Abstract:
When performing switching control of reception modes trading off reception sensitivity against power consumption in a reception environment, the receiving apparatus and control method of the present invention perform state transition without a reception error occurring due to switching control with the aid of a reception mode in which an intermediate reception performance is provided. The present invention is particularly useful to balance the reception performance with the battery duration in a battery-powered, portable receiving terminal such as a television receiver for a mobile terminal.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a receiving apparatus selecting an appropriate reception mode trading off reception performance against operation power according to a reception environment. 
       BACKGROUND ART 
       [0002]    In recent years, diversity reception method has been employed for small, mobile receiving terminals. That is, a small terminal usually has a low-gain antenna to reduce the size of its receiving antenna, and is used in an adverse reception environment, where the user performs reception while moving, for example. In response, diversity reception significantly improves reception sensitivity, where two antennas are used, and either one of the signals is selected or both signals are synthesized. 
         [0003]    However, diversity reception method has two series of antennas and receivers, and thus an increase of power consumption becomes a problem with a battery-powered mobile terminal. Under the circumstances, a method is proposed that satisfies both of improving reception performance and reducing power consumption. That is, high sensitivity precedes with diversity reception in an adverse reception environment; low power consumption precedes with receiving with one-series receiver alone (referred to as single reception, hereinafter) in a favorable reception environment. 
         [0004]    As prior art document information related to this patent application, patent literature 1 is known, for example. However, diversity reception has significantly favorable reception sensitivity compared to single reception, resulting in frequent switching between diversity reception and single reception when switching control is performed according to a reception environment, which may cause a reception error. More specifically, at an input level between that for a reception sensitivity in diversity reception and that in single reception, switching between diversity reception and single reception occurs frequently because an input level range exists in which reception cannot be performed by single reception but can be by diversity reception with a sufficient margin. 
         [0005]      FIG. 7  is an example control flow of a conventional case where switching is performed between the diversity reception mode and single reception mode. First, controller  9  (refer to  FIG. 4 ) acquires a BER output from BER measuring unit  8  (refer to  FIG. 4 ). Next, when the current mode is the diversity reception mode, controller  9  compares the BER with the release threshold. When the BER is lower than the release threshold (Yes), which means the reception environment is favorable, controller  9  controls so as to switch to the single reception mode; when the BER is higher than the release threshold (No), controller  9  does not perform switching control, but the flow returns to the BER acquiring step. Meanwhile, when the current mode is the single reception mode, controller  9  compares the BER with the start-up threshold. When the BER is higher than the start-up threshold (Yes), which means the reception environment is adverse, controller  9  controls so as to switch to the diversity reception mode; when the BER is lower than the start-up threshold (No), controller  9  does not perform switching control, but the flow returns to the BER acquiring step. The difference in sensitivity between the diversity reception mode and single reception mode is as large as approximately 3 dB, and thus switching between the reception modes occurs periodically because level range A exists as described above, and additionally a reception error occurs because level range B exists.
   [Patent literature 1] Japanese Patent Unexamined Publication No. H11-150497     
       SUMMARY OF THE INVENTION 
       [0007]    The present invention improves conventional disadvantages, eliminates switching between reception modes frequently, and prevents a reception error. A receiving apparatus of the present invention includes a receiver capable of switching between a high-sensitivity mode, a power-saving mode having a reception sensitivity lower than that in the high-sensitivity mode, and an intermediate reception mode having a reception sensitivity lower than that in the high-sensitivity mode and higher than that in the power-saving mode; and a reception environment acquiring unit acquiring a reception environment, connected to the output side of the receiver. The receiving apparatus further includes a controller that switches the receiver, if the receiver is in the high-sensitivity mode, to the intermediate reception mode when a reception environment acquired by the reception environment acquiring unit becomes better than the release threshold; and if the receiver is in the intermediate reception mode, to the power-saving mode when a reception environment acquired by the reception environment acquiring unit becomes better than the first threshold. With this configuration, the difference in sensitivity between the high-sensitivity mode and intermediate reception mode, and that between the intermediate reception mode and power-saving mode are smaller than that between the high-sensitivity mode and power-saving mode, thereby preventing frequent switching caused by a large difference in sensitivity between the reception modes at switching control. That is, state transition between the reception modes are performed while suppressing a reception error occurring. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  is an operation flowchart of a receiving apparatus of the present invention. 
