U.S. patent application number 11/157392 was filed with the patent office on 2005-10-27 for antenna steering scheduler for mobile station in wireless local area network.
This patent application is currently assigned to IPR Licensing, Inc.. Invention is credited to Foore, Lawrence R., Gainey, Kenneth M..
Application Number | 20050239407 11/157392 |
Document ID | / |
Family ID | 29736643 |
Filed Date | 2005-10-27 |
United States Patent
Application |
20050239407 |
Kind Code |
A1 |
Foore, Lawrence R. ; et
al. |
October 27, 2005 |
Antenna steering scheduler for mobile station in wireless local
area network
Abstract
Methods of scheduling optimization of communications used with
Wireless Local Area Network (WLAN) equipment that employs steerable
directional antennas. The methods may use and are compatible with
Media Access Control (MAC) layers of IEEE 802.11 group of
standards. The methods do not depend on any particular PHY layer
standard.
Inventors: |
Foore, Lawrence R.; (Palm
Bay, FL) ; Gainey, Kenneth M.; (Satellite Beach,
FL) |
Correspondence
Address: |
HAMILTON, BROOK, SMITH & REYNOLDS, P.C.
530 VIRGINIA ROAD
P.O. BOX 9133
CONCORD
MA
01742-9133
US
|
Assignee: |
IPR Licensing, Inc.
Wilmington
DE
|
Family ID: |
29736643 |
Appl. No.: |
11/157392 |
Filed: |
June 21, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11157392 |
Jun 21, 2005 |
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10462569 |
Jun 16, 2003 |
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6911948 |
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60389477 |
Jun 17, 2002 |
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Current U.S.
Class: |
455/63.4 |
Current CPC
Class: |
H04B 7/0408 20130101;
H04W 74/0808 20130101; H04W 88/02 20130101; H04W 72/046 20130101;
H04W 16/28 20130101 |
Class at
Publication: |
455/063.4 |
International
Class: |
H04B 001/00 |
Claims
What is claimed is:
1. A method for controlling a directional antenna used by a
wireless data network subscriber station having a virtual carrier
sense state and a physical carrier sense state, the antenna
operable in an omni-directional mode and in a directional mode,
comprising the steps of: determining the virtual carrier sense
state; determining the physical carrier sense state; comparing the
virtual carrier sense state and the physical carrier sense state;
and if the virtual carrier sense state and the physical carrier
sense state do not concur, then operating the antenna in the
omni-directional mode.
2. A wireless data network subscriber station having a subscriber
station identifier, a virtual carrier sense state, and a physical
carrier sense state comprising: an antenna operable in an
omni-directional mode and in an optimization steering mode, and a
computation device, the computation device processing a received
frame and operating the antenna in the optimization steering mode
if the virtual carrier sense state and the physical carrier sense
state concur, a source identifier is a preferred source identifier,
and a destination identifier is not the subscriber station
identifier.
3. The wireless data network subscriber station of claim 2, wherein
if the virtual carrier sense state and the physical carrier sense
state do not concur, then operating the antenna in the
oni-directional mode.
4. The wireless data network subscriber station of claim 2, wherein
operation of the antenna in optimization steering mode ends after
the frame is entirely received.
5. The wireless data network subscriber station of claim 2, wherein
at least one additional frame is received while operating the
antenna in the optimization steering mode.
6. The wireless data network subscriber station of claim 5, wherein
operation of the antenna in optimization steering mode ends after
the last additional frame is entirely received.
7. The wireless data network subscriber station of claim 2, wherein
if the virtual carrier sense state and the physical carrier sense
state do not concur, ending operating the antenna in the
optimization steering mode.
8. The wireless data network subscriber station of claim 2, wherein
if the antenna is operated in the optimization steering mode and
the virtual carrier sense state and the physical carrier sense
state do not concur, operating the antenna in an omni-directional
mode.
9. The wireless data network subscriber station of claim 2, wherein
the preferred source is an access point.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 10/462,569 filed on Jun. 16, 2003 which claims the benefit of
U.S. Provisional Application No. 60/389,477, filed on Jun. 17,
2002, the entire teachings of which are herein incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] Wireless data communication equipment, such as Wireless
Local Area Network (WLAN) devices, are finding widespread use in
personal computer applications. They have become relatively
inexpensive to deploy, finding economical use even in home computer
networks.
[0003] The technology supporting the Institute of Electrical and
Electronics Engineers (IEEE) 802.11 standards and other similar
networking standards allows stations (STAs), e.g., portable
computers, to be mobile while remaining connected to a WLAN via
radio or infrared communications to access points (APs) or other
STAs. These standards are designed as several layers of
communication protocols. A physical layer (PHY) in the STAs
provides low-level transmission means by which the STAs
communicate. Above the PHY is a Media Access Control layer (MAC)
that provides services, such as authentication, de-authentication,
privacy, association, disassociation, etc.
