U.S. patent application number 11/680455 was filed with the patent office on 2008-08-28 for neighbor discovery in a wireless system.
This patent application is currently assigned to QUALCOMM, INCORPORATED. Invention is credited to Santosh Abraham, Arnaud Meylan, Sanjiv Nanda, Shravan K. Surineni.
Application Number | 20080205340 11/680455 |
Document ID | / |
Family ID | 39651103 |
Filed Date | 2008-08-28 |
United States Patent
Application |
20080205340 |
Kind Code |
A1 |
Meylan; Arnaud ; et
al. |
August 28, 2008 |
NEIGHBOR DISCOVERY IN A WIRELESS SYSTEM
Abstract
Beacons may be grouped to facilitate neighbor discovery in a
wireless network. For example, neighboring access devices such as
IEEE 802.11 access points may cooperate to transmit beacons in a
group. In this way, a wireless device seeking to discover the
neighboring access devices may scan for the beacons for a shorter
period of time. An indication may be provided to enable a wireless
device to more efficiently scan the beacons. For example, the
indication may indicate the channel the wireless device should scan
to receive the next beacon that is to be transmitted. In addition,
the indication may include information relating to the transmission
time of the next beacon.
Inventors: |
Meylan; Arnaud; (San Diego,
CA) ; Abraham; Santosh; (San Diego, CA) ;
Surineni; Shravan K.; (Waltham, MA) ; Nanda;
Sanjiv; (Ramona, CA) |
Correspondence
Address: |
QUALCOMM INCORPORATED
5775 MOREHOUSE DR.
SAN DIEGO
CA
92121
US
|
Assignee: |
QUALCOMM, INCORPORATED
San Diego
CA
|
Family ID: |
39651103 |
Appl. No.: |
11/680455 |
Filed: |
February 28, 2007 |
Current U.S.
Class: |
370/331 ;
370/338 |
Current CPC
Class: |
Y02D 70/142 20180101;
H04W 48/12 20130101; H04W 48/18 20130101; H04W 92/20 20130101; Y02D
30/70 20200801; Y02D 70/22 20180101; H04W 8/005 20130101; H04W
52/0216 20130101; Y02D 70/146 20180101 |
Class at
Publication: |
370/331 ;
370/338 |
International
Class: |
H04Q 7/00 20060101
H04Q007/00 |
Claims
1. A method of using beacon-related information, comprising: using,
by a wireless device, an indication regarding transmission of at
least one next beacon by at least one neighboring access point,
wherein each beacon of the at least one next beacon comprises an
identifier of an associated wireless network; and scanning, by the
wireless device, for the at least one next beacon.
2. The method of claim 1, wherein the indication identifies at
least one channel upon which the at least one next beacon will be
transmitted.
3. The method of claim 2, wherein the indication further identifies
at least one time at which the at least one next beacon will be
transmitted.
4. The method of claim 1, wherein the indication identifies any
channels that are not being used by the at least one neighboring
access point.
5. The method of claim 1, wherein: the indication comprises a
function; and using the indication comprises using the function to
determine at least one time at which the at least one next beacon
will be transmitted and/or at least one channel upon which the at
least one next beacon will be transmitted.
6. The method of claim 1, wherein using the indication comprises
determining when and on which channel to scan for the at least one
next beacon.
7. The method of claim 1, further comprising waking from a power
save mode to scan, during a wake time period, for the at least one
next beacon from the at least one neighboring access point; wherein
using the indication comprises determining at least one channel to
scan and at least one time to scan during the wake time period.
8. The method of claim 1, wherein: the at least one next beacon
comprises a set of beacons that are grouped together in time and by
radio channel; and the wireless device uses the indication to scan
for the set of beacons.
9. The method of claim 1, wherein: the at least one next beacon
comprises a plurality of beacons transmitted during a defined time
period; the wireless device uses the indication to scan for the
plurality of beacons transmitted during the defined time period;
and each of the beacons is associated with a different wireless
network.
10. The method of claim 9, wherein successive beacons are separated
in time by one of a set of defined spacings.
11. The method of claim 1, wherein: the wireless device scans for a
first beacon on a first channel; the at least one next beacon
comprises a second beacon; and the wireless device identifies,
based on the indication and the first channel, a second channel to
scan for the second beacon.
12. The method of claim 11, wherein: the at least one next beacon
further comprises a third beacon; and the wireless device
identifies, based on the indication and the second channel, a third
channel to scan for the third beacon.
13. The method of claim 1, wherein: the wireless device receives
the indication from an access point; or the indication is
programmed into the wireless device.
14. The method of claim 1, wherein the wireless device uses the
indication to identify neighboring access points between which the
wireless device may roam.
15. The method of claim 1, wherein the wireless device uses the
indication to reduce beacon scan time.
16. The method of claim 1, wherein the wireless device uses the
indication to increase time spent in power save mode.
17. An apparatus for using beacon-related information, comprising:
a scan controller adapted to use an indication regarding
transmission of at least one next beacon by at least one
neighboring access point, wherein each beacon of the at least one
next beacon comprises an identifier of an associated wireless
network; and a scanner adapted to scan for the at least one next
beacon.
18. The apparatus of claim 17, wherein the indication identifies at
least one channel upon which the at least one next beacon will be
transmitted.
19. The apparatus of claim 18, wherein the indication further
identifies at least one time at which the at least one next beacon
will be transmitted.
20. The apparatus of claim 17, wherein: the indication comprises a
function; and the scan controller is further adapted to use the
function to determine at least one time at which the at least one
next beacon will be transmitted and/or at least one channel upon
which the at least one next beacon will be transmitted.
21. The apparatus of claim 17, further comprising a mode controller
adapted to cause the scanner to wake from a power save mode to
scan, during a wake time period, for the at least one beacon from
the at least one neighboring access point; wherein the scan
controller is further adapted to determine, based on the
indication, at least one channel to scan and at least one time to
scan during the wake time period.
22. The apparatus of claim 17, wherein the at least one next beacon
comprises a set of beacons that are grouped together in time; and
the scan controller is further adapted to use the indication to
cause the scanner to scan for the set of beacons.
23. The apparatus of claim 17, wherein: the at least one next
beacon comprises a plurality of beacons transmitted during a
defined time period; the scan controller is further adapted to use
the indication to cause the scanner to scan for the plurality of
beacons transmitted during the defined time period; and each of the
beacons is associated with a different wireless network.
24. The apparatus of claim 23, wherein successive beacons are
separated in time by one of a set of defined spacings.
25. The apparatus of claim 17, wherein the scan controller is
further adapted to use the indication to identify neighboring
access points between which the apparatus may roam.
26. The apparatus of claim 17, wherein the scan controller is
further adapted to use the indication to reduce beacon scan time,
increase time spent in power save mode, or reduce beacon scan time
and increase time spent in power save mode.
27. An apparatus for using beacon-related information, comprising:
means for using an indication regarding transmission of at least
one next beacon by at least one neighboring access point, wherein
each beacon of the at least one next beacon comprises an identifier
of an associated wireless network; and means for scanning for the
at least one next beacon.
28. The apparatus of claim 27, wherein the indication identifies at
least one channel upon which the at least one next beacon will be
transmitted.
29. The apparatus of claim 28, wherein the indication further
identifies at least one time at which the at least one next beacon
will be transmitted.
30. The apparatus of claim 27, wherein: the indication comprises a
function; and the means for using the indication determines at
least one time at which the at least one next beacon will be
transmitted and/or at least one channel upon which the at least one
next beacon will be transmitted.
31. The apparatus of claim 27, further comprising means for waking
the means for scanning from a power save mode to scan, during a
wake time period, for the at least one beacon from the at least one
neighboring access point; wherein the means for using the
indication determines, based on the indication, at least one
channel to scan and at least one time to scan during the wake time
period.
32. The apparatus of claim 27, wherein: the at least one next
beacon comprises a set of beacons that are grouped together in
time; and the means for using the indication uses the indication to
cause the means for scanning to scan for the set of beacons.
33. The apparatus of claim 27, wherein: the at least one next
beacon comprises a plurality of beacons transmitted during a
defined time period; the means for using the indication uses the
indication to cause the means for scanning to scan for the
plurality of beacons transmitted during the defined time period;
and each of the beacons is associated with a different wireless
network.
