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.

Description:
PRIORITY APPLICATION 
       [0001]    This application is a continuation of U.S. application Ser. No. 12/843,663, filed Jul. 26, 2010, which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    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 
       [0003]    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. 
         [0004]    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. 
         [0005]    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 
         [0006]      FIG. 1  illustrates an access point and wireless stations in a wireless local area network, in accordance with some embodiments; 
           [0007]      FIG. 2  illustrates a transmission timeline between the access point and the wireless stations, in accordance with some embodiments; 
           [0008]      FIG. 3  illustrates a procedure for an access point to request sounding measurements, in accordance with some embodiments; 
           [0009]      FIG. 4  illustrates a procedure for a wireless station to respond to a sounding request, in accordance with some embodiments; 
           [0010]      FIG. 5  illustrates a functional block diagram of an access point, in accordance with some embodiments; and 
           [0011]      FIG. 6  illustrates a functional block diagram of a wireless station, in accordance with some embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    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. 
         [0013]      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. 
         [0014]    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. 
         [0015]    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 . 
         [0016]    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. 
         [0017]    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 . 
         [0018]    Although three STAs  108  are presented for illustrative purposes, any number of STAs may be employed. 
         [0019]      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 . 
         [0020]    Stations STA 1   202 , STA 2 ,  204  and STA 3   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 . 
         [0021]      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. 
         [0022]      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. 
         [0023]    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. 
         [0024]      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. 
         [0025]    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. 
         [0026]    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. 
         [0027]    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. 
         [0028]      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. 
         [0029]    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. 
         [0030]    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. 
         [0031]    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. 
         [0032]    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. 
         [0033]    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. 
         [0034]    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 . 
         [0035]    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. 
         [0036]    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. 
         [0037]    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.