Error rate measuring apparatus and error count display method

An error rate measuring apparatus includes error counting means for comparing bit string data obtained by converting a signal received from the device under test with error data, counting the number of FEC symbol errors by each codeword length in a case where the number of FEC symbol errors is less than the threshold value, and collectively counting the number of FEC symbol errors of codeword lengths in a case where the number of FEC symbol errors is equal to or greater than the threshold value, and display control means for displaying and controlling a list of collected results of the number of FEC symbol errors of each codeword length.

TECHNICAL FIELD

The present invention relates to an error rate measuring apparatus that transmits a known pattern (pulse amplitude modulation 4 (PAM4) signal) as a test signal to a device under test in a state in which the device under test has transited to a state of a signal pattern return and measures a bit error rate of input data returned and received from the device under test with the transmission of the test signal, and in particular, measures whether or not a forward error correction (FEC) operation of the device under test is possible, and an error count display method.

BACKGROUND ART

For example, as disclosed in Patent Document 1 described below, an error rate measuring apparatus is hitherto known as an apparatus that transmits a test signal of a known pattern including fixed data to a device under test and compares a signal under test returned and received from the device under test with the transmission of the test signal with a reference signal to be a reference in units of bits to measure a bit error rate (BER)

In an error rate measuring apparatus disclosed in Patent Document 2 described below, symbol/bit measurement of a PAM4 signal is performed, and an error count and an error rate of each of the symbols and the bits are acquired and displayed in a table format.

Incidentally, in a case where a PAM is particularly used as the test signal, while a large amount of transmission can be realized compared to Non Return to Zero (NRZ), an Eye opening is small, and thus, a signal to noise ratio (SNR) is damaged compared to the NRZ. For this reason, as the number of symbols increases, the influence of noise also becomes large, and it is extremely difficult to make errors zero. Therefore, it is desirable to count FEC symbol errors that occur in a region corresponding to a communication standard of the device under test to be measured and to measure whether or not error correction based on forward error correction (FEC) is possible.

RELATED ART DOCUMENT

Patent Document

DISCLOSURE OF THE INVENTION

Problem that the Invention is to Solve

However, in the error rate measuring apparatus of the related art, since a function of measuring a codeword is not provided, there is a problem in that it is not possible to recognize the number of FEC symbols to be an error and the distribution of the number of errors in a codeword, and it is not possible to efficiently proceed debugging of the device under test.

Accordingly, the invention has been accomplished in view of the above-described problem, and an object of the invention is to provide an error rate measuring apparatus and an error count display method capable of enabling confirmation of an error count and a distribution of FEC symbol errors in a codeword.

Means for Solving the Problem

To achieve the above-described object, there is provided an error rate measuring apparatus1according to a first aspect of the invention that inputs an NRZ signal of a known pattern as a test signal to a device under test W, receives a signal from the device under test with the input of the test signal, and measures whether or not a forward error correction (FEC) operation of the device under test is possible based on a comparison result of the received signal and the test signal. The error rate measuring apparatus includesan operation unit4that sets a codeword length, an FEC symbol length, and a threshold value composed of a positive integer including zero of the FEC corresponding to a communication standard of the device under test,error counting means7afor comparing bit string data obtained by converting the signal received from the device under test with error data, counting FEC symbol errors by each codeword length in a case where the number of FEC symbol errors is less than the threshold value, and collectively counting FEC symbol errors of codeword lengths in a case where the number of FEC symbol errors is equal to or greater than the threshold value, anddisplay control means7bfor displaying and controlling a list of collected results of the number of FEC symbol errors of each codeword length individually counted in a case where the number of FEC symbol errors is less than the threshold value and the number of FEC symbol errors of codeword lengths collectively counted in a case where the number of FEC symbol errors is equal to or greater than the threshold value, on a display screen in a table format based on counting results of the error counting means.

According to a second aspect of the invention, there is provided an error rate measuring apparatus1that inputs a PAM4 signal of a known pattern as a test signal to a device under test W, receives a signal from the device under test with the input of the test signal, and measures whether or not an FEC operation of the device under test is possible based on a comparison result of the received signal and the test signal. The error rate measuring apparatus includesan operation unit4that sets a codeword length, an FEC symbol length, and a threshold value composed of a positive integer including zero of the FEC corresponding to a communication standard of the device under test,data division means3dafor dividing symbol string data obtained by converting the signal received from the device under test into most significant bit string data and least significant bit string data,error counting means7afor comparing each of the most significant bit string data and the least significant bit string data divided by the data division means with error data, counting FEC symbol errors in each of the most significant bit string data and the least significant bit string data by each codeword length in a case where the number of FEC symbol errors is less than the threshold value, and collectively counting FEC symbol errors of codeword lengths in a case where the number of FEC symbol errors is equal to or greater than the threshold value, anddisplay control means7bfor displaying and controlling a list of collected results of the number of FEC symbol errors of each codeword length individually counted in a case where the number of FEC symbol errors is less than the threshold value and the number of FEC symbol errors of codeword lengths collectively counted in a case where the number of FEC symbol errors is equal to or greater than the threshold value, on a display screen in a table format based on counting results of the error counting means.

