Abstract:
The present invention aims to provide a technical solution for recognizing a target device from a plurality of devices as follows: sending a first and second wireless signal to a plurality of devices and determining the target device according to the signal strength differences between the first and second signal strengths. By using the technical solutions of the present invention, the “near-far-effect” caused by a single antenna can be overcome, and different offsets in the measured received signal strengths caused by the diversity of the receiving antennas can also be eliminated, and thus the accuracy of recognition is improved efficiently.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to recognition of devices, particular to recognizing devices via the signal strength of the wireless signals received by devices. 
       BACKGROUND OF THE INVENTION 
       [0002]    Currently, wireless lighting control is becoming more and more popular with the deployment of ZigBee™, Bluetooth™, and other wireless protocols. However, there still lacks an effective mechanism for directional control. For example, with directional control, users can control a light, such as controlling the turning on/off and light intensity, through “pointing” to it. 
         [0003]    Directional control is helpful in large rooms where there are many lights installed. For example, in a large meeting room, the presenter may want to turn off the lights close to the projector screen, while turning on the other lights. With directional control, the presenter can remain at his position and simply point the hand-held controller to the light he wants to control, and then turn it on or off. 
         [0004]    The most straightforward way to enable wireless directional control is to use directional antenna and distinguish lights by their different received signal powers. However, when a directional antenna is adopted, there exists a defect called “near-far effect”. That is, although directional antenna may induce a higher received signal power at the light that it points to, the lights near the controller may also have very high received signal power due to the very short propagation distance. Thus it is difficult to determine which light the user actually wants to control merely based on the signal strength. Moreover, the diversity of the antennas installed in the lights may also introduce different offsets in the measured received signal strength and thus introduce errors into the recognition. 
         [0005]      FIG. 1  illustrates a typical radiation pattern of a directional antenna in different directions. The power gain of the directional antenna in different directions is denoted as G (θ,φ) (simply referred as “directional gain” hereinafter). Suppose the transmitting power is P T , the actual power received by a receiver not only depends on the transmitting power P T  and the gain of the transmitting antenna, but also depends on other factors such as the gain of the receiving antenna, the distance, the frequency of the wireless signals, etc. The signal strength difference of two wireless signals respectively received by two lights not only depends on the gain of the transmitting antenna, but also depends on the gain of the two receiving antennas and the distances between the two receiving antennas and the transmitting antennas. In other words, if the signal strength of a wireless signal received by light R 1  is greater than that of light R 2 , it cannot be concluded that light R 1  is located in the direction of the maximal radiation of the transmitting antenna or light R 1  is the target light the subscriber wants to control. 
       SUMMARY OF THE INVENTION 
       [0006]    To solve the above issues, there is provided in an embodiment of the present invention a technical solution for recognizing a target device from a plurality of devices as follows: sending a first and a second wireless signals to a plurality of devices and determining the target device according to the signal strength differences between the first and second signal strengths. 
         [0007]    According to an embodiment of the present invention, there is provided a method for recognizing a target device. The method comprises the steps of: sending a first and second wireless signal to a plurality of devices; obtaining, from each device, a first and a second signal strengths respectively representing the signal strength of the first and the second wireless signals received by the device, or a signal strength difference between the first and the second signal strengths; and determining the target device according to the obtained signal strengths or the signal strength differences. 
         [0008]    According to an embodiment of the present invention, there is provided a wireless controller for recognizing a target device. The wireless controller comprises a first transmitter, an obtainer and a determiner. The first transmitter is configured to send a first and a second wireless signals to a plurality of devices. The obtainer is configured to obtain, from each device, a first and a second signal strength respectively representing the signal strength of the first and the second wireless signals received by the device, or a signal strength difference between the first and the second signal strengths. The determiner is configured to determine the target device according to the obtained signal strengths or the obtained signal strength differences. 
         [0009]    Preferably, the first transmitter of the wireless controller comprises an omnidirectional antenna, a first directional antenna and a first controller, wherein the first controller controls the omnidirectional antenna and the first directional antenna to respectively send the first and second wireless signals to the plurality of devices. 
         [0010]    Preferably, the first transmitter of the wireless controller comprises a second directional antenna and a second controller, wherein the second controller controls the second directional antenna to send the first and second wireless signals to the plurality of devices by way of symmetrically deviating a predetermined angle from a predetermined direction. 
         [0011]    Preferably, the first transmitter of the wireless controller comprises a third directional antenna, a fourth directional antenna and a third controller, wherein, the third controller controls the third directional antenna and the fourth directional antenna to respectively send the first and second wireless signals to the plurality of devices in a way of symmetrically deviating a predetermined angle from a predetermined direction. 
         [0012]    According to an embodiment of the present invention, there is provided a device comprising a receiver, a determiner and a second transmitter, wherein the receiver is configured to receive two wireless signals sent by a wireless controller; the determiner is configured to determine the signal strength of the two wireless signals or their difference; the second transmitter is configured to send the signal strength or their difference to the wireless controller. 
