Abstract:
A light communication system, a transmitter and a receiver are provided. The light communication system includes the transmitter and the receiver. The transmitter has a first processing unit and a light-emitting element. The first processing unit produces a transmission signal. The light-emitting element produces light to carry the transmission signal. The receiver has a first variable lens, a photosensitive element and a second processing unit. The first variable lens changes the propagation path of the light. The photosensitive element senses the light passed through the first variable lens to produce a receiving signal. The second processing unit controls the first variable lens based on the signal quality of the receiving signal to change the equivalent channel between the transmission signal and the receiving signal. Therefore, the transmission capability of the light communication system is enhanced.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claimed priority to Taiwanese Patent Application No. 101131125, filed on Aug. 28, 2012. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to light communication techniques, and, more particularly, to a light communication system, a transmitter and a receiver. 
         [0004]    2. Description of Related Art 
         [0005]    In optical communication systems and radio frequency (RF) communication systems, the optical characteristics and the RF characteristics are quite different. In the RF communication systems, designs and selections of the “antennas” or precoding techniques can be used to change the equivalent channel in order to enhance the transmission capability of the RF communication system. Such design concepts in the optical communication system have not yet been developed, but the “antennas” in RF communication are analogous to the “lens” of optical communication as optical lens may be used as a transmission medium for the light. 
         [0006]    Light-emitting diodes (LEDs) play an important role in the optical communication systems. In recent years, LEDs have achieved significant improvement in terms of performance and brightness, and gradually replace the traditional light sources, such as fluorescent lamps and incandescent lamps. Due to their fast response, LEDs are not only used in lighting systems, but are also used for data transmission. 
         [0007]    In terms of data transmission, a transmitter and a receiver in an optical communication system are used for transmission and reception of signals, respectively. Specifically, the transmitter may use the light emitted by an LED to carry signals, and the receiver may use a fixed-focus lens together with a photodiode or a photodetector to receive the light emitted by the LED and decode the signals from the received light. 
         [0008]    However, in the above known technique, the receiver (such as a mobile communication apparatus) may move freely in the space, but the fixed focus lens can only provide a fixed focal length and a fixed axial direction. These cannot not be adjusted in accordance with the movement of the receiver, so as a result, the light emitted by the transmitter is scattered or focused with low optical density on the light-emitting diode or the photodetector, resulting in poor quality of the signals received by the receiver and lowering of the transmission capacity of the optical communication system. 
         [0009]    Therefore, how to solve the above shortcomings of the prior art has become an important issue for those skilled in the art. 
       SUMMARY 
       [0010]    The present disclosure provides a light communication system, which includes a transmitter and a receiver. The transmitter includes a first processing unit that generates a transmission signal, and a light-emitting unit that emits light that carries the transmission signal. The receiver includes a first variable lens that receives the light emitted by the light-emitting device and changes a propagation path of the light, a photosensitive element that senses the light passing through the first variable lens to produce a receiving signal, and a second processing unit that controls the first variable lens according to a signal quality of the receiving signal in order to change an equivalent channel between the transmission signal and the receiving signal. 
         [0000]    The present disclosure further provides a transmitter, which includes a processing unit, a light-emitting element and a variable lens. The processing unit generates a transmission signal. The light-emitting element emits light for carrying the transmission signal. The variable lens changes a propagation path of the light in order for an external receiver to receive the light passing through the variable lens so as to produce a receiving signal. The processing unit produces a control signal based on a feedback signal from the receiver, and uses the control signal to control the variable lens accordingly, which changes the propagation path of the light and an equivalent channel between the transmission signal and the receiving signal. 
         [0011]    The present disclosure further provides a receiver, which includes a variable lens, a photosensitive element and a processing unit. The variable lens changes a propagation path of light emitted by an external transmitter, in which the light carrying a transmission signal produced by the transmitter. The photosensitive element senses the light passing through the variable lens and generates a receiving signal. The processing unit generates a control signal based on a signal quality of the receiving signal and uses the control signal to control the variable lens accordingly, which changes the propagation path of the light and an equivalent channel between the transmission signal and the receiving signal. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]    The present disclosure can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a schematic block diagram depicting a Single-Input Single-Output (SISO) light communication system in accordance with the present disclosure; 
           [0014]      FIG. 2  is a schematic block diagram depicting a SISO light communication system in accordance with the present disclosure, wherein a transmitter and a receiver both have a variable lens; 
           [0015]      FIG. 3  is a schematic block diagram depicting a Multi-Input Multi-Output (MIMO) light communication system in accordance with the present disclosure; and 
           [0016]      FIG. 4  is a schematic block diagram depicting a MIMO light communication system in accordance with the present disclosure, wherein a transmitter and a receiver both have variable lenses. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a through understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing. 
