Patent Publication Number: US-9414380-B2

Title: Millimeter-wave communication station and method for multiple-access beamforming in a millimeter-wave communication network

Description:
This application is a continuation of U.S. patent application Ser. No. 12/574,140, filed on Oct. 6, 2009, now issued as U.S. Pat. No. 8,625,565, which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments pertain to millimeter-wave communication stations and methods for performing beamforming. Some embodiments pertain to wireless networks that use millimeter-wave frequencies to communicate, such as wireless personal area networks (WPANs) and wireless local area networks (WLANs). Some embodiments relate to millimeter-wave networks operating in accordance with specifications of the wireless gigabit alliance (WGA). 
     BACKGROUND 
     Many conventional wireless networks communicate using microwave frequencies generally ranging between two and ten gigahertz (GHz). These systems generally employ either omnidirectional or low-directivity antennas primarily because of the comparatively long wavelengths of the frequencies used. The low directivity of these antennas limits the throughput of such systems, making applications such as real-time video streaming and high-definition television (HDTV) difficult to implement. The millimeter-wave band has the available spectrum and is capable of providing significantly higher-level throughputs; however, due to higher attenuation levels of millimeter-waves, more directional antennas and beamforming techniques are employed. Beamforming allows a pair of stations to achieve a desirable link budged for subsequent communications. 
     One issue with millimeter-wave networks is collisions that occur between communication stations attempting to establish or reestablish a link and perform beamforming training. Conventionally, only a single communication station at a time is able to perform beamforming training with the network coordinator (e.g., a Piconet Coordinator Point (PCP), Access Point, or Coordination Point). This may result in a significant delay when multiple responding stations are attempting to establish or reestablish a link at the same time (i.e. within the same beacon interval). 
     Thus, there are general needs for millimeter-wave communication stations and methods for multiple-access beamforming that allow more than one responding station to perform beamforming training with a network coordinator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a millimeter-wave communication network, in accordance with some embodiments; 
         FIG. 2A  illustrates a plurality of antenna sectors provided by an array antenna of a millimeter-wave communication station, in accordance with some embodiments; 
         FIG. 2B  illustrates a portion of an array antenna, in accordance with some embodiments; 
         FIG. 3  illustrates the slot structure of a beamforming training period, in accordance with some embodiments; 
         FIG. 4  illustrates a configuration of a sector-sweep slot, in accordance with some embodiments; 
         FIG. 5  illustrates communications between an initiating station and responding stations for multiple-access beamforming, in accordance with some embodiments; 
         FIG. 6  illustrates communications between an initiating station and responding stations for multiple-access beamforming, in accordance with some alternate embodiments; 
         FIG. 7  is a block diagram of a millimeter-wave communication station, in accordance with some embodiments; and 
         FIG. 8  is a procedure for multiple-access beamforming, 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  is a millimeter-wave communication network in accordance with some embodiments. Millimeter-wave communication network  100  includes a plurality of millimeter-wave communication stations  101 - 104  that communicate using millimeter waves. Millimeter-wave communication stations  101 - 104  may utilize array antennas  111  to communicate within one or more antenna sectors. One of the stations, such as communication station  101 , may act as the network coordinator (such as a PCP) to coordinate communications among the communication stations  101 - 104  and control access to the wireless medium. The network coordinator may broadcast a beacon frame that indicates the length of a beacon interval during which communications are to take place. The beacon frame may be received by the other stations  102 - 104 , thereby informing the other stations  102 - 104  as to when the next beacon interval will occur. In some embodiments, the next beacon interval may be identified by a beacon transmission. 
     In accordance with some embodiments, communication station  101  may act as an initiating station to initiate beamforming training (BFT) with other communication stations, such as stations  102 - 104 , which may be referred to as responding stations. In these embodiments, the initiating station  101  may perform multiple-access beamforming with one or more responding stations, such as responding stations  102  and  103 . The initiating station  101  may announce a number of sector-sweep (SS) slots of a BFT period and a number of SS frames within each SS slot. The initiating station  101  may receive one or more SS frames from two or more of the responding stations within one of the SS slots of the BFT period and may transmit one or more SS feedback frames to the responding stations within the one SS slot to indicate an antenna configuration to the responding stations for communication with the initiating station  101 . The indicated antenna configuration may refer to a particular antenna sector. 