         [0013]    By using the technical solutions of the present invention, the “near-far-effect” caused by a single antenna can be overcome, and different offsets in the measured received signal strengths caused by the diversity of the receiving antennas can also be eliminated, and thus the accuracy of recognition is improved efficiently. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Other purpose, aspects and advantages of the present invention will become clear and prominent after reading the description with reference to the accompanying drawings, in which identical reference numerals denote identical or like components: 
           [0015]      FIG. 1  shows a schematic view of the power gain of a directional antenna in different directions; 
           [0016]      FIG. 2  shows a scenario of an embodiment of the present invention; 
           [0017]      FIG. 3  shows a schematic flow chart of the method of recognizing a target device from a plurality of device  23  according to another embodiment of the present invention; 
           [0018]      FIG. 4  shows a block diagram of the first transmitter of the wireless controller  21  according to one embodiment of the present invention; 
           [0019]      FIGS. 5(   a ) and  5 ( b ) respectively show schematic views of the beam forming of an omnidirectional antenna and a directional antenna according to one embodiment of the present invention; 
           [0020]      FIG. 6  shows the flow chart of the sub-steps of step S 301  shown in  FIG. 3 ; 
           [0021]      FIG. 7  shows another block diagram of the first transmitter of the wireless controller  21  according to one embodiment of the present invention; 
           [0022]      FIG. 8  shows a schematic view of the beam forming of a second adjustable-beam directional antenna  71 ; 
           [0023]      FIGS. 9(   a ) and  9 ( b ) respectively show schematic views of the beam forming of the second adjustable-beam antenna  71  with its maximum radiation being upward and downward oriented by the same predefined angle along the axis Z; 
           [0024]      FIG. 10  shows the schematic view of the transmitting power gain of the first and second wireless signals. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 2  shows a schematic view of a scenario of an embodiment of the present invention. There are a wireless controller  21  and four devices  23 - 1 ,  23 - 2 ,  23 - 3  and  23 - 4  in  FIG. 2 . For simplicity,  FIG. 2  only shows four devices, but those skilled in the art should understand that the number of the devices is not limited. And the device  23  may be any controllable devices, such as luminaries etc. 
         [0026]    In  FIG. 2 , the wireless controller  21  comprises a first transmitter  211 , an obtainer  212  and a first determiner  213 . Each device comprises a receiver  231 , a second determiner  232  and a second transmitter  233 . 
         [0027]      FIG. 3  shows a schematic flow chart of the method of the wireless controller  21  recognizing a target device from a plurality of devices  23  according to another embodiment of the present invention. The flowchart of  FIG. 3  will be described in detail below in conjunction with the scenario of  FIG. 2 . 
         [0028]    Firstly, in step S 301 , the first transmitter  211  of the wireless controller  21  sends a first and second wireless signal to a plurality of devices  23 . 
         [0029]    Then, in step S 302 , the obtainer  212  of the wireless controller  21  obtains a first and second signal strength respectively representing the signal strength of the first and second wireless signal received by each device, or a signal strength difference between the first and the second signal strengths. 
         [0030]    Specifically, step S 302  can be implemented in several ways. For example, after each device  23  receives the first and second wireless signals transmitted by the wireless controller  21 , the second determiner  232  determines a signal strength difference between the first and second signal strengths, and then the second transmitter  233  sends the signal strength difference to the wireless controller  21 . 
         [0031]    Below is another example of the implementation of step S 302 . The second determiner  232  of each device  23  determines the signal strength of the first and second wireless signals received respectively, and then the second transmitter  233  sends the signal strength of the first and second signals to the wireless controller  21 . The wireless controller  21  computes the difference between the signal strengths of the first and second signals. Or each device  23  may send the signal strength of the first and second signals to another item of equipment, the equipment may compute the difference between the signal strengths of the first and second signals and send the difference to the wireless controller  21 . 
         [0032]    Lastly, in step S 303 , the first determiner  213  of the wireless controller  21  determines the target device according to the signal strengths of the first and second signals or their difference for each device  23  obtained by the obtainer  212 . In step S 303 , the first determiner  213  determines as being the target device the device corresponding to the maximum or minimum signal strength difference among all the signal strength differences or the two signal strengths having the maximum or minimum signal strength difference, according to the way of sending the first and second signals. This will be described in detail later. 
         [0033]    Preferably, before step S 301  shown in  FIG. 3 , the wireless controller  21  can receive operation instructions which triggers step S 301  and its subsequent steps. These operation instructions may be sent by users or other devices (not shown in  FIG. 2 ). For example, once a projector is turned on, it may send a signal to the wireless controller  21  for indicating turning off the lights close to the projector screen. 
         [0034]    It should be noted that the operation instruction is not the only way to trigger step S 301  and its subsequent steps. In some automatic tests, the wireless controller  21  can also trigger step S 301  and its subsequent steps by automatic detection of the existence of items of equipment by way of infrared detection etc. 
         [0035]    After the first determiner  231  of the wireless controller  21  has determined the target device, the wireless controller  21  sends the received operation instructions to the operation apparatus of the target device (not shown in  FIG. 2 ). The operation apparatus executes the corresponding operations against the target device according to the operation instructions. For example, the device  23  is a light, its corresponding operation apparatus includes a switch or a brightness adjustment apparatus etc. 
