Patent Publication Number: US-2005135321-A1

Title: Spatial wireless local area network

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application is related to U.S. patent application ______, filed on ______. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates generally to wireless networks, and, more particularly, to a spatial wireless local area network.  
      2. Description of the Related Art  
      A wireless Local Area Network (LAN) is a flexible data communications system that can either replace or extend a traditional, wired LAN to provide added functionality. A traditional, wired LAN sends data packets from one piece of equipment to another across cables or wires. For example, wired LANs may use a shared architecture in which multiple devices may communicate by exchanging data packets via each cable or wire, i.e. the devices share the cables or wires. Wired LANs may also use a switched architecture in which each device may communicate via a switch by transmitting data packets along a dedicated cable or wire coupled to the switch.  
      Instead of the wires used in wired LANs, a wireless LAN relies upon radio waves to transfer data between one or more fixed or mobile units and one or more access points. Data is superimposed onto a radio wave through a process called modulation, and the carrier radio wave then acts as the transmission medium. Wireless LANs are typically believed to be intrinsically shared media, at least in part because air cannot be switched like wires, and a variety of shared wireless network standards have become popular. Examples of shared wireless network standards are the 802.11× standards ratified by the Institute of Electrical and Electronics Engineering (IEEE), which include the 802.11, 802.11a, 802.11b (also known as Wi-Fi), and 802.11g standards. Wireless LANs are used in various vertical and horizontal applications (e.g., retail, manufacturing, logistics, healthcare, education, public space, etc.). Recently, there has been a surge in the deployment of 802.11-based wireless infrastructure networks to provide wireless internet access services, especially in public “hot spots” covering airports, hotels, coffee shops, and the like.  
      Many wireless LANs use a so-called single-in-single-out (SISO) cellular sharing architecture. In the SISO architecture, a coverage area is divided into a number of cells. Mobile units within each cell may transmit and receive signals to or from an access point associated with the cell. However, only one mobile unit at a time may transmit signals to the access point, and the access point may only transmit signals to one mobile unit at a time. Consequently, many mobile units may have to compete for bandwidth in the SISO cellular sharing architecture. Moreover, the SISO cellular sharing architecture is not scalable.  
      Multiple-in-single-out (MISO) wireless LAN architectures have been developed, at least in part to increase coverage areas. For example, an access point may direct many focused beams of radio waves, typically referred to as pencil beams, simultaneously towards the plurality of mobile units. Each pencil beam may transmit a signal having an increased bit-rate and/or range between the access point and a corresponding one of the mobile units. However, MISO wireless LAN architectures that direct many pencil beams towards the mobile units may require complex tracking algorithms to maintain contact between the mobile units and the access point. A MISO wireless LAN architecture also typically requires complex control mechanisms to resolve channel contention, which may limit the scalability of the MISO wireless LAN architecture.  
      Multiple-in-multiple-out (MIMO) shared wireless LAN architectures have also been proposed. For example, a spatial multiplexing mode may be used to increase the bit rate for data sent from an access point and a single mobile user. In the spatial multiplexing mode, sometimes referred to as a fat-pipe mode, a single high-speed data stream, e.g. a 200 Mbps stream, may be divided into several lower speed streams, e.g. four 50 Mbps streams, at the access point. The divided streams may then be transmitted to the mobile user, where they are combined into a single stream. However, the divided streams are only suitable for providing a high-speed connection between the access point and the single mobile user. For another example, a spatial diversity mode may be used to increase the accuracy of the data stream by transmitting each bit from multiple antennae at different times.  
     SUMMARY OF THE INVENTION  
      In one aspect of the instant invention, a method used in a wireless local area network is provided. The method includes receiving a plurality of signals from a first plurality of antennae substantially concurrently at a second plurality of antennae, the plurality of signals having a substantially common frequency. The method also includes determining at least one transmission channel between the first and second pluralities of antennae using the plurality of signals.  