     The responding stations transmit a limited number of SS frames per SS slot based on the number of SS frames announced by the initiating station  101 . The responding stations may transmit any additional SS frames in a next SS slot of the beamforming training period. Accordingly, more than one responding station can perform beamforming within a beacon interval. Furthermore, the limitation on the number of SS frames within an SS slot helps reduce collisions, which may increase the success rate of SS frames being received by the initiating station  101 . For multiple-access beamforming, the initiating station is configured to receive at least two reverse sector-sweep frames from two or more of the responding stations within either a single sector-sweep slot or separate sector-sweep slots of the beamforming training period. These embodiments are described in more detail below. 
     In some embodiments, communication stations  101 - 104  may use the same frequency band for transmitting and receiving. In these embodiments, the communication stations  101 - 104  may employ a time-division multiplexed (TDM) communication technique. 
     In some embodiments, communication stations  101 - 104  of millimeter-wave communication network  100  may communicate substantially in accordance with specific communication standards or proposed specifications, such as the Institute of Electrical and Electronics Engineers (IEEE) standards, including the IEEE 802.15 standards and proposed specifications for millimeter-wave communications (e.g., the IEEE 802.15 task group 3c Call For Intent (CFI) dated December 2005), although the scope of the invention is not limited in this respect as they may also be suitable to transmit and/or receive communications in accordance with other techniques and standards. For more information with respect to the IEEE 802.15 standards, please refer to “IEEE Standards for Information Technology—Telecommunications and Information Exchange between Systems”—Part 15. In some embodiments, communication stations  101 - 104  of millimeter-wave communication network  100  may communicate substantially in accordance within accordance with specifications of the WGA. 
       FIG. 2A  illustrates a plurality of antenna sectors provided by an array antenna of a millimeter-wave communication station, in accordance with some embodiments. An array antenna, such as array antenna  111  ( FIG. 1 ), may be used to provide the plurality of antenna sectors  221 . Although  FIG. 2A  shows only twelve antenna sectors  221  for illustrative purposes, array antenna  111  may provide a lesser or greater number of antenna sectors  221 . In some embodiments, the array antenna  111  may provide up to fifty or more antenna sectors  221 . 
       FIG. 2B  illustrates a portion of an array antenna, in accordance with some embodiments. In these embodiments, portion  222  may be a portion of an array antenna, such as array antenna  111  ( FIG. 1 ), and may comprise a plurality of antenna elements  224  configured to transmit and receive millimeter-wave signals within antenna sectors  221  ( FIG. 2A ) utilizing beamforming techniques. The plurality of antenna elements  224  may provide a higher gain and allow beamwidth and beam direction to be controlled by signal processing techniques either in analog or digital domain. In these embodiments, array antenna  111  may operate as a phased array with a predetermined spacing between the antenna elements  224 . 
     In some embodiments, the millimeter-wave communication stations  101 - 104  ( FIG. 1 ) may utilize one or more array antennas  111  which may be configured to selectively transmit in each antenna sector  221 . In some embodiments, at least two antenna elements  224  may be used per each antenna sector  221 . In some embodiments, the array antenna  111  may comprise up to  64  or more antenna elements  224  configurable to transmit in any one or more of the antenna sectors  221 . 
       FIG. 3  illustrates the slot structure of a beamforming training period, in accordance with some embodiments. Beacon interval (BI)  301  includes a BFT period  306 , which may comprise a number of SS slots  304  and may be preceded by one or more beacon transmissions, which may be collectively referred to as beacon time (BT)  302 . Beacon intervals  301  may repeat on a regular basis as illustrated. 
     In accordance with multiple-access beamforming embodiments, the initiating station may announce the number of SS slots  304  of the BFT period  306  and the number of sector sweep SS frames of each SS slot  304  in a beacon transmission of the current beacon interval  301 . A beacon transmission may comprise a sector sweep comprising beacon frames transmitted by the initiating station  101  for receipt by responding stations, such as responding stations  102 - 104 . In these embodiments, the announced number of SS slots  304  of the BFT period  306  may follow the BT  302  in the current beacon interval  301 . In other words, the beacon transmission announcing the number of SS slots  304  precedes the SS slots  304 . In some embodiments, the BFT period  306  is an association beamforming training (A-BFT) period, although this is not a requirement. 
       FIG. 4  illustrates a configuration of a sector-sweep slot, in accordance with some embodiments. The SS slot  304  comprises a first duration  404  for the number of SS frames per SS slot  304  announced by the initiating station  101 , and a second duration  408  for a single SS feedback frame. In some embodiments, each SS slot  304  may include propagation delay time (aPropDelay)  401  to account for a propagation delay between the initiating station  101  ( FIG. 1 ) and a responding station  102  ( FIG. 1 ), and beamforming interface space (BFIS)  403  (or a short inter Frame Space (SIFS)) between the first duration  404  and the second duration  408 . The first duration  404  may be a time duration (aSSDuration) for a responding station  102  to transmit the predetermined number of SS frames to the initiating station. The second duration  408  may be a time duration (aSSFBDuration)  408  for the initiating station  101  to transmit at least the single SS feedback frame to one of the responding stations  102 . In these embodiments, the BFIS  403  may be a constant and may also be provided after second duration  408 . 
       FIG. 5  illustrates communications between an initiating station and responding stations for multiple-access beamforming, in accordance with some embodiments. For multiple-access beamforming, the initiating station  101  may transmit one or more beacon frames  502  as a sector sweep  501  within the BT  302  of the current beacon interval  301  ( FIG. 3 ). The sector sweep  501  may comprise a plurality of beacon frames  502  and may indicate that the initiating station  101  wishes to perform BFT. The initiating station  101  may announce in the beacon transmission the number of SS slots  304  of the BFT period  306  ( FIG. 3 ) and the number of SS frames of each SS slot  304 . 
     The initiating station  101  may receive one or more SS frames  504 ,  506  from two or more of the responding stations within one of the SS slots  304  of the BFT period  306  ( FIG. 3 ). In response, the initiating station  101  may transmit one or more SS feedback frames  508  to the responding stations  102  and  103  within the SS slot  304 . The SS feedback frames  508  may be used to indicate the antenna configuration for communication with the initiating station  101  to the responding stations  102  and  103 . In accordance with some embodiments, the responding stations  102  and  103  transmit a limited number of SS frames  504  per SS slot  304  based on the number of SS frames announced by the initiating station  101 . The responding stations may transmit any additional SS frames  504  in a next SS slot of the BFT period  306 . 
     In these embodiments, the number of SS frames per SS slot  304  that is announced in the beacon transmission may be a total number of SS frames that can be transmitted in an SS slot  304 . If a responding station has, for example, thirty-six antenna sectors but the SS slot  304  can only admit six SS frames  504 , the responding station will use six SS slots  304  to complete a full reverse sector sweep. 
     Although the network coordinator for millimeter-wave communication network  100  is described herein as the initiating station (i.e., the station that is initiating beamforming), this is not a requirement as any station, not necessarily the network coordinator, may operate as an initiating station and initiate beamforming. 
     In some embodiments, the initiating station  101  may perform multiple-access beamforming for scheduling A-BFT with one or more responding stations in millimeter-wave communication network  100 . In these embodiments, more than one responding station is able to schedule and perform A-BFT within a single beacon interval. 
     In some embodiments, the antenna configuration indicated in the SS feedback frames  508  may indicate an antenna sector  221  ( FIG. 2A ) for each of the responding stations to use in communicating with the initiating station  101 . In these embodiments, the initiating station  101  may use the SS frames  504  from the responding stations to identify the antenna sector  221  of a responding station from which the highest quality SS frame was received. The initiating station may indicate the antenna sector  221  to the responding stations in an SS feedback frame  508  for use in subsequent communications by the responding stations. The SS frames  504  from the responding stations may also indicate to the initiating station  101  that a responding station wishes to complete BFT and subsequently communicate with the initiating station  101 . The SS frames  504  from the responding stations may also indicate to the initiating station  101  the antenna sector  221  that the initiating station is to use for communication with each responding station. 
     In some embodiments, the sector sweep  501  comprises a beacon frame  502  transmitted in each of a plurality of antenna sectors of the initiating station  101  during the current beacon transmission. The responding stations, such as responding stations  102  and  103 , may transmit one SS frame  504  in each of their antenna sectors. The responding stations  102  and  103  remain in a receive mode to receive a beacon frame and an SS feedback frame  508  from the initiating station  101 . The initiating station  101  may remain in a receive mode to receive an SS frame  504  from the responding stations  102  and  103 . In some embodiments, the responding stations  102  and  103  remain in an omni-directional receive mode to receive the SS feedback frames  508 , although this is not a requirement. In some embodiments, a responding station may transmit more than one SS frame  504  in each of their antenna sectors, although this is not a requirement. 
     Random Backoff Embodiments: 
     In accordance with some random-backoff embodiments, a responding station may initiate a random backoff procedure at the start of the BFT period  306  to determine with which SS slot  304  of the BFT period  306  to begin transmissions of the SS frames  504 . The responding station may limit the number of SS frames  504  transmitted per SS slot  304  as indicated by the initiating station  101  in the beacon transmission. The responding station may resume transmission of the SS frames  504  at a start of a next SS slot within the current BFT period  306  when the responding station  102  has more SS frames  504  to transmit. 
     In accordance with these random-backoff embodiments, when the responding station  102  does not receive an SS feedback frame  508  from the initiating station  101  until completion of a reverse sector sweep  503 , the responding station  102  may retransmit the SS frames  504  within the same BFT period  306  of the current beacon interval  301 . The responding station  102  may also initiate a random backoff procedure to determine which SS slot following the completion of a prior reverse sector sweep  503  to retransmit the SS frames  504 . SS frames  504  may be considered reverse SS frames. 
     In these random-backoff embodiments, the initiating station  101  may schedule time in the beacon interval  301  for each of the responding stations to complete beamforming, including performing a beamforming refinement phase (BRP) within the current beacon interval  301  or the next beacon interval. The initiating station  101  may transmit a schedule in SS feedback frames  508  to indicate to each responding station when to perform beamforming refinement. In these embodiments, feedback frames  508  may be referred to as grant frames. In some embodiments, the BRP may occur anytime in the beacon interval  301  after a responding station has completed the SS phase in the BFT period  306 . During the BRP, beamforming coefficients may be generated to direct antenna beams for reception and transmission of signals with the other station. 
     In some embodiments, the initiating station  101  may send more than a single SS feedback frame  508  within the SS slot  304  when there is time remaining in the SS slot  304 . In an example embodiment in which the size of SS slot  304  is eight frames, if there are two responding stations that have one and two antenna sectors respectively, only two SS frames are needed to complete a reverse sector sweep  503 . After completion of their reverse sector sweeps  503 , additional time remains in the current SS slot  304  for the initiating station  101  to send SS feedback frames  508  to both of these responding stations. In these embodiments, the second duration  408  ( FIG. 4 ) is not limited to a single SS feedback frame  508 . 
       FIG. 6  illustrates communications between an initiating station and responding stations for multiple-access beamforming, in accordance with some alternate embodiments. As shown in  FIG. 6 , the initiating station  101  may transmit beacon frames  502  during beacon time  302 . In these alternate embodiments, a responding station, such as responding station  102 , may transmit one SS frame  604  within a first SS slot  603  of the BFT period  306  following the beacon transmission. When an SS feedback frame  608  is not received by the responding station  102  until after completion of its entire reverse sector sweep, the responding station  102  may initiate a backoff procedure to determine a backoff period  606  comprising a random number of SS slots  304  to delay transmissions of additional SS frames  605  within the BFT period  306 . At the completion of the SS frame  605 , the responding station  102  may switch to a receive mode to receive an SS feedback frame  609 . In these embodiments, a reverse sector sweep may comprise all SS frames transmitted by a responding station. The responding station may transmit one SS frame in each antenna sector. 
     In these alternate embodiments, a responding station  102  may refrain from delaying transmissions of the additional SS frames  605  after the backoff period  606  when an SS feedback frame is received during the backoff period  606 . The responding station may also stop transmitting any of the additional SS frames  605  after an SS feedback frame  609  is received. 
     In these alternate embodiments, when the remaining time in the BFT period  306  after the backoff period  606  is less than the time for an SS frame  605  and an SS feedback frame  608 , the responding station may remain in receive mode until the end of the BFT period (e.g., in case it is able to receive an SS feedback frame  609 ). 
     As illustrated in the example of  FIG. 6 , each responding station  102 ,  103  and  104  may have a different number of antenna sectors and, accordingly, the time that each station completes a reverse transmit sector sweep is different. For example, responding station  102  may have a single antenna sector and transmit a single SS frame  604  for its reverse sector sweep, while responding station  103  may have three antenna sectors and may transmit three SS frames  614  for its reverse sector sweep, and responding station  104  may have sixteen antenna sectors and may transmit sixteen SS frames  624  for its reverse sector sweep. In this example, since responding station  103  did not receive a sector sweep feedback frame during transmission of it reverse sector sweep (i.e., three SS frames  614 ), it may initiate a backoff procedure to determine a backoff period  616  to delay transmissions of additional reverse SS frames  615  within the BFT period  306 . 
       FIG. 7  is a block diagram of a millimeter-wave communication station, in accordance with some embodiments. Millimeter-wave communication station  700  may include, among other things, an array antenna  722 , beamforming circuitry  702 , transmitter circuitry  706 , receiver circuitry  708  and processing circuitry  704 . Millimeter-wave communication station  700  may be suitable for use as any one or more of millimeter-wave communication stations  101 - 104  ( FIG. 1 ) and as discussed above. Array antenna  722  may include a plurality of antenna elements and may be configured to communicate in a plurality of antenna sectors, such as antenna sectors  221   FIG. 2A . In some alternate embodiments, millimeter-wave communication station  700  may utilize a switched-beam antenna, although the scope of the embodiments is not limited in this respect. In some alternate embodiments, millimeter-wave communication station  700  may utilize a single antenna element, although the scope of the embodiments is not limited in this respect. 