34. The apparatus of claim 33, wherein successive beacons are
separated in time by one of a set of defined spacings.
35. The apparatus of claim 27, wherein the means for using the
indication uses the indication to identify neighboring access
points between which the apparatus may roam.
36. The apparatus of claim 27, wherein the means for using the
indication uses the indication to reduce beacon scan time, increase
time spent in power save mode, or reduce beacon scan time and
increase time spent in power save mode.
37. A computer program product comprising: computer-readable medium
comprising code for causing at least one computer to: use an
indication regarding transmission of at least one next beacon by at
least one neighboring access point, wherein each beacon of the at
least one next beacon comprises an identifier of an associated
wireless network; and scan for the at least one next beacon.
38. The computer program product of claim 37, wherein the
indication identifies at least one channel upon which the at least
one next beacon will be transmitted.
39. The computer program product of claim 38, wherein the
indication further identifies at least one time at which the at
least one next beacon will be transmitted.
40. The computer program product of claim 37, wherein: the
indication comprises a function; and the code for causing the at
least one computer to use the indication comprises code for causing
the at least one computer to determine at least one time at which
the at least one next beacon will be transmitted and/or at least
one channel upon which the at least one next beacon will be
transmitted.
41. The computer program product of claim 37, wherein the
computer-readable medium further comprises code for causing the at
least one computer to wake from a power save mode to scan, during a
wake time period, for the at least one beacon from the at least one
neighboring access point; wherein the code for causing the at least
one computer to use an indication comprises code for causing the at
least one computer to determine at least one channel to scan and at
least one time to scan during the wake time period.
42. The computer program product of claim 37, wherein: the at least
one next beacon comprises a set of beacons that are grouped
together in time; and the code for causing the at least one
computer to scan comprises code for causing the at least one
computer to scan for the set of beacons.
43. The computer program product of claim 37, wherein: the at least
one next beacon comprises a plurality of beacons transmitted during
a defined time period; the code for causing the at least one
computer to scan comprises code for causing the at least one
computer to scan for a plurality of beacons transmitted during a
defined time period; and each of the beacons is associated with a
different wireless network.
44. The computer program product of claim 43, wherein successive
beacons are separated in time by one of a set of defined
spacings.
45. The computer program product of claim 37, wherein the code for
causing the at least one computer to use the indication comprises
code for causing the at least one computer to identify neighboring
access points between which the at least one computer may roam.
46. The computer program product of claim 37, wherein the code for
causing the at least one computer to use the indication comprises
code for causing the at least one computer to use the indication to
reduce beacon scan time, increase time spent in power save mode, or
reduce beacon scan time and increase time spent in power save
mode.
47. A method of providing beacons by an access point, comprising:
cooperating, with at least one other access point, to determine
when to transmit beacons of associated time division multiplexed
wireless networks, wherein each beacon comprises an identifier of
one of the time division multiplexed wireless networks; and
transmitting the beacons of at least one of the networks.
48. The method of claim 47, wherein the access points transmit the
beacons so that the beacons are not overlapping in time.
49. The method of claim 47, wherein all of the beacons, to be sent
by the access points using a given channel, are sent consecutively
in time.
50. The method of claim 47, further comprising maintaining at least
one defined spacing between successive transmissions of the
beacons.
51. The method of claim 50, wherein, when a next beacon and a
previous beacon are sent on different channels, the at least one
defined spacing is more than a channel switching time of a radio of
a wireless device that is adapted to receive the next beacon and
the previous beacon.
52. The method of claim 47, wherein: the access points repetitively
transmit a group of the beacons associated with at least a portion
of the wireless networks; each beacon in the group of beacons is
associated with a different one of the wireless networks; and the
access points transmit the beacons in each group within a defined
period of time.
53. The method of claim 52, wherein the defined period of time is
less than a beacon interval.
54. The method of claim 47, wherein the access points cooperate to
successively transmit, in turn, one of the beacons associated with
each of the wireless networks.
55. The method of claim 47, wherein cooperating comprises
establishing beacon transmission times to: reduce a total time used
to transmit a set of non-time overlapping beacons; and provide
reduced beacon scan time and total search time for a wireless
device that is adapted to receive the beacons.
56. The method of claim 47, further comprising: determining a
beacon transmission time of one of the access points; and using the
beacon transmission time to establish target beacon transmit times
for a set of the access points in a given geographical area.
57. The method of claim 47, further comprising generating an
indication regarding transmission of at least one next beacon by
the at least one other access point.
58. The method of claim 57, wherein the indication identifies at
least one channel upon which the at least one next beacon will be
transmitted.
59. The method of claim 58, wherein the indication identifies at
least one time at which the at least one next beacon will be
transmitted.
60. The method of claim 57, wherein the indication comprises a
function for determining at least one time at which the at least
one next beacon will be transmitted and/or at least one channel
upon which the at least one next beacon will be transmitted.
61. The method of claim 57, wherein the indication identifies,
based on a first channel, a second channel to scan for the at least
one next beacon.
62. The method of claim 61, wherein the indication identifies,
based on the second channel, a third channel to scan for the at
least one next beacon.
63. The method of claim 47, further comprising transmitting an
indication identifying any channels that are not being used by the
access points.
64. An access point apparatus for providing beacons, comprising: a
controller adapted to cooperate, with at least one other access
point, to determine when to transmit beacons of associated time
division multiplexed wireless networks, wherein each beacon
comprises an identifier of one of the time division multiplexed
wireless networks; and a transmitter for transmitting the beacons
of at least one of the networks.
65. The apparatus of claim 64, wherein the access points transmit
the beacons so that the beacons are not overlapping in time.
66. The apparatus of claim 64, wherein all of the beacons, to be
sent by the access points using a given channel, are sent
consecutively.
67. The apparatus of claim 64, wherein the access points maintain
at least one defined spacing between successive transmissions of
the beacons.
68. The apparatus of claim 64, wherein the controller is further
adapted to cooperate to establish transmission times for the
beacons to: reduce a total time used to transmit a set of non-time
overlapping beacons; and provide reduced beacon scan time and total
search time for a wireless device that is adapted to receive the
beacons.
69. The apparatus of claim 64, wherein the controller is further
adapted to: determine a beacon transmission time of one of the
access points; and use the beacon transmission time to establish
target beacon transmit times for a set of the access points in a
given geographical area.
70. The apparatus of claim 64, further comprising an indication
generator adapted to generate an indication regarding transmission
of at least one next beacon by the at least one other access
point.
71. The apparatus of claim 70, wherein the indication identifies at
least one channel upon which the at least one next beacon will be
transmitted.
72. The apparatus of claim 71, wherein the indication identifies at
least one time at which the at least one next beacon will be
transmitted.
73. The apparatus of claim 70, wherein the indication comprises a
function for determining at least one time at which the at least
one next beacon will be transmitted and/or at least one channel
upon which the at least one next beacon will be transmitted.
74. An access point apparatus for providing beacons, comprising:
means for cooperating, with at least one other access point, to
determine when to transmit beacons of associated time division
multiplexed wireless networks, wherein each beacon comprises an
identifier of one of the time division multiplexed wireless
networks; and means for transmitting the beacons of at least one of
the networks.
75. The apparatus of claim 74, wherein the access points transmit
the beacons so that the beacons are not overlapping in time.
76. The apparatus of claim 74, wherein all of the beacons, to be
sent by the access points using a given channel, are sent
consecutively.
77. The apparatus of claim 74, further comprising means for
maintaining at least one defined spacing between successive
transmissions of the beacons.
78. The apparatus of claim 74, wherein the means for cooperating
further establishes beacon transmit times to: reduce a total time
used to transmit a set of non-time overlapping beacons; and provide
reduced beacon scan time and total search time for a wireless
device that is adapted to receive the beacons.
79. The apparatus of claim 74, further comprising: means for
determining a beacon transmission time of one of the access points;
and means for using the beacon transmission time to establish
target beacon transmit times for a set of the access points in a
given geographical area.
80. The apparatus of claim 74, further comprising means for
generating an indication regarding transmission of at least one
next beacon by the at least one other access point.
81. The apparatus of claim 80, wherein the indication identifies at
least one channel upon which the at least one next beacon will be
transmitted.
82. The apparatus of claim 81, wherein the indication identifies at
least one time at which the at least one next beacon will be
transmitted.