According to a third aspect of the invention, there is provided an error count display method for an error rate measuring apparatus1that inputs a non return to zero (NRZ) signal of a known pattern as a test signal to a device under test W, receives a signal from the device under test with the input of the test signal, and measures whether or not an FEC operation of the device under test is possible based on a comparison result of the signal received from the device under test and the test signal. The error count display method includesa step of, at an operation unit4, setting a codeword length, an FEC symbol length, and a threshold value composed of a positive integer including zero of the FEC corresponding to a communication standard of the device under test,a step of, at error counting means7a, comparing bit string data obtained by converting the signal received from the device under test with error data, counting FEC symbol errors by each codeword length in a case where the number of FEC symbol errors is less than the threshold value, and collectively counting FEC symbol errors of codeword lengths in a case where the number of FEC symbol errors is equal to or greater than the threshold value, anda step of, at display control means7b, displaying and controlling a list of collected results of the number of FEC symbol errors of each codeword length individually counted in a case where the number of FEC symbol errors is less than the threshold value and the number of FEC symbol errors of codeword lengths collectively counted in a case where the number of FEC symbol errors is equal to or greater than the threshold value, on a display screen in a table format based on counting results of the error counting means.

According to a fourth aspect of the invention, there is provided an error count display method for an error rate measuring apparatus1that inputs a PAM4 signal of a known pattern as a test signal to a device under test W, receives a signal from the device under test with the input of the test signal, and measures whether or not an FEC operation of the device under test is possible based on a comparison result of the received signal and the test signal. The error count display method includesa step of, at an operation unit4, setting a codeword length, an FEC symbol length, and a threshold value composed of a positive integer including zero of the FEC corresponding to a communication standard of the device under test,a step of, at data division means3da, dividing symbol string data obtained by converting the signal received from the device under test into most significant bit string data and least significant bit string data,a step of, at error counting means7a, comparing each of the most significant bit string data and the least significant bit string data divided by the data division means with error data, counting FEC symbol errors in each of the most significant bit string data and the least significant bit string data by each codeword length in a case where the number of FEC symbol errors is less than the threshold value, and collectively counting FEC symbol errors of codeword lengths in a case where the number of FEC symbol errors is equal to or greater than the threshold value, anda step of, at display control means7b, displaying and controlling a list of collected results of the number of FEC symbol errors of each codeword length individually counted in a case where the number of FEC symbol errors is less than the threshold value and the number of FEC symbol errors of codeword lengths collectively counted in a case where the number of FEC symbol errors is equal to or greater than the threshold value, on a display screen in a table format based on counting results of the error counting means.

Advantage of the Invention

According to the invention, it is possible to confirm an error count and a distribution of FEC symbol errors to be an error in a codeword, and to efficiently proceed debugging.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a mode for carrying out the invention will be described in detail referring to the accompanying drawings.

An error rate measuring apparatus according to the invention transmits a test signal of a known pattern to a device under test in a state in which the device under test has transited to a state of signal pattern return and measures an error rate of a received signal returned from the device under test with the transmission of the test signal.

As shown inFIG.1, an error rate measuring apparatus1of an embodiment has a function of measuring whether or not a forward error correction (FEC) operation of a device under test W is possible based on a comparison result of a received signal from the device under test W when an NRZ signal of a known pattern with an inserted error or a PAM4 signal having four symbol values is input as a test signal to the device under test W, and the test signal, and schematically includes a signal generator2, an error detector3, an operation unit4, a storage unit5, a display unit6, and a control unit7.

In the embodiment, the configuration and processing content for realizing the function of measuring whether or not the FEC operation of the device under test W is possible is primarily described.

The signal generator2generates, as reference data based on a multi-value signal, an NRZ signal in a system in which there is no return to zero between bits or a PAM4 signal formed of desired symbol string data (data of a string of symbols having symbol values of 0, 1, 2, 3).

In a case of generating the PAM4 signal, as shown inFIG.1, the signal generator2schematically includes a first signal generation unit2a, a second signal generation unit2b, and a signal synthesis and output unit2c.

The PAM4 signal has amplitude that is divided into four kinds for each symbol, as shown inFIG.2and has four different voltage levels V1, V2, V3, and V4of amplitude. An entire amplitude voltage range H is divided into a low voltage range H1, a medium voltage range H2, and a high voltage range H3in an ascending order of the voltage levels, and is formed of consecutive ranges based on three eye pattern openings.

Upon generating a desired PAM4 symbol string in a known pattern including fixed data, the first signal generation unit2agenerates a most significant bit (MSB) string signal that is added to a least significant bit (LSB) string signal to be generated by the second signal generation unit2bto generate the PAM4 signal.

