conditional report 32 or a periodic report 33.
The conditional report 32 can provide an absolute threshold 34, a serving AP
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threshold 35 or a serving AP periodic range 36. The absolute threshold 34
includes an absolute threshold PSNI 37 and an absolute threshold RCPI 38. The
serving AP threshold 35 includes a serving AP threshold PSNI 4 7 and a serving
AP threshold RCPI 48. The serving AP periodic range 36 includes a serving AP
periodic range PSNI 57 and a serving AP periodic range RCPI 58. The periodic
report 33 includes a periodic report PSNI 67 and a periodic report RCPI 68.
[0051] In addition, the single report 31 may be conditionally reported based
on an absolute threshold 34 including absolute threshold PSNI 37 and absolute
threshold RCPI 38. Also, the single report 31 may be conditionally reported
based on the serving AP threshold 35 including serving AP threshold PSNI 4 7
and serving AP threshold RCPI 48. The serving AP periodic range is not used for
the single report 31, but may provide the serving AP periodic range 36 including
serving AP periodic range PSNI 57 and serving AP periodic range RCPI 58 for
periodic measurement reporting.
[0052] The single and periodic measurements 27, 28 are measurement
types. The single report 31, conditional report 32, periodic report The absolute
threshold 34, serving AP threshold 35 and serving AP periodic range 36 trigger
events. The measurement results are the single report PSNI 27, single report
RCPI 28, absolute threshold PSNI 37, absolute threshold RCPI 38, serving AP
threshold PSNI 47, serving AP threshold RCPI 48, serving AP periodic range
PSNI 57, serving AP periodic range RCPI 58, periodic report PSNI 67 and
periodic report RCPI 68. For conditional reporting, event detection triggers one
or more of these single event reporting outputs or periodical reporting outputs.
[0053] Figure 3 is a graph showing the effects of absolute threshold on data
rate selection, and illustrates variation of measurement quantity against time for
three different channels having 5.5 Mbps, 2.0 Mbps and 1.0 Mbps rates
respectively. At an initial time of the graph, STA 1 receives a low PSNI level
from the AP as measured at the STA, substantially below an absolute threshold.
The rate is established at 1Mbps. STA 2 and STA 3 have PSNI levels above the
threshold level. As time progresses, STA 3 has received PSNI levels which
exceed a second threshold and then drops down to below the absolute threshold.
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STA 3 thus can change to the 5.5 Mbps rate, but must drop down to the 2 Mbps
rate and eventually the 1 Mbps rate as the PSNI level drops. STA 2 remains at
the 2 Mbps rate until later, when STA 2 has sufficient PSNI levels to change to
the 5.5 Mbps rate. These changes in PSNI levels can also be used to change APs
by selecting the AP with a higher rate or PSNI level, should resources from that
AP be available.
[0054] Figure 4 is a graph showing a relative threshold which uses the
serving AP for a handoff. This figure also illustrates variation of measurement
quantity against time for AP 1 and AP 2 intersecting at a location showing the
reporting event. The graph shows the signals received by a STA from a first AP
(Serving AP) and a second AP (AP 2). The measurement for the servicing AP is
made lower by an offset, in which PSNI is made lower, in order to favor AP 2.
Thus the measurement of PSNI for the serving AP is made artificially lower by
the offset. This causes an early trigger ofthe handoffas a result ofthe offset.
[0055] Figure 5 is a graph showing the effect of a reporting offset and
shows relative threshold triggers for AP 1, 2 and 3 showing the reporting range
and when the reporting terminates. The graph illustrates timeslot ISCP versus
time showing the ISCP threshold and the reporting event. Event triggered and
periodic reports of the PSNI levels each show the instance of a reduced PSNI
level as a result of the offset. The reporting of the serving AP 3 continues during
a peak period ofPSNI reported from a third AP, AP 3, but discontinues when the
signal from AP 3 drops below the offset reporting of PSNI from the serving AP.
[0056] Figure 6 is a graph showing the RCPI level of a serving AP. The
triggering event here is an absolute threshold exceeded. The triggering event
triggers a report.
[0057] 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 ofthe
preferred embodiments) or in various combinations with or without other
features and elements of the present invention.

I/WE CLAIM:
1. An apparatus comprising:
a receiver to receive from a wireless communication station a beacon
request comprising a measurement request field, the measurement request field
comprising a measurement duration field and a mode field, the measurement
duration field to indicate a measurement duration of a requested measurement;
and
a transmitter to transmit a beacon report to the wireless communication
station based on the measurement request field,
wherein, when the mode field comprises an active mode value or a passive
mode value, the beacon report comprises a report based on detection, according to
the measurement duration, of one or more of probe responses or beacons, and,
when the mode field comprises a beacon table mode value, the beacon report
comprises a current content of beacon information without additional
measurement.
2. The apparatus of claim 1, wherein, when the mode field comprises the
active mode value, the transmitter is to broadcast a probe request.