83. The apparatus of claim 80, wherein the indication comprises a
function for determining at least one time at which the at least
one next beacon will be transmitted and/or at least one channel
upon which the at least one next beacon will be transmitted.
84. A computer program product for an access point comprising:
computer-readable medium comprising code for causing at least one
computer to: cooperate, with at least one other access point, to
determine when to transmit beacons of associated time division
multiplexed wireless networks, wherein each beacon comprises an
identifier of one of the time division multiplexed wireless
networks; and transmit the beacons of at least one of the
networks.
85. The computer program product of claim 84, wherein the access
points transmit the beacons so that the beacons are not overlapping
in time.
86. The computer program product of claim 84, wherein all of the
beacons, to be sent by the access points using a given channel, are
sent consecutively.
87. The computer program product of claim 84, wherein the access
points maintain at least one defined spacing between successive
transmissions of the beacons.
88. The computer program product of claim 84, wherein the
computer-readable medium further comprises code for causing the at
least one computer to establish beacon transmission times to:
reduce a total time used to transmit a set of non-time overlapping
beacons; and provide reduced beacon scan time and total search time
for a wireless device that is adapted to receive the beacons.
89. The computer program product of claim 84, wherein the
computer-readable medium further comprises code for causing the at
least one computer to: determine a beacon transmission time of one
of the access points; and use the beacon transmission time to
establish target beacon transmit times for a set of the access
points in a given geographical area.
90. The computer program product of claim 84, wherein the
computer-readable medium further comprises code for causing the at
least one computer to generate an indication regarding transmission
of at least one next beacon by the at least one other access
point.
91. The computer program product of claim 90, wherein the
indication identifies at least one channel upon which the at least
one next beacon will be transmitted.
92. The computer program product of claim 91, wherein the
indication identifies at least one time at which the at least one
next beacon will be transmitted.
93. The computer program product of claim 90, wherein the
indication comprises a function for determining at least one time
at which the at least one next beacon will be transmitted and/or at
least one channel upon which the at least one next beacon will be
transmitted.
Description
BACKGROUND
[0001] 1. Field
[0002] This application relates generally to communications, and to
discovering neighboring devices in a wireless system.
[0003] 2. Background
[0004] A wireless local area network ("WLAN") such as an IEEE
802.11-based network enables wireless devices within the coverage
area of the network to communicate with one another and, typically,
with other devices that are coupled to another network. For
example, an 802.11-based access point may include a radio for
communicating with mobile stations within its coverage area and
also some form of connection to another network (e.g., a wide area
network such as the Internet).
[0005] In some applications several WLANs may be deployed as
neighboring networks to provide a wider collective coverage area.
For example, in an enterprise deployment several access points may
be located throughout the facility (e.g., a building or campus)
such that the coverage areas of adjacent access points overlap to
some extent. In this way, a mobile station may maintain local area
network connectivity as it roams through the enterprise facility.
That is, as the wireless station moves from the coverage area of
one WLAN to the coverage area of another WLAN the station may
disassociate from the first WLAN and associate with the second
WLAN.
[0006] Here, provisions may be made to provide a station with
information regarding WLANs in the immediate vicinity to enable the
station to efficiently roam between neighboring WLANs. For example,
a station may continually monitor the signal strength of signals
received from nearby WLANs. In this way, the station may determine
which WLAN provides the best connectivity at a given geographical
location. A station may thereby elect to switch from one WLAN to
another in an attempt to maintain a high quality of service.
[0007] The 802.11 standard defines both active and passive
techniques for a station to acquire information regarding
neighboring WLANs. For example, a station may actively scan the
802.11 channels by successively sending a probe request over each
channel and waiting for a probe response from any nearby access
points operating on that channel. The station may thereby obtain
information regarding neighboring WLANs via information provided in
the probe responses. A station utilizing active scanning, however,
expends power and increases the load on the wireless channel by
repeatedly transmitting probes. In addition, in some areas (e.g.,
different countries) a station may not be authorized to transmit
probes on certain channels. Hence, additional provisions may need
to be taken to avoid potential regulatory issues associated with
active scanning.
[0008] Alternatively, a station may passively scan for traffic on
each of the 802.11 channels to determine whether there are any
nearby WLANs. To determine more information about any access points
deployed in a given channel, the station may scan for beacons
transmitted by each access point. In some applications, however, an
access point may have a relatively long beacon interval (e.g., on
the order of a second). Hence, a station may expend a considerable
amount of power scanning for beacons for relatively long periods of
time on each channel. Moreover, in the event the station is
associated with an access point on a given channel, data
transmissions between the station and the access point may be
adversely affected when the station is scanning on other
channels.
[0009] To improve the efficiency of active or passive scanning
operations, 802.11 specifies a technique for providing a list of
neighboring access points to any stations in the immediate area.
For example, an access point may send a neighbor report to each of
its associated stations. The neighbor report may include the list
of neighboring access points, the channel employed by each access
point, the beacon interval for each access point, the time
synchronization function ("TSF") offset for each access point, and
other information.
[0010] Through the use of such information, a station may more
efficiently scan for beacons from each of the neighboring access
points. Specifically, a station may determine when and on which
channels the beacons will be sent. Consequently, the station may
not need to passively scan for long periods of time or employ
active scanning to acquire information (e.g., associated signal
strength) relating to neighboring access points.
[0011] In practice, the target beacon transmit times ("TBTTs") of
the various access points in a basic service set affect how quickly
a station may acquire information about the neighboring access
points on the various channels. For example, if beacons are sent at
substantially the same time on two or more different channels, the
station may need to wait several more TBTTs before it can decode
all of the beacons of the neighboring access points.
SUMMARY
[0012] A summary of sample aspects of the disclosure follows. For
convenience, one or more of such aspects may be referred to herein
simply as "some aspects."
[0013] The disclosure relates in some aspects to techniques for
facilitating roaming between neighboring wireless local area
networks ("WLANs"). For example, various techniques are disclosed
relating to enabling a wireless device to efficiently scan for
beacons from neighboring access devices.
[0014] In some aspects neighboring access devices (e.g., access
points such as 802.11-based access points) cooperate to transmit
beacons. For example, beacons from different access points may be
transmitted in a consecutive, non-overlapping order. Moreover, a
known spacing may be defined between successive beacon
transmissions such that all of the beacons in a given set of
beacons are transmitted in a grouped manner over a relatively short
period of time. As an example, a first access point may transmit
its beacon at a defined time, and a second access point may
transmit its beacon a defined amount of time following the beacon
of the first access point, where the defined amount of time is
relatively short.
[0015] Through the use of such a beacon transmission scheme, a
wireless device (e.g., an 802.11-based station) synchronized with
the system and aware of the transmission times of the beacons may
efficiently scan for them. For example, the station may wake from a
power save mode to scan for the group of beacons then return to the
power save mode once all of the beacons in the group have been
received. Given that the beacons may be spaced closely together in
time, the scan time of the wireless device may be reduced in
comparison to conventional scanning techniques. Consequently, the
station may increase the amount of time it spends in power save
mode, thereby increasing the standby time of the station.
[0016] In some aspects provisions may be made to enable a wireless
device (e.g., an 802.11-based station) to determine which channel
should be scanned and when the channel should be scanned to receive
the next beacon. For example, an access point or some other device
that has information regarding the deployed channels and the beacon
timing of the neighboring access points may send an indication
(e.g., in a beacon) including this information to its associated
stations. In some aspects the indication comprises a function that
identifies a channel to be scanned (and, optionally, a scan time)
based on the previous channel that was scanned. In some aspects an
indication may identify unused channels. A station may then use
this information to avoid scanning those channels.
[0017] In some aspects a method of using beacon-related information
comprises using, by a wireless device, an indication regarding
transmission of at least one next beacon by at least one
neighboring access point, wherein each beacon of the at least one
next beacon comprises an identifier of an associated wireless
network; and scanning, by the wireless device, for the at least one
next beacon.
[0018] In some aspects an apparatus for using beacon-related
information comprises a scan controller adapted to use an
indication regarding transmission of at least one next beacon by at
least one neighboring access point, wherein each beacon of the at
least one next beacon comprises an identifier of an associated
wireless network; and a scanner adapted to scan for the at least
one next beacon.
[0019] In some aspects an apparatus for using beacon-related
information comprises means for using an indication regarding
transmission of at least one next beacon by at least one
neighboring access point, wherein each beacon of the at least one
next beacon comprises an identifier of an associated wireless
network; and means for scanning for the at least one next
beacon.
