JP4657223B2 - Modulation error calculation device and method, digital broadcast receiver, and digital broadcast wave measurement device - Google Patents

Description

  The present invention relates to a modulation error measuring apparatus, a digital broadcast receiver, and a digital broadcast wave measuring apparatus for measuring a modulation error such as a modulation error ratio (MER) of a digital modulation signal. The digital broadcast wave measuring device is mainly used by receiver / transmitter development manufacturers and broadcasters for the purpose of evaluating terrestrial digital broadcast receivers and confirming reception areas. MER, C / N, BER measurement, electric field strength measurement, propagation delay profile measurement, etc.

  In digital modulation, basic parameters of a carrier wave are changed in several stages, and one piece of information of a digital signal is assigned to each of several stages. For example, when the parameter to be changed in several steps is the phase of the carrier wave, if the digital signal to be transmitted is a binary value of “0” and “1”, as shown in FIG. In phase 0, the digital signal “1” is assigned to phase π. If the digital signal to be transmitted is four values from “0” to “3”, as shown in FIG. 2, the signal “0” is in phase π / 4, the signal “1” is in phase 3π / 4, and the signal “ 2 ”is assigned to phase 5π / 4 and signal“ 3 ”is assigned to phase 7π / 4.

  In the demodulation, the value of the parameter of the carrier wave is recognized and a digital value corresponding to this is obtained. The digital multilevel modulation method includes digital frequency modulation (FSK: Frequency Shift Keying) that assigns digital values to the high and low frequencies of the carrier, and digital amplitude modulation (ASK: Amplitudey Shift Keying) that assigns digital values to the high and low frequencies of the carrier. System, digital phase modulation (PSK: Phase Shift Keying) that assigns digital values to the phase of the carrier, and quadrature amplitude modulation (QAM: assigns digital values to both amplitude and phase by using two orthogonal carriers) Quadraturc Amplitude Modulation) method.

  The modulation error ratio (MER) is an index representing the reception performance in a circuit that receives and demodulates a digital signal subjected to digital multilevel modulation, and can be obtained by demodulating to a demapping format. Modulation error ratio is proportional to BER and C / N, so it can be used for diversity synthesis in diversity digital broadcasting receivers with multiple receiver / demodulators, as well as performance evaluation of receiver / demodulators. it can.

  The modulation error ratio is widely known as an index for grasping the transmission state of a digital multi-level modulated signal. For example, Japanese Patent Application Laid-Open No. 2004-140697 discloses a calculation method thereof.

  A conventional method for calculating the modulation error ratio will be described with reference to FIG. In FIG. 3, a black circle represents an ideal signal point of QPSK (Quandrature Phase Shift Keying) in carrier n, and a white circle represents received data in carrier n. For all valid data carriers of the received signal within a predetermined period, the distance between the position on the IQ plane of the data obtained by demodulation and the position on the IQ plane of the ideal signal point closest to the data Zn. Further, the size of the ideal signal point closest to the data obtained by demodulation on the IQ plane, that is, the position of the ideal signal point closest to the data obtained by demodulation on the IQ plane and the IQ plane. The distance from the coordinate origin (0, 0) is Dn.

  When the sum of Dn in the target carrier is ΣDn and the sum of Zn in the target carrier is ΣZn, the modulation error ratio (MER) in dB is expressed by the following equation (1).

MER (dB) = 10 * log ₁₀ (ΣDn / ΣZn) (1)
JP 2004-140697 A

  However, when the MER is calculated by the above method, as shown in FIG. 4, even if the reception data corresponding to the upper right ideal signal point at the time of transmission deteriorates as shown in FIG. When the variation becomes large, there may occur a case where an ideal signal point different from that at the time of transmission is erroneously determined as the ideal signal point closest to the data. Then, an error occurs in the ideal signal point closest to the data, and the error Z is also calculated in order to calculate the distance Z between the erroneously determined ideal signal point and the data, and the MER obtained thereby is calculated. The value of becomes less reliable as an index representing performance, and the proportional relationship with C / N and BER also does not hold.

  The white triangle (Δ) in FIG. 5 indicates the relationship between MER and C / N when MER is calculated by the above method. As shown by the broken line, it can be seen that when C / N is small, MER is not in a proportional relationship with C / N.

