U.S. patent application number 14/518707 was filed with the patent office on 2015-02-05 for wireless communication methods and components that implement handoff in wireless local area networks.
This patent application is currently assigned to InterDigital Technology Corporation. The applicant listed for this patent is InterDigital Technology Corporation. Invention is credited to Christopher R. Cave, Angelo A. Cuffaro, Frank La Sita, Paul Marinier, Vincent Roy, Athmane Touag.
Application Number | 20150036661 14/518707 |
Document ID | / |
Family ID | 35852945 |
Filed Date | 2015-02-05 |
United States Patent
Application |
20150036661 |
Kind Code |
A1 |
Marinier; Paul ; et
al. |
February 5, 2015 |
WIRELESS COMMUNICATION METHODS AND COMPONENTS THAT IMPLEMENT
HANDOFF IN WIRELESS LOCAL AREA NETWORKS
Abstract
This invention relates to wireless local area networks, and
particularly to the IEEE 802.11 family of standards. It consists of
a method and apparatus that can be implemented in access points
(APs) and subscriber wireless transmit/receive units (WTRUs), in
order to allow an AP to initiate re-association of a WTRU to itself
or a different AP. The invention improves the robustness of the
network by enabling more efficient load balancing, congestion
control, and roaming, without compromising the user experience.
Inventors: |
Marinier; Paul; (Brossard,
CA) ; Roy; Vincent; (Longueuil, CA) ; Cave;
Christopher R.; (Dollard-des-Ormeaux, CA) ; La Sita;
Frank; (Setauket, NY) ; Cuffaro; Angelo A.;
(Laval, CA) ; Touag; Athmane; (Chomedey Laval,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
InterDigital Technology Corporation |
Wilmington |
DE |
US |
|
|
Assignee: |
InterDigital Technology
Corporation
Wilmington
DE
|
Family ID: |
35852945 |
Appl. No.: |
14/518707 |
Filed: |
October 20, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13242464 |
Sep 23, 2011 |
8867487 |
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14518707 |
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12759525 |
Apr 13, 2010 |
8027312 |
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13242464 |
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11018182 |
Dec 21, 2004 |
7706326 |
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12759525 |
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60608768 |
Sep 10, 2004 |
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Current U.S.
Class: |
370/331 |
Current CPC
Class: |
H04W 36/08 20130101;
H04W 88/08 20130101; H04W 36/06 20130101; H04W 84/12 20130101; H04W
28/18 20130101 |
Class at
Publication: |
370/331 |
International
Class: |
H04W 36/08 20060101
H04W036/08; H04W 28/18 20060101 H04W028/18; H04W 88/08 20060101
H04W088/08; H04W 84/12 20060101 H04W084/12 |
Claims
1.-25. (canceled)
26. A method for use in a wireless transmit/receive unit (WTRU),
the method comprising: receiving, from an Institute of Electrical
and Electronics Engineers (IEEE) 802.11 access point (AP), a
request message on a first channel associated with a first set of
communication parameters; determining whether to accept or reject
association with the IEEE 802.11 AP on a second channel based on
the request message; transmitting a response message to the IEEE
802.11 AP using the first set of communication parameters, wherein
the response message indicates whether the WTRU accepts or rejects
association with the IEEE 802.11 AP on the second channel; and on a
condition the WTRU accepts association with the IEEE 802.11 AP on
the second channel, reconfiguring to communicate via a second set
of communication parameters, and communicating with the IEEE 802.11
AP using the second set of communication parameters.
27. The method of claim 26, wherein the request message includes:
an identifier of the IEEE 802.11 AP on the second channel, the
second set of communication parameters, and a field that indicates
whether disassociation of the WTRU from the IEEE 802.11 AP on the
first channel is immediate.
28. The method of claim 26, further comprising: on a condition the
WTRU accepts association with the IEEE 802.11 AP on the second
channel, transmitting a notification message to the IEEE 802.11 AP
using the first set of communication parameters, wherein the
notification message indicates whether disassociation of the WTRU
from the IEEE 802.11 AP on the first channel is immediate.
29. The method of claim 27, wherein the identifier of the AP is a
Basic Service Set Identifier (BSSID).
30. The method of claim 26, wherein the second set of communication
parameters includes an indication of the second channel of the IEEE
802.11 AP.
31. The method of claim 26, wherein the request message is a
management frame.
32. The method of claim 26, wherein the request message includes a
field that indicates whether disassociation of the WTRU from the
IEEE 802.11 AP on the first channel is immediate.
33. A wireless transmit/receive unit (WTRU), the WTRU comprising: a
transceiver configured to receive from an Institute of Electrical
and Electronics Engineers (IEEE) 802.11 access point (AP), a
request message on a first channel associated with a first set of
communication parameters; a processor configured to determine
whether to accept or reject association with the IEEE 802.11 AP on
a second channel based on the request message; the transceiver
further configured to transmit a response message to the IEEE
802.11 AP using the first set of communication parameters, wherein
the response message indicates whether the WTRU accepts or rejects
association with the IEEE 802.11 AP on the second channel; and on a
condition the WTRU accepts association with the IEEE 802.11 AP on
the second channel, the transceiver further configured to
communicate with the IEEE 802.11 AP using a second set of
communication parameters.
