JP2007235801A - Fading estimate apparatus for receiving a plurality of channels, high frequency receiver using the same, and fading estimate method used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an erroneous fading frequency from being detected when a received channel is switched. <P>SOLUTION: Fading correction steps 93b, 99b for receiving outputs of fading detection steps 93a, 99a and a selection signal are provided. When the selection signal is changed, the fading correction steps 93b, 99b correct output values of the fading correction steps 93a, 99a calculated at channels before the change depending on a difference from the channels, and consequently, the fading frequency can be detected with high accuracy even when the received channel is switched. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fading estimation apparatus for multi-channel reception that estimates fading degrees for a plurality of channels, a high-frequency receiving apparatus using the same, and a fading estimation method used for these.

  In recent years, television receivers have been installed in mobile phones, automobiles, and the like in response to requests for watching TV broadcast programs while moving. Now, how a TV broadcast is received while moving by such a television receiver will be described with reference to the drawings. FIG. 12 is an explanatory diagram showing a state in which a TV broadcast is received during movement. The TV broadcast wave is radiated from the broadcast antenna 2 of the broadcast station 1 into the air. In the automobile 3, a TV broadcast wave is received by the antenna 4 attached to the automobile 3. At this time, the TV broadcast wave received by the antenna 4 includes the direct wave 5 directly input from the broadcast antenna 2 to the antenna 4 and the TV broadcast wave radiated from the broadcast antenna 2 reflected on the ground or a building. And a reflected wave 6 input to the antenna 4.

  Here, the direct wave 5 and the reflected wave 6 have different path lengths from the broadcast antenna 2 to the antenna 4. That is, since the reflected wave 6 is reflected once and reaches the antenna 4, the path length of the reflected wave 6 is longer than that of the direct wave 5. When such a direct wave 5 and a reflected wave 6 are input to the antenna 4, the TV broadcast wave at the antenna 4 becomes a signal in which the phases of the direct wave 5 and the reflected wave 6 are combined. The phase difference between the direct wave 5 and the reflected wave 6 changes due to the change in the path length accompanying the movement of the automobile 3. As a result, the level of the signal obtained by combining the direct wave 5 and the reflected wave 6 fluctuates (so-called fading), and reception quality deteriorates due to this fading. Therefore, in order to improve the reception quality due to such fading, a so-called diversity high-frequency receiver is used.

  A conventional high frequency receiving apparatus will be described below with reference to the drawings. FIG. 13 is a circuit block diagram of a conventional high-frequency receiving device. In FIG. 13, the conventional high frequency receiver 11 is a diversity system, and two sets of antennas 4a and 4b, and two sets of receivers 11a and 11b are connected to each of the antennas 4a and 4b. The outputs of these receivers 11 a and 11 b are output from the output terminal 13 via the demodulation circuit 12. Here, the output of the receiver 11a is connected to the detector 14a, and the signal level output from the receiver 11a is detected. The output of the detector 14a is supplied to the fading detection means 16 via the A / D converter 15a.

  A power supply circuit 17 is inserted between the fading detection means 16 and the power supply terminal of the receiver 11b. Here, the fading detection means 16 detects fading of the input signal. When no fading is detected, the power supply circuit 17 turns off the power of the receiver 11b to detect fading. In such a case, the receiver 11b is turned on.

  Next, the operation of the conventional fading detection means 16 will be described. FIG. 14 is an explanatory diagram of a fluctuation amount calculation method in the fading detection means. In FIG. 14, the horizontal axis is time, and the vertical axis is signal level. 14, the fading detection means 16 acquires a signal level value 21 from the output of the A / D converter 15 at a predetermined time interval, and a change point 22a at which the signal level 21 changes from decrease to increase. 22b is detected, and the fading frequency is detected by measuring a time 23a between the change point 22a and the change point 22b. Then, the frequency calculated in this way is compared with a threshold value, and the power supply circuit 17 is turned on when the fading frequency is equal to or higher than a specified value.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
JP 2001-345760 A

  However, the position of the broadcast antenna 2 may be different depending on the receiving channel. That is, the phase of the reflected wave 6 and the direct wave 5 differs depending on the channel. For example, in such a conventional fading detection means 16, when the reception channel is changed immediately after the change point 22b, the fading frequency is determined by the time 23b between the change point 22b before the channel change and the change point 22c after the channel change. Will be calculated. Therefore, when the channel is switched, a frequency different from the actual fading frequency is calculated.

  Therefore, the present invention has been made to solve this problem, and an object of the present invention is to provide a multi-channel reception fading estimation apparatus capable of accurately detecting fading frequencies even when the reception channel is switched.

  In order to achieve this object, the fading estimation apparatus for multi-channel reception according to the present invention is provided with fading correction means in which the output of the fading estimation means is supplied to one input and the selection signal is supplied to the other input. When the selection signal is changed from the first channel to the second channel, the fading correction means outputs the output of the fading detection means in the first channel to the first and second channels. In accordance with the difference between the channels, the fading degree is corrected to be reduced. This achieves the intended purpose.

  As described above, according to the present invention, a high-frequency signal having a plurality of channels including at least a first channel and a second channel having a frequency lower than that of the first channel is supplied. Channel selection means for selecting and receiving based on a selection signal for selecting a desired channel, and fading to which the output of the channel selection means is connected in order to detect the degree of fading of the output signal output from the channel selection means And a fading correction unit that supplies the output of the fading detection unit to one input and the selection signal to the other input, and the selection signal is supplied from the first channel. When the channel is changed to the second channel, the fading correction unit outputs the fading detection unit in the first channel. The a said first and a plurality of channels receiving fading estimation apparatus for correcting a direction of the fading degree is reduced according to the difference between the second channel.

  As a result, the multi-channel reception fading estimation apparatus estimates fading in the channel after the change using the fading degree detected before the channel change and the selection signal, so that fading can be performed accurately even when the channel is changed. The degree can be estimated.

  Further, since the fading degree after the channel change is estimated from the fading degree before the channel change, the fading degree can be specified in a short time even when the channel is changed.

(Embodiment 1)
Hereinafter, the present embodiment will be described with reference to the drawings. FIG. 1 is a circuit block diagram of a high frequency receiving apparatus using fading detection means in the present embodiment. In FIG. 1, the same components as those in FIG. 12 are denoted by the same reference numerals, and the description thereof is simplified.