[0020] In some aspects a computer program product comprising
computer-readable medium comprises code for causing at least one
computer to use an indication regarding transmission of at least
one next beacon by at least one neighboring access point, wherein
each beacon of the at least one next beacon comprises an identifier
of an associated wireless network; and code for causing the at
least one computer to scan for the at least one next beacon.
[0021] In some aspects a method of providing beacons by an access
point comprises cooperating, with at least one other access point,
to determine when to transmit beacons of associated time division
multiplexed wireless networks, wherein each beacon comprises an
identifier of one of the time division multiplexed wireless
networks; and transmitting the beacons of at least one of the
networks.
[0022] In some aspects an access point apparatus for providing
beacons comprises a controller adapted to cooperate, with at least
one other access point, to determine when to transmit beacons of
associated time division multiplexed wireless networks, wherein
each beacon comprises an identifier of one of the time division
multiplexed wireless networks; and at least one transmitter for
transmitting the beacons of at least one of the networks.
[0023] In some aspects an access point apparatus for providing
beacons comprises means for cooperating, with at least one other
access point, to determine when to transmit beacons of associated
time division multiplexed wireless networks, wherein each beacon
comprises an identifier of one of the time division multiplexed
wireless networks; and means for transmitting the beacons of at
least one of the networks.
[0024] In some aspects a computer program product for an access
point comprises code for causing at least one computer to
cooperate, with at least one other access point, to determine when
to transmit beacons of associated time division multiplexed
wireless networks, wherein each beacon comprises an identifier of
one of the time division multiplexed wireless networks; and code
for causing the at least one computer to transmit the beacons of at
least one of the networks.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] These and other features, aspects and advantages of the
disclosure will be more fully understood when considered with
respect to the following detailed description, appended claims and
accompanying drawings, wherein:
[0026] FIG. 1 is a simplified block diagram of several sample
aspects of a communication system employing access devices and
wireless user devices;
[0027] FIG. 2 is a flowchart of several sample aspects of
operations that may be performed to obtain information about
neighboring access devices;
[0028] FIG. 3 is a simplified diagram of several sample timing
diagrams illustrating beacon transmission and scanning;
[0029] FIG. 4 is a simplified diagram of several sample timing
diagrams illustrating beacon transmission and scanning;
[0030] FIG. 5 is a simplified block diagram of several sample
aspects of an access point;
[0031] FIG. 6 is a flowchart of several sample aspects of
operations that may be performed by an access point;
[0032] FIG. 7 is a simplified block diagram of several sample
aspects of a wireless station;
[0033] FIG. 8 is a flowchart of several sample aspects of
operations that may be performed by a wireless station;
[0034] FIG. 9 is a simplified block diagram of several sample
aspects of a wireless device; and
[0035] FIG. 10 is a simplified block diagram of several sample
aspects of an access device.
[0036] In accordance with common practice the various features
illustrated in the drawings may not be drawn to scale. Accordingly,
the dimensions of the various features may be arbitrarily expanded
or reduced for clarity. In addition, some of the drawings may be
simplified for clarity. Thus, the drawings may not depict all of
the components of a given apparatus or method. Finally, like
reference numerals may be used to denote like features throughout
the specification and figures.
DETAILED DESCRIPTION
[0037] Various aspects of the disclosure are described below. It
should be apparent that the teachings herein may be embodied in a
wide variety of forms and that any specific structure, function, or
both being disclosed herein is merely representative. Based on the
teachings herein one skilled in the art should appreciate that an
aspect disclosed herein may be implemented independently of any
other aspects and that two or more of these aspects may be combined
in various ways. For example, an apparatus may be implemented or a
method may be practiced using any number of the aspects set forth
herein. In addition, such an apparatus may be implemented or such a
method may be practiced using other structure, functionality, or
structure and functionality in addition to or other than one or
more of the aspects set forth herein.
[0038] FIG. 1 illustrates sample aspects of a communication system
100 providing WLAN coverage via several neighboring access devices
(e.g., access points) 102A, 102B, and 102C. The access devices
102A-C are coupled to a switch 104 that provides connectivity to a
wide area network ("WAN") 106 such as the Internet.
[0039] Each of the access devices 102A-C provides wireless
connectivity via a time division multiplexed network for wireless
devices (e.g., user devices) within the coverage area (not shown)
of that access device. The access devices 102A-C thus collectively
provide the overall WLAN coverage area of the system 100. For
example, a wireless device 108 at the location represented by the
solid box may be within the coverage areas of access devices 102A
and 102B. Thus, the wireless device 108 may receive beacons from
each of the access devices 102A and 102B as represented by the
lines 110A and 110B. As a wireless device 108 roams from the
location represented by the solid box to the location represented
by the dashed box, the wireless device 108 enters the coverage area
of access device 102C and exits the coverage area of access device
102A. Thus, the wireless device 108 may now receive beacons from
the access devices 102B and 102C as represented by the dashed lines
112A and 112B.
[0040] As the wireless device 108 roams through the overall WLAN
coverage area provided by the system 100, the wireless device 108
may determine which access device currently provides the best
connectivity for the wireless device 108. For example, the wireless
device 108 may repeatedly scan for beacons from nearby access
points and measure the signal strength (e.g., power) associated
with each of the beacons. The wireless device 108 may thus elect to
associate with the access point that currently provides optimum
connectivity as indicated by maximum received beacon signal
strength. The wireless device 108 may utilize other criteria
relating to optimum connectivity. For example, optimum connectivity
may be associated with a more desirable service (e.g., different
content or data rates).
[0041] The wireless device 108 may continue to scan for beacons on
a regular (e.g., periodic) basis to determine when to disassociate
with one access device and associate with another access device.
For example, at some point in time another wireless device may
provide better connectivity for the wireless device 108 as it
continues to roam through the overall WLAN coverage area. In
addition, signal conditions or services provided within a given
WLAN coverage area may change over time.
[0042] The access devices 102A-C and the wireless device 108 may
take various forms depending on the requirements of a given
application. For example, a user device may comprise a cellular
phone, a smart phone, a cordless phone, a laptop computer, a PDA, a
wireless modem, a mobile device, a handset, a handheld device, a
satellite radio, a global positioning system, or some other
communication device. A user device also may be referred to as user
equipment, an access terminal, a station, a wireless communication
device, a terminal, a user terminal, mobile equipment, a subscriber
unit, or described using some other terminology. Similarly, an
access device may take any suitable form that facilitates providing
access to such wireless devices.
[0043] Several techniques that may be used to enable a wireless
device to more efficiently scan for beacons will now be discussed
in conjunction with FIG. 2. For convenience, the operations of FIG.
2 (and any other flowchart herein) may be described in conjunction
with specific components (e.g., the components of FIG. 1). It
should be appreciated, however, that these operations may be
performed in conjunction with other components.
[0044] As represented by block 202 the access devices in a given
geographical area (e.g., neighboring access points) may cooperate
(e.g., over a wireless medium or over a wired network) to select
their respective beacon transmission schedules. For example, the
transmission times of the beacons may be selected such that the
beacons are transmitted in groups.
[0045] FIG. 3 illustrates, in a simplified manner, sample groupings
of beacons 302A-F from three access devices. Here, a timing diagram
304A represents beacon transmissions from an access device A via a
first channel (designated as channel A). A timing diagram 304B
represents beacon transmissions from an access device B via a
second channel (channel B). A timing diagram 304C represents beacon
transmissions from an access device C via a third channel (channel
C).
[0046] Arrows 306A and 306B represent the target beacon transmit
times ("TBTTs") for access device A. In practice, beacons may not
always be transmitted at the TBTTs due to, for example, the
presence of other traffic on the channel. To reduce the complexity
of FIG. 3, TBTT arrows are not depicted for timing diagrams 304B
and 304C.
[0047] An arrow 308 represents the designated time between
successive beacons for a given access device, commonly referred to
as the beacon interval. In the example of FIG. 3, the access
devices A-C utilize beacon intervals of the same length. It should
be appreciated, however, that different access devices may employ
beacon intervals of differing lengths. For convenience, the length
of each beacon 302A-F is shown as being relatively long as compared
to the length of the beacon interval. In practice, however, the
beacon interval may be significantly longer that the transmission
time of a beacon.
