U.S. patent application number 11/534190 was filed with the patent office on 2007-12-20 for techniques for wireless deployment.
This patent application is currently assigned to IBAHN GENERAL HOLDINGS CORPORATION. Invention is credited to Michael David Drews, Wael R. Midani, Gary L. Smith, John Thomas Welch.
Application Number | 20070291711 11/534190 |
Document ID | / |
Family ID | 38861456 |
Filed Date | 2007-12-20 |
United States Patent
Application |
20070291711 |
Kind Code |
A1 |
Welch; John Thomas ; et
al. |
December 20, 2007 |
TECHNIQUES FOR WIRELESS DEPLOYMENT
Abstract
A variety of techniques are described in which wireless access
points or base stations are deployed in wireless networks to
achieve geographic isolation, i.e., distinct zones of operation
having well-defined geographic boundaries, and increased overall
capacity in an area having a high population of access and client
devices.
Inventors: |
Welch; John Thomas; (Orem,
UT) ; Smith; Gary L.; (Lindon, UT) ; Drews;
Michael David; (Sandy, UT) ; Midani; Wael R.;
(West Valley, UT) |
Correspondence
Address: |
BEYER WEAVER LLP
P.O. BOX 70250
OAKLAND
CA
94612-0250
US
|
Assignee: |
IBAHN GENERAL HOLDINGS
CORPORATION
South Jordan
UT
|
Family ID: |
38861456 |
Appl. No.: |
11/534190 |
Filed: |
September 21, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60813993 |
Jun 14, 2006 |
|
|
|
Current U.S.
Class: |
370/338 |
Current CPC
Class: |
H04W 48/18 20130101;
H04W 88/08 20130101; H04W 48/20 20130101; H04B 15/00 20130101; H04B
7/10 20130101; H04W 48/02 20130101; H04W 16/18 20130101 |
Class at
Publication: |
370/338 |
International
Class: |
H04Q 7/24 20060101
H04Q007/24 |
Claims
1. A wireless network, comprising a plurality of access devices for
enabling wireless access to the network by a plurality of client
devices, a first one of the access devices being configured to
inhibit association of the client devices with the first access
device at data rates below a predetermined data rate, thereby
creating a zone of operation outside of which the client devices
are unlikely to associate with the first access device.
2. The wireless network of claim 1 wherein each of the access
devices is configured to transmit probes to the client devices and
to receive responses from the client devices corresponding to the
probes, the first access device further being configured to inhibit
association of the client devices with the first access device
where receipt of the responses occurs more than a predetermined
time period after transmission of the corresponding probes.
3. A wireless network, comprising a plurality of access devices for
enabling wireless access to the network by a plurality of client
devices, each of the access devices being configured to transmit
probes to the client devices and to receive responses from the
client devices corresponding to the probes, a first one of the
access devices being configured to inhibit association of the
client devices with the first access device where receipt of the
responses occurs more than a predetermined time period after
transmission of the corresponding probes, thereby creating a zone
of operation outside of which the client devices are unlikely to
associate with the first access device.
4. A wireless network, comprising a plurality of access devices for
enabling wireless access to the network by a plurality of client
devices, each of the access devices being configured to transmit
probes to the client devices and to receive responses from the
client devices corresponding to the probes, a first one of the
access devices being configured to determine distances from the
first access device to the client devices with reference to time
periods associated with the probes and the corresponding
responses.
5. The wireless network of claim 4 wherein the first access device
is further configured to inhibit association of selected ones of
the client devices with the first access device where the distances
associated with the selected client devices are greater than a
predetermined distance, thereby creating a zone of operation
outside of which the client devices are unlikely to associate with
the first access device.
6. The wireless network of claim 4 wherein a first one of the
distances is from the first access device to a first one of the
client devices, and wherein second and third ones of the access
devices are configured to determine second and third distances from
the second and third access devices, respectively, to the first
client device, the wireless network further comprising a first
process operating in the network which is operable to determine a
position of the first client device with reference to the first,
second, and third distances.
7. The wireless network of claim 6 wherein the first process is
further operable to facilitate association of the first client
device with one of the access devices with reference to the
position of the first client device.
