# Patent

## Title
Method and devices for multiple station sounding in a wireless local area network

## Abstract

Embodiments of a method and apparatus for obtaining sounding measurements between an access point and a wireless station within a wireless local area network are described. Some embodiments relate to Wi-Fi networks and networks operating in accordance with one of the IEEE 802.11 standards. Some embodiments may allow an access point to request that multiple stations compute sounding measurements with minimal time delay between measurements. Other embodiments may be described and claimed.

## Background
PRIORITY APPLICATION
This application is a continuation of U.S. application Ser. No. 12/843,663, filed Jul. 26, 2010, now issued as U.S. Pat. No. 8,630,195, which is incorporated herein by reference in its entirety.


TECHNICAL FIELD
Various embodiments described herein relate to apparatus and methods associated with wireless local area network communication. Some embodiments relate to Wireless Fidelity (Wi-Fi) networks and networks operating in accordance with one of the IEEE 802.11 standards. Some embodiments relate to communications and data transmission between an access points (AP) and wireless local area network devices or stations (STAs).
BACKGROUND
In a wireless local area network it is occasionally useful to perform sounding measurements of the communications environment between the access point and the wireless stations. These sounding measurements may provide data for use in beamforming and multiple input multiple output (MIMO) antenna operations. It is often desirable for an access point to request sounding information from multiple stations in parallel in order to obtain this information while maintaining singular communication link conditions.
Currently, an access point may request a sounding from a station by sending an announce message followed by a null data packet (NDP) sounding message directed to that station. This procedure may be repeated for each station, which can be time consuming and inefficient and may result in an unacceptable delay between the sounding measurements performed at each of the stations.
Thus, there are general needs for apparatus and efficient methods for an access point to request that multiple stations compute sounding measurements with minimal time delay between measurements.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates an access point and wireless stations in a wireless local area network, in accordance with some embodiments;
FIG. 2 illustrates a transmission timeline between the access point and the wireless stations, in accordance with some embodiments;
FIG. 3 illustrates a procedure for an access point to request sounding measurements, in accordance with some embodiments;
FIG. 4 illustrates a procedure for a wireless station to respond to a sounding request, in accordance with some embodiments;
FIG. 5 illustrates a functional block diagram of an access point, in accordance with some embodiments; and
FIG. 6 illustrates a functional block diagram of a wireless station, in accordance with some embodiments.