3. The apparatus of claim 1, wherein the measurement request field
comprises a channel number field comprising one octet to indicate a channel for
the requested measurement.
4. The apparatus of claim 1, wherein the measurement request field
comprises a Basic Service Set Identifier (BSSID) field comprising six octets to
indicate a BSSID for the requested measurement.
5. The apparatus of claim 1, wherein the passive mode value comprises a
value of “0”, the active mode value comprises a value of “1”, and the beacon
table mode value comprises a value of “2”.
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6. The apparatus of claim 1, wherein the measurement duration field
comprises two octets to indicate the measurement duration in Time Units (TU).
7. The apparatus of any one of claims 1-6, wherein, when the measurement
request field comprises a zero reporting condition value, the transmitter is to
transmit the beacon report after each measurement.
8. The apparatus of any one of claims 1-6, wherein, when the measurement
request field comprises a non-zero reporting condition value, the transmitter is to
transmit the beacon report based on a condition represented by the non-zero
reporting condition value.
9. The apparatus of any one of claims 1-6 comprising an antenna.
10. An apparatus comprising:
a transmitter to transmit to a wireless communication station a beacon
request comprising a measurement request field, the measurement request field
comprising a measurement duration field and a mode field, the measurement
duration field to indicate a measurement duration of a requested measurement, the
mode field comprising a value selected from a plurality of predefined values
comprising at least an active mode value, a passive mode value and a beacon table
mode value, the active mode value and the passive mode value to indicate a
request for a report based on detection, according to the measurement duration, of
one or more of probe responses or beacons, the beacon table mode value to
indicate a request for a current content of beacon information without additional
measurement; and
a receiver to receive a beacon report from the wireless communication
station based on the measurement request field.
11. The apparatus of claim 10, wherein the active mode value is to indicate to
the wireless communication station to broadcast a probe request.
15 INTL-718-IN-DIV
12. The apparatus of claim 10, wherein the measurement request field
comprises a channel number field comprising one octet to indicate a channel for
the requested measurement.
13. The apparatus of claim 10, wherein the measurement request field
comprises a Basic Service Set Identifier (BSSID) field comprising six octets to
indicate a BSSID for the requested measurement.
14. The apparatus of claim 10, wherein the passive mode value comprises a
value of “0”, the active mode value comprises a value of “1”, and the beacon
table mode value comprises a value of “2”.
15. The apparatus of claim 10, wherein the measurement duration field
comprises two octets to indicate the measurement duration in Time Units (TU).
16. The apparatus of any one of claims 10-15, wherein the measurement
request field comprises a zero reporting condition value to indicate transmission
of the beacon report after each measurement.
17. The apparatus of any one of claims 10-15, wherein the measurement
request field comprises a non-zero reporting condition value to indicate
transmission of the beacon report based on a condition represented by the nonzero
reporting condition value.
18. The apparatus of any one of claims 10-15 comprising an antenna.
19. A method comprising:
receiving from a wireless communication station a beacon request
comprising a measurement request field, the measurement request field
comprising a measurement duration field and a mode field, the measurement
duration field to indicate a measurement duration of a requested measurement;
and
16 INTL-718-IN-DIV
transmitting a beacon report to the wireless communication station based
on the measurement request field,
wherein, when the mode field comprises an active mode value or a passive
mode value, the beacon report comprises a report based on detection, according to
the measurement duration, of one or more of probe responses or beacons, and,
when the mode field comprises a beacon table mode value, the beacon report
comprises a current content of beacon information without additional
measurement.
20. The method of claim 19 comprising, when the mode field comprises the
active mode value, broadcasting a probe request.
21. The method of claim 19, wherein the measurement request field comprises
a channel number field comprising one octet to indicate a channel for the
requested measurement.
22. The method of claim 19, wherein the measurement request field comprises
a Basic Service Set Identifier (BSSID) field comprising six octets to indicate a
BSSID for the requested measurement.
23. The method of claim 19 comprising, when the measurement request field
comprises a zero reporting condition value, transmitting the beacon report after
each measurement.
24. The method of claim 19 comprising, when the measurement request field
comprises a non-zero reporting condition value, transmitting the beacon report
based on a condition represented by the non-zero reporting condition value.
25. A method comprising:
transmitting to a wireless communication station a beacon request
comprising a measurement request field, the measurement request field
comprising a measurement duration field and a mode field, the measurement
17 INTL-718-IN-DIV
duration field to indicate a measurement duration of a requested measurement, the
mode field comprising a value selected from a plurality of predefined values
comprising at least an active mode value, a passive mode value and a beacon table
mode value, the active mode value and the passive mode value to indicate a
request for a report based on detection, according to the measurement duration, of
one or more of probe responses or beacons, the beacon table mode value to
indicate a request for a current content of beacon information without additional
measurement; and
receiving a beacon report from the wireless communication station based
on the measurement request field.
26. An apparatus comprising means to cause a wireless communication device
to perform the method of any one of claims 19-25.