8. A wireless network, comprising a plurality of access points for
enabling wireless access to the network by a plurality of client
devices, a first one of the access points being configured to
facilitate association of the client devices with the first access
point by broadcasting a first set of service set identifiers, the
first access point further being configured to facilitate
association of selected ones of the client devices in response to
transmissions from the selected client devices identifying
additional service set identifiers not included in the first set of
service set identifiers.
9. The wireless network of claim 8 wherein the first access device
is further configured to inhibit association of the client devices
with the first access device at data rates below a predetermined
data rate, thereby creating a zone of operation outside of which
the client devices are unlikely to associate with the first access
device.
10. The wireless network of claim 9 wherein each of the access
devices is configured to transmit probes to the client devices and
to receive responses from the client devices corresponding to the
probes, the first access device further being configured to inhibit
association of the client devices with the first access device
where receipt of the responses occurs more than a predetermined
time period after transmission of the corresponding probes.
11. The wireless network of claim 8 wherein each of the access
devices is configured to transmit probes to the client devices and
to receive responses from the client devices corresponding to the
probes, the first access device further being configured to inhibit
association of the client devices with the first access device
where receipt of the responses occurs more than a predetermined
time period after transmission of the corresponding probes, thereby
creating a zone of operation outside of which the client devices
are unlikely to associate with the first access device.
12. The wireless network of claim 8 wherein each of the access
devices is configured to transmit probes to the client devices and
to receive responses from the client devices corresponding to the
probes, the first access device further being configured to
determine distances from the first access device to the client
devices with reference to time periods associated with the probes
and the corresponding responses, a first one of the distances being
from the first access device to a first one of the client devices,
and wherein second and third ones of the access devices are
configured to determine second and third distances from the second
and third access devices, respectively, to the first client device,
the wireless network further comprising a first process operating
in the network which is operable to determine a position of the
first client device with reference to the first, second, and third
distances.
13. The wireless network of claim 12 wherein the first process is
further operable to facilitate association of the first client
device with one of the access devices with reference to the
position of the first client device.
14. A wireless network, comprising a plurality of access devices
for enabling wireless access to the network by a plurality of
client devices, first ones of the access devices being configured
to transmit signals having a first polarization, and second ones of
the access devices being configured to transmit signals having a
second polarization different from the first, wherein the first and
second access devices are deployed to mitigate friendly
interference among the access devices.
15. The wireless network of claim 14 wherein the first polarization
comprises a clockwise polarization and the second polarization
comprises a counter-clockwise polarization.
16. The wireless network of claim 14 wherein the first and second
access devices are deployed to provide a high-noise environment for
the client devices such that each of the client devices tends to
migrate to a nearest one of the first and second access devices.
Description
RELATED APPLICATION DATA
[0001] The present application claims priority under 35 U.S.C.
119(e) to U.S. Provisional Patent Application No. 60/813,993 for
TECHNIQUES FOR WIRELESS DEPLOYMENT TO MAXIMIZE CAPACITY AND
GEOGRAPHIC ISOLATION filed on Jun. 14, 2006 (Attorney Docket No.
STSNP009P), the entire disclosure of which is incorporated herein
by reference for all purposes.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to wireless networks and, in
particular, to a variety of techniques for the deployment and
operation of access points in wireless networks to improve capacity
and geographic isolation.
[0003] Wireless networks typically employ egress/access devices,
commonly referred to as access points, which form points of
presence for client radio devices. An access point may act alone in
its function but is often deployed in an array or cellular
structure with predictable and overlapping coverage from cell to
cell. Client devices act as end-points for telemetry and data
transferred to and from access points, or as processing points for
the telemetry. In a conventional wireless network having multiple
access points, a client device will typically associate with the
access point for which it experiences the most favorable
signal-to-noise ration (SNR). The client will then attempt to
remain associated with that access point for as long as possible
(e.g., by tuning down the data transfer rate).
[0004] To avoid interference between adjacent access points,
conventional wireless networks often employ different channels
within the RF band of interest for different access points, e.g.,
channels 1, 6, and 11 in the RF band associated with IEEE 802.11,
the set of standards relating to wireless local area networks.