  The configuration of the high-frequency receiving device 51 in the present embodiment will be described with reference to FIG. Television broadcast waves (used as an example of a high-frequency signal) from about 50 MHz to about 900 MHz are input to the antennas 4a and 4b. Each of these antennas 4a and 4b is connected to a receiver 52 (used as an example of a channel selection unit) and a receiver 53 (used as an example of a channel selection unit). Note that two sets of the same antenna 4a and antenna 4b and two sets of the receiver 52 and the receiver 53 are used.

  Both the outputs of the receiver 52 and the receiver 53 are connected to the demodulation circuit 54. Since the demodulation circuit 54 in this embodiment is integrated (configured in an IC), the high-frequency receiving device 51 can be reduced in size.

  Here, the demodulation circuit 54 has the following configuration. The output of the receiver 52 is connected to the input terminal 54a of the demodulation circuit 54. On the other hand, the output of the receiver 53 is connected to the input terminal 54 b of the demodulation circuit 54. The signals supplied to the input terminal 54a and the input terminal 54b are supplied to the detector 55a and the detector 55b, respectively. The outputs of the detector 55a and the detector 55b are supplied to the A / D converter 56a and the A / D converter 56b, respectively, and the output signals of the detector 55a and the detector 55b are converted into digital signals. . The outputs of these A / D converter 56a and A / D converter 56b are connected to Fourier transform means 57a and Fourier transform means 57b, respectively. These Fourier transform means 57a and Fourier transform means 57b develop a signal converted into a digital signal on the frequency axis, and a so-called Fourier expansion process is performed. As a result, a signal is extracted for each frequency axis called a subcarrier.

  The outputs of the Fourier transform means 57a and the Fourier transform means 57b are output to the weighting means 58a and the weighting means 58b, respectively. The output of the weighting means 58a is connected to one input of the synthesizer 59, and the output of the weighting means 58b is connected to the other input. The synthesizer 59 synthesizes the output signal of the weighting means 58 a and the output signal of the weighting means 58 b and supplies the synthesized signal to the deinterleave circuit 60.

  At this time, in order for the deinterleaving circuit 60 to perform good demodulation processing, the signal level has upper and lower limit levels, and the weighting means 58a and weighting means 58b make the signal level within this level range. The level is adjusted. For this purpose, the output of the composition ratio setting means 61 is connected to the weighting means 58a and the weighting means 58b. For example, the synthesis ratio setting unit 61 detects the subcarrier levels of the output signals from the Fourier transform unit 57a and the Fourier transform unit 57b, and sets the synthesis ratio according to the level ratio. As a result, the synthesizer 59 synthesizes at a ratio corresponding to the synthesis ratio determined by the synthesis ratio setting means 61. In any case, the signal combining ratio in the combiner 59 is set so that the ratio of the signal from the better reception state is increased. Next, the deinterleave circuit 60 is supplied with the output signal of the combiner 59 and demodulates the signal. The signal demodulated by the deinterleave circuit 60 is error-corrected by the error correction circuit 62 and output from the output terminal 54c.

  The bit error rate detection circuit 63 is connected to the output of the error correction circuit 62 and calculates the bit error rate from the signal output from the error correction circuit 62. Further, the output of the synthesizer 59 is supplied to the C / N detector 64 to detect the C / N value of the synthesized signal.

  The control circuit 65 is used as an example of a circuit including a fading detection means, a fading correction means, a threshold setting means, and a comparison means. The receiver 52 or the receiver 53 and the control circuit 65 are used to control a plurality of channels. As an example of a fading estimation device for reception), the output of the demodulation circuit 54 is supplied to operate one of the receiver 52 and the receiver 53 (single operation), or the receiver 52 and the receiver 53 It is determined whether to operate both (diver operation). For this purpose, a power circuit 66a and a power circuit 66b are inserted between the control circuit 65 and the power terminals of the receiver 52 and the receiver 53, respectively. The power supply circuit 66a and the power supply circuit 66b turn on / off the power of the receiver 52 and the receiver 53, respectively, according to an instruction signal from the control circuit 65.

  Further, the memory 22 and the input key 67 are connected to the control circuit 65. A selection signal for receiving the desired reception channel is input from the input key 67. Further, the bit error rate detection circuit 63, the C / N detector 64, the synthesis ratio setting means 61 and the outputs of the detector 55a and the detector 55b are connected to the control circuit 65, while the output of the control circuit 65 is synthesized. It is connected to the ratio setting means 61.

  Next, the operation of the high-frequency receiver 51 configured as described above will be described. First, the relationship between the moving speed, the reception channel, and the fading frequency, and the relationship between the fading frequency and the required C / N value are described. explain. FIG. 2A is a relationship diagram between the time when the automobile 3 travels at a constant speed at a low speed and the level detected by the detector. FIG. 2B shows the automobile 3 travels at a constant speed at a high speed. It is a relationship diagram between the time in the case and the level detected by the detector. 2A and 2B, the horizontal axis 71 indicates time, and the vertical axis 72 indicates the level of the signal detected by the detector.

  In FIG. 2A, when the automobile 3 moves at a constant speed, the detected signal level 73 fluctuates with a constant period 74 (frequency). This is called fading (hereinafter, this fading frequency is called a fading frequency and used as an example of the degree of fading). This occurred because the phase of the direct wave 5 and the reflected wave 6 shifted due to the change in the path length from the broadcast antenna 2 with the movement of the automobile 3, and the signals having the shifted phases were combined. Is. It has also been found that this fading frequency changes according to the moving speed of the automobile 3. As shown in FIG. 2B, when the moving speed of the automobile 3 is fast, the signal level 75 fluctuates quickly, and the period 76 is shorter than the period 74 when the moving speed is slow. That is, when the moving speed is slow, the fading frequency is small, and when the moving speed is fast, the fading frequency is also large.

  Next, the relationship between the reception channel (frequency) and the fading frequency will be described. When the reception channel (frequency) is low, the fading frequency is small because the wavelength is long. On the other hand, when the reception channel (frequency) is high, the fading frequency becomes large because the wavelength is short.

  FIG. 3 is a relationship diagram between the fading frequency in the high frequency receiver 51 and the required C / N value in the high frequency receiver 51 according to the present embodiment. However, FIG. 3 shows a case where there is no change in the channel received by the high-frequency receiving device 51 and only the moving speed changes. In FIG. 3, the horizontal axis 81 indicates the fading frequency (or moving speed), and the vertical axis 82 indicates the C / N value (hereinafter referred to as required C / N value) when the bit error rate is 0.0002 in the high frequency receiver 51. Say).

