U.S. patent application number 11/743847 was filed with the patent office on 2007-08-30 for systems and methods for reducing communication unit scan time in wireless networks.
This patent application is currently assigned to Intel Corporation. Invention is credited to Shahrnaz Azizi, FNU Tejaswini.
Application Number | 20070201420 11/743847 |
Document ID | / |
Family ID | 34313712 |
Filed Date | 2007-08-30 |
United States Patent
Application |
20070201420 |
Kind Code |
A1 |
Tejaswini; FNU ; et
al. |
August 30, 2007 |
SYSTEMS AND METHODS FOR REDUCING COMMUNICATION UNIT SCAN TIME IN
WIRELESS NETWORKS
Abstract
A communication unit operates in a wireless-networking
environment and maintains a mapping for active channels and
associated network identifiers. The communication unit may
associate with a wireless network using the mapping for one or more
of the active channels having a selected network identifier. For
associations and reassociations with wireless networks, the
communication unit may selectively scan the channels having mapping
stored in a table to more quickly identify active channels and
thereby reduce scan time. In some embodiments, an access point may
perform channel-width measurements and radar detection using the
bitmap.
Inventors: |
Tejaswini; FNU; (San Diego,
CA) ; Azizi; Shahrnaz; (San Diego, CA) |
Correspondence
Address: |
SCHWEGMAN, LUNDBERG, WOESSNER & KLUTH, P.A.
P.O. BOX 2938
MINNEAPOLIS
MN
55402
US
|
Assignee: |
Intel Corporation
|
Family ID: |
34313712 |
Appl. No.: |
11/743847 |
Filed: |
May 3, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10669478 |
Sep 23, 2003 |
|
|
|
11743847 |
May 3, 2007 |
|
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Current U.S.
Class: |
370/338 |
Current CPC
Class: |
H04W 48/16 20130101;
H04W 84/12 20130101 |
Class at
Publication: |
370/338 |
International
Class: |
H04Q 7/24 20060101
H04Q007/24 |
Claims
1. A method for reducing scan time by a mobile communication unit
comprising: maintaining a single mapping within the mobile
communication unit for one or more active channels associated with
a single network identifier; and tuning to one of the active
channels using the single mapping to allow the mobile communication
unit to either associate or reassociate with a wireless network
having the associated network identifier.
2. The method of claim 1 further comprising scanning to determine
network identifiers associated with the one or more active
channels, and wherein the maintaining comprises: generating one or
more single bitmaps for the one or more active channels associated
with single network identifiers; and storing the bitmaps in a
bitmap table, and wherein to either associate or reassociate, the
method comprises: scanning the one or more active channels
identified in the bitmap table; and refraining from scanning for
channels not identified in the bitmap table to reduce scan
time.
3. The method of claim 1 further comprising: scanning predetermined
channels to identify network identifiers associated with active of
the predetermined channels; and generating a bitmap for the active
channels and their associated network identifiers, wherein the
predetermined channels are predetermined for a geographic
location.
4. The method of claim 2 wherein associating comprises sending an
association request on a channel associated with a selected network
identifier through an access point, wherein a network associated
with the selected network identifier authenticates the
communication unit in response to the association request.
5. The method of claim 4 wherein the associating further comprises:
sending the selected network identifier to the network-interface
circuitry; retrieving the bitmap associated with the selected
network identifier by the driver circuitry; tuning, in response to
the bitmap, to a channel for sending the association request; and
sending the association request to the access point over a wireless
link using an antenna.
6. The method of claim 1 further comprising passively scanning
channels, and waiting for receipt of a beacon frame, the beacon
frame including the network identifier associated with one of the
scanned channels.
7. The method of claim 6 wherein passively scanning channels
further comprises receiving a probe response directed to another
communication unit on one of the channels, the probe response
including the network identifier associated with an active
channel.
8. The method of claim 7 wherein the scanning further comprises
active scanning for predetermined channels by: transmitting a probe
request on at least one of the predetermined channels; and waiting
to receive a probe response from an access point, the probe
response including the network identifier associated with an active
channel.
