JP5257748B2 - Modulation error ratio measuring apparatus and measuring method - Google Patents

Description

  The present invention relates to a modulation error ratio measuring apparatus.

  In an ISDB-T (Integrated Services Digital Broadcasting Terrestrial) system used for terrestrial digital broadcasting, the signal quality of a transmitter that measures the signal quality of a modulation parameter 1 to the OFDM (Orthogonal Frequency Division Multiplexing) signal that is a digital broadcast signal is measured. (MER: Modulation Error Ratio). The MER is determined by the power ratio between the measurement signal and the vector error of the ideal constellation point closest to the measurement signal. Conventionally, in MER measurement, a transmission multiplex control signal (TMCC signal: Transmission and Multiplexing Configuration and Control) included in a measurement signal is decoded, and each layer (A layer, B layer, C layer) of terrestrial digital broadcasting is decoded. It was necessary to acquire the modulation method and the number of segments, which are transmission parameters, and to select an ideal constellation point table to be compared with a measurement signal.

  As a technique related to MER measurement, Patent Document 1 is disclosed. Patent Document 1 discloses a modulation error ratio measuring apparatus that simply measures the modulation error ratio of each layer in a digital broadcast signal. Hereinafter, the modulation error ratio measuring apparatus disclosed in Patent Document 1 will be described with reference to FIGS. First, FIG. 1 shows the configuration of the modulation error ratio measuring apparatus disclosed in Patent Document 1. The modulation error ratio measuring apparatus in FIG. 1 includes a signal conversion unit 10, a signal parameter detection unit 20, and a measurement unit 30.

The signal conversion unit 10 includes a frequency conversion unit 11, an A / D conversion unit 12, and an FFT (Fast Fourier Transform) unit 13.
The frequency conversion unit 11 branches and inputs a digital broadcast signal transmitted from a transmitter (not shown). The digital broadcast signal is a transmission signal defined in ISDB-T. The frequency conversion unit 11 converts the frequency of the digital broadcast signal into an intermediate frequency (IF) and outputs it to the A / D conversion unit 12 as an intermediate frequency signal.
The A / D converter 12 inputs the intermediate frequency signal from the frequency converter 11. The A / D converter 12 A / D converts the intermediate frequency signal into a digital signal. The A / D conversion unit 12 performs quadrature demodulation on the digital signal, converts the digital signal into a baseband signal including an I layer and a Q layer, and outputs the baseband signal to the FFT unit 13.
The FFT unit 13 inputs a baseband signal. The FFT unit 13 performs OFDM demodulation on the baseband signal by FFT processing, converts the baseband signal into a frequency axis signal, and detects a subcarrier. The FFT unit 13 equalizes the frequency axis signal based on the frequency characteristic of the propagation path, and outputs the signal to the signal parameter detection unit 20 and the measurement unit 30.

  The signal parameter detection unit 20 inputs a frequency axis signal from the signal conversion unit 10. The signal parameter detection unit 20 demodulates and decodes the TMCC signal included in the frequency axis signal, acquires signal parameters such as the number of segments and the modulation method for each layer in the digital broadcast signal, and outputs them to the measurement unit 30.

  The measurement unit 30 includes a selection switching unit 31, a comparison unit 36, an MER calculation unit 37, an ideal constellation point table 32 for 64QAM (Quadrature Amplitude Modulation), an ideal constellation point table 33 for 16QAM, and a QPSK (Quadrature Phase Shift Keying). ) Ideal constellation point table 34, and ideal constellation point 40 of BPSK (Binary Phase Shift Keying) ideal constellation point table 35.

The selection switching unit 31 inputs a signal parameter from the signal parameter detection unit 20. The selection switching unit 31 selects an ideal constellation point table according to the modulation method for each layer of the digital broadcast signal based on the signal parameter. The selection switching unit 31 outputs the selected ideal constellation point table (hereinafter referred to as a selected ideal constellation point table) and signal parameters to the comparison unit 36.
Here, FIG. 2 to FIG. 5 show ideal constellation point tables for the respective modulation schemes. FIG. 2 shows an ideal constellation point table 32 for 64QAM. FIG. 3 shows an ideal constellation point table 33 for 16QAM. FIG. 4 shows an ideal constellation point table 34 for QPSK. FIG. 5 shows an ideal constellation point table 35 for BPSK.

