Abstract:
The present invention suggests an apparatus for detecting the operation status of a fluorescent light source. The apparatus comprises an antenna for receiving and sending electromagnetic waves. The apparatus further comprises a modulation frequency correlator and a signal generator for generating an indication signal. According to a second aspect the present invention proposes a method for detecting the operation status of a fluorescent light source. The method comprises the steps of: receiving an electromagnetic wave; detecting a modulation of the received electromagnetic wave; correlating the modulation frequency of the received electromagnetic wave with a predetermined frequency; generating an indication signal if a correlation between the modulation frequency and the predetermined frequency is detected.

Description:
FIELD 
       [0001]    The invention is related to an apparatus and a method for detecting fluorescent lighting in a room. In particular, the present invention is related to apparatus according to claim  1  and a method according to claim  4 . 
       BACKGROUND 
       [0002]    The deployment of sensor based systems offers many opportunities for providing new services and applications in the home. In particular, in the area of home networking, a Wi-Fi home gateway platform may include an interface with an advanced search and recommendation engine allowing home users to access their preferred or personalized content. In addition to that, background algorithms may utilize additional information which is collected in the home of the user to improve recommendations for media consumption or other purposes. Such kind of information includes e.g. time, date, and ambient temperature. It has been found useful to have information about the lighting in a room, if it is turned on or off. In the following this information is called operational status of the lighting. In conjunction with calendar and time information, the information about the status of lighting enables an adapted algorithm to provide more insight into the living habits inside a home. 
         [0003]    Information about the operational status of the lighting is also interesting information with regard to improving the management of power consumption in homes. In this context, there is an increasing demand for data about energy consuming devices. The lighting of rooms in homes and buildings is one factor that has to be taken into account in this general consideration. Energy disaggregation is a common keyword for this kind of research activities. 
         [0004]    Combining the data collection in the home of a user with a residential gateway makes sense because the residential gateway provides an interface between a home network and a public network such as the Internet. The residential gateway comprises the full interaction between services and devices supported by the residential gateway which provides a number of additional enablers for supporting the home user. Multiple home devices are able to handle multiple media streams and the flows are directed to the most appropriate devices while other devices are informed about the incoming stream. Recording of media information is supported if needed. Thus, in the gateway there is already plenty of information available to generate recommendations to users with regard to media consumption. Consequently, it also makes sense for the gateway to capture context information such as information about the lighting in the home. 
         [0005]    Modern gateways already support algorithms generating user recommendations based on a database about user preferences. Typically the database is built up over a long term. More advanced technologies also utilize the context information related to the user preferences and habits. 
         [0006]    The context information includes e.g. the location of the user, activity, ambient temperature, lighting and others. Such kind of information can include for example at what time of the date the lighting is turned on and where. 
         [0007]    Today the presence or absence of lighting is detected in consumer products with photo sensors, e.g. photodiodes or photovoltaic cells. A typical application is the detection of ambient light to adjust the brightness of a display. 
         [0008]    Taking this as a starting point the present invention aims at an alternative approach for detecting fluorescent lighting. 
       SUMMARY OF INVENTION 
       [0009]    According to a first aspect the present invention suggests an apparatus for detecting the operation status of a fluorescent light source. The apparatus comprises an antenna for receiving and sending electromagnetic waves. The antenna is coupled with the receiver device. The antenna is also coupled with a correlator circuit configured to detect the presence of a modulation in the received electromagnetic wave. If the correlator circuit detects the presence of a modulation in the received electromagnetic wave then the correlator circuit causes a signal generator to generate an indication signal. 
         [0010]    An embodiment of the inventive apparatus comprises an amplitude detector which advantageously can be a narrowband amplitude detector. 
         [0011]    Advantageously the apparatus can be communicatively coupled by the antenna to other wireless communication devices. In this case the coupling the apparatus and the other wireless communication devices can be accomplished by electromagnetic waves in the 2.4 GHz or 5 GHz band transmitted between the antenna and at least one antenna connected to the other wireless communication devices. 
         [0012]    According to a second aspect the present invention suggests a method for detecting the operation status of a fluorescent light source, wherein the method comprises the following steps:
       receiving an electromagnetic wave;
           detecting the presence of a modulation in the received electromagnetic wave;   correlating the modulation frequency of the received electromagnetic wave with a predetermined frequency;   generating an indication signal if a correlation between the detected modulation frequency and the predetermined frequency is detected.   
               
 
         [0017]    Advantageously an embodiment of the inventive method can comprise further the step of utilizing the indication signal as input information for enhancing the functionality of a consumer electronic devices. 