34. The WTRU of claim 33, wherein the request message includes: an
identifier of the IEEE 802.11 AP on the second channel, the second
set of communication parameters, and a field that indicates whether
disassociation of the WTRU from the IEEE 802.11 AP on the first
channel is immediate.
35. The WTRU of claim 33, further comprising: on a condition the
WTRU accepts association with the IEEE 802.11 AP on the second
channel, the transceiver further configured to transmit a
notification message to the IEEE 802.11 AP using the first set of
communication parameters, wherein the notification message
indicates whether disassociation of the WTRU from the IEEE 802.11
AP on the first channel is immediate.
36. The WTRU of claim 34, wherein the identifier of the AP is a
Basic Service Set Identifier (BSSID).
37. The WTRU of claim 33, wherein the second set of communication
parameters includes the second channel of the IEEE 802.11 AP.
38. The WTRU of claim 33, wherein the request message is a
management frame.
39. The WTRU of claim 33, wherein the request message includes a
field that indicates whether disassociation of the WTRU from the
IEEE 802.11 AP on the first channel is immediate.
40. A method for use in an Institute of Electrical and Electronics
Engineers (IEEE) 802.11 access point (AP), the method comprising:
sending a request message to a wireless transmit/receive unit
(WTRU) on a first channel associated with a first set of
communication parameters; receiving a response message from the
WTRU on the first channel associated with the first set of
communication parameters, wherein the response message indicates
whether the WTRU accepts or rejects association with the IEEE
802.11 AP on a second channel; and on a condition the WTRU accepts
association with the IEEE 802.11 AP on the second channel,
communicating with the WTRU using a second set of communication
parameters.
41. The method of claim 40, wherein the request message includes:
an identifier of the IEEE 802.11 AP on the second channel, the
second set of communication parameters, and a field that indicates
whether disassociation of the WTRU from the IEEE 802.11 AP on the
first channel is immediate.
42. The method of claim 40, further comprising: on a condition the
WTRU accepts association with the IEEE 802.11 AP on the second
channel, receiving a notification message from the WTRU using the
first set of communication parameters, wherein the notification
message indicates whether disassociation of the WTRU from the IEEE
802.11 AP on the first channel is immediate.
43. The method of claim 41, wherein the identifier of the AP is a
Basic Service Set Identifier (BSSID).
44. The method of claim 40, wherein the second set of communication
parameters includes the second channel of the IEEE 802.11 AP.
45. The method of claim 40, wherein the request message is a
management frame.
46. The method of claim 40, wherein the request message includes a
field that indicates whether disassociation of the WTRU from the
IEEE 802.11 AP on the first channel is immediate.
47. An Institute of Electrical and Electronics Engineers (IEEE)
802.11 access point (AP), the AP comprising: a transceiver
configured to send a request message to a wireless transmit/receive
unit (WTRU) on a first channel associated with a first set of
communication parameters; the transceiver further configured to
receive a response message from the WTRU on the first channel
associated with the first set of communication parameters, wherein
the response message indicates whether the WTRU accepts or rejects
association with the IEEE 802.11 AP on a second channel; and on a
condition the WTRU accepts association with the IEEE 802.11 AP on
the second channel, the transceiver further configured to
communicate with the WTRU using a second set of communication
parameters.
48. The AP of claim 47, wherein the request message includes: an
identifier of the IEEE 802.11 AP on the second channel, the second
set of communication parameters, and a field that indicates whether
disassociation of the WTRU from the IEEE 802.11 AP on the first
channel is immediate.
49. The AP of claim 47, further comprising: on a condition the WTRU
accepts association with the IEEE 802.11 AP on the second channel,
the transceiver further configured to receive a notification
message from the WTRU using the first set of communication
parameters, wherein the notification message indicates whether
disassociation of the WTRU from the IEEE 802.11 AP on the first
channel is immediate.
50. The AP of claim 48, wherein the identifier of the AP is a Basic
Service Set Identifier (BSSID).
51. The AP of claim 47, wherein the second set of communication
parameters includes an indication of the second channel of the IEEE
802.11 AP.
52. The AP of claim 47, wherein the request message is a management
frame.
53. The AP of claim 47, wherein the request message includes a
field that indicates whether disassociation of the WTRU from the
IEEE 802.11 AP on the first channel is immediate.
Description
CROSS REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/242,464, filed on Sep. 23, 2011, which is a
continuation of U.S. patent application Ser. No. 12/759,525, filed
on Apr. 13, 2010, which issued as U.S. Pat. No. 8,027,312 on Sep.
27, 2011, which is a continuation of U.S. patent application Ser.
No. 11/018,182, filed Dec. 21, 2004, which issued as U.S. Pat. No.
7,706,326 on Apr. 27, 2010, which claims priority from U.S.
Provisional Patent Application No. 60/608,768, filed Sep. 10, 2004,
each of which is incorporated by reference as if fully set forth
herein.
FIELD OF INVENTION
[0002] The present invention relates to wireless local area
networks (WLANs) and to methods and apparatus that facilitate a
wireless transmit/receive unit (WTRU) to "roam" by switching from
communication via one communication station to another. In
particular, the invention is advantageously employed by WTRUs
configured to operate in WLANs compliant with the IEEE 802
standards where the WTRUs are able to conduct wireless
communications with WLAN access points (APs) and to continue a
wireless communication while switching from a wireless link with
one AP to a wireless link with another AP.
