Patent Publication Number: US-8115678-B1

Title: Generating an array correlation matrix using a single receiver system

Description:
RELATED APPLICATION 
     This application claims benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 61/133,902, entitled “Antenna Array Measurement Technique,” filed Jul. 3, 2008, by Carlos R. Costas, which is incorporated herein by reference. 
     TECHNICAL FIELD 
     This invention relates generally to the field of antenna systems and more specifically to generating an array correlation matrix using a single receiver system. 
     BACKGROUND 
     In certain situations, a communication system may employ a receiver for each antenna element of an antenna array. Using a receiver for each antenna element, however, may yield a heavy, less efficient, and more expensive system. 
     SUMMARY OF THE DISCLOSURE 
     In accordance with the present invention, disadvantages and problems associated with previous techniques for generating an array correlation matrix may be reduced or eliminated. 
     According to one embodiment, generating an array correlation matrix includes interfacing with an antenna system that has antenna elements. The antenna elements receive incoming signals, and each antenna generates a response signal in response to receiving the signals. The following is performed for a number of iterations to yield summed signals: controlling weights of the antenna elements to weight the response signals; and receiving a summed signal comprising a sum of the weighted signals. An array correlation matrix is generated from the summed signals. 
     Certain embodiments of the invention may provide one or more technical advantages. A technical advantage of one embodiment may be that an array correlation matrix may be calculated by a single receiver system. A single receiver system, for example, a single channel receiver system, may be more economical than other receiver systems. 
     Certain embodiments of the invention may include none, some, or all of the above technical advantages. One or more other technical advantages may be readily apparent to one skilled in the art from the figures, descriptions, and claims included herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates one embodiment of a communication system that generates an array correlation matrix from summed signals from a single channel receiver system; and 
         FIG. 2  illustrates an example of a method for generating an array correlation matrix that may be used by the communication system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention and its advantages are best understood by referring to  FIGS. 1 and 2  of the drawings, like numerals being used for like and corresponding parts of the various drawings. 
       FIG. 1  illustrates one embodiment of a communication system  10  that generates an array correlation matrix from summed signals from a single channel receiver system. A communication system  10  that has a single channel receiver system, instead of a receiver for each antenna element, may be smaller, lighter, and more economical. 
     In the illustrated embodiment, communication system  10  may include an antenna system  20  and a receiver system  24 . Antenna system  10  may include antenna elements  30  and a signal summation module  32 . Receiver system  24  may include an interface (IF)  40 , logic  42 , and memory  44 . Logic  42  may include a processor  46  and a matrix generator  36 . A weight calculator  34  may be located at antenna system  20  or receiver system  24 . 
     In one example of operation, communication system  10  generates an array correlation matrix by performing the following to yield summed signals: control weights of antenna elements  30  to weight response signals generated by antenna elements  30 , and generate a summed signal comprising a sum of the weighted signals. Matrix generator  36  generates an array correlation matrix from the summed signals. More details are provided herein. 
     In certain embodiments, antenna system  20  may be a smart antenna system (or an adaptive array antenna). Antenna system  20  may use smart signal processing to identify a spatial signal signature (such as the direction of arrival (DOA)) of a signal, and calculate beamforming vectors from the signature to track and locate the antenna beam on a target. In certain embodiments, antenna system  20  may have an antenna array. Antenna system  20  may have any suitable number of antenna elements  30 . For example, antenna system  20  may have less than 5, 5 to 10, 10 to 100, or greater than 100 antenna elements  30 . Antenna elements  30  each receive and/or transmit signals, which typically communicate information. 
     Weight calculator  34  calculates weights applied to the response signals. The weights may be used to yield measurements that can be used to determine individual signals, that is, to separate signals of each antenna element  30  from the signals of other antenna elements  30 . For example, the weights may be selected to yield an orthogonal measurement for each antenna element. The weights are described in more detail with reference to  FIG. 2 . In the example, summation module  32  sums weighted signals to yield a summed signal. 
     Receiver system  24  receives signals from antenna system  20  and may extract information communicated in the signals. Receiver system  24  may be any suitable system that receives signals, for example, a single channel receiver system. In certain embodiments, receiver system  24  may estimate an array correlation matrix from signals from antenna system  20 . The array correlation matrix indicates correlation of antenna elements  30 . An example of a method that receiver system  24  may use to estimate the array correlation matrix is described in more detail with reference to  FIG. 2 . 
     A component of system  10  may include an interface, logic, memory, and/or other suitable element. An interface receives input, sends output, processes the input and/or output, and/or performs other suitable operation. An interface may comprise hardware and/or software. 
     Logic performs the operations of the component, for example, executes instructions to generate output from input. Logic may include hardware, software, and/or other logic. Logic may be encoded in one or more tangible media and may perform operations when executed by a computer. Certain logic, such as a processor, may manage the operation of a component. Examples of a processor include one or more computers, one or more microprocessors, one or more applications, and/or other logic. 
     In particular embodiments, the operations of the embodiments may be performed by one or more computer readable media encoded with a computer program, software, computer executable instructions, and/or instructions capable of being executed by a computer. In particular embodiments, the operations of the embodiments may be performed by one or more computer readable media storing, embodied with, and/or encoded with a computer program and/or having a stored and/or an encoded computer program. 
     A memory stores information. A memory may comprise one or more tangible, computer-readable, and/or computer-executable storage medium. Examples of memory include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), database and/or network storage (for example, a server), and/or other computer-readable medium. 
       FIG. 2  illustrates an example of a method for generating an array correlation matrix that may be used by communication system  10  of  FIG. 1 . A receiver system  24  facilitates operation of an antenna array of antenna system  20  at step  210 . In certain embodiments, antenna system  10  includes antenna elements i=1, . . . , N, where N represents the number of antenna elements  30 . An antenna element i generates a response signal x i  in response to an incoming signal s i . Response signal vector  x  may be written as: 
                     x   _     =       ⁢           a   _     ⁡     (   θ   )       ·       s   _     ⁡     (   k   )         +       n   _     ⁡     (   k   )                     =       ⁢         [       a   ⁡     (     θ   1     )       ⁢           ⁢     a   ⁡     (     θ   2     )       ⁢           ⁢     a   ⁡     (     θ   3     )       ⁢           ⁢     a   ⁡     (     θ   4     )       ⁢   …   ⁢           ⁢     a   ⁡     (     θ   N     )         ]     ·     [             s   1     ⁡     (   k   )                   s   2     ⁡     (   k   )                   s   3     ⁡     (   k   )               ⋮               s   D     ⁡     (   k   )             ]       +       n   _     ⁡     (   k   )                     
where ā(θ) represents the steering vector for direction θ,  s (k) represents the incident signal vector, and  n (k) represents a noise vector.
 