         [0018]    The invention proposes a cost effective implementation of the method in any wireless device by direct coupling to existing radio modules. The invention exploits the interaction of electromagnetic waves with fluorescent light tubes or compact fluorescent light bulbs during the propagation of the electromagnetic wave. The interaction is based on the working principle of fluorescent lighting and gives rise to amplitude modulation of the electromagnetic wave at twice the frequency of the AC voltage supply and its harmonics. The presence absence of 100 Hz frequency harmonics in the received signal of the electromagnetic wave due to the interaction with fluorescent light is used as an indicator of the operation status of the fluorescent lighting and enables to detect whether the lighting is on or off. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]    In the drawing, an embodiment of the present invention is shown. The same or similar components are labeled with same or similar reference numbers. 
           [0020]      FIG. 1  schematically illustrates a room with a fluorescent light tube, a residential gateway and a set-top box; 
           [0021]      FIG. 2A and 2B  show a simplified 2-ray propagation model of electromagnetic waves in the room of  FIG. 1 ; 
           [0022]      FIGS. 3A and 3B  show the signal level of the received electromagnetic wave when the fluorescent light tube is ON or OFF, respectively; 
           [0023]      FIGS. 4A and 4B  show the signal level of a received electromagnetic wave when a compact fluorescent light bulb is ON or OFF, respectively; 
           [0024]      FIG. 5  shows a schematic block diagram of the residential gateway of  FIG. 1 ; and 
           [0025]      FIG. 6  shows a schematic block diagram of a modulation detector included in the residential gateway of  FIG. 5 ; and 
           [0026]      FIG. 7  shows a flow diagram illustrating the method according to the invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]      FIG. 1  schematically illustrates a room  100 . A fluorescent light tube  101  is mounted on the ceiling  102  of the room  100 . In the room  100  there is also a gateway device  103  providing an access point to external networks such as PSTN, cable TV, and Internet. The access to external networks is symbolized in  FIG. 1  by the double-headed arrow  108 . Further details of the gateway  103  will be described further below in connection with  FIG. 5 . The gateway device  103  is provided with several transmission antennas  104 . In the room there is also a set-top box  105  which is also provided with several antennas  106 . In  FIG. 1  only two of the antennas  104  and  106 , respectively, are shown. In other embodiments of the present invention the gateway device  103  and the set-top box  105  are provided with only one antenna each. The antennas  104  and  106  enable a wireless bi-directional communication between the gateway device  103  and the set-top box  105 . This wireless communication is based on transmitted and received electromagnetic waves establishing wireless data communication between the devices. In  FIG. 1  the electromagnetic waves are symbolized by arrows  107 . 
         [0028]    The fluorescent light tube  101  is filled with a gas at low-pressure, e.g. mercury vapor, argon, xenon, neon or krypton. The inner surface of the tube is coated with a fluorescent coating (not shown). The light tube  101  comprises at its ends two electrodes (not shown) made of coiled tungsten. 
         [0029]    During operation of the light tube  101  the electrodes are heated and emit free electrons into the gas filled inner volume of the light tube  101 . Once the electrons have left the electrodes into the inner volume of the light tube  101 , an electric field generated by a voltage applied between the two electrodes accelerates the electrons. The electrons travel with an increasing speed from the one electrode to the other electrode until they collide with a gas atom inside the light tube. If an electron has accumulated sufficient energy to excite an atom, the atom emits invisible ultraviolet light. The ultraviolet light is absorbed by the coating which finally emits visible light. 
         [0030]    The accelerating electric field is generated by the AC mains voltage and therefore fluctuates at the mains frequency, e.g. 50 Hz in Europe. It is noted, however, that the invention does not depend on the mains frequency. The specific value of 50 Hz has only exemplary character. During one full period of the AC mains supply voltage, the mains voltage takes on a positive and negative maximum value. At the same time the AC current flowing between the electrodes of the light tube  101  takes on two maximum values. But the two maximum currents flow in opposite directions in the light tube because of the reversal of the polarity of the mains supply voltage. The current is carried by the free electrons traveling inside the light tube  101 . When the current through the light tube  101  is maximum then there is also a maximum number of electrons inside the light tube and at the same time there is maximum light emission. When the current through the light tube is minimum then there is a minimum number of electrons inside the light tube  101  and there is minimum light emission. In consequence, the light emission fluctuates at a frequency of  100  Hz between the maximum and minimum values in synchronism with the number of free electrons and current flow inside the light tube  101 . In compliance with usual terminology, the number of free electrons in the gas volume is described as electron density. 
