U.S. patent application number 11/784651 was filed with the patent office on 2007-08-16 for method and apparatus for antenna steering for wlan.
This patent application is currently assigned to IPR Licensing, Inc.. Invention is credited to John E. Hoffmann, Kevin P. Johnson, George Rodney JR. Nelson, John A. Regnier.
Application Number | 20070189325 11/784651 |
Document ID | / |
Family ID | 32511352 |
Filed Date | 2007-08-16 |
United States Patent
Application |
20070189325 |
Kind Code |
A1 |
Hoffmann; John E. ; et
al. |
August 16, 2007 |
Method and apparatus for antenna steering for WLAN
Abstract
A Station Management Entity (SME) steers a directional antenna
for a station to communicate with an Access Point (AP) in an 802.11
protocol system. The SME can steer the antenna before or after an
802.11 station has authenticated and associated with the Access
Point. During a passive scan, the steering process cycles through
the available antenna positions and monitors an AP beacon signal to
determine a best position based on, for example, a Received Signal
Strength Indication (RSSI). During an active scan where access
probing is used, the steering process cycles through the antenna
positions and monitors a probe response to determine the best
antenna position. Additional scans may be performed based on a
decision that the received signal level of the currently selected
antenna position has dropped below a predetermined threshold.
Inventors: |
Hoffmann; John E.;
(Indialantic, FL) ; Nelson; George Rodney JR.;
(Merritt Island, FL) ; Regnier; John A.; (Palm
Bay, FL) ; Johnson; Kevin P.; (Palm Bay, FL) |
Correspondence
Address: |
VOLPE AND KOENIG, P.C.;DEPT. ICC
UNITED PLAZA, SUITE 1600
30 SOUTH 17TH STREET
PHILADELPHIA
PA
19103
US
|
Assignee: |
IPR Licensing, Inc.
Wilmington
DE
|
Family ID: |
32511352 |
Appl. No.: |
11/784651 |
Filed: |
April 9, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10675563 |
Sep 30, 2003 |
7212499 |
|
|
11784651 |
Apr 9, 2007 |
|
|
|
60414946 |
Sep 30, 2002 |
|
|
|
Current U.S.
Class: |
370/464 |
Current CPC
Class: |
H04B 17/318 20150115;
H04B 7/088 20130101 |
Class at
Publication: |
370/464 |
International
Class: |
H04J 15/00 20060101
H04J015/00 |
Claims
1. A method for operating a directional antenna in a wireless
communication system comprising: causing metrics for each of a
plurality of antenna angles to be calculated in a medium access
control (MAC) layer; providing said metrics to a Station Management
Entity (SME) separate from said MAC layer; and directing the
antenna to a best antenna angle based on input from said SME.
2. The method of claim 1, further comprising receiving in the MAC
layer an access point signal for each antenna angle; said access
point signal used to calculate each of said metrics.
3. The method of claim 2, wherein each of said access point signals
is received from a respective access point.
4. The method of claim 3, further comprising accessing the access
point associated with said best antenna angle in said MAC
layer.
5. The method of claim 2, wherein said access point signal is a
beacon signal.
6. The method of claim 5, further comprising measuring said beacon
signal.
7. The method of claim 6, wherein said best antenna angle is based
on a signal quality measurement of said beacon signal.
8. The method of claim 7, wherein the signal quality measurement
includes at least one of the following: signal-to-noise ratio
(SNR), energy-per-bit per total noise (Eb\No), received signal
strength indicator (RSSI), and a carrier to interference ratio
(C\I).
9. The method of claim 1, wherein said MAC Layer determines the
metrics as a function of received energy by the directional antenna
in the antenna angles.
10. A mobile station in a wireless communication system comprising:
a Station Management Entity (SME) for directing a directional
antenna to a best antenna angle; said best antenna angle determined
using metrics calculated in a Medium Access Control (MAC) layer,
external to said SME, for each of a plurality of antenna
angles.