         [0036]    In the following section, the detailed procedures of sending the first and second wireless signals by the first transmitter  211  of the wireless controller  21  will be exemplarily described. 
         [0037]      FIG. 4  shows a block diagram of the first transmitter  221  according to one embodiment of the present invention. The first transmitter  211  comprises an omnidirectional antenna  41 , a first directional antenna  42  and a first controller  43 .  FIGS. 5(   a ) and  5 ( b ) respectively show schematic views of the beam forming of the omnidirectional antenna  41  and the directional antenna  42 . 
         [0038]    Below, an embodiment of sending the first and the second wireless signals by the first transmitter  211  to the plurality of devices  23  in step S 301  will be described.  FIG. 6  shows a flow chart of sub-steps of step S 301 . 
         [0039]    Firstly, in step S 601 , the first controller  43  controls the omnidirectional antenna  41  to send the first wireless signal to the plurality of devices  23 . 
         [0040]    Preferably, the first controller  43  may comprise a microcontroller and a RF control chip. The microcontroller controls the omnidirectional antenna to send the first wireless signal via the RF control chip. 
         [0041]    The first wireless signal has the signal features which can be recognized by each device  23 . For example, the first signal may have a predefined frame structure that contains a preamble code and a flag indicating that the first wireless signal is sent by the omni-directional antenna  41  for measuring the signal strength and so on. The first wireless signal may comprise one or multiple wireless signals. If the first wireless signal comprises multiple wireless signals, each wireless signal of the multiple signals may further comprise the information on the amount of first wireless signal, the sequence number of the current signal etc. 
         [0042]    Then, instep S 602 , the first controller  43  controls the first directional antenna  42  to send the second wireless signal to the plurality of devices  23 , wherein the maximum power gain direction of the first directional antenna  42  substantially points to the target device. 
         [0043]    It should be noted that, if the operation instruction is sent by a user, the “pointing” action can be done by the user before the first and the second wireless signals are sent by the wireless controller  21 . For example, the user makes the wireless controller  21  point to the device that the user wants to control (the controller may indicate to the user that the wireless controller has pointed to the device via a laser beam), and then presses a button to send the corresponding operation instruction. 
         [0044]    If an operation instruction is sent by other devices or the wireless controller  21  triggers the transmission process automatically, the “pointing” action can be done automatically by the wireless controller  21 . 
         [0045]    Similarly to the first wireless signal, the second wireless signal also has the signal features that can be recognized by each device  23 . For example, the second signal may have a predefined frame structure that contains a preamble code and a flag indicating that the second signal is sent by the first directional antenna  42  for measuring the signal strength and so on. The second wireless signal may comprise one or multiple wireless signals. If the second wireless signal comprises multiple wireless signals, each wireless signal of the multiple wireless signals may further comprise the information on the amount of the second wireless signal, the sequence number of the current signal etc. 
         [0046]    If the first and second wireless signals comprise multiple wireless signals, the signal strengths of the first and second signals received by the device  23  comprise the mean or weighted mean of the signal strengths of the received multiple wireless signals. The value of the weighted coefficients can be selected based on experience values of the actual system. By using multiple wireless signals in the first and second signals, the interference of some sudden accidental factors (e.g. burst noise) can be reduced, the stability and robustness of the system can be enhanced and the accuracy of the recognition result can be increased. 
         [0047]    Preferably, the first and second wireless signals may be orthogonal. The meaning of orthogonality comprises different orthogonal ways, such as being orthogonal in time, being orthogonal in frequency, Code Division Multiple Access or arbitrary combination among them etc. For multiple signals in the first or second signals, they should also be orthogonal to each other, including being orthogonal in time, being orthogonal in frequency, Code Division Multiple Access or any combination among them etc. 
         [0048]    It should be noted that if the first and second wireless signals are not orthogonal to each other in time, e.g. being orthogonal in frequency or Code Division Multiple Access, there is no sequence between step S 601  and S 602  as shown in  FIG. 6 . They can be performed at the same time or at different times. Even if only orthogonality in time is adopted, there is also no sequence between the two steps except that they cannot be performed at the same time. 
         [0049]    After that, the obtainer  212  of the wireless controller  21  obtains, from each device  23 , a signal strength difference between the first and second signal strengths. Then the first determiner  213  determines as being the target device the device corresponding to the minimum difference among all the signal strength differences computed by subtracting the signal strength of the second wireless signal from that of the first wireless signal or the maximum difference among all the signal strength differences computed by subtracting the signal strength of the first wireless signal from that of the second wireless signal. 
         [0050]    Below, the procedure that the first determiner  213  of the wireless controller  21  determines the target device corresponding to the maximum or minimum signal strength differences of the first and second wireless signals will be analyzed. 
         [0051]    Without loss of generality, the receiver  231  of the device  23 - 1  and  23 - 2  comprises a receiving antenna and a control chip. The form and the gain of the receiving antennas are not limited and also no similarity is required. In addition, optionally, the first and second wireless signals comprise only one wireless signal. 
         [0052]    Then the signal strengths of the first wireless signal sent by the omnidirectional antenna  41  and received by the device  23 - 1  and  23 - 2  can be represented by the following two formulae: 
         [0000]    
       
