U.S. patent application number 14/816545 was filed with the patent office on 2015-11-26 for method and system for explicit ap-to-ap sounding in an 802.11 network.
The applicant listed for this patent is Magnolia Broadband Inc.. Invention is credited to Haim HAREL, Stuart S. JEFFERY, Kenneth KLUDT.
Application Number | 20150341807 14/816545 |
Document ID | / |
Family ID | 53719069 |
Filed Date | 2015-11-26 |
United States Patent
Application |
20150341807 |
Kind Code |
A1 |
JEFFERY; Stuart S. ; et
al. |
November 26, 2015 |
METHOD AND SYSTEM FOR EXPLICIT AP-TO-AP SOUNDING IN AN 802.11
NETWORK
Abstract
A method of one AP accessing a channel occupied by a neighboring
AP within CCA range, by acquiring channel knowledge via performing
cooperative sounding and setting a null towards the neighboring AP,
under certain conditions verifications, is provided herein. The
method may include: transmitting and receive signals via a
plurality of radio circuitries connected to plurality of antennas;
monitoring signals received by the radio circuitries and generating
a 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; and instructing
the radio circuitries to transmit a sounding sequence to the list
of neighboring access points, and receive Channel State Information
(CSI).
Inventors: |
JEFFERY; Stuart S.; (Los
Altos, CA) ; HAREL; Haim; (New York, NY) ;
KLUDT; Kenneth; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Magnolia Broadband Inc. |
Englewood |
NJ |
US |
|
|
Family ID: |
53719069 |
Appl. No.: |
14/816545 |
Filed: |
August 3, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14449431 |
Aug 1, 2014 |
9100154 |
|
|
14816545 |
|
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|
61955433 |
Mar 19, 2014 |
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Current U.S.
Class: |
370/254 |
Current CPC
Class: |
H04L 5/0023 20130101;
H04L 5/005 20130101; H04L 5/0033 20130101; H04L 5/0053 20130101;
H04L 25/0206 20130101; H04B 7/0452 20130101; H04W 24/02 20130101;
H04L 5/0073 20130101; H04B 7/0617 20130101; H04W 88/08 20130101;
H04W 84/12 20130101 |
International
Class: |
H04W 24/02 20060101
H04W024/02; H04B 7/04 20060101 H04B007/04; H04L 5/00 20060101
H04L005/00 |
Claims
1. An access point (AP) comprising: a plurality of antennas; a
plurality of radio circuitries configured to transmit and receive
signals via the plurality of antennas; and a baseband processor
configured to monitor the signals received by the radio circuitries
and generates a list of neighboring co-channel access points (APs),
each is further located within a clear channel assessment (CCA)
range of said access point, wherein the baseband processor is
further configured to establish a subgroup of neighboring
co-channel APs which agree to join an access point sounding set
(APSS), instruct the radio circuitries to transmit a sounding
sequence to said APSS, and receive channel state information (CSI)
therefrom.
2. The access point according to claim 1, wherein the baseband
processor is further configured to set weights on the radio
circuitries to produce a null at one or more antennas of said APSS
which currently transmits on a same frequency channel and download
a packet to a station (STA), or a group of STAs.
3. The access point according to claim 2, wherein the null weights
are determined via explicit sounding process invoked between said
access point and each of the APSS, based on APSS Null Data Packet
(NDP) announcement by said AP and response by APSS.
4. The access point according to claim 3, wherein the AP sends an
APSS NDP announcement to all APs in APSS, followed by an NDP, and a
V compressed response from a first neighboring AP and a series of
poll requests to a next neighboring AP and a corresponding V
compressed response, until all APs in APSS are polled and all V
compressed responses are consummated, wherein V is a compressed
matrix representing the channel response.
5. The access point according to claim 3, wherein the APSS NDP
announcement and NDP comprise an APSS ID field replacing in the
IEEE 802.11ac MU MIMO sounding protocol the STA ID field.
6. The access point according to claim 3, wherein the Poll Request
field is retrofitted to address a neighboring APs rather than STAs
in the IEEE 802.11ac MU MIMO sounding protocol.
7. A method of performing an explicit sounding process to
neighboring access points (APs) by a beamformer access point (AP)
comprising: transmitting and receiving signals via a plurality of
radio circuitries connected to a plurality of antennas; monitoring
the signals received by the radio circuitries and generating a list
of neighboring co-channel access points, each being located within
a clear channel assessment (CCA) range of the access point;
establishing a subgroup of neighboring co-channel APs which agree
to join an access point sounding set (APSS); and instructing the
radio circuitries to transmit a sounding sequence to the list of
neighboring co-channel access points, and receive channel state
information (CSI) from APs in APSS.