11. The mobile station of claim 10, further comprising an antenna
control unit coupled to the directional antenna that receives input
from said SME based on said metrics.
12. The mobile station of claim 11, wherein an access point signal
is received by the MAC layer for each of said antenna angles, said
access point signal used by said MAC layer to calculate each of
said metrics.
13. The mobile station of claim 11, wherein the SME causes said MAC
layer to calculate said metrics.
14. The mobile station of claim 13, wherein the SME causes the MAC
layer to determine the metrics, for each of the antenna angles, as
a function of energy received by the directional antenna.
15. The mobile station of claim 13, wherein the SME causes the MAC
layer to transmit a signal to the access point and to measure a
response from the access point.
16. The mobile station of claim 12, wherein said access point
signal is a beacon signal.
17. The mobile station of claim 16, further comprising measuring
said beacon signal.
18. The mobile station of claim 17, wherein said best antenna angle
is based on a signal quality measurement of said beacon signal.
19. The mobile station of claim 18, wherein the signal quality
measurement includes at least one of the following: signal-to-noise
ratio (SNR), energy-per-bit per total noise (Eb\No), received
signal strength indicator (RSSI), and a carrier to interference
ratio (C\I).
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/675,563 filed on Sep. 30, 2003 which claims
the benefit of U.S. Provisional Application No. 60/414,946 filed on
Sep. 30, 2002. The entire teachings of the above applications are
incorporated herein by reference.
BACKGROUND
[0002] The 802.11 Institute of Electrical and Electronic Engineers
(IEEE) standards defines a specification for stations to be moved
within a facility and remain connected to a Wireless Local Area
Network (WLAN) via Radio Frequency (RF) transmissions to Access
Points (AP) connected to a wired network. A physical layer in the
stations and access points controls the modulation and signaling
format used by the stations and access points to communicate. Above
the physical layer is a Medium Access Control (MAC) layer that
provides services such as authentication, deauthentication,
privacy, association, disassociation, etc.
[0003] In operation, when a station comes on-line, the physical
layer in the station and access points first establish wireless
communication with each other, followed by the MAC layer
establishing access to the network via an access point.
[0004] Typically, in 802.11 stations or access points, the signals
are RF signals, transmitted and received by monopole antennas. A
monopole antenna provides transmissions in all directions generally
in a horizontal plane. Monopole antennas are susceptible to effects
that degrade the quality of communication between the station and
access points, such as reflection or diffraction of radio wave
signals caused by intervening walls, desks, people, etc.,
multipath, normal fading, Rayleigh fading, and so forth. As a
result, efforts have been made to mitigate signal degradation
caused by these effects.
[0005] A technique known as "antenna diversity" counteracts the
degradation of RF signals. Antenna diversity uses two antennas that
are connected to a transmitter/receiver via an antenna diversity
switch. The theory behind using two antennas for antenna diversity
is that, at any given time, one of the two antennas is likely
receiving a signal that is not affected by the effects of, say,
multi-path fading. The system using the two antennas selects the
unaffected antenna via the antenna diversity switch.
SUMMARY
[0006] Using antenna diversity techniques, signal degradation
caused by multi-path fading or other effects that reduce RF signal
quality can be improved by selecting the diversity antenna that is
receiving the RF signal at a higher strength. However, each of the
diversity antennas is an omni-directional antenna (e.g., monopole
antenna), so the system employing the antenna cannot steer the
antenna away from a source of interference or achieve any gain
beyond what one omni-directional antenna inherently provides.
[0007] It would be better if a station or access point using an
802.11 protocol were to use a directional antenna to improve system
performance.
[0008] Accordingly, the principles of the present invention provide
a technique for steering a directional/multi-element antenna in an
802.11 protocol system for a station to communicate with the Access
Point (AP) in an Extended Service Set (ESS) network or other
network structure having wireless access points. This approach has
minimal impact on network efficiency as the approach can be
accomplished within the current 802.11 protocols. Unless otherwise
specified, a reference herein to this "802.11 protocol" or "802.11
standard" includes the 802.11, 802.11a, 802.11b, and 802.11g
protocols and standards.
