U.S. patent number 9,271,176 [Application Number 14/472,759] was granted by the patent office on 2016-02-23 for system and method for backhaul based sounding feedback.
This patent grant is currently assigned to Magnolia Broadband Inc.. The grantee listed for this patent is Magnolia Broadband Inc.. Invention is credited to Phil F. Chen, Haim Harel, Stuart S. Jeffery, Kenneth Kludt.
United States Patent |
9,271,176 |
Chen , et al. |
February 23, 2016 |
System and method for backhaul based sounding feedback
Abstract
A system and method for backhaul based explicit sounding
feedback of 802.11 AP to AP channel state information (CSI) so that
inter AP interference can be reduced and multiple APs transmissions
that can occur simultaneously on the same radio channel. A
modification may be made to APs such that they can accurately
measure the CSI between them that in turn enables their respective
beamformer to create pattern nulls toward each other while
simultaneously developing pattern enhancements toward their
intended station. An AP may send a sounding packet to its
associated STAs, poll explicit feedbacks from STAs and receive
backhaul CSI feedbacks from neighboring APs. There is no additional
Wi-Fi overhead in physical layer. Backhaul feedback link is
established through direct peer-to-peer (P2P) link which bypassed
the sounding controller to reduce CSI feedback delay.
Inventors: |
Chen; Phil F. (Denville,
NJ), Jeffery; Stuart S. (Los Altos, CA), Kludt;
Kenneth (San Jose, CA), Harel; Haim (New York, NY) |
Applicant: |
Name |
City |
State |
Country |
Type |
Magnolia Broadband Inc. |
Englewood |
NJ |
US |
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Assignee: |
Magnolia Broadband Inc.
(Englewood, NJ)
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Family
ID: |
54192351 |
Appl.
No.: |
14/472,759 |
Filed: |
August 29, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150281993 A1 |
Oct 1, 2015 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61971685 |
Mar 28, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B
7/024 (20130101); H04B 7/0626 (20130101); H04W
24/10 (20130101); H04B 17/00 (20130101); H04B
7/14 (20130101); H04B 7/04 (20130101); H04B
7/0632 (20130101); H04L 1/00 (20130101); H04W
40/02 (20130101); H04B 7/0452 (20130101) |
Current International
Class: |
G01R
31/08 (20060101); H04W 24/10 (20090101); H04W
40/02 (20090101) |
Field of
Search: |
;370/230-253,328-339 |
References Cited
[Referenced By]
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2 498 462 |
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Sep 2012 |
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EP |
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2009-182441 |
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Aug 2009 |
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JP |
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2009-278444 |
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Nov 2009 |
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JP |
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WO 03/047033 |
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Jun 2003 |
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WO |
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WO |
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WO |
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WO 2011/060058 |
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May 2011 |
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WO |
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WO 2013/192112 |
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Dec 2013 |
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WO |
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Primary Examiner: Zaidi; Iqbal
Attorney, Agent or Firm: Pearl Cohen Zedek Latzer Baratz
LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of prior U.S. Provisional
Application Ser. No. 61/971,685 filed Mar. 28, 2014, which is
incorporated herein by reference in its entirety.
Claims
What is claimed is:
1. A method implemented in an access point (AP) configured to
exchange messages with at least one associated station (STA) via a
wireless channel, the AP comprising: a plurality of antennas, radio
circuitry configured to transmit and receive via said antennas, and
a baseband processor, the method comprising: establishing a
backhaul link with at least one co-channel neighboring AP, sending
a sounding packet to said at least one associated STA over the
wireless channel, obtaining channel state information (CSI)
feedback from said at least one co-channel neighboring AP via the
backhaul link, determining that the radiation pattern of the AP
towards said at least one co-channel neighboring AP can be reduced
sufficient to protect the AP from interference from the at least
one co-channel neighboring AP, generating a radiation pattern that
is reduced towards said at least one co-channel AP, and exchanging
messages with at least one associated station (STA) via a wireless
channel at the same time as generating said reduced radiation
pattern, wherein prior to said determining, generating and
exchanging, determining that a network allocation vector (NAV) for
the channel is set by one said co-channel neighboring AP, and
wherein said determining uses the CSI, obtained via a backhaul
link, for a co-channel neighboring AP that has set the NAV.
2. The method according to claim 1 wherein the at least one
co-channel neighboring AP is operating within a clear channel
assessment (CCA) range of said AP.
3. The method according to claim 1 wherein establishing said
backhaul link comprises: transmitting a query for an address of
said at least one co-channel neighboring AP; and receiving a
response comprising an address for each said at least one
co-channel AP.
4. The method according to claim 3 comprising: sending said query
to a controller, receiving said response from said controller, and
establishing said backhaul link with said at least one co-channel
neighboring AP as a peer-to-peer (P2P) link which bypasses said
controller.
5. The method according to claim 1 in which said obtaining
comprises obtaining CSI for multiple co-channel neighboring APs and
the method further comprises comprising compiling a table of most
recently obtained CSI for said multiple co-channel neighboring
APs.
6. The method according to claim 1 further comprising detecting a
sounding packet sent by a co-channel neighboring AP via a wireless
channel to at least one STA associated with the neighboring AP, and
in response to said detecting sending CSI to said at least one
neighboring AP via a backhaul link.
7. The AP according to claim 1, the baseband processor is
configured to query the sounding controller about the neighboring
AP's backhaul IP address by decoded MAC transmitter address in
received beacon.