         [0018]      FIG. 1  is a schematic block diagram depicting a Single Input Single Output (SISO) light communication system  100  in accordance with the present disclosure, wherein a receiver includes a variable lens. 
         [0019]    As shown, the light communication system  100  is a SISO system, that is, the transmitter  110  of the light communication system  100  includes only one single light-emitting unit  112 , and the receiver  120  includes only one single photosensitive element  122 . In other embodiments, the light communication system  100  can also be a Multi Input Multi Output (MIMO), a Single Input Multi Output (SIMO), or a Multi Input Single Output (MISO) system. 
         [0020]    The light communication system  100  is applicable to a wireless communication system or a lighting system, and includes the transmitter  110  and the receiver  120 . 
         [0021]    The transmitter  110  includes a first processing unit  111  and the light-emitting unit  112 . The first processing unit  111  is used for generating a transmission signal  130 . The light-emitting unit  112  can be provided on a platform  140  or a planar surface for carrying the light  131  of the transmission signal  130 . 
         [0022]    The transmitter  110  can be, for example, a transmitter, a transmitting module, a wireless communication device or a lighting device. The first processing unit  111  can be, for example, a processor, a controller, an encoder or a converter. The light-emitting unit  112  can be, for example, a LED, a laser light or infrared. The transmission signal  130  can be a digital signal or an analog signal. The light  131  can be visible light or invisible light with different wavelengths. 
         [0023]    The receiver  120  includes a first variable lens  121 , the photosensitive element  122 , and a second processing unit  123 . The first variable lens  121  is used in conjunction with the photosensitive element  122  for adjusting the propagation path of the light  131  emitted by the light-emitting unit  112 . The photosensitive element  122  can be provided on a platform  141  or a planar surface for sensing or receiving the light  131  passing through the first variable lens  121  and generating a receiving signal  132 . 
         [0024]    The second processing unit  123  is used for generating a first control signal  133  based on the signal quality of the receiving signal  132  and using the first control signal  133  to control the curvature, the angle, the thickness, the focal length or the axial direction of the first variable lens  121  or the spacing between the first variable lens  121  and the photosensitive element  122  accordingly, thereby changing the propagation path of the light  131 , and the equivalent channel between the transmission signal  130  and the receiving signal  132 . 
         [0025]    Assuming a narrowband communication, a mathematical model between the transmission signal  130 , the receiving signal  132  and the equivalent channel can be expressed using the following function: 
         [0000]        r ( n )= h*x ( n )+ v ( n ), 
         [0026]    wherein r(n) is the receiving signal  132  including noise, h is the equivalent channel between the transmission signal  130  and the receiving signal  132 , x(n) is the transmission signal  130 , v(n) is the noise, and n is a time series. 
         [0027]    However, the above narrowband communication is only one embodiment of the present disclosure; the light communication system of the present disclosure is also applicable to broadband communication. 
         [0028]    The above receiver  120  can be, for example, a receiver, a receiving module, a wireless communication device or a lighting device. The first variable lens  121  can be, for example, a liquid lens, a voice coil motor for lens, a MEMS-based variable micro-lens or piezoelectric material (Pb(ZrTi)O 3  or PZT)-based variable lens. The photosensitive element  122  can be, for example, a photodiode, a photo-detector or an image sensor. The second processing unit  123  can be, for example, a processor, a controller or a converter. The receiving signal  132  can be a digital signal or an analog signal. 
         [0029]    The above signal quality can include, for example, Received Signal Strength Indication (RSSI), Signal-to-Interference-plus-Noise Ratio (SINR), Bit Error Rate (BER) or Frame Error Rate (FER). 
         [0030]      FIG. 2  is a schematic block diagram depicting a SISO light communication system in accordance with the present disclosure, wherein a transmitter and a receiver both have a variable lens. 
         [0031]    The light communication system of  FIG. 2  is substantially the same with the light communication system  100  of  FIG. 1 , so the parts that are the same will not be repeated, and the major difference is described as follows. 
         [0032]    In the light communication system  100  of  FIG. 2 , the transmitter  110  further includes a second variable lens  113 . The second variable lens  113  is used in conjunction with the light-emitting unit  112  for adjusting the propagation path of the light  131  emitted by the light-emitting unit  112 . 
         [0033]    The first processing unit  111  produces a second control signal  135  based on a feedback signal  134  from the second processing unit  123 , and uses the second control signal  135  to control the curvature, the angle, the thickness, the focal length or the axial direction of the second variable lens  113  or the spacing between the second variable lens  113  and the light-emitting unit  112  accordingly, thereby changing the propagation path of the light  131 , and in turn the equivalent channel. 