     Steps  214  through  224  describe applying N weight vectors W j  to yield N measured summed signals y j , where j represents a measurement iteration, j=1, . . . , M, from which receiver system  24  can estimate individual response signals x i . In the embodiments, receiver system  24  may instruct weight calculator  34  to apply different weight vectors W j  for any suitable number of iterations, such as M=N iterations. 
     Receiver system  24  instructs weight calculator  34  to apply weight vector W j  of weights w i  to response signals x i  at step  214 . In certain embodiments, a weight vector W j  applied at an iteration j may be expressed as:
 
W j =  w [w 1  w 2  w 3  w 4  . . . w N ] T  
 
     In certain embodiments, a weight vector W j  may be selected to yield a summed signal that is an orthogonal measurement. In the embodiments, weight vectors W j  may be calculated according to orthogonal codes, for example, Hadamard codes generated using a Hadamard matrix. For example, for N=4, the following weight matrix may be used: 
                                                             w 1     w 2     w 3     w 4                                                                  W 1     1   1   1   1           W 2     1   −1   1   −1           W 3     1   1   −1   −1           W 3     1   −1   −1   1                        
In the example, each row represents a weight vector W j  with weights w i  designated by the columns.
 
     Summing module  32  sums the weighted signals at step  220 . The summed signals are measured at step  222 . The measured summed signals y for sample k may be expressed as:
 
 y ( k )=   w     T   ·  x   ( k )
 
     There may be a next weight vector W j  to apply at step  224 . If there is a next weight vector W j , the method returns to step  214 , where receiver system  24  instructs weight calculator  34  to apply the next weight vector W. If there is no next weight vector W j  at step  224 , the method proceeds to step  226 . 
     Receiver system  24  estimates an array correlation matrix from the measured signals at steps  226  through  230 . The inverse of the weights is applied to measured signals y i  at step  226 . For example, the following is the inverse of the above weight matrix: 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
             
            
               
                   
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     Response signals are estimated at step  228 . In certain embodiments, receiver system  24  establishes N equations representing the N signals. The equations may be solved using linear algebra to separate the signals. In certain embodiments, the N equations include N unknowns and are solved to yield values for the unknowns. The unknowns are used to estimate individual response signals. The individual antenna response signals may be expressed as:
 
   x   ( k )=(   w     i   T ) −1   ·y   i ( k )
 
     Receiver system  24  then estimates an array correlation matrix from estimated response signals x i  at step  230 . The array correlation matrix R xx  may be estimated in any suitable manner, for example, utilizing standard statistical signal processing such as:
 
 R   xx   =E[  x ·  x     H ]
 
where H represents the Hermetian transposed operator. The method then terminates.
 
     Modifications, additions, or omissions may be made to the systems disclosed herein without departing from the scope of the invention. The components of the systems may be integrated or separated. Moreover, the operations of the systems may be performed by more, fewer, or other components. Additionally, operations of the systems may be performed using any suitable logic comprising software, hardware, and/or other logic. As used in this document, “each” refers to each member of a set or each member of a subset of a set. 
     Modifications, additions, or omissions may be made to the methods disclosed herein without departing from the scope of the invention. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. 
     Although this disclosure has been described in terms of certain embodiments, alterations and permutations of the embodiments will be apparent to those skilled in the art. Accordingly, the above description of the embodiments does not constrain this disclosure. Other changes, substitutions, and alterations are possible without departing from the spirit and scope of this disclosure, as defined by the following claims.