           [0009]      FIG. 2  shows reception sensitivity characteristics in the diversity reception mode and single reception mode of the present invention. 
           [0010]      FIG. 3  is a block diagram of a receiver according to the present invention. 
           [0011]      FIG. 4  is a block diagram of a receiving apparatus according to the present invention. 
           [0012]      FIG. 5  shows reception sensitivity characteristics in a conventional diversity reception mode and single reception mode. 
           [0013]      FIG. 6  shows detailed reception sensitivity characteristics in a conventional diversity reception mode and single reception mode. 
           [0014]      FIG. 7  is an operation flowchart of a conventional receiving apparatus. 
       
    
    
     REFERENCE MARKS IN THE DRAWINGS 
       [0000]    
       
         
           
               1  Receiving apparatus 
               2  First receiver 
               3  Second receiver 
               4  Diversity processing unit 
               5  Error corrector 
               6  Decoder 
               7  Display unit 
               8  BER measuring unit 
               9  Controller 
               10  Receiver 
               11  Antenna 
               12  RF filter 
               13  RFGCA 
               14  Mixer 
               15  VCO 
               16  RFAGC 
               17  IF filter 
               18  IFGCA 
               19  ADC 
               20  Demodulator 
           
         
       
     
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0035]    Hereinafter, a description is made for a concrete exemplary embodiment according to the present invention. In  FIG. 4 , receiving apparatus  1  includes first receiver  2 ; second receiver  3 ; and diversity processing unit  4  connected to the output sides of first receiver  2  and second receiver  3 . Receiving apparatus  1  further includes error corrector  5  connected to the output side of diversity processing unit  4 ; decoder  6  connected to the output side of error corrector  5 ; display unit  7  connected to the output side of decoder  6 ; BER (bit error rate) measuring unit  8  connected to error corrector  5 ; and controller  9  controlling first receiver  2  and second receiver  3  according to a signal from BER measuring unit  8 . Similar configurations of receiving apparatus  1  include one having all of these components and one having one or more of the components. 
         [0036]    With the configuration, receiving apparatus  1  operates in the diversity reception mode, where diversity processing is performed with first receiver  2  and second receiver  3 ; and in the single reception mode, where only one of first receiver  2  and second receiver  3  is used and the other is powered off. In whichever reception mode, decoder  6  can restore a signal output from error corrector  5  to data for the transmission side, and display unit  7  can display the data restored. 
         [0037]      FIG. 5  shows reception sensitivity characteristics in the diversity reception mode and single reception mode. The horizontal axis represents the input level to the receiver; the vertical axis, the error rate (BER) of a reception signal. A reception sensitivity is generally defined by an input level at which the BER reaches a limit value (BER limit, hereinafter) below which the decoder can restore transmission data normally. In the example of  FIG. 5 , the reception sensitivity in the single reception mode is −98 dBm and that in the diversity reception mode is −101 dBm, which means the diversity reception mode has a sensitivity better than that in the single reception mode by 3 dB. Meanwhile, the receiver composed of a high-frequency circuit, which generally consumes large power, consumes significantly large power in the diversity reception mode compared to the single reception mode, where one of the receivers is powered off. Here, the values (−98 dBm, −101 dBm, 3 dB) in the above example, varying depending on the performance of receiving apparatus  1 , are shown by way of example. 