[0009] In one embodiment, the technique can come into operation
before and after an 802.11 station has authenticated and associated
with a network access point connected to a wired network. The wired
network is referred to interchangeably herein as a distribution
system. It is assumed that the initial antenna scan is accomplished
within the Medium Access Control (MAC) layer. During a passive
scan, the steering process cycles through the available antenna
positions and monitors a signal metric associated with a beacon
signal or other predetermined signal to determine a best antenna
pointing direction. During an active scan where access probing is
used, the process cycles through the antenna positions and monitors
a signal metric associated with a probe response signal to
determine the best antenna position.
[0010] Once the station has authenticated and associated with the
network, additional scans may be performed, optionally based on a
determination that the received signal level has dropped below some
threshold.
[0011] A directional antenna in a wireless local area network
(WLAN) environment results in improved range and data rates for
users and increases network efficiency for the network.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0012] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of preferred embodiments of the invention, as
illustrated in the accompanying drawings in which like reference
characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, emphasis instead being
placed upon illustrating the principles of the invention.
[0013] FIG. 1A is a schematic diagram of a wireless local area
network (WLAN) employing the principles of the present
invention;
[0014] FIG. 1B is a schematic diagram of a station in the WLAN of
FIG. 1A performing an antenna scan;
[0015] FIG. 2A is an isometric view of a station of FIG. 1A having
an external directive antenna array;
[0016] FIG. 2B is an isometric view of the station of FIG. 2A
having the directive antenna array incorporated in an internal
PCMIA card;
[0017] FIG. 3A is an isometric view of the directive antenna array
of FIG. 2A;
[0018] FIG. 3B is a schematic diagram of a switch used to select a
state of an antenna element of the directive antenna of FIG.
3A;
[0019] FIG. 4 is a flow diagram of a first process used by a
station of FIG. 1;
[0020] FIG. 5 is a flow diagram of a second process used by a
station of FIG. 1;
[0021] FIG. 6 is a flow diagram of a passive scan routine used by
the processes of FIGS. 4 and 5;
[0022] FIG. 7 is a flow diagram of an active scan routine used by
the processes of FIGS. 4 and 5; and
[0023] FIG. 8 is a diagram of software and hardware elements
executing in the station of FIG. 2A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0024] A description of preferred embodiments of the invention
follows.
[0025] FIG. 1A is a block diagram of a wireless local area network
(WLAN) 100 having a distribution system 105. Access points 110a,
110b, and 110c are connected to the distribution system 105 via
wired connections such as wired Local Area Networks (LANs). Each of
the access points 110 has a respective zone 115a, 115b, 115c in
which it is capable of transmitting and receiving RF signals to and
from stations 120a, 120b, and 120c, which are supported with
Wireless Local Area Network (WLAN) hardware and software to access
the distribution system 105.
[0026] FIG. 1B is a block diagram of a subset of the network 100 in
which the second station 120b, employing the principles of the
present invention, is shown in more detail. The second station 120b
generates directive antenna lobes 130a-130i (collectively, lobes
130) from a directive antenna array. The directive antenna array is
interchangeably referred to herein as a directional antenna. As
discussed in detail beginning in reference to FIG. 2A, the second
station 120b uses the directive antenna array to scan its
environment to determine a direction to a "best" access point 110a,
110b.
[0027] The scan may be performed in a passive mode, in which the
second station 120b listens for beacon signals emitted by the
access points 110a, 110b. In 802.11 systems, the beacon signals are
generally sent every 100 msec. So, for the nine antenna lobes 130,
the process takes about 1 second to cycle through the antenna lobe
directions and determine the best angle.
[0028] In an active scan mode, the second station 120b sends a
probe signal to the access points 110a, 110b and receives responses
to the probe signal from the access points 110a, 110b. This probe
and response process may be repeated for each antenna scan
angle.
