JP2020120250A - FEC error adding device, test signal generating device using the same, and FEC error adding method - Google Patents

Abstract

To provide an FEC error adding device, a test signal generating device using it, and an FEC error adding method that can generate a test signal for testing an FEC function of a communication apparatus that receives PAM4 signals.SOLUTION: An FEC error adding device includes: an error signal generating unit 22 that generates an error signal for continuously adding errors at predetermined bit intervals to one or both of the MSB and LSB of a PAM4 signal including a plurality of FEC code words composed of a plurality of FEC symbols; an error adding unit 23 that performs an XOR operation of the MSB and LSB and the error signal in bit units and adds the errors to the PAM4 signal; and a CW number calculation unit 25e that calculates a minimum number of FEC code words necessary for achieving a desired bit error rate of a test signal and the number of FEC code words having error FEC symbols included in the minimum number of FEC code words.SELECTED DRAWING: Figure 1

Description

The present invention relates to an FEC error adding device, a test signal generating device using the FEC error adding device, and an FEC error adding method, and more particularly to generating a test signal for measuring an error rate of a communication device based on a communication standard using forward error correction. FEC error adding device for doing so, a test signal generating device using the same, and an FEC error adding method.

2. Description of the Related Art In recent years, communication systems have been increasing in speed, and various communication devices that make up the communication systems have been improved in performance. A bit error rate defined as a comparison between the number of bit errors in received data and the total number of received data is known as one of indicators of signal quality evaluation in these communication devices.

In the standards such as 100G and 400G defined by IEEE, in order to respond to an ultra-high bit rate, transmission by a PAM4 signal is prescribed instead of transmission by a PAM2 (NRZ) signal which has been used so far. The PAM4 signal is composed of four PAM4 symbols consisting of "00", "01", "10", and "11".

Forward error correction coding (hereinafter, also referred to as “FEC coding”) technology is used in transmission by the PAM4 signal. For example, as shown in FIG. 5, in FEC encoding by RS-FEC (544, 514) defined in IEEE802.3, a parity part composed of 30 FEC symbols and a message part composed of 514 FEC symbols are included. An FEC codeword is generated having 544 FEC symbols of

Since the FEC codeword includes the parity part of this 30 FEC symbol, it is possible for the FEC decoder of the communication device on the receiving side to correct the error of up to 15 FEC symbols per FEC codeword. Note that one FEC symbol consists of 10 bits, but if the number of error bits included in one FEC symbol is in the range of 1 to 10, the FEC symbol includes an FEC symbol including an error (hereinafter, also referred to as “error FEC symbol”). Becomes

The FEC codeword is converted into a PAM4 signal through processes such as Gray coding, interleaving, precoding, and PAM4 encoding.

FIG. 6 is a schematic diagram for explaining interleaving of FEC codewords. In the 200G or 400G standard defined in IEEE802.3bs, two Reed-Solomon encoders A and B convert two messages A and B into two FEC codewords A and B, respectively.

Further, FIG. 6 shows a situation in which a burst error of 18 FEC symbols is added to two interleaved FEC codewords A and B. The FEC symbols extracted from the two FEC codewords A and B by the interleaving are rearranged so as to be adjacent to the FEC symbols from the different FEC codewords, and are distributed to, for example, 16 lanes. To be done. As a result, the burst error of 18 FEC symbols is distributed to the two FEC codewords A and B by 9 FEC symbols each, and the error is corrected by the FEC decoder.

Therefore, in order to ensure that the FEC codeword A cannot be corrected by the FEC decoder, it is necessary to add a burst FEC symbol error to the data of 32 FEC symbols transmitted in one lane. Since the burst bit error is removed by PAM4 precoding, it is difficult to make the error uncorrectable by the FEC decoder. Therefore, in order to make the FEC codeword uncorrectable by the FEC decoder, it is necessary to add a burst FEC symbol error. Here, the burst bit error is a plurality of consecutive error bits. On the other hand, a burst FEC symbol error is a plurality of consecutive error FEC symbols in one FEC codeword, and can be generated by providing only one error bit in each consecutive FEC symbol. The burst FEC symbol error generated in this way is not removed by PAM4 precoding.

Conventionally, an error addition device that adds an error to a data signal has been used to generate a test signal for measuring an error rate for a communication device having an FEC function (see, for example, Patent Document 1).

