Abstract:
A method for receiving radio frequency signals by using an access point. The access point contains a plurality of smart antennas and a processor. The method includes following steps: (a) using the plurality of smart antennas to receive first radio signals at a first time, the first radio signals including a plurality of vectors, each vector having a phase; (b) using the processor to sum up vectors having the same phase in the first radio signals received by the plurality of smart antennas respectively and to compare sums of the vectors having the same phase to find a first phase; (c) using the processor to weigh second radio signals received by the plurality of smart antennas at a second time according to the first phase and to sum up the weighed second radio signals.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method for receiving radio signals by using an access point, and more particularly, to a method for weighing radio signals received by the access point at a second time with a set of weighing factors generated according to radio signals received by the access point at a first time.  
           [0003]    2. Description of the Prior Art  
           [0004]    Owing to the rapid development of wireless communications technologies, an access points (AP) is becoming one of the most popular communications tools. An AP receives radio signals transmitted by a wireless network subscriber with an appendant antenna.  
           [0005]    Please refer to FIG. 1, which is a schematic diagram of a plurality of radio signals  10  projected onto an AP  20  according to the prior art. The AP  20  comprises an antenna  12 . An angle θ is included between the AP  20  and wave fronts of the radio signals  10 . A distance between two neighboring radio signals (for example, nodes M and N shown in FIG. 1) is d. Because a path difference between any two neighboring radio signals equals d cos θ, if d cos θ is a multiple of the wavelength of the radio signals  10 , the intensity of a radio signal projected onto node M equals the intensity of a radio signal projected onto node N. On the contrary, if d cos θ is not a multiple of the wavelength of the radio signals  10 , the intensity of a radio signal projected onto node M does not equal the intensity of a radio signal projected onto node N. That is, if d cos θ is a multiple of the wavelength of the radio signals  10 , and the intensity of a radio signal projected onto node M is stronger than that of a radio signal projected onto a node neighboring to node M, the intensity of a radio signal projected onto node N is also stronger than that of radio signals projected onto nodes neighboring to node N. Therefore, if the AP  20  receives itself radio signals  10  with only one antenna, a user for the AP  20  has to move the antenna  12  of the AP  20  to a position near node M (or node N) from time to time to get the radio signals having the strongest intensity.  
           [0006]    In order to solve the above-mentioned problem, prior art APs adopt diversity antennas to receive the radio signals  10 . Please refer to FIG. 2, which is a schematic diagram of another AP  30  according to the prior art. The AP  30  comprises a first antenna  32 , a second antenna  34 , a controller  36 , a switching circuit  38 , and a receiver  40 . The controller  36  controls the switching circuit  38  to selectively connect the first antenna  32  or the second antenna  34  to the receiver  40  by periodically detecting the power of radio signals received by the first antenna  32  and by the second antenna  34 . For example, if the controller  36  detects that the power of radio signals received by the second antenna  34  is greater than that of radio signals received by the first antenna  32  during a first period, the controller  36  then controls the switching circuit  38  to connect the second antenna  34  to the receiver  40 . Thus, the receiver  40  of the AP  30  continues to receive radio signals transmitted from the second antenna  34  during the first period. As another example, if the controller  36  detects that the power of radio signals received by the first antenna  32  is greater than that of radio signals received by the second antenna  34  during a second period, the controller  36  then controls the switching circuit  38  to connect the first antenna  32  to the receiver  40 . Thus, the receiver  40  of the AP  30  continues to receive radio signals transmitted from the first antenna  32  during the second period. Therefore, with the help of the controller  36  and the switching circuit  38 , a user of the AP  30  does not need to move the AP  30  from time to time to receive radio signals with higher intensity. However, because the AP  30  receives radio signals with only one antenna at the same time, the signal-to-noise ratio of radio signals received by the AP  30  is not high.  
         SUMMARY OF THE INVENTION  
         [0007]    It is therefore a primary objective of the claimed invention to provide a method for receiving radio signals having as high intensities as possible by using an access point to solve the above-mentioned problems.  
           [0008]    According to the claimed invention, the access point comprises a plurality of smart antennas and a processor. The method comprises following steps: (a) using the plurality of smart antennas to receive first radio signals at a first time, the first radio signals comprising a plurality of vectors, each vector having a phase; (b) using the processor to sum up vectors having the same phase in the first radio signals received by the plurality of smart antennas respectively and to compare sums of the vectors having the same phase to find a first phase; (c) using the processor to weigh second radio signals received by the plurality of smart antennas at a second time according to the first phase and to sum up the weighed second radio signals. It is an advantage of the claimed invention that a method for weighing radio signals received by the plurality of antennas of the AP with a plurality of weighting factors generated by the processor of the AP based on radio signals received by the plurality of antennas of the AP at a first time can improve SNR.  