         [0038]    In  FIG. 4 , controller  9  performs switching control between the diversity reception mode and single reception mode according to a reception environment. Means for acquiring a reception environment include various methods such as those using automatic gain control (AGC), carrier-to-noise (C/N) ratio, and BER, where a method of using BER is described as an example in this embodiment. That is, when a BER output from BER measuring unit  8  (i.e. reception environment acquiring unit) is lower than a threshold preliminarily set, the input level to the receiver is high, which is judged as a favorable reception environment, and the reception mode is switched from the diversity reception mode with high sensitivity to the single reception mode with low sensitivity. Hereinafter, a threshold of a BER at which switching is performed from the diversity reception mode to the single reception mode is referred to as a release threshold. Meanwhile, when a BER output from BER measuring unit  8  is higher than a threshold preliminarily set, the input level to the receiver is low, which is judged as an adverse reception environment, and the reception mode is switched from the single reception mode with low sensitivity to the diversity reception mode with high sensitivity. Hereinafter, a threshold of a BER at which switching is performed from the single reception mode to the diversity reception mode is referred to as a start-up threshold. Owing to this control, the power consumption is reduced in the single reception mode for a favorable reception environment; the reception performance is ensured in the diversity reception mode for an adverse reception environment. 
         [0039]    However, the difference in reception sensitivity between the single reception mode and diversity reception mode is as large as approximately 3 dB, and thus switching occurs frequently at an intermediate input level between them. This phenomenon is described using  FIG. 6 , which shows the release threshold and start-up threshold aforementioned. In a level range (level range A, hereinafter) lower than input level a at which the start-up threshold is reached in the single reception mode and additionally higher than input level c at which the release threshold is reached in the diversity reception mode, if the receiver is in the single reception mode, the BER is higher than the start-up threshold in and thus controller  9  switches the reception mode to the diversity reception mode; and if the receiver is in the diversity reception mode, the BER is lower than the release threshold, and thus controller  9  switches the reception mode to the single reception mode. Consequently, switching occurs periodically between the single reception mode and diversity reception mode, and when receiving apparatus  1  is steadily present in this level range A, switching between the reception modes occurs frequently. 
         [0040]    Furthermore, in a level range (level range B, hereinafter) lower than input level b (i.e. sensitivity level) at which the error limit is reached in the single reception mode and additionally higher than input level c at which the release threshold is reached in the diversity reception mode, switching occurs periodically, generating a reception error. That is to say, errors exceeding the BER limit occur during the single reception mode, and thus decoder  6  at the subsequent stage cannot restore transmission data normally. Here, level range A and level range B can be narrowed by setting a low value to the release threshold. However, to do so, the measurement accuracy for a BER needs to be raised. For this reason, the measurement time needs to be prolonged, which reduces the following capability to the change of the reception environment. In digital broadcasting (one-segment broadcasting) for mobile terminals as a concrete example, the data transmission speed of an MPEG transport stream (TS) is approximately 416 kbps, and thus to measure the BER to an accuracy of 1E-6, measurement needs to be made for approximately 2 seconds, which is not allowable in terms of following capability in adaptive control. 
         [0041]    Under the circumstances, the present invention employs a third reception mode (referred to as intermediate reception mode, hereinafter) having a reception sensitivity lower than that in the diversity reception mode and higher than that in the single reception mode. An intermediate reception mode can be created by deteriorating the sensitivity in the diversity reception mode any way. 