Japanese Patent No. 5215881

In error rate measurement, in order to evaluate the FEC function of a communication device, it is necessary to add FEC symbol errors that cannot be corrected by the FEC decoder of the communication device. For a PAM4 signal in which two different guarded FEC codewords by two Reed-Solomon encoders are interleaved, one or both of the MSB (most significant bit) and LSB (least significant bit) of the PAM4 symbol Error cannot be added to generate the burst FEC symbol error, the two guards cannot be error-corrected at the same time.

However, since the error adding device disclosed in Patent Document 1 does not include means for separating the PAM4 signal into MSB and LSB, it is not possible to add a bit error to one or both of MSB and LSB. Therefore, the above conventional error adding device cannot add a burst FEC symbol error to a PAM4 signal in which two guarded FEC codewords by two Reed-Solomon encoders are interleaved. There was a problem.

The present invention has been made to solve such a conventional problem, and is an FEC error adding device capable of generating a test signal for testing the FEC function of a communication device that receives a PAM4 signal. It is an object of the present invention to provide a test signal generator using the method and an FEC error adding method.

In order to solve the above-mentioned problems, an FEC error adding apparatus according to the present invention is an FEC error adding apparatus for adding an error to a PAM4 signal including a plurality of FEC codewords each including a plurality of FEC symbols. And an LSB, an error signal generator that generates an error signal for continuously adding the error to one or both of the MSB and the LSB at a predetermined bit interval, the MSB and the LSB. An exclusive OR operation with the error signal is performed on a bit-by-bit basis, and an error addition unit that outputs a bit string obtained as a result of the operation and a bit string of the MSB and the LSB output from the error addition unit are combined. A synthesizing unit for generating the error-added PAM4 signal and outputting the error-added PAM4 signal as a test signal, a bit error rate input unit for inputting the bit error rate of the test signal, and the test An error FEC symbol number input to which the number of the error FEC symbols included in the FEC codeword having the error FEC symbol that is the FEC symbol to which the error is added is input from among the plurality of FEC codewords included in the signal Section, an error bit number input section for inputting the number of error bits included in the error FEC symbol, a CW size input section for inputting the number of bits forming the FEC codeword, and the bit error rate input Unit, the number of error FEC symbols input to the error FEC symbol number input unit, the number of error bits input to the error bit number input unit, and the CW size input A minimum number of the FEC codewords necessary to realize the bit error rate based on the number of bits input to the unit, and the error FEC symbol included in the minimum number of the FEC codewords. A CW number calculation unit that calculates the number of FEC codewords, wherein the error signal generation unit calculates the CW number by the minimum number of consecutive FEC codewords calculated by the CW number calculation unit. And outputting the error signal for generating the test signal including the FEC codeword having the number of the error FEC symbols calculated by the unit.

With this configuration, the FEC error adding apparatus according to the present invention can generate a test signal for testing the FEC function of the communication device that receives the PAM4 signal. The FEC error adding apparatus according to the present invention can easily generate a test signal that can or cannot be error-corrected by the FEC decoder of the communication device under test by changing the parameter such as the bit error rate. You can

Further, in the FEC error adding apparatus according to the present invention, the error signal generating unit outputs one error FEC symbol for every n FEC codewords in the minimum number of consecutive FEC codewords in the test signal. The error signal is generated such that the pattern including the FEC code word having the same is repeated m times and the pattern including the FEC code word having one error FEC symbol for every n+1 FEC code words is repeated p times. It may be configured to generate.

With this configuration, the FEC error adding apparatus according to the present invention continuously adds errors to the MSB and LSB of the PAM4 signal at predetermined bit intervals, so that the FEC codewords including burst errors are temporally evenly spaced. Can be generated with. As a result, the FEC error adding apparatus according to the present invention can generate a test signal that enables efficient error rate measurement in a short time.

Also, a test signal generator according to the present invention outputs a PAM4 signal including the FEC error adding device described above and a plurality of FEC codewords including a plurality of FEC symbols to the dividing unit of the FEC error adding device. And a section.

With this configuration, the test signal generator according to the present invention can generate a test signal for testing the FEC function of the communication device that receives the PAM4 signal.