[0029] Continuing to refer to FIG. 1B, during either a passive or
an active scan, the second station 120b uses the directive antenna
array to scan the RF airways in search of signals from the access
points 110. At each scan direction, the second station 120b
measures the received beacon signal or probe response and
calculates a respective metric for that scan angle. Examples of the
metrics include Received Signal Strength Indication (RSSI),
Carrier-to-Interference ratio (C/I), Signal-to-Noise ratio (Eb/No),
or other suitable measure of the quality of the received signal or
signal environment. Based on the metrics, the second station 120b
can determine a "best" direction to communicate with one of the
access points 110a, 110b.
[0030] The scans may occur before or after the second station 120b
has authenticated and associated with the distribution system 105.
Thus, the initial antenna scan may be accomplished within the
Medium Access Control (MAC) layer. Alternatively, the initial scan
may be accomplished external from the MAC layer. Similarly, scans
occurring after the second station 120b has authenticated and
associated with the distribution system 105 may be accomplished
within the MAC layer or by processes occurring external from the
MAC layer.
[0031] FIG. 2A is a diagram of the first station 120a that is
equipped with a directive antenna array 200a. In this embodiment,
the directive antenna array 200a is external from the chassis of
the first station 120a.
[0032] The directive antenna array 200a includes five monopole
passive antenna elements 205a, 205b, 205c, 205d, and 205e
(collectively, passive antenna elements 205) and one monopole,
active antenna element 206. The directive antenna element 200a is
connected to the first station 120a via a Universal System Bus
(USB) port 215.
[0033] The passive antenna elements 205 in the directive antenna
array 200a are parasitically coupled to the active antenna element
206 to facilitate beam angle direction changes. Changing the beam
angle direction may allow for at least one antenna beam to be
rotated 360 in increments associated with the number of passive
antenna elements 205. Less than full 360 rotations and
sub-incremental direction changes are also possible.
[0034] In some embodiments, the directive antenna array 200a
supports an omni-directional mode defined by an omni-directional or
substantially omni-directional antenna pattern (not shown). The
stations 120 may use the omni-directional antenna pattern for
Carrier Sense prior to transmission or to assess by way of
comparison current performance of directional mode versus
omni-directional mode. In an `ad hoc` network, the stations 120 may
revert to an omni-only antenna configuration since communicating
with other stations 120 can occur in any direction.
[0035] FIG. 2B is another embodiment of the first station 120a that
includes a directive antenna array 200b deployed on a Personal
Computer Memory Card International Association (PCMCIA) card 220.
The PCMCIA card 220 is disposed in the chassis of the first station
120a in a typical manner. The PCMCIA card 220 communicates with a
processor (not shown) in the first station 120a via a typical
computer bus. The directive antenna array 200b deployed as the
PCMCIA card 220 provides the same functionality as the stand-alone
directive antenna array 200a discussed above in reference to FIG.
2A.
[0036] It should be understood that various other forms of
directional antennas can be used. For example, the directive
antenna arrays 200b may include one active antenna element
electromagnetically coupled to multiple passive antenna elements.
In another embodiment, the directive antenna arrays 200 may include
multiple active and multiple passive antenna elements. In yet
another embodiment, the directive antenna arrays 200 may include
multiple active antenna elements and a single passive antenna
element. In still a further embodiment, the directive antenna
arrays 200 may include all active antenna elements.
[0037] FIG. 3A is a detailed view of the directive antenna array
200a that includes the multiple passive antenna elements 205 and
one active antenna element 206 as discussed above in reference to
FIGS. 2A and 2B. As shown in this detailed view, the directive
antenna array 200a may also include a ground plane 330 to which the
passive antenna elements 206 are electrically connected.