DETAILED DESCRIPTION
The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in, or substituted for, those of other embodiments. Embodiments set forth in the claims encompass all available equivalents of those claims.
FIG. 1 illustrates an access point and wireless stations in a wireless local area network in accordance with some embodiments. Wireless network 100 includes an access point (AP) 102 and one or more stations (STAs) 108. In some embodiments, the wireless network 100 may be a Wi-Fi network in accordance with specific communication standards, such as the Institute of Electrical and Electronics Engineers (IEEE) standards, including IEEE 802.11-2007 and/or 802.11(n) standards and/or proposed specifications for WLANs including the IEEE 802.11(ac) standard.
In the wireless network 100 it may be useful to perform sounding measurements of the communications environment between the AP 102 and the STAs 108. These sounding measurements may provide data for use in beamforming and multiple input multiple output (MIMO) antenna operations.
In some embodiments, AP 102 may request soundings from STAs 108 by transmitting an announce message 104 and a null data packet (NDP) sounding message 106, which may be received by STAs 108. In response, the STAs 108 may compute sounding measurements 110 and transmit them back to AP 102. In some embodiments, the announce message 104 may precede the NDP sounding message 106 or the NDP sounding message 106 may precede the announce message 104.
In some embodiments, it may be advantageous for an AP 102 to request sounding information from multiple STAs 108 in parallel in order to minimize the effect of changing communication link conditions. This may be useful, for example, in the case of beamforming on the downlink (DL) multiuser (MU) MIMO transmission. In some embodiments, this may be accomplished by transmitting the announce message 104 as a broadcast message containing the unicast recipient addresses (RAs) of the STAs 108 for which sounding is desired. In some embodiments, this may be accomplished by transmitting the announce message 104 as a multicast message containing the group address for the group of STAs 108 for which sounding is desired. In some embodiments, this may be accomplished by transmitting the announce message 104 as a multicast message associating a list of unicast RAs of the STAs 108 for which sounding is desired with a multicast group address.
In some embodiments, the order of the RAs in the announce message 104 may determine the order in which the STAs 108 respond with sounding measurements 110.
Although three STAs 108 are presented for illustrative purposes, any number of STAs may be employed.
FIG. 2 illustrates a transmission timeline between the access point and the wireless stations, in accordance with some embodiments. AP 200 transmits an announce message 208 and an NDP sounding message 210. In some embodiments, the announce message 208 may precede the NDP sounding message 210 or the NDP sounding message 210 may precede the announce message 208. The time interval between the announce message 208 and the NDP sounding message 210 may be a reduced interframe spacing (RIFS) 220 as shown. In some embodiments, the time interval between the announce message 208 and the NDP sounding message 210 may be a short interframe spacing (SIFS) 222.
Stations STA1 202, STA2, 204 and STA3 206 respond to the NDP sounding message 210 by computing and transmitting sounding measurements 212, 214 and 216. Although three STAs are presented for illustrative purposes, any number of STAs may be employed. The time interval between the sounding measurements 212, 214 and 216 may be a short interframe spacing (SIFS) 222.
FIG. 3 illustrates a procedure for an access point to request sounding measurements, in accordance with some embodiments. Procedure 300 may be performed by an AP, such as AP 102 (FIG. 1). Operation 310 comprises transmitting an NDP sounding message from the AP to the STAs. Operation 320 comprises transmitting an announce message from the AP to the STAs. The announce message may be a multicast message or a broadcast message. Operation 330 comprises including a list of unicast RAs of the STAs for which a sounding measurement is requested in the announce message. Operation 340 comprises ordering the list of RAs to identify the order of response from the STAs.
FIG. 4 illustrates a procedure for a wireless station to respond to a sounding request, in accordance with some embodiments. Procedure 400 may be performed by an STA, such as STA 108 (FIG. 1). Operation 410 comprises receiving an NDP sounding message from the AP. Operation 420 comprises receiving an announce message from the AP containing a list of STAs to provide sounding measurements. Operation 430 comprises determining if the STA is on the list. Operation 440 comprises resetting the sounding measurement if the STA is not on the list. Operation 450 comprises computing a sounding measurement if the STA is on the list. Operation 460 comprises transmitting the sounding measurement at a time based on the ordering of the STAs in the list. In some embodiments, the time of transmission is determined such that a short interframe spacing (SIFS) is achieved between the sounding measurement transmissions from each STA.
Although the individual operations of procedures 300 and 400 are illustrated and described as separate operations, one or more of the individual operations may be performed concurrently, and nothing requires that the operations be performed in the order illustrated. Furthermore, some operations may be optional.
FIG. 5 illustrates a functional block diagram of an access point, in accordance with some embodiments. Access point 500 may include a transceiver circuit 504 and a processing circuit 506. Transceiver circuit 504 may be coupled to one or more antennas 508 for transmitting and receiving messages from wireless stations, such as STA 108 (FIG. 1). In accordance with some embodiments, the AP 500 may be configured to operate in a wireless local area network. In some embodiments, the wireless local area network may be a Wi-Fi network operating in accordance with the 802.11 standard.
In these embodiments, the processing circuit 506 may determine a plurality of STAs which are to provide a sounding measurement. In these embodiments, the transceiver circuit 504 may transmit an NDP sounding message and an announce message. The announce message may identify the plurality of STAs which are to provide a sounding measurement in response to the NDP sounding message. In some embodiments, the transceiver circuit 504 may transmit the NDP sounding message prior to the announce message.
In some embodiments, the transceiver circuit 504 may transmit the announce message as a multicast message. In some embodiments, the transceiver circuit 504 may transmit the announce message as a broadcast message. In some embodiments, the announce message may contain a list of unicast recipient addresses (RAs) of the STAs.
In some embodiments, the processing circuit 506 may further order the list of RAs to identify an order of the response sounding measurements of the STAs.
FIG. 6 illustrates a functional block diagram of a wireless station in accordance with some embodiments. Station 600 may include a transceiver circuit 604 and processing circuit 606. Transceiver circuit 604 may be coupled to one or more antennas 608 for transmitting and receiving messages from access points, such as AP 102 (FIG. 1). In accordance with some embodiments, the STA 600 may be configured to operate in a wireless local area network. In some embodiments, the wireless local area network may be a Wi-Fi network operating in accordance with the 802.11 standard.
In these embodiments, the transceiver circuit 604 may receive an NDP sounding message and an announce message. The announce message may identify a plurality of STAs which are to provide a sounding measurement in response to the NDP sounding message. In some embodiments, the transceiver circuit 604 may receive the NDP sounding message prior to the announce message.
In these embodiments, the processor circuit 606 may recognize that the STA is one of the plurality of STAs identified in the announce message. In some embodiments, the processor circuit 606 may further compute a sounding measurement in response to the recognition.
In some embodiments, the processing circuit 606 may further recognize that the STA is not one of the plurality of STAs identified in the announce message and may then reset the sounding measurement in response to the recognition.
In some embodiments the transceiver circuit 604 further transmits a computed sounding measurement. In some embodiments, the transceiver circuit 604 transmits the sounding measurement at a time based on the ordering of the STAs in the announce message. In some embodiments, the time of transmission is determined such that a short interframe spacing (SIFS) is achieved between the sounding measurement transmissions from each STA.
In some embodiments, STA 600 may be part of a portable wireless communication device, such as a personal digital assistant (PDA), a laptop or portable computer with wireless communication capability, a web tablet, a wireless telephone, a wireless headset, a pager, an instant messaging device, a digital camera, an access point, a television, a smart phone, or other device that may receive and/or transmit information wirelessly.
Antennas 508 and 608 may comprise one or more directional or omnidirectional antennas, including, for example, dipole antennas, monopole antennas, patch antennas, loop antennas, microstrip antennas or other types of antennas suitable for transmission of RF signals. In some embodiments, instead of two or more antennas, a single antenna with multiple apertures may be used. In these embodiments, each aperture may be considered a separate antenna. In some multiple-input multiple-output (MIMO) embodiments, antennas 508 and 608 may be effectively separated to take advantage of spatial diversity and the different channel characteristics that may result between each of antennas 508 and 608.
Although AP 500 and STA 600 are illustrated as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, some elements may comprise one or more microprocessors, DSPs, application-specific integrated circuits (ASICs), radio-frequency integrated circuits (RFICs) and combinations of various hardware and logic circuitry for performing at least the functions described herein. In some embodiments, the functional elements of AP 500 and STA 600 may refer to one or more processes operating on one or more processing elements.
Embodiments may be implemented in one or a combination of hardware, firmware and software. Embodiments may also be implemented as instructions stored on a computer-readable storage medium, which may be read and executed by at least one processor to perform the operations described herein. A computer-readable medium may include any tangible medium for storing in a form readable by a machine (e.g., a computer). For example, a computer-readable medium may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, and flash-memory devices.
The Abstract is provided to comply with 37 C.F.R. Section 1.72(b) requiring an abstract that will allow the reader to ascertain the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to limit or interpret the scope or meaning of the claims. The following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment.