Careful control of the signal intensities for adjacent access
points is also used to reduce the likelihood that the access points
will interfere with each other.
[0005] In a wireless network based on IEEE 802.11 or similar
technologies, it is desirable that client devices be able to roam
seamlessly from one access point to another. In some applications,
it is also desirable to provide and support a variety of
functionalities including, for example, independent data paths,
multiple data types, independent user permissions, and independent
security protocols allowing or restricting access or content based
on geographic or venue locations within an environment which may
offer little restriction to radio frequency propagation. For
example, it may be desirable to enable a user at a venue with the
proper permissions to roam from a public area such as a hallway or
lobby into a meeting room or convention area. In these new areas
the user would then have access to data and permissions not allowed
or available in the public area. The capability of restricting the
area of influence or usability by defining strict geographic
boundaries, i.e., geographic isolation, enhances or enables a wide
variety of services such as, for example, E-911, Point location
(i.e., a "You Are Here" service), billing by location, traffic
management, data security, access control, etc.
[0006] Geographic isolation may be conventionally achieved by
restricting the broadcast power of the transmitting access point or
base station, and in some circumstances the transmitting power of
the client devices. In some applications the Effective Isotropic
Radiated Power (EIRP) of both the access point and client device
may be restricted. This approach is highly effective in large open
areas but breaks down in confined areas such as inside buildings or
dense urban environments in which "canyon effects" tend to deduct
signal.
[0007] In some applications, the attenuation presented by
structures in the environment may not present a substantial barrier
to signal propagation. This may be especially true, for example, in
conference or office environments that may only be separated by
glass, or thin, movable partitions. It is often not technically
feasible to "dial down" the power of a transceiver to the point
where it would continue to be useful in its intended area without
transmitting beyond such barriers. In addition, reducing the
transmission power of access points increases areas of shadow (or
signal detected from other access points), while decreasing the
ratio of signal to noise. These are both undesirable results in
that they increase the likelihood that a client device might roam
to an out-of-area access point. And even where this technique may
be used successfully, it can be easily defeated by the use of
relatively hi-gain antennas on client devices that enable reaching
far beyond the intended area of geographic isolation.
[0008] Accurate determination of the location of client devices may
also be used to achieve the goals associated with geographic
isolation. That is, if the position of a client device is known
within an environment, access to services may be controlled on that
basis. Presently, wireless systems and devices rely on averaged
signal strength from a known source point for location telemetry.
The accuracy of the location can be improved upon, by a process
known as triangulation. Triangulation is a process by which the
location of a radio transmitter can be determined by measuring
either the radial distance, or the direction, of the received
signal from three different points. For example, the distance to a
cell phone may be determined by measuring the relative time delays
of the normal communications signal from the phone to three
different base stations. Signal strength measurements in
combination with triangulation have proven to be quite accurate in
open environments. However, closed environments such as building
interiors and dense urban areas present conditions which seriously
degrade the efficacy of such techniques.
[0009] That is, the combination of reflection, refraction,
multi-path, and signal absorption in such environments form complex
boundary conditions making position predictions based on signal
strength and triangulation tricky and often inaccurate. Methods to
correct for these effects involve highly complex modeling and
mapping of signal levels in the environment. And unfortunately,
this time consuming and expensive "correction" falls apart if even
a small change occurs from the baseline mapping. These small
changes include thing like a door opening or closing, a curtain
being opened exposing a reflective pane of glass, or even something
as innocuous as the variable flow of water in plumbing.
[0010] Another conventional approach to determining the location of
client devices is accomplished using global positioning systems
(GPS) technologies. Unfortunately, such technologies are not always
reliable inside buildings or in dense urban environments in that
the reach of GPS equipment is limited by the attenuation caused by
surrounding structures. GPS solutions also involve the use of
secondary equipment, increasing system costs and introducing an
additional point of failure.
[0011] In view of the foregoing, it is desirable to provide
improved techniques for deploying wireless access points, base
stations and the like.