      In another aspect of the present invention, an access point in a wireless local area network is provided. The access point includes a first plurality of antennae capable of receiving, substantially concurrently at a substantially common frequency, a plurality of signals from at least one mobile unit, each of the at least one mobile unit being associated with a second plurality of antennae. The access point also includes a processor communicatively coupled to the first plurality of antennae and capable of determining at least one transmission channel corresponding to the at least one mobile unit using the plurality of signals.  
      In yet another aspect of the present invention, a mobile unit for use in a wireless local area network is provided. The mobile unit includes a first plurality of antennae capable of receiving, substantially concurrently at a substantially common frequency, a plurality of signals from a second plurality of antennae associated with an access point. The mobile unit also includes a processor communicatively coupled to the first plurality of antennae and capable of determining a transmission channel corresponding to the mobile unit using the plurality of signals.  
      In a further aspect of the present invention, a wireless local area network is provided. The wireless local area network includes at least one access point having a first plurality of antennae capable of receiving and transmitting a plurality of signals substantially concurrently at a substantially common frequency. The wireless local area network also includes a plurality of mobile units, each mobile unit having a second plurality of antennae capable of receiving and transmitting a plurality of signals substantially concurrently at the substantially common frequency. The access point also includes a processor communicatively coupled to the first plurality of antennae and capable of determining a plurality of transmission channels using a plurality of signals transmitted by the second plurality of antennae associated with each of the mobile units and associating at least one of the plurality of transmission channels with a corresponding one of the mobile units. The mobile units also include a processor communicatively coupled to the plurality of antennae and capable of determining at least one transmission channel corresponding to the mobile unit using a plurality of signals transmitted by the first plurality of antennae associated with the access point. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:  
       FIG. 1  shows one exemplary embodiment of a wireless local area network including at least one access point and a plurality of mobile units;  
       FIG. 2A  illustrates one embodiment of an access point, such as the access point shown in  FIG. 1 ;  
       FIG. 2B  illustrates one embodiment of a mobile unit, such as the mobile unit shown in  FIG. 1 ;  
       FIG. 3A  conceptually illustrates an exemplary embodiment of an downstream transmission that may be performed by the wireless local area network shown in  FIG. 1 ;  
       FIG. 3B  conceptually illustrates an exemplary embodiment of a upstream transmission that may be performed by the wireless local area network shown in  FIG. 1 ; and  
       FIG. 4  shows an exemplary cellular wireless local area network. 
    
    
      While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.  
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS  
      Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.  
       FIG. 1  shows one exemplary embodiment of a wireless local area network  100 . In the illustrated embodiment, the wireless local area network  100  is deployed within an interior space  110 , which includes a plurality of rooms  115 ( 1 - 3 ). However, it will be appreciated by those of ordinary skill in the art that the present invention is not limited to wireless local area networks  100  that are deployed within interiors such as the interior space  110 . In various alternative embodiments, some or all of the wireless local area network  100  may be deployed at any desirable location inside or outside of the interior space  110 , as well as in any desirable number of rooms within the interior space  110 .  
      The wireless local area network  100  shown in  FIG. 1  includes an access point  120  and mobile units  125 ( 1 - 3 ). In various alternative embodiment, the mobile units  125 ( 1 - 3 ) may be cellular telephones, personal data assistants, bar code scanners, portable computers, desktop computers, and the like. Although three mobile units  125 ( 1 - 3 ) are shown in the exemplary embodiment of the wireless local area network  100 , persons of ordinary skill in the art will appreciate that the present invention is not limited to three mobile units  125 ( 1 - 3 ) and that, in alternative embodiments, more or fewer mobile units  125 ( 1 - 3 ) may be used.  