9. A mobile system that scans channels of wireless networks with a
reduced scan time comprising: network-interface circuitry to
maintain a mapping for active channels and associated network
identifiers; and transceiver circuitry to tune to one of the active
channels using the mapping for the active channel to allow either
an association or a reassociation with a wireless network having a
selected network identifier, wherein the mapping comprises one of a
bitmap, an array, a linked list, or a hash table.
10. A method comprising: identifying valid channels for a
geographic region in which a communication unit is located;
transmitting a probe request on a predetermined subset of the
identified valid channels; and waiting for receipt of either a
beacon frame or a probe-response frame on channels of the
identified valid channels other than the channels of the
predetermined subset, the probe-response frame being directed to
another communication unit.
11. The method of claim 10 wherein the transmitting the probe
request is performed for channels of the predetermined subset
identified a channel mapping stored in the communication unit, the
mapping comprising one of either a bitmap, an array, a linked list,
or a hash table.
12. The method of claim 11 wherein for channels of the
predetermined subset, the method comprises waiting, in response to
transmission of the probe request, for a probe-response frame
directed to the communication unit, the probe-response frame
including a network identifier.
13. The method of claim 12 further comprising: generating bitmaps
valid channels for which a probe-response frame or beacon-frame is
received; and re-associating with a network using at least one of
the bitmaps.
14. The method of claim 9 wherein at least one of the transmitting
and the waiting is performed sequentially for each of the
identified valid channels.
Description
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/669,478, filed on Sep. 23, 2003, which is
incorporated herein by reference.
TECHNICAL FIELD
[0002] Embodiments of the present invention pertain to wireless
communications and in particular, to communication units that
associate with wireless networks.
BACKGROUND
[0003] Wireless networks, such as wireless local area networks
(WLANs), utilize various operating channels depending on their
geographic region. At power up and during their operation,
communication units scan channels for their geographic region to
determine which channels are active. Channel scans also allow a
communication unit to determine network identifiers, such as
service set identifiers (SSIDs), associated with the active
channels. Scanning is generally performed when a communication unit
wishes to associate with (e.g., become part of or join) a wireless
network, and when a communication unit wishes to re-associate with
a network. Communication units may maintain connectivity with a
network by scanning followed by an association and/or reassociation
process, if required. Communication units may also perform scans to
monitor network changes including the creation of new networks,
among other things. As a result, a communication unit may spend a
considerable amount of time and resources scanning for active
channels.
[0004] One problem with channel scanning is that the time it takes
(e.g., up to two or more seconds) is fairly significant in a
wireless-networking environment where associations and
reassociations can occur on a frequent and regular basis. Another
problem with channel scanning is that it consumes resources of the
communication unit, requiring increased processing and battery
capability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The appended claims are directed to some of the various
embodiments of the present invention. However, the detailed
description presents a more complete understanding of embodiments
of the present invention when considered in connection with the
figures, wherein like reference numbers refer to similar items
throughout the figures and:
[0006] FIG. 1 illustrates an operational environment in which some
embodiments of the present invention may be practiced;
[0007] FIG. 2 is a block diagram of a communication unit in
accordance with some embodiments of the present invention;
[0008] FIG. 3 illustrates a bitmap table in accordance with some
embodiments of the present invention;
[0009] FIG. 4 is a flow chart of a comprehensive scanning procedure
in accordance with some embodiments of the present invention;
and
[0010] FIG. 5 is a flow chart of a selective channel scanning
procedure in accordance with some embodiments of the present
invention.
DETAILED DESCRIPTION
[0011] The following description and the drawings illustrate
specific embodiments of the invention sufficiently to enable those
skilled in the art to practice them. Other embodiments may
incorporate structural, logical, electrical, process, and other
changes. Examples merely typify possible variations. Individual
components and functions are optional unless explicitly required,
and the sequence of operations may vary. Portions and features of
some embodiments may be included in or substituted for those of
others. The scope of embodiments of the invention encompasses the
full ambit of the claims and all available equivalents of those
claims.