  The required C / N characteristic curve 83 tends to increase the required C / N value when the fading frequency is very low (moving speed is low) and when the fading frequency is very high (moving speed is high). is doing. According to the experiments by the inventors, in the low-speed moving region 84 whose fading frequency is about 20 Hz or less (equivalent to about 45 Km / H when 13ch is received), the required C / N value increases as the moving speed decreases. It was confirmed that It was also confirmed that the required C / N value increases as the moving speed increases in the high-speed moving region 85 where the fading frequency is about 70 Hz (the moving speed is equivalent to about 130 Km / H when receiving 13ch) or more. In the middle speed movement region 86 during this period, it has been confirmed that the required C / N value does not change greatly and the required C / N is the smallest value in this state. When the moving speed is 0, since there is no fading, the required C / N is reduced accordingly.

  Therefore, the control circuit 65 in the present embodiment estimates the fading frequency based on the signal level detected by the detector 55a and the detector 55b, and switches between single reception and diversity reception according to the fading frequency. is there.

  FIG. 4 is an operation flowchart of the control circuit 65 in the present embodiment. In FIG. 4, when a selection signal is input from the input key 67, in the diver operation step 91, a signal to turn on both the receiver 52 and the receiver 53 is output to the power supply circuit 66a and the power supply circuit 66b. To do. As a result, both the receiver 52 and the receiver 53 are operated, and an operation of synthesizing and receiving these outputs (a so-called diversity method, hereinafter referred to as a diver operation) is performed. At this time, the selection signal is stored in the memory.

  First, switching from the diver operation to the single operation (received by only one of the receiver 52 and the receiver 53) will be described. After the diver operation step 91, a bit error rate determination step 92 is performed. In this bit error rate determination step 92, if the bit error rate detected by the bit error rate detection circuit 63 is larger than a predetermined error rate threshold 92a, the diver operation is continued. On the other hand, when the bit error rate detected by the bit error rate detection circuit 63 is smaller than a predetermined bit error rate threshold 92a, a fading detection step 93a (used as an example of fading detection means) is performed. . In the fading detection step 93a, the signal level of the detector 55a or the detector 55b is read and the fading frequency is detected. Although this estimation method will be described in detail later, the amount of change in the signal level within a predetermined unit time is calculated, and the number of small changes is counted as a count value. In this method, attention is paid to the fact that the amount of change is small at the peak portion where the change in signal level is small, and the fading frequency is estimated based on how many points have such a small amount of change.

  A fading correction step 93b (used as an example of fading correction means) is provided after the fading detection step 93a. In this fading correction step 93b, it is determined whether or not the reception channel is changed. If there is no change in the reception channel, the count value counted in the fading detection step 93a is output. On the other hand, when the channel is changed, the count value counted in the fading detection step 93a is corrected by the selection signals before and after the change.

  In threshold setting step 94 (used as an example of threshold setting means), the required C / N value corresponding to the count value calculated in fading detection step 93a or fading correction step 93b is switched from diver operation to single operation. The threshold value 95 is set. Here, the memory 22 stores a table in which required C / N values corresponding to the count values are stored in correspondence with each other. In the threshold setting step 94, the required C / N values corresponding to the calculated count values are stored. From the table and set as the threshold value 95.

  Next, in a comparison step 96 (used as an example of comparison means), the detected C / N value detected by the C / N detector 64 is compared with the threshold 95 set in the threshold setting step 94. If the detected C / N value is smaller than the threshold value 95, the process returns to the diver operation step 91, and the reception by the diversity method is continued. On the other hand, when the detected C / N value detected is larger than the threshold value 95, a tuner selection determination step 97 is performed. At this time, it is necessary to take into account that the bit error rate deteriorates by switching from diver reception described later to single operation. Therefore, a value obtained by multiplying the C / N value detected by the C / N detector 64 by the specified value is used as the detected C / N value. In this embodiment, it is assumed that the deterioration of C / N due to the switching to the single operation is deteriorated according to the combination ratio of the combination ratio setting means 61, and a value obtained by multiplying the detected C / N value by the combination ratio is set. The detected C / N value is used.

  For example, when the combination ratio of the receiver 52 and the receiver 53 is 8: 2, it is assumed that 20% C / N is deteriorated by switching to the single operation, and the C / N value detected in the comparison step 96 is assumed. A value obtained by multiplying by 0.8 is set as a detected C / N value, and this detected C / N value is compared with the threshold value 95. In this case, since the detected C / N value is corrected, the threshold value 95 for switching from the diver operation to the single operation is set equal to the required C / N value.

  In this embodiment, in order to estimate the C / N value after switching to the single operation, the correction is performed by multiplying the composite ratio in the comparison step 96. However, in the threshold setting step 94, the required C / N is corrected. The threshold value 95 may be set by dividing a value according to the composition ratio with respect to the value. Further, in the present embodiment, correction is performed according to the composition ratio, but this may be a constant value.

  Next, in a tuner selection determination step 97, the combination ratio of the combination ratio setting means 61 is detected and it is determined which combination ratio of the receiver 52 and the receiver 53 is smaller. Then, in the single operation step 98 after the tuner selection determination step 97, the receiver is turned off with respect to the power supply circuit of the receiver having the lower combination ratio selected in the tuner selection determination step 97. A signal is sent out. As a result, the operation of the receiver having the better reception quality is continued and switched to the single operation. This can reduce the deterioration of the C / N value when switching to single reception.

  Next, switching from single operation to diver operation will be described. After the single operation step 98, a fading detection step 99a (used as another example of fading detection means) is performed. In the fading detection step 99a, similarly to the fading detection step 93a, signals from the detector 55a and the detector 55b are detected, and the fluctuation amount of the signal level within the unit time is calculated. In this fading detection step 99a, the fading frequency is detected by the same method as in fading detection step 93a.

  After the fading detection step 99a, a fading correction step 99b (used as an example of fading correction means) is performed. In this fading correction step 99b, it is determined whether or not the reception channel has been changed. If there is no change in the reception channel, the count value counted in the fading detection step 99a is output. On the other hand, when the channel is changed, similarly to the fading correction step 93b, the count value counted in the fading detection step 99a is corrected by the selection signal before and after the change.

  In the threshold setting step 100, the required C / N value corresponding to the count value calculated in the fading detection step 99 a or the count value corrected in the fading correction step 99 b is acquired from the memory 22 and set as the threshold 101. Then, in the comparison step 102 (used as an example of comparison means), the detected C / N value detected by the C / N detector 64 is compared with the threshold value 101. In the comparison step 102, when the detected C / N value is equal to or greater than the threshold value 101, the process returns to the fading detection step 99a, and the single operation is continued as it is. On the other hand, when the detected C / N value is smaller than the threshold value 101, the process returns to the diver operation step 91 and is switched to the diver operation.