The second signal generation unit2bgenerates the least significant bit string signal that is added to the most significant bit string signal generated by the first signal generation unit2ato generate the PAM4 signal.

Examples of specific bit string signals that are generated by the first signal generation unit2aand the second signal generation unit2binclude periodic patterns, such as various pseudo random patterns (Pseudo Random Bit Sequence (PRBS)) including PRBS7 (pattern length: 27−1), PRBS9 (pattern length: 29−1), PRBS10 (pattern length: 210−1), PRBS11 (pattern length: 211−1), PRBS15 (pattern length: 215−1), and PRBS20 (pattern length: 220−1), evaluation patterns for evaluating PAM including PRBS13Q, PRBS31Q, and SSPRQ, and a Reed-Solomon Forward Error Correction (RS-FEC) encoded scrambled idle pattern.

The signal synthesis and output unit2cadds the most significant bit string signal generated by the first signal generation unit2aand the least significant bit string signal generated by the second signal generation unit2bto output the PAM4 signal. The PAM4 signal is input as a test signal of a known pattern to the device under test W in measuring an error rate or the like of the device under test W.

An error that is inserted into the test signal is optional. For example, any FEC symbol error is inserted in a case of checking FEC error tolerance of the device under test W. Furthermore, in a case of confirming tolerance of the device under test W, an error is inserted, and in a case where the device under test W confirms an error with any other test signals, an error is not inserted and confirmation is performed with a capture function.

The error detector3receives a signal to be output from the device under test W with the input of the NRZ signal or the PAM4 signal and measures the error rate or the like when the NRZ signal or the PAM4 signal to be reference data is input as the test signal of the known pattern from the signal generator2to the device under test W, and as shown inFIG.1, includes a signal reception unit3a, a synchronization detection unit3b, a position information storage unit3c, a data comparison unit3d, and a data storage unit3e.

In a case where the test signal input to the device under test W is the NRZ signal, the signal reception unit3asamples the NRZ signal received from the device under test W in a predetermined sampling period to convert the signal into bit string data (data of a bit string having 0 and 1). The bit string data converted by the signal reception unit3ais input to the synchronization detection unit3b.

In a case where the test signal input to the device under test W is the PAM4 signal, the signal reception unit3asamples the PAM4 signal received from the device under test W in a predetermined sampling period to convert the signal into symbol string data (data of a string of symbols having symbol values of 0, 1, 2, and 3). The symbol string data converted by the signal reception unit3ais input to the synchronization detection unit3b.

In a case where the test signal input to the device under test W is the NRZ signal, the synchronization detection unit3bsynchronously fetches the reference data that is data of the bit string of the NRZ signal to be a reference read from the storage unit5and the bit string data of the NRZ signal received from the device under test W and output from the signal reception unit3aat a setting timing set in advance by the operation unit4, and outputs the fetched bit string data to be input data to the data comparison unit3d.

In a case where the test signal input to the device under test W is the PAM4 signal, the synchronization detection unit3bsynchronously fetches reference data that is data of the symbol string of the PAM4 signal to be a reference read from the storage unit5and the symbol string data of the PAM4 signal received from the device under test W and output from the signal reception unit3aat a setting timing set in advance by the operation unit4, and outputs the fetched symbol string data to be input data to the data comparison unit3d.

The setting timing is set in advance by the operation unit4, for example, on the setting screen (not shown) of the display unit6, and is a timing at which a trigger signal is generated in response to a user's instruction, a timing at which a designated number of FEC symbol errors occur in one codeword length (for example, in a case where one codeword is 544 FEC symbols, and the user wants to capture at a timing at which 16 FEC symbol errors occur, synchronization is achieved at a timing at which 16/544 FEC symbol errors occur), or a timing at which a designated number of FEC symbol errors continuously occur (synchronization is achieved at a timing at which continuous FEC symbol errors occur by a number designated by the user, regardless of a Codeword).

When synchronization is achieved, the synchronization detection unit3bnotifies the data comparison unit3dthat synchronization is achieved, and stores a synchronous position representing a position of a bit or a symbol in the reference data when synchronization is achieved, in the position information storage unit3c.

When synchronization of the reference data and the bit string data of the NRZ signal or the symbol string data of the PAM4 signal from the signal reception unit3ais achieved by the synchronization detection unit3b, the position information storage unit3cstores the synchronous position representing the position of the bit or the symbol in the reference data when synchronization is achieved.

In a case where the test signal input to the device under test W is the NRZ signal, the data comparison unit3dcaptures the head of one FEC symbol (10 bits or 20 bits) of the bit string data fetched synchronously with the reference data (test signal) at the setting timing by the synchronization detection unit3band compares each bit with error data (“1”) to detect bit errors of each one codeword length. That is, in a case where the bit of the bit string data is “1”, this is detected as a bit error. The head of one FEC symbol of the bit string data is detected by making the counter of the data comparison unit3drun free to assume the head.