[0012] FIG. 1 illustrates an operational environment in which some
embodiments of the present invention may be practiced.
Communication environment 100 may include one or more communication
units (CUs) 102, which may communicate with one or more access
points (AP) 104 over wireless communication channels 106. Channels
106 may comprise bi-directional communication links. CUs 102 may
include, for example, mobile units such as personal digital
assistants (PDAs), laptop and portable computers with wireless
communication capability, web tablets, wireless telephones,
wireless headsets, pagers, instant messaging devices, MP3 players,
digital cameras, and other devices that may receive and/or transmit
information wirelessly. In some embodiments, CUs 102 may also
include access points, although the scope of the invention is not
limited in this respect.
[0013] In some embodiments, CUs 102 and APs 104 may communicate in
accordance with one or more communication standards, such as one of
the IEEE 802.11(a), (b) or (g) standards, the Digital Video
Broadcasting Terrestrial (DVB-T) broadcasting standard, and/or the
High performance radio Local Area Network (HiperLAN) standard. In
other embodiments, CUs 102 may communicate with one or more of APs
104 using a multi-carrier transmission technique, such as an
orthogonal frequency division multiplexing (OFDM) technique that
uses orthogonal subcarriers to transmit information within an
assigned spectrum. Other wireless local area network (LAN) and
wireless wide area network (WAN) communication techniques may also
be suitable for communications between communication units 102 and
access points 104.
[0014] In addition to facilitating communications between CUs 102,
in some embodiments, APs 104 may be coupled with one or more
networks, such as an intranet or the Internet, allowing CUs 102 to
access such networks. Although FIG. 1 illustrates point-to-point
communications (e.g., where an access point synchronizes with a
network), embodiments of the present invention may also be suitable
to point-to-multipoint communications (e.g., peer-to-peer
communications in which communication units may share the
responsibility for synchronizing with a network). For example, some
embodiments of the present invention are applicable to
communications between CUs 102 and APs 104 over channels 106 in
accordance with a basic service set (BSS) mode. Some embodiments of
the present invention, however, are equally applicable to direct
communications over links 108 between CUs 102 in an ad-hoc mode. In
these embodiments, CUs 102 may use channels of an independent basic
service set (IBSS), although the scope of the invention is not
limited in this respect. In these embodiments, the IBSS channels
may be a subset of the channels that are valid for a particular
geographic region, although the scope of the invention is not
limited in this respect.
[0015] In order to associate with a network through one of APs 104,
conventional communication units may scan all channels for their
geographic region to determine which channels are active and to
determine network identifiers (e.g., SSIDs) associated with the
active channels. This scanning is generally performed each time a
communication unit wishes to associate with (e.g., become part of
or join) a wireless network, and each time the communication unit
wishes to re-associate with a network. As mentioned earlier, a
problem with such channel scanning is that it takes time (e.g., up
to two or more seconds), which is significant in a
wireless-networking environment where associations and
re-associations may occur on a frequent and regular basis.
Furthermore, the operating system as well as other wireless LAN
applications may request the communication unit to perform
periodic-comprehensive scans. Since these periodic-comprehensive
scans may be performed fairly often (e.g., approximately once a
minute), they can adversely affect the throughput and/or
performance of the communication unit, and even disrupt
higher-layer protocols such as the file-transfer protocol
(FTP).
[0016] In accordance with some embodiments of the present
invention, a communication unit, such as one of CUs 102, may reduce
scan/association time by maintaining a single bitmap for one or
more active channels associated with a single network identifier.
The communication unit may associate and/or reassociate with a
wireless network using network-interface circuitry and the bitmap
for one or more of the active channels associated with a selected
network identifier. In some embodiments, communication units 102
may further reduce scan time by engaging in mixed mode scanning. In
these embodiments, active scans may be performed for some
predetermined channels, and passive scans may be performed for some
other channels. Active and passive scans, in accordance with some
embodiments of the present invention, are described in more detail
below.