## Claims

1. A wireless station (STA) comprising:
a transceiver circuit to:
receive a null data packet (NDP) message from a wireless access point (AP); and
receive a Very High Throughput (VHT) NDP Announcement message, the VHT NDP Announcement message including a listing of a plurality of stations (STAs); and

a processor circuit to:
determine that an identifier of the wireless STA is listed first in the listing of the plurality of STAs included in the VHT NDP Announcement message; and
responsive to determining that the identifier is first in the listing of the plurality of STAs:
calculate a VHT Compressed Beamforming feedback message based upon the NDP message; and
cause the transceiver circuit to transmit the VHT Compressed Beamforming feedback message immediately after a short interframe space (SIFS) that occurs after receiving the NDP message.

2. The wireless STA of claim 1, wherein the wireless STA operates in accordance with an IEEE 802.11ac standard, and wherein the transceiver circuit is configured to receive a downlink multiple user multiple input multiple output (MU-MIMO) transmission from the AP, the AP configuring the MU-MIMO transmission based on the VHT Compressed Beamforming feedback message.

3. The wireless STA of claim 2, wherein the wireless STA is part of one of: a laptop computer, a smart phone, and a tablet.

4. The wireless STA of claim 3, wherein the transceiver circuit is configured to receive a downlink beamformed signal from the AP, the AP utilizing the VHT Compressed Beamforming feedback message to calculate parameters of the downlink beamformed signal.

5. The wireless STA of claim 1, wherein the VHT NDP Announcement message is received before the NDP message.

6. The wireless STA of claim 4, wherein the NDP message is received immediately after a short interframe space (SIFS) after receiving the VHT NDP Announcement message.