SUMMARY OF THE INVENTION
[0012] According to a specific embodiment of the present invention
a wireless network is provided which includes a plurality of access
devices for enabling wireless access to the network by a plurality
of client devices. A first one of the access devices is configured
to inhibit association of the client devices with the first access
device at data rates below a predetermined data rate, thereby
creating a zone of operation outside of which the client devices
are unlikely to associate with the first access device.
[0013] According to another specific embodiment, a wireless network
is provided which includes a plurality of access devices for
enabling wireless access to the network by a plurality of client
devices. Each of the access devices is configured to transmit
probes to the client devices and to receive responses from the
client devices corresponding to the probes. A first one of the
access devices is configured to inhibit association of the client
devices with the first access device where receipt of the responses
occurs more than a predetermined time period after transmission of
the corresponding probes, thereby creating a zone of operation
outside of which the client devices are unlikely to associate with
the first access device.
[0014] According to yet another specific embodiment, a wireless
network is provided which includes a plurality of access devices
for enabling wireless access to the network by a plurality of
client devices. Each of the access devices is configured to
transmit probes to the client devices and to receive responses from
the client devices corresponding to the probes. A first one of the
access devices is configured to determine distances from the first
access device to the client devices with reference to time periods
associated with the probes and the corresponding responses.
According to one such embodiment, the first access device is
further configured to inhibit association of selected ones of the
client devices with the first access device where the distances
associated with the selected client devices are greater than a
predetermined distance, thereby creating a zone of operation
outside of which the client devices are unlikely to associate with
the first access device.
[0015] According to another such embodiment, a first one of the
distances is from the first access device to a first one of the
client devices. Second and third ones of the access devices are
configured to determine second and third distances from the second
and third access devices, respectively, to the first client device.
A first process operating in the network is operable to determine a
position of the first client device with reference to the first,
second, and third distances. According to an even more specific
embodiment, the first process is further operable to facilitate
association of the first client device with one of the access
devices with reference to the position of the first client
device.
[0016] According to a still further embodiment, a wireless network
is provided which includes a plurality of access points for
enabling wireless access to the network by a plurality of client
devices. A first one of the access points is configured to
facilitate association of the client devices with the first access
point by broadcasting a first set of service set identifiers. The
first access point is further configured to facilitate association
of selected ones of the client devices in response to transmissions
from the selected client devices identifying additional service set
identifiers not included in the first set of service set
identifiers.
[0017] According to yet a further specific embodiment, a wireless
network is provided which includes a plurality of access devices
for enabling wireless access to the network by a plurality of
client devices. First ones of the access devices are configured to
transmit signals having a first polarization. Second ones of the
access devices are configured to transmit signals having a second
polarization different from the first. The first and second access
devices are deployed to mitigate friendly interference among the
access devices. According to a more specific embodiment, the first
and second polarizations are clockwise and counter-clockwise
polarizations. According to another more specific embodiment,
deployment of the first and second access devices results in a
high-noise environment for the client devices such that each of the
client devices tends to migrate to a nearest one of the first and
second access devices.
[0018] A further understanding of the nature and advantages of the
present invention may be realized by reference to the remaining
portions of the specification and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a simplified network diagram of an exemplary
wireless local area network in which embodiments of the present
invention may be implemented.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0020] Reference will now be made in detail to specific embodiments
of the invention including the best modes contemplated by the
inventors for carrying out the invention. Examples of these
specific embodiments are illustrated in the accompanying drawings.
While the invention is described in conjunction with these specific
embodiments, it will be understood that it is not intended to limit
the invention to the described embodiments. On the contrary, it is
intended to cover alternatives, modifications, and equivalents as
may be included within the spirit and scope of the invention as
defined by the appended claims. In the following description,
specific details are set forth in order to provide a thorough
understanding of the present invention. The present invention may
be practiced without some or all of these specific details. In
addition, well-known features may not have been described in detail
to avoid unnecessarily obscuring the invention.