[0017] Although some embodiments of the present invention are
described and illustrated for a mobile-communication unit, the
scope of the present invention is not limited in this respect.
Embodiments of the present invention are also applicable to access
points which may perform neighborhood discovery, radar detection,
and channel-width selection (e.g., per revisions of some IEEE
802.11 standards), among other things. As used herein and in the
claims, the term "bitmap" may include any type of mapping including
a bitmap, an array, a linked list, a hash table, etc.
[0018] FIG. 2 is a block diagram of a communication unit in
accordance with some embodiments of the present invention.
Communication unit (CU) 200 may be suitable for use as one or more
of CUs 102 (FIG. 1) and/or AP 104 (FIG. 1) although other
communication devices may also be suitable for use. CU 200 may
include network-interface module 202, operating system 204 and I/O
206, as well as other hardware and software elements that allow the
communication unit to serve its primary purpose.
[0019] In some embodiments, network-interface module 202 may
include transceiver circuitry and firmware 212 for receiving and/or
transmitting radio frequency (RF) communications with antenna 208.
RF signals received from antenna 208 may be down-converted to
baseband signals and baseband signals may be up-converted for
transmission by antenna 208. Network-interface module 202 may also
include baseband circuitry (not separately illustrated) to convert
between baseband signals and data signals that may be used by data
processing circuitry and operating system 204. In accordance with
some embodiments of the present invention, interface 202 may detect
packets and synchronize to symbol boundaries and may use a sequence
of training symbols having a set of known characteristics. Antenna
208 may comprise a directional or omnidirectional antenna,
including, for example, a dipole antenna, a monopole antenna, a
loop antenna, a microstrip antenna or other type of antenna
suitable for reception and/or transmission of RF signals that may
be processed by CU 200.
[0020] In accordance with some embodiments of the present
invention, network-interface module 202 may also include driver
circuitry and firmware 210 which may maintain a bitmap for active
channels and their associated network identifiers. Transceiver
circuitry and firmware 212 may responsively tune to one or more of
the active channels using the bitmap for the one or more active
channels to allow the communication unit to either associate or
reassociate with a wireless network having a selected network
identifier.
[0021] In accordance with some embodiments, CU 200 may initially
scan for active channels to determine network identifiers
associated with one or more active channels and to generate bitmaps
for the active channels. The bitmaps may be stored in
channel-bitmap table 214. Table 214 may associate the bitmaps and
network identifiers for the active channels. In some embodiments,
driver circuitry and firmware 210 may generate and maintain the
bitmaps in table 214, and it may provide a bitmap to transceiver
circuitry and firmware 212 for tuning to one or more channels in
response to receipt of a network identifier (e.g., an SSID) from
operating system 204.
[0022] In some embodiments, CU 200 may scan predetermined or
selected channels to identify network identifiers associated with
the predetermined channels that are active, and CU 200 may generate
a bitmap for the active channels and their associated network
identifiers. In some embodiments, the predetermined channels may be
predetermined for a geographic location of the communication
unit.
[0023] Communication unit 200 may associate with a wireless network
by sending an association request on a channel having a selected
network identifier through an access point. The selected network
may authenticate the communication unit in response to a prior
authentication request. As part of associating or reassociating,
operating system 204 may provide a selected or predetermined
network identifier to network-interface module 202, and driver
circuitry and firmware 210 may retrieve a bitmap for the one or
more channels associated with the network identifier. The retrieved
bitmap may be provided to firmware of transceiver circuitry and
firmware 212 to tune to the one or more channels for sending the
association/reassociation request. Transceiver circuitry and
firmware 212 may send the association/reassociation request to an
access point, such as one of APs 104 (FIG. 1) over a wireless link,
such as one of channels 106 (FIG. 1), using an antenna, such as
antenna 208. In some embodiments, the network identifiers comprise
service set identifiers (SSIDs), although the scope of the
invention is not limited in this respect.