BACKGROUND
[0003] Wireless communication systems are well known in the art.
Generally, such systems comprise communication stations, which
transmit and receive wireless communication signals between each
other. Depending upon the type of system, communication stations
typically are one of two types of wireless transmit/receive units
(WTRUs): one type is the base station, the other is the subscriber
unit, which may be mobile.
[0004] The term base station as used herein includes, but is not
limited to, a base station, access point, Node B, site controller,
or other interfacing device or WTRU in a wireless environment, that
provides other WTRUs with wireless access to a network with which
the AP is associated.
[0005] The term wireless transmit/receive units (WTRU) as used
herein includes, but is not limited to, a user equipment, mobile
station, fixed or mobile subscriber unit, pager, or any other type
of device capable of operating in a wireless environment. Such
WTRUs include personal communication devices, such as phones, video
phones, and Internet ready phones that have network connections. In
addition, WTRUs include portable personal computing devices, such
as PDAs and notebook computers with wireless modems that have
similar network capabilities. WTRUs that are portable or can
otherwise change location are referred to as mobile units.
[0006] Typically, a network of base stations is provided wherein
each base station is capable of conducting concurrent wireless
communications with appropriately configured WTRUs, as well as
multiple appropriately configured base stations. Some WTRUs may
alternatively be configured to conduct wireless communications
directly between each other, i.e., without being relayed through a
network via a base station. This is commonly called peer-to-peer
wireless communications. Where a WTRU is configured to communicate
directly with other WTRUs it may itself also be configured as and
function as a base station. WTRUs can be configured for use in
multiple networks, with both network and peer-to-peer
communications capabilities.
[0007] One type of wireless system, called a wireless local area
network (WLAN), can be configured to conduct wireless
communications with WTRUs equipped with WLAN modems that are also
able to conduct peer-to-peer communications with similarly equipped
WTRUs. Currently, WLAN modems are being integrated into many
traditional communicating and computing devices by manufacturers.
For example, cellular phones, personal digital assistants, and
laptop computers are being built with one or more WLAN modems.
[0008] Popular WLAN environments with one or more WLAN base
stations, typically called access points (APs), include those
constructed according to one or more of the IEEE 802 family of
standards. Access to these networks usually requires user
authentication procedures. Protocols for such systems are presently
being standardized in the WLAN technology area. One such framework
of protocols is represented by the IEEE 802 family of
standards.
[0009] A basic service set (BSS) is the basic building block of an
IEEE 802.11 WLAN, which comprises WTRUs also referred to as
stations (STAs). A set of STAs which can talk to each other can
form a BSS. Multiple BSSs are interconnected through an
architectural component called a distribution system (DS), to form
an extended service set (ESS). An access point (AP) is a WTRU that
provides access to the DS by providing DS services, and generally
allows concurrent access to the DS by multiple STAs.
[0010] A network of WTRUs operating with peer to peer
communications in an IEEE 802.11 environment, typically referred to
as "ad hoc" mode, is also called an "independent BSS." In an
independent BSS, two or more WTRUs establish communication among
themselves without the need of a coordinating network element. No
AP-to-network infrastructure is required. However, an AP can be
configured to use the ad hoc protocols and act as the WTRUs do in
peer to peer communications. In such case an AP may act as a bridge
or router to another network or to the Internet.
[0011] A WTRU that starts an ad hoc network selects the ad hoc
network's operating parameters, such as the service set identifier
(SSID), channel, and beacon timing, and transmits this information
in communication frames, for example, in beacon frames. As other
WTRUs join the ad hoc network, they detect and use the ad hoc
network's operating parameters.
[0012] Where a network infrastructure is used and wireless
communications are controlled through APs, parameters such as the
SSID are normally specified by a network controller associated with
the APs. The APs periodically broadcast beacon frames to enable
WTRUs to identify the APs and attempt to establish communications
with them.
[0013] The SSID in an IEEE 802 based system can be a 32-character
unique identifier attached to a header of packets sent over a WLAN.
The SSID then acts as a password when a WTRU attempts to connect to
a BSS or an independent BSS. The SSID differentiates one WLAN from
another, so all base stations and all other devices connected to or
attempting to connect to a specific WLAN normally use the same
SSID. A device will not normally be permitted to join a BSS unless
it can provide the correct SSID.
[0014] In an AP-based WLAN, a mobile WTRU communicates wirelessly
with a specific AP when in the geographic service area of that AP.
The WTRU is said to be associated with the AP through which it is
conducting wireless communications. It is sometimes necessary or
desirable for a WTRU to change the AP with which it is associated.
For example, the WTRU may be experiencing poor signal conditions
because it is moving out of the geographic area served by the AP
with which it is associated. The need to associate to another AP
can also be caused by congestion arising in the basic service set
(BSS) served by that AP. Re-association is also referred to as
roaming, particularly if the WTRU has an assigned "home" AP (or
network of APs) and then "roams" when the WTRU communicates via a
different AP (or different network's AP).
[0015] In WLANs compliant with the current 802.11 standards, the
re-association of a WTRU to a new AP is initiated entirely by the
WTRU. To accomplish this, a WTRU must first identify APs in its
vicinity that can potentially provide network services to the WTRU.