8. The method according to claim 7, wherein the baseband processor
is further configured to set weights on the radio circuitries to
produce a null at one or more antennas of said APSS which currently
transmits on a same frequency channel and download a packet to a
station (STA), or a group of STAs.
9. The method according to claim 8, wherein the null weights are
determined via explicit sounding process invoked between said
access point and each of the APSS, based on APSS Null Data Packet
(NDP) announcement by said AP and response by APSS.
10. The method according to claim 9, wherein the AP sends an APSS
NDP announcement to all APs in APSS, followed by an NDP, and a V
compressed response from a first neighboring AP and a series of
poll requests to a next neighboring AP and a corresponding V
compressed response, until all APs in APSS are polled and all V
compressed responses are consummated, wherein V is a compressed
matrix representing the channel response.
11. The method according to claim 9, wherein the APSS NDP
announcement and NDP comprise an APSS ID field replacing in the
IEEE 802.11ac MU MIMO sounding protocol the STA ID field.
12. The method according to claim 9, wherein the Poll Request field
is retrofitted to address a neighboring APs rather than STAs in the
IEEE 802.11ac MU MIMO sounding protocol.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 14/449,431 filed on Aug. 1, 2014, which
claims benefit from U.S. Provisional Patent Application Ser. No.
61/955,433 filed on Mar. 19, 2014, all of which are incorporated
herein by reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to wireless
communication, and more specifically to high efficiency Wi-Fi.
BACKGROUND OF THE INVENTION
[0003] Prior to setting forth the background of the invention, it
may be helpful to set forth definitions of certain terms that will
be used hereinafter.
[0004] The term "Wi-Fi" as used herein is defined as any wireless
local area network (WLAN) products that are based on the Institute
of Electrical and Electronics Engineers (IEEE) 802.11
standards.
[0005] The term "Access Point" or "AP" as used herein is defined as
a device that allows wireless devices (also 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.
[0006] The term "client" as used herein is defined as any device
that has wireless communication capabilities, specifically, the
IEEE 802.11 standards. A client may be for example a smart
telephone, a laptop, a tablet or a personal computer (PC).
[0007] The notation "STA" as used herein is defined in as an IEEE
802.11 client.
[0008] The term "BSS" is an acronym for Basic Service Set, which is
typically a cluster of stations supported by an AP.
[0009] The term "node" as used herein is defined as general name
for both IEEE 802.11 AP and IEEE 802.11 STA.
[0010] The term "serving AP" as used herein is defined in relation
to one AP and one STA, wherein the STA is registered to the AP, and
the AP and STA are sending and receiving data to and from each
other.
[0011] The term "neighboring APs" or "neighboring nodes" relate to
two co-frequency (or co-channel) APs or nodes that are within each
other's sensitivity range, e.g. at least one of them can receive
the other in such an signal-to-noise ratio to allows decoding of
signals.
[0012] The term "CCA range" as used herein is a range between two
IEEE 802.11 nodes, wherein at least one node can receive the
other's transmission at a power level equal or larger than "CCA
Level" e.g. -82 dBm.
[0013] The term "CSMA/CA" stands for
Carrier-Sense-Multiple-Access/Collision-Avoidance, representing a
requirement to listen before transmitting in a multi-node wireless
system that shares a common channel on the basis of
first-come-first-served.
[0014] The term "preamble" as used herein describes a certain
802.11 transmitted signal modulation appearing at the beginning of
each packet, that when received by other 802.11 nodes, will force
them to yield channel access.
[0015] The notation "SINR" stands for Signal to Interference and
Noise.
[0016] The term "ACK" as used herein, stands for acknowledgement,
and is defined as the signal transmitted from an IEEE 802.11
receiving node to the IEEE 802.11 node that has transmitted a
packet to it, provided the packet was successfully received.
[0017] The term "time division duplex" (TDD) as used herein refers
to systems using the same frequency spectrum for methods of
communications in a time division manner such as Wi-Fi systems.
[0018] The term "channel sounding" as used herein refers to the
process defined in 802.11 specifications that enables the full
dimensionality of the radio channel to be determined. One sounding
technique described in the 802.11 specifications is for an AP to
transmit a Null Data Packet (NDP), a packet without a MAC
frame.
[0019] The term "implicit feedback" or "implicit sounding" as used
herein 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 the AP, is
assumed to be identical to the downlink one--based on reciprocity
principle--and is therefore is considered by the AP to represent
the channel towards the client/STA.
[0020] The term "explicit AP-STA feedback" or "explicit sounding"
as used herein refers to a procedure where AP transmissions are
channel estimated by the STA, and then fed back to the AP,
providing it with the magnitude of phase and amplitude differences
between the signals as transmitted by the AP vis-a-vis as received
by the client/STA, allowing it to gauge possible distortions and
correct them.