[0024] In some embodiments, the scanning performed by CU 200 may
comprise passive scanning. Passive scanning may include for some
embodiments, waiting at least a predetermined period of time for
possible receipt of a beacon frame and/or a probe-response frame
directed to another communication unit in response to a previously
transmitted probe request from that other communication unit. The
beacon frame may be broadcast by an access point on an active
channel and may include the network identifier associated with the
channel. In some embodiments, access points may send beacon frames
on a particular channel on a regular basis (e.g., once every 100 ms
or so) as part of their communications with communication units. In
general, a beacon frame identifies the network associated with the
channel it is being broadcast on, as well as other network-related
information. In accordance with some embodiments, CU 200 may build
bitmaps for these active channels using the information in the
beacon frame. The use of these internally stored bitmaps generated
by passive scanning may reduce scan time, which in turn may reduce
the total association and/or reassociation time, since subsequent
scans for association may be restricted to those channels that are
present in the bitmap.
[0025] In some embodiments of the present invention, the scanning
performed by CU 200 may comprise active scanning. Active scanning
may include, for predetermined channels, transmitting a probe
request on at least one of the predetermined channels. The channels
may be predetermined for a particular geographic region in which
the communication unit is set up to operate. When a probed channel
is active, the communication unit may receive a probe response from
an access point providing the channel. The probe response may
include the network identifier associated with an active channel.
In these embodiments, CU 200 may build bitmaps for these active
channels using the information in the probe response.
[0026] In some embodiments, the probe requests may comprise a
probe-request frame or message, and the probe response may comprise
a probe-response frame or message. In some embodiments, CU 200 may
transmit a probe request and wait for a probe response before
moving to a next channel selected from the list of predetermined
channels. In some embodiments, CU 200 may wait for about 10 ms for
a probe response, although the scope of the invention is not
limited in this respect. The use of these internally stored bitmaps
generated by active scanning may reduce scan time, which in turn
may reduce the total association and/or reassociation time. Since
an active scan may takes about 10 ms per channel as compared to
passive scan which may takes about 100 ms, this bitmap not only may
reduce the number of channels to be scanned but also may reduce the
time spent scanning in each channel.
[0027] In some embodiments, the predetermined channels may have
subset of channels which may be referred to as independent basic
service set (IBSS) channels for a geographic location of the
communication unit. In these embodiments, channel bitmaps for these
channels may be stored in IBSS channel-bitmap table 216. A
communication unit configured in BSS mode may perform active
scanning in the IBSS channels even when these channels are not
active (e.g., are used by a network). In a mixed-mode scanning
embodiment, CU 200 may perform both passive and active scanning,
which may further reduce scan time, and which in turn may reduce
the total association and/or reassociation time. Furthermore,
run-time latencies may be reduced due to periodic-comprehensive
scans. It should be noted that mixed-mode scans using an IBSS
channel set in BSS mode may be particularly useful for runtime
comprehensive scans because a communication unit may scan valid
channels irrespective of the SSID.
[0028] In some embodiments, I/O 206 may be configured to allow a
user to select a network. In these embodiments, the user may select
a network by inputting a network name, network identifier (such as
an SSID), or other network description. In these embodiments,
operating system 204 may determine the network identifier and
provide it to interface circuitry 202 for association with the
network using the bitmap from table 214 for the network
identifier.
[0029] Although CU 200 is illustrated as a wireless communication
device, CU 200 may be almost any wireless or wireline communication
device, including a general purpose processing or computing system.
In some embodiments, CU 200 may be a battery-powered device. In
some of these embodiments, CU 200 may not require an external
antenna. Although CU 200 is illustrated as having several separate
functional elements, one or more of the functional elements may be
combined and may be implemented by combinations of
software-configured elements, such as processing elements including
digital signal processors (DSPs), and/or other hardware elements.
For example, operating system 204 as well as other elements of CU
200 may be implemented by processing elements, which may comprise
one or more microprocessors, DSPs, application specific integrated
circuits (ASICs), and combinations of various hardware and logic
circuitry for performing at least the functions described
herein.
