Patent Publication Number: US-6992621-B2

Title: Wireless communication and beam forming with passive beamformers

Description:
TECHNICAL FIELD 
   This disclosure relates in general to wireless communication and beam forming using passive beamformers and in particular, by way of example but not limitation, to improving at least one aspect of wireless communication by depopulating one or more ports of a passive beamformer and/or by increasing the order of a passive beamformer such as a Butler matrix. 
   BACKGROUND 
   In wireless communication, signals are sent from a transmitter to a receiver using electromagnetic waves that emanate from an antenna. These electromagnetic waves may be sent equally in all directions or focused in one or more desired directions. When the electromagnetic waves are focused in a desired direction, the pattern formed by the electromagnetic wave is termed a “beam” or “beam pattern.” Hence, the production and/or application of such electromagnetic beams are typically referred to as “beamforming.” 
   Beamforming may provide a number of benefits such as greater range and/or coverage per unit of transmitted power, improved resistance to interference, increased immunity to the deleterious effects of multipath transmission signals, and so forth. Beamforming can be achieved (i) using a finely tuned vector modulator to drive each antenna element to thereby arbitrarily form beam shapes, (ii) by implementing full adaptive beam forming, and (iii) by connecting a transmit/receive signal processor to each port of a Butler matrix. 
   A traditional Butler matrix is a passive device that forms beams of a pre-determined size and shape that emanate from an antenna array that is connected to the Butler matrix. The Butler matrix includes a first set of ports that connect to the antenna array and a second set of ports that connect to multiple transmit/receive signal processors. The first set of ports are denoted as antenna ports, and the second set of ports are denoted as transmit/receive ports. The number of ports in each of the first and second sets may be considered to determine the order of the Butler matrix. While not required, Butler matrices typically have an order that is a power of two, such as 4, 8, 16, 32, and so forth. In a conventional wireless communications environment, every port of the set of antenna ports of a Butler matrix is connected to an antenna element, and every port of the set of transmit/receive ports of a Butler matrix is connected to a signal processor. 
   By way of example, a Butler matrix may have an order of 16. In this case, there are 16 transmit/receive signal processors connected to the 16 transmit/receive ports of the Butler matrix, and there are 16 antenna elements connected to the 16 antenna ports of the Butler matrix. In operation, multiple individual beams of a fixed size and shape emanate from the antenna array. Signals transmitted in and received from each of the respective 16 beams map to a predetermined one of the 16 signal processors on the 16 transmit/receive ports of the Butler matrix. Thus, there is a one-to-one correspondence between (i) each beam formed by the combination of the Butler matrix and the antenna array and (ii) each signal processor that is connected to the Butler matrix. 
   Accordingly, there is a need for schemes and/or techniques for improving the variety and versatility of wireless communication and beamforming options. 
   SUMMARY 
   Improving at least one aspect of wireless communication and beamforming is enabled by depopulating one or more ports of a passive beamformer such as a Butler matrix and/or by increasing the order thereof. In conjunction with such depopulation, one or more signal selection schemes may be employed to select a transmit/receive (TRX) port for wireless communication from among multiple TRX ports of a passive beamformer. 
   In an exemplary described access station implementation, an access station for wireless communications includes: a Butler matrix that has “M” antenna ports and “N” TRX ports; wherein at least a portion of the “M” antenna ports and/or at least a portion of the “N” TRX ports are depopulated. 
   In another exemplary described access station implementation, an access station for wireless communications includes: a Butler matrix that has multiple antenna ports and multiple TRX ports; a signal processor; and a signal selection device that is capable of coupling the signal processor to a subset of the multiple TRX ports responsive to a signal quality determination, the signal selection device adapted to switch the signal processor from a first TRX port of the subset of TRX ports to a second TRX port of the subset of TRX ports. 
   In yet another exemplary described access station implementation, an access station for wireless communications includes: a passive beamformer having multiple antenna ports and multiple TRX ports; and an antenna array having multiple antenna elements that are coupled to at least a portion of the multiple antenna ports of the passive beamformer, the multiple TRX ports numbering more than the multiple antenna elements; wherein signals that are applied to the multiple TRX ports of the passive beamformer are transceived on multiple communication beams that are formed jointly by the passive beamformer and the antenna array, and wherein the access station is adapted to have an aiming resolution for communication beams of the multiple communication beams that is finer than a width of a narrowest communication beam of the multiple communication beams. 
   In an exemplary described method implementation, a method for an access station includes the actions of: comparing a first signal quality from a first communication beam to a second signal quality from a second communication beam; if the first signal quality is greater than the second signal quality, then transceiving from a first TRX port of a Butler matrix; and if the second signal quality is greater than the first signal quality, then transceiving from a second TRX port of the Butler matrix. 
   Other method, system, apparatus, access station, Butler matrix, arrangement, etc. implementations are described herein. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The same numbers are used throughout the drawings to reference like and/or corresponding aspects, features, and components. 
       FIG. 1  is an exemplary general wireless communications environment. 
       FIG. 2  is an exemplary wireless LAN/WAN (Wi-Fi)-specific wireless communications environment that includes a wireless input/output (I/O) unit. 
       FIG. 3  is an exemplary wireless I/O unit as shown in  FIG. 2  that includes a Butler matrix and an antenna array. 
       FIG. 4  illustrates an exemplary set of communication beams that emanate from an antenna array as shown in  FIG. 3 . 
       FIG. 5  illustrates exemplary beam widths of the set of communication beams as shown in  FIG. 4 . 
       FIG. 6  illustrates an exemplary Butler matrix with multiple transmit/receive (TRX) ports in a depopulated state. 
       FIG. 7  illustrates an exemplary Butler matrix with multiple antenna ports in a depopulated state. 
       FIG. 8  illustrates an exemplary Butler matrix with both multiple TRX ports in a depopulated state and multiple antenna ports in a depopulated state. 
       FIG. 9  illustrates another exemplary Butler matrix with both multiple TRX ports in a depopulated state and multiple antenna ports in a depopulated state. 
       FIG. 10  illustrates yet another exemplary Butler matrix with both multiple TRX ports in a depopulated state and multiple antenna ports in a depopulated state. 
       FIG. 11  illustrates a Butler matrix having at least one TRX port in a depopulated state that is coupled to an exemplary signal selection device. 
       FIG. 12  is a flow diagram that illustrates an exemplary method for using a Butler matrix having a TRX port that is in a depopulated state in conjunction with a signal selection device for transceiving communication signals. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is an exemplary general wireless communications environment  100 . Wireless communications environment  100  is representative generally of many different types of wireless communications environments, including but not limited to those pertaining to wireless local area networks (LANs) or wide area networks (WANs) (e.g., Wi-Fi) technology, cellular technology, trunking technology, and so forth. In wireless communications environment  100 , an access station  102  is in wireless communication with remote clients  104 ( 1 ),  104 ( 2 ). . .  104 (N) via communication links  106 ( 1 ),  106 ( 2 ). . .  106 (N), respectively. Although not required, access station  102  is typically fixed, and remote clients  104  are typically mobile. Also, although only three remote clients  104  are shown, access station  102  may be in wireless communication with many such remote clients  104 . 
   With respect to a Wi-Fi wireless communications system, access station  102  and/or remote clients  104  may operate in accordance with any IEEE 802.11 or similar standard. With respect to a cellular system, access station  102  and/or  11  remote clients  104  may operate in accordance with any analog or digital standard, including but not limited to those using time division/demand multiple access (TDMA), code division multiple access (CDMA), spread spectrum, some combination thereof, or any other such technology. 
   Access station  102  may be, for example, a nexus point, a trunking radio, a base station, a Wi-Fi switch, an access point, some combination and/or derivative thereof, and so forth. Remote clients  104  may be, for example, a hand-held device, a desktop or laptop computer, an expansion card or similar that is coupled to a desktop or laptop computer, a personal digital assistant (PDA), a car having a wireless communication device, a tablet or hand/palm-sized computer, a portable inventory-related scanning device, some combination thereof, and so forth. Remote clients  104  may operate in accordance with any standardized and/or specialized technology that is compatible with the operation of access station  102 . 
     FIG. 2  is an exemplary Wi-Fi-specific wireless communications environment  200  that includes a wireless input/output (I/O) unit  206 . Exemplary access station  202  is an example of an access station  102  (of  FIG. 1 ) that operates in accordance with a Wi-Fi-compatible or similar standard. Access station  202  is coupled to an Ethernet backbone  204 . Access station  202 , especially because it is illustrated as being directly coupled to Ethernet backbone  204  without an intervening Ethernet router or switch, may itself be considered a Wi-Fi switch. 
   Access station  202  includes wireless I/O unit  206 . Wireless I/O unit  206  includes an antenna array  208  that is implemented as two or more antennas, and optionally as a phased array of antennas. Wireless I/O unit  206  is capable of transmitting and/or receiving (i.e., transceiving) wireless communication(s)  106  via antenna array  208 . These wireless communication(s)  106  are transmitted to and received from (i.e., transceived with respect to) remote client  104 . 
     FIG. 3  is an exemplary wireless I/O unit  206  as shown in  FIG. 2  that includes a Butler matrix  302  and an antenna array  208 . Wireless I/O unit  206  also includes multiple signal processors (SPs)  304  and one or more baseband processors  306 . Baseband processors  306  accept communication signals from and provide communication signals to the multiple transmit and receive signal processors  304 . A separate baseband processor  306  may be assigned to each signal processor  304 , or a single baseband processor  306  may be assigned to more than one, and up to all, of the multiple signal processors  304 . 
   Exemplary Butler matrix  302  is a passive device that forms, in conjunction with antenna array  208 , communication beams using signal combiners, signal splitters, and signal phase shifters. Butler matrix  302  includes a first side with multiple antenna ports (designated by “A”) and a second side with multiple transmit and/or receive signal processor ports (designated by “TRX”). The number of antenna ports and TRX ports indicate the order of the Butler matrix. Butler matrix  302  includes 16 antenna ports and 16 TRX ports. Thus, Butler matrix  302  has an order of 16. 
   Although Butler matrix  302  is so illustrated, antenna ports and TRX ports need not be distributed on separate, much less opposite, sides of a Butler matrix. Also, although not necessary, Butler matrices usually have an equal number of antenna ports and transmit and/or receive signal processor ports (or TRX ports). Furthermore, although Butler matrices are typically of an order that is a power of two (e.g., 2, 4, 8, 16, 32, 64 . . . 2 n ), they may alternatively be implemented with any number of ports. 
   The sixteen antenna ports of Butler matrix  302  are numbered from  0  to  15 . Likewise, the sixteen TRX ports are numbered from  0  to  15 . Antenna ports  0 ,  1  . . .  14 , and  15  are coupled to and populated with sixteen antennas  208 ( 0 ),  208 ( 1 ).  208 ( 14 ), and  208 ( 15 ), respectively. Likewise, TRX ports  0 ,  1  . . .  14 , and  15  are coupled to and populated with sixteen signal processors  304 ( 0 ),  304 ( 1 ) . . .  304 ( 14 ), and  304 ( 15 ), respectively. These signal processors are also directly or indirectly coupled to baseband processors  306  as indicated by the dashed lines. It should be noted that one or more active components (e.g., a power amplifier (PA), a low-noise amplifier (LNA), etc.) may also be coupled on the antenna port side of Butler matrix  302 . 
   In an exemplary transmission operation, communication signals are provided from baseband processors  306  to the multiple transmit and/or receive signal processors (SP)  304 . The multiple signal processors  304  forward the communication signals to the TRX ports  0 ,  1  . . .  14 , and  15  of Butler matrix  302 . After signal combination, signal splitting, and signal phase shifting, Butler matrix  302  outputs communication signals on the antenna ports  0 ,  1  . . .  14 , and  15 . Individual antennas  208  wirelessly transmit the communication signals, as altered by Butler matrix  302 , from the antenna ports in predetermined beam patterns. The beam patterns are predetermined by the shape, orientation, constituency, etc. of antenna array  208  and by the alteration of the communication signals as “performed” by Butler matrix  302 . In addition to transmissions, wireless signals such as wireless communications  106  (of  FIGS. 1 and 2 ) are received responsive to the communication beams formed by antenna array  208  in conjunction with Butler matrix  302  in an inverse process. 
     FIG. 4  illustrates an exemplary set of communication beams  402  that emanate from the antenna array  208  as shown in  FIG. 3 . In a described implementation, antenna array  208  includes sixteen antennas  208 ( 0 ),  208 ( 1 ). . .  208 ( 14 ), and  208 ( 15 ) (as shown in  FIG. 3 ). Also, a Butler matrix  302  (not explicitly shown in  FIG. 4 ) that is coupled to antenna array  208  is of a 16 th  order. 
   From the sixteen antennas  208 ( 0 ) . . .  208 ( 15 ), sixteen different communication beams  402 ( 0 ) . . .  402 ( 15 ) are formed as the wireless signals emanating from antennas  208  add and subtract from each other during electromagnetic propagation. Communication beams  402 ( 1 ) . . .  402 ( 15 ) spread out symmetrically from the central communication beam  402 ( 0 ). The narrowest beam is the central beam  402 ( 0 ), and the beams become wider as they spread outward from the center. For example, beam  402 ( 15 ) is slightly wider than beam  402 ( 0 ), and beam  402 ( 5 ) is wider than beam  402 ( 15 ). Also, beam  402 ( 10 ) is wider still than beam  402 ( 5 ). 
   The indices  0  . . .  15  for the sixteen different communication beams  402 ( 0 ) . . .  402 ( 15 ) may correspond to the indices  0  . . .  15  of the antenna ports of Butler matrix  302  as well as the indices  0  . . .  15  of the TRX ports thereof. However, no single communication beam  402 (x) necessarily corresponds to a single antenna port x of Butler matrix  302  because each communication beam  402  is formed from the interplay of electromagnetic radiation with respect to multiple, including all, of the antennas of antenna array  208 . 
   Due to real-world effects of the interactions between and among the wireless signals as they emanate from antenna array  208  (e.g., assuming a linear antenna array in a described implementation), communication beam  402 ( 8 ) is degenerate such that its beam pattern is formed on both sides of antenna array  208 . These real-world effects also account for the increasing widths of the other beams  402 ( 1  . . .  7 ) and  402 ( 15  . . .  9 ) as they spread outward from central beam  402 ( 0 ). 
     FIG. 5  illustrates exemplary beam widths of the set of sixteen communication beams  402 ( 0  . . .  15 ) as shown in  FIG. 4 . The different beams are indicated by the same indices in  FIG. 5  as they are in  FIG. 4  above. As also noted above, the beam widths of the sixteen different beams  0  . . .  15  increase as the beams diverge from central beam  0 . It should be noted that the overall beam pattern may be considered to have seventeen different beams (instead of sixteen different beams) if degenerate beam  8  is counted as two different beams, even though transceived communication signals associated therewith map to a single signal processor (SP) via a single TRX port of a corresponding Butler matrix (not shown in  FIG. 5 ). 
   The beam widths of the sixteen beams  0  . . .  15  are indicated in degrees within the ovals of  FIG. 5 . Each of the indicated beam widths are approximate and may be applicable only to this described implementation. By way of example, beam  0  is 6° wide, beam  4  is 7° wide, and beam  9  is 10° wide. The beam widths of the different beams increase in width with a left/right symmetry about the central beam  0 . Thus, beams  2  and  14  are both 7° wide, and beams  6  and  10  are both 8° wide. Table 1 also indicates the beam widths in degrees for the sixteen beams  0  . . .  15 . 
   
     
       
         
             
           
             
               TABLE 1 
             
           
          
             
                 
             
             
               Exemplary set of sixteen beam widths in degrees. 
             
          
         
         
             
             
             
          
             
                 
               Beam Index 
               Approximate Beam Width 
             
             
                 
                 
             
             
                 
               0 
               6° 
             
             
                 
               1 and 15 
               6° 
             
             
                 
               2 and 14 
               7° 
             
             
                 
               3 and 13 
               7° 
             
             
                 
               4 and 12 
               7° 
             
             
                 
               5 and 11 
               8° 
             
             
                 
               6 and 10 
               8° 
             
             
                 
               7 and 9  
               10°  
             
             
                 
               8 
               16° 
             
             
                 
                 
               (×2 for both sides) 
             
             
                 
                 
             
          
         
       
     
   
   In a described implementation, all sixteen beams  0  . . .  15  are not utilized for wireless communications. Specifically, beams  7  and  9  are not used because they  8  are too wide and/or indiscriminate to be sufficiently beneficial. Furthermore, beam  8  is also ignored because its degenerate nature makes it even more difficult for it to be effectively utilized. These unused beams  7 ,  8 , and  9  are indicated by dashed lines in  FIG. 5 . The effective coverage zone is therefore less than 180°. In this described implementation, the angle measurement of the covered area corresponds to approximately 96°. This 96°, which is indicated in  FIG. 5  within a rectangle, reflects an arc between beam  6  and beam  10 , as numbered. 
   An access station  202  (of  FIG. 2 ) that omits/ignores beams  7 ,  8 , and  9  may therefore be placed in a corner of a building or other environment because of the 96° angle of coverage from an antenna array  208 . Also, TRX ports  7 ,  8 , and  9  of a Butler matrix (e.g., of  FIG. 3 ) may be depopulated because wireless communications on beams  7 ,  8 , and  9  are not effectuated. 
   It should be noted that beams  7 ,  8 , and  9  need not be ignored and that the TRX ports  7 ,  8 , and  9  of a Butler matrix  302  may be populated with signal processors (SP)  304  even if the beams  7 ,  8 , and  9  are ignored. Also, if a Butler matrix  302  is of an order other than 16, then different communication beams and possibly a different total number of such communication beams may be ignored for efficiency and/or simplicity reasons when such different communication beams are too indiscriminate and/or too degenerate. 
     FIG. 6  illustrates an exemplary Butler matrix  302  with multiple transmit and/or receive signal processor (TRX) ports in a depopulated state. Butler matrix  302  is a 16 th  order (e.g., a 16×16) Butler matrix. It has sixteen antenna (A) ports  0  . . .  15  and sixteen TRX ports  0  . . .  15 . Each antenna port  0  . . .  15  is coupled to an antenna  208 . Thus, every antenna port is coupled to one of the sixteen antennas  208 ( 0  . . .  15 ). However, each TRX port  0  . . .  15  is not simultaneously coupled to a signal processor (SP)  304 . Instead, every two TRX ports are coupled to one of eight signal processors  304 ( 0 ),  304 ( 1 ).  304 ( 6 ), and  304 ( 7 ). 
   Specifically, signal processor  304 ( 0 ) is coupled to TRX port  0  or  1 , and signal processor  304 ( 1 ) is coupled to TRX port  2  or  3 . Similarly, signal processor  304 ( 6 ) is coupled to TRX port  12  or  13 , and signal processor  304 ( 7 ) is coupled to TRX port  14  or  15 . Each signal processor  304  is able to switch between being coupled to one of two TRX ports as specifically indicated by the dashed arrows at signal processor  304 ( 0 ). This switching may be based, for example, on some quality measure. Exemplary approaches and methods for switching between TRX ports based on one or more quality measures are described further below with reference to  FIGS. 11 and 12 . 
   By way of example, signal processor  304 ( 0 ) may transceive communication signals via TRX port  0  or TRX port  1  of Butler matrix  302 . When coupled to TRX port  0 , signal processor  304 ( 0 ) “sees” (e.g., is able to transceive wireless communications via) a communication beam  0  that is formed by the combined action/configuration of Butler matrix  302  and antenna array  208 . On the other hand, when coupled to TRX port  1 , transceiver  304 ( 0 ) sees a communication beam  1  that is formed by the combined action/configuration of Butler matrix  302  and antenna array  208 . Other signal processors  304  may similarly see two different communication beams one beam at a time. 
   More specifically, for an implementation that is described also with reference to  FIG. 5 , each signal processor  304  sees approximately twice as many total degrees of coverage as it would if Butler matrix  302  were in a fully populated state, but each signal processor  304  sees the same number of degrees of angular coverage as it would in a fully populated state at any single moment. For example, signal processor  304 ( 0 ) is switching between TRX ports  0  and  1  and thus between communication beams  0  and  1 . Communication beams  0  and  1  are both 6°. Consequently, signal processor  304 ( 0 ) sees (6+6) or 12° of the total coverage area in angular units of 6° at any single moment. 
   A single signal processor  304  such as signal processor  304 ( 0 ) is thus able to see two different antenna beam patterns, such as beams  402 ( 0 ) and  402 ( 1 ) (as shown in  FIG. 4 ). Signal processor  304 ( 0 ) can therefore handle remote clients  104  that are located in either (or both) of beams  402 ( 0 ) and  402 ( 1 ). Also, eight signal processors  304 ( 0  . . .  7 ) can handle remote clients  104  that are located in up to sixteen different beams  402 ( 0 . . .  15 ). 
   In this described implementation, financial resources can thus be conserved by depopulating half of the TRX ports of a Butler matrix  302 . This depopulation precipitates several effects. For example, in addition to switching overhead and/or delays, there is a concomitant reduction in simultaneous signal handling capability at access station  202  (of  FIG. 2 ). However, when wireless communication is effectuated using a packet-based approach, the same total number of remote clients  104  can likely be serviced, even though the total number of remote clients  104  that can be serviced simultaneously decreases by approximately one-half. 
     FIG. 7  illustrates an exemplary Butler matrix  302  with multiple antenna ports in a depopulated state. Butler matrix  302  is a 16 th  order Butler matrix, and it also has sixteen antenna ports  0  . . .  15  and sixteen TRX ports  0  . . .  15 . Each TRX port  0  . . .  15  is coupled to a signal processor (SP)  304 . Thus, every TRX port is coupled to one of the sixteen signal processors  304 ( 0  . . .  15 ). However, each antenna port  0  . . .  15  is not coupled to an antenna  208 . Instead, every other antenna port of the sixteen antenna ports  0  . . .  15  is coupled to one of eight antennas  208 ( 0 ),  208 ( 1 ).  208 ( 6 ), and  208 ( 7 ). 
   Half of the sixteen antenna ports  0  . . .  15  of Butler matrix  302  are thus depopulated and the other half are populated. Specifically, antenna  208 ( 0 ) is coupled to antenna port  0 , and antenna  208 ( 1 ) is coupled to antenna port  2 . Similarly, antenna  208 ( 6 ) is coupled to antenna port  12 , and antenna  208 ( 7 ) is coupled to antenna port  14 . In other words, antennas  208 ( 0  . . .  7 ) are coupled to antenna ports  0 ,  2 ,  4 ,  6 ,  8 ,  10 ,  12 , and  14 , respectively, of Butler matrix  302 . 
   Assuming that other spatial parameters are maintained (e.g., that the distance between adjacent antenna elements of antenna array  208  are relatively unchanged), the width of each individual communication beam (not explicitly shown in  FIG. 7 ) that emanates from the combination of Butler matrix  302  and antenna array  208  approximately doubles. In this described implementation, each individual communication beam width is (inversely) related to the maximum spacing between the two antenna elements of the antenna array that are farthest apart. Specifically, an antenna array with twice the maximum spacing has a communication beam width that is half as wide, and vice versa. Consequently, an antenna array with half the antenna elements, with the same inter-element spacing, results in half the maximum antenna array width and therefore a communication beam width that is twice as wide. 
   In other words, each of the sixteen different communication beams of a half-way populated Butler matrix  302  is approximately twice as wide as it would be if Butler matrix  302  were fully populated. For example, central communication beam  402 ( 0 ) (of  FIG. 4 ) is approximately 6° wide, but an un-illustrated central communication beam emanating from antenna array  208  of  FIG. 7  is approximately 12° wide. 
   Each of the sixteen signal processors of signal processors  304 ( 0  . . .  15 ) may elect to effectively see half of one of these sixteen communication beams that are twice as wide as they would be if the sixteen antenna ports  0  . . .  15  of Butler matrix  302  were fully populated. More specifically, each signal processor  304  may actually transceive signals across the entire (e.g., 12° for a central beam) width of the communication beam. However, the beam steering resolution is finer than the beam width. In this case, the beam steering can occur in 6° increments while the beam width is at least 12°. 
   Hence, as desired and/or as detected from a signal quality perspective, signal processors  304  can elect to transceive over only the central half of each 12°-wide communication beam where the signal power is strongest. If the signal is being transceived to/from a point that is located outside this central portion of a communication beam, then a signal processor  304  (and/or a TRX port) that corresponds to an adjacent beam can assume transceiving responsibilities with respect to the central portion of the adjacent communication beam, especially if the signal quality of the resulting transceived signal is superior in the adjacent communication beam. In other words, the aiming resolution for the different communication beams as seen at the TRX ports of Butler matrix  302  of  FIG. 7  is finer than the beam widths of the actual communication beams that emanate from the combination of Butler matrix  302  and antenna array  208  in  FIG. 7 . 
   Thus, each signal processor  304  that is connected to a different TRX port of Butler matrix  302  is associated with a different communication beam that is emanating from antennas  208 ( 0  . . .  7 ). Although each such different communication beam is 12° wide, the respective peaks of the different communication beams may be directionally pointed every 6°. Analogous situations are described further below with particular reference to  FIGS. 8–10 . 
   In this described implementation, antenna array cost, size, and complexity can be reduced by depopulating half of the antenna ports of a Butler matrix  302 . This depopulation precipitates several effects. For example, although the number of communication beams emanating from the antenna array remains constant, the width of each communication beam doubles and the overlap between communication beams increases. However, the beam steering capability of a related wireless I/O unit  206  maintains the same directionality resolution from the perspective of angular aiming precision for each signal processor  304 . In other words, the number of pointing directions to which the communication beams can be aimed does not change. 
     FIG. 8  illustrates an exemplary Butler matrix  302  with both multiple TRX ports in a depopulated state and multiple antenna ports in a depopulated state. Eight antennas  208  are coupled to eight different antenna ports, and eight signal processors (SPs)  304  are coupled to sixteen different TRX ports. Specifically, the eight antennas  208 ( 0 ),  208 ( 1 ). . .  208 ( 6 ), and  208 ( 7 ) are coupled to the eight antenna ports  1 ,  3  . . .  13 , and  15 , respectively. Also, the eight signal processors  304 ( 0 ),  304 ( 1 ). . .  304 ( 6 ), and  304 ( 7 ) are coupled to the sixteen TRX ports  0 / 1 ,  2 / 3  . . .  12 / 13 , and  14 / 15 , respectively, taken two at time. In a described implementation, it is assumed that the antenna element  208 ( 0  . . .  7 ) spacing in  FIG. 8  is the same as that for antenna array  208  in  FIG. 6  and that the linear dimension of the array with half as many elements is one-half that of  FIG. 6 . 
   Although the communication beams (not explicitly shown in  FIG. 8 ) that emanate from the eight antennas  208 ( 0  . . .  7 ) in conjunction with Butler matrix  302  are doubly wide as compared to a fully populated antenna array  208 , the steering resolution of communications transceived therewith still corresponds to a fully populated antenna array  208  as seen at the TRX ports  0  . . .  15 . This aspect of  FIG. 8  is analogous to the Butler matrix permutation of  FIG. 7  as described above. 
   However, an individual signal processor  304  is not assigned to each TRX port full time. Instead, every two TRX ports share a single signal processor  304 . Each signal processor  304  switches between being coupled (physically, operationally, and/or functionally) to one of two TRX ports as again indicated by the dashed lines at signal processor  304 ( 0 ). This aspect of  FIG. 8  is analogous to the Butler matrix permutation of  FIG. 6  as described above. 
   The individual effects of depopulating the antenna ports and of depopulating the TRX ports of Butler matrix  302  are thus jointly experienced by the permutation of  FIG. 8 . For example, signal processor  304 ( 6 ) sees a first “doubly-wide” communication beam that corresponds to TRX port  12  when coupled thereto, and signal processor  304 ( 6 ) sees a second “doubly-wide” communication beam that corresponds to TRX port  13  when coupled thereto. However, a distance between the peaks of the first and the second “doubly-wide” communication beam is not doubly-wide. In a described implementation, the first and the second “doubly-wide” communication beams are each 12° wide, but the distance between their peaks is only 6°. 
     FIG. 9  illustrates another exemplary Butler matrix  302  with both multiple TRX ports in a depopulated state and multiple antenna ports in a depopulated state. Butler matrix  302  is still a 16 th  order Butler matrix with sixteen antenna ports  0  . . .  15  and sixteen TRX ports  0  . . .  15 , but it has only four antennas  208 ( 0  . . .  3 ) and four signal processors  304 ( 0  . . .  3 ) coupled thereto. 
   Four antennas  208  are coupled to four different antenna ports, and four signal processors  304  are coupled to sixteen different TRX ports. Specifically, the four antennas  208 ( 0 ),  208 ( 1 ),  208 ( 2 ), and  208 ( 3 ) are coupled to the four antenna ports  3 ,  7 ,  11 , and  15 , respectively. Also, the four signal processors  304 ( 0 ),  304 ( 1 ),  304 ( 2 ), and  304 ( 3 ) are coupled to the sixteen TRX ports  0 / 1 / 2 / 3 ,  4 / 5 / 6 / 7 ,  8 / 9 / 10 / 11 , and  12 / 13 / 14 / 15 , respectively, taken four at time. 
   Each of the communication beams (not explicitly shown in  FIG. 9 ) that emanate from antennas  208  in conjunction with Butler matrix  302  are four times wider than the communication beams that would emanate from sixteen antennas  208  if Butler matrix  302  were fully populated. However, the aiming resolution in angular degrees may be maintained from the perspective of TRX ports  0  . . .  15 . 
   The sixteen TRX ports  0  . . .  15  are coupled to four different signal processors  304 ( 0  . . .  3 ) such that only four of the sixteen TRX ports  0  . . .  15  are being used to transceive communication signals at any one moment. The particular TRX port of four possible TRX ports to which a given individual signal processor  304  is coupled is effectuated by a switching mechanism that is described further below with reference to  FIGS. 11 and 12 . 
   Thus, a wireless I/O unit  206  implementation may include a Butler matrix  302  that has been three-quarters depopulated with respect to either or both of the antenna ports and the TRX ports. It should be noted that other depopulation proportions besides one-half and three-quarters may alternatively be employed. Furthermore, such depopulation proportions need not be related to a power of two even though the complexity of such implementations that do deviate from a power of two consequently increases. 
     FIG. 10  illustrates yet another exemplary Butler matrix  302  with both multiple TRX ports in a depopulated state and multiple antenna ports in a depopulated state. In this permutation, sixteen different antennas  208 ( 0  . . .  15 ) and sixteen different signal processors  304 ( 0  . . .  15 ) are coupled to Butler matrix  302  as was also illustrated in  FIG. 3 . However, Butler matrix  302  in  FIG. 10  is of a 32 nd  order (e.g., a 32×32 Butler matrix). It has thirty-two antenna ports  0  . . .  31  and thirty-two TRX ports  0  . . .  31 . 
   Specifically, the sixteen antennas  208 ( 0 ) . . .  208 ( 2 ) . . .  208 ( 12 ) . . .  208 ( 15 ) are coupled to sixteen antenna ports  0  . . .  4  . . .  24  . . .  30 , respectively, of the thirty-two total antenna ports  0  . . .  31 . Also, the sixteen signal processors  304 ( 0 ).  304 ( 2 ) . . .  304 ( 14 ), and  304 ( 15 ) are coupled to the thirty-two TRX ports  0 / 1  . . .  4 / 5  . . .  28 / 29 , and  30 / 31 , respectively, taken two at time. 
   With this permutation, supplanting a passive 16×16 Butler matrix  302  with a passive 32×32 Butler matrix  302  adds little to the cost of a wireless I/O unit  206  (of  FIG. 2 ) while simultaneously augmenting the angular aiming resolution of the covered area. In a described implementation, it is assumed that the physical parameters for antenna array  208  of  FIG. 3  and for antenna array  208  of  FIG. 10  are similar or analogous. Consequently, each communication beam emanating from either such antenna array  208  is 6° wide. However, the steering resolutions differ between the two configurations. 
   Specifically, the steering resolution for antenna array  208  of  FIG. 3  is 6°. The steering resolution for antenna array  208  of  FIG. 10 , on the other hand, is 3°. For example, signal processor  304 ( 2 ) may transceive using a first communication beam that corresponds to TRX port  4  or using a second communication beam that corresponds to TRX port  5 . Although each of these first and second communication beams is 6° wide, the angular distance between their peaks is only 3°. Thus, the communication beam steering resolution is finer than the communication beam width. Furthermore, the combination of the sixteen antennas  208 ( 0  . . .  15 ) and Butler matrix  302  effectively produces thirty-two different communication beams. 
   Other antenna array  208  and Butler matrix  302  configurations can alternatively be implemented. For example, a sixteen element antenna array  208  like that of  FIG. 10  may be coupled to a Butler matrix  302  that is of a 64 th  order. In this case, each resulting communication beam is still 6° wide. However, each resulting communication beam may be steered in increments of 1.5° from the perspective of the TRX ports  0  . . .  63  of such a 64 th  order Butler matrix  302 . 
   The various permutations of  FIGS. 6–10  have been described with regard to the implementation illustrated in  FIG. 3 . As a result,  FIGS. 6–9  are described as having a Butler matrix  302  that has antenna and/or TRX ports in a depopulated state. Also,  FIG. 10  is described as supplanting a Butler matrix  302  of a first order with a Butler matrix  302  of a second, higher order. It should be understood, however, that (i) depopulating a Butler matrix  302  and (ii) altering the order of a Butler matrix  302  while not increasing the number of antennas or transceivers are analogous and equivalent situations and/or operations. In other words, they may be considered as two sides of the same coin that only appear to differ based on the selection of a relevant initial condition and/or on the selection of a desired terminology. 
   As alluded to above individually, various Butler matrix port population configurations relate to various effects. Assume that a Butler matrix is fully populated at both its antenna ports and its TRX ports in an original configuration. For a first permutation, the TRX ports of the Butler matrix are depopulated, but the population of the antenna ports is unchanged. In this case, the cost of implementing such a permutation may be decreased by eliminating signal processors. Furthermore, the gain as well as the coverage and range may be maintained at a level comparable to that of the original, fully-populated state. There may be, however, a small performance penalty with respect to the number of remote clients that can be simultaneously serviced. 
   For a second permutation, the antenna ports of the Butler matrix are depopulated, but the population of the TRX ports is unchanged. In this case, the widths of the multiple communication beams are increased (e.g., doubled), but the signal processors can effectively steer each beam at an angular differential that is less than the beam widths. Thus, the same beam aiming resolution may be maintained because steering directionality is controllable at a resolution that is finer than the beam width. 
   In a third permutation, neither the antenna ports nor the TRX ports are depopulated, but the order of the Butler matrix is increased. The cost is approximately unchanged because Butler matrices are inexpensive relative to the remaining components of a wireless access station. Although the coverage area remains approximately the same, the gain and the range both increase. This increase can be approximately 40% when the order of a Butler matrix is doubled. 
     FIG. 11  illustrates a Butler matrix  302  that has at least one TRX port in a depopulated state and that is coupled to an exemplary signal selection device  1102 . An M×N order Butler matrix  302  has “M” antenna ports  0  . . . M−1 and “N” TRX ports  0  . . . N−1 in which M and N may be equal or unequal. In this described implementation, each of the M antenna ports  0  . . . M−1 is coupled to one of M antennas  208 ( 0  . . . M−1). However, this description is also applicable to permutations with depopulated antenna ports. 
   The M antennas  208 ( 0 ),  208 ( 1 ) . . .  208 (M−1), which together form an antenna array  208 , operate in combination with Butler matrix  302  to form multiple communication beams of a communication beam pattern  1106 . In a described implementation and as illustrated, antenna array  208  and Butler matrix  302  jointly form N communication beams  1106 ( 0 ),  1106 ( 1 ) . . .  1106 (N−1). Although not so illustrated, these N communication beams  1106 ( 0  . . . N−1) may form an overall beam pattern identical, similar, and/or analogous to that of  FIGS. 4 and 5 , depending on the number of antennas  208 , the order of Butler matrix  302 , and so forth. 
   Signal processor (SP)  304 ( 0 ) is indirectly coupled to Butler matrix  302  by way of signal selection device  1102 . Signal selection device  1102  selects the TRX port to which signal processor  304 ( 0 ) should be coupled from among two or more TRX ports of Butler matrix  302 . Signal selection device  1102  thus enables one or more signal processors  304  to implement or facilitate one or more kinds of signal selection schemes (e.g., such as those based on diversity) with respect to different communication beams  1106 . 
   In the illustrated implementation, signal selection device  1102  selects from between TRX ports  0  and  1  of Butler matrix  302  for signal processor  304 ( 0 ) as indicated by the dashed lines. This selection is made responsive to one or more communication signals from remote clients  104  (of  FIGS. 1 and 2 ) that are located in or near communication beam  1106 ( 0 ) and/or communication beam  1106 ( 1 ). This selection may be made using signal quality determiner  1104 . 
   Signal quality determiner  1104  determines the signal quality of transceived signals as present at TRX port  0  and TRX port  1 . This signal quality may include and/or relate to signal-to-noise ratio (SNR), interference level(s), multi-path variable(s) (e.g., a lowest delay spread), some combination thereof, and so forth. After signal quality determiner  1104  measures or otherwise determines at least one signal quality, signal selection device  1102  may analyze the determined signal quality in order to select the better (or best) TRX port. 
   In the illustrated implementation, signal selection device  1102  interprets the signal quality to select TRX port  0  or TRX port  1 . For example, signal selection device  1102  may select the port having the better signal quality. This signal quality may reflect the better of two versions of a single signal from a single remote client  104 , the better of two different signals from two different remote clients  104 , the better communication beam  1106  (e.g., communication beam  1106 ( 0 ) or  1106 ( 1 )) for transceiving a single signal from a single remote client  104 , and so forth. Both of signal selection device  1102  and signal quality determiner  1104  may be comprised of hardware, software, firmware, some combination thereof, and so forth. 
     FIG. 12  is a flow diagram  1200  that illustrates an exemplary method for using a Butler matrix having a TRX port that is in a depopulated state in conjunction with a signal selection device for transceiving communication signals. Such a signal selection device may be a separate or an integrated component or feature of an access station; also, such a signal selection device may be a standard or a specialized component or feature of the access station. 
   Flow diagram  1200  includes eight blocks  1202 – 1216  that may be implemented with any appropriate hardware, software, firmware, some combination thereof, and so forth and with any appropriate signal selection scheme. However, to improve clarity an exemplary implementation of the method of flow diagram  1200  is described with particular reference to  FIG. 11 . 
   It should be noted (i) that the order in which the multiple blocks  1202 – 1216  are illustrated and/or described is not intended to be construed as a limitation and (ii) that the actions of any number of the described blocks, or portions thereof, can be combined or rearranged in any order to implement one or more methods for improving wireless communication and/or beamforming with Butler matrices. 
   At block  1202 , a signal quality determiner is switched to a first TRX port of a Butler matrix. For example, signal quality determiner  1104  may be switched to TRX port  0  of Butler matrix  302  (of  FIG. 11 ). At block  1204 , a signal quality from a first beam of the Butler matrix (in conjunction with an antenna array that is coupled thereto) is determined. For example, a first signal quality of a signal that is being transmitted or received within or proximate to communication beam  1106 ( 0 ) is determined using signal quality determiner  1104 . 
   At block  1206 , the signal quality determiner is switched to a second TRX port of the Butler matrix. For example, signal quality determiner  1104  may be switched to TRX port  1  of Butler matrix  302 . At block  1208 , a signal quality from a second beam of the Butler matrix (in conjunction with the antenna array that is coupled thereto) is determined. For example, a second signal quality of a signal that is being transmitted or received within or proximate to communication beam  1106 ( 1 ) is determined using signal quality determiner  1104 . The determined first and second signal qualities may relate to the same signal with respect to the different communication beams  1106 ( 1 ) and  1106 ( 2 ), to different versions of the same signal, to different signals, and so forth. 
   At block  1210 , the signal quality from the first beam of the Butler matrix is compared to the signal quality from the second beam of the Butler matrix. For example, signal selection device  1102  may compare the first signal quality that is related to communication beam  1106 ( 0 ) to the second signal quality that is related to communication beam  1106 ( 1 ). At block  1212 , it is determined from the comparison whether the signal quality from the first beam of the Butler matrix is greater than the signal quality from the second beam of the Butler matrix. This determination may be accomplished, for example, by signal selection device  1102  determining a greater of two values for SNR, for interference level(s), for multi-path variable(s), some combination thereof, and so forth. 
   If the signal quality from the first beam of the Butler matrix is greater than the signal quality from the second beam of the Butler matrix (as determined at block  1212 ), then the first TRX port of the Butler matrix is selected for transceiving at block  1214 . For example, signal selection device  1102  may couple signal processor  304 ( 0 ) to TRX port  0  of Butler matrix  302 . If, on the other hand, the signal quality from the first beam of the Butler matrix is not determined to be greater than the signal quality from the second beam of the Butler matrix, then the second TRX port of the Butler matrix is selected for transceiving at block  1216 . For example, signal selection device  1102  may couple signal processor  304 ( 0 ) to TRX port  1  of Butler matrix  302 . 
   In a described implementation, the actions of the eight (8) blocks  1202 – 1216  are performed when at least one signal is present at one or more TRX ports. Any of many possible schemes may be implemented between the arrival of signals and/or for detecting a signal, as indicated by arrows  1218 (A),  1218 (B), and  1218 (C). For example, a signal quality may be measured on each TRX port until a signal is detected. The signal quality for the detected signal is then determined on at least two TRX ports (and possibly over all TRX ports) to determine the better or best TRX port for receiving the signal. That better or best TRX port is then used for that signal until the transmission ceases, or until another signal quality measuring across multiple TRX ports is warranted (e.g., because of signal quality degradation, a timer expiration, etc.). The signal quality measuring/detecting may then continue and/or may also be continuing while the actions of flow diagram  1200  are occurring. 
   The implementations described hereinabove and illustrated in FIGS.  3  and  6 – 12  focus on a Butler matrix as an exemplary passive beamformer. However, other realizations for a passive beamformer may alternatively be used. For example, in addition to a Butler matrix, a passive beamformer may be implemented as a Rotman lens, a canonical beamformer, a lumped-element beamformer with static or variable inductors and capacitors, and so forth. For instance, a first Rotman lens with “x” TRX ports and “y” antenna ports can be substituted with a second Rotman lens with “x+w” (where w is positive) TRX ports to achieve a finer beam aiming resolution. 
   Although methods, systems, apparatuses, arrangements, schemes, approaches, and other implementations have been described in language specific to structural and functional features and/or flow diagrams, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or flow diagrams described. Rather, the specific features and flow diagrams are disclosed as exemplary forms of implementing the claimed invention.