8. An access point (AP) configured to exchange messages with at
least one associated station (STA) via a wireless channel, the AP
comprising: a plurality of antennas, radio circuitry configured to
transmit and receive via said antennas, and a baseband processor,
wherein the baseband processor is configured to cause the AP to:
establish a backhaul link with at least one co-channel neighboring
AP, send a sounding packet to said at least one associated STA over
the wireless channel, wherein the sounding packet is sent according
to the multi-user multiple input multiple output (MU-MIMO) sounding
protocol, obtain channel state information (CS I) feedback from
said at least one neighboring AP via the backhaul link and from its
associated STAs over-the-air according to the MU-MIMO sounding
protocol, and determine one or more weights for signals transmitted
to or received from said antennas to generate a radiation pattern
to reduce interference between said AP and at least one co-channel
neighboring AP based on said CSI feedback.
9. The AP according to claim 8 wherein the radio circuitry is
configured to operate in compliance with the IEEE 802.11
standard.
10. An access point (AP) configured to exchange messages with at
least one associated station (STA) via a wireless channel, the AP
comprising: a plurality of antennas, radio circuitry configured to
transmit and receive via said antennas, and a baseband processor,
wherein the baseband processor is configured to: establish a
backhaul link with at least one neighboring AP, detect a sounding
packet sent by the neighboring AP to at least one associated STA
over the wireless channel, send channel state information (CSI) to
said at least one neighboring AP via the backhaul link, indicate
that it is capable of responding to sounding packets by
transmitting identification of this capability, wherein the
identification of this capability is transmitted in a beacon
management frame of the AP, and operate in compliance with the IEEE
802.11 standard and to register its backhaul IP address, Wi-Fi
SSID, and Wi-Fi MAC address to a sounding controller via a backhaul
link at power-up.
11. A communication system comprising a plurality of access points
(APs) each configured to: exchange messages with at least one
associated station (STA) via a wireless channel, establish a
backhaul link with at least one co-channel neighboring AP, send a
sounding packet to said at least one associated STA over the
wireless channel, obtain channel state information (CSI) feedback
from said at least one neighboring AP via the backhaul link, the
system further comprising a sounding controller for registration of
said APs, each AP being configured to register with said sounding
controller, determine that the radiation pattern of the AP towards
said at least one co-channel neighboring AP can be reduced
sufficient to protect the AP from interference from the at least
one co-channel neighboring AP, generate a radiation pattern that is
reduced towards said at least one co-channel AP, and exchange
messages with at least one associated station (STA) via a wireless
channel at the same time as generating said reduced radiation
pattern, wherein prior to said determining, generating and
exchanging, determining that a network k allocation vector (NAV)
for the channel is set by one said co-channel neighboring AP, and
wherein said determining uses the CSI, obtained via a backhaul
link, for a co-channel neighboring AP that has set the NAV.
Description
FIELD OF THE INVENTION
The present invention relates generally to the field of wireless
communication, and more specifically to high efficiency Wi-Fi
systems.
BACKGROUND
Prior to setting forth a short discussion of the related art, it
may be helpful to set forth definitions of certain terms that will
be used hereinafter. Some of these terms are defined in the
Institute of Electrical and Electronics Engineers (IEEE) 802.11
specification but it should be appreciated that the invention is
not limited to systems and methods complying with the IEEE 802.11
specification.
The term "Wi-Fi" is used to refer to technology that allows
communication devices to interact wirelessly based on the Institute
of Electrical and Electronics Engineers (IEEE) 802.11 standards.
The wireless communication may use microwave bands, e.g. in the 2.4
GHz to 5 GHz range.
The term "AP" is an acronym for Access Point and is used herein to
define a device that allows wireless devices (known as User
Equipment or "UE") to connect to a wired network using Wi-Fi, or
related standards. The AP usually connects to a router (via a wired
network) as a standalone device, but it can also be an integral
component of the router itself.
The term "UE" is an acronym for User Equipment(s) and is an example
of a station, e.g. Wi-Fi station (STA) that may attach to an
AP.
The term "associated STA" as used herein refers to a STA that is
served by a certain AP, for example with a certain Service Set
Identifier (SSID).
The term "station" or STA is a term used for any participant on the
network, for example as used in the 802.11 specification. Both UEs
and APs are considered in this context to be examples of stations.
In the following the abbreviation STA is used for stations whose
packets are detected by a Wi-Fi RDN station implementing
embodiments of the invention.
BSS is acronym for Basic Service Set, which is typically a cluster
of Stations associated with an AP dedicated to managing the BSS. A
BSS built around an AP is called an infrastructure BSS. The term
"backhaul" is used in the following to denote a communication path
between two APs or base stations, for example using a different
protocol from that used for wireless communication between an AP or
base station and supported equipment or STA. The 802.11
specification does not provide for communication between APs. A
backhaul link may operate outside a wireless, e.g. Wi-Fi,
environment in which APs or base stations and associated UEs or
other STAs are operating, or use one or more different channels
from those used by APs to communicate with their associated
stations. A backhaul link may use any combination of wired and
wireless communication including but not limited to a cellular
communication network, Ethernet, and the internet.
"Beacon transmission" refers to periodical information transmission
which may include system information.
HT-LTF is an acronym for high throughput long training field as
defined in the 802.11 specification.
MPDU is an acronym for media access code (MAC) protocol data unit
as defined in the 802.11 specification.
NAV is an acronym for network allocation vector as defined in the
802.11 specification.
NDP is an acronym for null data packet.
PPDU is an acronym for physical layer convergence procedure (PLCP)
protocol data unit as defined in the 802.11 specification.
The term "sounding" refers to a channel calibration procedure
involving the sending of a packet, called a "sounding packet" from
one participant on a network to another, for example as defined in
the 802.11 specifications.
VHT is an acronym for very high throughput as defined in the 802.11
specification.