         
           
             
               
                 
                   
                     
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         [0000]    wherein P R1   o  and P R2   o  are signal strengths of the first wireless signal sent by the omnidirectional antenna  41  and received by the device  23 - 1  and  23 - 2  respectively, P T   o  is the transmitting power of the omnidirectional antenna  41 , G T   O  is the gain of the omnidirectional antenna  41 , G R1  and G R2  are the gains of the receiving antennas of the receiver  231  of the device  23 - 1  and  23 - 1  respectively, d 1  and d 2  are the distance between the omnidirectional antenna  41  and the receiving antenna of the device  23 - 1  and  23 - 2  respectively, and f O  is the frequency of the first wireless signal sent by the omni-directional antenna  41 . 
         [0053]    The signal strength of the second wireless signal sent by the first directional antenna  42  and received by the device  23 - 1  and  23 - 2  can be represented by the following two formulae: 
         [0000]    
       
         
           
             
               
                 
                   
                     
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         [0000]    wherein P R1   D  and P R2   D  are signal strengths of the second wireless signal sent by the first directional antenna  42  and received by the receiving antennas of the device  23 - 1  and  23 - 2  respectively, P T   D  is the transmitting power of the first directional antenna  42 , and G T   D (θ 1 ,φ 1 ) and G T   D (θ 2 ,φ 2 ) are the directional gains from the first directional antenna  42  to the receiving antennas of the device  23 - 1  and  23 - 2  respectively. As the receiving antennas of the device  23 - 1  and  23 - 2  remain unchanged, G R1 , G R2 , d 1  and d 2  in formulae (3) and (4) has the same meaning as in formulae (1) and (2). f D  is the frequency of the second wireless signal sent by the first directional antenna  42 . f O  and f D  can be the same or can be different. 
         [0054]    By subtracting formula (1) from formula (3), and subtracting formula (2) from formula (4), the following formulae (5) and (6) are obtained: 
         [0000]        P   R1   D ( dBm )− P   R1   O ( dBm )= P   D   T ( dBm )− P   T   O ( dBm )+101 gG   T   D (θ 1 ,φ 1 )−101 gG   T   O −201 gf   D +201 gf   O   (5)
 
         [0000]        P   R2   D ( dBm )− P   R2   O ( dBm )= P   T   D ( dBm )− P   T   O ( dBm )+101 gG   T   D (θ 2 ,φ 2 )−101 gG   T   O −201 gf   D +201 gf   O   (6)
 
         [0055]    By subtracting formula (6) from formula (5), formula (7) is obtained: 
         [0000]      [ P   R1   D ( dBm )− P   R1   O ( dBm )]−[ P   R2   D ( dBm )− P   R2   O ( dBm )]=101 gG   T   D (θ 1 ,φ 1 )−101 gG   T   D (θ 2 ,φ 2 )  (7)
 