  The comparison unit 36 receives the frequency axis signal from the FFT unit 13. The comparison unit 36 also receives the selected ideal constellation point table and signal parameters. The comparison unit 36 divides the frequency axis signal into each layer from the A layer to the C layer based on the signal parameter, and demodulates the frequency axis signal by a demodulation method corresponding to each layer to obtain the measurement constellation point 41. Further, the comparison unit 36 estimates an ideal constellation point 40 corresponding to the measurement constellation point 41 based on the selected ideal constellation point table corresponding to each layer. Based on the estimated ideal constellation point 40 (hereinafter, “estimated ideal constellation point”) and the measurement constellation point 41, the comparison unit 36 obtains an error vector that is a point error between both constellation points. The comparison unit 36 outputs the estimated ideal constellation point and the error vector to the MER calculation unit 37.

  The MER calculation unit 37 calculates the MER based on the estimated ideal constellation point and the error vector. The MER calculation unit 37 outputs the MER to the subsequent process. In the subsequent processing, MER is output to a display unit (not shown).

  FIG. 6 shows the relationship between the ideal constellation point 40 and the measurement constellation point 41. In actual MER calculation, the ideal constellation point 40 in FIG. 6 is an estimated ideal constellation point. In FIG. 6, when the ideal constellation point 40 is (Iid, Qid) and the measurement constellation point 41 is (Irx, Qrx), the point error (δI, δQ) between the ideal constellation point 40 and the measurement constellation point 41 is shown. Are δI = Irx−Iid and δQ = Qrx−Qid.

であり、ポイント誤差の誤差ベクトル４３（Ｄ）は、

であり、ＭＥＲは、理想コンスタレーションベクトル４２と誤差ベクトル４３の電力比で求められ、

である。 The ideal constellation vector 42 (S) of the ideal constellation point 40 is

The error vector 43 (D) of the point error is

MER is obtained by a power ratio between the ideal constellation vector 42 and the error vector 43, and

It is.

The above is the description of the modulation error ratio measuring apparatus disclosed in Patent Document 1. Thus, in the conventional MER measurement, it was necessary to detect the signal parameter by combining the TMCC signal with hardware.
JP 2005-026780 A

  An object of the present invention is to provide a modulation error ratio measuring apparatus capable of calculating MER with a simple configuration.

  A modulation error ratio measuring apparatus according to the present invention includes a common ideal constellation table including ideal constellation points included in an ideal constellation table corresponding to each of a plurality of modulation schemes, and a frequency axis signal of a digital broadcast signal demodulated by OFDM. The measurement ideal constellation point and the measurement constellation point corresponding to the measurement constellation point are estimated based on the ideal constellation point included in the common ideal constellation table. And a MER calculator for calculating a modulation error ratio based on the estimated ideal constellation point and the error vector.

  The modulation error ratio measurement method includes a step of including an ideal constellation point included in an ideal constellation table corresponding to each of a plurality of modulation methods in a common ideal constellation table, and measurement from a frequency axis signal of an OFDM demodulated digital broadcast signal. Obtaining a constellation point, estimating an estimated ideal constellation point corresponding to the measurement constellation point based on the ideal constellation point included in the common ideal constellation table, and the estimated ideal constellation point and the measurement constellation A step of calculating an error vector from the point, and a step of calculating a modulation error ratio based on the estimated ideal constellation point and the error vector.

  According to the present invention, it is possible to provide a modulation error ratio measuring apparatus capable of calculating MER with a simple configuration.

  A modulation error ratio measuring apparatus according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

[Description of configuration]
First, the configuration of the modulation error ratio measuring apparatus in this embodiment will be described. FIG. 7 shows the configuration of the modulation error ratio measuring apparatus in this embodiment. The modulation error ratio measurement apparatus according to the present embodiment includes a signal conversion unit 10 and a measurement unit 30.

  The signal conversion unit 10 includes a frequency conversion unit 11, an A / D conversion unit 12, and an FFT unit 13. Each configuration of the signal conversion unit 10 is the same as that of the prior art described with reference to FIG.