The specific Carrier Sense Multiple Access/Collision Avoidance
(CSMA/CA) mechanism used in the 802.11 Media Access Control (MAC)
is referred to as the distributed coordination function (DCF). A
station that wishes to transmit first performs a clear channel
assessment (CCA) by sensing the medium for a fixed duration, the
DCF inter-frame space (DIFS).
SIFS, Short Inter Frame Space, as defined in the 802.11
specifications is the period between reception of the data frame
and transmission of the ACK. SIFS is shorter than DIFS.
The term Clear Channel Assessment (CCA) as used herein refers to a
CCA function, e.g. as defined in the 802.11 specification.
The term "MIMO" is an acronym for multiple input multiple output
and as used herein, is defined as the use of multiple antennas at
both the transmitter and receiver to improve communication
performance. MIMO offers significant increases in data throughput
and link range without additional bandwidth or increased transmit
power. It achieves this goal by spreading the transmit power over
the antennas to achieve spatial multiplexing that improves the
spectral efficiency (more bits per second per Hz of bandwidth) or
to achieve a diversity gain that improves the link reliability
(reduced fading), or increased antenna directivity.
"Channel estimation" is used herein to refer to estimation of
channel state information (CSI) which describes properties of a
communication link such as signal to noise ratio "SNR" and signal
to interference plus noise ratio "SINR". Channel estimation may be
performed by user equipment or APs as well as other components
operating in a communications system.
The term "beamforming" sometimes referred to as "spatial filtering"
as used herein, is a signal processing technique used in antenna
arrays for directional signal transmission or reception. This is
achieved by combining elements in the array in such a way that
signals at particular angles experience constructive interference
while others experience destructive interference. Beamforming can
be used at both the transmitting and receiving ends in order to
achieve spatial selectivity. The operation of attempting to achieve
destructive interference in order to cancel a signal in a
particular direction or angle is referred to as "nulling". Complete
cancellation of a signal is not usually achieved in practice and a
"null" in a radiation pattern may refer to a minimum in signal
strength. The lower the signal strength, the "deeper" the null is
said to be.
The term "beamformer" as used herein refers to analog and/or
digital circuitry that implements beamforming and may include
combiners and phase shifters or delays and in some cases amplifiers
and/or attenuators to adjust the weights of signals to or from each
antenna in an antenna array. Digital beamformers may be implemented
in digital circuitry such as a digital signal processor (DSP),
field-programmable gate array (FPGA), microprocessor or the central
processing unit "CPU" of a computer to set the weights as may be
expressed by phases and/or amplitudes of the above signals. Various
techniques are used to implement beamforming including: Butler
matrices, Blass Matrices and Rotman Lenses. In general, most
approaches may attempt to provide simultaneous coverage within a
sector using multiple beams.
SUMMARY
Wi-Fi is a time division duplex system (TDD), where the
transmitting and receiving functions use the same channel,
implemented with a limited amount of frequency resources that use
techniques of collision avoidance (CSMA/CA) to allow multiple
stations, user equipment's (UEs) and APs, to share the same
channel.
In many deployments APs on the same radio channel are within CCA
range of each other. Thus an AP maybe blocked from transmitting to
its client STA (typically a UE) due to activity of a nearby AP as
noted in FIG. 1.
Multi-User MIMO (MU_MIMO) capable APs can develop complex antenna
patterns that support simultaneous enhancing and nulling in
specific directions. According to embodiments of this invention,
nulling at one AP may be set toward a co-channel AP in order to
achieve the combined effect of reducing interference to the
co-channel AP and reducing interference from the co-channel AP. The
quality of this null, e.g. the effectiveness of the interference
reduction, can be enhanced through the use of CSI information
exchanged between the one AP and the co-channel AP. However it is
not provided as part of the over-the-air (OTA) standard for APs to
communicate with each other.
According to embodiments of the invention, an access point or
components within the AP, e.g., a processor or baseband processor,
or radio circuitries, is configured to exchange messages with at
least one associated station (STA) over a wireless, or over-the-air
channel. The AP may comprise a plurality of antennas, radio
circuitry configured to transmit and receive via said antennas and
a baseband processor, and may be equipped with beamforming
capability. According to embodiments of the invention, the baseband
processor is configured to establish a backhaul link with at least
one neighboring AP which may be operating within a clear channel
assessment (CCA) range of said AP. The AP may then transmit or send
a sounding packet to its at least one associated STA over-the-air,
or via the wireless channel, and obtain CSI feedback from said at
least one neighboring AP via the backhaul link.
A method according to embodiments of the invention may be
implemented in or by an AP and may include establishing a backhaul
link with at least one co-channel neighboring AP, sending a
sounding packet to said at least one associated STA over the
wireless channel, and obtaining channel state information (CSI)
feedback from said at least one co-channel neighboring AP via the
backhaul link.
Embodiments of the invention may also be implemented in the
neighboring AP. This may include establishing a backhaul link with
at least one neighboring AP, detecting a sounding packet sent by
the neighboring AP to at least one associated STA over the wireless
channel, and sending channel state information (CSI) to said at
least one neighboring AP via the backhaul link.
Embodiments of the invention may also comprise an AP that is
configured to implement both methods described above, whereby an AP
can transmit or send or receive CSI via a backhaul link with
another AP.
An AP according to embodiments of the invention is sometimes
referred to in the following as a "beamforming AP" to distinguish
it from a neighboring AP. A beamforming AP may also be referred to
as a MIMO AP. The neighboring AP may or may not have beamforming
capability.
According to embodiments of the invention, an AP equipped with
beamforming capability can both enhance its signal to its client
STA while simultaneously nulling its signal toward a neighboring AP
which may be interfering. According to embodiments of the invention
this can be achieved by providing to the beamforming AP CSI
relating to the neighboring AP.