This is conventionally achieved by a scanning process, which may be
active or passive.
[0016] In active scanning, the WTRU transmits probe requests on one
or more channels on which the WTRU is configured to communicate.
The WTRU selects a new AP from among the APs from which it receives
probe responses. In passive scanning, the WTRU dwells on the
channels it can use in an attempt to receive beacon packets
transmitted by APs which serve the geographic location where the
WTRU is then located. The WTRU then selects a new AP from among the
APs from which it receives beacon packets. Both active and passive
scanning can take a significant amount of time in terms of being
able to maintain an ongoing communication, particularly when the
WTRU is moving.
[0017] The inventors have recognized that it is sometimes desirable
that an AP take the initiative of reassociating a WTRU. For
example, APs (or some other node controlling the WTRU's behavior)
may determine a current "load" condition based on the collective
volume of wireless communication traffic due to the number of WTRUs
associated with the AP and/or the types of communications being
conducted. Also a WTRU may be located at a location served by
several neighboring APs each of which may be using a different
channel from among the set of channels over which the WTRU can
communicate. Where the collective traffic volume is relatively high
(heavy load) for one AP and the volume of traffic on one or more
neighboring APs is relatively low (light load), it would be
desirable that one or more WTRUs associated with the heavily loaded
AP re-associate with a neighboring lightly loaded AP.
[0018] In WLANs compliant with the current 802.11 standards,
however, these re-associations take place only if WTRUs associated
with the heavily loaded AP are equipped with a sophisticated
algorithm allowing them to autonomously decide re-association to
another available AP is desirable, based on traffic estimations on
the channels. It is difficult to be certain that all WTRUs would be
equipped with such an algorithm, and the design and implementation
of such an algorithm can be quite complex. Even if all WTRUs
operating in a given geographical area are equipped with such an
algorithm, it is difficult to guarantee that the WTRUs would not
re-associate to other APs in a disorderly fashion, possibly
resulting in multiple re-associations taking place back and forth
between the same APs.
[0019] To avoid these issues, the inventors have considered
potential solutions. For example, a heavily loaded AP could
forcefully disassociate some selected WTRUs, hoping that these
WTRUs would then find another AP with which they can re-associate.
It could also induce disassociations indirectly by reducing the
transmission power level of certain key packets it transmits, for
example, beacon or probe response packets. The problem with these
disassociation techniques is that they can result in a disruption
of service unacceptable to certain WTRU users, for example, users
of real-time services such as voice or video. This disruption is
caused by the WTRU having to scan for a new AP after
disassociation, a process which can take a significant amount of
time. In consideration of the overall problems, the inventors have
recognized it would be desirable to provide for allowing an AP to
initiate the re-association of a WTRU from one AP to another
without loss of performance.
SUMMARY
[0020] A communication method, system and components are provided
that includes a hand-shaking procedure allowing a WTRU
communicating with a network station via a first set of
communication parameters, to handoff to another network station for
communication via a second set of communication parameters.
Preferably, an original access point (AP) of a wireless local area
network (WLAN) requests or commands the WTRU to handoff to a target
AP. As an alternative, a target AP of a WLAN can request or command
the WTRU to handoff to the target AP from an original AP with which
the WTRU is communicating.
[0021] Preferably, in an IEEE 802 type WLAN context, four distinct
scenarios are provided for, which may be implemented individually
or in combination for a particular WLAN, namely:
[0022] 1. An original AP requests a WTRU to handoff to a target AP.
The WTRU then decides whether to handoff or not, and communicates
its decision to the original AP. In the case where the WTRU decides
to go forward with the handoff, the WTRU reconfigures its channel,
BSSID, etc. for the target AP, and sends to the target AP a
confirmation message indicating that it has completed the
re-association.
[0023] 2. An original AP commands a WTRU to handoff to a target AP.
The WTRU then reconfigures its channel, BSSID, etc. for the target
AP, and sends to the target AP a confirmation message indicating
that it has completed the re-association.
[0024] 3. A target AP commands a WTRU to handoff to the target AP.
The WTRU then notifies an original AP with which it is
communicating of its imminent handoff, reconfigures its channel,
BSSID, etc. for the target AP, and sends to the target AP a
confirmation message indicating that it has completed the
re-association.
[0025] 4. A target AP requests the WTRU to handoff to the target
AP. The WTRU decides whether to handoff or not, and communicates
its decision to the target AP. In the case where the WTRU decides
to go forward with the handoff, the WTRU notifies an original AP
with which it is communicating of its imminent handoff,
reconfigures its channel, BSSID, etc. for the target AP, and sends
to the target AP a confirmation message indicating that it has
completed the re-association.
[0026] A more detailed understanding of the invention may be had
from the following description of a preferred embodiment, given by
way of example, and to be understood in conjunction with the
accompanying drawings, wherein like elements are designated by like
numerals.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0027] FIG. 1 is a system overview diagram illustrating WLAN
communication.
[0028] FIG. 2 is a diagram showing an overview of a system in
accordance with the present invention, in which a mobile WTRU is
exiting the service area of an original AP and is entering the
service area of a target AP.
[0029] FIG. 3 is a diagram showing the signaling exchange for a
first scenario in which an original AP requests a WTRU to handoff
to a target AP.