           [0009]    These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a schematic diagram of radio signals projected onto an access point according to the prior art.  
         [0011]    [0011]FIG. 2 is a function block diagram of an access point according to the prior art.  
         [0012]    [0012]FIG. 3 is a schematic diagram of radio signals projected onto an access point according to the present invention.  
         [0013]    [0013]FIG. 4 is a function block diagram of the access point shown in FIG. 3.  
         [0014]    [0014]FIG. 5 is a flow chart of a method for receiving radio signals by using the access point shown in FIG. 4 according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    Principles applied by the present invention are described as follows: Please refer to FIG. 3, which shows a plurality of radio signals  44  transmitted by a wireless network subscriber (not shown) to the AP  50  according to the present invention. The AP  50  comprises a plurality of smart antennas  52 . As shown in FIG. 3, because an angle θ is included between the wave fronts of the radio signals  44  and the AP  50 , and a distance between two neighboring smart antennas  52  is d, a path difference between radio signals received by two neighboring smart antennas  52  is d cos θ. Therefore radio signals received by the plurality of smart antennas  52  of the AP  50  at a first time are  
                 Y        (   t   )       =       S        (   t   )       *     [                  -   2                   j          π   λ     ·   0   ·   d                   cos                 θ                    -   2                   j          π   λ     ·   1   ·   d                   cos                 θ           ⋯                -   2                   j            2      π     λ     ·     (     N   -   1     )     ·   d                   cos                 θ             ]         ,           (     Eq   .              1     )                               
 
         [0016]    wherein S(t) is a radio signal received by a smart antenna indicated by an arrow shown in FIG. 3, and N is the number of the plurality of smart antennas  52 . Then project Y(t) onto an orthogonal basis to generate a projected radio signal V(t). That is,  
             V        (   t   )       =         Y        (   t   )       *     [                  -              j2π     ·   0   ·     0   /   M                      -              j2π     ·   0   ·     1   /   M             ⋯                -   j2π     ·   0   ·       (     M   -   1     )     /   M                          -              j2π     ·   1   ·     0   /   M             ⋯       ⋯       ⋯           ⋮       ⋮       ⋱       ⋮                    -              j2π     ·     (     N   -   1     )     ·     0   /   M             …       ⋯                -              j2π     ·     (     N   -   1     )     ·       (     M   -   1     )     /   M               ]       =       S        (   t   )       *   Q         ,     
        wherein                            Q   T     =     [               y   0     ·            -   j                   2                   π   ·   0   ·     0   /   M             +       y   1     ·            -   j                   2                   π   ·   0   ·     1   /   M             +   …   +       y     N   -   1       ·            -   j                   2                   π   ·   0   ·       (     M   -   1     )     /   M                             y   0     ·            -   j                   2                   π   ·   1   ·     0   /   M             +       y   1     ·            -   j                   2                   π   ·   1   ·     1   /   M             +   …   +       y     N   -   1       ·            -   j                   2                   π   ·   1   ·       (     M   -   1     )     /   M                       ⋮                 y   0     ·            -   j                   2                   π   ·     (     N   -   1     )     ·     0   /   M             +       y   1     ·            -   j                   2                   π   ·     (     N   -   1     )     ·     1   /   M             +   …   +                 y     N   -   1       ·            -   j                   2                   π   ·     (     N   -   1     )              (     M   -   1     )     /   M                 ]       ,                         
 
         [0017]    , wherein y h  is a radio signal received by the (h+1)th smart antenna  52  of the AP  50 , and y h e −j2πhm/M  is the (m+1)th component of a frequency spectrum having a resolution of M and projected by radio signals received by the (h+1)th smart antenna  52  onto the orthogonal basis. Each element of V(t) represents a sum of components having the same phase and projected by radio signals received by the plurality of smart antenna  52  onto the orthogonal basis. Then calculate a phase θ′ corresponding to the largest value in V(t). For example, if the largest value in V(t) is the m′th component, because λ, M, and d are all constants, the phase θ′ equals cos −1 (m′λ/Md). Then weigh radio signals received by the plurality of smart antenna  52  at a second time with corresponding weighing factors calculated according to the phase θ′. The weighing factor corresponding to the radio signal received by the hth smart antenna at the second time is e j2π(h−1)/λ*d cos θ′ =e j2n(h−1)m′/M . Therefore, radio signals received by the plurality of smart antennas  52  of the AP  50  at the second time are transformed to be  
           Y′ ( t )= Y ( t )* W=s ( t )[e j2π·0·d(cos θ′−cos θ)/λ   e   j2π·1·d(cos θ′−cos θ)/λ   + . . . e   j2π·(N−1)·d(cos θ′−cos θ)/λ ],  
         [0018]    wherein,  
             W   =       [                             j            2      π     λ     ·   0   ·   d                   cos                   θ   ′                                       j            2      π     λ     ·   1   ·   d                   cos                   θ   ′                   ⋮                               j            2      π     λ     ·     (     N   -   1     )     ·   d                   cos                   θ   ′                 ]     .             (     Eq   .              2     )                               
 
         [0019]    In the Eq. 2, when M approaches infinity, the phase θ approaches the angle θ. In this case, the signal-to-noise (SNR) of radio signals received by the AP  50  is N times that of radio signals received by the smart antenna  52  indicated by the arrow shown in FIG. 3.  