[0030] FIG. 3 illustrates a bitmap table in accordance with some
embodiments of the present invention. Bitmap table 300 may be
generated by a communication unit, such as one or more of CUs 102
(FIG. 1) and/or CU 200 (FIG. 2). In some embodiments, bitmap table
300 may be generated by an access point, such as AP 104 (FIG. 1).
In some embodiments, bitmap table 300 may be generated by driver
circuitry, such as driver circuitry and firmware 210 (FIG. 2) and
stored as channel-bitmap table 214 (FIG. 2), although the scope of
the invention is not limited in this respect. Although bitmap table
300 is illustrated as a table, those skilled in the art will
appreciate that the information may be stored in other data
structures, such as hash tables.
[0031] Bitmap table 300 may include column 302 comprising network
identifiers, column 304 comprising one or more channels
corresponding to the network identifier of column 302, and column
306 comprising a bitmap generated for the one or more channels of
column 304. As illustrated in table 300, channel scanning by a
communication unit may have identified SSID #1 on channels 1 and 4,
resulting in the generation of a bitmap, such as bitmap
"0.times.9". The particular bitmap may depend on the valid channel
set for the geographic region for which table 300 is being
generated for. For example, when the valid channel set is comprised
of channels 1 through 10 and SSID #1 were present on channels 1 and
4, the resulting bitmap may be "0.times.9" depending on the valid
channel set. This particular bitmap may allow the transceiver
circuitry to tune to channels 1 and 4 when provided by the driver
circuitry. As also illustrated in table 300, a channel scan may
have identified SSID #2 on channels 2 and 4 resulting in the
generation of a bitmap, such as bitmap "0.times.a". This particular
bitmap may allow the transceiver circuitry to tune to channels 2
and 4 when provided by the driver circuitry.
[0032] In accordance with some embodiments, a transceiver, such as
transceiver circuitry and firmware 212 (FIG. 2), tunes to the
channels in a serial manner. A scan implementation layer of a media
access controller (e.g., a MAC) may control the duration of dwell
time per channel. For example if the scan was implemented in
firmware and the channel bitmap was being maintained in a driver,
the driver may send a "scan command" to firmware along with the
bitmap of the channels to scan. The firmware may then start a loop
to scan through these channels, one at a time. In these
embodiments, the transceiver may be tuned to a specific channel for
a certain duration, which may depend on the protocol and may be
implementation specific. At the end of this duration, the firmware
may tune the transceiver to the next channel in the bitmap and may
repeat the process. An example of a procedure for performing
periodic-comprehensive scans is illustrated below in FIG. 4.
[0033] A communication unit may perform association scans and/or
runtime periodic-comprehensive scans. In accordance with
embodiments of the present invention, scan time may be reduced in
association scans at least because of the channel bitmaps based on
SSIDs generated with the help of periodic-comprehensive scans. In
some embodiments, these SSID-based channel bitmaps may restrict an
association scan to the channels enabled in the bitmap. The
communication unit may perform active scans on the channels present
in the bitmap. In a periodic-comprehensive scan, the scan time may
be reduced at least because of mixed mode scanning. The
communication unit may use the IBSS channels bitmap even when the
unit is configured for BSS mode and may actively scan the IBSS
channels. On the remaining channels, the communication unit may
perform active and/or passive scans. When the IBSS channel bitmap
is not used, the communication unit may have performed passive
scans on the IBSS channel when there was no wireless LAN activity
in those channels. This is further illustrated below in FIG. 4.
[0034] In some embodiments, bitmaps may be generated for access
points that are configured in a stealth mode. In stealth mode, the
access point does not include a network identifier (e.g., an SSID)
in its beacons or beacon frames. In these embodiments, a
communication unit may construct a channel bitmap for channels on
which beacons with missing identifiers are received. These bitmaps
may also be maintained in the driver circuitry or firmware and may
be used in subsequent association and/or reassociation attempts by
a communication unit.
[0035] In some embodiments, a communication unit may regularly
maintain and update bitmap table 300 by performing periodic
maintenance scans. As a result of a periodic maintenance scan, a
bit map corresponding to a channel for a certain access point or
network identifier may be disabled if signals are not received by
the access point during a predetermined number of such periodic
scans or after a predetermined period of time.