In a case where the test signal input to the device under test W is the NRZ signal, the data comparison unit3ddivides the bit string data fetched synchronously with the reference data (test signal) at the setting timing by the synchronization detection unit3bby one FEC symbol length (10 bits or 20 bits) and detects FEC symbol errors at one FEC symbol interval. For example, in a case where one FEC symbol length is 10 bits, the bit string data is divided by 10 bits, and in a case where an error occurs even in one bit within 10 bits, this is detected as one FEC symbol error.

In a case where the test signal input to the device under test W is the NRZ signal, the data comparison unit3dsections the bit string data fetched synchronously with the reference data (test signal) at the setting timing by the synchronization detection unit3bat the codeword length and detects FEC symbol error of each codeword of a sectioned region.

In a case where the test signal input to the device under test W is the PAM4 signal, the data comparison unit3dcaptures the head of one FEC symbol (10 bits or 20 bits) of the symbol string data fetched synchronously with the reference data (test signal) at the setting timing by the synchronization detection unit3bto divide the symbol string data into most significant bit string data (hereinafter, referred to as MSB data) and least significant bit string data (hereinafter, referred to as LSB data) by data division means3da, and compares each of the MSB data and the LSB data with the error data (“1”) to detect each of a most significant bit error (hereinafter, referred to as an MSB error) and a least significant bit error (hereinafter, referred to as an LSB error) of each one codeword length. That is, in a case where the divided MSB data is “1”, this is detected and counted as an MSB error, and in a case where the divided LSB data is “1”, this is detected as an LSB error. The head of one FEC symbol of the symbol string data is detected by making the counter of the data comparison unit3drun free to assume the head.

In a case where the test signal input to the device under test W is the PAM4 signal, the data comparison unit3ddivides MSB data and LSB data by one FEC symbol length (10 bits or 20 bits), and detects FEC symbol errors in each of the MSB data and the LSB data at one FEC symbol interval. For example, in a case where one FEC symbol length is 10 bits, the MSB data and the LSB data are divided by 10 bits, and in a case where an error occurs even in one bit within 10 bits, this is detected as one FEC symbol error.

In a case where the test signal input to the device under test W is the PAM4 signal, the data comparison unit3dsections the MSB data and the LSB data at the codeword length and detects FEC symbol errors of each codeword of a sectioned region.

InFIG.1, for convenience of description, although a configuration in which the data comparison unit3dincludes the data division means3dahas been described, the data division means3dacan be configured of a known PAM decoder, for example.

The data storage unit3estores comparison result data of the data comparison unit3d, or the like along with the bit string data or the symbol string data synchronized with the reference data.

The operation unit4also functions as setting means, and is configured of, for example, a user interface, such as an operation knob, various keys, switches, or buttons of the error rate measuring apparatus1ofFIG.1, or softkeys on a display screen of the display unit6. The operation unit4executes various kinds of setting regarding an error rate measurement, such as setting of the setting timing, designation of a block of the bit string data or the symbol string data displayed on the display screen (the capture screen6aofFIGS.3A and3B) of the display unit6, setting of baud rate or generation conditions of a bit string or a symbol string, and an instruction to start or end the error rate measurement.

FIG.3Ashows an example of a setting screen11on which setting parameters (one codeword length of the FEC, one FEC symbol length, and an FEC Symbol Error Threshold (a threshold value of FEC symbol errors for starting capture) of the FEC) to a signal received from the device under test W are set.

“FEC Symbol Error Threshold” as the threshold value is arbitrarily set as a value of a positive integer including zero by an operation of the operation unit4. In performing FEC evaluation based on a communication standard, such as IEEE802.3ck, when the threshold value is set to “8” in a case where the test signal input to the device under test W is the NRZ signal, and the threshold value is set to “16” in a case where the test signal input to the device under test W is the PAM4 signal, it is possible to perform evaluation about whether or not the test signal input to the device under test W conforms to the communication standard.

On the setting screen11ofFIG.3A, as “Number of FEC Symbols in a Codeword” indicating the length of one codeword of the FEC, one codeword is displayed by, for example, a violet bar-shaped graphic12of which the length is partially omitted and which is sectioned by FEC symbols.

At a position directly below the graphic12of “Number of FEC Symbols in a Codeword”, an input box13for selecting and setting the number of FEC symbols forming “Codeword Length” from a pull-down menu is displayed. The setting screen11ofFIG.3Ashows a state in which “544” is selected and set in the input box13.

At a position directly above the graphic12of “Number of FEC Symbols in a Codeword”, “Bit Length in an FEC Symbol” that is indicated as forming a part of a codeword by a dotted line and is color-coded is displayed by a bar-shaped graphic14. For example, color-coding display is performed in such a manner that the graphic14of the FEC symbol is blue and portions corresponding to a graphic12aof the codeword except for the graphic14of the FEC symbol are violet.