CSI can be derived by the neighboring AP either implicitly or
explicitly. The use of the term "implicit" or "implicitly" in this
context refers to a process used for TDD protocols such as Wi-Fi,
where both down and up links share the same spectrum. In the
aforementioned process, the uplink channel estimated by an AP is
assumed to be identical to the downlink one, based on the
reciprocity principle. Therefore, in an example of this process,
the channel from an STA towards an AP is considered by the AP to
represent the channel from the AP towards the STA. Conversely, the
use of the term "explicit" or "explicitly" in this context refers
to a procedure where CSI is fed back. In an example of an explicit
process between AP and STA, AP transmissions are channel estimated
by the STA, and then fed back to the AP, providing the AP with, for
example, the magnitude of phase and amplitude differences between
the signals as transmitted by the AP vis-a-vis as received by the
client/STA. Such information may allow the AP to gauge possible
distortions in signals and correct them.
According to embodiments of the invention, CSI is provided that
relates to a channel between one AP and another. There is no
provision in the Wi-Fi standards for APs to communicate directly
with each other. Therefore although one AP may receive, or detect,
transmissions from another AP that are not directed to it, no
mechanism is provided for it to respond using Wi-Fi protocol.
Explicit feedback is more accurate, and therefore more useful for
generating a high quality null toward a STA or an AP. Embodiments
of the invention enable explicit CSI measurement between compatible
APs so that inter AP interference can be reduced, "compatible"
referring to APs according to embodiments of the invention. However
high quality of this kind may not always be required and
embodiments of the invention may use implicit CSI.
APs having the capability to implement embodiments of the invention
may register with a controller via the backhaul, for example in
order to obtain the address of a neighboring AP. This controller
may take the form of a server, for example, and is referred to in
the following as a sounding controller. According to other
embodiments of the invention a new procedure is developed that
enables an AP to establish a direct peer-to-peer (P2P) backhaul
link with a nearby compatible AP which bypasses the sounding
controller to reduce CSI feedback delay.
Embodiments of the invention may also comprise a system comprising
multiple APs, each configured to implement any of the foregoing
methods, as well as a sounding controller for registration of said
APs, each AP being configured to register with the sounding
controller.
Embodiments of the invention comprise a method whereby an AP may
obtain feedback, for example explicit feedback, from a co-channel
AP as an extension of the standard procedure of obtaining CSI
information from a UE or other STA which it is supporting.
According to embodiments of the invention, an AP may transmit or
send a sounding packet to its associated STAs, poll feedback from
STAs and receive backhaul feedback from one or more neighboring
APs. According to embodiments of the invention this may be achieved
with no additional Wi-Fi overhead in the physical layer, e.g.
channel occupancy. In this manner an AP may have timely CSI, for
example based on feedback from a co-channel AP, which by its nature
may be explicit, enabling it to develop a high quality null toward
that AP.
According to other embodiments of the invention an AP may
dynamically adjust any of the sounding rate, the sounding data
quality and the specific STA to which sounding is directed, for
example based on changes in environment.
According to other embodiments of the invention, when a beamforming
AP has data to send to a supported UE or other STA and finds that
its own channel is not clear, for example due to the CCA having
been set by one or more other APs, then the beamforming AP may
determine whether the quality of the CSI data that it possess will
enable it to reduce the transmission of the beamforming AP toward
one or more of the other APs. This reduction in transmission may be
achieved with a pattern that has one or more nulls reduce the
transmission of the beamforming AP toward one or more other
concurrently operating APs. This may enable the beamforming AP not
to interfere with the activity of the one or more other
concurrently operating APs. The beamforming AP may then be able to
deliver an acceptable signal to a UE or other STA which it is
supporting. If a beamformer AP can meet this criteria, it may
proceed to send data to the UE or other STA.
As stated above, according to embodiments of the invention, a
beamformer AP determines if the CSI data it has at this specific
moment is of sufficient quality. The AP's analysis may consider any
of (a) how many milliseconds have elapsed since the last CSI update
it received, (b) the stability of the CSI data--e.g. how rapidly is
it changing and (c) the absolute quality of the CSI data versus
what is required for sufficient nulling depth.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, and in order to show
how it may be implemented, references are made, purely by way of
example, to the accompanying drawings in which like numerals
designate corresponding elements or sections.
FIG. 1 shows a typical operational environment with multiple APs in
CCA range according to embodiments of the invention;
FIG. 2 is a block diagram illustrating an AP within CCA range of a
neighboring AP, in accordance with some embodiments of the present
invention.
FIG. 3 illustrates an example of backhaul based sounding feedback
system comprising two APs and a sounding controller connected by a
IP network for backhaul based sounding feedback, according to
embodiments of the invention;
FIG. 4 shows an example of an 802.11 AC MU-MIMO sounding message
flow according to embodiments of the invention;
FIG. 5 shows a high level message flow of backhaul based sounding
feedback among a beamformer AP, a neighboring AP and a sounding
controller according to embodiments of the invention;
FIG. 6 illustrates a process flow of a neighboring AP receiving a
sounding message and sending a backhaul based CSI feedback message
according to embodiments of the invention; and
FIG. 7 illustrates a flow chart of beamformer AP determining to
ignore the NAV set by another AP and proceed to send data to a UE,
or to wait for channel is clear according to embodiments of the
invention;
FIG. 8 illustrates how an AP equipped with beamforming can null its
signal toward an interfering AP while transmitting to its client
STA (a UE) in a typical operational environment with multiple APs
in CCA range, according to embodiments of the invention; and
FIG. 9 shows the structure of the frame used in a beacon
transmission, where backhaul CSI feedback capability is indicated
in the optional vendor specific portion of the frame in accordance
with some embodiments of the present invention.