[0021] The term "associated STA" as used herein refers to a STA
that is served by a certain AP with a certain Service Set
Identifier (SSID).
[0022] The term "non-associated STA" as used herein refers to a STA
within the range of the non-serving AP.
[0023] The acronym "NAV" stands for Network-Allocation-Vector and
represents virtual carrier sense mechanism, used by a Wi-Fi
transmitting message to broadcast the predicted duration of its
transmission, signaling to other nodes how long the channel will be
occupied.
[0024] The acronym "RTS" stands for Request-To-Send, and represents
a message transmitted by one Wi-Fi node to another, probing it for
information about its availability to receive data, per the Wi-Fi
Alliance protocol.
[0025] The acronym "CTS" stands for Clear-To-Send, and represents a
positive response from the other node to the node originating the
RTS, indicating to the requesting node that the channel is clear
from its point of view as well.
[0026] The notation "DURATION" is a message embedded in both RTS
and CTS, representing a prediction of the future traffic about to
be transmitted between two nodes that have captured the channel;
other nodes that receive it, must clear the channel as long as the
DURATION has not expired; other nodes that have received the RTS
but received the CTS (hidden nodes) will avoid accessing the
channel, allowing the receiving node to successfully complete the
reception.
[0027] The acronym "FLA" stands for Fast Link Adaptation, and
represents processes that reduce transmitting side learning time of
the receiver's SINR.
[0028] The acronym "MCS" stands for Modulation Coding Scheme,
mapping SINR to modulation order and code rate.
[0029] The term "beamformer" as used herein relates to a node that
generates a spatial pattern, created by two or more antennas,
formed in such a way that significantly in the power level received
by a given receiver being a "beamformee".
[0030] The term "null" as used herein, is a spatial pattern,
created by two or more antennas, formed in such a way that
significantly reduces the power level received by a given receiver
(e.g., a local minimum). An "Rx Null" is a null formed by a
receiver's antennas weight in order to decrease undesired signal
level. A "Tx Null" is formed by transmitter's antennas weights in
order to decrease its undesired transmitted signal at remote
receiver's input.
[0031] The term "actual null depth" as used herein, is the
estimated value of the null after a certain time period has elapse
since the last explicit sounding in which the amplitude and the
phase have drifted so as to yield null degradation. The actual null
depth is the original null taking account the estimated null
degradation.
[0032] APSS is an acronym for AP Sounding Set. This is a cluster of
APs that work together with mutual sounding process to reduce
interference according to this invention.
[0033] The term "AP Beacon" is a management signal that is
transmitted at regular intervals (typically about 10 times per
second) that indicates capability of the AP. The Beacon frame
contains both mandatory information (such as SSID) and optional
data that may include vendor specific information. This vendor
specific data field is used to indicate the AP as an APSS
capable.
[0034] AP* indicates an AP which is compatible with APSS, meaning
it is equipped with special software so that it can participate in
APSS, either as a sounder or as a responder.
[0035] AP*_1 indicated an AP that initiates the APSS process. If
multiple AP* are present, then multiple APSS's exist.
[0036] APSS_ID indicated an N bit random code selected by AP*_1 to
identify the APSS that it has created (e.g. N=12).
[0037] AP*_i indicates an AP member in a group of APs that is a
recipient of an AP*_1's initiation of an APSS process, where I {2 .
. . n} is the designator for the different AP* that are members of
the APSS_ID. Also labeled as "Compatible Access Point".
[0038] According to current IEEE 802.11 air protocols, two
neighboring APs can download traffic (e.g. radio signals including
data) over the same frequency channel to their respective STAs at
the same time as long as these APs are not within CCA range of each
other. When an RTS/CTS procedure is used, an additional condition
is introduced. Namely, a legacy STA receiving the download traffic
from its serving AP, must not be within CCA range of other
neighboring APs or the STA they are supporting, if the AP is
occupying the channel.
[0039] In many deployments APs on the same radio channel are within
CCA range of each other; thus, an AP may be blocked from
transmitting to its client STA due to activity of a neighboring
nearby AP.
SUMMARY OF THE INVENTION
[0040] Embodiments of the present invention disclose a protocol
modification that allows a group of 802.11 nodes that are MIMO
capable, to access an occupied channel, using novel procedure that
enables acquiring knowledge of the channel between APs, based on
setting up an explicit beamformer-beamformee handshake.
[0041] According to some embodiments, an AP equipped with Tx/RX
MIMO capability may serve several STAs while simultaneously null
its transmitted signal toward the interfering AP, based on
acquiring channel knowledge via a sounding process targeted at
neighboring APs, similar to explicit sounding process defined for
802.11ac beamforming and MU-MIMO targeted at served STAs.