         [0056]    As can be seen from formula (7), the terms on the right-hand side of the equation are only relevant to the directional gain of the first directional antenna  42 . For example, when a user is using the wireless controller  21 , the desired target device is always located in the maximum radiation direction of the first directional antenna  42  of the wireless controller  21 . Therefore it can be judged according to formula (7) that if the device  23 - 1  is the target device, the right-hand part of formula (7) is always positive, i.e. as compared with other devices, the signal strength difference computed by subtracting the signal strength of the first wireless signal received by the target device from the signal strength of the second wireless signal received by the target device is maximum or the signal strength difference computed by subtracting the signal strength of the second wireless signal received by the target signal from the signal strength of the first wireless signal received by the target device is minimum. 
         [0057]    Therefore, after the obtainer  212  has obtained the signal strength differences between the first and the second wireless signals received by each device  23 , the first determiner  213  can determine the device corresponding to the maximum signal strength difference among all the signal strength differences computed by subtracting the received signal strength of the first wireless signal from that of the second wireless signal or the minimum signal strength difference among all the signal strength differences computed by subtracting the received signal strength of the second wireless signal from that of the first wireless signal as the target device. 
         [0058]    It should be noted that the aforementioned omnidirectional antenna  41  is only quasi omnidirectional. In practice, it is impossible to make the omnidirectional antenna  41  have exactly the same gain in all directions. However, even if some differences are introduced to the gains of the omnidirectional antenna  41  in different directions, the above deduction still holds. The detailed analysis will be described as follows. 
         [0059]    If some differences are introduced to the gains of the omni-directional antenna  41  in different directions, the formula (7) can be rewritten as: 
         [0000]      [ P   R1   D ( dBm )− P   R1   O ( dBm )]−[ P   R2   D ( dBm )− P   R2   O ( dBm )]=[101 gG   T   D (θ 1 ,φ 1 )−101 gG   T   D (θ 2 ,φ 2 )]−[101 gG   T   O (θ 1 ,φ 1 )−101 gG   T   O (θ 2 ,φ 2 )]  (8)
 
         [0000]    wherein G T   O (θ 1 ,φ 1 ) and G T   O (θ 2 , φ 2 ) are the gains of the omnidirectional antenna  41  in the direction from the omnidirectional antenna  41  to the device  23 - 1  and  23 - 2  respectively. In practice, the diversity of the omnidirectional antenna  41  in different directions is far smaller than that of the first directional antenna  42 . Therefore, if the device  23 - 1  is the target device, the right-hand part of the formula is always positive and the above deduction still holds. 
         [0060]      FIG. 7  shows another block diagram of the first transmitter  211  of the wireless controller  21  according to another embodiment of the present invention. In  FIG. 7 , the first transmitter  211  comprises a second directional antenna  71  adjustable in the beam direction and a second controller  72 . The schematic view of the beam forming of the second directional antenna  71  may refer to  FIG. 5(   b ). 
         [0061]    Another embodiment of sending the first and second signals from the first transmitter  211  of the wireless controller  21  to the plurality of devices  23  in step S 301  will be described below. 
         [0062]    The second controller  72  controls the second directional antenna  71  to send the first and second wireless signals to the plurality of devices  23  by way of symmetrically deviating a predefined angle from a predefined direction. Preferably, the predefined direction is the direction that is the maximum radiation direction of the second directional antenna  71  pointing to the target device. For example, when a user is using the wireless controller  21 , he usually makes the wireless controller  21  point to the device he wants to control and then sends a command by an action such as pressing a key. In some automatic tests, the “pointing” action can also be done by the wireless controller  21 . 
         [0063]    Specifically, the second controller  72  adjusts the beam direction of the second directional antenna  71  to make the maximum radiation direction of the second directional antenna deviate by a predefined angle θ from the predefined direction. Then the second controller  72  controls the second directional antenna  71  to send the first wireless signal to the plurality of devices  23 . After that, the second controller  72  controls the second directional antenna  71  to make its maximum radiation direction deviate by a predefined angle θ from the predefined direction in the opposite direction relative to the direction of sending of the first signal, and then sends a second wireless signal to the plurality of devices  23 . The predefined angle θ is usually a small angle, and its value depends on the actual wireless controller  21  and the property of the antennas of the devices  23  (e.g. the beam forming property of the adjustable directional antennas). 
         [0064]    Preferably, the functions of the second controller  72  can be implemented by the microcontroller and the RF control chip. 
         [0065]    After that, the obtainer  212  obtains the signal strength differences between the first and second wireless signals received by each device  23 . Then the first determiner  213  determines as being the target device the device corresponding to the signal strength difference having the minimum absolute among all the signal strength differences of the plurality of devices  23 . 
         [0066]    The procedure that the first determiner  213  determines the device corresponding to the signal strength difference having the minimum absolute among all the signal strength differences will be analyzed below. Without loss of generality, still suppose that the first and second wireless signals comprise only one wireless signal. 
         [0067]    To facilitate the description, the aforementioned procedure will be analyzed with the example of the direction control in the X-Z plane. Those skilled in the art should understand that the analysis in the X-Y plane or in the Y-Z plane is the same as that in the X-Z plane. 
         [0068]      FIG. 8  shows a schematic view of the beam forming of a second adjustable-beam directional antenna  71 . The devices  23 - 1  and  23 - 2  are located in two different directions in the X-Z plane, and their angular distance from the second directional antenna  71  is α. Without loss of generality, suppose the device  23 - 1  is the target device and located in the maximum radiation direction of the second directional antenna  71  with its beam forming not being adjusted, namely the predefined direction. The angular coordinates of the device  23 - 1  and  23 - 2  are (0,φ) and (α,φ) respectively. 
         [0069]      FIGS. 9(   a ) and  9 ( b ) respectively show schematic views of the beam forming of the second adjustable-beam antenna  71  with its maximum radiation being upward and downward oriented by the same predefined angle along the axis Z. According to antenna theory, the gain of the second directional antenna  71  in the maximum radiation direction changes little or remains almost unchanged when its beam forming is adjusted by a small angle. And the gains of the second directional antenna  71  are symmetric to its maximum radiation direction. By using this property, the gains of the transmitting antenna of the first and second wireless signals received by the device  23 - 1  are G T (θ,φ) and G T (θ,φ) respectively, and gains of the transmitting antenna of the first and second wireless signals received by the device  23 - 2  are G T (θ+α,φ) and G T (θ−α,φ) respectively, as shown in  FIG. 10 . 
         [0070]    Under the circumstances shown in  FIG. 9(   a ), the signal strengths of the first wireless signal received by the devices  23 - 1  and  23 - 2  can be expressed as the formulae (9) and (10) respectively: 
         [0000]    
       