         [0042]    As an example of creating an intermediate reception mode, there is a method that lowers the gain of an RFGCA (radio frequency gain control amplifier) contained in the receiver, which is described using  FIG. 3 . Receiver  10  in  FIG. 3  corresponds to first receiver  2  or second receiver  3  in  FIG. 4 . In  FIG. 3 , receiver  10  is composed of antenna  11 ; RF filter  12  connected to antenna  11 ; RFGCA  13  connected to RF filter  12  and RFAGC (radio frequency automatic gain control)  16  (described later); VCO (voltage controlled oscillator)  15 ; mixer  14  connected to RFGCA  13  and VCO  15 ; IF filter  17  connected to mixer  14 ; IFGCA  18  connected to IF filter  17 ; ADC (analog digital converter)  19  connected to IFGCA  18 ; demodulating unit  20  connected to ADC  19 ; and RFAGC  16  connected to mixer  14 . Controller  9  located outside receiver  10  is connected to RFAGC  16 . With this configuration, receiver  10  suppresses unnecessary waves contained in a reception signal received by antenna  11  using RF filter  12 , and controls so that the signal level falls within a given level range using RFGCA  13 . Next, receiver  10  mixes a local signal output from VCO  15  with an output signal from RFGCA  13  using mixer  14  to convert it to a predetermined intermediate frequency (IF). Next, receiver  10  removes unnecessary waves other than those in a given band from an output signal from mixer  14  with IF filter  17  to perform the final signal filtration, and then performs gain control with IFGCA  18  so that the input range of ADC  19  is met. Next, receiver  10  A/D-converts an output signal from IFGCA  18  to a digital signal with ADC  19  (i.e. A/D converter) and demodulates it with demodulating unit  20  to be connected to the diversity processing unit (not shown) in the subsequent stage. Reception sensitivity S of a receiving apparatus is generally defined by a noise figure determined by a signal band width and temperature; noise figure F determined by the configuration of the receiver; and a required C/N determined by a modulation method of a signal, which is expressed by expression (1) below, where K represents the Boltzmann constant; T, temperature; and B, signal band width. 
         [0000]        S=KTB+F+C/N   (1) 
         [0043]    Here, a description is made that the reception sensitivity can be deteriorated by lowering the gain of RFGCA  13 . Assuming that the gain of the RFGCA is G 1 , the noise figure is F 1 , and the noise figure subsequent to mixer  14  (included) is F 2 , then noise figure F of the entire receiver is expressed by expression (2) below. 
         [0000]        F=F 1+( F 2−1)÷ G 1  (2) 
         [0044]    That is to say, reducing gain G 1  of the RFGCA increases noise figure F of the entire receiving apparatus, which consequently increases the reception sensitivity S of the receiving apparatus in expression (1), causing the reception sensitivity to deteriorate. With the aid of this relationship, controller  9  forcibly sets a control value to RFAGC  16  controlling the gain of RFGCA  13  for the two series of receivers (i.e. first receiver  2 , second receiver  3 ) in the diversity reception mode. As a result, an intermediate reception mode is created that has a reception sensitivity lower than that in the diversity reception mode and higher than that in the single reception mode. 
         [0045]    Besides this method, the next means can be utilized as a means of creating an intermediate reception mode. That is, by restricting (reducing) a current value of each circuit in receiver  10  to restrict the amplification degree of the transistors, the gain and noise figure are deteriorated, which causes the reception sensitivity to deteriorate. In this case, less power is consumed during a period of the intermediate reception mode than the diversity reception mode, which is more effective to reduce power consumption. Alternatively, an intermediate reception mode can be created by decreasing the conversion accuracy of A/D conversion in ADC  19  to deteriorate the sensitivity. Although other methods of creating an intermediate reception mode exist, the present invention has curative properties against a reception error caused by periodic switching independently of a way an intermediate reception mode is created. 
         [0046]    A description is made for the operation of switching with the aid of an intermediate reception mode using  FIG. 2 . An intermediate reception mode is created so that its reception sensitivity is lower than that in the diversity reception mode and higher than that in the single reception mode. In the example of  FIG. 2 , reception sensitivity f in the intermediate reception mode is lower than reception sensitivity g in the diversity reception mode and higher than reception sensitivity c in the single reception mode. Here, in terms of switching control between the diversity reception mode and intermediate reception mode, input level e at which the start-up threshold is reached in the intermediate reception mode is lower than input level d at which the release threshold is reached in the diversity reception mode, and thus level range A shown in  FIG. 6  does not exist, resulting in no periodical switching occurring. Meanwhile, in terms of switching control between the intermediate reception mode and single reception mode, in level range A determined by input level a at which the start-up threshold is reached in the single reception mode and by input level b at which the release threshold is reached in the intermediate reception mode, periodical switching between the intermediate reception mode and single reception mode occurs. However, input level c at which the BER limit is reached in the single reception mode is lower than input level b, and thus level range B shown in  FIG. 6  does not exist, resulting in no reception error occurring even during a period of the single reception mode. 