[0021] FIG. 1 is a simplified network diagram of an exemplary
wireless local area network 100 in which embodiments of the present
invention may be implemented. Wireless access points 102 in
conjunction with switch 103 provide access to network 100 to a
variety of client devices. It should be noted at the outset that
the equipment and network configuration shown merely represent one
example of the wide variety of environments in which the invention
may be practiced. For example, wireless access points 102 may be
implemented according to any of IEEE 802.11b, 802.11g, 802.11a,
802.16, etc., and may represent products provided by suppliers such
as, for example, Colubris Networks of Waltham, Mass., or Cisco
Systems of San Jose, Calif. Additionally, the connection between
access points 102 and the network (as represented by switch 103
which may itself represent one or more of a wide variety of
switches and routers) is represented as wireless, but may be wired.
In general, the techniques described herein are more widely
applicable and should not be limited to the network configurations,
standards, or vendors referred to herein.
[0022] In addition, the various functionalities described herein
may be implemented in a variety of ways. For example, various
aspects of these functionalities may be implemented in hardware,
firmware, or software associated with the various devices in a
wireless network. These devices include wireless access points or
base stations, associated computing devices (e.g., servers and
switches), and, in some cases, the client devices operating in the
network. The functionalities may be performed or controlled by a
single device, or may be performed in a distributed manner by more
than one device in the network. Thus, although exemplary
embodiments described herein may refer to particular approaches to
implementing the various functionalities of the invention, those of
skill in the art will understand that these references are not
intended to limit the invention.
[0023] It should also be noted that, as used herein, the term
"client device" refers to any of a wide variety of devices which
operate in a wireless network including, for example, any type of
wireless computing device (e.g., laptops, handheld devices, etc.),
any type of wireless telecommunications device (e.g., cell phones,
messaging clients, etc.), inventory devices (e.g., point-of-sale,
bar code scanners, etc.), or devices performing functions as
peripherals to standard or common digital or analog systems.
[0024] According to various embodiments of the invention,
techniques are provided which may be used individually or in
various combinations to implement functionalities typically
associated with geographic isolation in complex wireless
environments, e.g., providing different levels of access or service
in well-defined geographic zones of operation. In contrast with
conventional approaches which attempt to mitigate the effects of
noisy environments, some of the embodiments of the invention
actually take advantage of low signal-to-noise ratios and signal
distortion to achieve these functionalities. For example, according
to some embodiments, signal interference and/or signal distortion
may cause client devices to disassociate from access points or base
stations in predictable and intended ways even in the presence of
very high signal levels.
[0025] In systems employing IEEE 802.11 or similar wireless
technologies, each session for packet transfer, including the
connection data rate, is negotiated between the client and the
wireless access point. That is, the client and the access point
negotiate the data rate on a packet-by-packet basis. Therefore,
according to a specific embodiment of the invention, restricting
the data rate at which a client is allowed to associate controls
the usable sphere of influence or operational zone of the access
point.
[0026] As will be understood, it is difficult for a client to
maintain a data rate of 11 Mbps (802.11b) or 54 Mbps (802.11a,
802.11g) connecting to an access point through an obstruction; even
a window or thin partition. As the signal passes through a barrier
it is distorted due to reflection and refraction from the barrier
regardless of the strength of the signal. These effects are further
exacerbated by the "noise" associated with other nearby access
points. Thus, by enforcing a minimum data transfer rate, when the
client leaves a hotel conference room, for example, it cannot "turn
down" the data transfer rate to stay associated with the access
point in the conference room and so will disconnect as desired.
[0027] According to some embodiments, the ability to enforce a
minimum data transfer rate may be enabled using existing access
point features which provide control over the data transfer rate.
For example, some access points may be configured to set a maximum
data rate for QoS purposes, i.e., to keep some devices from
starving other devices. Such a feature may also facilitate
compatibility with certain client devices that only handle specific
data rates (i.e., as opposed to all the rates specified by the
standards). As will be understood, this minimum data rate may be
adjusted so that the usable area is appropriate for the room
configuration or the desired geographic zone size.