The FEC error adding method according to the present invention is an FEC error adding method of adding an error to a PAM4 signal including a plurality of FEC codewords each including a plurality of FEC symbols, and dividing the PAM4 signal into MSB and LSB. An error signal generating step of generating an error signal for continuously adding the error to one or both of the MSB and the LSB at a predetermined bit interval, and exclusion of the MSB and the LSB from the error signal. The error addition step of performing the logical OR operation on a bit-by-bit basis and outputting the bit string obtained as a result of the operation, and the bit string of the MSB and the LSB output from the error adding step are combined to add the error. A synthesizing step of generating a PAM4 signal and outputting the PAM4 signal to which the error is added as a test signal, a bit error rate input step of inputting a bit error rate of the test signal, and a plurality of test signals included in the test signal. An error FEC symbol number input step of inputting the number of the error FEC symbols included in an FEC codeword having an error FEC symbol that is the FEC symbol to which the error is added among the FEC codewords; The error bit number input step for inputting the number of error bits included in the symbol, the CW size input step for inputting the number of bits constituting the FEC codeword, and the input step for the bit error rate input step. Bit error rate, the number of error FEC symbols input in the error FEC symbol number input step, the number of error bits input in the error bit number input step, and the CW size input step A minimum number of FEC codewords required to achieve the bit error rate based on the number of bits, and a number of FEC codewords having the erroneous FEC symbols included in the minimum number of FEC codewords; In the error signal generating step, the minimum number of consecutive FEC codewords calculated in the CW number calculating step is calculated in the CW number calculating step. And outputting the error signal for generating the test signal including an FEC codeword having a number of the error FEC symbols.

With this configuration, the FEC error adding method according to the present invention can generate a test signal for testing the FEC function of the communication device that receives the PAM4 signal. The FEC error adding method according to the present invention can easily generate a test signal that can or cannot be error-corrected by the FEC decoder of the communication device under test by changing parameters such as a bit error rate. You can

Further, in the FEC error adding method according to the present invention, the error signal generating step includes one error FEC symbol for every n FEC codewords in the minimum number of consecutive FEC codewords in the test signal. The error signal is generated such that the pattern including the FEC code word having the same is repeated m times and the pattern including the FEC code word having one error FEC symbol for every n+1 FEC code words is repeated p times. It may be configured to generate.

With this configuration, in the FEC error adding method according to the present invention, errors are continuously added to the MSB and LSB of the PAM4 signal at predetermined bit intervals, so that FEC codewords including burst errors are evenly spaced in time. Can be generated with. As a result, the FEC error adding apparatus according to the present invention can generate a test signal that enables efficient error rate measurement in a short time.

The present invention provides an FEC error addition device capable of generating a test signal for testing the FEC function of a communication device that receives a PAM4 signal, a test signal generation device using the FEC error addition device, and an FEC error addition method. Is.

It is a block diagram which shows the structure of the test signal generator which concerns on embodiment of this invention. It is a figure for demonstrating the appearance timing of an error FEC codeword controlled by the control part of the FEC error addition apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the addition timing of the error with respect to a PAM4 signal controlled by the control part of the FEC error addition apparatus which concerns on embodiment of this invention. FIG. 7 is a sequence diagram for explaining processing of an FEC error adding method using the FEC error adding device according to the embodiment of the present invention. It is a figure which shows the structure of the FEC codeword of RS-FEC(544,514). It is a schematic diagram for explaining interleaving.

Embodiments of an FEC error adding apparatus, a test signal generating apparatus using the same, and an FEC error adding method according to the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a test signal generator 100 according to an exemplary embodiment of the present invention includes a PAM4 signal output unit 10 and an FEC error adder for adding an error to a PAM4 signal including a plurality of FEC codewords each including a plurality of FEC symbols. The device 20 is provided, and a test signal is output to a device under test (DUT) 200.

The PAM4 signal output unit 10 includes a MAC frame data output unit 11, an FEC encoder 12, and a PAM4 processing unit 13. The MAC frame data output unit 11 outputs the MAC frame data for testing the DUT 200 to be tested to the FEC encoder 12 as test signal data.

The FEC encoder 12 performs FEC coding on the data of the MAC frame output from the MAC frame data output unit 11 to sequentially generate FEC codewords composed of a plurality of FEC symbols. In the present embodiment, it is assumed that the FEC encoding by the FEC encoder 12 corresponds to RS-FEC (544, 514) defined in IEEE802.3.