[0038] In operation, one state of the directive antenna array 200a
provides a directive antenna lobe 300 angled away from antenna
elements 205a and 205e. This is an indication that the antenna
elements 205a and 205e are in a "reflective" mode, and the antenna
elements 205b, 205c, and 205d are in a "transmissive" mode. In
other words, the mutual coupling between the active antenna element
206 and the passive antenna elements 205 allows the mode settings
of the passive antenna elements 205 to control the direction of the
directive antenna lobe 300. As should be understood, different mode
combinations result in different antenna lobe 300 patterns and
angles.
[0039] FIG. 3B is a schematic diagram of an example circuit that
can be used to set the passive antenna element 205a in a reflective
or transmissive mode. The reflective mode is indicated by a
representative "elongated" dashed line 305, and the transmissive
mode is indicated by a "shortened" dashed line 310. The
representative dashed lines 305 and 310 are also representative of
the electrical termination associated with the passive antenna
element 205a. For example, electrically connecting the passive
antenna element 205a to a ground plane 330 via an inductive element
320 sets the passive antenna element 205a in reflective mode, and
electrically connecting the passive antenna element 205a to the
ground plane 330 via a capacitive element 325 sets the passive
antenna element 205a in transmissive mode.
[0040] Electrically connecting the passive antenna element 205a
through the inductive element 320 or capacitive element 325, or,
more generally, a reactive element, may be done via a switch 315.
The switch 315 may be a mechanical or electrical switch capable of
electrically connecting the passive antenna element 205a to the
ground plane 330 or reactive element in a manner suitable for this
application. The switch 315 is set via a control signal 335 in a
typical switch control manner.
[0041] In the case of the directive antenna array 205a of FIG. 3A,
both passive antenna elements 205a and 205e are connected to the
ground plane 330 via respective inductive elements 320. At the same
time, in the example of FIG. 3A, the other passive antenna elements
205b, 205c, and 205d are electrically connected to the ground plane
330 via respective capacitive elements 325. Capacitively coupling
all of the passive elements 325 causes the directive antenna array
200a to form an omni-directional antenna beam pattern.
[0042] It should be understood that other electrical terminating
devices may also be used between the passive antenna elements 205
and ground plane 330, such as delay lines and lumped
impedances.
[0043] Now that a brief introduction of the 802.11 protocol and
directional antenna operation has been discussed, a detailed
discussion of steering a directional antenna through use of a
Station Management Entity (SME) and the 802.11 protocol is
presented below.
[0044] Referring now to FIG. 8, a SME 800, MAC layer 805, and
physical (PHY) layer 810 are shown in a generalized arrangement,
sometimes referred to as an 802.11 stack. In this arrangement, the
SME 800 is in communication with the MAC layer 805 and PHY layer
810. The SME 800 is a layer-independent entity that may be viewed
as a separate management plane or residing "off to the side" from
the MAC layer 805 and PHY layer 810. The SME 800, MAC layer 805,
and PHY layer 810 may communicate through various media, such as
via a system bus, physical cable interconnection, or network
connection. For example, the SME 800 may be a standalone software
application or applet executing in a personal computer that is
being used as a station 120a, as described above. The MAC layer 805
and PHY layer 810 may be implemented in software or firmware
operating in a plug-in PCI or PCMCIA card 220 installed in the
station 120a. In this embodiment, the MAC layer 805 and PHY layer
810 use standard protocols in accordance with the 802.11 standards.
In this way, the SME 800 can be downloaded from a server on the
Internet (not shown), for example, and be capable of interacting
with the MAC layer 805 and PHY layer 810 in a plug-and-play
manner.
[0045] The SME 800 may be partially or fully updated on occasion to
facilitate updating or exchanging the directive antenna array 205a
with an antenna array having a different configuration. The SME 800
may include an interface driver (not shown). The interface driver
is sometimes included as part of the SME 800 while other times
provided as a separate module. The interface module can send
commands to an antenna controller 815 and receive feedback from the
antenna controller 815. The commands cause the directive antenna
array 205a to steer an antenna beam during a scan when searching
for a "best" access point 110.