         [0031]    Electromagnetic waves impinging from the outside onto the light tube  101  will interact with an electron density inside the light tube  101  fluctuating at a frequency of 100 Hz between the maximum value and the minimum value. Consequently, the reflective properties of the light tube  101  for external electromagnetic waves change at the same frequency of 100 Hz from being a good reflector (reflective phase) to being almost transparent (transparent phase). The fluctuation of the reflective properties of the light tube  101  gives rise to an amplitude and phase modulation of electromagnetic waves impinging on the light tube  101 . This will be explained in greater detail in conjunction with a simple 2-wave-propagation model which is laid out in  FIGS. 2A and 2B . 
         [0032]      FIG. 2A  is a simplified representation of the room  100  of  FIG. 1 . In  FIG. 2A  only antennas  104  and  106  are shown from gateway  103  and set-top box  105 , respectively. As shown in  FIG. 2A , an electromagnetic wave propagates from transmitting antenna  104  to receiving antenna  106  using 2 different paths. There is a direct path indicated with an arrow D. There are also two indirect paths, namely an indirect path of the electromagnetic wave indicated by an arrow Rc. Along the path Rc, the electromagnetic wave is reflected at the ceiling of the room  100  when the light tube  101  is in its transparent phase. There is another indirect path of the electromagnetic wave indicated with an arrow Rf. Along the path Rf, the electromagnetic wave is reflected at the light tube  101  when it is in its reflective phase. 
         [0033]    As it is illustrated in  FIG. 2B  by means of a vector diagram of the signal components mentioned in connection with  FIG. 2A , the total received signal level of the electromagnetic wave is different for the reflective and the transparent phase of the light tube  101 . In the transparent phase of the light tube  101 , the total signal level is equal to 
         [0000]    
       
      
       Tc=D+Rc  
      
     
         [0000]    where D is the portion of the direct signal and Rc is the portion of the component reflected by the ceiling  102 . 
         [0034]    In the reflective phase of the light tube  101 , the total signal level of the electromagnetic wave is equal to 
         [0000]    
       
      
       Tf=D+Rf  
      
     
         [0000]    where D is the portion of the direct signal and Rf is the portion of the component reflected by the light tube  101 . 
         [0035]    Thus, as shown in  FIG. 2B  and explained above, the level of the total received signal fluctuates in amplitude and phase between Tc and Tf values at the same rate as the fluorescent light, i.e. at 100 Hz. A double headed arrow  201  shows in the vector diagram the fluctuation between Tc and Tf. More generally, D represents the total signal resulting from the combination of paths of the electromagnetic wave which do not interact with the fluorescent lighting. Rf and Rc represent the combination of paths having interacted with the fluorescent tube  101  either in its reflective or transparent phase. 
         [0036]    As shown in  FIG. 3A and 3B , the described phenomenon is measurable with an electromagnetic wave at a frequency of 5 GHz.  FIG. 3A  shows the received spectrum of the 5 GHz electromagnetic wave when the fluorescent lighting is off. In  FIG. 3B  the spectrum of the 5 GHz electromagnetic wave is shown when the fluorescent lighting is on. As can be clearly seen in  FIG. 3B  the signal level of the electromagnetic wave is modulated at a frequency of 100 Hz. One unit in horizontal direction in  FIGS. 3A and 3B  corresponds to a frequency difference of 100 Hz. The maxima of the signal level signal are separated by 100 Hz. Similar results can be found with an electromagnetic wave having a frequency of 2.4 GHz. 
         [0037]    The principles of the present invention work in the same way for elongated fluorescent light tubes and for compact fluorescent light tubes. 
         [0038]    In  FIGS. 4A and 4B  corresponding measurements are shown for compact fluorescent light bulbs. Again the modulation of the signal level at the frequency of 100 Hz is clearly visible. 
         [0039]    For the sake of brevity, the invention is only described in connection with elongated fluorescent light tube. 
         [0040]    The present invention will make use of this modulation of the signal level of the received signal in order to detect if the fluorescent lighting is in its on or off state in a room where electromagnetic waves are propagating. 
         [0041]    Compact fluorescent light bulbs are frequently operated at high frequencies like 10 kHz. However, measurements only showed a 100 Hz modulation of the radiofrequency electromagnetic waves. For the sake of completeness it is also mentioned that no modulation of the radiofrequency electromagnetic waves could be found when light emitting diodes where used as light source. In conclusion, the 100 Hz modulation of the radiofrequency electromagnetic waves is caused by the physical effects inherently linked with the light generation in fluorescent light sources. 
         [0042]      FIG. 5  shows the gateway  103  in greater detail. For the sake of simplicity only one antenna  104  is shown in  FIG. 5 . However, in other embodiments the gateway  103  is provided with a plurality of antennas. 