         
           
             
               
                 
                   
                     P 
                     
                       R 
                        
                       
                           
                       
                        
                       
                         1 
                         ′ 
                       
                     
                   
                   = 
                   
                     
                       P 
                       T 
                     
                     + 
                     
                       20 
                        
                       lg 
                        
                       
                         c 
                         
                           4 
                            
                           π 
                         
                       
                     
                     + 
                     
                       10 
                        
                       
                         
                           lgG 
                           T 
                         
                          
                         
                           ( 
                           
                             θ 
                             , 
                             ϕ 
                           
                           ) 
                         
                       
                     
                     + 
                     
                       10 
                        
                       
                         lgG 
                         
                           R 
                            
                           
                               
                           
                            
                           1 
                         
                       
                     
                     - 
                     
                       20 
                        
                       lg 
                        
                       
                           
                       
                        
                       d 
                        
                       
                           
                       
                        
                       1 
                     
                     - 
                     
                       20 
                        
                       
                         lgf 
                         
                           D 
                           ′ 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
             
               
                 
                   
                     P 
                     
                       R 
                        
                       
                           
                       
                        
                       
                         2 
                         ′ 
                       
                     
                   
                   = 
                   
                     
                       P 
                       T 
                     
                     + 
                     
                       20 
                        
                       
                           
                       
                        
                       lg 
                        
                       
                         c 
                         
                           4 
                            
                           π 
                         
                       
                     
                     + 
                     
                       10 
                        
                       
                           
                       
                        
                       
                         
                           lgG 
                           T 
                         
                          
                         
                           ( 
                           
                             
                               θ 
                               + 
                               α 
                             
                             , 
                             ϕ 
                           
                           ) 
                         
                       
                     
                     + 
                     
                       10 
                        
                       
                         lgG 
                         
                           R 
                            
                           
                               
                           
                            
                           2 
                         
                       
                     
                     - 
                     
                       20 
                        
                       lg 
                        
                       
                           
                       
                        
                       d 
                        
                       
                           
                       
                        
                       2 
                     
                     - 
                     
                       20 
                        
                       lg 
                        
                       
                           
                       
                        
                       
                         f 
                         
                           D 
                           ′ 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
         [0000]    Wherein P R1′  and P R2′  are the signal strengths of the first wireless signal sent by the second directional antenna  71  and received by the receiving antenna of the device  23 - 1  and  23 - 2  respectively, P T  is the transmitting power of the second directional antenna  71 , G R1  and G R2  are gains of the receiving antenna of the device  23 - 1  and  23 - 2  respectively, d 1  is the distance between the second directional antenna  71  and the receiving antennas  231 - 1  of the device  23 - 1 , d 2  is the distance between the second directional antenna  71  and the receiving antennas  231 - 2  of the device  23 - 2 , and f D′  is the frequency of the wireless signal sent by the second directional antenna  71 . 
         [0071]    Under the circumstances shown in  FIG. 9(   b ), the signal strengths of the second wireless signal received by the devices  23 - 1  and  23 - 2  can be expressed as the formulae (11) and (12) respectively: 
         [0000]    
       
         
           
             
               
                 
                   
                     P 
                     
                       R 
                        
                       
                           
                       
                        
                       
                         1 
                         ″ 
                       
                     
                   
                   = 
                   
                     
                       P 
                       T 
                     
                     + 
                     
                       20 
                        
                       lg 
                        
                       
                         c 
                         
                           4 
                            
                           π 
                         
                       
                     