[0030] FIG. 4 is diagram showing the signaling exchange for a
second scenario in which an original AP commands a WTRU to handoff
to a target AP.
[0031] FIG. 5 is a diagram showing the signaling exchange for a
third scenario in which a target AP commands a WTRU to handoff to a
target AP.
[0032] FIG. 6 is a diagram showing the signaling exchange for a
fourth scenario in which a target AP requests a WTRU to handoff to
a target AP.
TABLE-US-00001 [0033] TABLE OF ACRONYMS AP Access Point BSS Base
Station System BSSID Base Station System Identifier DRI Directed
Re-association Indication DRCf Directed Re-association Confirmation
DRCm Directed Re-association Command DRRq Directed Re-association
Request DRRsp Directed Re-association Response DS Distribution
System ESS Extended Service Set PDA Personal Digital Assistant STA
Station WLAN Wireless Local Area Network WTRU Wireless
Transmitter/Receiver Unit
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)
[0034] The terms access point (AP), original AP, target AP, and
wireless transmit/receive unit (WTRU) are used as described above.
The present invention provides a wireless radio access network
having a plurality of networked APs through which wireless network
services are provided for one or more WTRUs. The invention is
particularly useful when used in conjunction with mobile WTRUs, as
they travel across the respective geographic areas of service
coverage provided by respective APs. The WTRUs can have an
integrated or installed wireless WLAN device, such as 802.11(a),
802.11(b), 802.11(g) or 802.11(n) compliant device, in order to
communicate. However, the invention is applicable in any wireless
system.
[0035] The term directed re-association request (DRRq) means a
signal directed to a WTRU requesting the WTRU reconfigure itself
for communication with a different network station such as a target
AP. In a WLAN IEEE 802.11 context, the DRRq can be sent by either
the original AP or the target AP.
[0036] The information contained in the DRRq preferably includes
data sufficient to identify a target AP and to enable the WTRU to
communicate with the target AP. This information preferably
includes the channel of the target AP, an identifier of the target
AP (MAC address, IP address, etc.), the target BSSID, the target AP
capabilities, etc. The DRRq preferably also includes timing
information as to when handoff is scheduled. A flag or special
value for a timing field can be used to indicate that handoff is
meant to be immediate. The DRRq can also include signaling-specific
information such as which signaling steps are needed in the
exchange. For example, the DRRq can indicate if the target AP
expects to receive a directed re-association confirmation, or if
the original AP expects to receive a directed re-association
indication.
[0037] In the case where a DRRq is sent from a target AP, the
target AP preferably uses the same channel to send the DRRq to the
WTRU as is being used by the WTRU and an original AP with which the
WTRU is communicating. In a preferred embodiment, the DRRq is
implemented as a unicast frame, more specifically as a control
frame, as a management frame or as the payload of a data frame. In
alternative embodiments, this signaling can also be implemented
using a multicast or broadcast message.
[0038] The term directed re-association response (DRRsp) means a
signal, from the WTRU to which the DRRq was sent, directed to the
network station which sent the DRRq. The DRRsp preferably indicates
whether the WTRU accepts or rejects the request to reconfigure
itself for communication with a different network station such as a
target AP.
[0039] The term directed re-association command (DRCm) means a
signal from a network station directed to a WTRU, commanding the
WTRU to reconfigure itself for communication with a different
network station such as a target AP. In the IEEE 802.11 context,
the DRCm can be sent by either an original AP or a target AP. The
WTRU is expected to follow the DRCm and thus need not send a DRRsp
to the network station that sent the DRCm. The DRCm preferably
contains the same target AP information as described above for the
DRRq.
[0040] In the case where the DRCm is sent from a target AP, the
target AP preferably uses the same channel to send the DRCm to the
WTRU as is being used by the WTRU and an original AP with which the
WTRU is communicating. In a preferred embodiment, the DRCm is
implemented as a unicast frame, more specifically as a control
frame, as a management frame or as the payload of a data frame. In
alternative embodiments, this signaling can also be implemented
using a multicast or broadcast message.
[0041] The term directed re-association confirmation (DRCf) means a
signal from a WTRU to a network station such as a target AP after
the WTRU has reconfigured itself to communicate with that station.
The DRCf confirms that the WTRU has reconfigured itself. The DRCf
is used to prevent the undesirable scenario in which a target AP
starts sending packets to the WTRU before the WTRU has successfully
re-associated to the target AP. This can result in a target AP
needlessly transmitting and retransmitting frames to a WTRU that
was expected to reconfigure itself to the target AP, but did not do
so. In such a case, the number of frames buffered in the target AP
could be substantial, and could lead to a reduction in the
efficiency of the wireless medium due to the exponentially
increasing back off window associated with multiple
retransmissions. Also, if a target AP does not receive a DRCf
indicating that re-association was successful within a desired time
out period, the target AP can eventually release any radio
resources that it may have reserved for the WTRU.
[0042] The information contained in a DRCf preferably includes data
sufficient to identify an original AP with which the WTRU is
communicating, a target AP, and the WTRU. In an IEEE 802.11
context, the DRCf preferably includes indications of the
communication channels, identifiers (MAC addresses, IP addresses,
etc.), and BSSIDs used by each, and the capabilities of the target
and original APs. The DRCf may also include timing information as
to when handoff occurred. In a preferred embodiment, the DRCf is
implemented as a unicast frame, more specifically as a control
frame, a management frame or as payload of a data frame. In
alternative embodiments, this signaling can also be implemented
using a multicast or broadcast message.