  An object of the present invention is to provide a modulation error calculation apparatus and method, a digital broadcast receiver, and a digital broadcast wave measuring apparatus that can calculate a modulation error with high reliability even when the reception state deteriorates. .

  According to the first aspect of the present invention, in the modulation error calculation apparatus, a multilevel digital modulation signal is received and demodulated, and the position of the received data on each IQ data plane on the IQ plane and the received data First means for obtaining a distance Z between the nearest ideal signal point and a position on the IQ plane, for each of the effective data carriers, an absolute value of the I-axis component and an absolute value of the Q-axis component of the received data, respectively. Second means for determining that the carrier is a modulation error calculation target carrier only when the absolute value of the I-axis component and the Q-axis component of the ideal signal point closest to the received data is larger, and a predetermined period The sum of distances Z calculated by the first means for the effective data carriers determined by the second means among all the effective data carriers in Based on, characterized in that it comprises a third means for calculating a modulation error.

  According to a second aspect of the present invention, in the modulation error calculating apparatus, a multi-value digital modulation signal is received and demodulated, and the position of the received data on each IQ data plane on the IQ plane and the received data A first means for obtaining a distance Z between the closest ideal signal point and the position on the IQ plane, a distance between the ideal signal point closest to the received data on the IQ plane and the origin of the IQ plane Second means for obtaining D, for each effective data carrier, the absolute value of the I-axis component of the ideal signal point closest to the received data is the absolute value of the I-axis component and the absolute value of the Q-axis component of the received data. Only when the value and the absolute value of the Q-axis component are larger than the third means for determining the carrier as a carrier for calculating the modulation error, and among the all valid data carriers within a predetermined period, the third means The modulation error is calculated based on the sum of the distances Z calculated by the first means and the sum of the distances D calculated by the second means for the effective data carrier determined to be a calculation target. The fourth means is provided.

  According to a third aspect of the present invention, in the modulation error calculation method, a multilevel digital modulation signal is received and demodulated, the position of the received data on each IQ data plane on the IQ plane, and the received data A first step for obtaining a distance Z between the nearest ideal signal point and a position on the IQ plane, for each of the effective data carriers, an absolute value of the I-axis component and an absolute value of the Q-axis component of the received data, respectively. A second step of determining that the carrier is a modulation error calculation target carrier only when the absolute value of the I-axis component and the Q-axis component of the ideal signal point closest to the received data is greater than the absolute value, and a predetermined period Of the valid data carriers, the valid data carriers determined to be calculated by the second step are calculated by the first step. Based on the sum of that distance Z, characterized in that it comprises a third step of calculating a modulation error.

  According to a fourth aspect of the present invention, in the modulation error calculation method, a multilevel digital modulation signal is received and demodulated, and the position of the received data on each IQ valid data carrier on the IQ plane, and the received data A first step of obtaining a distance Z between the closest ideal signal point and a position on the IQ plane; a distance between the ideal signal point closest to the received data on the IQ plane and the origin of the IQ plane; The second step of obtaining D, for each effective data carrier, the absolute value of the I-axis component of the ideal signal point closest to the received data is the absolute value of the I-axis component and the Q-axis component of the received data. The third step of determining the carrier as a carrier for which a modulation error is to be calculated only when the value and the absolute value of the Q-axis component are larger, and among all valid data carriers within a predetermined period, Based on the sum of the distances Z calculated by the first step and the sum of the distances D calculated by the second step for the effective data carrier determined to be calculated by the third step, the modulation error The fourth step of calculating is provided.

  According to a fifth aspect of the present invention, a digital broadcast receiver includes the modulation error calculating device according to the first or second aspect.

  According to a sixth aspect of the present invention, a digital broadcast wave measuring device includes the modulation error calculating device according to the first or second aspect.

  According to a seventh aspect of the present invention, there is provided a diversity-type digital broadcast receiver having a plurality of branches each having a receiving / demodulating unit, and each branch includes the modulation error calculating device according to the first or second aspect. And means for comparing the performance of each branch using the modulation error measured by the modulation error calculation device in each branch, and means for determining the branch to be operated in the single reception mode based on the comparison result of the performance comparison means It is characterized by having.

  According to the first to fourth aspects of the invention, a highly reliable modulation error can be calculated even when the reception state is deteriorated.

  According to the invention described in claim 2 or 4, even if the distance D between the position of the ideal signal point closest to the received data on the IQ plane and the origin of the IQ plane varies for each carrier. The modulation error can be calculated accurately.