The FEC codeword of RS-FEC (544, 514) generated by the FEC encoder 12 has 544 FEC symbols including a parity part of 30 FEC symbols and a message part of 514 FEC symbols. Have. Since the FEC codeword includes the parity part of this 30 FEC symbol, it is possible for the FEC decoder on the DUT 200 side to correct an error of up to 15 FEC symbols per 1 FEC codeword. Note that one FEC symbol consists of 10 bits, but if the number of error bits included in one FEC symbol is in the range of 1 to 10, the FEC symbol becomes an error FEC symbol including an error.

The PAM4 processing unit 13 is configured to generate a PAM4 signal including a plurality of FEC codewords output from the FEC encoder 12 by performing processing such as Gray coding and PAM4 encoding defined in IEEE802.3. ing. The PAM4 signal is composed of four PAM4 symbols consisting of "00", "01", "10", and "11".

The FEC error adding device 20 includes a dividing unit 21, an error signal generating unit 22, an error adding unit 23, a combining unit 24, a control unit 25, a display unit 26, and an operation unit 27.

The division unit 21 is configured to divide the PAM4 signal output from the PAM4 processing unit 13 of the PAM4 signal output unit 10 into MSB (most significant bit) and LSB (least significant bit) of the PAM4 symbol.

The error signal generator 22 is adapted to generate an error signal for continuously adding an error to the MSB and the LSB of the PAM4 signal output from the divider 21 at predetermined bit intervals.

Under the control of the control unit 25, it is assumed that the error signal output from the error signal generation unit 22 is timing-adjusted so as to be synchronized with the MSB and LSB bit string signals output from the division unit 21.

The error adding unit 23 performs an exclusive OR (XOR) operation of the MSB and LSB of the PAM4 signal output from the dividing unit 21 and the error signal output from the error signal generating unit 22 on a bit-by-bit basis, and performs the operation. The resulting bit string is output.

The combining unit 24 combines the MSB and LSB bit strings output from the error adding unit 23 to generate an error-added PAM4 signal, and outputs the error-added PAM4 signal to the DUT 200 as a test signal. It has become.

The DUT 200 performs a process reverse to that of the PAM4 processing unit 13 on the test signal output from the test signal generating device 100 to restore the FEC codeword with an error added, and the restored FEC codeword by the FEC decoder. It is designed to be decoded.

The control unit 25 is composed of, for example, a microcomputer including a CPU, a ROM, a RAM, a HDD, a personal computer, or the like, and controls the operation of each of the above-described units included in the test signal generator 100. Further, the control unit 25 transfers a predetermined program stored in the ROM or the like to the RAM and executes the program so that a bit error rate input unit 25a, an error FEC symbol number input unit 25b, an error bit number input unit 25c, which will be described later, The CW size input unit 25d, the CW number calculation unit 25e, and the CW timing control unit 25f can be configured by software.

The bit error rate input unit 25a, the error FEC symbol number input unit 25b, the error bit number input unit 25c, the CW size input unit 25d, the CW number calculation unit 25e, and the CW timing control unit 25f are the FPGA (Field Programmable Gate Array). ) Or an ASIC (Application Specific Integrated Circuit). Alternatively, the bit error rate input unit 25a, the error FEC symbol number input unit 25b, the error bit number input unit 25c, the CW size input unit 25d, the CW number calculation unit 25e, and the CW timing control unit 25f are hardware processing by digital circuits. It is also possible to appropriately combine the above and software processing by a predetermined program.

The bit error rate input unit 25a is configured to input a desired bit error rate ER of the test signal output from the combining unit 24 in response to a user's operation on the operation unit 27.

The error FEC symbol number input unit 25b, among the plurality of FEC codewords included in the test signal according to the user's operation on the operation unit 27, has an FEC codeword having an error FEC symbol (hereinafter, referred to as “error FEC codeword”). (Also referred to as “”), the desired number of error FEC symbols sE is input.

The error bit number input unit 25c is configured to input a desired number bE of error bits included in the error FEC symbol in response to a user's operation on the operation unit 27.

The CW size input unit 25d is configured to input the number of bits forming the FEC codeword (hereinafter, also referred to as “CW size”) CW _size in response to a user's operation on the operation unit 27. For example, in the case of RS-FEC (544,514), the CW size is 5440 bits.