  As described above, since both the switching from the diver operation to the single operation and the switching from the single operation to the diver operation are determined by the C / N value, the switching can be performed quickly. Therefore, it is possible to improve the reception state in a short time even if the reception quality deteriorates suddenly during single reception. On the other hand, since switching from the diver operation to the single operation is fast, power consumption can be reduced accordingly.

  When the channel is changed, the fading frequency of the channel after the change is corrected, so that the fading frequency can be detected with high accuracy even when the channel is changed. Accordingly, since the required C / N value can be set with high accuracy even when the channel is changed, it is possible to reduce erroneous switching of the diversity single operation. This makes it possible to obtain a stable reception quality. Further, since the fading frequency is specified without waiting for the time until the fading frequency is specified by the fading detection means, the reception quality can be improved quickly even when the channel is switched. This is particularly useful when directly entering the channel you want to see directly.

  In the present embodiment, fading correction step 93b and fading correction step 99b are provided before threshold setting steps 94 and 100, and correction is performed in fading correction steps 93b and 99b. However, instead of these fading correction step 93b and fading correction step 99b, in threshold setting step 94 (used as another example of fading correction means) or threshold setting step 100 (used as another example of fading correction means) The fading degree with respect to the channel change may be corrected. That is, the required C / N value corresponding to the reception channel and the count value at the fading detection step is stored in the memory 22 in the memory. And it is also possible to correct by reading the count value corresponding to the changed channel from this table. In this case, since the fading correction step 93b and the fading correction step 99b are not necessary, the fading correction process is accelerated. Further, the fading detection step 93a and fading detection step 99a in the present embodiment may be replaced with other detection methods such as conventional fading detection means, and even in this case, the fading frequency is accurately detected when the channel is switched. Can do.

  Further, the fading degree is detected for switching, the required C / N value corresponding to the fading degree is set as a threshold value, and the single operation and the diver operation are switched according to the threshold value. The deterioration of quality can be improved, and good reception can be realized even when moving. Furthermore, even when the reception state deteriorates due to a change in moving speed, it is possible to quickly switch to diversity reception, so that it is possible to realize good reception quality regardless of the moving speed. Furthermore, since it can be switched optimally according to the degree of fading, the power consumption can be reduced compared to the case where the degree of fading is not determined.

  Next, detection of fading frequency in fading detection step 93a and fading detection step 99a will be described in detail. FIG. 5 is a flowchart of the fading detection step in the present embodiment. FIG. 6A is an explanatory diagram of a sampling method when the fading frequency is low, and FIG. 6B is an explanatory diagram of a variation amount calculation method. FIG. 7A is an explanatory diagram of a sampling method when the fading frequency is high, and FIG. 7B is an explanatory diagram of a variation amount calculation method.

  In sampling step 103 (used as an example of sampling means) in FIG. 5, the signal level 112 detected by the detector 55a or detector 55b is set to a predetermined number of signal level values 113 at regular time intervals 111. The signal level value 121 is acquired. The acquired signal level value 113 and signal level value 121 are sequentially stored in the memory 22. In the fluctuation amount calculation step 104 (used as an example of the fluctuation amount detection means), among the signal level value 113 and the signal level value 121 stored in the memory 22, fluctuations of n signal level values acquired successively. An amount 114 and a variation amount 122 are calculated. At this time, as the fluctuation amount 114 and the fluctuation amount 122, a variance value at n signal levels is used, or a value obtained by averaging n fluctuation amounts between two signal levels obtained successively. .

  Here, in the counting step 105 (used as an example of a counting means), the value of the fluctuation amount is compared with a predetermined threshold value 115, and counting is performed when the fluctuation amount is smaller than the threshold value 115. Then, the above steps are repeated until the calculation of m variation amounts is completed in the variation amount number determination step 106.

  Here, when the fading frequency is low, the amount of fluctuation in the vicinity of the maximum value of the signal level is small, so the count value in the counting step 105 is large. On the other hand, when the fading frequency is high, the amount of fluctuation in the vicinity of the maximum value of the signal level is larger and the count value obtained by the counting step 105 is smaller than when the fading frequency is low. Accordingly, since the degree of the region where the detected signal level change amount is small can be detected from the count value in the counting step 105, the fading frequency can be detected.

  Now, this detection method will be described in more detail with reference to the drawings. In order to make this operation easy to understand, the fluctuation amount is calculated by using five (n = 5) signal level values for convenience, and the fading frequency is estimated by 20 fluctuation amounts (m = 20). . In FIG. 6A, the horizontal axis represents time, and the vertical axis represents the signal level. First, in the sampling step 103, the signal level 112 detected by the detector 55a or the detector 55b is sequentially sampled at the time interval 111, and the signal level value 113 is stored in the memory 22 in the order of the acquired time. At this time, in the sampling step 103, five signal level values from the signal level value 113a to the signal level value 113e are acquired. Note that the time interval 111 in this embodiment is 1 millisecond.

  Next, in FIG.6 (b), a horizontal axis is time and a vertical axis | shaft is a value of fluctuation amount. In the fluctuation amount calculation step 104, the fluctuation amount 114a is calculated from the values of the five signal level values 113a to 113e acquired in the sampling step 103. In the present embodiment, the fluctuation amount 114a uses a variance value obtained by root mean square of the signal level value 113a to the signal level value 113e.

  In the counting step 105, the calculated fluctuation amount is compared with the threshold value 115, and when the fluctuation amount is equal to or less than the threshold value 115, the count is incremented. For example, since the fluctuation amount 114a is larger than the threshold value 115, it is not counted and the count value remains zero.

  At this time, since the number of fluctuation amounts is one, the sampling step 103 is repeated again after the counting step 105 by the number determination step 106. At this time, in the sampling step 103, only one new signal level value 113f is obtained and stored in place of the oldest signal level value 113a stored in the memory 22. In this way, in the fluctuation amount calculation step 104, the fluctuation amount 114b is calculated from the values of the signal level value 113b to the signal level value 113f. Here, in the counting step 105, the fluctuation amount 114b is compared with the threshold value 115. Also in this case, since the fluctuation amount 114b is equal to or greater than the threshold value 115, it is not counted and the count value remains 0.