[0046] In accordance with the 802.11 standard, the MAC layer 805
can determine signal metrics, such as signal-to-noise ratio,
associated with RF signals communicated via the directive antenna
205a or other form of antenna. The MAC layer 805 employs the PHY
layer 810 to convert and RF signal to a baseband signal, and
vice-versa. The MAC layer 805 can use the PHY layer 810 to provide
signal-related parameters, such as Received Signal Strength
Indication (RSSI), Signal Quality (SQ), and indicated data rate.
The MAC layer 805 may then provide the metrics to the SME 800 in
the form of a datum associated with one antenna beam direction or a
table of data associated with multiple antenna beam directions. The
SME 800 may cause the MAC layer 805 to provide the metrics through
use of commands or requests.
[0047] In operation, the SME 800 may cause the MAC layer 805 to
provide metrics associated with respective beam angles of the
directive antenna array 205a. Based on the metrics and
predetermined criteria, the SME 800 may steer the directive antenna
array 205a to a selected direction associated with an access point
110.
[0048] In a passive scan embodiment, the MAC layer 805 may be
caused to determine the metrics as a function of received RF energy
by the directive antenna array 205a in the respective beam angles.
For example, the metrics may be higher for signal strength of a
beacon signal received from a first access point 110a as compared
to signal strength of a beacon signal received from a second access
point 110b. In an active scan embodiment, the SME 800 may cause the
MAC layer 805 (i) to transmit a signal via the physical layer 810
to at least one access point 110a, 110b, or 110c and (ii) to
measure a response from the access point(s) 110.
[0049] The MAC layer 805 may also provide the metrics or table of
metrics to the SME 800 based on previously calculated or measured
metrics. For example, a periodic or event-driven event may cause
the MAC layer 805 to determine the metrics and provide the metrics
to the SME 800 on an "as needed," "as requested," or predefined
basis. The station 120a may associate with the distribution system
via the access point 110, and the MAC layer 805 may provide the
metrics to the SME 800 before or after the associating with the
distribution system, optionally in a pre-selected manner.
[0050] The SME 800 may issue commands to the antenna controller
815, which sends control signals 820 to the directive antenna array
205a. The control signals 820 may change the state of connection to
reactances 320, 325 associated with the antenna elements 205 in the
directive antenna array 200a, which, in turn, causes the antenna
beam angle to change. The SME 800 may coordinate this action with
causing the MAC layer 805 to provide the metrics associated with
the antenna beam angles. For example, the SME 800 may command the
directive antenna array 200 to steer its antenna beam from angle to
angle in a step-and-hold manner while concurrently commanding the
MAC layer 805 to measure the signal strength in a corresponding
wait-and-measure manner until a metric is associated with each
access point 110 at each antenna beam angle.
[0051] Based on the metrics, the SME 800 may issue further commands
to the antenna controller 815 to steer the antenna beam in a
direction associated with an access point 110. For example, the
antenna beam may be steered to point directly toward an access
point 110a or in the direction of a stronger multi-path that is
associated with the same access point 110a. In this way, the SME
800 can use the best path for associating the station 120a with the
selected access point 110a.
[0052] The SME 800 may invoke an omni-directional beam angle by the
directive antenna array 205a on a predetermined, event-driven, or
random basis to determine whether the selected antenna beam
direction is still the most suitable direction for communicating
with the access point 110a. The metrics may correspond to beam
angles relative to one access point 110a or multiple access points
110a, 110b.
[0053] When scanning (i.e., searching) for a best access point 110
with which to associate, the SME 800 may command or request the MAC
layer 805 to return metrics for multiple beam angles and multiple
beacon signals. When determining whether a different antenna beam
direction would provide an improved communications path, the SME
800 may perform a re-scan. The re-scan may be performed during an
idle period (i.e., no data transmission or reception is occurring),
or the re-scan may be "woven-in" during non-idle periods, in which
case unused or predefined overhead bits or bytes may be used for
transmitting/receiving signals to be measured or transmitting probe
requests.