      Voice and/or data signals may be transmitted between the access point  120  and the mobile units  125 ( 1 - 3 ). In one embodiment, the voice and/or data signals may be transmitted between the access point  120  and the mobile units  125 ( 1 - 3 ) using a modulated radio signal having a common frequency, such as a 2.4 GHz modulated carrier radio signal. Alternatively, a 5 GHz modulated carrier radio signal may be used. The voice and/or data signals typically travel between the access point  120  and the mobile units  125 ( 1 - 3 ) along a plurality of paths  130 ( 1 - 6 ). In the interest of clarity, only six paths  130 ( 1 - 6 ) are shown in  FIG. 1 . However, persons of ordinary skill in the art will appreciate that the number of possible paths between the access point  120  and the mobile units  125 ( 1 - 3 ) is essentially infinite.  
      The distribution of potential paths between the access point  120  and the mobile units  125 ( 1 - 3 ) depends upon the location of the access point  120  and the mobile units  125 ( 1 - 3 ), the configuration of the interior space  110  and the rooms  115 ( 1 - 3 ), as well as the location and/or shape of any other obstructions, such as the obstruction  135  shown in  FIG. 1 . For example, the path  130 ( 1 ) may pass substantially directly from the mobile unit  125 ( 1 ) to the access point  120 , whereas the path  130 ( 2 ) may reflect from a wall of the room  115 ( 1 ). For another example, the paths  130 ( 3 - 4 ) between the mobile unit  125 ( 2 ) and the access point  120  may pass from the room  115 ( 2 ) to the room  115 ( 1 ) via a doorway  140 ( 1 ), and may then reflect from one or more walls of the room  115 ( 1 ). For yet another example, the paths  130 ( 5 - 6 ) between the mobile unit  125 ( 3 ) and the access point  120  may pass from the room  115 ( 3 ) to the room  115 ( 1 ) via a doorway  140 ( 2 ), and may then reflect from the obstruction  135  and one or more walls of the room  115 ( 1 ). Although not shown in  FIG. 1 , additional paths may pass through the walls and/or obstructions  135 .  
      The voice and/or data signals transmitted by the access point  120  and/or the mobile units  125 ( 1 - 3 ) may differ from the corresponding voice and/or data signals received by the access point  120  and/or the mobile units  125 ( 1 - 3 ). For example, variations in the lengths of the paths  130 ( 1 - 6 ) may result in variations in the signal amplitude, phase, arrival time, frequency distribution, intensity, and other like attributes of signals transmitted between the access point  120  and the mobile units  125 ( 1 - 3 ). For another example, variations in the number of reflections along the paths  130 ( 1 - 6 ), as well as variations in the reflectance of the reflecting surfaces, may also result in variations in the amplitude, phase, frequency distribution, intensity, and other like attributes of signals transmitted between the access point  120  and the mobile units  125 ( 1 - 3 ). The aforementioned changes in the voice and/or data signals as they travel along the plurality of paths  130 ( 1 - 6 ) between the access point  120  and the mobile units  125 ( 1 - 3 ) are generally referred to by persons of ordinary skill in the art as multi-path fading of the voice and/or data signals.  
       FIG. 2A  illustrates one embodiment of an access point  200 , such as the access point  120  shown in  FIG. 1 . The access point  200  includes a plurality of antennae  201 ( 1 - 4 ) that may be coupled to a transmitter  205  and a receiver  210 . The antennae  201 ( 1 - 4 ) are each capable of transmitting an independent signal provided by the transmitter  205  and of receiving an independent signal that may be provided to the receiver  210 . The antennae  201 ( 1 - 4 ) are also capable of transmitting or receiving the independent signals concurrently at a substantially common frequency. For example, the antennae  201 ( 1 - 4 ) may be capable of concurrently receiving or transmitting up to four independent modulated 2.4 GHz radio signals. However, the present invention is not limited to receiving or transmitting modulated radio signals at any particular frequency. For example, in one alternative embodiment, four independent modulated 5 GHz radio signals may be used. Although the embodiment of the access point  200  illustrated in  FIG. 2A  includes four antennae  201 ( 1 - 4 ) capable of concurrently receiving or transmitting up to four independent signals, the present invention is not so limited. In various alternative embodiments, any desirable plurality of antennae  201 ( 1 - 4 ), each capable of concurrently receiving or transmitting an independent signal, may be included in the access point  200 .  