[0048] In FIG. 3 the beacons transmission times are defined such
that for every beacon interval a group of beacons includes one
beacon from each access device. Specifically, one group of beacons
consists of the beacons 302A, 302C, and 302E and another group of
beacons consists of the beacons 302B, 302D, and 302F. Here, it may
be seen that the access devices may transmit the beacons in a given
group of beacons (e.g., beacons 302A, 302C, and 302E) in a
consecutive, non-overlapping order.
[0049] FIG. 3 also illustrates that all of the beacons in a given
group may be transmitted over a relatively short period of time.
For example, a relatively short spacing may be defined between
successive beacon transmissions. In the example of FIG. 3, spacings
310A and 310B are defined as the time between the TBTTs of the
different access devices. It should be appreciated, however, that
the spacing may be defined in other ways. For example, the spacing
may be defined as the time period between the end of one beacon and
the beginning of another beacon.
[0050] The length of the defined (e.g., known) spacing between
beacons may depend on various factors. In an implementation where
successive beacons in a group are transmitted over different
channels (e.g., as in the example of FIG. 3), the spacing between
beacons may be longer than the channel switching time (e.g., on the
order of 1 millisecond) of a radio of a wireless device that is
adapted to receive the beacons. For example, in this case a spacing
defined as the time between the end of one beacon and the beginning
of the next beacon would be set to be longer than the switching
time. In contrast, in an implementation where successive beacons in
a group are transmitted over the same channel, a shorter spacing
may be employed since the radio of the wireless device will not
need to switch to another channel to scan for the next beacon.
[0051] Various techniques may be employed to define the grouping
and timing of beacons for neighboring access devices. In some
implementations a switch or other suitable device (e.g., switch 104
in FIG. 1) may determine the beacons schedules for a set of
neighboring access devices. For example, the switch 104 may define
the TBTTs for each access device to provide a desired grouping of
and spacing between the beacons. In addition, the TBTTs may be
assigned to the neighboring access devices to define a desired
beacon transmission order. That is, the TBTTs may be used to
control which access device transmits the first beacon, which
access device transmits the second beacon, and so forth. The switch
104 may then send messages to each access device to inform the
access devices of the presence of neighboring access devices and
the corresponding beacon schedules. A synchronization protocol may
be operated on the wired network between the switch and the access
devices to give them a common time reference as described
below.
[0052] In some aspects neighboring access devices may cooperate
with one another to define their beacon schedules. For example, one
or more of the access devices may send messages to the other access
devices to inform the access devices of the presence of neighboring
access devices. The neighboring access devices may then negotiate
to select the channel(s) and/or beacon transmission time(s) to be
used by each access device.
[0053] Provisions also may be made to ensure that each access
device continues to transmit its beacons at the proper time. For
example, the relative timing of the access devices may be
synchronized on a regular basis over the air or over the wired
network to compensate for problems such as clock drift or slightly
different access device clock frequencies that may otherwise cause
the relative timing of the beacon transmission to change over time.
In this way, relatively constant time synchronization function
("TSF") offsets may be maintained between the neighboring access
devices.
[0054] In some aspects one access device may be designated as a
primary access device upon which the timing of the other
neighboring access devices depends. For example, the first access
device to be activated in a given geographical area may be
designated as the primary access device, and a suitable TBTT and
beacon interval assigned to that access device. The timing of any
access devices subsequently activated in that geographical area may
then be based on (e.g., synchronized to) the first access
device.
[0055] Referring again to FIG. 2, as represented by block 204 an
indication regarding the beacon transmission schedules may be
provided to any wireless device that may receive beacons from any
of the access devices. Such an indication may include, for example,
information relating to the channels to be scanned, information
relating to times at which scanning should commence, or both. In
some aspects the indication may identify one or more channels that
are not currently being used by any of the neighboring access
points (e.g., to the extent this is known by a coordinating access
point that generates the indication).
[0056] In the example of FIG. 3, an indication may indicate that
one access device operates on channel A, another operates on
channel B, and another operates on channel C. The indication also
may indicate the order the channels should be scanned (e.g.,
channel A, then B, then C). In addition, or in the alternative, the
indication may indicate that one or more channels (e.g., channels
D-G) are not currently being used by any neighboring access
device.
[0057] Furthermore, the indication may indicate when a given
channel may be scanned. The timing aspect of the indication may
include, for example, a set of (e.g., one or more of) a reference
to a TBTT, a beacon interval, a TSF offset, a defined spacing
(e.g., time delay) between beacons, some other suitable timing
information, or some combination of these parameters.
[0058] In some aspects the indication may comprise or relate to a
function that provides beacon-related information. For example, a
wireless device may use such a function to determine, based on one
or more input parameters, the beacon transmission parameters (e.g.,
channel and/or timing) of the next beacon or beacons that will be
transmitted. The input parameters may include, for example, the
beacon transmission parameters of the last beacon that was
received, the current time, some other suitable parameter, or some
combination of these parameters.
[0059] Table 1 illustrates an example of a function that may be
used to derive beacon transmission information. The function
identifies the next channel to be scanned based on the previous
channel that was scanned (or the current channel being scanned). In
Table 1 the next channel information is in the second column while
the previous channel information is in the first column. In
addition, the function identifies the time to scan the next beacon.
In this example the timing is made with respect to the timing of
the previous (or current) beacon. Specifically, in the third column
of Table 1 scanning for the beacon on channel B or C may commence
one beacon spacing (e.g., the spacing between beacons 302A and 302C
in FIG. 3) after the end of the current beacon (the beacon of
channel A or B, respectively). In addition, scanning for the beacon
on channel A may commence a time period after the end of the
current beacon (the beacon of channel C), where the time period is
equal to the beacon interval (e.g., interval 308) minus three
beacon length times (e.g., lengths of beacons 302A, 302C, and
302E).
TABLE-US-00001 TABLE 1 FUNCTION NEXT BEACON INFORMATION PREVIOUS
TIME TO CHANNEL NEXT CHANNEL NEXT BEACON A B +BEACON SPACING B C
+BEACON SPACING C A BEACON INTERVAL - 3 * BEACON LENGTHS
[0060] In some aspects the indication may comprise or relate to a
function that provides only beacon timing-related information. For
example, referring to FIG. 4 and Table 2, in some implementations
multiple access devices may utilize a common channel. Here, timing
diagrams 402A, 402B and 402C represent beacon transmissions from
access devices A, B, and C, respectively over a given channel.
Specifically, access device A transmits beacon 404A shortly after
time T0, access device B transmits beacon 404B shortly after time
T1, and access device C transmits beacon 404C shortly after time
T2. In the example of FIG. 4, the beacons 404A, 404B, and 404C are
transmitted during a single beacon interval 406.
[0061] The function of Table 2 may be used identify the time for
scanning the next beacon based on the beacon that is currently
being scanned or the beacon that was last scanned. For example, in
Table 2 if the current beacon is for access device A, the next time
to scan (for the beacon of access device B) is time T1.
TABLE-US-00002 TABLE 2 FUNCTION PREVIOUS BEACON ACCESS DEVICE TIME
TO WAKE A T1 B T2 C T3
[0062] It should be appreciated based on the above that an
indication relating to the transmissions of beacons may take
various forms and include various types of information. For
example, in some aspects the functions described above also may
utilize timing information relating to the transmission of the
previous beacon to determine the channel(s) and/or timing for the
next beacon(s). It should also be appreciated that grouping the
beacons of a given channel may also prove useful for a station that
does not utilize or know about the timing function described
herein. For example, the higher concentration of beacons may, on
average, reduce the beacon search time.
[0063] FIG. 4 illustrates that in some aspects the beacons may not
be closely grouped together in time. Here, an advantage may still
be achieved by simply maintaining a known timing of (e.g., known
spacings between) the beacons since a wireless device need only
scan at the defined times. It should be appreciated, however, that
in some aspects closely grouped beacons may be employed in a system
where two or more of the access devices utilize the same
channel.
[0064] In some aspects the indication may specify which channel to
scan but not specify a time to scan. In this case, a wireless
device may simply scan for a beacon on a designated channel and,
once the beacon is received, switch to the next designated channel.
In a related manner the indication may simply identify any unused
channels. Through the use of such an indication, the wireless
device may identify any channels it does not need to scan. The
above approaches may still provide an advantage over conventional
systems since the wireless device need not blindly search all of
the channels for beacons.