[0036] FIG. 4 is a flow chart of a comprehensive scanning procedure
in accordance with some embodiments of the present invention.
Procedure 400 may be performed by a communication unit, such as one
or more of CUs 102 (FIG. 1) or CU 200 (FIG. 2), although other
communication units may also be used to perform procedure 400. In
some embodiments, procedure 400 may be performed by an access
point, such as AP 104 (FIG. 1).
[0037] Operation 402 selects a valid channel set for the geographic
region where the communication unit resides. In some embodiments,
the communication unit may use an internal global-positioning
receiver to identify the geographic region. The channels valid for
various geographic regions may be stored in memory of the
communication unit. In some embodiments, operation 402 may select a
first channel of a set of channels that are valid for the
geographic region, and operations 404 through 410 may be performed
for the selected channel.
[0038] Operation 404 determines whether the selected channel is
enabled in the IBSS channel bitmap. When the channel is enabled,
operation 406 may be performed which includes performing an active
scan. When the channel is not enabled in the IBSS channel bitmap,
operation 408 may be performed which includes performing a passive
scan.
[0039] For example, valid channels for a particular geographic
region may comprise channels 1 through 7 and IBSS channels may be a
subset of the valid channels and may comprise channels 2, 4 and 6.
The IBSS channel bitmap may be 0.times.2A, which may be based on
channels 1 through 7 being active and channels 2, 4 and 6 being
selected by the bitmap for tuning.
[0040] In operation 406, the communication unit may perform an
active scan on the selected channel. The active scan may include
tuning to the selected channel, sending a probe request, and
waiting for a probe response. Operation 406 allows the
communication unit configured to work in BSS mode to take advantage
of the IBSS bitmap for the periodic-comprehensive scans. Operation
406 may also allow the communication unit to perform active scans
on the IBSS channels even though the IBSS channels may not be
active.
[0041] In operation 408, the communication unit may perform a
passive scan on the selected channel. The passive scan may include
tuning to the selected channel and waiting for at least
approximately a beacon interval to receive beacons. If a beacon is
not received within a predetermined period of time, operation 402
may be repeated for a next channel. Upon completion of operation
408, the communication unit may repeat operation 402 for other
channels. Channels may be tuned to in any order, and there is no
requirement that the channels be tuned to in any order.
[0042] In operation 410, the data received in either operation 408
or 410 may be recorded for the selected channel. The data may
include one or more SSIDs and other data about the access point or
wireless network.
[0043] Operation 412 determines if there are additional channels
remaining for the geographic region. When there are additional
channels, operations 402 through 410 may be repeated for the
remaining channels. When there are no more additional channels,
operation 414 may be performed which ends the
periodic-comprehensive scan of procedure 400.
[0044] FIG. 5 is a flow chart of a selective channel scanning
procedure in accordance with some embodiments of the present
invention. Selective channel scanning procedure 500 may be
performed by a communication unit, such as one or more of CUs 102
(FIG. 1) or CU 200 (FIG. 2), although other communication units may
also be used to perform procedure 500. In some embodiments,
procedure 500 may be performed by an access point, such as AP 104
(FIG. 1).
[0045] In operation 502, a communication unit may perform an
initial scan to identify active channels and, in many cases, their
network identifiers. The initial scan may be a comprehensive scan,
such as the periodic-comprehensive scan described in procedure 400
(FIG. 4) to identify all active channels. In some embodiments, the
communication unit may perform passive scans on certain channels,
while in other embodiments (e.g., mixed-mode embodiments) the
communication unit may perform an active scan (e.g., operation 504)
on certain channels and a passive scan (e.g., operation 506) on
other or remaining channels.
[0046] In operation 508, a communication unit may generate a bitmap
for the active channels identified in operations 502-506. In some
embodiments, a single bitmap may be computed for one or more
channels having the same network identifier.