At a position directly above the graphic14of “Bit Length in an FEC Symbol”, an input box15for selecting and setting the number of bits (10 bits or 20 bits) of “FEC symbol Length” from a pull-down menu is displayed. The setting screen ofFIG.3Ashows a state in which “10” is selected and set in the input box15.

In addition, below the graphic12of “Number of FEC Symbols in a Codeword”, as an error included in one codeword, a graphic16of “Bit Error” and a graphic17of “FEC Symbol Error” are color-coded and displayed in a graphic12bof one Codeword. For example, color-coding display is performed in such a manner that the graphic12bof one Codeword is violet, the graphic16of “Bit Error” is yellow, and the graphic17of “FEC symbol Error” is red.

At a position directly above the graphic12bof one Codeword where the graphic16of “Bit Error” and the graphic17of “FEC symbol Error” are displayed, an input box18for setting a threshold value of “FEC symbol Error Threshold” using an equality sign (=), an inequality sign with an equality sign (≥), and a numeral is displayed.

At a position directly below of the graphic12bof one Codeword where the graphic16of “Bit Error” and the graphic17of “FEC Symbol Error” are displayed, an input box19for inputting the number of FEC symbols forming one codeword is displayed.

Then, in an upper portion of the setting screen11ofFIG.3A, a selection item20of “FEC symbol Capture Setting” is displayed. As shown inFIG.3B, in regard to the selection item20of “FEC Symbol Capture Setting”, selection items of settings according to a communication standard are displayed in a pull-down menu. In an example ofFIG.3B, “Variable”, “50G PAM4”, “100G PAM4”, and “25G NRZ” are displayed as selection items in a pull-down menu.

FIG.3Ashows a state in which “Variable” is selected as the selection item20of “FEC symbol Capture Setting”. In the state in which “Variable” is selected, it is possible to allow free selection and input to each input box from the pull-down menu.

In the example ofFIG.3A, “50G PAM4”, “100G PAM4”, and “25G NRZ” can be selected as the selection item20of a preset setting, and in a case where any preset setting is selected, respective parameters based on a communication standard of the selected preset setting is automatically set.

For example, in a case where “50G PAM4” is selected as the preset setting, the respective parameters are automatically set in such a manner that the codeword length is “544”, the FEC symbol length is “10”, and the FEC symbol Error Threshold is “16”.

In a case where “100G PAM4” is selected as the preset setting, the respective parameters are automatically set in such a manner that the codeword length is “272”, the FEC symbol length is “20”, and the FEC symbol Error Threshold is “16”.

In a case where “25G NRZ” is selected as the preset setting, the respective parameters are automatically set in such a manner that the codeword length is “528”, the FEC symbol length is “10”, and the FEC symbol Error Threshold is “8”.

In this way, on the setting screen11ofFIG.3A, a configuration relationship of the FEC symbol to one codeword and a correspondence relationship of the FEC symbol error to one codeword are graphically displayed in an identifiable manner. With this, it is possible to allow the user to set the respective parameters of the FEC to the signal received from the device under test W after visually recognizing the configuration relationship or the correspondence relationship of “Number of FEC Symbols in a Codeword”, “Bit Length in an FEC Symbol”, “Bit Error”, and “FEC Symbol Error” even though the user is not an expert who knows the communication standard.

On the setting screen11ofFIG.3A, although a case where “Bit Length in an FEC Symbol”, and “Bit Error” and “FEC symbol Error” are vertically arranged centering on “Number of FEC Symbols in a Codeword” and are graphically displayed has been shown such that the configuration relationship of “Number of FEC Symbols in a Codeword”, “Bit Length in an FEC Symbol”, “Bit Error”, and “FEC Symbol Error” is easily visually recognized, the invention is not limited to this arrangement. For example, “Bit Length in an FEC Symbol”, and “Bit Error” and “FEC Symbol Error” may be reversely arranged or “Bit Length in an FEC Symbol”, and “Bit Error” and “FEC Symbol Error” may be arranged above or below “Number of FEC Symbols in a Codeword” and may be graphically displayed.

The storage unit5stores a bit string of the NRZ signal or a symbol string of the PAM4 signal (a string of symbols having symbol values of 0, 1, 2, and 3) input to the device under test W as a test signal of a known pattern from the signal synthesis and output unit2c. The bit string of the NRZ signal or the symbol string of the PAM4 signal input to the device under test W as the test signal of the known pattern is reference data to be a reference for comparison with input data that is generated from the signal received from the device under test W.

The storage unit5stores a counting result of error counting means7adescribed below of the control unit7. In addition, the storage unit5stores information regarding the setting timing, the baud rate, the generation conditions of the bit string or the symbol string, and the like. Such information can be appropriately selected and set by the operation unit4through the user interface.

A configuration may be made in which, in a case where the control unit7or the signal generator2can recognize the bit string of the NRZ signal or the symbol string of the PAM4 signal to be the test signal, the bit string of the NRZ signal or the symbol string of the PAM4 signal that is the test signal of the known pattern, that is, the reference data is stored from the control unit7or the signal generator2to the storage unit5.