  The measurement unit 30 includes a comparison unit 36, a MER calculation unit 37, and a common ideal constellation point table 38.

The common ideal constellation point table 38 is an ideal constellation point table that can be used in common in all segments of the digital broadcast signal. FIG. 8 shows the common ideal constellation point table 38. As shown in FIG. 8, the common ideal constellation point table 38 includes each ideal constellation point 40 of the ideal constellation point table of a plurality of modulation schemes. In the present embodiment, the plurality of modulation schemes are the aforementioned modulation schemes. That is, the common ideal constellation point table 38 includes the 64QAM ideal constellation point table 32 shown in FIG. 2, the 16QAM ideal constellation point table 33 shown in FIG. 3, and the QPSK ideal constellation point shown in FIG. Each ideal constellation point of the table 34 and the ideal constellation point table 35 for BPSK shown in FIG. 5 is included.
In this embodiment, since an OFDM signal based on ISDB-T is assumed, the common ideal constellation point table 38 includes an ideal constellation point table based on each of the modulation schemes described above. However, the modulation method of the ideal constellation point table included in the common ideal constellation point table 38 is not limited to this.

In the present embodiment, the comparison unit 36 obtains an error vector from the measurement constellation point 41 using each ideal constellation point included in the common ideal constellation point table 38. Therefore, there is no need to demodulate and decode the TMCC signal included in the digital broadcast signal transmitted from the transmitter and select the selected ideal constellation point table based on the TMCC signal. Thereby, the configuration of the signal parameter detection unit 20 and the selection switching unit 31 described above is not necessary, and MER can be measured with a simple configuration.
The comparison unit 36 receives the frequency axis signal from the FFT unit 13. The comparison unit 36 demodulates the frequency axis signal to obtain a measurement constellation point 41. Further, the comparison unit 36 estimates an ideal constellation point 40 corresponding to the measurement constellation point 41 based on each ideal constellation point in the common ideal constellation point table 38. The comparison unit 36 obtains an error vector based on the estimated ideal constellation point 40 (hereinafter, estimated ideal constellation point) and the measurement constellation point 41. The comparison unit 36 outputs the estimated ideal constellation point and the error vector to the MER calculation unit 37.

  The MER calculation unit 37 calculates the MER based on the estimated ideal constellation point and the error vector, using the above-described MER calculation formula (3). The MER calculation unit 37 outputs the MER to the subsequent process.

  The above is the description of the configuration of the modulation error ratio measuring apparatus in the present embodiment.

[Description of operation method]
Next, an operation method of the modulation error ratio measuring apparatus according to this embodiment will be described with reference to FIG. FIG. 9 shows an operation flow of the modulation error ratio measuring apparatus according to this embodiment.

(Step S10)
The frequency conversion unit 11 branches and inputs a digital broadcast signal transmitted from a transmitter (not shown). The frequency conversion unit 11 converts the frequency of the digital broadcast signal into an intermediate frequency, and outputs the converted signal to the A / D conversion unit 12 as an intermediate frequency signal (IF: Intermediary Frequency).

(Step S20)
The A / D converter 12 inputs the intermediate frequency signal from the frequency converter 11. The A / D converter 12 A / D converts the intermediate frequency signal into a digital signal. The A / D conversion unit 12 performs quadrature demodulation on the digital signal, converts the digital signal into a baseband signal including an I layer and a Q layer, and outputs the baseband signal to the FFT unit 13.

(Step S30)
The FFT unit 13 inputs a baseband signal. The FFT unit 13 performs OFDM demodulation on the baseband signal by FFT processing, converts the baseband signal into a frequency axis signal, and detects a subcarrier. The FFT unit 13 equalizes the frequency axis signal based on the frequency characteristics of the propagation path, and outputs the equalized signal to the measurement unit 30.

(Step S40)
The comparison unit 36 of the measurement unit 30 inputs the frequency axis signal from the FFT unit 13. The comparison unit 36 demodulates the frequency axis signal to obtain a measurement constellation point 41. Furthermore, the comparison unit 36 estimates an ideal constellation point 40 corresponding to the measurement constellation point 41 based on each ideal constellation point included in the common ideal constellation point table 38. The comparison unit 36 obtains an error vector based on the estimated ideal constellation point 40 (hereinafter, estimated ideal constellation point) and the measurement constellation point 41. Hereinafter, the comparison unit 36 outputs the estimated ideal constellation point and the error vector to the MER calculation unit 37.