         [0020]    For example, if the AP  50  comprises only two smart antennas, just as the prior art AP  30  does, the SNR of radio signals received by the AP  50  is (1+10*log2 dB) times as large as that of radio signals received by the AP  30 .  
         [0021]    Please refer to FIG. 4, which is a function block diagram of the AP  50  according to the present invention. The AP  50  comprises a plurality of smart antenna  52  for receiving a plurality of radio frequency (RF) signals  80  and for transforming the plurality of RF signals  80  to a plurality of base band signals  82 , a processor  56  electrically connected to the plurality of smart antennas  52  for processing base band signals  82  transmitted from the plurality of smart antennas  52 , a plurality of weighing modules  54  corresponding to the plurality of smart antennas  52  and electrically connected to the processor  56  and to the plurality of smart antennas  52  in a one-to-one manner, an adder  58  electrically connected to the plurality of weighing modules  54 , and a receiver  60  electrically connected to the adder  58 . The distance between two neighboring smart antennas is d. The RF signals  80  conform to the IEEE 802a/b/g standard. The adder  58  is used to sum up the weighed base band signals transmitted from the plurality of weighing modules  54  and to transmit the summed weighed base band signals to the receiver  60 .  
         [0022]    Please refer to FIG. 5, which illustrates a flow chart of a method  100  for receiving the RF signals  80  by using the AP  50  according to the present invention. The method  100  comprises following steps:  
         [0023]    Step  102 : start;  
         [0024]    Step  104 : use the plurality of smart antennas  52  of the AP  50  to receive the RF signals  80  at a first time;  
         [0025]    Step  106 : use the plurality of smart antennas  52  to transform the RF signals  80  into base band signals  82 ;  
         [0026]    Step  108 : use the processor  56  to transform the base band signals  82  into a plurality of signals, each signal having a predetermined phase;  
         [0027]    (That is, project the base band signal  82  onto the orthogonal basis to generate the plurality of signals.)  
         [0028]    Step  110 : determine the greatest signal in the plurality of signals generated in step  108  and calculate a phase θ corresponding to the greatest signal;  
         [0029]    Step  112 : use the processor  56  to calculate a plurality of weighing factors for the plurality of weighing modules  54  according to the phase θ;  
         [0030]    Step  114 : use each of the weighing modules  54  to weigh base band signals transmitted from a smart antenna  52  corresponding to the weighing module at a second time with a weighing factor corresponding to the weighing module  54 ;  
         [0031]    Step  116 : use the adder  58  to sum up all the weighed base band signals transmitted from the weighing modules  54 ; Step  118 : use the receiver  60  to receive signals transmitted from the adder  58 ; and  
         [0032]    Step  126 : end.  
         [0033]    In the method  100 , steps  108 ,  110 , and  112  need not be executed during every period. The processor  56  is allowed to execute the steps  108 ,  110 , and  112  for every predetermined number of the periods. Compared to radio signals, AP  50  moves very slow. That is, as  10  or even  100  periods of the radio signals have passed, variation of relative displacement between the AP  50  and the wireless network subscriber or between the AP  50  and the environment surround the AP  50  still can be neglected, and so can d cos θ. Therefore, the weighing factors calculated according to a phase θ still can be utilized to weigh radio signals received by the AP  50  for the following ten (or  100 ) periods.  
         [0034]    In the prior art AP  30 , the controller  36  controls the switching circuit  38  to connect the receiver  40  to the first antenna  32  or to the second antenna  34  according to powers of radio signals received by the first antenna  32  and the power of radio signals received by the second antenna  34 . The receiver  40  of the AP  30  can only receive radio signals transmitted from one antenna, so the SNR of radio signals received by the AP  30  is therefore low.  
         [0035]    In contrast to the prior art, the present invention can provide a method for receiving wireless signals by using an AP. The AP comprises a plurality of antennas. The method calculates a plurality of weighting factors based on radio signals received by the plurality of antennas of the AP at a first time and weighs radio signals received by the plurality of antennas of the AP at a second time with the plurality of weighting factors to improve SNR.  
         [0036]    Following the detailed description of the present invention above, those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.