[0043] The term directed re-association indication (DRI) means a
signal from a WTRU to a network station with which the WTRU had
been in communication, such as an original AP, after the WTRU has
been requested or commanded by another station, such as a target
AP, to reconfigure itself and the WTRU is proceeding to do so. The
DRI is preferably used to indicate to an original AP that the WTRU
will reconfigure itself to a target AP. The DRI allows an original
AP to stop transmitting packets to the WTRU (which would result in
inefficient use of the wireless medium) and to forward any buffered
packets to the target AP. The DRI also allows an original AP to
release any radio resources that it may have reserved for the
WTRU.
[0044] In an IEEE 802.11 context, the information contained in the
DRI preferably includes the channel of the target AP, an identifier
of the target AP (MAC address, IP address, etc.), the target BSSID,
the target AP capabilities, etc. The DRI can also include timing
information as to when handoff is scheduled. A flag or special
value for a timing field can be used to indicate that the handoff
is meant to be immediate. In a preferred embodiment, the DRI is
implemented as a unicast frame, more specifically as a control
frame, a management frame or as payload of a data frame. In
alternative embodiments, this signaling could also be implemented
using a multicast or broadcast message.
[0045] Referring to FIG. 1, a WLAN is illustrated in which WTRUs
conduct wireless communications via a network station, in this case
an AP. The AP is connected with a DS. The AP is shown as conducting
communications with five WTRUs. Such a configuration is also called
a basic service set (BSS) within WLAN contexts. Generally, the WLAN
system supports WTRUs with different data rates. In some cases an
AP is configured to support multiple types of WTRUs, such as
802.11(b) and 802.11(g) compliant WTRUs.
[0046] Referring to FIG. 2, a WLAN is illustrated having two APs,
denoted original and target. A WTRU is shown conducting wireless
communications via the original AP. The WTRU is disposed in an area
served by both the original AP and the target AP so that it is
possible for the WTRU to "hand off" its communication from via the
original AP to the target AP.
[0047] Conventionally in an IEEE 802.11 WLAN, the WTRU will
initiate a handover operation from the original AP to the target AP
when, for example, the WTRU begins to move further away from the
original AP and towards the target AP. For such WTRU initiated
handover, the handover operation must be complete before the WTRU
is out of range of the original AP in order to avoid interruption
of an ongoing wireless communication being conducted by the
WTRU.
[0048] In accordance with the present invention, the WLAN is
provided with further functionality by permitting the APs to also
decide if and when handoff should occur. This functionality permits
the WLAN to address congestion issues arising due to differing
traffic in the respective cells or services areas of the respective
APs. This is beneficial to improve the robustness of the network by
enabling efficient load balancing and congestion control algorithms
without compromising the user experience. It also enables more
efficient roaming. Depending on the implementation of the
invention, the original AP and/or the target AP can request and/or
command the WTRU to handoff to the target AP. Preferably, in an
IEEE 802 type WLAN context four distinct scenarios are provided
for, which may be implemented individually or in combination for a
particular WLAN.
[0049] Referring to FIG. 3, a first scenario is depicted where the
original AP requests the WTRU to handoff to the target AP. The WTRU
then decides whether to handoff or not, and communicates its
decision to the original AP. In the case where the WTRU decides to
go forward with the handoff, the WTRU then reconfigures its
channel, BSSID, etc. for the target AP, and sends to the target AP
a confirmation message indicating that it has completed the
re-association. The reconfiguration process itself is preferably
essentially the same as for a conventional WTRU initiated handover,
but one of the APs preferably provides the reconfiguration data
concerning the target AP in DRRq messaging.
[0050] As a first step, the original AP determines that the WTRU
should be redirected to a target AP. This decision can be based on
the type and amount of communication traffic the original AP is
conducting in comparison with the target AP. The original AP then
sends a DRRq to the WTRU requesting that the WTRU handoff to the
target AP. The WTRU determines if it accepts the redirection
request, and communicates its decision to the original AP via a
DRRsp. This option permits, for example, the WTRU to determine if a
desired Quality of Service is available from the target AP. In the
case where the WTRU accepts the request to handoff to the target
AP, the WTRU reconfigures itself to the target AP, and sends to the
target AP a DRCf, confirming that it has handed off.
[0051] Referring to FIG. 4, a second scenario is depicted where the
original AP commands a WTRU to handoff to a target AP. Based on
this command, the WTRU reconfigures its channel, BSSID, etc. for
the target AP, and sends to the target AP a confirmation message
indicating that it has completed the re-association.
[0052] In this scenario, when the original AP determines that the
WTRU should be redirected to a target AP, it sends to the WTRU a
DRCm commanding that it handoff to the target AP. The WTRU
reconfigures itself to the target AP, and sends to the target AP a
DRCf. Where DRCm messaging is used, it is preferred that the WLAN
make a determination that a desired Quality of Service is available
from the target AP before issuing such a command. Such a
determination can be based upon geolocation information of the WTRU
either obtained from the WTRU via signaling or calculated by the
WLAN based on signals or measurement reports received from the
WTRU.