[0028] An example may be illustrative. A client device 104 may
initially be associated with an access point 102-1 with a strong
signal in the public area 106 of a hotel. The client 104 then
wanders into another area (e.g., a private meeting room 108 with
different security, permissions, and access rules) while still
associated to the public area access point 102-1. Because of the
noise and/or distortion caused by the physical barriers (even low
attenuation barriers) and competing access points (e.g., lost node
scenario), the client device 104 breaks its connection with the
public area access point 102-1 within a few packets (regardless of
its data rate or, to a large margin, link strength) and probes for
available access points for its service set identifier (SSID). When
an access point receives the probe, it advertises its availability,
and subsequently the access point and client device initiate the
procedures for association and authentication.
[0029] Due to its closer proximity, the private meeting area access
point 102-2 (i.e., the access point or one of a group of access
points intended for that private meeting area) is the first to
respond (i.e., the near/far scenario). The client then associates
to the closer (i.e., the private meeting area) access point 102-2
and becomes party to the permissions, restrictions, security, and
benefits associated with that geographic operational zone. Some
time later the client device 104 may physically leave the area by
simply passing through an exit. Then, due to the signal attenuation
and distortions caused by the environment's boundary conditions
(e.g., physical barriers and reflective/multipath conditions) the
client 104 is incapable of sustaining the predetermined connection
data rate (e.g., 11 or 54 Mb under 802.11b and 802.11a/g
respectively). And because the private area access point 102-2 is
configured to refuse any lower data rates, the client is forced
back to the public area access point 102-1.
[0030] According to another specific embodiment of the invention,
the operational zone of an access point is controlled with
reference to the amount of time required for round trip
communications between the access point and associated client
devices. Everything between an access point and a client device
involves some form of a handshake. Often this takes the form of a
probe and response, e.g., an acknowledgment (ACK) request to and an
ACK response from the client device, and is handled on the PHY
(tertiary) level of the device technology. As dictated by the laws
of physics relating to signal propagation, the round trip time of
these handshakes, e.g., the time required for an ACK response from
the client, represents the distance from the access point.
Therefore, according to a specific embodiment of the invention,
where the client is further than some distance from the access
point, e.g., the ACK response takes longer than some programmable
time period, the client is not allowed to associate (or continue to
associate) with the access point.
[0031] According to a specific embodiment, the ACK response time of
the access point (e.g., 102-3) is manipulated such that client
devices (e.g., device 110) outside of a desired range 114 are
unable to respond to an ACK from the access point 102-3 within the
response time, while client devices inside range 114 (e.g., device
116) can. This approach makes it possible to significantly limit
the range of an access point (i.e., the access point will not wait
long enough for a distant client's response to reach it), while
still providing a high enough RF signal to account for shadows or
weak spots within the intended coverage area of the access point
(e.g., meeting room 117).
[0032] According to yet another specific embodiment, the
operational zone of an access point is again defined with reference
to the amount of time required for round trip communications
between the access point and associated client devices. According
to this approach, the response time is used to determine the
distance to the client (as opposed to simply setting the acceptable
response time to prevent associations). This distance is then used
to make decisions such as, for example, determining whether or not
a connection will be allowed or maintained. In IEEE 802.11 systems,
the Logical Link Control (LLC) and Media Access Control (MAC)
layers employ at least five distribution services which can be
exploited for such information. The simplest is the wait state
which is controllable and can be monitored at the PHY level. The
advantage of this approach is that it can be implemented and/or
manipulated at the lowest network level, therefore requiring less
processing time. However, any probe and response may be employed
for this purpose.
[0033] A numerical example may be illustrative. When a TCP packet
is transmitted in an IEEE 802.11 network, the receiving device
sends an ACK 212.18 .mu.s after receiving the packet. This
represents the time required by the receiving device to process an
18 byte preamble (144 .mu.s), a 6 byte header (48 .mu.s), 14 bytes
of ACK data (10.18 .mu.s), and interface space (10 .mu.s). If the
round trip time as measured by the transmitting device is 213.3
.mu.s, this represents a signal propagation time to the receiver
and back of 01.12 .mu.s (1120 .eta.s). Because the distance between
the transmitting and receiving devices is the measurement needed,
the travel time is divided by two 1120 .eta.s/2=560 .eta.s. Because
radio waves propagate about 11.8 inches in 1 .eta.s, the distance
between the devices is approximately 560.times.11.8/12=550.7 feet.