7. A non-transitory machine readable medium that stores instructions which when performed by a wireless station (STA), cause the wireless STA to perform operations comprising:
receiving a null data packet (NDP) message from a wireless access point (AP);
receiving a Very High Throughput (VHT) NDP Announcement message, the VHT NDP Announcement message including a listing of a plurality of stations (STAs);
determining that an identifier of the wireless STA is listed first in a listing of a plurality of STAs included in the VHT NDP Announcement message; and
responsive to determining that the identifier is first in the listing of the plurality of STAs:
calculating a VHT Compressed Beamforming feedback message based upon the NDP message; and
transmitting the VHT Compressed Beamforming feedback message immediately after a short interframe space (SIFS) that occurs after receiving the NDP message.

8. The machine readable medium of claim 7, wherein the VHT NDP Announcement message is a broadcast message sent to the plurality of STAs.

9. The machine readable medium of claim 7, wherein the AP utilizes the VHT Compressed Beamforming feedback message to calculate beamforming parameters to the wireless STA.

10. The machine readable medium of claim 7, wherein the VHT NDP Announcement message is received before the NDP message.

11. The machine readable medium of claim 7, wherein the NDP message is received immediately after a short interframe space (SIFS) after receiving the VHT NDP Announcement message.

12. A non-transitory machine readable medium that stores instructions which when performed by an Access Point (AP), cause the AP to perform operations comprising:
transmitting a null data packet (NDP) message; and
transmitting a Very High Throughput (VHT) NDP Announcement, the announce message identifying a plurality of stations (STAs) in a listing of stations, the listing of stations providing respective identifiers for the plurality of STAs which are to provide a VHT Compressed Beamforming feedback message in response to the NDP message, wherein the VHT Compressed Beamforming feedback message provided from the plurality of STAs in response to the NDP message is transmitted at respective times, and wherein data from the VHT NDP Announcement message is used by at least one of the plurality of STAs to determine the time for transmitting the VHT Compressed Beamforming feedback message by the at least one STA.

13. The machine readable medium of claim 12, wherein the operations comprise transmitting the VHT NDP Announcement message prior to the NDP message.

14. The machine readable medium of claim 13, wherein the AP operates in a wireless network in accordance with an IEEE 802.11(ac) standard, and wherein the operations comprise: performing a downlink multiple user multiple input multiple output (MU-MIMO) transmission configured based on the VHT Compressed Beamforming feedback message to the at least one STA.

15. The machine readable medium of claim 14, wherein the operations comprise:
receiving a VHT Compressed Beamforming feedback message from the at least one of the STAs prior to receiving a VHT Compressed Beamforming feedback message from the remaining of the identified plurality of STAs.

16. The machine readable medium of claim 12, wherein the VHT NDP Announcement message is a broadcast message.

17. The machine readable medium of claim 12, wherein the operations comprise receiving a VHT Compressed Beamforming feedback message from the at least one of the STAs prior to receiving a VHT Compressed Beamforming feedback message from the remaining of the identified plurality of STAs.

18. An Access Point (AP) comprising:
a processing circuit to determine a plurality of stations (STAs) which are to provide a Very High Throughput (VHT) Compressed Beamforming feedback message; and
a transceiver circuit to:
transmit a null data packet (NDP) message; and
transmit a VHT NDP Announcement message, the announce message identifying the plurality of STAs in a listing of stations, the listing of stations providing respective identifiers for the plurality of STAs which are to provide a VHT Compressed Beamforming feedback message in response to the NDP message, wherein the VHT Compressed Beamforming feedback message provided from the plurality of STAs in response to the NDP message is transmitted at respective times, and wherein data from the VHT NDP Announcement message is used by at least one of the plurality of STAs to determine the time for transmitting the VHT Compressed Beamforming feedback message by the at least one STA.

19. The AP of claim 18, wherein the transceiver circuit is configured to send the VHT NDP Announcement message prior to the NDP message.

20. The AP of claim 18, wherein the AP operates accordance with an IEEE 802.11(ac) standard, and wherein the transceiver circuit performs a downlink multiple user multiple input multiple output (MU-MIMO) transmission based on the VHT Compressed Beamforming feedback message.

21. The AP of claim 18, wherein the VHT NDP Announcement message is a broadcast message.

22. The AP of claim 18, wherein the transceiver circuit is configured to receive a VHT Compressed Beamforming feedback message from the at least one of the STAs prior to receiving a VHT Compressed Beamforming feedback message from the remaining of the identified plurality of STAs.