[0053] Referring to FIG. 5, a third scenario is depicted where the
target AP commands a WTRU to handoff to the target AP. The WTRU
then notifies an original AP with which it is communicating of its
imminent handoff, reconfigures its channel, BSSID, etc. for the
target AP, and sends to the target AP a confirmation message
indicating that it has completed the re-association.
[0054] In this scenario, the target AP preferably determines that
the WTRU should be redirected to the target AP. The target AP can,
for example, be configured to make a determination that a desired
Quality of Service is available from the target AP before issuing
such a command based on intercepting signals from the WTRU that are
directed to the original AP or based on the target AP obtaining
measurements reports from the original AP through inter-AP
signaling. Intercepting signals from the WTRU may not be effective
if the WTRU is using a directional antenna for its signaling to the
original AP. The target AP sends to the WTRU a DRCm commanding that
the WTRU handoff to the target AP. Preferably, the target AP uses
the channel currently used by the WTRU in communicating via the
original AP for sending the DRCm. After sending the DRCm, further
communication between the target AP and the WTRU is then preferably
on the target AP's operating channel. The WTRU sends to the
original AP a DRI communicating that it will reconfigure to the
target AP. The WTRU then reconfigures itself to the target AP, and
sends to the target AP a DRCf, confirming that it has handed
off.
[0055] Referring to FIG. 6, a fourth scenario is depicted where the
target AP requests the WTRU to handoff to the target AP. The WTRU
decides whether to handoff or not, and communicates its decision to
the target AP. In the case where the WTRU decides to go forward
with the handoff, the WTRU notifies the original AP with which it
is communicating of its imminent handoff, reconfigures its channel,
BSSID, etc. for the target AP, and sends to the target AP a
confirmation message indicating that it has completed the
re-association.
[0056] In this fourth scenario, the target AP determines that the
WTRU should be redirected to the target AP. Preferably, the target
AP uses the channel being used by the WTRU in communicating with
the original AP to send to the WTRU a DRRq requesting that the WTRU
handoff to the target AP. The target AP subsequently communicates
with the WTRU on the target AP's preferred operating channel. The
WTRU determines if it accepts the redirection request. It
communicates its decision to the target AP via a DRRsp, preferably
on the target AP's operating channel. In the case where the WTRU
accepts the request to handoff to the target AP, the WTRU sends to
the original AP a DRI communicating its decision, preferably on the
original channel that had been used in communications with the
original AP. The WTRU then reconfigures itself to the target AP,
and sends to the target AP a DRCf, confirming that it has handed
off.
[0057] One alternative in the fourth scenario is to combine the
DRRsp with the DRCf (or treat the DRCf as the DRRsp) where the WTRU
determines to accept the redirection request from the target AP.
This alternative eliminates the need for the WTRU to switch between
communication parameters multiple times during handover. This
alternative implies that either the origin AP or the target AP are
using the same channel or that, after sending the DRRq, the target
AP remains on the origin AP channel until it received the DRCf.
[0058] The method by which the AP driving the handoff procedure
determines which AP is a suitable or desired candidate to be the
target AP can include, for example, the WTRU reporting a list of
candidate APs, inter-AP signaling, centralized decision-making
performed at a central controller, or any other suitable
method.
[0059] In implementation, a preferred WTRU includes a transceiver
and a processor selectively configured to implement handoff of
wireless communication from via a first access point (AP) using a
first set of communication parameters to via a second AP using a
second set of communication parameters based on AP initiated
messaging. The transceiver is preferably configured to receive a
re-association message using the first set of communication
parameters, which identifies the second AP and second set of
communication parameters. The processor is operatively associated
with the transceiver and is preferably configured to selectively
reconfigure the transceiver to communicate via the second set of
communication parameters in response to a received re-association
message such that the transceiver is enabled to transmit a
reconfiguration confirmation to the second AP using the second set
of communication parameters. Preferably, the WTRU is configured to
operate in an IEEE 802.11 compliant system so that the transceiver
is configured to communicate in a predetermined frame format. A
re-association message from the first AP is then preferably
received in a directed re-association command frame and the
reconfiguration confirmation to the second AP is transmitted in a
directed re-association confirmation frame.
[0060] The WTRU wherein the processor can be configured to direct
the transceiver to transmit to the first AP a re-association
indication message in connection with processing a received
re-association message which is a re-association command sent by
the second AP before reconfiguring the transceiver to communicate
via the second set of communication parameters. Where the WTRU is
configured to operate in an IEEE 802.11 compliant system using a
predetermined frame format, the processor is preferably configured
to direct the transceiver to receive a re-association message from
the second AP in a directed re-association command frame, to
transmit the re-association indication to the first AP in a
directed re-association indication frame, and to transmit the
reconfiguration confirmation to the second AP in a directed
re-association confirmation frame.
[0061] The WTRU processor can be configured to make a decision
regarding reconfiguration to communicate via the second set of
communication parameters in response to a received re-association
request. In such case the processor is preferably configured to
direct the transceiver to transmit the decision to the AP from
which the re-association request was received in a directed
re-association response message such that the processor directs the
transceiver to be reconfigured to communicate via said second set
of communication parameters where the decision is to proceed with
re-association. Where the WTRU is configured to operate in an IEEE
802.11 compliant system using predetermined frame formats, the
processor is preferably configured to direct the transceiver to
receive a re-association request in a directed re-association
request (DRRq) frame from the first AP, to transmit the decision
regarding re-association in a directed re-association response
(DRRsp) frame using the first set of communication parameters, and
to transmit the reconfiguration confirmation in a directed
re-association confirmation (DRCf) frame using the second set of
communication parameters.