                     + 
                     
                       10 
                        
                       
                         
                           lgG 
                           T 
                         
                          
                         
                           ( 
                           
                             θ 
                             , 
                             ϕ 
                           
                           ) 
                         
                       
                     
                     + 
                     
                       10 
                        
                       
                         lgG 
                         
                           R 
                            
                           
                               
                           
                            
                           1 
                         
                       
                     
                     - 
                     
                       20 
                        
                       lg 
                        
                       
                           
                       
                        
                       d 
                        
                       
                           
                       
                        
                       1 
                     
                     - 
                     
                       20 
                        
                       
                         lgf 
                         
                           D 
                           ′ 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
             
               
                 
                   
                     P 
                     
                       R 
                        
                       
                           
                       
                        
                       
                         2 
                         ″ 
                       
                     
                   
                   = 
                   
                     
                       P 
                       T 
                     
                     + 
                     
                       20 
                        
                       
                           
                       
                        
                       lg 
                        
                       
                         c 
                         
                           4 
                            
                           π 
                         
                       
                     
                     + 
                     
                       10 
                        
                       
                           
                       
                        
                       
                         
                           lgG 
                           T 
                         
                          
                         
                           ( 
                           
                             
                               θ 
                               - 
                               α 
                             
                             , 
                             ϕ 
                           
                           ) 
                         
                       
                     
                     + 
                     
                       10 
                        
                       
                         lgG 
                         
                           R 
                            
                           
                               
                           
                            
                           2 
                         
                       
                     
                     - 
                     
                       20 
                        
                       lg 
                        
                       
                           
                       
                        
                       d 
                        
                       
                           
                       
                        
                       2 
                     
                     - 
                     
                       20 
                        
                       lg 
                        
                       
                           
                       
                        
                       
                         f 
                         
                           D 
                           ′ 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
         [0000]    Wherein P R1″  and P R2″  are the signal strengths of the second wireless signal sent by the second directional antenna  71  and received by the receiving antenna of the devices  23 - 1  and  23 - 2  respectively. 
         [0072]    By subtracting formula (9) from formula (11) and formula (10) from formula (12), formulae (13) and (14) are obtained: 
         [0000]        P   R1″   −P   R1′ =0  (13)
 
         [0000]        P   R2″   −P   R2′ =101 gG   T (θ−α,φ)−101 g   T (θ+α,φ)  (14)
 
         [0073]    As can be seen from formulae (13) and (14), the signal strength difference between the first and the second wireless signals received by the device  23 - 1  or  23 - 2  is not relevant to the gain of the receiving antenna, and not relevant to the distance between the second directional antenna  71  and the receiving antenna of the device  23 - 1  or  23 - 2  either, and is relevant only to the direction of the device  23 - 1  or  23 - 2  relative to the direction of the first transmitter  211  and the directional gain of the second directional antenna  71 . 
         [0074]    As can be seen from formulae (13) and (14), as compared with other devices, the absolute signal strength difference between the first and second wireless signals received by the target device is the smallest. Therefore, after the obtainer  212  has obtained the signal strength differences between the first and second wireless signals received by each device  23 , the first determiner  213  can determine as being the target device the device corresponding to the minimum absolute signal strength difference among all the signal strength differences computed by subtracting the strength difference of the second wireless signal from that of the first wireless signal. 
         [0075]    In consideration of the side lobe effect of the directional gain of the second directional antenna  71 , in order to further increase the accuracy of the recognition, the second controller  72  can further control the second directional antenna  71  to send a third wireless signal to the plurality of devices  23  so that the maximum radiation direction of the second directional antenna  71  points to the target device. 
         [0076]    After the receiver  231  of each device  23  receives the third wireless signal, the second determiner  232  determines the signal strength of the third wireless signal, which is also referred as the third signal strength. And then the second transmitter  233  sends the third signal strength to the wireless controller  21 . 
         [0077]    Similar to the first and second wireless signals, the third wireless signal also has the signal features that can be recognized by each device  23 , e.g. a predefined frame structure that contains a preamble code and a flag indicating that the third wireless signal is sent by the second directional antenna  71  for measuring the signal strength etc. The frame structure of the third wireless signal can be the same as that of the first or second wireless signal, and of course they can be different. The third wireless signal can comprise one or multiple wireless signals. If the third wireless signal comprises multiple wireless signals, each wireless signal of the multiple wireless signals can further comprise the information on the amount of the third wireless signals, the sequence number of the current signal etc. 
         [0078]    If the third wireless signal comprises multiple wireless signals, the signal strength of the third wireless signal received by each device  23  comprises the mean or weighted mean of the signal strengths of the multiple signals. The value of the weighted coefficients can be selected according to the experience values of the actual system operation. By using multiple wireless signals, the interference of some sudden accidental factors (e.g. burst noise) can be reduced, the stability and robustness of the system can be enhanced and the accuracy of the recognition result can be increased. 
         [0079]    Based on the signal strengths of the first, second and third wireless signals received by each of a plurality of devices  23 , or their differences, the first determiner  213  of the wireless controller  21  determines the target device, i.e. considering the first, second and third wireless signals together and determining the target device according to them. 
         [0080]    Preferably, the first determiner  213  can, among the devices having a relatively high third signal strength, determine the device corresponding to the first and second signal strengths having the minimum absolute of signal strength difference as the target device. Specifically, based on factors such as the transmitting antenna, the receiving antenna, the transmission environment and so on, a proper predefined threshold can be set, devices having the signal strength above the predefined threshold can be determined as devices having a relatively high third signal strength. 
         [0081]    Moreover, according to formula (15), the first determiner  213  determines the device corresponding to the minimum weighted sum of the reciprocal of the third signal strength and the absolute difference between the first and the second signal strengths as the target device, i.e. the device having the smallest W is the target device. 
         [0000]    
       