  According to the fifth aspect of the present invention, a digital broadcast receiver capable of calculating a highly reliable modulation error even when the reception state is deteriorated can be obtained.

  According to the sixth aspect of the invention, it is possible to obtain a digital broadcast wave measuring apparatus that can calculate a modulation error with high reliability even when the reception state is deteriorated.

  According to the seventh aspect of the present invention, when switching from the diversity reception mode to the single mode reception mode, it is possible to more accurately select a branch to be operated in the single mode reception mode than using the conventional MER.

  Embodiments of the present invention will be described below with reference to the drawings.

[1] Description of the concept of the present invention In the conventional method, when the reception state deteriorates and the variation in data from the ideal signal point becomes large, a signal point different from that at the time of transmission is changed to the ideal signal point closest to the data. There are cases where it is erroneously determined that there is. Such erroneous determination is a phenomenon that easily occurs between ideal signal points adjacent in the I-axis direction or the Q-axis direction.

  The white circles in FIG. 6 indicate QPSK (Quandrature Phase Shift Keying) ideal signal points, and the black circles and white circles in FIG. 7 indicate 16 QAM ideal signal points. The white circles in FIG. 7 indicate the ideal signal points having the maximum absolute value for both IQs among the 16QAM ideal signal points.

  In a modulation method in which ideal signal points are arranged at equal intervals on the IQ plane, such as QPSK and 16QAM, there are four ideal signal points P1 to P4 having the maximum absolute value for both the I coordinate value and the Q coordinate value. is there.

  As indicated by the hatched portion in FIGS. 6 and 7, for each ideal signal point P1 to P4, the absolute value of each of the I coordinate value and the Q coordinate value is the I coordinate value and Q coordinate value of the ideal signal point. For data in a region larger than the absolute value, the distance from other ideal signal points is larger than the distance from the ideal signal point, so that erroneous determination is less likely to occur. In the present invention, a highly reliable modulation error ratio is calculated by using only the carriers corresponding to these areas among the effective data carriers as the calculation target data of the modulation error ratio.

[2] Description of the configuration of a digital broadcast receiver having a modulation error ratio calculation circuit

  FIG. 8 shows an electrical configuration of a digital broadcast receiver provided with a modulation error ratio calculation circuit.

  The tuner 11 receives an RF signal modulated by an OFDM (Orthogonal Frequency Divisional Multiplexing) modulation method via the antenna 10 and down-converts it into a baseband signal. The AGC unit 12 sets the received signal obtained by the tuner 11 to a desired power value according to the control signal generated based on the power of the signal measured by the demodulator 16 at the subsequent stage.

  The A / D conversion unit 13 converts the analog signal output from the AGC unit 12 into a digital signal, and uses a Hilbert transform or the like to generate a real axis (I axis) component signal and an imaginary axis (Q axis) component. Signal. The synchronization unit 14 performs synchronization processing, and the FFT unit 15 performs high-speed Fourier transform, whereby the time axis data obtained by the A / D conversion unit 13 is converted into frequency data.

  The demodulator 16 performs various demodulation processes such as differential demodulation corresponding to the modulation method. The transmission path estimation unit 17 estimates transmission path characteristics. The equalization unit 18 obtains an I-axis component and a Q-axis component of the received data and a transfer function by equalization processing.

  The demapping unit 19 obtains the position of all ideal signal points on the IQ plane based on the transfer function, and compares this with the received data to obtain the ideal signal point closest to the received data (Viterbi hard decision processing). . Further, the demapping unit 19 obtains the values converted into a format that can be subjected to the Viterbi soft decision processing by obtaining the directions and sizes of the received data viewed from the ideal signal point in the I and Q axis directions. Viterbi soft decision processing refers to processing for obtaining the distance between the ideal signal point closest to the received data and the received data.

  The deinterleaving unit 20 performs processing necessary for digital demodulation of the OFDM signal, such as frequency deinterleaving processing, time deinterleaving processing, energy despreading processing, and Viterbi soft decision processing.

  Data obtained by the demapping unit 19 is sent to the modulation error ratio calculation circuit 50. The modulation error ratio calculation circuit 50 includes a D calculation unit 51, a Z calculation unit 52, a modulation error ratio calculation target carrier determination unit 53, a ΣD calculation unit 54, a ΣZ calculation unit 55, and a MER calculation unit 56.