The drawings together with the following detailed description are
designed make the embodiments of the invention apparent to those
skilled in the art.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
It is stressed that the particulars shown are for the purpose of
example and solely for discussing the preferred embodiments of the
present invention, and are presented in the cause of providing what
is believed to be the most useful and readily understood
description of the principles and conceptual aspects of the
invention. In this regard, no attempt is made to show structural
details of the invention in more detail than is necessary for a
fundamental understanding of the invention. The description taken
with the drawings makes apparent to those skilled in the art how
the several forms of the invention may be embodied in practice.
The invention is not limited in its application to the details of
construction and the arrangement of the components set forth in the
following descriptions or illustrated in the drawings. The
invention is applicable to other embodiments and may be practiced
or carried out in various ways. Also, it is to be understood that
the phraseology and terminology employed herein is for the purpose
of description and should not be regarded as limiting.
In description that follows, APs are assumed to operate in 40 MHz
band, with 4 antennas and use 400 nanosecond inter-symbol spacing.
The ideas described can be adjusted for other bandwidths and other
AP antenna configurations. In the following, an asterisk, e.g. AP*,
indicates that an AP is compatible with backhaul based CSI feedback
according to embodiments of the invention. This may mean for
example that an AP is equipped with software, for example installed
in the baseband processor, so that it can participate in backhaul
based CSI feedback, either as a sounder or as a responder. AP*_1
refers to an AP that initiates registration with a sounding
controller on its backhaul network, sometimes referred to in the
following as a beamforming AP. AP*_i, where i {2 . . . n} is a
designator for the different AP*s that are members of backhaul
based sounding feedback links with AP*_1, some of which may be
referred to as neighboring APs.
APs according to embodiments of the invention may use an unmodified
802.11ac Null Packet Protocol procedure to transmit or send
sounding, which may be received by all compatible APs as well as
STAs within CCA range. An AP may then receive other APs' CSI
feedback from one or more backhaul links. AP*_1 may build or
compile a table or other data structure storing most recent CSI
values for each AP*_i that has been sounded. When AP*_1 has data to
send to a UE and finds one or more AP*_i has triggered CCA, AP*_1
may determine whether an antenna pattern can be created by it that
will: null concurrent one or more AP*_i so that AP*_1's radiation
toward the one or more AP*_i is below a CCA limit; and create
acceptable beam toward UE_1. If such a pattern can be created,
AP*_1 may create the pattern and proceed to send data to the
UE.
FIG. 1 shows a basic Wi-Fi environment including multiple
neighboring co-channel APs, AP*_1, AP*_2 and AP_3 and respective
associated stations (STAs), which in this embodiment are shown as
UEs, UE_1, UE_2 and UE_3. AP*_i where i {2 . . . n} indicates an AP
that has the capability to implement embodiments of this invention,
which may for example be implemented in the form of a software
enhancement. For example, hardware described herein may be
configured to carry out embodiments of the present invention by
executing software or code. AP*_1 is going to transmit or send
MU_MIMO data to UEs supported by it, one of which is UE_1, and will
sound them prior to sending data. Supposing that AP*_2 is
considered by AP*_1 to be a good candidate to null, determined by
relative signal levels, geometry, etc., AP*_1 will start the
sounding procedure when the NAV for AP*_1 is NOT set, meaning the
channel is clear and all the APs in CCA range are not active.
Each of AP*_1, AP*_2 and AP_3 may have a radiation pattern shown in
FIG. 1 as a circle centered on the respective AP, for example
pattern 106 for AP*_1, 107 for AP*_2 and 108 for AP_3. FIG. 1 also
shows propagation path 103 between AP*_1 and UE_1, propagation path
109 between AP*_1 and AP*_2, and propagation path 110 between AP_3
and AP*_1.
FIG. 2 is a block diagram illustrating an AP 210 within CCA range
of a neighboring AP 203, in accordance with some embodiments of the
present invention. AP 210 may include for example a plurality of
antennas 10-1 to 10-N, radio circuitry in the form of a plurality
of radio circuits 20-1 to 20-N configured to transmit and receive
signals via respective antennas 10-1 to 10-N in compliance with the
IEEE 802.11 standard, and a baseband processor 30. AP 210 may be
configured to transmit and receive signals within a clear channel
assessment (CCA) range of neighboring AP 203 which has a plurality
of antennas 203A and may be configured to transmit and receive
signals in a co-channel shared with AP 210 in compliance with the
IEEE 802.11 standard.
Baseband processor 30 may be configured to monitor signals received
by the radio circuits 20-1 to 20-N and generate a set or list of
neighboring co-channel access points that each has plurality of
antennas and are further located within a clear channel assessment
(CCA) range of the access point. Baseband processor 30 may be
further configured to instruct radio circuits 20-1 to 20-N to
transmit a sounding sequence to the list of neighboring access
points, and receive Channel State Information (CSI) therefrom. The
sounding sequence may comprise a sequence of control frames sent to
beamformees and data frames indicative of the channel from the
beamformee.
