Abstract:
An arrangement for activating and deactivating automatic noise cancellation (ANC) in a mobile station, in which there are an ANC facility ( 3 ) for suppressing background noise in an incoming audio signal, as well as circuits for activating and deactivating the ANC, includes automatic detection ( 10 ) of the need for ANC according to a selected criterion, for example, a set noise level, the detection circuit configuration ( 10 ) being arranged to automatically control the activation and deactivation of the ANC facility ( 3 ).

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an arrangement for activating and deactivating automatic noise cancellation (ANC) in a mobile station, in which there is an ANC circuit for removing background noise from an audio signal and circuits for activating and deactivating ANC.  
         BACKGROUND OF THE INVENTION  
         [0002]    Automatic noise cancellation is used to remove background noise from an incoming audio signal. This feature is generally separately activated and deactivated. Its continuous use is not desirable, as it increases the power consumption of the mobile station. Usually the user must select, from the mobile station&#39;s settings, the method of using the ANC, which can be, for example, ‘Always ON’ or ‘Manual’. The former results in unnecessary power consumption while the latter is difficult for the user, because it demands several key strokes, which additionally must often be made during a call.  
           [0003]    The theory and operating methods of automatic noise cancellation are widely known. U.S. Pat. Nos. 5,406,635 (Järvinen) and 5,839,101 (Vähätalo) disclose certain methods for limiting background noise in a mobile station. The publication ‘IEEE Signal Processing Magazine’; S. J. Elliot, August 1993 features an extensive presentation of the history of noise cancellation technology and certain present methods. Background noise cancellation can be based either on the analysis of frequency fields (e.g., adaptive filters) or on active feedback on background noise obtained with the aid of an additional microphone, in cases in which this is possible.  
           [0004]    All the methods have the drawback that they cause an increase in power consumption, which, in mobile stations, means a shorter period of operation for each battery charge. Thus, the use of ANC is only desirable when it is really necessary.  
           [0005]    The present invention is intended to create an arrangement for activating and deactivating automatic noise cancellation when it is required.  
         SUMMARY OF THE INVENTION  
         [0006]    According to the invention, this purpose is achieved in such a way that the system includes an automatic circuit  42  configuration detecting a need for ANC, according to a selected criterion, the detection circuit configuration being arranged to automatically control the activation and deactivation of ANC. According to one preferred embodiment, the detection circuit configuration includes a comparison circuit for comparing the set criterion value with the volume level of the mobile station device, in such a way that the comparison circuit activates ANC at the set sound volume value.  
           [0007]    According to a second preferred embodiment, if there is an additional microphone in the mobile station for measuring background noise, the detection circuit configuration includes a comparison circuit for comparing the set criterion value with the measured value of the background noise, in such a way that the comparison circuit activates ANC at the set volume level of the background noise.  
           [0008]    Once the ANC setting criteria has been made, the user need no longer take care of activating and deactivating ANC.  
           [0009]    With the aid of the invention, automatic noise cancellation will only be activated when it is really necessary, thus avoiding unnecessary power consumption. Other advantages and embodiments of the invention will become apparent in connection with the examples described later.  
           [0010]    Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are intended solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    In the following, the invention is examined with reference to the accompanying figures, in which:  
         [0012]    [0012]FIG. 1 shows a schematic diagram of a mobile station equipped with noise cancellation,  
         [0013]    [0013]FIG. 2 shows a flow chart of the noise cancellation of the embodiment of FIG. 1,  
         [0014]    [0014]FIG. 3 shows a schematic diagram of a mobile station according to a second embodiment, and  
         [0015]    [0015]FIG. 4 shows a flow chart of the noise cancellation of the embodiment of FIG. 3. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    In both cases, the schematic diagrams of the examples of FIG. 1 and  3  show the operational configuration of the mobile station. Naturally, the signal is processed digitally. Thus, the ‘bypass connection’ of the noise cancellation (ANC) takes place by forwarding the flow of bits, which arrives at the ANC&#39;s incoming register, directly to the following stages, i.e. to the input register of the speech coding, without processing. When the noise cancellation has been activated, before the flow of bits arriving at the incoming register of the ANC is forwarded, it is subject to processing, which is, as such, known.  