  Based on the data obtained by the demapping unit 19, the D calculation unit 51 determines the position of the ideal signal point closest to the received data on the IQ plane and the coordinate origin (0 on the IQ plane) for each valid data carrier. , 0) is calculated. The distance D calculated by the D calculation unit 51 is given to the ΣD calculation unit 54.

  For each valid data carrier, the Z calculator 52 determines the position of the received data on the IQ plane and the ideal signal point closest to the received data on the IQ plane based on the data obtained by the demapping unit 19. A distance Z to the position is calculated. The distance Z calculated by the Z calculating unit 52 is given to the ΣZ calculating unit 55.

  Based on the data obtained by the demapping unit 19 for each valid data carrier, the modulation error ratio calculation target carrier determination unit 53 determines that the absolute value of the I-axis component and the absolute value of the Q-axis component of the received data are It is determined whether or not a calculation target condition that the absolute value of the I coordinate value and the Q coordinate value of the ideal signal point closest to the data is greater than the absolute value is satisfied, and the determination results are used as the ΣD calculation unit 54 and the ΣZ calculation unit. 55.

  The ΣD calculation unit 54 cumulatively adds the distances D calculated for the carriers determined to satisfy the calculation target condition by the modulation error ratio calculation target carrier determination unit 53, and adds up the sum ΣD every predetermined time. Ask for. The ΣZ calculation unit 55 cumulatively adds the distance Z calculated for the carrier determined to satisfy the calculation target condition by the modulation error ratio calculation target carrier determination unit 53, and adds the sum ΣZ every predetermined time. Ask for.

  The MER calculation unit 56 is based on the following equation (2) based on ΣD calculated every predetermined time by the ΣD calculation unit 54 and ΣZ calculated every predetermined time by the ΣZ calculation unit 55 every predetermined time. The modulation error ratio (MER) in dB units is calculated.

MER (dB) = 10 * log ₁₀ (ΣD / ΣZ) (2)

  When MER is simply used as a performance index, the arithmetic circuit can be simplified by calculating a value that is not in dB units as shown in the following equation (3).

  MER = ΣD / ΣZ (3)

  In addition, when obtaining the equivalent C / N from the MER, it is only necessary to add about 2.3 dB to the MER in dB unit, so that the equivalent C / N is obtained and output as shown in the following equation (4). Also good. However, the value of 2.3 dB is a value that changes due to noise in the transmission line equivalent circuit of the demodulator.

  Equivalent C / N (dB) = MER (dB) +2.3 (dB) (4)

  The black triangles (）) in FIG. 5 indicate the relationship between MER and C / N when MER is calculated by the method according to this embodiment. It can be seen that even when C / N is small, MER maintains a proportional relationship with C / N.

  When the MER is calculated by the method of the present embodiment, the obtained MER has a proportional relationship with C / N and BER regardless of the reception state, so that C / N and BER need not be measured. Therefore, the reception performance can be known with higher accuracy than the conventional method.

  In the above embodiment, the modulation error ratio (MER) is calculated. However, a modulation error (for example, 1 / ΣZ) may be obtained based only on ΣZ and used as an index of performance.

  Embodiments in the case where the present invention is applied to a diversity type digital broadcast receiver will be described below.

  FIG. 9 shows an electrical configuration of a diversity type digital broadcast receiver.

  Reference numerals 101 and 201 denote antennas. A receiving / demodulating unit 102 on the branch A side connected to the antenna 101 includes the circuit from the tuner 11 to the demapping unit 19 in FIG. 8 and the modulation error ratio calculating circuit 50 in the first embodiment. A receiving / demodulating unit 202 on the branch B side connected to the antenna 201 includes the circuit from the tuner 11 to the demapping unit 19 in FIG. 8 and the modulation error ratio calculating circuit 50 in the first embodiment.

  Reference numeral 103 denotes a diversity combining unit that synthesizes and outputs the data demodulated by the receiving / demodulating unit 102 on the branch A side and the data demodulated by the receiving / demodulating unit 202 on the branch B side. And output. Reference numeral 104 denotes a demodulation unit that performs deinterleaving, Viterbi decoding, and the like on the symbols obtained by the diversity combining unit 103.

  Reference numeral 110 denotes a seamless switching control unit. The seamless switching control unit 110 includes a performance comparison unit 111 and a switching determination unit 112.