[0065] Provisions also may be made to account for changes in an
indication for a given set of access points over time. Such a
change may be due to a change in traffic or signal conditions, the
reassignment of the channels or beacon transmission times used by a
given access device, the addition or removal of an access device in
a communication system, or some other circumstance. Consequently,
the type of indication used in a given system and/or the content of
the indication may be dynamically updated.
[0066] An indication may be provided to a wireless device in
various ways. For example, in a typical implementation an access
device or some other device may send an indication to a wireless
device via a beacon or some other suitable signal. As an example of
the latter case, when a wireless device associates with an access
device, the access device may send a message including the
indication to the wireless device. In addition, a station may send
a message to an access point requesting the indication. In some
implementations the indication may be programmed into the wireless
device. For example, in implementations where the beacon
transmission schedules are assigned in a relatively static manner,
a user, a system administrator, a manufacturer, or some other
entity may program the indication into the wireless device the
first time the wireless device is activated. Such programming may
be accomplished, for example, by using the functionality of the
wireless device, a programming device, or both.
[0067] Referring again to FIG. 2, as represented by block 206 once
the neighboring access devices are configured and operating, they
will transmit their beacons according to their respective beacon
schedules. Thus, in the example of FIG. 3, access device A will
transmit its beacon, then after a delay equal to a defined time
period, access device B will transmit its beacon, and so forth.
[0068] As represented by block 208, in concurrence with the
operations of block 206, the wireless device may use the indication
to efficiently scan for the beacons from the neighboring access
devices. For example, rather than blindly scanning channels for
beacons from access devices, the wireless device may use the
indication to scan an appropriate channel at an appropriate
time.
[0069] Referring again to FIG. 3, the timing diagram 312 represents
timing that may be associated with a wireless device. Based on the
indication (e.g., the function of Table 1) the wireless device may
be configured to scan the channels in the appropriate order. Thus,
in the example of FIG. 3, a wireless device may first scan channel
A. After receiving the beacon from access device A, the wireless
device may then scan channel B, and so forth.
[0070] Here, provisions may be made to account for any delay in the
transmission of one or more beacons. For example, if the wireless
device determines upon scanning a channel that a device other than
the expected access device is current using the channel, the
wireless device may continue to scan that channel until the access
device is able to send its beacon over the channel. Alternatively,
the wireless device may proceed with the scanning of the other
channels then rescan the missed channel at a later time (e.g.,
during the next beacon interval). In the event the wireless device
scans a beacon of an access device with which it is associated and
the beacon indicates that there is downlink traffic available for
the wireless device, the wireless device may attempt to receive the
downlink traffic before continuing with the neighbor beacon scan
operation.
[0071] Provisions also may be made to account for the circumstance
where a wireless device is not within an effective coverage area of
a neighboring access device. That is, in the event the wireless
device cannot receive the beacon that will be transmitted next, the
wireless device may still use the indication to determine the next
beacon to be transmitted after that one (i.e., in the next, next
beacon). In the example of Table 1, the access device may thus use
the information in the table to skip a row.
[0072] At block 208 in FIG. 2 the wireless device also may use the
indication to scan the channels at appropriate times. For example,
referring to FIG. 3 the wireless device may scan channels A, B, and
C over time intervals 314A, 314B, and 314C, respectively, based on
the timing information in the indication (e.g., the third column of
Table 1). Referring to FIG. 4 the wireless device may scan the
channel over time intervals 408A, 408B, and 408C, respectively,
associated with timing diagram 410 based on the timing information
in the indication (e.g., Table 2). Here, it should be appreciated
that the scanning time intervals 314A-C and 408A-C may take into
account deviations in system timing, channel switching times, and
other factors that may affect the precise timing of the beacons.
For example, the time intervals 314A-C and 408A-C may be defined to
start some time before an expected TBTT and commence some time
after the time the beacon is expected to end.
[0073] FIGS. 3 and 4 illustrate that through the use of the
indication, the wireless device may reduce the amount of time it is
scanning for beacons from neighboring access devices. Here, by
knowing where and when to scan, the wireless device may not need to
scan for much more time than the cumulative lengths of the beacons.
Consequently, power consumption associated with this scanning may
be reduced in comparison with conventional scanning techniques. In
addition, in the event the wireless device is associated with an
access device on a given channel, the wireless device may remain on
that channel for longer periods of time. Consequently, there may be
a reduction in any negative impact on traffic to and from the
wireless device that may otherwise result from lengthy scans on
other channels.
[0074] The wireless device also may utilize the beacon-related
indication to increase the amount of time the wireless device
spends in a power save mode (e.g., an inactive state). For example,
in the event the wireless device is not actively sending or
receiving data, the wireless device may switch to a power save mode
to reduce the amount of power that it consumes. However, it may be
desirable for the wireless device to continue to acquire current
information about nearby access devices so that the wireless device
may readily associate with the best access device when it
eventually needs to send or receive data.
[0075] Accordingly, the wireless device may use the indication to
wake from the power save mode at the appropriate times to scan for
beacons from neighboring access devices. Referring again to FIG. 3,
the lower levels 316A and 316B of the timing diagram 312 represent
the time the wireless device is in a power save mode (e.g.,
inactive state). Conversely, the higher levels 318A and 318B of the
timing diagram 312 represent the time the wireless device is in an
awake mode (e.g., active state). FIG. 4 includes similar lower
levels 412A, 412B, and 412C representative of a power save mode and
higher levels 414A, 414B, and 414C representative of an awake
mode.
[0076] From FIGS. 3 and 4 it may be appreciated that in the absence
of other traffic (e.g., normal beacon scanning or
connection-related traffic) the wireless device may remain in power
save mode except when it needs to scan for beacons from neighboring
access devices. This is in contrast with conventional techniques
where the wireless device may need to scan one or more channels for
relatively long periods of time in an attempt to locate beacons on
that channel or those channels. Consequently, a wireless device
employing the teachings above may consume less power and,
consequently, have a longer standby time than a wireless device
employing conventional techniques.
[0077] Referring again to FIG. 2, as represented by block 210 the
wireless device may use the information obtained from the beacons
to determine which access device provides the best connectivity. As
discussed above, this may involve analyzing the signal levels of
the beacons to identify an access device associated with the best
signal quality. In addition, the wireless device may analyze
information contained in the beacons to determine whether a given
access device provides more desirable services or quality of
service.
[0078] It should be appreciated that various modifications may be
made to the above examples consistent with the teachings herein.
For example, in some aspects signals other than beacons may be used
to provide the beacon-related functionality described herein. Thus,
other types of signals that comprise an identifier of a network may
be utilized to obtain information regarding neighboring access
devices. Here, an identifier of a network may take various forms
including, for example, an address such as a media access control
("MAC") address.
[0079] An apparatus or method involving the grouping of beacons or
proving a beacon schedule indication may be implemented in a
variety of ways. For convenience, additional details will now be
described in the context of an 802.11-based system. It should be
appreciated, however, that the teachings herein are not limited to
this type of system or to the components and operations
specifically set forth herein. For example, other protocols and
techniques may be employed to group beacons or provide an
indication as taught herein.
[0080] In an 802.11-based system, groups of devices cooperate to
form basic service sets in an attempt to enable each group of
devices to effectively communicate without substantial interference
from neighboring groups of devices. For example, a first basic
service set may be established on a particular wireless channel
whereby all communications (e.g., data frames) include a basic
service set identifier that uniquely defines that basic service
set. Thus, a neighboring basic service set that operates on a
different channel will not substantially interfere with the first
basic service set due to the differing operating frequencies.
Conversely, devices of a neighboring basic service set that
operates on the same channel as the first basic service set will
not process transmissions from the first basic service set because
those devices use a different basic service set identifier.
[0081] A basic service set may be established in various ways. In a
typical application an access point (e.g., that provides access to
another network) establishes the basic service set and, to some
extent, controls traffic flow over the basic service set. Here, the
access point generates periodic beacons to enable a wireless
station to locate the basic service set and to facilitate traffic
control in the basic service set. For example, a wireless station
entering the coverage area of an access point may scan for beacons,
and then associate with the access point to join the basic service
set. Once the station joins the basic service set, the access point
may route data from the network to the station and route data from
the station to the network.