         [0047]    In addition, to eliminate level range A as well, the following method can be used. That is, a fourth reception mode with its reception sensitivity lower than that in the intermediate reception mode and higher than that the single reception mode is newly created, and switching control is performed using the four reception modes in sequence. Further, five or more reception modes may exist. 
         [0048]    A description is made for a concrete example of controlling with the configuration of this embodiment using  FIG. 1 , which shows an example of the control method according to the present invention. In the single reception mode after a BER is acquired, controller  9  (refer to  FIG. 4 ) controls so as to switch to the intermediate reception mode if the BER is higher (Yes) than the start-up threshold. In the diversity reception mode, controller  9  controls so as to switch to the intermediate reception mode if the BER is lower (Yes) than the release threshold. In the intermediate reception mode, controller  9  controls so as to switch to the diversity reception mode if the BER is higher (Yes) than the start-up threshold; controls so as to switch to the single reception mode if the BER is lower (Yes) than the release threshold; and does nothing, but the flow returns to the BER acquiring step if the BER is lower (No) than the start-up threshold and higher (No) than the release threshold. With this control flow, switching control can be performed between the three reception modes according to a reception environment, enabling level ranges A and B to be narrowed or eliminated. 
         [0049]    From the above-described description, when performing switching control of the reception modes trading off reception sensitivity against power consumption according to a reception environment, using the configuration of this embodiment suppresses a reception error occurring caused by periodical switching, thereby implementing smooth switching control. 
         [0050]    Here, in this embodiment, the description is made for the example of switching between the diversity reception mode and single reception mode. However, the present invention is effective in a receiving apparatus with only one series of receiver (i.e. not structured for diversity). That is, in terms of the circuitry of the receiver, smooth switching control is possible in the same way with the aid of an intermediate reception mode when controlling so as to switch the reception modes between the high-sensitivity mode with high reception sensitivity with large power consumption and the power-saving mode with small power consumption with low reception sensitivity according to a reception environment. 
         [0051]    In this case, the performance difference in mobile reception characteristics (Reilly characteristic) between the high-sensitivity mode and power-saving mode is generally small or zero. Consequently, adaptive switching between the reception modes is effective near the reception sensitivity level while being ineffective near the mobile reception sensitivity level, which is higher than the reception sensitivity level, resulting in characteristic degradation caused by switching in some cases. To avoid this phenomenon occurring, the adaptive switching control is stopped to enter the power-saving mode when the input level stays beyond a certain level (e.g. higher than the reception sensitivity level). Alternatively, other methods may be used. For example, the receiving apparatus is provided with a movement detector (not shown), and the adaptive switching control is stopped to enter the power-saving mode when the apparatus is moving at a given speed or faster. 
         [0052]    Other than an adaptive control of reception modes trading off reception sensitivity against power consumption, when performing adaptive switching control between various types of reception modes (e.g. disturbance characteristic to power consumption, frequency characteristic to power consumption, temperature characteristic to power consumption), creating an intermediate reception mode for respective characteristics eliminates a reception error occurring. More specifically, a reception error is eliminated by setting the disturbance characteristic in the second reception mode (intermediate) so as to be lower than the disturbance characteristic in the first reception mode (high-sensitivity) and higher than that in the third reception mode (power-saving). In the same way, a reception error is eliminated by setting the frequency characteristic in the second reception mode (intermediate) so as to be lower than the frequency characteristic in the first reception mode (high-sensitivity) and higher than that in the third reception mode (power-saving). Further, a reception error is eliminated by setting the temperature characteristic in the second reception mode (intermediate) so as to be lower than the temperature characteristic in the first reception mode (high-sensitivity) and higher than that in the third reception mode (power-saving). 
       INDUSTRIAL APPLICABILITY 
       [0053]    In a small, mobile receiving terminal, the present invention eliminates frequent switching occurring between the reception modes in diversity reception method where two antennas are used, and either one of the reception signals is selected or both signals are synthesized, to prevent occurrence of a reception error, which is industrially useful.