     In accordance with some embodiments, beamforming circuitry  702  may configure array antenna  722  to transmit an SS frame (e.g., one of beacon frames  502  of  FIG. 5 ) separately in each of the antenna sectors  221 . Beamforming circuitry  702  may also configure array antenna  722  to receive the reverse sector-sweep frames (e.g., frames  504  and  506  of  FIG. 5 ). 
     In accordance with some embodiments, when millimeter-wave communication station  700  operates as an initiating station  101  for performing multiple-access beamforming with one or more responding stations, such as responding stations  102  and  103 , the processing circuitry  704  may be configured to announce a number of SS slots  304  ( FIG. 3 ) of a BFT period  306  ( FIG. 3 ) and a number of SS frames of each SS slot  304 . The receiver circuitry  708  may be configured to receive one or more SS frames  504 ,  506  from two or more of the responding stations within one of the SS slots  304  of the BFT period  306 . The transmitter circuitry  706  may be configured to transmit one or more SS feedback frames  508  to the responding stations within the one SS slot  304  to indicate to the responding stations an antenna configuration for communication with the initiating station  101 . 
     In accordance with some embodiments, when millimeter-wave communication station  700  operates as a responding station, such as responding station  102 , for performing multiple-access beamforming with an initiating station, the processing circuitry  704  may receive an announcement from an initiating station, such as initiating station  101 , announcing a number of SS slots  304  of a BFT period  306  and a number of SS frames of each SS slot  304 . The transmitter circuitry  706  may transmit one or more SS frames  504 ,  506  to the initiation station within one of the SS slots  304  of the BFT period  306 . The receiver circuitry  708  may be configured to receive one or more SS feedback frames  508  within the one SS slot  304  indicating an antenna configuration for communication with the initiating station. The responding station may be configured to transmit a limited number of SS frames  504  per SS slot  304  based on the number of SS frames announced by the initiating station, and each transmitted SS frame from the initiating station may indicate the an antenna configuration for communicating with the responding station. The responding station may also be configured to transmit any additional SS frames  504  in a next SS slot of the beamforming training period  306 . 
     In accordance with some embodiments, when the millimeter-wave communication station  700  operates as a responding station, such as responding station  102 , for performing multiple-access beamforming with an initiating station, such as initiating station  101 , the processing circuitry  704  may be configured to initiate a random backoff procedure at the start of a BFT period  306  to determine which SS slot  304  of the BFT period  306  to begin transmissions of an SS frame  504 . The processing circuitry  704  may also be configured to limit a number of SS frames  504  transmitted per SS slot  304  as indicated by the initiating station. The transmitter circuitry  706  may be configured to resume transmission of SS frames  504  at a start of a next SS slot within a current BFT period  306  when the responding station has more SS frames  504  to transmit. 
     Millimeter-wave communication station  700  may include other circuitry for communicating millimeter-wave wireless communication signals, including 60 GHz wireless technologies. In some embodiments, millimeter-wave communication station  700  can be used to provide a flexible interface that can be efficiently embedded into home media gateways, cell phones, flat panel televisions (TVs), set-top boxes, Blu-ray players, digital cameras, personal computers (PCs), laptops, and many other multimedia and communication devices. Although millimeter-wave communication station  700  is 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 millimeter-wave communication station  700  may refer to one or more processes operating on one or more processing elements. 
       FIG. 8  is a procedure for multiple-access beamforming, in accordance with some embodiments. Procedure  800  may be performed by millimeter-wave communication stations, such as millimeter-wave communication stations  101 - 104  ( FIG. 1 ). 
     In operation  802 , the initiating station  101  may announce the number of SS slots  304  ( FIG. 3 ) of a BFT period  306  ( FIG. 3 ) and a number of SS frames of each SS slot  304 . 
     In operation  804 , the initiating station  101  may receive one or more SS frames  504 ,  506  ( FIG. 5 ) from two or more of the responding stations within one of the SS slots  304  of the BFT period  306 . The responding stations may transmit a limited number of SS frames  504  per SS slot  304  based on the number of SS frames announced by the initiating station  101 . 
     In operation  806 , the initiating station may transmit one or more SS feedback frames  508  ( FIG. 5 ) to the responding stations within the one SS slot  304  to indicate an antenna configuration to the responding stations for communication with the initiating station  101 . The responding stations may transmit any additional SS frames  504  in a next SS slot of the beamforming training period  306 . 
     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.