         [0017]    The invention can be implemented in different types of mobile station (TDMA, CDMA, digital/analog).  
         [0018]    The schematic diagram according to FIG. 1 shows a digital mobile station, in which the speech to be sent, which comes to the microphone  1 , is converted into digital form by an A/D converter  2 , the noise is suppressed, if necessary, by noise cancellation (ANC facility  3 ), and the speech is coded in speech coding  4 , after which processing of the baseband frequency signal takes place in the block  5 , as is known. Next, the signal is converted to a radio frequency and transmitted  6  through a duplex filter (DPLX) and an antenna (ANT). The known operations of the receiver branch  7  are carried out when speech is received in the receiver, and it is reproduced in the loudspeaker  8 . In addition, FIG. 1 is marked with a means  13 , the significance of which is explained later, for showing the state information of the mobile station.  
         [0019]    In the description according to FIG. 1, volume level control  9 , the information available from which is exploited by the automatic detection circuit configuration  10  to detect a need for noise cancellation, is connected to the receiver branch  7 . This too is actually implemented by means of software, which is explained later. In any event, the noise cancellation is activated and deactivated automatically, with only the receiver volume level control value and the state information of the mobile station being exploited to detect a need for it.  
         [0020]    Automatic detection can be implemented by means of software in many different ways. Thus, FIG. 2 shows only one possible implementation, in the form of a program flow chart. When the mobile station is closed, the program monitors the loop formed by an initial check  20 . Once a call is connected, the execution changes to monitoring the level of the volume level of the loop  21 . If the volume level is not increased, the program returns to check  22  the status. If the volume level is increased, the execution moves to checking  23  the trigger level and returns, unless the trigger level is reached. If the check  23  detects that the trigger level has been reached, the program activates the ANC, stage  24 . From this, the execution must move to the checking stages in the opposite direction. When a call is connected and remains at the same sound level, the execution runs around the loop in stages  25 , ‘Volume level reduced’ and  28 , ‘Call ended?’. If the volume level is reduced, check  26 , ‘Trigger level achieved’, follows, from which the execution returns to stage  25 , if the trigger level has not been achieved and the call is still connected. If the trigger level has been reached, the program deactivates the ANC in stage  27  and returns to the initial check  20 .  
         [0021]    The program flow can also incorporate more complex initializations, for example, an initial state check of the volume level setting and, according to it, a move to either stage  21  or stage  25 .  
         [0022]    [0022]FIG. 3 shows a schematic diagram of a second embodiment while FIG. 4 shows a corresponding flow chart. The same reference numbers as above are used for operationally corresponding components. Thus, in the digital mobile station according to FIG. 3, the speech that comes from the microphone  1  is also converted using an A/D converter  2 , the noise is cancelled, if necessary, by noise cancellation (ANC facility  3 ), and the speech is coded in speech coding  4 , after the baseband frequency signal is processed in block  5 . Similarly, after this the signal is converted to a radio frequency and transmitted by a transmitter  6 , through a duplex filter (DPLX) and an antenna (ANT). The known operations of the receiver branch  7  are carried out in this case too, when speech is received and it is repeated by the loudspeaker  8 .  
         [0023]    Unlike in FIG. 1, in the embodiment of FIG. 3, a separate microphone  11  and an A/D converter  12  are used to detect background noise. This is primarily exploited in the noise cancellation itself (ANC facility  3 ), but also in detecting  10  a need for ANC. Here too, detection  13  of the state of the mobile station is exploited when detecting a need for ANC. The corresponding program flow chart is somewhat simpler, because the criterion value required for the program is constant, FIG. 4. Thus, from the initial state check  20  the flow goes to monitor the first trigger level check  23 , from which, if the trigger level is exceeded, ANC is activated, stage  3 , and the program then goes to the second trigger level check  26 . From here the execution returns to the initial check  20 , through the deactivation of the ANC, stage  27 , if the trigger level has been reached (downwards). Otherwise, the execution runs around a loop through the call state check  28  and the second trigger level check  26 .  
         [0024]    In this case too, the program can be supplemented and adapted in many different ways.  
         [0025]    Thus, while there have been shown and described and pointed out fundamental novel features of the present invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices described and illustrated, and in their operation, and of the methods described may be made by those skilled in the art without departing from the spirit of the present invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.