[0042] Embodiments of a MU-MIMO procedure are described herein,
enabling a neighboring AP to access a channel already occupied by
another downloading AP; the procedure may be initiated by
establishing a subgroup of neighboring APs which agree to adhere to
a mutual sounding protocol, e.g. subscribe to an AP Sounding Set
(APSS), exchanging invites and accepts to the set, and performing
mutual sounding handshakes that enable acquisition of each other's
channel information, consequently used for null setting towards
each other--also labeled as beamformer-beamformee nulling
process.
[0043] Each of the aforementioned member AP may perform an APSS
initialization by surveying the neighboring co-channel APs
periodically, listing those who are within its CCA range, and
eliminating from the list ones that are not APSS capable, and ones
that are too strong to be nulled, e.g., ones that cannot be pushed
below CCA Level via nulling, either due to limited nulling
capability, or due to a very close proximity, or both.
[0044] The aforementioned beamformer's nulling capability is
defined as the power level difference between its trained null
towards the Beamformee, and its Omni directional antenna pattern,
as received by the Beamformee's receiver.
[0045] Such nulling capability is estimated by a beamformer AP via
periodical sounding of the APs that are within its CAA range, and
by then interpolating the acquired phase and amplitude accuracy
deterioration over time, which has elapsed from last sounding.
[0046] Successful nulling capability verification may allow a
beamformer AP to access (for downloading purposes) a channel
occupied by the downloading beamformee AP, provided certain
additional conditions are met.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] The subject matter regarded as the invention is particularly
pointed out and distinctly claimed in the concluding portion of the
specification. The invention, however, both as to organization and
method of operation, together with objects, features, and
advantages thereof, may best be more fully understood by reference
to the following detailed description when read with the
accompanying drawings in which:
[0048] FIG. 1A is a block diagram illustrating a typical
operational environment in accordance with the prior art;
[0049] FIG. 1B is a block diagram illustrating an access point with
transmit and receive MIMO capability;
[0050] FIG. 2 is a block diagram illustrating an example of the
effect of using nulling in accordance with some embodiments of the
present invention;
[0051] FIG. 3 is an initialization phase in accordance with some
embodiments of the present invention;
[0052] FIG. 4 is an example of APSS message flow in accordance with
some embodiments of the present invention;
[0053] FIG. 5 is an APSS sounding announcement in accordance with
some embodiments of the present invention;
[0054] FIG. 6 is an APSS Null Data Package in accordance with some
embodiments of the present invention;
[0055] FIG. 7 is an APSS feedback in accordance with some
embodiments of the present invention;
[0056] FIG. 8A is a flow chart for an AP serving a single STA at a
given time (SU-MIMO) in accordance with some embodiments of the
present invention;
[0057] FIG. 8B is a flow chart for an AP serving multiple
simultaneous STAs (MU-MIMO) in accordance with some embodiments of
the present invention;
[0058] FIG. 9 is an example of fading gradient in accordance with
some embodiments of the present invention;
[0059] FIG. 10 is a null deterioration chart as a function of phase
and amplitude imbalance, in accordance with some embodiments of the
present invention; and
[0060] FIG. 11 shows the structure of the Beacon frame, where APSS
capability is indicated in the optional vendor specific portion of
the frame in accordance with some embodiments of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0061] In the following description, various aspects of the present
invention will be described. For purposes of explanation, specific
configurations and details are set forth in order to provide a
thorough understanding of the present invention. However, it will
also be apparent to one skilled in the art that the present
invention may be practiced without the specific details presented
herein. Furthermore, well-known features may be omitted or
simplified in order not to obscure the present invention.
[0062] Unless specifically stated otherwise, as apparent from the
following discussions, it is appreciated that throughout the
specification discussions utilizing terms such as "processing,"
"computing," "calculating," "determining," or the like, refer to
the action and/or processes of a computer or computing system, or
similar electronic computing device, that manipulates and/or
transforms data represented as physical, such as electronic,
quantities within the computing system's registers and/or memories
into other data similarly represented as physical quantities within
the computing system's memories, registers or other such
information storage, transmission or display devices.
[0063] FIG. 1A is an apparatus illustrating an area covered by two
access points in accordance with the prior art. AP_1 101 is assumed
to be equipped with an omni directional antenna pattern 105, that
schedules downloading a packet to one of its served Stations STA_1
102, and is blocked by its previously set NAV or DURATION invoked
by a neighboring AP_2 103 which has already seized the channel.
[0064] The reason for the protocol's requirement that prohibits
AP_1 from transmitting is to avoid harmful interference to the
AP_2's session, as well as in consideration of a possible harmful
interference of AP_2 transmission to AP_1's contemplated package
delivery.
[0065] It is noted that in cases depicted in FIG. 1A, such mutual
harmful interference are not likely to affect the success of actual
downlink reception by the respective STAs, being out of range;
however, AP_1 101 access to the channel is prohibited in order to
guarantee the ACK 110 response from STA_2 104 will not be jammed.