The display unit6is configured of, for example, a liquid crystal display or the like in the error rate measuring apparatus1ofFIG.1, and displays the setting screen regarding an error rate measurement, each compliance test (a test about whether or not the device under test W conforms to the communication standard) including the error rate measurement, the capture screen, and the like under the control of display control means7bdescribed below. The display unit6also has an operation function of the operation unit4, such as softkeys on the display screen.

The display unit6displays a measurement screen21in a display form shown inFIG.4or a measurement screen in a display form shown inFIG.5, for example, in addition to the setting screen11ofFIG.3Aunder the control of display control means7bdescribed below. The measurement screen21ofFIG.4or the measurement screen22ofFIG.5includes a simple setting display region23and a measurement result display region24.

The simple setting display region23is a region where setting parameters (one codeword length, one FEC symbol length, and the FEC Symbol Error Threshold (the threshold value of symbol errors for starting capture) of the FEC) to the signal received from the device under test W are simply set.

Moreover, in the simple setting display region23, as “Number of FEC Symbols in a Codeword” indicating the length of one codeword of the FEC, an input box25for selecting and setting the number of FEC symbols forming “Codeword Length” from a pull-down menu is displayed. The simple setting display region23ofFIG.4or5shows a state in which “544” is selected and set in the input box25.

On a right side of “Number of FEC Symbols in a Codeword”, an input box26for selecting and setting the number of bits of “Bit Length in an FEC Symbol” forming a part of a codeword from a pull-down menu is displayed. The simple setting display region23ofFIG.4or5shows a state in which “10” is selected and set in the input box26.

Below “Number of FEC Symbols in a Codeword”, an input box27for setting the threshold value of “FEC Symbol Error Threshold” using an equality sign (=), an inequality sign with an equality sign (≥) and a numeral is displayed. The simple setting display region23ofFIG.4or5shows a state in which the threshold value of “FEC Symbol Error Threshold” is set to “15 or more”.

In the simple setting display region23, as “Preset”, selection items28of settings according to the communication standard are displayed in a pull-down menu. For example, “Variable”, “50G PAM4”, “100G PAM4”, and “25G NRZ” are displayed as the selection items28of “Preset” in a pull-down menu. The simple setting display region23ofFIG.4shows a state in which “50G NRZ” is selected and set as the preset setting. Furthermore, the simple setting display region23ofFIG.5shows a state in which “50G PAM4” is selected and set as the preset setting. In a case where “Variable” is selected and set as “Preset”, it is possible to allow the user to arbitrarily set the values of “Number of FEC Symbols in a Codeword”, “Bit Length in an FEC Symbol”, and “FEC Symbol Error Threshold” according to the communication standard of the device under test W.

The measurement result display region24is a region where a measurement result regarding errors based on counting of the error counting means7adescribed below is displayed. For example, in the measurement result display region24ofFIG.4, an error rate and an error count value of each of Uncorr. Codeword (Codeword on which forward error correction is impossible), Total, INS, and OMI are displayed. In the measurement result display region24ofFIG.5, an error rate and an error count value of each of Uncorr. Codeword (Codeword on which forward error correction is impossible), PAM4 Symbol, and Bit are displayed.

The display unit6displays a counting result display screen31in a display form shown inFIG.6or a counting result display screen32in a display form shown inFIG.7under the control of the display control means7bdescribed below.

On the counting result display screen31ofFIG.6, a counting result of the error counting means7adescribed below in a case where the test signal input to the device under test W is the NRZ signal is displayed. On the counting result display screen32ofFIG.7, a counting result of the error counting means7adescribed below in a case where the test signal input to the device under test W is the PAM4 signal is displayed.

Moreover, in a display region31aof an upper portion of the counting result display screen31ofFIG.6, the error rate and the error count value in Codeword (Uncorr. Codeword) on which forward error correction is impossible, FEC Symbol, and Bit (Total, INS, OMI) are displayed. The counting result display screen31ofFIG.6shows a state in which the error rate: 5.00E-04 and the error count value: 50 are displayed as the counting result in Codeword on which the forward error correction is impossible.

In a display region32aof an upper portion of the counting result display screen32ofFIG.7, an error rate and an error count value of each of MSB, LSB, and MSB+LSB in FEC Symbol and Bit (Total, INS, OMI) are displayed, and an error rate and an error count value of MSB+LSB in Codeword (Uncorr. Codeword) on which forward error correction is impossible are displayed. The counting result display screen32ofFIG.7shows a state in which the error rate: 3.00E-04 and the error count value: 30 are displayed as the counting result of MSB+LSB in Codeword on which forward error correction is impossible.