[0054] In one embodiment, the SME 800 can scan for (i) a best beam
direction to a predetermined access point or (ii) a best beam
direction to a non-predetermined access point. In either case, the
SME 800 may cause (i.e., command or request) the MAC layer 805 to
return metrics or a table of metrics for multiple beam angles and
at least one beacon signal. After selecting the best beam direction
based on the metrics or table of metrics, the SME 800 steers the
antenna beam of the directive antenna array 205a in the selected
direction through techniques discussed above in reference to FIGS.
3A and 3B.
[0055] FIG. 4 is a flow diagram of a process 400 executed by the
stations 120 according to the principles of the present invention
for use in the WLAN 100 (FIG. 1B). The process 400 may be an
embodiment of a subset of SME 800 commands executed by a processor
in the station 120.
[0056] The process 400 begins in step 405 in which the station 120
is powered up. In step 410, the station 120 goes through an
initialization process. At some point following station
initialization 410, the process 400 enters into a routine 411 that
executes commands that communicate with the MAC and physical layers
of the 802.11 protocol. The routine 411 communicates first (step
413) with the physical layer and second (step 417) with the MAC
layer 417.
[0057] The physical layer communications (step 413) includes a
set-up 415, where initialization and communication processes occur
at the physical layer of the 802.11 protocol. Other processes
occurring at the physical layer may also occur at this stage of the
process 400.
[0058] In the MAC layer communications (step 417), the process 400
continues with first determining whether passive or active scanning
is to be used (Step 420) by the station 120 to determine a "best"
antenna pointing angle. If passive scanning is to be used, the
process 400 continues in a passive scan routine 425 (FIG. 6). If an
active scanning is to be used, the process 400 continues at an
active scan routine 430 (FIG. 7). Following the passive or active
scan routines, the process 400 continues (step 435) by determining
whether an access point 110 has been located by the selected scan
routines 425 or 435.
[0059] If an access point 110 has not been located, the process 400
continues to scan (steps 420-430) for an access point 110 until
reaching a predetermined timeout, in which case omni-directional
mode is used as a default. If an access point 110 has been located,
the process 400 continues at a set-up process (step 440), which
again employs the MAC layer 417. The set-up process (step 440) may
include performing authentication, privacy, association, and so
forth as defined by the 802.11 protocol. Following set-up (step
440), the process 400 continues with a station/distribution system
operation process 445 (FIG. 5).
[0060] FIG. 5 is a flow diagram of the station/distribution system
operation process 445, which is executed in the stations 120 at the
SME 800 level. The process 445 includes typical operations
occurring within the station 120a and supports interfacing between
the station 120a and the distribution system 105 via an access
point 110. The process 445 may also reassess the antenna beam
direction to determine a "best" direction. Reassessing the antenna
beam direction may be performed on (i) a periodic basis, (ii) when
the level of a received signal or other signal quality metric falls
below a predetermined threshold, or (iii) based on other event
driven or non-event driven criteria. The example discussed herein
is based on a count-down timing model executed on the first station
120a.
[0061] Continuing to refer to FIG. 5, the process 445 begins in
step 505. In step 510, the process 445 determines whether the
station 120 is still connected to the distribution system 105. If
the station 120a is connected, then, in step 515, the process 445
calculates a received signal level. In step 520, the process 445
determines whether the signal level is below a predetermined
threshold. If the signal is not below the predetermined threshold,
the process 445 continues in step 525 in which the station and
distribution system operations continue.
[0062] In step 530, the process 445 determines whether a signal
level count-down timer is equal to zero. If the signal level
count-down timer equals zero, the process 445 loops back to step
510 to determine whether the station 120a is still connected to the
distribution system 105 via respective access point 110a. If the
signal level count-down timer does not equal zero, the process 445
continues at step 525. The count-down timer may be re-initialized
in a typical manner at an appropriate stage of the process 445,
such as step 510.