An access point may therefore be set, for example, to deny a client
access or to terminate a connection if the client is over 400 feet
away (i.e., if round trip time for the probe/ACK is longer than
212.99 .mu.s after the probe is sent). The client is then forced to
associate with an alternate access point. According to some
implementations, reflections due to barriers will add small travel
time to the wave front and may need to be accounted for.
[0034] According to some embodiments, the distances a, b, and c of
a client 118 from multiple access points (e.g., 102-1, 102-4, and
102-5) may be determined. These distances may then be employed
(e.g., by an agent (e.g., server 120) in communication with the
multiple access points) to determine a position of the client (as
opposed to a linear distance from a particular access point) so
that a decision may be made based on the client's position as to
which AP the client should associate with, and/or the types of
services to be made available to the client. The determination of
position may be done to varying degrees of precision and may be
accomplished, for example, using any of a wide variety of
triangulation algorithms known in the art.
[0035] As will be appreciated with reference to the above-described
embodiments, a wireless network may be constructed according to the
invention in which multiple access points or base stations operate
in well-defined geographic zones of operation. However, in some
situations, circumstances beyond the control of the network
provider may interfere with such carefully configured environments.
For example, a network configured in accordance with the invention
may be deployed in a hotel, but a wireless hotspot in an adjacent
coffee house might flood the carefully constructed network with its
transmissions. Because FCC regulations prohibit the jamming of such
signals, it is likely that devices associated with hotel guests may
request connection to the SSID associated with the coffee house
access point instead of one of the access points in the hotel.
[0036] One approach to this problem would be to configure the
hotel's access points to respond to a client's response to a probe
from the coffee house access point. However, current
top-of-the-line access points only allow specification of limited
number of SSIDs. Given that SSIDs are specified with up to 32
alphanumeric characters, such an approach would undesirably force
the hotel to use the SSIDs of the adjacent businesses rather than
the ones they would like to use. Therefore, according to a specific
embodiment, wireless access points implemented in accordance with
the invention are enabled to accept connections from client devices
even where the requested SSID is not one of the ones specified for
those access points. This "wild card" response to any SSID probe
makes it virtually impossible for any client device to associate
with an access point out of the desired area. That is, the access
points within the desired area will respond to probes from the
client devices before the access points outside of the desired
area, and the client devices will associate preferentially with the
access point that responds first. This will effectively circumvent
any attempt to associate with the access point outside of the
desired area, and will increase the number of devices and network
traffic for the access points inside the desired area. According to
more specific embodiments, the foregoing approach may be employed
in combination with one or more geographic area restriction
techniques to inhibit devices outside of the desired area from
associating with access points within the desired area.
[0037] As mentioned above, the approaches to geographic isolation
and client location described herein may be used individually or in
various combinations to achieve the desired zone of operation
and/or related functionality. For example, it is clear from FIG. 1
that the range 114 defined around access point 102-3 extends into
the adjacent meeting room 108 and the public area 106. That is, the
geographic zone defined by the single technique relating to device
response time defines a spherical region around access point 102-3
which extends beyond the intended coverage area, i.e., meeting room
117. However, if this technique is combined with the technique in
which a minimum or specific data rate is enforced (e.g., as
described above with reference to meeting room 108), this could
have the effect of eliminating the portions of the spherical zone
represented by range 114 outside of room 117. That is, because
client devices outside of room 117 will not be able to sustain the
data rate required by access point 102-3 (e.g., because of the
intervening walls), they will not be able to associate with that
access point even if they are within range 114.
[0038] In another example, the technique described above in which
the position of client device 118 is determined may be combined
with the response time technique to improve the reliability with
which the geographic isolation and related functionality may be
effected. That is, in addition to determining which access point
with which client 118 should associate, the association would only
be allowed if client 118 was able to respond to the selected access
point within the programmed response time.
[0039] As will be understood, the foregoing combinations are
described by way of example. A variety of other combinations of the
described techniques and their equivalents and variants will be
apparent to those of skill in the art and are therefore included
within the scope of the invention.
