Patent Publication Number: US-2007111689-A1

Title: Apparatus for selecting a receiver among a plurality of receivers in a diversity receiver system based upon automatic gain correction

Description:
PRIORITY INFORMATION  
      This application is a continuation of co-pending Ser. No. 09/509,643 filed Mar. 30, 2000. 
    
    
     BACKGROUND OF THE INVENTION  
      The invention relates to diversity receivers, and in particular to selecting a receiver among a plurality of receivers in a diversity receiver system based upon automatic gain correction.  
      Diversity receiving systems with several receivers are used, for example, in vehicles. The receivers can be, for example, audio and video receivers.  
      Reception and reproduction of video pictures in stationary receiving stations poses no difficulties, because the reception conditions remain largely constant. On the other hand, the reception conditions for a mobile receiving station can vary considerably, depending on the nature of the terrain. For instance, if the mobile receiving station is situated in mountainous terrain, echoes can cause considerable interference with reception. In the radio shadow of mountains or hills, the radio connection can even break down completely, so that, in place of a video picture, only noise is visible on the screen.  
      In the meantime, motor vehicles such as, for example, passenger cars, long-distance buses, and railroad cars, are being equipped with television receivers and screens, so that messages can be displayed, for example traffic reports sent by video text, or, the travelers can be entertained with television programs. The receiving conditions in a moving receiving station vary considerably in some circumstances, due to the terrain through which the receiving station is currently passing. Consequently, this will subject the travelers who are watching television to unpleasant and considerable eye strain, because the picture quality can vary to a great extent. For example, if the vehicle is passing through a radio shadow, the viewers will see only noise on the screen. Looking at a television program with such interference subjects the viewers to fatigue rather than entertainment.  
      It is known that the reception of radio signals in mobile receiving stations can be improved by multi-path reception, also referred to as “diversity”. By antenna diversity is understood a receiver which can be connected to one of several antennas, generally spatially separated from one another, while by frequency diversity is understood a system consisting of several receivers which receive the same signals or the same programs on different frequencies. The signals delivered by the antennas in the case of antenna diversity and by the receivers in the case of frequency diversity are tested for their quality, so as to forward and process the best quality signal.  
     SUMMARY OF THE INVENTION  
      It is therefore the object of the invention to specify, for a diversity receiving system with several receivers, to select the receiver with the best reception.  
      The invention achieves this object by comparing the levels of the control signals of the automatic gain control of the receivers, and selecting that receiver whose control signal has the lowest level.  
      The invention starts from the idea that the level of the control signal of the automatic gain control of a receiver (e.g., a television receiver) is a measure of the reception level. If the level of the control signal reaches its maximum, the reception level is too low; on the other hand, if the level of the control signal reaches its minimum, the reception level lies in the optimum range.  
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       FIG. 1  is a block diagram illustration of a first embodiment of the invention; and  
       FIG. 2  is a block diagram illustration of a second embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to  FIG. 1 , two receivers E 1  and E 2  (e.g., television receivers) receive the same program, with an antenna A 1  and A 2 , respectively. The two control signals AGC 1  and AGC 2  of the two receivers E 1  and E 2  are compared in a comparator VL. Via the controllable changeover switch U, the comparator VL selects the output of that receiver whose control signal has the lower level. Consequently, the output signal S of the receiver whose control signal has the lower level is always forwarded for further processing. More than two receivers can also exist here.  
      The second embodiment of the invention, shown in  FIG. 2 , will now be described and explained.  
      The second embodiment differs from the first one in that the output of the comparator VL is not connected to the control input of the controllable changeover switch U, but to the first control input of a block synchronizer BS. The output signal S of one of the two receivers E 1  or E 2  is conducted to the second control input of the block synchronizer BS. The control output of the block synchronizer BS is connected to the control input of the controllable changeover switch U.  
      The second embodiment of the invention is suited for the block transmission of signals. The block synchronizer BS receives from the comparator VL a control signal for switching over to one receiver if the level of the control signal of the other receiver becomes greater than the level of the control signal of the first receiver. However, the block synchronizer BS does not switch over to another receiver immediately, but only at the end or beginning of a block. In other words, the block synchronizer BS executes switchover processes with block synchronization. No switchovers are executed within a block.  
      The second embodiment is especially well suited for a diversity receiving system with television receivers. The switchover process from one receiver to another takes place with line or picture synchronization.  
      With a third advantageous embodiment of the invention, switchover to another receiver occurs only if the lowest level differs from the levels of the other control signals by a specific minimum value. This measure of providing a hysteresis prevents unnecessary switchover processes.  
      A special advantage of the invention is that the control signal is present in any case, and the invention can be implemented with only small expense—only a comparator and a controllable changeover switch are needed.  
      The invention is not limited to television receivers. It is suited for receivers of all kinds for diversity receiving systems. The invention is especially suited for mobile diversity receiving systems, such as are installed for example in vehicles. This can apply to audio and/or video receiving systems. A future application for digital audio transmission is also conceivable.