[0047] In operation 510, the bitmaps generated for the one or more
active channels and their associated network identifiers (e.g.,
SSIDs) may be stored in a bitmap table, such as table 300 (FIG. 3).
In some embodiments, operations 502 through 510 may be performed
sequentially for each channel being scanned, or sequentially for
each active channel identified, although the scope of the invention
is not limited in this respect. There is no requirement for
sequential tuning to channels, and embodiments of the present
invention are applicable to tuning to channels in any order.
[0048] In operation 512, the communication unit may associate with
a network using the channel bitmap for a channel having the
network's identifier. The network may be predetermined,
preprogrammed into the communication unit, or selected by a user.
In some embodiments, the particular network may be selected by the
communication unit based on a preprogrammed set of guidelines based
on, for example, cost of service, quality of service, security,
and/or bandwidth of the network connection.
[0049] Operation 514 determines if the association with a network
has been lost. When the association has not been lost, operation
516 may be performed in which the communication unit may wait until
it is time to perform a periodic-comprehensive scan, such as the
periodic-comprehensive scan of procedure 400 (FIG. 4).
[0050] When operation 514 determines that the association has been
lost, operation 518 may be performed. In some embodiments,
operation 518 may be performed when the communication unit
determines that association has been lost while waiting to perform
a periodic-comprehensive scan, rather than performing the
periodic-comprehensive scan.
[0051] In operation 518, the communication unit may selectively
scan for active channels identified in the bitmap table. In some
embodiments, the communication unit may first selectively scan for
active channels identified in the bitmap table having selected or
predetermined network identifiers, and if no such active channels
are identified, the communication unit may then scan the other
channels identified as valid channels for the geographic region. In
some embodiments, operation 518 may include periodic maintenance
scans. In some embodiments, operation 518 may include active scans
(e.g., operation 504) as well as passive scans (e.g., operation
506).
[0052] In operation 520, the communication unit may associate
and/or reassociate with a network based on the selective scanning
performed in operation 518. In some embodiments, the operating
system of the communication unit may provide a network identifier,
such as an SSID, to the network-interface circuitry and the driver
circuitry may responsively provide the corresponding bitmap to the
transceiver circuitry for tuning to the one or more channels
corresponding to the bitmap.
[0053] Operations 518 and 520 may be performed on a regular basis
by a communication unit as the communication unit changes location
and engages in communications with one or more access points.
Through the use of selective scanning, the amount of time and
resources required may be reduced.
[0054] Although the individual operations of procedures 400 and 500
are illustrated and described as separate operations, one or more
of the individual operations may be performed concurrently, and
nothing requires that the operations be performed in the order
illustrated.
[0055] Embodiments of the invention may be implemented in one or a
combination of hardware, firmware and software. Embodiments of the
invention may also be implemented as instructions stored on a
machine-readable medium, which may be read and executed by at least
one processor to perform the operations described herein. A
machine-readable medium may include any mechanism for storing or
transmitting information in a form readable by a machine (e.g., a
computer). For example, a machine-readable medium may include
read-only memory (ROM), random-access memory (RAM), magnetic disk
storage media, optical storage media, flash-memory devices,
electrical, optical, acoustical or other form of propagated signals
(e.g., carrier waver, infrared signals, digital signals, etc.), and
others.
[0056] It is emphasized that the Abstract is provided to comply
with 37 C.F.R. Section 1.72(b) requiring an abstract that will
allow the reader to ascertain the nature and gist of the technical
disclosure. It is submitted with the understanding that it will not
be used to limit or interpret the scope or meaning of the
claims.
[0057] In the foregoing detailed description, various features are
occasionally grouped together in a single embodiment for the
purpose of streamlining the disclosure. This method of disclosure
is not to be interpreted as reflecting an intention that the
claimed embodiments of the subject matter require more features
that are expressly recited in each claim. Rather, as the following
claims reflect, inventive subject matter lies in less than all
features of a single disclosed embodiment. Thus the following
claims are hereby incorporated into the detailed description, with
each claim standing on its own as a separate preferred
embodiment.
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