Specifically, in the example of FIG. 1A AP_1's 101 harmful
interference 109 toward AP_2 103, may jam STA_2 ACK 110 reception
by AP_2's receiver resulting in a need for retransmission.
[0066] FIG. 1B is a block diagram illustrating an AP 110 within CCA
range of a neighboring AP 103, in accordance with some embodiments
of the present invention. AP 110 may include for example a
plurality of antennas 10-1 to 10-N, a plurality of radio
circuitries 20-1 to 20-N configured to transmit and receive signals
via a plurality of antennas 10-1 to 10-N in compliance with the
IEEE 802.11 standard, and a baseband processor 30. AP 110 may be
configured to transmit and receive signals within a clear channel
assessment (CCA) range of neighboring AP 103 which has a plurality
of antennas and may be configured to transmit and receive signals
in a co-channel shared with AP 110 in compliance with the IEEE
802.11 standard.
[0067] Baseband processor 30 may be configured to monitor signals
received by the radio circuitries 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
circuitries 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 being a sequence
of control frames sent to beamformees and data frames indicative of
the channel from the beamformee.
[0068] FIG. 2 is a block diagram in which the baseband processor
may further be configured to set weights on the radio circuitries
to produce a null at one or more receiving antennas of the listed
neighboring access point which currently transmits on the same
frequency channel. The FIG. 2 layout describes an apparatus that is
similar to the one illustrated in FIG. 1A, but with APs equipped
with features according to embodiments of the present invention
labeled AP*_1 201 and AP*_2 203 respectively. These features may
allow an AP to use another AP's busy channel under certain
conditions. Embodiments of the present invention are based on AP*_1
201 driving a null on both the receive and the transmit paths,
towards AP*_2 203, thus protecting both of their ACK receptions,
207 and 210, from each other's transmissions. When AP*_1 Omni
radiation pattern 205 is replaced by novel radiation pattern 212 in
both up and down links, then both 208 and 209 harmful interference
signals are reduced. When such a reduction is estimated by AP*_1
201 to reach a level that allows both ACK 210 and ACK 207 to be
successfully received, and when other conditions described below
are met, then AP*_1 201 may proceed to download a packet to STA_1
202, while AP*_2 203 is downloading its packet to STA_2 204. It is
noted that the aforementioned nulling is based on cooperative
process between the participating APs which belong to the same AP
Sounding Set (APSS), as will be detailed herein.
[0069] According to some embodiments, an explicit sounding process
invoked between the access point and each of the listed neighboring
access points.
[0070] FIG. 3 is a flowchart illustrating a high level process
according to embodiments of the invention of inviting and accepting
of sounding invitations between APs that are equipped with the
aforementioned cooperative nulling capability, committing to
respond to sounding requests from other set members. Embodiments of
the process 300 start with scanning all neighboring APs that are
APSS compatible and are within CCA range 301. Then, a list up to 8
strongest RSSI's (or a different number) is generated 301-B. Then
the first AP*_i from the list is being picked from the list 302.
AP*_1 then sends Request-to-Join-APSS to the picked AP*_i 303. An
AP*_i which receives a Request-to-join, may respond with
ACK-to-APSS, or alternatively, may not respond; in one embodiment,
such a decision is based on limiting the response to the immediate
neighboring AP*_i which project the most interference, for example
limit to 4 APs with the strongest RSSI.
[0071] In a case that AP*_1 receives any ACK-to-APSS response 304,
AP*_1 updates its APSS table 305. In a case AP*_1 does not receive
any ACK-to-APSS response, the next AP*_i from the list is being
picked and the method goes on to the AP*_1 sending
Request-to-Join-APSS to the picked AP*_i 303 and so forth. When a
Request-to-Join is not being responded with ACK-to-APSS, AP*_i may
re-send the Request-to-Join several times, (e.g. resending the
Request-to-Join three times, each request being sent a few
milliseconds after the previous request) before proceeding to next
neighboring AP*_i 306, and revisit the non-responding AP*_i after
an extended time period, e.g. 1 minute.
[0072] One embodiment of the invention has APSS compatible AP
indicate their capability by a flag set in a vendor specific
information element (for example Element Identifier (ID) 122) in
the beacon management frame (See e.g. FIG. 11), in which case only
APSS capable APs within CCA range are probed with a
Request-to-Join-APSS (AP Sounding Set) 303. APs that are within
reception range may elect to respond with ACK-to-APSS 304; APs that
elect to respond are doing it with a ACK-to-APSS 304, and then time
stamping and RSSI are logged per BSSID 305 as outlined in table 307
of the figure.