  Then, the signal level value acquired sequentially is calculated. When the fluctuation amount 114g in the signal level value 113g to the signal level value 113k is calculated, the value of the fluctuation amount 114g becomes smaller than the threshold value 115. Therefore, it is counted in the counting step 105 and the count value becomes 1.

  Similarly, the remaining 13 fluctuation amounts 114h to 114t are calculated based on five consecutive signal level values of the signal level value 113h to the signal level value 113x. By such a procedure, calculation of 20 variation amounts (variation amount 114a to variation amount 114t) is completed from 24 signal level values (signal level value 113a to signal level value 113x). At this time, since eight values of the fluctuation amount 114g to the fluctuation amount 114n are equal to or less than the threshold value 115, the count value in the counting step 105 is 8.

  Next, a case where large frequency fading is detected using the above-described method will be described. In FIG. 7A, the horizontal axis represents time, and the vertical axis represents the signal level. In FIG. 7B, the horizontal axis is time, and the vertical axis is the value of variation. Since the signal level changes abruptly when the fading frequency is high, the variance of those values increases and the value of the fluctuation amount increases. Accordingly, the 20 fluctuation amounts (variation amount 122a to fluctuation amount 122t) calculated from the 24 signal level values (signal level value 121a to signal level value 121x) are the fluctuation amounts (variation amounts 114a to 114a to when the frequency is small). The value is larger than the fluctuation amount 114t).

  That is, in the counting step 105, the number of objects whose fluctuation amount is smaller than the threshold 115 is reduced. For example, in the case of FIG. 7B, the number of fluctuations smaller than the threshold value 115 is only the fluctuation quantity 122d, the fluctuation quantity 122l, and the fluctuation quantity 122t, so the count value in the counting step 105 is 3.

  As described above, if the count value counted in the counting step 105 is large, the fading frequency is small. Conversely, if the count value is small, the fading frequency is large. Therefore, if the above method is used, the fading frequency can be estimated from the count value counted in the counting step 105.

  In this embodiment, the fluctuation amount is calculated as soon as five signal level values are prepared. After obtaining and storing the 24 signal level values, the fluctuation amount is calculated from the 24 signal level values. You may calculate 20 pieces. In this case, since it is not necessary to complete the calculation of the fluctuation amount during the sampling time, the calculation time of the fluctuation amount may be long, and it is possible to perform complicated calculation processing or data for calculating the fluctuation amount. It is also possible to increase the number of. Even when the sampling time is shorter than the calculation time of the fluctuation amount, it is not necessary to execute the calculation and the sampling in parallel, and the circuit configuration of the control circuit 65 can be simplified. Similarly, the counting step 105 may calculate the count value by comparing 20 fluctuation amounts at once.

  If the fading estimation method as described above is used, the fluctuation of the signal level can be accurately detected in the fluctuation amount calculation step 104. As a result, the count value in the counting step 105 can accurately represent the degree of length of the region where the slope near the maximum value is small. Therefore, since the fading frequency can be estimated using the count value, the fading frequency can be detected without measuring the valley time, and the detection time can be shortened even when the fading frequency is small.

  Here, especially when the frequency of the reception channel is low, the wavelength is long, so that the fading frequency is also low, and the time during which the level falls due to this fading becomes long. On the other hand, when the frequency is high as in a device such as a mobile phone, the fading frequency becomes high even when moving at the same low speed, and the time during which the level drops due to fading becomes short. Therefore, especially in a low-speed movement in a channel having a low frequency, the fading frequency becomes small, and the time for the level to drop becomes long. Therefore, the present invention is particularly suitable for use in a receiver for receiving a mobile TV broadcast in which a wide band from a low frequency to a high frequency is used and a moving speed is low. Good reception is possible regardless of the channel and moving speed.

  Since the latest signal level value is calculated by adding the weight of the past signal level value, the amount of variation taking into account the past history is calculated. Further, since the variance value obtained by the root mean square of the five acquired signal level values is used as the fluctuation amount, the variation amount of the acquired signal level can be detected with high accuracy. In other words, the length of the region with small variation can be detected with high accuracy.

  Further, since the determination is made at the peak portion of the mountain where the signal level is high, it is difficult to be influenced by noise and the like, and even when the signal level of the input TV broadcast wave is small, the fading frequency can be detected with high accuracy.

  According to the inventors' experiment, it was confirmed that the fading frequency can be estimated accurately under the following conditions. Specifically, assuming that the interval for acquiring the signal level value is 1 millisecond, the amount of variation is calculated from 10 (n = 10) signal level values, and in order to determine the fading frequency, 100 variation values (m = 100) was used to estimate the fading frequency, and the fading frequency could be detected with high accuracy. In this case, the determination time is about 110 milliseconds.

  In this embodiment, the degree of dispersion is calculated by the mean square of the signal level values, but other weighted averages may be used for this. Further, the fading frequency may be estimated from the number of times of passing through a threshold value within a unit time, the signal level value in the unit time, and the average of the differential values.

  Next, fading correction step 93b and fading correction step 99b will be described in detail with reference to the drawings. FIG. 8 is a flowchart of the fading correction step in the present embodiment. In FIG. 8, a first channel determination step 125 is performed. In this channel determination step 125, the selection signal input from the input key 67 is compared with the selection signal stored in the memory to determine whether or not the desired reception channel has been changed. If the channel is not changed, the count value detected in the fading detection step 93a is output as it is. On the other hand, when it is determined in the channel determination step 125 that the channel has been changed, a correction step 126 is performed.

  Here, in the channel determination step 125, when the channel difference can substantially ignore the influence on the fading frequency, such as when the reception frequency before and after the channel change is close, the channel is not changed. judge. Therefore, in the channel determination step 125, the number of channel changes before and after the channel change is compared with a predetermined threshold value. If the number of channel changes before and after the channel change is equal to or greater than a predetermined value, it is determined that the channel has been changed, and a correction step 126 is performed.

  On the other hand, when the channel change before and after the channel change is less than a predetermined value, it is determined that the channel has not been changed, and the count value before the channel change is maintained and output. In this case, the data acquired before the change is reset at the reset step 127. By doing so, the count value before the channel change is maintained until the fading based on the level value acquired after the channel change is confirmed. In this way, fading can be specified quickly because the correction step 126 is not performed.

  In the channel determination step 125 in this embodiment, when the number of channels before and after the change is within 20 channels, it is determined that there is no channel change.