[0082] In other applications a set of stations may cooperate to
form a basic service set. For example, in an independent basic
service set implementation (e.g., an ad hoc network) functionality
that may otherwise be provided by an access point (e.g., generating
beacons) may be implemented in and shared among several neighboring
stations.
[0083] In an 802.11 implementation the access devices 102A-C of
FIG. 1 may comprise access points ("APs") and the wireless device
108 may comprise a wireless station ("STA"). Here, each access
point may establish a unique network defined by a unique basic
service set identifier. Sample implementation details of these
components will be discussed in conjunction with FIGS. 5, 6, 7, and
8.
[0084] FIG. 5 illustrates several sample aspects of an access point
500. Briefly, the access point 500 includes a radio 502 adapted to
establish wireless communications with, for example, nearby
stations. A beacon transmission cooperation controller 504 is
adapted to communicate with a switch, other access points, or other
devices to define a beacon transmission schedule. A clock 506 and a
clock synchronization component 508 are adapted to provide clock
signals for the access point 500 to facilitate precise timing of
beacon transmissions and other operations. A beacon generator 510
is adapted to generate beacons in accordance with the beacon
transmission schedule. To reduce the complexity of FIG. 5, other
components commonly found in an access point are not shown.
[0085] Sample operations of the access point 500 will be discussed
in more detail in conjunction with the flowchart of FIG. 6. In
particular, FIG. 6 relates to operations that may be performed to
define a beacon transmission schedule and provide an indication
regarding the beacon transmission schedule to nearby stations.
[0086] As represented by block 602, the access point 500 (e.g., the
controller 504) may determine whether there are any neighboring
access points. In a typical implementation, the controller 504 may
obtain information regarding neighboring access points from a
switch or other device with which each of the neighboring access
points is associated. For example, a switch may maintain
information indicating where the access points are located with
respect to one another in a given geographical area. Then, based on
this information, the switch may identify a given set of access
points as being neighboring access points. Alternatively, in some
implementations the access points may scan the wireless medium or
communicate with one other to identify neighboring access points.
In any event, it should be appreciated that a given communication
system may employ one or more sets of neighboring access
points.
[0087] As represented by block 604, the access point 500 may
synchronize its timing with the timing of the neighboring access
points. For example, as discussed above the access point 500 (e.g.,
the controller 504) may obtain timing information such as beacon
timing information (e.g., TBTT and beacon interval) of a designated
primary access point from the switch 104 (FIG. 1) or some other
device. The clock synchronization component 508 may use this
information or other suitable information to synchronize the clock
506 with the clock of the primary access point. As discussed above,
operations such as these may be repeated on a regular basis to
maintain synchronization over time.
[0088] As represented by block 606, the access point 500 (e.g., the
controller 504) may cooperate with one or more neighboring access
points to determine a beacon transmission schedule. For example,
the controller 504 may communicate with a switch, an access point,
some other device, or a combination of these devices to select
channels for the access points, beacon transmission times, or both.
As discussed above, this may involve defining TBTTs for each access
point such that for a given beacon interval the beacons from the
access points are transmitted in a group with a defined (e.g.,
known) spacing between subsequent beacons. To this end, the
controller 504 may select beacon transmission times, send beacon
transmission times to another device, receive beacon transmission
times from another device, or perform some combination of these
operations. As illustrated in FIG. 5, beacon-related information
512 for the access point 500 and beacon-related information 514 for
neighboring access points may be stored in the access point 500
(e.g., in a data memory). The information 512 may include, for
example, a beacon interval 516 and TBTT 518 of the access point.
The information 514 may include, for example, one or more TBTTs 520
and one or more channels 522 used by the neighboring access
points.
[0089] As represented by block 608, at some point an indication
relating to the beacon transmission schedule is generated. In some
aspects the access point 500 may generate the indication. For
example, an indication generator 524 may use the information 512
and 514 to generate a next beacon indication 526 that may be
included in beacon information 528 that the access point 500
transmits in each beacon. As discussed herein, the next beacon
indication 526 may comprise information or a function indicative of
the channel and/or the timing of one or more next beacons. FIG. 5
also illustrates that the beacon information 528 includes a network
identifier 530 that may uniquely identify the wireless network
provided by the access device 500. For example, in some
implementations the network identifier 530 may comprise an address
(e.g., a MAC address) or some other suitable information.
[0090] In some implementations the access point 500 may receive the
indication from another device. In this case, the access point 500
may simply maintain the next beacon indication 526 (e.g., in a data
memory) for subsequent transmission in its beacons.
[0091] As represented by block 610, at some point in time the
indication is provided to any stations that may enter the coverage
area of any one of the neighboring access points. Continuing with
the example where the access point 500 supplies or maintains the
indication, the access point 500 (e.g., a transmitter in the radio
502) sends the beacon or some other suitable signal including the
next beacon indication 526 over its wireless network. In this way,
any stations entering the coverage area of the access point 500 may
receive the beacon or other signal and extract the indication 526
from the beacon.
[0092] FIG. 7 illustrates several sample aspects of a wireless
station 700. Briefly, the station 700 includes a radio 702 adapted
to establish wireless communications with, for example, nearby
access points. A beacon transmission information acquisition
controller 704 is adapted to communicate with an access point or
some other device to obtain information relating to beacon
transmissions. A clock 706 and a clock synchronization component
708 are adapted to provide clock signals for the station 700 to
facilitate precise timing of reception of beacons and other
operations. A beacon scan controller 710 is adapted to control the
scanning for beacons. A power mode (e.g., state) controller 712 is
adapted to control the mode of one or more components of the
station 700. A beacon signal analyzer 714 is adapted to analyze
received beacons or other signals. To reduce the complexity of FIG.
7, other components commonly found in a station are not shown.
[0093] Sample operations of the station 700 will be discussed in
more detail in conjunction with the flowchart of FIG. 8. In
particular, FIG. 8 relates to operations that may be performed to
obtain an indication relating to beacon transmission schedules and
to receive beacons or other signals from one or more access points
(e.g., neighboring access points).
[0094] As represented by block 802, the station 700 (e.g., the
controller 704) may obtain an indication regarding beacon
transmission schedules of neighboring access points. For example,
the controller 704 may communicate with another device such as a
programming device or an access point to receive a next beacon
indication. In the latter case, a scanner in the radio 702 may scan
for beacons from an associated access point or some other access
point and provide the beacon information including a next beacon
indication to the controller 704. The controller 704 may then store
any received next beacon indication (e.g., a function as discussed
herein) 716 in a data memory for later use by the beacon scan
controller 710.
[0095] As represented by block 804, the station 700 may enter a
power save mode to conserve power when it is not actively
transmitting or receiving data. For example, the power mode
controller 712 may set the station 700 to a power save mode (e.g.,
a suspended state) 718 or to a wake mode (e.g., an active state)
720. In some applications a power save mode may result in one or
more of the components of the station 700 being temporarily
disabled or turned off. Here, however, power may still be supplied
to other components of the station 700. For example, to maintain
state information during the power save mode, power may be supplied
to at least a portion of data memory in the station 700. It should
be appreciated that the power mode controller 712 may utilize other
modes (states) in addition to or instead of one or more of the
modes 718 and 720.
[0096] Various components may be controlled by the power mode
controller 712. For example, in some aspects the power mode
controller 712 may control one or more components associated with
lower layer processing in the station (e.g., the radio 702). In
other aspects the power mode controller 712 may control other
components of the station 700.
[0097] As represented by block 806, the station 700 (e.g., under
the control of the controller 712) may wake from the power save
mode to scan for beacons during the wake time period. As discussed
above in conjunction with FIG. 3, the wake time period may
correspond to the periods 318A and 318B. Thus, the wake time period
may be defined based on the beacon transmission schedule
information provided to the station 700 (e.g., the indication
716).
[0098] As represented by block 808, the station 700 (e.g., the
beacon scan controller 710) uses the indication 716 to commence
scanning for the first beacon (e.g., beacon 302A) in a given group
of beacons (e.g., beacons 302A, 302C, and 302E). Here, the beacon
scan controller 710 (e.g., a scan information derivation component
722) may determine which channel is to be scanned next and when
scanning should commence on that channel based on current beacon
information 724 maintained in the station 700. The information 724
may identify, for example, the last channel that was scanned 726
and/or timing associated with the last scan (e.g., the TBTT of the
corresponding access point) 728. With reference to the beacon
indication function of Table 1, the current channel information 726
may correspond to information for the first column in the
table.