         [0034]    The above feedback signal  134  can include, for example, signal quality information, direction information, channel information or precoding information. 
         [0035]      FIG. 3  is a schematic block diagram depicting a MIMO light communication system  200  in accordance with the present disclosure, wherein a transmitter includes a variable lens. 
         [0036]    As shown, the light communication system  200  is a MIMO system, that is, a transmitter  210  of the light communication system  200  includes a plurality of light-emitting unit  212 , and a receiver  220  includes a plurality of photosensitive element  222 . 
         [0037]    The light communication system  200  is applicable to a wireless communication system or a lighting system, and includes the transmitter  210  and the receiver  220 . 
         [0038]    The transmitter  210  includes a first processing unit  111  and the plurality of light-emitting units  212 . The first processing unit  211  is used for generating a plurality of transmission signals  230 . The light-emitting units  212  can be provided on a platform  240  or a planar surface for carrying the light  231  of the transmission signals  230 . In this embodiment, the numbers of light-emitting units  212  and the transmission signals  230  are both two. 
         [0039]    The transmitter  210  can be, for example, a transmitter, a transmitting module, a wireless communication device or a lighting device. The first processing unit  211  can be, for example, a processor, a controller, an encoder or a converter. The light-emitting units  112  can be, for example, LEDs, laser lights or infrared lights. The transmission signals  230  can be digital signals or analog signals. The light  231  can be visible light or invisible light with different wavelengths. 
         [0040]    The receiver  220  includes a plurality of first variable lenses  221 , the plurality of photosensitive element  222 , and a second processing unit  223 . In this embodiment, the numbers of first variable lenses  221  and the photosensitive elements  222  are both four. 
         [0041]    The first variable lenses  221  are used in conjunction with the photosensitive elements  222  for adjusting the propagation path of the light  231  emitted by the light-emitting units  212 . The photosensitive elements  222  can be provided on a platform  241  or a planar surface for sensing or receiving the light  231  passing through these first variable lenses  221  and generating a plurality of receiving signals  232 . 
         [0042]    The second processing unit  223  is used for generating a plurality of first control signals  233  based on the signal qualities of the receiving signals  232  and using the first control signals  233  to control the curvatures, the angles, the thicknesses, the focal lengths or the axial directions of the first variable lenses  221  or the spacing between the first variable lenses  221  and the photosensitive elements  222  accordingly, thereby changing the propagation path of the light  231 , and the equivalent channels between the transmission signals  230  and the receiving signals  232 . 
         [0043]    Assuming there are two transmission signals  230  and four receiving signals  232  and a narrowband communication, a mathematical model between the transmission signals  230 , the receiving signals  232  and the equivalent channels can be expressed by the following matrix: 
         [0000]    
       
         
           
             
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         [0044]    wherein r 1 (n)-r 4 (n) are the receiving signals  232  including noises, h 11 -h 42  are the equivalent channels between the transmission signals  230  and the receiving signals  232 , x 1 (n)-x 2 (n) are the transmission signals  230 , v 1(n)-v   4 (n) are the noises, and n is a time series. 
         [0045]    As described before, the light communication system of the present disclosure is also applicable to broadband communication. 
         [0046]    The above signal qualities can include, for example, Received Signal Strength Indication (RSSI), Signal-to-Interference-plus-Noise Ratio (SINR), Bit Error Rate (BER), Frame Error Rate (FER) or the rank of the matrix. 
         [0047]      FIG. 4  is a schematic block diagram depicting a MIMO light communication system in accordance with the present disclosure, wherein a transmitter and a receiver both have variable lenses. 
         [0048]    The light communication system of  FIG. 4  is substantially the same with the light communication system  200  of  FIG. 3 , so the parts that are the same will not be repeated, and the major difference is described as follows. 
         [0049]    In the light communication system  200  of  FIG. 4 , the transmitter  210  further includes a plurality of second variable lenses  213 . The transmitter  210  has two second variable lenses  213  in this embodiment. The second variable lenses  213  are used in conjunction with the light-emitting units  212  for adjusting the propagation path of the light  231  emitted by the light-emitting units  212 . 
         [0050]    The first processing unit  211  produces a plurality of second control signals  235  based on feedback signals  234  from the second processing unit  223 , and uses the second control signals  235  to control the curvatures, the angles, the thicknesses, the focal lengths or the axial directions of the second variable lenses  213  or the spacing between the second variable lenses  213  and the light-emitting units  212  accordingly, thereby changing the propagation path of the light  231 , and in turn the equivalent channels. 
         [0051]    The above feedback signals  234  can include, for example, signal quality information, direction information, channel information, precoding information or information on the rank of the matrix. 
         [0052]    It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.