  Here, when the reception channel (frequency) becomes low, the wavelength becomes long and the fading frequency becomes low. Conversely, when the reception channel (frequency) becomes higher, the wavelength becomes longer and the fading frequency becomes higher. Therefore, in the correction step 126, when the reception channel is changed from a low channel to a high channel (in the direction of increasing the frequency), the count value is decreased. Conversely, when the reception channel is changed from a high channel to a low channel (in the direction of decreasing frequency), the count value is increased. In other words, when the frequency of the received channel is changed in a direction in which the frequency is increased, the fading degree is corrected so that the fading degree is increased. When the frequency is changed in a direction in which the frequency is decreased, the fading degree is reduced. This is a correction.

  Therefore, the memory 22 stores a correspondence table between the selection signal and the count value. In the fading correction step 126, the count value counted in the fading detection step 93a is corrected and output according to the difference between the channels (frequency) before and after the change based on this table.

  A reset step 127 is provided after the correction step 126. In the reset step 127, the signal level value 113 or the signal level value 121, the fluctuation amount 114 or the fluctuation amount 122 stored in the memory 22 is deleted. In this way, once the data before the channel change is erased, the fading frequency after the channel change is detected by the value obtained after the channel change. Therefore, the accuracy of the fading frequency detected after the channel change is increased.

  Further, fading detection steps 93a and 99a and fading correction steps 93b and 99b in the present embodiment may be used in search reception. The so-called search reception is a case where the reception channels are sequentially changed and received one by one. In this case, the channel is changed when the predetermined number of channels is increased or decreased from the search start channel. Judge as. In this case, in the channel determination step 125, the difference between the search start channel and the current search channel is compared with a predetermined value. However, if the current search channel exceeds a predetermined value and it is determined in the channel determination step 125 that the channel has been changed, the difference between the channel determined to have been changed and the current search channel is calculated. Compare with a predetermined value. As a result, fading can be quickly identified even during a search.

  In the present embodiment, the outputs of the detector 55a and the detector 55b are supplied to the control circuit 65, but this may be supplied from the A / D converter 56a and the A / D converter 56b. In this case, since it is not necessary to separately perform A / D conversion, it is not necessary to separately provide an A / D converter in the integrated circuit constituting the control circuit 65. Therefore, the integrated circuit constituting the control circuit 65 can be reduced in size, and the high frequency receiver 51 can be reduced in size.

  At this time, if the sampling frequency of the A / D converter 56a and the A / D converter 56b is the same as the frequency of the signal output from the receivers 52 and 53, the A / D converter 56a and the A / D converter 56b can also be used as the detector 55a and the detector 55b. In this case, since the detector 55a and the detector 55b are not required, the high-frequency receiving device 51 can be reduced in size and price.

  In general, a gain control amplifier (not shown) is inserted between the input terminal 54a and the detector 55a of the demodulation circuit 54 and between the input terminal 54b and the detector 55b, and these gain control amplifiers. An AGC circuit is inserted between each control terminal and the detector 55a or 55b. The control circuit 65 may be supplied with the output signal of this AGC circuit. In this case, unnecessary high-frequency noise is cut by the low-pass filter provided in the AGC circuit, so that erroneous determination due to noise is less likely to occur.

(Embodiment 2)
Hereinafter, the present embodiment will be described with reference to the drawings. FIG. 9 is a block diagram of high-frequency receiving apparatus 131 in the present embodiment. In FIG. 9, the TV broadcast signal input to the antenna 4 is supplied to the input terminal 131 a of the high frequency receiving device 131. The TV broadcast signal supplied to the input terminal 131a is supplied to the variable gain amplifier 132 and amplified to a level corresponding to the control signal supplied to the gain control terminal 132a.

  In the mixer 133, the output of the variable gain amplifier 132 is supplied to one input, and the signal of the local oscillator 134 is supplied to the other input. Then, the input TV broadcast signal and the signal of the local oscillator 134 are mixed and converted to a specified frequency signal, and in this embodiment, converted to an intermediate frequency of 4 MHz. Although the intermediate frequency in this embodiment is 4 MHz, this may be determined as appropriate according to the input frequency or the like. The mixer 133 may be a mixer that performs direct I and Q conversion (so-called direct conversion).

  An AGC circuit 135 is inserted between the output of the mixer 133 and the gain control terminal 132a. The AGC circuit 135 detects the level of the signal output from the variable gain amplifier 132. When the detected signal level is equal to or higher than a limit level (so-called strong electrolysis) that saturates and generates distortion in the mixer 133, the AGC circuit 135 reduces the gain of the variable gain amplifier 132. That is, the variable gain amplifier 132 attenuates and outputs a signal above the limit level to a constant level signal below the limit level. Therefore, the mixer 133 is less likely to be distorted.

  The output of the mixer 133 is supplied to the filter 136 to suppress unnecessary signals other than the received channel. In the present embodiment, the filter 136 is a band-pass filter having a frequency of 4 MHz as the center and a pass band of 6 MHz. When a mixer that performs direct conversion is used as the mixer 133, a low-pass filter is used as the filter 136.

  The output of the filter 136 is supplied to the demodulation circuit 138 via the variable gain amplifier 137. In this demodulation circuit 138, the input signal is demodulated and error-corrected, and output from the output terminal 131b.

  Here, the detector 139 is supplied with the output of the variable gain amplifier 137 and detects the signal level of the signal output from the variable gain amplifier 137. A gain control circuit 140 is inserted between the detector 139 and the gain control terminal 137a of the variable gain amplifier 137, and a direct current corresponding to the difference between the level detected by the detector 139 and a predetermined level value. Output a signal. For this purpose, the gain control circuit 140 includes a comparator that outputs a voltage corresponding to the difference between the output of the detector 139 and the reference voltage, and a low-pass filter (not shown) supplied with the output of the comparator. It is out.

  Here, the output of the filter 136 is also supplied to the fading detector 151, and the fading frequency of the output signal of the filter 136 is detected. The fading detector 151 includes a detector 152 to which the output of the filter 136 is supplied, an A / D converter 153 to which the output of the detector 152 is supplied, and the A / D converter 153 and a gain control circuit. And a control circuit 154 provided between the control circuit 154 and a memory 155 connected to the control circuit 154.

  Note that the fading frequency is detected by the control circuit 154 in the present embodiment using the same detection method as the fading detection step 93a, fading detection step 99a, fading correction step 93b, and fading correction step 99b in the first embodiment.