(Step S50)
The MER calculation unit 37 calculates the MER based on the estimated ideal constellation point and the error vector, using the above-described MER calculation formula (3). The MER calculation unit 37 outputs the MER to the subsequent process.

  The above is the description of the operation method of the modulation error ratio measuring apparatus in the present embodiment.

  As described so far, the common ideal constellation point table 38 includes the ideal constellation point table 40 of the ideal constellation point table for each modulation method used in the digital broadcast signal. Since the common ideal constellation point table 38 can be used in common for all segments of the digital broadcast signal, it is not necessary to select the selected ideal constellation point based on the signal parameters included in the TMCC signal. The comparison unit 36 obtains an estimated ideal constellation point from the common ideal constellation point table 38 based on the measurement constellation point 41. The comparison unit 36 calculates an error vector based on the estimated ideal constellation point and the measurement constellation point 41, and the MER calculation unit 37 calculates MER based on the estimated ideal constellation point and the error vector. With this configuration, the configuration of the conventional signal parameter detection unit 20, the selection switching unit 31, and the like becomes unnecessary, and the modulation error ratio can be measured with a simple configuration.

  Although the present invention has been described with reference to the embodiment, the present invention is not limited to the above embodiment. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

It is a figure which shows the conventional modulation error ratio measuring apparatus. It is a figure which shows the ideal constellation point table 32 for 64QAM. It is a figure which shows the ideal constellation point table 33 for 16QAM. It is a figure which shows the ideal constellation point table 34 for QPSK. It is a figure which shows the ideal constellation point table 35 for BPSK. It is a figure which shows the relationship between the ideal constellation point 40 and the measurement constellation point 41. FIG. It is a figure which shows the structure of the modulation error ratio measuring apparatus in this embodiment. It is a figure which shows the common ideal constellation point table. It is an operation | movement flow of the modulation error ratio measuring apparatus in this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Signal conversion part 11 Frequency conversion part 12 A / D conversion part 13 FFT part 20 Signal parameter detection part 30 Measurement part 31 Selection switching part 32 64QAM ideal constellation point table 33 16QAM ideal constellation point table 34 QPSK ideal constellation Constellation point table 35 ideal constellation point table 36 for BPSK comparison unit 37 MER calculation unit 38 common ideal constellation point table 40 ideal constellation point 41 measurement constellation point 42 ideal constellation vector 43 error vector

Claims (4)

A common ideal constellation table including ideal constellation points included in an ideal constellation table corresponding to each of a plurality of modulation methods;
A measurement constellation point is obtained from the frequency axis signal of the digital broadcast signal demodulated by OFDM, and an estimated ideal constellation point corresponding to the measurement constellation point is obtained based on the ideal constellation point included in the common ideal constellation table. A comparison unit that estimates and calculates an error vector between the estimated ideal constellation point and the measurement constellation point;
A modulation error ratio measurement apparatus comprising: a MER calculation unit that calculates a modulation error ratio based on the estimated ideal constellation point and the error vector. The modulation error ratio measuring apparatus according to claim 1,
The common ideal constellation table includes the ideal constellation points included in the ideal constellation table for 64QAM, 16QAM, QPSK, and BPSK. Including an ideal constellation point included in an ideal constellation table corresponding to each of a plurality of modulation methods in a common ideal constellation table;
Obtaining a measurement constellation point from the frequency axis signal of the OFDM demodulated digital broadcast signal;
Estimating an estimated ideal constellation point corresponding to the measurement constellation point based on the ideal constellation point included in a common ideal constellation table;
Calculating an error vector between the estimated ideal constellation point and the measurement constellation point;
A modulation error ratio measurement method comprising: calculating a modulation error ratio based on the estimated ideal constellation point and the error vector. A modulation error ratio measuring method according to claim 3,
The common ideal constellation table includes the ideal constellation points included in the ideal constellation table for 64QAM, 16QAM, QPSK, and BPSK.

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