In a display region31bof a lower portion of the counting result display screen31ofFIG.6or in a display region32bof a lower portion of the counting result display screen32ofFIG.7, a collected result of the number of FEC symbol errors of each codeword of the region sectioned at the codeword length (a collected result of the number of FEC symbol errors of each codeword length individually counted by the error counting means7adescribed below in a case where the number of FEC symbol errors is less than the threshold value and the number of FEC symbol errors of codeword lengths collectively counted by the error counting means7adescribed below in a case where the number of FEC symbol errors is equal to or greater than the threshold value) is displayed in a list in a table format. The list collects the number of FEC symbol errors less than the threshold value (the FEC Symbol Error Threshold set on the setting screen11ofFIGS.3A and3B, the measurement screen21ofFIG.4, or the measurement screen22ofFIG.5) and an error count (Uncorrectable Codeword) of FEC symbol errors equal to or greater than the threshold value.

The list of the display region31bin the counting result display screen31ofFIG.6indicates that, among “100000” codewords, codewords where the number of the FEC is “99900”, codewords where the number of the FEC symbol errors is “5” is “5”, codewords where the number of the FEC symbol errors is “6” is “20”, codewords where the number of the FEC symbol errors is “7” is “25”, and codewords where the number of the FEC symbol errors is “equal to or greater than the threshold value (FEC Symbol Error Threshold=16)” is “50”.

The list of the display region32bin the counting result display screen32ofFIG.7shows that, among “100000” codewords, codewords where the number of the FEC symbol errors is is “99950”, codewords where the number of the FEC symbol errors is “7” is “10”, codewords where the number of the FEC symbol errors is “15” is “5”, and codewords where the number of the FEC symbol errors is “equal to or greater than the threshold value (FEC Symbol Error Threshold=16)” is “30”.

As the collected result of the number of the FEC symbol errors of the codewords of the region sectioned at the codeword length described above, the error counts in the list of the display region31bofFIG.6or the display region32bofFIG.7can also be displayed by a histogram, a pie graph, or the like such that the user can recognize the collected result at a ratio.

The control unit7is configured of a central processing unit (CPU) and a storage element, such as a read only memory (ROM) or a random access memory (RAM), to measure an error rate of the PAM4 signal, integrally controls the signal generator2, the error detector3, the operation unit4, the storage unit5, and the display unit6, and includes the error counting means7aand the display control means7b.

In a case where the test signal input to the device under test W is the NRZ signal, the error counting means7aperforms counting (including counting codewords) of bit errors detected by the data comparison unit3d, counting of FEC symbol errors detected at one FEC symbol interval, and counting of FEC symbol errors of each codeword length of the region sectioned at the codeword length. In regard to the FEC symbol errors of each codeword length, the number of the FEC symbol errors less than the threshold value is counted individually and the number of the FEC symbol errors equal to or greater than the threshold value is collectively counted.

In a case where the test signal input to the device under test W is the PAM4 signal, the error counting means7aperforms counting (including counting codewords) of the MSB errors and the LSB errors detected by the data comparison unit3d, counting of the FEC symbol errors detected at one FEC symbol interval, and counting of the FEC symbol errors of MSB data+LSB data of each codeword length of the region sectioned at the codeword length. In regard to the FEC symbol errors of each codeword length, the number of the FEC symbol errors less than the threshold value is counted individually and the number of the FEC symbol errors equal to or greater than the threshold value is collectively counted.

The display control means7bcontrols display on the display screen of the display unit6, for example, the setting screen11ofFIG.3A, the measurement screen21ofFIG.4or the measurement screen22ofFIG.5, or the counting result display screen31ofFIG.6or the counting result display screen32ofFIG.7.

The display control means7bdisplays and controls the list in which the number of the FEC symbol errors less than the threshold value (FEC Symbol Error Threshold) and the number of the FEC symbol errors equal to or greater than the threshold value on the counting result display screen31ofFIG.6or the counting result display screen32ofFIG.7are collected, based on the counting results of the error counting means7a.

Next, as a processing operation of error counting of the error rate measuring apparatus1configured as above, cases classified based on whether the test signal input to the device under test W is the NRZ signal or the PAM4 signal will be described referring toFIGS.6and7.

As shown inFIG.6, first, the setting parameters to the received signal from the device under test W are set by the operation unit4(ST1). Specifically, on the setting screen11ofFIG.3Aor in the simple setting display region23of the measurement screen21ofFIG.4, one codeword length, one FEC symbol length, and the FEC Symbol Error Threshold are set based on the communication standard of the device under test W to be measured or the preset setting (for example, 25G NRZ) corresponding to the communication standard is selected and set.

After the above-described setting ends, the NRZ signal (25G NRZ or the like conforming to the setting parameters) of the known pattern with an inserted error is input as the test signal to the device under test W by the signal generator2(ST2).

Then, a signal returned from the device under test W the input of the test signal to the device under test W is received and converted into bit string data by the signal reception unit3a(ST3).