[0073] Once the list of APSS is established, each AP*_i can try to
access an occupied channel following the APSS procedure which is
based on expanding the 802.11ac multi-user-MIMO (MU_MIMO) explicit
sounding.
[0074] In essence, the APSS process in one embodiment differs from
the existing MU-MIMO by replacing one of the simultaneously served
STAs with a neighboring AP; specifically, an AP that is capable of
serving L simultaneous STAs, is configured to serve only L-1 STAs
while nulling a neighboring AP which is currently occupying the
channel.
[0075] FIG. 4 is a diagram illustrating protocol sequence enabling
embodiments of the present invention. Specifically, APs that adhere
to APSS require air protocol modifications that support AP to AP
explicit sounding as described in the invention. In the example
shown, and similarly to MU-MIMO (IEEE 802.11ac), AP*_1 issues an
NDP Announcement to several APs in APSS. As opposed to MU-MIMO, one
of these nodes is not a client STA, but rather a given AP*_i. As
shown in the example, the first to respond is the AP*_2, and
following are polling and responses towards and from AP*_3's, and
subsequently to AP*_4. In another embodiment, this order may be
altered.
[0076] According to some embodiments of the present invention,
beamformer AP*_1 may send an NDP announcement to the listed
neighboring beamformees APs, followed by an NDP, and a compressed
matrix V representing the channel response (herein: compressed V
response) from a first neighboring AP*_i and a series of poll
requests to a next beamformee neighboring AP*_i and a corresponding
V compressed response, until all listed neighboring beamformees
neighboring APs are polled and all V compressed responses are
consummated.
[0077] FIG. 5 is a timing diagram 500 illustrating a modification
of the MU-MIMO protocol in the NDP announcement field 505,
facilitating an APSS messaging in accordance with embodiments of
the present invention. The NDP announcement exhibits an identical
structure to 802.11 AC NDP announcement with following changes:
APSSID contains the APSS ID that is established when APSS is
established while other fields have identical role to 802.11AC
sounding.
[0078] More specifically, the two byte STA field 506 of the MU-MIMO
protocol is retrofitted into a APSS ID field 501, rather than a STA
field, containing similar structure, i.e. a subfield APSS ID (e.g.
12 bits), a subfield indicating the FB feedback type being used
(e.g. 1 bit), and a subfield NC the Number of Columns in the
feedback matrix (e.g. 3 bits).
[0079] According to some embodiments of the present invention, the
APSS NDP announcement and NDP may include an APSS ID field
replacing in the MU MIMO protocol the STA ID field.
[0080] FIG. 6 is a timing diagram 600 illustrating the MU-MIMO
protocol. NDP 602 according the MU-MIMO protocol is shown here in
detail illustrating that the APSS process remains unchanged and
specifically it is identical to the MU-MIMO corresponding field of
IEEE 802.11ac. By way of non-limiting example, assuming a 4 antenna
AP, operating in 40 MHz bandwidth, there would be 4 VHT-LTF
sub-frames, with 6 symbols per sub-frames for 96 .mu.sec as
illustrated herein.
[0081] FIG. 7 is a timing diagram 700 illustrating a breakdown of
the Poll Request field 702. According to some embodiments of the
present invention, the Poll Request field may be retrofitted (e.g.,
used for a different purpose without altering the basic structure
of the protocol and its fields) to address neighboring beamformees
APs rather than STAs in the MU MIMO protocol. Specifically, fields
704 and 706 that were originally reserved for STAs in the MU-MIMO
protocol are now reserved for APs.
[0082] There is a set of topologic conditions and qualifications
that are verified before an AP*_1 may perform an APSS process and
access the busy channel: the beamformer AP is outside the CCA range
of the STA currently served by the beamformee AP; the beamformee AP
is outside the CCA range of the STA to be served by the Beamformer
AP; both served STAs are verified to be located closer than the
edge of their serving cells, since their corresponding AP*'s'
sensitivity is slightly reduced by minor residual interference
caused by the APSS process conditions are outlined as follows:
[0083] Beamformer AP identifies the Beamformee served station by
decoding the destination field, and either does not identify such a
STA MAC address in its neighborhood, or receives it at RSSI<CCA
level; [0084] Beamformer AP identifies the MCS transmitted by the
Beamformee AP to its served STA, and uses it in order to calculate
the proximity of said STA to the Beamformee's cell edge, e.g. low
MCS may indicate large range, and if so, will refrain from
accessing the channel; [0085] The beamformer AP will use RTS/CTS
for serving the STA it is intending to download data to, in order
to make sure said STA will not be jammed by the beamformee AP; and
[0086] The beamformer AP will gauge the RSSI of the CTS coming from
the STA it is intending to serve, calculates the proximity of the
STA to the beamformer AP's cell edge, in which case it will refrain
from accessing the channel.