  The performance comparison unit 111 includes a MER calculated by the reception / demodulation unit 102 on the branch A side (MER calculated by the method of the first embodiment) and a MER (implementation) calculated by the reception / demodulation unit 202 on the branch B side. Based on MER calculated by the method of Example 1, the performances of both receiving / demodulating units are compared.

  The switching determination unit 112 selects either the single reception mode or the diver reception mode based on the BER (bit error rate) calculated by the Viterbi decoding unit in the demodulation unit 104. When the BER is smaller than the threshold, the single reception mode is selected, and when the BER is greater than or equal to the threshold, the diversity reception mode is selected. When the diversity reception mode is selected, both the reception / demodulation units 102 and 202 are operated, and the diversity combining unit 103 combines the data from both reception / demodulation units 102 and 202.

  When the single reception mode is selected, the branch side reception / demodulation unit of the reception / demodulation units 102 and 202 on the branch A side and B side, which is determined to have higher performance by the performance comparison unit 111, is operated. And the operation of the receiving / demodulating unit on the other branch side is stopped.

  FIG. 10 shows the operation of the digital broadcast receiver of FIG.

  First, the operation of the reception / demodulation unit of the stopped branch is turned on, and diversity reception combining is turned on (step S1). That is, both reception / demodulation units 102 and 202 are put into an operating state, and the diversity combining unit 103 is instructed to combine the data from both reception / demodulation units 102 and 202. In this case, diversity reception is performed.

  Next, it is determined whether or not switching from the diversity reception mode to the single reception mode has occurred (step S2). That is, in the diversity reception mode, the switching determination unit 112 determines whether the single reception mode is selected.

  If switching from the diversity reception mode to the single reception mode has not occurred, the process returns to step S1. When switching from the diversity reception mode to the single reception mode occurs, it is determined whether the performance of the branch A is higher than the performance of the branch B based on the determination result of the performance comparison unit 111 (step S3). If the performance of the branch A is high, the operation of the reception / demodulation unit 202 on the branch B side is stopped (step S4). Thereby, the single reception by the branch A is performed. Then, it is determined whether or not switching from the single reception mode to the diversity reception mode has occurred (step S5).

  If switching from the single reception mode to the diversity reception mode does not occur, the process returns to step S4. When the switching from the single reception mode to the diversity reception mode occurs, the process returns to step S1.

  If the performance of the branch B is high in step S3, the operation of the reception / demodulation unit 102 on the branch A side is stopped (step S6). Thereby, the single reception by the branch B is performed. Then, it is determined whether or not switching from the single reception mode to the diversity reception mode has occurred (step S7).

  If switching from the single reception mode to the diversity reception mode does not occur, the process returns to step S6. When the switching from the single reception mode to the diversity reception mode occurs, the process returns to step S1.

  In the second embodiment, the MER obtained by the receiving / demodulating units 102 and 202 on the branch A side and the B side is a highly accurate MER as in the first embodiment. Therefore, MER can be used to compare the performance of branch A and branch B without using C / N or BER. As a result, it is sufficient to provide only one demodulator 104 that performs deinterleaving, Viterbi decoding, etc. necessary for calculating C / N and BER, and the configuration is simplified.

  Although the receiving / demodulating units 102 and 202 calculate the modulation error ratio (MER), the modulation error (for example, 1 / ΣZ) is calculated based only on ΣZ and is given to the performance comparing unit 111. May be.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

When the parameter to be changed in several steps is the phase of the carrier wave and the digital signal to be transmitted is a binary value of “0” and “1”, it is a schematic diagram showing the phase to which each value is assigned. When the parameter to be changed in several stages is the phase of the carrier wave and the digital signal to be transmitted has four values “0” to “3”, it is a schematic diagram showing the phase to which each value is assigned. It is a schematic diagram for demonstrating the conventional calculation method of a modulation error ratio. It is a schematic diagram for demonstrating the problem of the conventional method. It is a graph which shows the relationship between MER and C / N at the time of calculating MER by the conventional method, and the relationship between MER and C / N at the time of calculating MER by this invention method. It is a schematic diagram which shows the ideal signal point of QPSK. It is a schematic diagram which shows the ideal signal point of 16QAM. It is a block diagram which shows the electrical constitution of the digital broadcast receiver provided with the modulation error ratio calculation circuit. It is a block diagram which shows the electrical constitution of the digital broadcasting receiver of a diversity system. 10 is a flowchart showing an operation of the digital broadcast receiver of FIG. 9.