[0040] Due to the limited capacity of and high demands placed on
wireless access points, it is often necessary to provide additional
access points in some applications in order to better serve the
volume of client devices. However, a problem arises relating to
interference between and among closely spaced access points (often
referred to as "friendly" system noise). This interference can
result in protection mechanisms (e.g., clear to send/clear to
receive cycles, or carrier sense multiple access) being enabled
which, in turn, cause the network to slow down. In addition, such
interference can compromise data integrity, causing packet retries
and thereby further reducing system performance.
[0041] As mentioned above, current practice is to select different
channels for closely spaced access points to minimize interference
(e.g., use of channels 1, 6, and 11 in the 802.11b/g band are often
recommended by manufacturers for this purpose because they do not
overlap). However, such an approach is not adequate for the access
point densities required in some applications. Therefore, according
to various embodiments of the present invention, the number and/or
density of access points is increased by the reduction of friendly
system noise to the access points while allowing a high level of
friendly system to the clients through the use of mixed
polarizations.
[0042] Transmitted radio signals reflect off objects creating a
condition called "multi-path" in which a signal follows several
paths to the receiver. On long point-to-point radio links
stratification of the atmosphere can create multiple paths by
refracting the signal. Because of their longer path lengths, these
reflected or refracted signals take longer to arrive at the
receiver where they can interfere with the main signal. It is
common for wireless systems to combine polarization diversity with
spatial diversity to take advantage of the multi-path condition.
This requires the installation of two antennas separated vertically
or horizontally. Vertical separation works well for longer
free-space line-of-sight links, while horizontal separation works
best for partially obstructed or non-line-of-sight links. The
signals received by both antennas are combined to enhance the
quality of the signal where multi-path exists. Mixed polarization
has been a common practice since the 1940s, and has been used as a
form of diversity in order to clear up signals, or in some cases to
co-locate like systems on a single structure for point-to-point
applications or for radar.
[0043] According to specific embodiments of the invention, adjacent
or closely spaced access points or base stations in a wireless
network are configured with different polarizations to enable
denser placement of these devices and to thereby increase the
capacity of the system. According to a specific embodiment,
opposing circular polarizations (e.g., clockwise and
counter-clockwise) are employed. In such an implementation,
transmissions from an antenna with a clockwise polarization have a
theoretical rejection ratio approaching 29 dB (and a practical
rejection ratio of 20 dB) when received by an antenna using a
counter-clockwise polarization. Embodiments of the invention take
advantage of this rejection ratio to reduce the likelihood of
friendly interference at the access point, thus increasing the
number of access points that can be deployed in a given
environment.
[0044] As mentioned above, client devices make the decision to
handoff from one access point to another based on the
signal-to-noise ratio they experience, thus allowing them to select
the most appropriate access point in a cluttered environment. As
such, a reduction of noise as experienced by the client device in
such an environment is undesirable. Fortunately, the mixed
polarization approach of the present invention does not reduce the
noise at the client. In some cases, such embodiments result in a
high noise environment for the client devices which, in turn,
advantageously causes the client devices to migrate to closer or
less populated access points or base stations.
[0045] While the invention has been particularly shown and
described with reference to specific embodiments thereof, it will
be understood by those skilled in the art that changes in the form
and details of the disclosed embodiments may be made without
departing from the spirit or scope of the invention. For example,
the mixed polarization technique described above could be combined
with any of the geographic isolation and client location techniques
described herein to implement a wireless network with high capacity
and well-defined zones of operation.
[0046] And despite references to a hotel environment, it will be
understood that the techniques described herein may be applied in a
wide variety of wireless network environments. For example,
wireless networks in manufacturing and warehouse facilities could
be improved using any of the techniques described herein. In
addition, the various techniques of the present invention may be
applied to wireless networks implemented with technologies outside
of the IEEE 802.11 family of standards, e.g., wireless
telecommunications networks.
[0047] Finally, although various advantages, aspects, and objects
of the present invention have been discussed herein with reference
to various embodiments, it will be understood that the scope of the
invention should not be limited by reference to such advantages,
aspects, and objects. Rather, the scope of the invention should be
determined with reference to the appended claims.
* * * * *