FIG. 3 illustrates an example of a backhaul-based sounding feedback
system according to embodiments of the invention. The system as
illustrated in FIG. 3 comprises two APs, labelled AP*_1 and AP*_2,
and a sounding controller 310 connected by an IP network 300 for
backhaul based sounding feedback according to embodiments of the
invention. In the illustrated system it is assumed that AP*s are
within CCA range of each other to establish a backhaul CSI feedback
link between them on an IP network. A channel sounding packet is
sent from AP*_1 over-the-air, for example using a wireless channel,
in this example via Wi-Fi communication. The packet may be
addressed to its associated STAs, e.g., STA_1 in FIG. 3, and may
also be received by neighboring AP*s, e.g. AP*_2. STAs may transmit
or send their CSI feedback over-the-air, e.g. over a wireless
channel, for example as standard procedures defined in 802.11n or
802.11ac. According to embodiments of the invention, at the same
time, neighboring AP*s send their CSI feedback through a backhaul
link comprising IP network 300. There is no need for any change to
Wi-Fi air interface protocol for backhaul based sounding feedback
and no additional overhead requirement in Wi-Fi physical layer
according to embodiments of the invention.
As will become clear in the following, the sounding controller 310
may function in a similar manner to a server. The sounding
controller 310 does not need to be a stand-alone item and its
functions may be incorporated into another component, such as an
existing server in the IP network.
802.11n channel sounding has two PPDU formats defined: the regular
or staggered PPDU, which carries a MAC frame, and the null data
packet (NDP), which does not carry a MAC frame. According to
embodiments of the invention, the NDP is used in a sequence from
which the addressing and other MAC related information can be
obtained from a MAC frame in a preceding PPDU. The normal or
staggered PPDU is simply a normal PPDU or a PPDU with additional
HT-LTFs that is used to sound the channel. It serves the dual
purpose of sounding the channel and carrying a MAC frame. The NDP
is only used to sound the channel.
Two sequences of NDP as sounding PPDU are possible for 802.11n
channel sounding: The first sequence is that NDP frame may follow
another PPDU where the preceding PPDU carries one or more MPDUs
which contain the HT Control field with the NDP Announcement bit
set to 1. The second possible sequence is when the NDP Announcement
PPDU solicits an immediate response then the NDP itself follows the
response PPDU from another STA.
Unlike 802.11n, the 802.11ac sounding sequence is separate from the
data sequence. Explicit feedback is the mechanism for obtaining CSI
(there is no implicit feedback). Only compressed-V (in the singular
value decomposition "SVD" of the channel) beamforming weights are
permitted (uncompressed-V and CSI are not supported). There is no
support for delayed feedback. Rather, in implementations according
to 802.11ac, feedback is returned during the SIFS after receiving
the VHT NDP. The VHT sounding sequence begins with a VHT NDP
Announcement frame sent by the beamformer and addressed to the
beamformees. This is followed by a VHT NDP frame for channel
sounding. The first beamformee responds SIFS after the VHT NDP with
a VHT Compressed Beamforming frame. The remaining STAs are polled
in turn with a Beamforming Report Poll frame to which they respond
with their VHT Compressed Beamforming frame.
FIG. 4 shows by way of example a standard 802.11ac MU-MIMO sounding
message flow: an AP transmits or sends an NDP_announcement,
followed by an NDP. The STA that was addressed in the receiver
field of the NDP_announcement is expected to respond with
compressed CSI information. After that, the AP polls the "other"
STAs. The "other" STAs know they might be polled as they are part
of the association identifier (ID) "AID" list which is part of the
NDP_announcement message. This same message flow may be used
without modification in embodiments of the invention. The same
applies to standard 802.11n channel sounding message flows.
FIG. 5 shows a high level message flow of backhaul based sounding
feedback among a beamformer AP, AP*_1, a neighboring AP, AP*_2 and
a sounding controller such as sounding controller 310 of FIG. 3
according to embodiments of the invention. Initially, neighboring
AP*_2 registers it backhaul IP address, Wi-Fi SSID and Wi-Fi MAC
address with a sounding controller on its backhaul network, e.g. IP
network 300, at power-up in flow 501. In flow 503, AP_*2 receives a
register confirmation on the backhaul network from the sounding
controller 310. After registration is confirmed in flow 503, the
neighboring AP*_2 broadcasts its backhaul CSI feedback capability
in beacon transmissions over the air to other APs including AP*_1,
as indicated by flow 505. AP*_1, which is a beamformer AP receives
a beacon transmission 505 from the neighboring AP*_2 and recognizes
neighboring AP*_2's backhaul CSI feedback capability. Next,
beamformer AP*_1 sends or transmits a query to the sounding
controller 310 in flow 507 about neighboring AP*_2's backhaul IP
address. This may be done using the decoded MAC transmitter address
in received beacon transmission 505. The sounding controller 310
responds with the backhaul address in flow 509. Beamformer AP*_1
then transmits or sends a connection request to AP*_2 in flow 511
and receives an accepted response in flow 513 to/from the
neighboring AP*_2 to establish a direct backhaul CSI feedback link,
a peer-to-peer (P2P) link which bypasses the sounding controller
310 to reduce CSI feedback delay.
After the neighboring AP*_2 receives a sounding packet, a null data
packet (NDP) or a data packet with extension HT-LTFs, from the
beamformer AP*_1 in flow 515, in response the neighboring AP*_2
transmits or sends a CSI feedback in flow 517 directly to
beamformer AP*_1 through the backhaul link. It should be noted that
according to embodiments of the invention, the CSI feedback is
transmitted or sent to AP*_1 by AP*_2 regardless of addressed
devices for the sounding packet or other packet sent in flow 515.
Such packets are usually addressed to STAs served by the sending
AP. However they may be detected and decoded by any AP within CCA
range of the sending AP. After receiving CSI feedback in flow 517,
according to embodiments of the invention AP*_1 may update a CSI
table with most recent CSI for AP*_2. The same process may apply to
any other AP*_i that sends feedback to AP*_1. Operations 515 and
517 may be repeated once the peer-to-peer link is established. In
other words there is no need for operations 501 to 513 to be
repeated before AP*_1 sends further sounding packets to its
associated stations and AP*_2.