[0062] The WTRU processor can be further configured to direct the
transceiver to use the second set of communication parameters to
send the directed reconfiguration response message in connection
with processing an association request received from the second AP.
The processor can also be configured to direct the transceiver to
transmit to the first AP a re-association indication using the
first set of communication parameters in connection with processing
an association request received from the second AP where the
decision is to proceed with re-association. Where the WTRU is
configured to operate in an IEEE 802.11 compliant system using
predetermined frame formats, the processor is preferably configured
to direct the transceiver to receive a re-association request in a
directed re-association request (DRRq) frame, to transmit the
re-association indication in a directed re-association indication
(DRI) frame and to transmit the reconfiguration confirmation in a
directed re-association confirmation (DRCf) frame. The WTRU
processor can then also be configured to direct the transceiver to
transmit the decision regarding re-association in a directed
re-association response (DRRsp) frame in advance of the DRI
frame.
[0063] Implementation on the network side is preferably through
providing WLAN APs that each include a transceiver and a processor
selectively configured to assist in handoff of a wireless
communications with such WTRUs to or from via particular APs. The
AP transceiver is preferably configured to provide wireless network
access for wireless transmit/receive units (WTRUs) using a defined
set of communication parameters. The AP processor is preferably
configured to make a decision regarding handing off, from or to the
AP, of a wireless communication conducted by a WTRU using a
pre-handoff set of parameters. The processor is configured to
direct the transceiver to transmit a re-association message, when a
handoff decision is made, that identifies an AP for handoff and a
post-handoff set of communication parameters using the pre-handoff
set of communication parameters. The AP's transceiver is preferably
configured to receive from a WTRU, that has received a
re-association message and is proceeding with handoff, a
reconfiguration confirmation where the AP is the AP identified for
handoff in the re-association message received by the WTRU.
[0064] For implementation of the second scenario above, the AP is
preferably configured to operate in an IEEE 802.11 compliant system
wherein the transceiver is configured to use a predetermined frame
format to transmit re-association messages to WTRUs in directed
re-association command frames and to receive reconfiguration
confirmations from WTRUs in directed re-association confirmation
frames.
[0065] The transceiver can be configured to receive from a WTRU,
that is conducting a wireless communication via the AP, a
re-association indication message indicating a handoff of the
communication to via another AP to implement the third scenario.
The processor is preferably configured to release resources
allocated for the communication in connection with receiving the
re-association indication message. Also for implementation of the
third scenario, the AP is preferably configured to operate in an
IEEE 802.11 compliant system wherein the transceiver is configured
to communicate in a predetermined frame format and the processor is
configured to direct the transceiver to transmit re-association
messages in directed re-association command frames, to receive
re-association indications in directed re-association indication
frames, and to receive reconfiguration confirmations in directed
re-association confirmation frames.
[0066] To implement the first scenario, the AP processor is
preferably configured to direct the transceiver to transmit a
re-association message, when a handoff decision is made, in the
form of a received re-association request and the transceiver is
configured to receive from WTRUs that have received a
re-association request from the AP, a directed re-association
response message reflecting a responsive WTRU decision regarding
proceeding with re-association. The AP is preferably configured to
operate in an IEEE 802.11 compliant system wherein the transceiver
is configured to use predetermined frame formats and the processor
is configured to direct the transceiver to transmit re-association
requests in directed re-association request (DRRq) frames, to
receive decisions regarding re-association in directed
re-association response (DRRsp) frames, and to receive
reconfiguration confirmations in directed re-association
confirmation (DRCf) frames.
[0067] For the fourth scenario, the AP transceiver is preferably
configured to use the post-handoff set of communication parameters
to receive a directed reconfiguration response message where the AP
processor has directed the transceiver to transmit a re-association
message using a pre-handoff set of communication parameters to a
WTRU that identifies the AP for handoff as the AP itself and
identifies the post-handoff set of communication parameters as said
first set of communication parameters. The AP transceiver is also
preferably configured to receive from a WTRU, that is conducting a
wireless communication via the AP, a re-association indication
message indicating a handoff of the communication to via another AP
and the processor is configured to release resources allocated for
the communication in connection with receiving the re-association
indication message.
[0068] For the first and fourth scenarios, the AP is preferably
configured to operate in an IEEE 802.11 compliant system wherein
the transceiver is configured to use predetermined frame formats.
The processor is then preferably configured to direct the
transceiver to transmit re-association requests in directed
re-association request (DRRq) frames, to receive re-association
indications in directed re-association indication (DRI) frames, to
receive reconfiguration confirmations in directed re-association
confirmation (DRCf) frames and to receive decisions regarding
re-association in directed re-association response (DRRsp)
frames.
[0069] Although the features and elements of the present invention
are described in the preferred embodiments in particular
combinations, each feature or element can be used alone (without
the other features and elements of the preferred embodiments) or in
various combinations with or without other features and elements of
the present invention.
* * * * *