  The output of the fading detector 151 is connected to the gain control circuit 140, and the time constant of the gain control circuit 140 is switched. For example, the switching of the time constant is performed by switching the capacitance of the capacitor constituting the low-pass filter of the gain control circuit 140 in the gain control circuit 140, or preparing a plurality of filters having different time constants in advance and switching the filter itself. Done in

  Here, the relationship between the time constant of the gain control circuit 140 and the reception quality will be described. Here, the C / N value is used as a representative of the reception quality. FIG. 10 is a relationship diagram showing the relationship between the fading frequency and the required C / N value of the high-frequency receiving device 131. In FIG. 10, the horizontal axis 161 is the fading frequency, and the vertical axis 162 is the required C / N value. The characteristic curve 163, the characteristic curve 164, and the characteristic curve 165 are required C / N value curves, and the time constant of the gain control circuit 140 decreases in the order of the characteristic curve 163, the characteristic curve 164, and the characteristic curve 165.

  According to the experiments by the inventors, there is the following relationship between the fading frequency and the required C / N value. Specifically, the characteristic curve 165 has the smallest required C / N value in a region where the fading frequency is lower than the frequency 166 (low-speed moving region 167). Between the frequency 166 and the frequency 168 (medium / low speed movement region 169), the characteristic curve 163 has the smallest required C / N value. The characteristic curve 164 has the smallest required C / N value between the frequency 168 and the frequency 170 (medium / high speed moving region 171). The characteristic curve 163 has the smallest required C / N value at a frequency of 170 or higher (high-speed moving region 172).

  In the experiments by the inventors, the frequency 166 was about 20 Hz, the frequency 168 was about 35 Hz, and the frequency 170 was about 65 Hz. It has also been confirmed that the required C / N value increases in the frequency of TV broadcast waves particularly at a fading frequency of 10 Hz or less and 50 Hz or more.

  The reason why the relationship between the fading frequency and the time constant becomes like this is not clear, but the inventors believe that the reason is as follows. Since the trough of the signal due to fading is improved, the cutoff frequency of the low-pass filter of the gain control circuit 140 should be equal to or higher than the fading frequency. Therefore, basically, the time constant should be reduced according to the fading frequency. However, when the time constant is small, it is considered that the stability of the control loop is lowered due to overshoot or delay at a high fading frequency. Therefore, it is considered that the stability of the control loop is increased and the required C / N value is decreased by making the time constant larger than that of the medium / high speed moving region 171.

  On the other hand, in the low-speed moving region 167, the reception quality is greatly deteriorated due to the long time of the valley portion. Therefore, the level correction in this valley portion is necessary. Here, the fading frequency in the low-speed movement is small, but the level suddenly drops in the valley portion, and the level change (slope) becomes large. Therefore, if the time constant is large, the control loop cannot follow sudden level fluctuations. Therefore, by reducing the time constant, the followability of the control loop in the valley is improved, and the required C / N value is reduced. I think it was possible.

  According to the experiments by the inventors, the required C / N value is smaller when the time constant in the low speed movement region 167 is smaller than the time constant in the medium / low speed movement region 169. This is because the change in the valley portion is smaller than that in the medium / low speed movement region 169, and even if the time constant is made smaller than that in the medium / low speed movement region 169, the stability of the control loop is deteriorated due to overshoot or the like. This is thought to be difficult.

  As described above, since the appropriate time constant varies depending on the fading frequency, the control circuit 154 switches the time constant according to the count value counted in the counting step 105. In the present embodiment, a memory 155 is connected to the control circuit 154, and a correspondence table between count values and set values of time constants is stored in the memory 155. As a result, a time constant suitable for the fading frequency can be obtained, so that the required C / N value of the high-frequency receiving device 131 can be reduced. Therefore, fading can be improved satisfactorily. In addition, since the count value after the channel change is calculated by correcting the count value before the channel change using the selection signal when the channel is changed, the time constant can be set quickly even when the channel is changed. Therefore, the reception quality can be improved quickly.

  If the time constant setting values corresponding to the reception channel and the count value are stored in the memory 155, the time constant setting values after the channel change can be directly output in the fading correction steps 93b and 99b. is there.

  Note that, in the fluctuation amount calculation step 104, the fluctuation amount is calculated based on the variance value in consideration of the past signal level history, so that the fluctuation of the signal level can be detected with high accuracy. Therefore, the count value in the counting step 105 can accurately represent the length of the region where the slope near the maximum value is small. Thereby, since a fading frequency can be estimated using a count value, detection time can be shortened with respect to a low fading frequency. Therefore, the required C / N value can be improved in a short time even for a fading frequency such as 10 Hz or less where the required C / N value deteriorates, and the deterioration of reception quality due to fading can be improved quickly.

  Further, in the present embodiment, since the signal from which unnecessary signals have been removed by the filter 136 is input to the detector 152, the detection by the detector 152 can reduce the influence on the interference signal and the like. Accordingly, the level detection accuracy of the detector 152 is improved, and control can be performed with high accuracy.

  Furthermore, by providing a variable gain amplifier 132 that operates in a strong electric field upstream of the detector 152, the detector 152 does not detect fading in the strong electric field region. This is because the signal level is high in a strong electric field, and the reception quality is unlikely to deteriorate even if fading occurs. On the other hand, if the time constant is reduced under a strong electric field, the influence of overshoot is likely to occur, and the stability of the control loop deteriorates. Therefore, since the detector 152 cannot detect fading under a strong electric field, the time constant is not switched under the strong electric field, so that the control loop is stabilized. In addition, since the frequency characteristic and the input dynamic range can be reduced for the detector 152, an inexpensive detector can be used. Therefore, a low-priced high frequency receiver 131 can be realized.

  In the present embodiment, a detector 152 is provided to estimate fading. However, with the following configuration, the detector 152 can be omitted, and the high-frequency receiver 131 can be reduced in size and price.

  The first is to make the A / D converter detect the signal by making the intermediate frequency and the sampling frequency of the A / D converter 153 the same. In this way, the A / D converter 153 can be used as the detector 152, and the detector 152 can be dispensed with. For example, in this embodiment, if the sampling frequency of the A / D converter 153 is 4 MHz, the detector 152 can be omitted.

  In addition, as shown in FIG. 11, the output of the detector 139 may be supplied to the A / D converter 153 so that the detector 152 is not necessary.