         
           
             
               
                 
                   W 
                   = 
                   
                     
                       
                         W 
                         1 
                       
                       · 
                       
                         1 
                         
                           P 
                           
                             Rm 
                             
                               ″ 
                                
                               ″ 
                             
                           
                         
                       
                     
                     + 
                     
                       
                         W 
                         2 
                       
                       · 
                       
                          
                         
                           
                             P 
                             
                               Rm 
                               ″ 
                             
                           
                           - 
                           
                             P 
                             
                               Rm 
                               ′ 
                             
                           
                         
                          
                       
                     
                   
                 
               
               
                 
                   ( 
                   15 
                   ) 
                 
               
             
           
         
       
     
         [0000]    Wherein, m=1, . . . , M, M is the number of devices, P Rm′ , P Rm″ , P Rm′″  are signal strengths of the first, second and third wireless signals received by the device m respectively, W 1  and W 2  are weighted coefficients which can be selected according to the actual system. Under the circumstances that both W 1  and W 2  are 1, the device corresponding to the minimum sum of the reciprocal of the third signal strength and the absolute difference between the first and second signal strengths is the target device. 
         [0082]    Those skilled in the art should understand that there are various ways to determine the target device based on the comprehensive consideration of the first, second and third signals. The present invention is not limited to the two aforementioned preferred embodiments. And various modifications can be made based on the two aforementioned preferred embodiments. 
         [0083]    As a variant of the structure shown in  FIG. 7 , the first transmitter  211  can also comprise a third and fourth directional antenna with the same directional gain, and a third controller. The two transmitting processes of the second directional antenna  71  shown in  FIG. 7  can be done by the third controller controlling the third and fourth directional antennas to send the first and second wireless signals at the same time. Obviously, if the first and second wireless signals are sent at the same time, they should satisfy the orthogonal requirement (e.g. Frequency Division Multiplex Access or Code Division Multiplex Access etc). The advantage of the solution is that it decreases the recognition process and reduces the user waiting time. The disadvantage is that it needs one more directional antenna, which will increase the cost. 
         [0084]    It should be noted that because it is inevitable to have error in practical operation, the terms “same” or “pointing” mentioned in this description refer to quasi same or quasi pointing, i.e. approximately same or approximately pointing, and not strictly completely same or pointing. 
         [0085]    Furthermore, distinguishing the first, second, third and fourth directional antennas is only for facilitating the description without other particular meanings. In fact, the first and second directional antennas can be the same as or different from the third and fourth directional antennas. 
         [0086]    What is more, although the first transmitter  211 , the obtainer  212 , the first determiner  213  and the recognizer  22  are integrated in the wireless controller  21  in  FIG. 2 , in practice the first transmitter  211  can be separate from the obtainer  212  and the first determiner  213 . Under the circumstances that the first transmitter  211  is separate from the obtainer  212  and the first determiner  213 , the communication between the obtainer  212  and the second transmitter  233  of each device  23  can be performed in the manner of wireless communication or wire communication. 
         [0087]    Moreover, the operating apparatus of each device  23  can be integrated in the device or be separate. For example, the device is a light, and its switch or its brightness adjustment apparatus is separate from the light. 
         [0088]    It should be further noted that wireless signal transmission protocols of the present invention are unlimited, including ZigBee™, Bluetooth™, IEEE802.11, NFC, UWB and so on. The carrier band of wireless signals is also not limited, for example, 2.4 GHz, infrared, ultrasonic, laser etc. are all applicable for the present invention. 
         [0089]    The embodiments of the present invention have been described above. It is to be understood that the present application is not limited to the specific embodiments described previously, and various modifications or alterations can be made by those skilled in the art within the scope of the appended claims.