After receiving CSI feedback at the end of the process flow shown
in FIG. 5, beamformer AP*_1 applies the CSI feedback to create a
radiation pattern, also known as a spatial signature, having a null
in transmission or reception toward the neighboring AP*_2. This may
reduce interference between the two APs, AP*_1 and AP*_2, for
example while beamformer AP*_1 is transmitting or sending a packet
to its associated STA. The creation of the radiation pattern is
explained with reference to FIG. 8 below.
For the least quantization distortion, CSI feedback uses 8 bits for
each real and 8 bits for each imaginary component of the channel
complex element between a transmit antenna and a receive antenna
per subcarrier which would have less quantization distortion than
compressed-V beamforming frame used in 802.11ac. Grouping of two or
four subcarriers can be used to reduce CSI feedback overhead.
FIG. 6 shows the process flow 600 in a neighboring AP, labelled
AP*_i according to embodiments of the invention. In operation 601,
AP*_i registers its backhaul IP address, Wi-Fi SSID and Wi-Fi MAC
address with a sounding controller, e.g. sounding controller 310,
on its backhaul network, e.g. IP network 300 at power-up and
receives the registration confirmation from the sounding controller
in operation 602. Then AP*_i listens for a feedback link connection
request, for example from AP*_1 in operation 603 and accepts the
backhaul feedback connection request to establish a direct
peer-to-peer connection for sounding feedback in operation 604.
According to embodiments of the invention, the real and imaginary
components I and Q of the channel information are uncompressed and
prepared for transmission. When a sounding packet from AP*_1 is
received by AP*_i at operation 605, AP*_i transmits or sends the
CSI data in operation 606 via the established backhaul feedback
link. Then AP*_i goes back to operation 605 where it continues to
receive next sounding packet from AP*_1.
FIG. 7 shows the process flow in a beamformer AP, labelled AP*_1,
according to embodiments of the invention, for transmitting or
sending data to an associated STA, labelled UE_1. When AP*_1 has
data to send to UE_1, it checks to see if NAV is set at operation
701. If not, e.g. the channel is not clear, AP*_1 proceeds to send
data at 702. However if NAV is set, then AP*_1 determines if the
NAV was set by one of its neighboring APs, AP*_i, that has backhaul
CSI feedback capability. AP*_1 checks if the CSI data from the
neighboring AP, AP*_i, is current or not at operation 703. Using
this current CSI data, AP*_1 determines whether it can reduce its
radiation pattern, e.g. generate a null, toward AP*_i sufficient to
protect it from interference from AP*_i, for example by checking
whether it will be protected by the CCA set threshold e.g. -82 dB,
and also support UE_1 at operation 704. If this condition can be
met, AP*_1 may ignore the NAV being set and proceed to send data to
UE_1 at operation 705. If this condition is not met, then it wait
until NAV clears at operation 706. There might be two active
neighboring AP*s and it might be possible for AP*_1 to create
multiple nulls.
Some embodiments of the invention do not require a modification to
the NDP_announcement and NDP messages. Consequently, the various
STAs will see the message flows as standard. AP*_1 receives CSI
information from each of the associated UEs that it polls over the
Wi-Fi air interface, for example as the standard MU_MIMO sounding
procedure. In addition, according to embodiments of the invention,
AP*_1 receives CSI information from AP*_2 via an established
backhaul link as shown in FIG. 3 and AP*_1 may then generate a
pattern as shown in FIG. 8.
FIG. 8 shows how an AP, AP*_1, equipped with beamforming capability
can both enhance its signal to a client STA, UE_1, while
simultaneously nulling its signal toward an interfering AP, AP*_2.
In FIG. 8, the same reference numerals are used to designate like
items in FIG. 1. In FIG. 8, the propagation path between AP*_1 and
AP*_2 is modified and referenced 209, and the overall radiation
pattern is modified and referenced 206.
AP*_1 performs the enhancement and nulling using CSI on the path
209 (109) between APs and on the path 103 between AP*_1 and UE_1.
The baseband processor in an AP according to embodiments of the
invention may be configured to apply weights to signals received by
or transmitted from AP antennas such that spatial signatures, or
radiation patterns, generated in downlink or uplink or both reduce
interferences between said Wi-Fi AP and at least one of the N
neighboring APs. The application of these weights may be based for
example on received CSI feedback from sounding. At the same time
the AP may transmit or send a data packet to a station (STA), or a
group of stations.
FIG. 8 illustrates schematically that the modification of the
radiation pattern results in a reduction of unwanted or
unintentional radiation between the two APs, as indicated by path
209. At the same time the radiation between AP*_1 and UE_1 may be
enhanced as indicated by the extension of the radiation pattern 206
around UE_1.
CSI can be developed either implicitly or explicitly. The use of
explicit feedback is more accurate, and therefore more useful that
implicit feedback for generating a high quality null toward a
neighboring AP.
According to embodiments of the invention, AP*_1 is able to
recognize nearby APs that are AP* compatible and able to support
communication between them. AP* capability can be added in as an
information element in the beacon transmission.
FIG. 9 is a diagram illustrating the structure of the 802.11 Beacon
Frame 900 in accordance with embodiments of the present invention.
This frame is transmitted by all 801.11 APs at a periodic rate,
typically 10 times per second. This beacon includes mandatory
information such as the SSID of the AP but can optionally include
other information, e.g. vendor specific data. According to
embodiments of the invention, the vendor specific data may start
with a device/vendor ID followed by a flag to indicate backhaul CSI
feedback capability. Where this becomes standardized, a specific
Information Element ID could be assigned to indicate this
capability rather than embedding this information in a vendor
specific data element.