[0004] Typically PHY electromagnetic signals are transmitted and
received at a STA by a monopole antenna. This type of antenna
typically consists of a single wire or patch antenna element. The
signal transmitted from a monopole antenna is omni-directional in
nature. That is, the signal is sent with the same signal strength
in all directions in a generally horizontal plane for a vertical
oriented antenna element. Reception of a signal with a monopole
antenna element is likewise omni-directional. A monopole antenna
thus does not differentiate in its ability to detect a signal in
one direction versus detection of the same or a different signal
coming from another direction.
[0005] Monopole antennas are susceptible to effects that degrade
the quality of communication between the STAs and APs, such as
reflection or diffraction of radio wave signals caused by
intervening objects, such as walls, desks, people, etc. These
objects create multi-path, normal statistical fading, Rayleigh
fading, and so forth.
[0006] Steerable directional antennas, i.e. antennas optimized for
communications in a particular direction in space, may improve
signal reception when used within the STAs and increase the
allowable distance between STAs and APs. Such antennas are known in
the prior art.
[0007] For example, U.S. Pat. No. 6,404,386 issued to Proctor, Jr.,
et al. on Jun. 11, 2002, entitled "Adaptive Antenna for Use in Same
Frequency Networks", incorporated by reference herein in its
entirety, describes a directional subscriber antenna apparatus. The
antenna provides a plurality of antenna elements, each coupled to a
respective signal control component such as a switch. The antenna
array creates a beamformer for signals to be transmitted from the
subscriber unit, and a directional receiving array to more
optimally detect and receive signals transmitted from the base
station. By directionally receiving and transmitting signals,
multi-path fading is greatly reduced. Various techniques for
determining the proper arrangement of signal control components for
each antenna element are accommodated with this design.
[0008] U.S. Pat. No. 6,396,456 issued to Chiang, et al. on May 28,
2002, entitled "Stacked Dipole Antenna for Use in Wireless
Communications Systems", is also incorporated by reference herein
in its entirety. This patent describes a dipole antenna element
fabricated with printed circuit board (PCB) photo-etching
techniques for precise control of the printed structure to
mass-produce antenna elements with repeatable features. The antenna
includes a planar substrate made of dielectric material, and can be
used to fabricate inexpensive steerable antenna arrays.
[0009] A detailed discussion of a directive antenna array is
provided in U.S. Patent Publication No. 2002/0008672, published
Jan. 24, 2002, entitled "Adaptive Antenna for Use in Wireless
Communications System", the entire teachings of which are
incorporated herein by reference. Example methods for optimizing
antenna direction based on received or transmitted signals by the
directive antenna array are also discussed therein and incorporated
herein by reference in their entirety.
SUMMARY OF THE INVENTION
[0010] Embodiments of present invention include methods and devices
for controlling a directional antenna used by a wireless data
network subscriber station having a virtual carrier sense state and
a physical carrier sense state, the antenna operable in an
omni-directional mode, in a directional mode, and in an
optimization steering mode. Embodiments of this invention also may
comprise a computation device. The operation of embodiments of this
invention may comprise determining the virtual carrier sense state,
determining the physical carrier sense state, comparing the virtual
carrier sense state and the physical carrier sense state, and if
the virtual carrier sense state and the physical carrier sense
state do not concur, then operating the antenna in the
omni-directional mode. The operation of embodiments of this
invention may also comprise selecting a preferred source
identifier, determining the subscriber station identifier,
receiving a frame having a source identifier and a destination
identifier, determining the virtual carrier sense state,
determining the physical carrier sense state, comparing the virtual
carrier sense state and the physical carrier sense state, and if
the virtual carrier sense state and the physical carrier sense
state concur, the source identifier is the preferred source
identifier, and the destination identifier is not the subscriber
station identifier, then operating the antenna in the optimization
steering mode.
[0011] The operation of the embodiments of this invention may also
comprise if the virtual carrier sense state and the physical
carrier sense state do not concur, then operating the antenna in
the omni-directional mode. The operation of embodiments of this
invention may also comprise receiving at least one additional frame
while operating the antenna in the optimization steering mode.
BRIEF DESCRIPTION OF THE DRAWINGS
[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. 1 is a schematic illustration of a wireless
network.
[0014] FIG. 2 is a schematic diagram of the structure of a STA
using an embodiment of this invention.
[0015] FIG. 3 is a flow diagram of a steering algorithm implemented
according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] A description of preferred embodiments of the invention
follows.
[0017] Some embodiments of the present invention use steerable
directional antennas, which are known in the pertinent art. This is
evidenced, in particular, by the patent documents mentioned above
in the Background section of this application. The following
describes the aspects of the directional antenna technology
pertinent to this invention.
[0018] A steerable directional antenna for the purposes of this
invention is a device with the following properties. It may be set
to operate in one of two modes: an omni-directional mode or a
directional mode. A controlling device to which the antenna is
connected controls the mode the antenna is set at any instant in
time. While in omni-directional mode, the antenna is not
substantially optimized for communications in any direction. While
in the directional mode, it has two properties: (a) the
communications using such antenna for some directions are more
optimal then for others, and (b) the controlling device may change
this direction or directions without the device being moved. Note
that these features are not tied to any part of the electromagnetic
spectrum, i.e. the antenna's operating range does not necessarily
have to be within the radio frequency band. Note also that a
steerable directional antenna may in fact consist of multiple
antenna elements.
[0019] A steerable directional antenna may be operated to determine
which direction to choose to optimize its functioning in the
directional mode under current conditions. For example, it may
measure how the relative quality of reception of a signal arriving
from a given source varies depending on the antenna's direction. In
this manner it is possible to choose the antenna's direction for
its optimal functioning in the directional mode. Such a mode of
operation of the antenna is called optimization steering and the
antenna performing the optimization steering is said to be in an
optimization steering mode. Note that the optimization steering may
be implemented, for example, as a series of measurements of
relative signal strength for different directions of antenna in
directional mode. Note also that implementation of the optimization
steering mode for a steerable directional antenna does not require
any additional antenna features. The details and strategy of
optimization steering are not pertinent to the present
invention.
[0020] Some embodiments of the present invention use various
embodiments of the ANSI/IEEE 802.11 Wireless LAN standard and
related standards, and specifically the MAC layer, as defined by
these standards (hereinafter, 802.11 MAC protocol). These standards
are known in the pertinent art. The following describes the aspects
of these standards pertinent to this invention. It should be
understood, however, that other wireless equipment operating with
other protocols may also be used.
[0021] The 802.11 standards are grounded in the notion of wireless
medium (WM) or simply medium, which they define as the medium used
to implement the transfer of protocol data units (PDUs) between
peer physical layer (PHY) entities of a wireless local area network
(LAN). In practical terms, these PDU are transmitted via
electromagnetic waves over the air. The common frequency ranges for
such transmission are the Radio Frequency (RF) and Infrared
Frequency (IR) bands.
[0022] The physical layer entities are classified as stations and
access points. A station (STA) is any device containing an IEEE
802.11 conformant Medium Access Control (MAC) and PHY interface to
the wireless medium. A typical STA is implemented as a computer,
but other devices, such as handheld devices, portable digital
assistants (PDA), and cellular mobile telephones may be used. An
access point (AP) is any entity that has station functionality and
provides access to the distribution services, i.e. the LAN
functionality, for associated STAs via the wireless medium. An AP
usually incorporates a stationary transceiver. It must be
understood that an AP is also a STA. The STAa that are not APs are
usually portable computers and similar devices.
[0023] FIG. 1 illustrates this arrangement. STAs 101, 102, and 103
are portable laptop or handheld computer devices. Each STA 101,
102, or 103 is with range of AP 100.
[0024] An integral part of these standards are physical and virtual
carrier-sense functions, which are used to determine the state of
the medium. When either function indicates a busy medium, the
medium is considered busy; otherwise, it is considered idle.
[0025] The physical carrier-sense mechanism depends on the PHY
informing the MAC whether the medium is busy or idle. The actual
determination depends on the PHY implementation. PHY
implementations are known in the pertinent art and their details
are not pertinent to this invention.
[0026] A virtual carrier-sense mechanism is achieved by
distributing reservation information announcing the impending use
of the medium. It is implemented within the MAC. The exchange of
RTS (ready to send) and CTS (clear to send) frames prior to the
actual data frame is one means of distribution of this medium
reservation information. The RTS and CTS frames contain a
Duration/ID field that defines the period of time that the medium
is to be reserved to transmit the actual data frame and the
returning ACK (acknowledgement) frame. All STAs within the
reception range of either the originating STA (which transmits the
RTS) or the destination STA (which transmits the CTS) learn of the
medium reservation.
[0027] Thus a STA may be unable to receive from the originating
STA, yet still know about the impending use of the medium to
transmit a data frame. This is important, for example, because
while a STA is in communication with an AP, i.e. within its
transmission range, it may not necessarily be within the
transmission range of another STA using the same AP. FIG. 1
schematically shows such a situation. Here the AP 100 is within
range of all three STAs 101, 102, and 103, but STAs 102 and 103 are
out of range of STA 101.
[0028] A network allocation vector (NAV) on each STA maintains a
prediction of future traffic on the medium based on duration
information that is announced in RTS/CTS frames prior to the actual
exchange of data. The carrier-sense mechanism combines the NAV
state and the STA's transmitter status with physical carrier sense
to determine the busy/idle state of the medium. The NAV may be
thought of as a counter, which counts down to zero at a uniform
rate. When the counter is zero, the virtual carrier-sense
indication is that the medium is idle; when nonzero, the indication
is busy. The medium is defined as busy whenever the STA is
transmitting.
[0029] Every STA operating under 802.11 MAC protocol at any time
can use two variables: one indicating the physical carrier state
(which is used in the Boolean sense) and the other indicating the
virtual carrier sense state and the duration of such state (which
is either zero or a positive number).
[0030] Another important feature of 802.11 MAC protocol is that
every MAC frame received by a STA contains an indicator of its
source and its destination and also of the length of the frame.
[0031] Some embodiments implemented on STAs also rely on two
additional variables: their own STA identifier (ID) and an ID of
the preferred AP, i.e. the preferred source.
[0032] Some embodiments of this invention implemented on STAs use
steerable directional antennas controllable by such STAs. They use
such antennas for communications with other STAs, including APs.
The optimization of communications performed in such embodiments
essentially consists of steering of the antenna's preferred
direction within a STA in the direction of its preferred AP.
[0033] FIG. 2 illustrates the functioning of a STA using an
embodiment of this invention. The arrangement of antenna array 121,
PHY 120, MAC 123, and other protocols 125 is unaffected by the
presence of an embodiment of this invention, i.e. the STA remains
IEEE 802.11 conformant. For example, more details of preferred
embodiment of a multi-element antenna array 121 and how it is
steerable can be found in patent applications referenced above. A
mode control algorithm 124, being a part of the embodiment, relies
on MAC 123 to provide it with data, as further explained below. The
mode control algorithm 124 controls the mode control and
optimization unit 122 putting it into one of three modes:
directional, omni directional, and optimization steering mode, the
nature of which is outlined above. Internal functioning of the mode
control and optimization unit 122 is not pertinent to this
invention.
[0034] One embodiment of this invention determines whether a STA
antenna must be in the omni-directional mode, directional mode, or
in the optimization steering mode, i.e. steering to orient itself
for optimal configuration with respect to its preferred AP. This
determination is accomplished in the following way (also shown as a
flowchart in FIG. 3).
[0035] The STA first chooses a preferred AP.
[0036] While its antenna is in the omni-directional mode 202 or
directional mode 201, the STA monitors the medium. When it begins
receiving a MAC frame, the STA checks whether the virtual and the
physical carrier sense concur, in states 204 or 203.
[0037] If one is busy and another is idle, or vice versa, then the
STA's antenna is put into the omni-directional mode 202 and the STA
awaits the arrival of the next frame.
[0038] Otherwise (i.e. when the virtual and the physical carrier
sense do concur) the frame's header is decoded, in states 206 and
205. The frame's source identifier is then compared with the
preferred AP's identifier, and the frame's destination identifier
is compared with the STA's identifier, in states 208 and 207.
[0039] If the source identifier is not the preferred AP's
identifier (i.e. the frame is not coming from where the STA would
steer toward) or the destination identifier is the STA's identifier
(i.e. the frame carries data intended for the STA) the antenna's
mode is not changed. It either stays in the omni-directional mode
202 or stays in the directional mode 201 pointing to the direction
where it was steered earlier.
[0040] If the source identifier is the preferred AP's identifier
(i.e. the frame is coming from where the STA would steer toward)
and the destination identifier is the STA's identifier (i.e. the
frame does not carry data intended for the STA) the antenna is
placed into the optimization steering mode 209 for one or several
frames' duration. This expected duration may be the expected length
of the transmitted frame (determined when the frame's header is
decoded) or the expected duration of transmission determined by the
value of the NAV counter. It stays in the optimization steering
mode 209 until one of the two events takes place: either (a) the
transmission ends normally at the expected moment, in which case
the antenna stays in the directional mode 201 pointing to the
direction chosen during the optimization steering, or (b) upon
arrival of a frame 212, the virtual and the physical carrier sense
no longer concur 210, in which case the antenna is put into the
omni-directional mode 202 and the STA awaits the arrival of the
next frame.
[0041] When the antenna is in the optimization steering mode 209,
its direction may be changed using the incoming signal from the
preferred AP for optimization of the communications with the
preferred AP.
[0042] Note that the above algorithm is equally compatible with any
kind of PHY layer capable of supporting the necessary features of
the MAC layer. In particular, the communications may take place
over any part of electromagnetic spectrum.
[0043] 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.
* * * * *