Explanation of symbols

DESCRIPTION OF SYMBOLS 50 Modulation error ratio calculation circuit 51 D calculation part 52 Z calculation part 53 Modulation error ratio calculation object carrier determination part 54 ΣD calculation part 55 ΣZ calculation part 56 MER calculation part 102,202 Reception / demodulation part 110 Seamless switching control part 111 Performance comparison Part 112 switching judgment part

Claims (7)

Receives and demodulates a multi-value digital modulation signal, and between the position on the IQ plane of the received data in each effective data carrier of the received signal and the position on the IQ plane of the ideal signal point closest to the received data A first means for determining the distance Z of
For each effective data carrier, the absolute value of the I-axis component and the absolute value of the Q-axis component of the ideal signal point closest to the received data are the absolute values of the I-axis component and the Q-axis component of the received data. The second means for determining that the carrier is a carrier for calculating the modulation error only when the carrier is larger than the value, and the effective that is determined to be the target for calculation by the second means among all the valid data carriers within the predetermined period. A third means for calculating a modulation error based on the sum of the distances Z calculated by the first means for the data carrier;
A modulation error calculation device comprising: Receives and demodulates a multi-value digital modulation signal, and between the position on the IQ plane of the received data in each effective data carrier of the received signal and the position on the IQ plane of the ideal signal point closest to the received data A first means for determining the distance Z of
A second means for obtaining a distance D between the position of the ideal signal point closest to the received data on the IQ plane and the origin of the IQ plane;
For each effective data carrier, the absolute value of the I-axis component and the absolute value of the Q-axis component of the ideal signal point closest to the received data are the absolute values of the I-axis component and the Q-axis component of the received data. The third means for determining that the carrier is a carrier for which a modulation error is to be calculated only when the carrier is larger than the value, and the valid that has been determined to be the target for calculation by the third means among all valid data carriers within a predetermined period. A fourth means for calculating a modulation error for the data carrier based on the sum of the distances Z calculated by the first means and the sum of the distances D calculated by the second means;
A modulation error calculation device comprising: Receives and demodulates a multi-value digital modulation signal, and between the position on the IQ plane of the received data in each effective data carrier of the received signal and the position on the IQ plane of the ideal signal point closest to the received data A first step for determining a distance Z of
For each effective data carrier, the absolute value of the I-axis component and the absolute value of the Q-axis component of the ideal signal point closest to the received data are the absolute values of the I-axis component and the Q-axis component of the received data. Only when the value is larger than the value, the second step in which the carrier is determined as a modulation error calculation target carrier, and among the valid data carriers within a predetermined period, the effective value determined as the calculation target in the second step. A third step of calculating a modulation error based on the sum of the distances Z calculated in the first step for the data carrier;
A modulation error calculation method comprising: Receives and demodulates a multi-value digital modulation signal, and between the position on the IQ plane of the received data in each effective data carrier of the received signal and the position on the IQ plane of the ideal signal point closest to the received data A first step for determining a distance Z of
A second step of obtaining a distance D between the position of the ideal signal point closest to the received data on the IQ plane and the origin of the IQ plane;
For each effective data carrier, the absolute value of the I-axis component and the absolute value of the Q-axis component of the ideal signal point closest to the received data are the absolute values of the I-axis component and the Q-axis component of the received data. Only when the value is larger than the value, the third step of determining the carrier as a carrier for calculating the modulation error, and the effective data determined to be the target of calculation by the third step among all the valid data carriers within the predetermined period A fourth step of calculating a modulation error for the data carrier based on the sum of the distances Z calculated by the first step and the sum of the distances D calculated by the second step;
A modulation error calculation method comprising: A digital broadcast receiver comprising the modulation error calculating device according to claim 1. A digital broadcast wave measuring apparatus comprising the modulation error calculating apparatus according to claim 1. A diversity-type digital broadcast receiver having a plurality of branches each having a receiving / demodulating unit, each branch including the modulation error calculating device according to claim 1, and calculating a modulation error in each branch A performance comparison unit that compares the performance of each branch using a modulation error measured by the apparatus, and a unit that determines a branch to be operated in the single reception mode based on a comparison result of the performance comparison unit Digital broadcast receiver.

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