According to embodiments of the invention, an AP may obtain
explicate feedback from a co-channel AP as an extension of the
standard procedure of obtaining CSI information from its supported
UE. In this manner the AP will have timely CSI information based on
feedback from the co-channel AP, enabling it to develop a high
quality null toward that AP. Embodiments of the invention do not
require a modification to the standard sounding approach used by
AP*_1 when it sends the NDP_announcement message. Consequently, the
various STAs will see the message flows as standard. AP*_1 receives
CSI information from co-channel neighboring AP, AP*_i, via an
established backhaul link between them and from each of its
associated UEs over the Wi-Fi air interface that it polls as the
standard MU_MIMO sounding procedure, and then AP*_1 generates a
pattern as shown in FIG. 8.
The methods described for embodiments of this invention can be
implemented in hardware, combination of hardware and software or
software only. A unique aspect of some embodiments is the
possibility for implementation completely in software, for example
by augmenting the notational algorithms of the 802.11xx protocol.
Thus embodiments of the invention may take the form of one or more
computer readable media, e.g. non-transitory computer readable
media, which when implemented on one or more processors in an AP
system to perform any of the methods described above.
The methods described herein are applicable to all versions of the
802.11 protocol, specifically 802.11a, b, g, n and ac.
As will be appreciated by someone skilled in the art, aspects of
the present invention may be embodied as a system, method or an
apparatus. Accordingly, aspects of the present invention may take
the form of an entirely hardware embodiment, an entirely software
embodiment (including firmware, resident software, micro-code,
etc.) or an embodiment combining software and hardware aspects that
may all generally be referred to herein as a "circuit," "module" or
"system." In one aspect the invention provides a computer readable
medium comprising instructions which when implemented on one or
more processors in a computing system causes the system to carry
out any of the methods described above. The computer readable
medium may be in non-transitory form.
The aforementioned block diagrams illustrate the architecture,
functionality, and operation of possible implementations of systems
and methods according to various embodiments of the present
invention. In this regard, each block in the flowchart or block
diagrams may represent a module, segment, or portion of code, which
comprises one or more executable instructions for implementing the
specified logical function(s). It should also be noted that, in
some alternative implementations, the functions noted in the block
may occur out of the order noted in the figures. For example, two
blocks shown in succession may, in fact, be executed substantially
concurrently, or the blocks may sometimes be executed in the
reverse order, depending upon the functionality involved. It will
also be noted that each block of the block diagrams and/or
flowchart illustration, and combinations of blocks in the block
diagrams and/or flowchart illustration, can be implemented by
special purpose hardware-based systems that perform the specified
functions or acts, or combinations of special purpose hardware and
computer instructions.
In the above description, an embodiment is an example or
implementation of the inventions. The various appearances of "one
embodiment," "an embodiment" or "some embodiments" do not
necessarily all refer to the same embodiments.
Although various features of the invention may be described in the
context of a single embodiment, the features may also be provided
separately or in any suitable combination. Conversely, although the
invention may be described herein in the context of separate
embodiments for clarity, the invention may also be implemented in a
single embodiment.
Reference in the specification to "some embodiments", "an
embodiment", "one embodiment" or "other embodiments" means that a
particular feature, structure, or characteristic described in
connection with the embodiments is included in at least some
embodiments, but not necessarily all embodiments, of the
inventions.
It is to be understood that the phraseology and terminology
employed herein is not to be construed as limiting and are for
descriptive purpose only.
The principles and uses of the teachings of the present invention
may be better understood with reference to the accompanying
description, figures and examples. It is to be understood that the
details set forth herein do not construe a limitation to an
application of the invention. Furthermore, it is to be understood
that the invention can be carried out or practiced in various ways
and that the invention can be implemented in embodiments other than
the ones outlined in the description above.
It is to be understood that the terms "including", "comprising",
"consisting" and grammatical variants thereof do not preclude the
addition of one or more components, features, steps, or integers or
groups thereof and that the terms are to be construed as specifying
components, features, steps or integers. If the specification or
claims refer to "an additional" element, that does not preclude
there being more than one of the additional element. It is to be
understood that where the claims or specification refer to "a" or
"an" element, such reference is not be construed that there is only
one of that element.
It is to be understood that where the specification states that a
component, feature, structure, or characteristic "may", "might",
"can" or "could" be included, that particular component, feature,
structure, or characteristic is not required to be included.
Where applicable, although state diagrams, flow diagrams or both
may be used to describe embodiments, the invention is not limited
to those diagrams or to the corresponding descriptions. For
example, flow need not move through each illustrated box or state,
or in exactly the same order as illustrated and described.
Methods of the present invention may be implemented by performing
or completing manually, automatically, or a combination thereof,
selected steps or tasks. The term "method" may refer to manners,
means, techniques and procedures for accomplishing a given task
including, but not limited to, those manners, means, techniques and
procedures either known to, or readily developed from known
manners, means, techniques and procedures by practitioners of the
art to which the invention belongs.
The descriptions, examples, methods and materials presented in the
claims and the specification are not to be construed as limiting
but rather as illustrative only. Meanings of technical and
scientific terms used herein are to be commonly understood as by
one of ordinary skill in the art to which the invention belongs,
unless otherwise defined.
The present invention may be implemented in the testing or practice
with methods and materials equivalent or similar to those described
herein. While the invention has been described with respect to a
limited number of embodiments, these should not be construed as
limitations on the scope of the invention, but rather as
exemplifications of some of the preferred embodiments. Other
possible variations, modifications, and applications are also
within the scope of the invention. Accordingly, the scope of the
invention should not be limited by what has thus far been
described, but by the appended claims and their legal
equivalents.
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