      In the illustrated embodiment, an access point processor  215  is communicatively coupled to the transmitter  205  and the receiver  210 . For example, the access point processor  215  may be physically coupled to the transmitter  205  and the receiver  210  by wires, conductive traces, and the like so that signals may be transmitted between the access point processor  215  and the transmitter  205  and the receiver  210 . As will be described in detail below, the receiver  210  may provide a signal indicative of the plurality of independent signals that may be received concurrently by the antennae  200 ( 1 - 4 ) to the access point processor  215 , which is capable of determining at least one transmission channel using the plurality of signals. For example, the access point processor  215  may determine a plurality of transmission channels that may be used to establish one or more communication links with a corresponding plurality of mobile units  125 ( 1 - 3 ).  
       FIG. 2B  illustrates one embodiment of a mobile unit  220 , such as the mobile units  125 ( 1 - 3 ) shown in  FIG. 1 . The mobile unit  220  includes a plurality of antennae  221 ( 1 - 4 ) that may be coupled to a transmitter  225  and a receiver  230 . The antennae  221 ( 1 - 4 ) are each capable of transmitting an independent signal provided by the transmitter  225 , such as a modulated 2.4 GHz radio signal, as described above. However, the present invention is not limited to transmitting modulated radio signals at any particular frequency. For example, in one alternative embodiment, a modulated 5 GHz radio signals may be used. In one embodiment, a single antenna  221 ( 1 ) is used to transmit the independent signal provided by the transmitter  225 . However, in alternative embodiments, any desirable number of the antennae  221 ( 1 - 4 ) may be used to transmit the independent signal provided by the transmitter  225 . For example, the transmitter  225  may provide phase-shifted versions of the independent signal to the antennae  221 ( 1 - 4 ).  
      The antennae  221 ( 1 - 4 ) are each capable of concurrently receiving an independent signal that may be provided to the receiver  230 . For example, the antennae  221 ( 1 - 4 ) may be capable of concurrently receiving up to four independent modulated 2.4 GHz radio signals. However, the present invention is not limited to receiving modulated radio signals at any particular frequency. For example, in one alternative embodiment, up to four independent modulated 5 GHz radio signals may be used. Although the embodiment of the mobile unit  220  illustrated in  FIG. 2A  includes four antenna  221 ( 1 - 4 ), the present invention is not so limited. In various alternative embodiments, any desirable number of antenna  221 ( 1 - 4 ), each capable of concurrently receiving or transmitting an independent signal at a common frequency, may be included in the mobile unit  220 . For example, a single antenna  221 ( 1 - 4 ) may be included in the mobile unit  220 .  
      In the illustrated embodiment, a mobile unit processor  235  is communicatively coupled to the transmitter  225  and the receiver  230 . For example, the mobile unit processor  235  may be physically coupled to the transmitter  225  and the receiver  230  by wires, conductive traces, and the like so that signals may be transmitted between the mobile unit processor  235  and the transmitter  225  and the receiver  230 . As will be described in detail below, the receiver  230  may provide a signal indicative of the plurality of independent signals that may be received concurrently by the antennae  221 ( 1 - 4 ) to the mobile unit processor  235 , which is capable of determining at least one transmission channel, e.g., between the mobile unit and the transmitting access point, using the plurality of signals. For example, the mobile unit processor  235  may determine a transmission channel between the mobile unit  125 ( 1 ) and the access point  120 , shown in  FIG. 1 .  