[0087] Additionally, in order to guarantee the AP*_i session is not
harmed by the AP*_1 access, a null depth verification and
validation is required.
[0088] FIGS. 8A and 8B outline the sequence for a Single User MIMO
(SU-MIMO) service with nulling of a neighboring AP, and a Multi
User MIMO (MU-MIMO) service with nulling of a neighboring AP,
respectively, according to embodiments of the present invention.
Within the first few microseconds of the APSS process, phase and
amplitude information accuracy are considered virtually perfect,
and capable of yielding a very deep null (e.g. better than 30
dB).
[0089] FIG. 8A illustrates flowchart 800A for SU-MIMO mode. In step
801-a AP*_1 has data for STA_x. In step 802-a the AP*_1 NAV is
checked whether it is set or not. In a case that the NAV is set, in
step 803-a it is checked whether the nulling capability of AP*_1 is
sufficient to guarantee no harm to AP*_i current session. In a case
it is sufficient, in step 805-a the NAV is ignored and the nulling
process proceeds to step 806-a for setting up a null towards AP*_i
and further to step 807-a to sending data to STA_x. In a case that
AP*_1 NAV is not set, the process goes on directly to step 807-a to
sending data to STA_x. In a case that the nulling capability of
AP*_1 is insufficient to guarantee no harm to AP*_i current
session, the process goes on to step 804-a to waiting for the NAV
to clear before sending data to STA_x.
[0090] FIG. 8B illustrates flowchart 800B for MU-MIMO mode. In step
801-b AP*_1 has data for STAs_x, y, and z. In step 802-b the AP*_1
NAV is checked whether it is set or not. In a case that the NAV is
set, in step 803-b it is checked whether the nulling capability of
AP*_1 is sufficient to guarantee no harm to AP*_i current session.
In case it is sufficient, in step 805-b the NAV is ignored and the
nulling process proceeds to step 806-b for setting up a null
towards AP*_i and further to step 807-b to sending data to STAs_x,
y, and z. In a case that AP*_1 NAV is not set, the process goes on
directly to step 807-b to sending data to STAs_x, y, and z. In a
case that the nulling capability of AP*_1 is insufficient to
guarantee no harm to AP*_i current session, the process goes on to
step 804-b to waiting for the NAV to clear before sending data to
STAs_x, y, and z.
[0091] As a non-zero time has elapsed between such last APSS
channel estimation and the usage of the acquired weights for
nulling, a null deterioration estimation is performed as described
below, and then a nulling capability is calculated as described
further, yielding actual null depth figure of merit
Null.sub.--depth.
[0092] Therefore, proceeding to AP*_1 access of the occupied
channel, is conditioned by measuring RSSI.sub.AP*.sub.--.sub.i of
the AP*_i as received by AP*_1, and verifying that
RSSI.sub.AP*.sub.--.sub.i-Null.sub.--depth<CCA Level (e.g. -82
dBm), or another agreed upon dynamically calculated CCA Level.
[0093] According to some embodiments of the present invention, a
decision to access a channel occupied by a listed compatible
neighboring AP within CCA range, may be subject to verification and
validation of the access point null's capability to reduce the
interference caused by the access point to the neighboring AP below
CCA Level, for at least one of the neighboring AP antennas.
[0094] According to some embodiments of the present invention, the
access point may be configured to keep or store records (e.g. on a
memory) of fading rates of each listed compatible neighboring APs
within CCA range, in terms of amplitude and phase variation over
time, and further calculates for each of the listed neighboring APs
the standard deviation 1.sigma., 2.sigma., 3.sigma. of the
amplitude and phase variations, and further estimates a
corresponding amplitude and phase drift rate.
[0095] According to some embodiments of the present invention, the
access point may be further configured to keep or store records of
fading rates of each listed compatible neighboring APs within CCA
range, in terms of amplitude and phase variation over time, and
further calculates for each of the listed compatible neighboring AP
within CCA range the standard deviation 1.sigma., 2.sigma.,
3.sigma. of the amplitude and phase variations, and further
estimates a corresponding amplitude and phase drift rate.
[0096] According to some embodiments of the present invention, the
access point may be further configured to estimate the nulling
capability by calculating the time elapsed between the last
sounding of the compatible neighboring AP within CCA range and the
time the condition is being examined, apply the amplitude and phase
drift rate, and further estimates the null depth degradation,
caused by the accumulated drift, yielding actual null depth.
[0097] According to some embodiments of the present invention, the
access point may be further configured to null compatible
neighboring AP within CCA range while downloading a packet to
served STA, in a case where the neighboring AP RSSI--Actual Null
Depth<CCA Level, provided several predefined topologic
conditions are met.
[0098] According to some embodiments of the present invention, the
topologic conditions may be defined as, for example: (i) the access
point is not within CCA range of the STA served by compatible
neighboring AP within CCA range (ii); the neighboring AP is not
within CCA range of the STA or STAs about to be served by the
access point (iii); and/or the served STAs are not on their
servicing cell's edges.
[0099] AP*_1 may perform periodical APSS sounding process with a
given AP*_i, when the AP*_i is not transmitting; such period are
preferably done at intervals larger than the maximum packet
duration (e.g. 7 ms or more).
[0100] According to some embodiments of the present invention, the
access point may perform the sounding of the listed neighbors that
have agreed to join the APSS, on a periodic basis, whenever a given
compatible neighboring AP within CCA range is not transmitting.
Such periods are preferably carried out at intervals longer than
the maximum packet duration (e.g. 7 ms or more).
[0101] According to some embodiments of the present invention, the
access point may be configured to limit a number of responses
produced by it so as to allocate up to approximately 10% of a
transmitting time to respond to sounding requests from the listed
neighboring access points.
[0102] According to some embodiments of the present invention, the
sounding of the listed neighboring access points may be performed
based on IEEE 802.11ac MU MIMO sounding procedure, wherein the
access point may respond to a limited number of compatible
neighboring APs including up to eight strongest RSSIs.
[0103] According to some embodiments of the present invention, the
access point may carry out an actual download of a packet to a STA,
or a group of STAs, while the channel may be occupied by a
compatible neighboring AP within CCA range, may be carried out with
such antenna pattern that may minimize the power received by at
least one of the neighboring AP antennas.
[0104] Following fading fluctuation over time, and average time
interval between consecutive APSS sounding, a phase and amplitude
gradients are calculated (e.g. standard deviation 1.sigma.,
2.sigma., 3.sigma.), and applied to a null deterioration chart (See
FIG. 10), yielding null depth figure of merit.
[0105] FIG. 9 is a diagram 900 illustrating AP*_1 assessment
process of fading, according to embodiments of the present
invention, based on logging phase and amplitude differences between
pairs of antennas, and determining fluctuations over time.
Transmitter 902 being an AP*_1 transmits a fading channel 905 to
receiver AP*_i 904. Fluctuations are shown over time in a phase
diagram 906 and amplitude diagram 908. In one embodiment, such
fluctuations are calculated as peak-to-peak phase changes over 5,
10, 20 and 50 ms wherein the largest 10 percent are not considered
(e.g. within two standard deviations 2.sigma.), yielding possible
accumulated phase and amplitude errors.
[0106] FIG. 10 is a graph diagram 1000 illustrating an example of
resultant calculations applied to calculation formula that
estimates a null deterioration in dB (vertical axis) versus phase
and amplitude setting inaccuracy in degrees (horizontal axis), the
different lines indicate different gains in dB. When applying phase
and amplitude imbalance, an effective or actual null depth is
derived, and then a nulling capability is verified as follows:
RSSI.sub.AP*.sub.--.sub.i-Null.sub.--Depth must in some embodiments
be lower than allowed CCA Level, in order to allow AP_* 1 to
proceed to accessing the busy channel.
[0107] FIG. 11 is a diagram illustrating the structure of the
802.11 Beacon Frame 1100 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. Typically the
vendor specific data may start with a device/vendor ID followed by
a flag to indicate APSS capability. Where APSS becomes
standardized, a specific Information Element ID could be assigned
to indicate capability rather than embedding this information in a
vendor specific data element.
[0108] According to some embodiments of the present invention, the
access point may include: a plurality of antennas; a plurality of
radio circuitries configured to transmit and receive signals via
the plurality of antennas; and a baseband processor configured to
monitor signals received by the radio circuitries and generate a
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.
[0109] The baseband processor may further be configured to instruct
the radio circuitries to transmit a sounding sequence to the list
of compatible neighboring access points, and receive Channel State
Information (CSI) from the compatible neighboring access points,
wherein the compatible neighboring access points indicate having a
capability of responding to sounding sequences by transmitting
identification of the capability in a beacon management frame. The
baseband configuration capabilities may be broadcasted to the
compatible neighboring access points via unused bits within the
beacon management frame.
[0110] As will be appreciated by one 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." For example, a baseband processor or other processor may
be configured to carry out methods of the present invention by for
example executing code or software.
[0111] The aforementioned flowcharts and 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.
[0112] 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.
[0113] 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.
[0114] 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 will further be recognized that the aspects of the
invention described hereinabove may be combined or otherwise
coexist in embodiments of the invention.
[0115] The principles and uses of the teachings of the present
invention may be better understood with reference to the
accompanying description, figures and examples.
[0116] It is to be understood that the details set forth herein do
not construe a limitation to an application of the invention.
[0117] 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.
[0118] 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.
[0119] 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
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.
[0120] 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. 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.
[0121] 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.
[0122] 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.
* * * * *