[0063] If the signal level is determined to be below the
predetermined threshold in step 520, the process 445 continues in
step 535 to execute the passive scan routine 425 (FIG. 6) or active
scan routine 435 (FIG. 7). Following execution of one of the
routines, the process 445 continues in step 540, in which a
determination is made as to whether the station 120 has selected to
access the distribution system 105 through a new access point 110.
If no change is made to the access point 110a, the process 445
continues at step 525. If a new access point has been selected, the
process 445 continues at step 440 in which authentication, privacy,
and association steps are performed at the MAC level of the 802.11
protocol, as discussed above.
[0064] If the station 120a is no longer connected to the
distribution system 105 via an access point 110 (e.g., user
directed station power down, out-of-range, etc.), the process 445
continues at step 545 to determine whether the station 120a has
been powered down by a user. If the station 120a has not been
powered down, the process 445 continues at step 555, which returns
to the physical layer set-up (step 415) of FIG. 4. Returning to the
physical layer set-up (step 415) occurs in this embodiment based on
an assumption that a communication error or out-of-range error has
interrupted communications between the station 120a and selected
access point 110. If the station 120a has been powered down, the
operation 445 continues at step 550 to power down the station 120a
in a typical manner.
[0065] FIG. 6 is a flow diagram of the passive scan routine 425
introduced in FIG. 4. The passive scan routine 425 starts in step
605 in which a counter i is set to zero. In step 610, the routine
425 determines whether all antenna angles have been tested. If not
all antenna angles have been tested, the routine 425 continues in
step 615 in which the station 120a receives access point beacon
signal(s) at angle i. In other words, the antenna angle is set to
angle i to listen for the beacon signal(s). In step 620, the beacon
signal(s) is/are measured. In step 625, the passive scan routine
425 calculates beacon signal(s) metric(s). In step 630, the counter
i is incremented to select the next angle supported by the
directive antenna array 200a (FIG. 2). The routine 425 continues in
step 610 and repeats until all antenna beam angles have been
tested.
[0066] Following testing of all antenna beam angles, the routine
425 continues in step 635, in which the routine 425 selects an
antenna angle that is a "best" angle at which to communicate with
an access point 110. Selection of the angle can be made according
to any number of criteria, including RSSI, C/I, Eb/No, or other
signal quality measure commonly known in the art. The passive scan
routine 425 returns to the calling routine (FIG. 4 or 5) in step
640 for continued processing.
[0067] FIG. 7 is a flow diagram of the active scan routine 430
introduced in FIG. 4. The active scan routine 430 begins in step
705, in which a counter i is set equal to zero. In step 710, the
routine 430 determines whether all antenna angles have been tested.
If no, then the routine 430 continues in step 715.
[0068] In step 715, the routine 430 sends a probe via RF signal
using the directive antenna array 200a to the access point(s) 110.
The routine 430 receives probe response(s) in step 720 from the
access point(s) 110. In step 725, the active scan routine 430
measures the probe response(s). In step 730, the active scan
routine 430 calculates metric(s) of the probe response(s). In step
735, the counter i is incremented to test the next antenna
angle.
[0069] After repeating the process for all antenna angles, in step
740, the active scan routine 430 selects the antenna angle that
provides the best or most suitable signal quality between the
station 120a and access point 110. In step 745, the active scan
routine 430 returns to the calling process of FIG. 4 or 5.
[0070] The methods and apparatus used to practice the embodiments
discussed above may be used in 802.11 networks or other wireless
networks, such as a Bluetooth network.
[0071] The processes of FIGS. 4-8 may be implemented in software,
firmware, or hardware. In the case of software, the software may be
stored on any type of computer-readable medium, such as ROM, RAM,
CD-ROM, or magnetic disc. Storage may be local to the station 120
or downloadable via a wired or wireless network, such as the
distribution system 105 via access points 110. The software may be
loaded and executed by a general purpose processor or
application-specific processor.
[0072] While this invention has been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
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