         [0043]    The connection of the gateway to external networks is symbolized with arrow  108  interfacing with a MIMO device  501 . One output  502  of the MIMO device  501  is connected with a power amplifier  503 . By means of a selection switch  504 , the power amplifier  503  is connected to the antenna  104  when the gateway  103  is in a sending mode. When the gateway  103  is in a receiving mode to receive electromagnetic waves (RF signal), then the selection switch  504  changes its state and connects the antenna  104  with a low noise amplifier  505 . The output of the low noise amplifier  505  is provided to an RF coupler  506 . The RF coupler  506  provides an output signal on the one hand to a narrow band amplitude detector  507  and on the other hand to an input  508  of the MIMO device  501 . The MIMO device forwards the received input signal to perform conventional signal processing in the gateway  103 . The narrow band amplitude detector  507  filters the electromagnetic wave which is received by the antenna  104 . The output of the narrowband amplitude detector  507  is provided to a frequency correlator  508  which detects if there is a modulation of the received RF (radio frequency) signal which is correlated with a reference frequency signal. The reference frequency signal is generated from a frequency signal provided at input  509  of the frequency correlator  508 . In the present embodiment of the invention, the reference frequency is the second harmonic of the mains AC frequency of 50 Hz, i.e. the reference frequency is 100 Hz. The frequency correlator  508  communicates an output signal to a signalization stage  510  which generates an indication signal if the frequency correlator  508  has detected that the RF signal level has a modulation which is correlated with the reference frequency. Then the signalization stage  510  produces an indication signal  511  for further usage in the gateway  103 . The group of components comprising the RF coupler  506 , the narrow band amplitude detector  507 , the frequency correlator  508 , and the signalization stage  510  form together a detection and signalization unit  512 . 
         [0044]      FIG. 6  shows the detection and signalization unit  512  of  FIG. 5  in greater detail. The RF signal received by the antenna  104  is coupled to the detection and signalization unit  512  by the RF coupler  506  and is provided to the narrowband detector  507 . The structure of the narrowband detector  507  is known in the prior art and therefore only symbolically indicated by a diode  601 , a capacitor  602  and an inductivity  603 . The output signal of the narrowband detector  507  is connected with the frequency correlator  508  and forms a first input signal for the frequency correlator  508 . The frequency correlator  508  receives as a second input signal a frequency signal  509  having the same frequency as the local mains frequency. In the present embodiment, the frequency signal has a frequency of 50 Hz and is used as input signal for a harmonics generator  604  generating the second harmonics of the frequency signal. The output of the harmonics generator  604  is the reference frequency signal having a frequency of 100 Hz. The 100 Hz reference frequency signal is provided to a mixer  605  where it is mixed with the output signal of the narrowband amplitude detector  507 . The mixer  605  produces a DC output signal which varies as a function of the presence or absence of a 100 Hz signal modulation detected in the output signal of the narrowband amplitude detector  507 . The output signal of the mixer  605  is provided as input signal to the signalization stage  510 . In the signalization stage  510 , this input signal is compared with a predetermined reference voltage Uref in a comparator  606 . If the output signal of the mixer  605  exceeds a predetermined threshold value which is defined by Uref then the signalization stage  510  generates the indication signal  511  indicating that the presence of fluorescent lighting has been detected. This indication signal is used e.g. in recommendation algorithms as it has been described in the introduction of the present invention. 
         [0045]    In countries having a mains frequency of 60 Hz the received signal level of the electromagnetic wave is modulated with a frequency of 120 Hz. Again, the modulation frequency is the second harmonic of the mains frequency. 
         [0046]      FIG. 7  is a flow diagram illustrating the method according to the invention. In step  701  an electromagnetic wave is received. In step  702  it is detected if the electromagnetic wave is modulated and subsequently—if such modulation is found—the modulation frequency is correlated with the predetermined frequency in step  703 . Finally, an indication signal is generated in step  704  if a correlation between the modulation frequency and the predetermined frequency is detected. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100  room 
           101  fluorescent light tube 
           102  ceiling 
           103  gateway device 
           104  antenna 
           105  set-top box 
           106  antenna 
           107  arrow (electromagnetic waves) 
           108  arrow (access to external networks) 
           201  double headed arrow (fluctuation between Tc and Tf) 
           501  MIMO device 
           502  output of MIMO device 
           503  power amplifier 
           504  selections switch 
           505  low noise amplifier 
           506  RF coupler 
           507  narrowband amplitude detector 
           508  frequency correlator 
           509  input of frequency correlator 
           510  signalization stage 
           511  indication signal 
           512  detection and signalization unit 
           601  diode 
           602  capacitor 
           603  inductivity 
           604  harmonics generator 
           605  mixer 
           606  comparator 
           701  . . .  704  method steps