[0099] Based on the above, the derivation component 722 generates
information 730 to be used for the next scan. Here, the information
730 may identify the next channel to be scanned 732 and the scan
timing 734. With reference again to Table 1, the channel
information 732 and the timing information 734 may correspond to
the second and third columns, respectively, in the table. The
timing information 734 may include information relating to the
start of the scan and the length of the scan. As an example of the
latter, information relating to the length of the beacons may be
used to define how long the scanning should performed. With
reference to FIG. 3, the scan period for the first beacon in the
group may comprise the period 314A. The scanner of the radio 702
may thus be tuned to the appropriate channel and activated for the
designate period of time to receive the beacon from the access
point (block 810).
[0100] As represented by blocks 812-818, the station 700 then
repeatedly scans for beacons from the other access points in the
group. At block 812 the station again uses the indication in
conjunction with the previous beacon information (e.g., relating to
the first beacon in the group) to scan for the next beacon (e.g.,
the second beacon in the group). At block 814 the station commences
scanning until the next beacon is received (block 816). As
represented by block 818 these operations are repeated until all of
the beacons in the group have been received. As illustrated in FIG.
3, these operations may be performed in a relatively short period
of time (e.g., scan periods 314A-C) when the beacons are
transmitted in a compact group. As a result, the station may expend
less power for scanning operations, may not spend a significant
amount of time scanning on other channels (e.g., other than the
channel of an associated access point), and may remain in a power
save state for longer periods of time.
[0101] As represented by block 820, as the station receives the
beacons (at blocks 810 and 816) the beacon signal analyzer 714 may
process each beacon and any information in the beacon to determine
which access point provides the best current connectivity. For
example, the beacon signal analyzer may measure signal strength
associated with each beacon and select the access point that
provides the beacon with the highest received signal strength as
the preferred access point. The operations of FIG. 8 may then be
repeated as necessary in an attempt to ensure that the station
maintains a current list of the neighboring access points and
information relating to the connectivity provided by those access
points. The station may therefore easily and quickly transition to
a different one of the neighboring access points as necessary to,
for example, maintain an acceptable quality of service.
[0102] In view of the above, it may be appreciated that various
advantages may be achieved in accordance with the teachings herein.
For example, the standby time of a wireless local area network
("WLAN") device may be increased by grouping beacons and/or
providing a beacon transmission indication to the device. Through
the use of such techniques, the scan time of the WLAN device may be
decreased and the amount of time spent in a power save mode may be
increase, thereby increasing the standby time of the device.
[0103] The teachings herein are applicable to a variety of
protocols, user devices and associated network components.
Accordingly, a user device may incorporate various components to
obtain connectivity to a network via various wireless platforms
such as Wi-Fi (802.11-based), WiMAX, other time-division
multiplexed networks, or any other suitable wireless platform.
Moreover, this may be accomplished through the use of various
architectures, protocols, specifications, or standards in addition
to or other than those that have been specifically described.
[0104] The components described herein may be implemented in a
variety of ways. For example, referring to FIG. 9, components 902,
904, and 906 may correspond at least in part to, for example,
previously discussed components 710, 702, and 712, respectively. In
some aspects these components may be incorporated in a component
900 that may correspond to, for example, component 700 in FIG. 7.
Referring to FIG. 10, components 1002, 1004, 1006, 1008, 1010, and
1012 may correspond at least in part to, for example, previously
discussed components 504, 502, 510, 504, 504, and 524,
respectively. In some aspects these components may be incorporated
in a component 1000 that may correspond to, for example, component
500 in FIG. 5. FIGS. 9 and 10 illustrate that in some aspects these
components may be implemented via appropriate processor components.
These processor components may in some aspects be implemented, at
least in part, using structure as taught herein. In some aspects a
processor may be adapted to implement a portion or all of the
functionality of one or more of these components. In some aspects
one or more of the components represented by dashed boxes are
optional.
[0105] In addition, the components and functions represented by
FIGS. 9 and 10, as well as other components and functions described
herein, may be implemented using any suitable means. Such means
also may be implemented, at least in part, using corresponding
structure as taught herein. For example, in some aspects means for
using an indication may comprise a scan controller, means for
scanning may comprise a scanner, means for waking may comprise a
mode controller, means for cooperating may comprise a beacon
transmission cooperation controller, means for transmitting may
comprise a transmitter, means for maintaining may comprise a beacon
generator, means for determining beacon transmission time may
comprise a beacon transmission cooperation controller, means for
using beacon transmission time may comprise a beacon transmission
cooperation controller, and means for generating an indication may
comprise an indication generator. One or more of such means also
may be implemented in accordance with one or more of the processor
components of FIGS. 9 and 10.
[0106] Those of skill in the art would understand that information
and signals may be represented using any of a variety of different
technologies and techniques. For example, data, instructions,
commands, information, signals, bits, symbols, and chips that may
be referenced throughout the above description may be represented
by voltages, currents, electromagnetic waves, magnetic fields or
particles, optical fields or particles, or any combination
thereof.
[0107] Those of skill would further appreciate that the various
illustrative logical blocks, modules, processors, means, circuits,
and algorithm steps described in connection with the aspects
disclosed herein may be implemented as electronic hardware (e.g., a
digital implementation, an analog implementation, or a combination
of the two, which may be designed using source coding or some other
technique), various forms of program or design code incorporating
instructions (which may be referred to herein, for convenience, as
"software" or a "software module"), or combinations of both. To
clearly illustrate this interchangeability of hardware and
software, various illustrative components, blocks, modules,
circuits, and steps have been described above generally in terms of
their functionality. Whether such functionality is implemented as
hardware or software depends upon the particular application and
design constraints imposed on the overall system. Skilled artisans
may implement the described functionality in varying ways for each
particular application, but such implementation decisions should
not be interpreted as causing a departure from the scope of the
present disclosure.
[0108] The various illustrative logical blocks, modules, and
circuits described in connection with the aspects disclosed herein
may be implemented or performed with a general purpose processor, a
digital signal processor ("DSP"), an application specific
integrated circuit ("ASIC"), a field programmable gate array
("FPGA") or other programmable logic device, discrete gate or
transistor logic, discrete hardware components, or any combination
thereof designed to perform the functions described herein. A
general purpose processor may be a microprocessor, but in the
alternative, the processor may be any conventional processor,
controller, microcontroller, or state machine. A processor may also
be implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0109] It is understood that any specific order or hierarchy of
steps in any disclosed process is an example of a sample approach.
Based upon design preferences, it is understood that the specific
order or hierarchy of steps in the processes may be rearranged
while remaining within the scope of the present disclosure. The
accompanying method claims present elements of the various steps in
a sample order, and are not meant to be limited to the specific
order or hierarchy presented.
[0110] The steps of a method or algorithm described in connection
with the aspects disclosed herein may be embodied directly in
hardware, in a software module executed by a processor, or in a
combination of the two. A software module (e.g., including
executable instructions and related data) and other data may reside
in a data memory such as RAM memory, flash memory, ROM memory,
EPROM memory, EEPROM memory, registers, a hard disk, a removable
disk, a CD-ROM, or any other form of computer-readable storage
medium known in the art. A sample storage medium may be coupled to
a machine such as, for example, a computer/processor (which may be
referred to herein, for convenience, as a "processor") such the
processor can read information (e.g., code) from and write
information to the storage medium. A sample storage medium may be
integral to the processor. The processor and the storage medium may
reside in an ASIC. The ASIC may reside in user equipment. In the
alternative, the processor and the storage medium may reside as
discrete components in user equipment. Moreover, in some aspects
any suitable computer-program product may comprise a
computer-readable medium comprising codes relating to one or more
of the aspects of the disclosure. In some aspects a computer
program product may comprise packaging materials.
[0111] The previous description of the disclosed aspects is
provided to enable any person skilled in the art to make or use the
present disclosure. Various modifications to these aspects will be
readily apparent to those skilled in the art, and the generic
principles defined herein may be applied to other aspects without
departing from the scope of the disclosure. Thus, the present
disclosure is not intended to be limited to the aspects shown
herein but is to be accorded the widest scope consistent with the
principles and novel features disclosed herein.
* * * * *