  Here, the demodulation circuit 138 includes a variable gain amplifier 202, an A / D converter 203, a demodulator 204, and an AGC circuit 205. The AGC circuit 205 is inserted between the A / D converter 203 and the gain control terminal of the variable gain amplifier 202 to constitute a feedback control loop. The output of the control circuit 154 is supplied to the AGC circuit 205 instead of the gain control circuit 140. The time constant of the AGC circuit 205 is switched according to the fading frequency. In this case, the detector 152 is not necessary, so that the high-frequency receiving device 131 can be reduced in size and price can be reduced. In this case, the time constant of the variable gain amplifier 202 is fixed.

  The fading estimation device for multi-channel reception according to the present invention has an effect that a fading frequency can be quickly detected when a reception channel is switched, and particularly when used for a high-frequency receiving device mounted on a mobile phone or the like used while moving. Useful.

Circuit block diagram of high-frequency receiver using fading detection means in the present embodiment (A) Relationship between time and AGC voltage when traveling at a constant speed at a low speed, (b) Relationship diagram between time and AGC voltage when traveling at a constant speed at a high speed Same as above, relationship diagram between fading frequency and required C / N value Operation flow chart of control circuit Same as above, flowchart of fading detection step (A) Sampling explanatory diagram when fading frequency is low, (b) Same as above, explanatory diagram of fluctuation amount calculation method (A) Sampling explanatory diagram when fading frequency is high, (b) Same as above, explanatory diagram of fluctuation amount calculation method Same as above, flowchart of fading correction step Circuit block diagram of the high-frequency receiving device according to the second embodiment of the present invention Same as above, relationship diagram between fading frequency and required C / N value Circuit block diagram of the high-frequency receiver Explanatory diagram showing how TV broadcasts are received while moving Circuit block diagram of conventional high-frequency receiver Explanation of detection method

Explanation of symbols

52 receiver 53 receiver 93a fading detection step 93b fading correction step

Claims (14)

A high-frequency signal having a plurality of channels including at least a first channel and a second channel having a frequency lower than the first channel is supplied, and a selection signal for selecting a desired channel from the high-frequency signals is provided. And a fading detection means to which the output of the channel selection means is connected to detect the fading degree of the output signal output from the channel selection means. When the output of the fading detection means is supplied and the fading correction means for supplying the selection signal is provided at the other input, and the selection signal is changed from the first channel to the second channel The fading correction means outputs the output of the fading detection means in the first channel to the first and second channels. A plurality of channels receiving fading estimation apparatus for correcting a direction of the fading degree is reduced according to the difference Le. The fading detection means is supplied with the output signal of the channel selection means, a sampling means for obtaining a predetermined number of level values during a predetermined time, and a plurality of continuous acquisitions by this sampling means. The fluctuation amount detecting means for detecting the fluctuation amount of each level value, the comparison means for comparing the fluctuation amount detected by the fluctuation amount detection means with a predetermined threshold, and the output of the comparison means are supplied. Counting means, and the counting means counts the number of times that the fluctuation amount is determined to be smaller than the threshold during the predetermined time, and outputs the counted number to the fading correction means, and the fading correction means When the selection signal is changed from the first channel to the second channel, the count values counted by the counting means in the first channel are changed to the first and second channels. A plurality of channels receiving fading estimation apparatus according to claim 1, fading degree depending on the difference between the channel is corrected in a direction to be smaller. The multi-channel according to claim 2, wherein the fluctuation amount detecting means calculates a plurality of absolute values of differences between two consecutively acquired level values and detects an average value of the absolute values of the differences as a fluctuation amount. Fading estimation apparatus for reception. The fading estimation apparatus for multi-channel reception according to claim 2, wherein the fluctuation amount detecting means detects a variance value of a plurality of level values continuously acquired by the sampling means as the fluctuation amount. The fading estimation apparatus for multi-channel reception according to claim 4, wherein the fluctuation amount detection means uses a weighted average value of a plurality of sampled level values as a variance value. The fading estimation apparatus for multi-channel reception according to claim 4, wherein the fluctuation amount detection means uses a mean square value of a plurality of sampled level values as a variance value. A fading estimation apparatus for multi-channel reception according to claim 1, a demodulation circuit to which an output signal of a channel selection means of the fading estimation apparatus for multi-channel reception is supplied, and either one of the channel selection means or the demodulation circuit A gain variable amplifier provided with a signal selected and received by the channel selection means, a detector supplied with the output of the variable gain amplifier, and an output of the detector supplied to one input A gain control circuit connected to the gain control terminal of the variable gain amplifier, the output of the multi-channel reception fading estimation device being supplied to the other input, and the gain control circuit In the high-frequency receiver that switches the time constant of the variable gain amplifier according to the output of the fading detection means, the reception channel of the channel selection means is If the 1 is changed to the second channel, the gain control circuit, high-frequency receiver for switching the time constant of the gain control circuit by an output of the fading compensation means. A fading estimation device for multi-channel reception according to claim 1, a demodulation circuit to which an output signal of channel selection means of the fading estimation device for multi-channel reception is supplied, an output of fading detection means, and the channel selection means A power supply circuit inserted between them, the channel selection means is composed of a plurality of receivers, and the power supply circuit turns on and off the receiver according to the output of the fading detection means, In the diversity high-frequency receiving apparatus that selectively combines the outputs of the receivers in the demodulation circuit, when the reception channel of the channel selection means is changed from the first channel to the second channel, the power supply circuit A high-frequency receiver that turns on and off the receiver according to the output of a fading correction means. Acquire a predetermined number of received signal levels at predetermined time intervals, store the acquired level values in a memory, and then perform fading from a plurality of level values stored in the memory. In the fading estimation method for multi-channel reception to be estimated, when the reception channel is changed, the fading in the reception channel after the change is made from the fading degree estimated before the change of the reception channel and the selection signal for switching the channel. A multi-channel reception fading estimation method for estimating the degree. The fading degree is estimated by calculating the fluctuation amount of a plurality of continuous level values stored in the memory, and then determining that the fluctuation amount is smaller than a predetermined threshold during the predetermined time. The fading estimation method for multi-channel reception according to claim 9, wherein the estimation is performed by counting the number of times received. The variation amount at a plurality of consecutive level values is calculated as a plurality of absolute values of differences between two consecutively acquired level values, and is defined as an average value of the absolute values of the differences. Fading estimation method for multi-channel reception. The fading estimation method for multi-channel reception according to claim 10, wherein the fluctuation amount is a variance value of a plurality of level values acquired successively. The fading estimation method for multi-channel reception according to claim 12, wherein the variance value is calculated using a weighted average. The fading estimation method for multi-channel reception according to claim 12, wherein the variance value is calculated using a mean square.

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