       FIG. 3A  conceptually illustrates an exemplary embodiment of a downstream transmission using the wireless local area network  100 . In the illustrated exemplary embodiment, the wireless local network  100  includes an access point  300  and mobile units (MU)  310  ( 1 - 4 ). Symbols S 1 , S 2 , S 3 , and S 4  may be transmitted by the access point  300 . For example, the access point  300  may transmit symbols S 1 , S 2 , S 3 , and S 4  concurrently at a common frequency using four or more antennae, such as the antennae  201 ( 1 - 4 ) shown in  FIG. 2 . Due to the aforementioned multi-path fading, the mobile units  310 ( 1 - 4 ) may concurrently receive the signals R 1 , R 2 , R 3 , and R 4 , which are related to the transmitted symbols S 1 , S 2 , S 3 , and S 4  by the matrix equation  
           R   i     =         ∑   j             ⁢       a   ij     ⁢     S   j         +     n   i         ,         
 where a i,j  are elements of a transmission matrix, and n i  represents the noise on a received channel i, e.g. a channel of the receiver and/or an antenna. 
 
      The mobile units  310 ( 1 - 4 ) estimate the transmission matrix a using at least a portion of the received signals R 1 , R 2 , R 3 , and R 4 . In one embodiment, each of the transmitted symbols, S j , includes a predetermined training sequence, T j , indicative of the transmission channel j. The training sequence, T j , may include a predetermined pilot sequence, p j  that is transmitted as a portion of a preamble signal. For example, the access point  300  may send each of a plurality of pilot sequences p 1 , p 2 , p 3 , p 4 , in one of a sequence of successive predetermined time slots.  
      The mobile units  310 ( 1 - 4 ) may identify the pilot sequences p 1 , p 2 , p 3 , p 4  transmitted by the access point  300  in the predetermined time slots and estimate at least a portion of the transmission matrix using the equation: a ij =R i /p j . The mobile units  310 ( 1 - 4 ) may then determine the appropriate transmission channel using the estimated transmission matrix a i,j  and thereby extract the appropriate symbol, S j . For example, the mobile unit  310 ( 1 ) may use the estimated transmission matrix a i,j  to extract the symbol S 1  from the concurrently received signals R 1 , R 2 , R 3 , and R 4 .  
       FIG. 3B  conceptually illustrates an exemplary embodiment of an upstream transmission using the wireless local area network  100 . In the illustrated exemplary embodiment, symbols S 1 , S 2 , S 3 , and S 4  may be transmitted by the mobile units (MU)  310 ( 1 - 4 ), respectively. Due to the aforementioned multi-path fading, the antennae  201 ( 1 - 4 ) on the access point  300  may concurrently receive the signals R 1 , R 2 , R 3 , and R 4 , which are related to the transmitted symbols S 1 , S 2 , S 3 , and S 4  by the matrix equation  
           R   i     =         ∑   j             ⁢       a   ij     ⁢     S   j         +     n   i         ,         
 where a i,j  are elements of a transmission matrix, and n i  represents the noise on a received channel i, e.g. a channel of the receiver and/or an antenna. 
 
      The access point  300  estimates the transmission matrix a i,j  using at least a portion of the received signals R 1 , R 2 , R 3 , and R 4 , which in this illustrative embodiment are received by at least the four antennae  201 ( 1 - 4 ). In one embodiment, each of the received symbols, R j , includes a predetermined training sequence, T j , indicative of the transmission channel j, which is transmitted by a respective one of the mobile units  310 ( 1 - 4 ). The training sequence, T j , may include a predetermined pilot sequence, p j  that is transmitted as a portion of a preamble signal. For example, the mobile units  310 ( 1 - 4 ) may each send a corresponding pilot sequence p 1 , p 2 , p 3 , p 4 , in one of a sequence of successive predetermined time slots.  