Next, the head of one FEC symbol (10 bits or 20 bits) of the bit string data fetched synchronously with the reference data (test signal) at the setting timing by the synchronization detection unit3bis captured, each bit is compared with the error data (“1”) by the data comparison unit3dto detect bit errors of each one codeword length, and the detected bit errors of each one codeword length are counted by the error counting means7a(ST4). In this case, the number of codewords is also counted. The head of one FEC symbol of the bit string data is detected by making the counter of the data comparison unit3drun free to assume the head.

Subsequently, the bit string data is divided by each one FEC symbol length, FEC symbol errors are detected at one FEC symbol interval, and the detected FEC symbol errors are counted by the error counting means7a(ST5). For example, in a case where one FEC symbol length is 10 bits, the bit string data is divided by 10 bits, and in a case where an error occurs even in one bit within 10 bits, this is detected and counted as one FEC symbol error.

In addition, the bit string data is sectioned at the codeword length, FEC symbol errors of each codeword of the sectioned region are detected, and the detected FEC symbol error of each codeword are counted by the error counting means7a(ST6).

Then, as the counting result of the error counting means7a, a collected result of the number of the FEC symbol errors of each codeword of the region sectioned at the codeword length is displayed on the counting result display screen31ofFIG.6in a list in a table format under the control of the display control means7b(ST7).

As shown inFIG.7, first, the setting parameters to the received signal from the device under test W are set by the operation unit4(ST11). Specifically, on the setting screen11ofFIG.3Aor in the simple setting display region23of the measurement screen22ofFIG.5, one codeword length, one FEC symbol length, and the FEC Symbol Error Threshold are set based on the communication standard of the device under test W to be measured or the preset setting (for example, 50G PAM4) corresponding to the communication standard is selected and set.

After the above-described setting ends, the PAM4 signal (for example, 50G PAM4 conforming to the setting parameters) of the known pattern with an inserted error is input as the test signal to the device under test W by the signal generator2(ST12).

Then, a signal returned from the device under test W with the input of the test signal to the device under test W is received and converted into symbol string data by the signal reception unit3a(ST13).

Next, the head of one FEC Symbol (10 bits or 20 bits) of the symbol string data fetched synchronously with the reference data (test signal) at the setting timing by the synchronization detection unit3bis captured, and the symbol string data is divided into MSB data and LSB data by the data division means3da(ST14). Then, each of the MSB data and the LSB data is compared with the error data (“1”) by the data comparison unit3dto detect MSB errors and LSB errors of each one codeword length, and the detected MSB errors and LSB errors of each one codeword length are counted by the error counting means7a(ST15). In this case, the number of codewords is also counted. The head of one FEC symbol of the symbol string data is detected by making the counter of the data comparison unit3drun free to assume the head.

The error data (“1”) is divided into error data for comparing with the MSB data and error data for comparing with the LSB data, in a case where the MSB data is “1”, this is detected and counted as an MSB error, and in a case where the LSB data is “1”, this is detected and counted as an LSB error.

Subsequently, the MSB data and the LSB data are divided by each one FEC symbol length, and FEC symbol errors are detected in each of the MSB data and the LSB data at one FEC symbol interval, and the detected FEC symbol errors are counted by the error counting means7a(ST16). For example, in a case where one FEC symbol length is 10 bits, the MSB data and the LSB data are divided by 10 bits, and in a case where an error occurs even in one bit within 10 bits, this is detected and counted as one FEC symbol error.

In addition, the MSB data and the LSB data are sectioned at the codeword length, FEC symbol errors of each codeword of the sectioned region are detected, and the detected FEC symbol error of each codeword are counted by the error counting means7a(ST17).

Then, as the counting result of the error counting means7a, a collected result of the number of the FEC symbol errors of each codeword of the region sectioned at the codeword length is displayed on the counting result display screen32ofFIG.7in a list in a table format under the control of the display control means7b(ST18).

Incidentally, in the above-described embodiment, as shown inFIG.1, although a configuration is made in which the signal generator2, the error detector3, the operation unit4, the storage unit5, the display unit6, and the control unit7are included in the error rate measuring apparatus1, the invention is not limited to this configuration. For example, the signal generator2and the error detector3can also be separately modularized or may be housed in individual housings, and can also be configured of an external apparatus, such as a personal computer to which the operation unit4and the display unit6are externally connected.

In this way, according to the embodiment, it is possible to confirm an error count and a distribution of FEC symbol errors to be an error in a codeword, and to efficiently perform debugging. In a case where a threshold value is set corresponding to the communication standard and a list in a format shown inFIG.6or7is displayed, it is possible to confirm whether or not the test signal input to the device under test W conforms to the communication standard, to perform evaluation.

Although the best mode of the error rate measuring apparatus and the error count display method according to the invention has been described above, the invention is not limited by the description and the drawings according to this mode. That is, it is a matter of course that other modes, examples, operation techniques and the like made by those skilled in the art based on this mode are all included in the scope of the invention.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS