# Patent

## Title
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).

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims benefit from U.S. provisional patent application Ser. No. 61/955,433 filed on Mar. 19, 2014, which is incorporated herein by reference in its entirety.


FIELD OF THE INVENTION
The present invention relates generally to wireless communication, and more specifically to high efficiency Wi-Fi.
BACKGROUND OF THE INVENTION
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.
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.
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.
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).
The notation “STA” as used herein is defined in as an IEEE 802.11 client.
The term “BSS” is an acronym for Basic Service Set, which is typically a cluster of stations supported by an AP.
The term “node” as used herein is defined as general name for both IEEE 802.11 AP and IEEE 802.11 STA.
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.
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.
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.
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.
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.
The notation “SINR” stands for Signal to Interference and Noise.
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.
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.
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.
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.
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-à-vis as received by the client/STA, allowing it to gauge possible distortions and correct them.
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).
The term “non-associated STA” as used herein refers to a STA within the range of the non-serving AP.
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.
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.
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.
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.
The acronym “FLA” stands for Fast Link Adaptation, and represents processes that reduce transmitting side learning time of the receiver's SINR.
The acronym “MCS” stands for Modulation Coding Scheme, mapping SINR to modulation order and code rate.
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”.
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.
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.
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.
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.
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.
AP*—1 indicated an AP that initiates the APSS process. If multiple AP* are present, then multiple APSS's exist.
APSS_ID indicated an N bit random code selected by AP*—1 to identify the APSS that it has created (e.g. N=12).
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”.
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.
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
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.
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.
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.
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.
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.
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.
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
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:
FIG. 1A is a block diagram illustrating a typical operational environment in accordance with the prior art;
FIG. 1B is a block diagram illustrating an access point with transmit and receive MIMO capability;
FIG. 2 is a block diagram illustrating an example of the effect of using nulling in accordance with some embodiments of the present invention;
FIG. 3 is an initialization phase in accordance with some embodiments of the present invention;
FIG. 4 is an example of APSS message flow in accordance with some embodiments of the present invention;
FIG. 5 is an APSS sounding announcement in accordance with some embodiments of the present invention;
FIG. 6 is an APSS Null Data Package in accordance with some embodiments of the present invention;
FIG. 7 is an APSS feedback in accordance with some embodiments of the present invention;
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;
FIG. 8B is a flow chart for an AP serving multiple simultaneous STAs (MU-MIMO) in accordance with some embodiments of the present invention;
FIG. 9 is an example of fading gradient in accordance with some embodiments of the present invention;
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
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
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.
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.
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.
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.
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.
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.
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.
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.
According to some embodiments, an explicit sounding process invoked between the access point and each of the listed neighboring access points.
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.
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.
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.
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 802.1 lac multi-user-MIMO (MU_MIMO) explicit sounding.
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.
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.
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.
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.
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).
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.
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 802.11 ac. 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 μsec as illustrated herein.
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.
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:

    
    
        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;
        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;

    
    
        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
        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.
    
    


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.
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).
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.
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.
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—depth.
Therefore, proceeding to AP*—1 access of the occupied channel, is conditioned by measuring RSSIAp*—i of the AP*_i as received by AP*—1, and verifying that RSSIAP*—i-Null—depth<CCA Level (e.g. −82 dBm), or another agreed upon dynamically calculated CCA Level.
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.
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 1σ, 2σ, 3σ of the amplitude and phase variations, and further estimates a corresponding amplitude and phase drift rate.
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 1σ, 2σ, 3σ of the amplitude and phase variations, and further estimates a corresponding amplitude and phase drift rate.
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.
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.
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.
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).
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).
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.
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.
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.
Following fading fluctuation over time, and average time interval between consecutive APSS sounding, a phase and amplitude gradients are calculated (e.g. standard deviation 1σ, 2σ, 3σ), and applied to a null deterioration chart (See FIG. 10), yielding null depth figure of merit.
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 2σ), yielding possible accumulated phase and amplitude errors.
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: RSSIAP*—i-Null—Depth must in some embodiments be lower than allowed CCA Level, in order to allow AP—* 1 to proceed to accessing the busy channel.
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.
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.
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.
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.
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.
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 will further be recognized that the aspects of the invention described hereinabove may be combined or otherwise coexist in embodiments of the invention.
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 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. 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.

## Claims

1. An access point 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 generate a list of neighboring co-channel access points, each neighboring co-channel access point having a plurality of antennas and each being located within a clear channel assessment (CCA) range of the access point,
wherein the baseband processor is further configured to instruct the radio circuitries to transmit a sounding sequence to the list of neighboring co-channel access points, and receive Channel State Information (CSI),
wherein the baseband processor is further configured to set weights on the radio circuitries to produce a null at one or more antennas of the listed neighboring co-channel access point which currently transmits on a same frequency channel and downloads of a packet to a station (STA), or a group of STAs,
wherein null weights are determined via an explicit sounding process invoked between the access point and each of the listed neighboring co-channel access points, based on a null data packet (NDP) announcement by a nulling AP and response by a nulled AP,
wherein the access point sounding set (APSS) NDP announcement and NDP comprise an access point sounding set ID field replacing an STA ID field in a MU MIMO protocol.

2. The access point according to claim 1, wherein a beamformer AP sends an NDP announcement to listed neighboring beamformees APs, followed by an NDP, and a V compressed response from a first neighboring AP and a series of poll requests to a next beamformee neighboring AP and a corresponding V compressed response, until all listed neighboring beamformees neighboring APs are polled and all V compressed responses are consummated, wherein V is a compressed matrix representing the channel response.

3. An access point 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 generate a list of neighboring co-channel access points, each neighboring co-channel access point having a plurality of antennas and each being located within a clear channel assessment (CCA) range of the access point,
wherein the baseband processor is further configured to instruct the radio circuitries to transmit a sounding sequence to the list of neighboring co-channel access points, and receive Channel State Information (CSI),
wherein the baseband processor is further configured to set weights on the radio circuitries to produce a null at one or more antennas of the listed neighboring co-channel access point which currently transmits on a same frequency channel and downloads of a packet to a station (STA), or a group of STAs,
wherein null weights are determined via an explicit sounding process invoked between the access point and each of the listed neighboring co-channel access points, based on a null data packet (NDP) announcement by a nulling AP and response by a nulled AP, and a series of poll requests to a next beamformee neighboring AP and a corresponding response, and
wherein a Poll Request field is retrofitted to address a neighboring beamformee AP rather than a STA in a MU MIMO protocol.

4. The access point according to claim 1, wherein the access point performs the sounding of listed neighbors that have agreed to join the APSS, on a periodic basis, when a given compatible neighboring AP within CCA range is not transmitting.

5. The access point according to claim 1, further configured to limit a number of responses produced by the access point so as to allocate up to approximately 10% of a transmitting time to respond to sounding requests from the listed neighboring co-channel access points.

6. The access point according to claim 1, wherein the sounding of the listed neighboring co-channel access points is performed based on IEEE 802.11ac MU MIMO sounding procedure, wherein the access point responds to a limited number of compatible neighboring APs-comprising up to 8 strongest received signal strength indicators (RSSIs).

7. The access point according to claim 1, wherein an actual download of a packet to a STA, or a group of STAs, while the channel is occupied by a compatible neighboring AP within CCA range, is done with such antenna pattern that minimizes the power received by at least one of the neighboring AP antennas.

8. The access point according to claim 1, wherein a decision to access a channel occupied by a listed compatible neighboring AP within CCA range, is conditioned by 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.

9. The access point according to claim 1, the access point being configured to keep 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 neighboring APs the standard deviation 1σ, 2σ, and 3σ of the amplitude and phase variations, and further estimates a corresponding amplitude and phase drift rate.

10. The access point according to claim 5, wherein the access point is configured to keep 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 1σ, 2σ, and 3σ of the amplitude and phase variations, and further estimates a corresponding amplitude and phase drift rate.

11. The access point according to claim 7, 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.

12. The access point according to claim 7, further configured to null compatible neighboring AP within CCA range while downloading a packet to served STA, in a case where the neighboring APRSSI−Actual Null Depth<CCA Level, provided predefined topologic conditions are met.

13. The access point according to claim 12, wherein said predefined topologic conditions are defined as: (i) the access point is not within CCA range of the STA served by compatible neighboring AP within CCA range; or (ii) the neighboring AP is not within CCA range of the STA or STAs about to be served by the access point; or (iii) the served STAs are not on their servicing cell's edges.

14. A method of performing an explicit sounding process to neighboring access points by a beamformer access point 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 neighboring co-channel access point having a plurality of antennas and each being 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 co-channel access points, and receive Channel State Information (CSI) from the neighboring access points,
setting weights on the radio circuitries to produce a null at one or more antennas of the listed neighboring co-channel access point which currently transmits on a same frequency channel and download of a packet to a STA, or a group of STAs,
wherein null weights are determined via an explicit sounding process invoked between the access point and each of the listed neighboring co-channel access points, based on a null data packet (NDP) announcement by a nulling AP and response by a nulled AP, and
wherein the access point sounding set (APSS) NDP announcement and NDP comprise an access point sounding set ID field replacing an STA ID field in a MU MIMO protocol.

15. The method according to claim 14, wherein the access point performs the sounding on a sequential and periodic basis, when a given compatible neighboring AP within CCA range is not transmitting.

16. The method according to claim 14, wherein the sounding of the listed neighboring co-channel access points is performed based on IEEE 802.11ac MU MIMO sounding procedure wherein the access point is configured to respond to a limited number of immediate compatible neighboring APs-comprising up to 8 strongest received signal strength indicators (RSSIs).

17. The method according to claim 14, wherein an actual download of a packet to a STA, or a group of STAs, while the channel is occupied by an neighboring AP, is done with such antenna pattern that minimizes the power received by at least one of the neighboring AP antennas.

18. The method according to claim 14, wherein a decision to access a channel occupied by a listed a compatible neighboring AP within CCA range, is conditioned by verification and validation of the access point null's capability to reduce the interference caused by the access point to the compatible neighboring AP below CCA Level, for at least one of the neighboring AP antennas.

19. The method according to claim 14, further comprising keeping records of fading rates of each listed a compatible neighboring AP within CCA range, in terms of amplitude and phase variation over time, and further calculates for each of the listed AP the standard deviation 1σ, 2σ, and 3σ of the amplitude and phase variations, and further estimates a corresponding amplitude and phase drift rate.

20. The method according to claim 19, further comprising keeping records of fading rates of each listed a compatible neighboring AP within CCA range, in terms of amplitude and phase variation over time, and further calculates for each of the listed AP the standard deviation 1σ, 2σ, and 3σ of the amplitude and phase variations, and further estimates a corresponding amplitude and phase drift rate.

21. The method according to claim 20, further comprising estimating the nulling capability by calculating the time elapsed between the last sounding of the neighboring AP 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.

22. The method according to claim 21, further comprising nulling a compatible neighboring AP within CCA range while downloading a packet to served STA, in a case where a compatible neighboring APRSSI−Actual Null Depth<CCA, provided it meets predefined topologic conditions.

23. The method according to claim 22, wherein the predefined topologic conditions are defined as: (i) the access point is not within CCA range of the STA served by a compatible neighboring AP within CCA range; or (ii) the neighboring AP is not within CCA range of the STA or STAs about to be served by the access point; or (iii) the served STAs are not on their servicing cell's edges.