      The access point  300  may identify the pilot sequences p 1 , p 2 , p 3 , p 4  transmitted by the mobile units  310 ( 1 - 4 ) in the predetermined time slots and estimate the transmission matrix using the equation: a ij =R i /p j . In one embodiment, the transmission channels corresponding to each of the mobile units  310 ( 1 - 4 ) are then estimated using the estimated transmission matrix a i,j , which may be used by the access point  300  to extract the symbols S 1 , S 2 , S 3 , and S 4 . For example, access point  300  may use the estimated transmission matrix a i,j  to extract the symbols S 1 , S 2 , S 3 , and S 4  from the concurrently received signals R 1 , R 2 , R 3 , and R 4 .  
       FIG. 4  shows an exemplary cellular wireless local area network  400  including a plurality of access points  405  (also labeled with letters A, B, C) coupled to a network controller  410  by a bus  420 . The type of network controller  410  and bus  420  is not material to the present invention and, in various alternative embodiments, any desirable type of network controller  410  and bus  420  may be used. In the illustrated embodiment, each of the access points  405  includes four antennae  430 . However, it will be appreciated by those of ordinary skill in the art that the present invention is not limited to access points  405  that include four antennae  430 . In alternative embodiments, the access points  405  may include any desirable plurality of antenna  430 .  
      The access points  405  may be used to establish a plurality of transmission channels to mobile units (not shown) within a plurality of cells  440 . In the illustrated embodiment, the access point  405  indicated by the letter A may be used to establish a plurality of transmission channels to mobile units within the cells  440  indicated by the letter A, the access point  405  indicated by the letter B may be used to establish a plurality of transmission channels to mobile units within the cells  440  indicated by the letter B, and the access point  405  indicated by the letter C may be used to establish a plurality of transmission channels to mobile units within the cells  440  indicated by the letter C.  
      As described in detail above, each of the access points  405  is capable of concurrently transmitting or receiving voice and/or data signals on a plurality of transmission channels at a common frequency, such as a 2.4 GHz carrier frequency. However, the present invention is not limited to receiving modulated radio signals at any particular frequency. For example, in one alternative embodiment, a 5 GHz carrier frequency may be used. Each cell  440  may include a plurality of layers  445 ( 1 - 4 ) corresponding to the plurality of transmission channels. Although four layers  445 ( 1 - 4 ) are shown in  FIG. 4 , the present invention is not so limited. In alternative embodiments, any desirable number of layers  445 ( 1 - 4 ) corresponding to a desired number of transmission channels, up to a number equal to the number of antenna  430  coupled to each access point  405 , may be provided.  
      By providing the plurality of transmission channels, indicated in  FIG. 4  by the plurality of layers  445 ( 1 - 4 ), the cellular wireless local area network  400  may concurrently communicate with a plurality of mobile units (not shown) in each cell  440  using a carrier wave having a substantially common frequency. Consequently, the capacity of the cellular wireless local area network  400  may be increased. For example, in the illustrated embodiment, the capacity of the cellular wireless local area network  400  may be increased by as much as a factor of four.  
      Moreover, more than one of the transmission channels provided by the cellular wireless local area network  400  may be utilized by a single mobile unit. Thus, mobile units may utilize the cellular wireless local area network  400  in a variety of alternative modes, including a spatial multiplexing mode, a fat-pipe mode, a progressive bit rate mode, a spatial diversity mode, a space-time coding mode, and the like. In one embodiment of the progressive bit rate mode, a mobile unit may use a plurality of transmission channels to increase the overall bit rate that may be transmitted between the mobile unit and the access point  405 . For example, a mobile unit in a four-channel system may utilize two of the four 50 Mbps transmission channels to achieve an overall bit rate of approximately 100 Mbps. Alternatively, in one embodiment of the spatial diversity mode, a mobile unit may use a plurality of transmission channels to increase the accuracy of transmissions between the mobile unit and the access point  405 . For example, the mobile unit may transmit the same data independently along two transmission channels so that the number of transmission errors may be reduced by, e.g., comparing the data received independently along the two transmission channels.  
      The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.