The CW number calculation unit 25e inputs the bit error rate ER input to the bit error rate input unit 25a, the number of error FEC symbols sE input to the error FEC symbol number input unit 25b, and the error bit number input unit 25c. the number of error bits bE, and, based on the CW size _{CW size} input to the CW size input unit 25d, and the minimum number of FEC codewords required in order to achieve a desired bit error rate, FEC of the minimum number The number of error FEC codewords included in the codeword is calculated.

The CW timing control unit 25f causes the minimum number of consecutive FEC codewords calculated by the CW number calculation unit 25e to generate a test signal including the number of erroneous FEC codewords calculated by the CW number calculation unit 25e. , And generates a timing signal for controlling the timing of the error signal output from the error signal generator 22.

The error signal generator 22 generates an error signal according to the timing signal output from the CW timing controller 25f. For example, this error signal causes a pattern containing one erroneous FEC codeword for every n FEC codewords to be repeated m times in the minimum number of consecutive FEC codewords in the test signal, and n+1 FEC codewords. A pattern including one erroneous FEC codeword for each codeword is repeated p times.

The display unit 26 is composed of a display device such as an LCD or a CRT, and displays various display contents according to a control signal from the control unit 25. Further, the display unit 26 displays operation targets such as soft keys for setting various conditions, pull-down menus, and text boxes.

The operation unit 27 is for receiving an operation input by the user, and is configured by, for example, a touch panel provided on the surface of the display screen of the display unit 26. Alternatively, the operation unit 27 may include an input device such as a keyboard or a mouse. Further, the operation unit 27 may be configured by an external control device that performs remote control by a remote command or the like.

The operation input to the operation unit 27 is detected by the control unit 25. For example, the operation unit 27 can be used to select the data of the MAC frame to be output from the MAC frame data output unit 11, and the user can arbitrarily specify various parameters such as ER, sE, bE, and CW _size described later. is there.

Hereinafter, an example of processing executed by the bit error rate input unit 25a, the error FEC symbol number input unit 25b, the error bit number input unit 25c, the CW size input unit 25d, the CW number calculation unit 25e, and the CW timing control unit 25f will be described. To do.

First, when the user operates the operation unit 27, the bit error rate ER, the error FEC symbol number sE per FEC codeword, the error bit number bE per error FEC symbol, and the CW size CW _size are respectively changed. It is input to the input unit 25a, the error FEC symbol number input unit 25b, the error bit number input unit 25c, and the CW size input unit 25d.

The bit error rate ER (=α×10 ^−N ) is the bit error rate ER, the number of error FEC symbols per FEC codeword sE, the number of error bits per error FEC symbol bE, the CW size CW _size , and the FEC code of interest. The number of words T _CW and the number of erroneous FEC codewords E _CW included in the T _CW FEC codewords are used to represent the following equation (1).

ここで、式（１）の分母は注目する全ビット数であり、分子は注目する全ビット数に含まれる誤りビット数を表している。

Here, the denominator of Expression (1) is the total number of bits of interest, and the numerator represents the number of error bits included in the total number of bits of interest.

Expression (1) can be transformed into Expression (2). As described above, since an error FEC symbol can be generated by including one error bit in the FEC symbol, the number of error bits bE per error FEC symbol is set to 1 in Expression (2).

Subtracting Equation (2), the numerator and denominator are as shown in Equation (3) and Equation (4), respectively.

ここで、式（３）及び式（４）の分母は、式（２）の分子と分母の最大公約数である。式（３）で与えられるＴ_ＣＷの値は、所望のビット誤り率ＥＲを実現するために必要なＦＥＣコードワードの最小数である。また、式（４）で与えられるＥ_ＣＷの値は、Ｔ_ＣＷ個のＦＥＣコードワードに含まれる誤りＦＥＣコードワードの数である。

Here, the denominators of equations (3) and (4) are the greatest common divisors of the numerator and denominator of equation (2). The value of _TCW given by equation (3) is the minimum number of FEC codewords needed to achieve the desired bit error rate ER. The value of E _CW given by the equation (4) is the number of error FEC codewords included in the T _CW FEC codewords.

That is, the CW number calculation unit 25e calculates T _CW and E _CW according to the equations (3) and (4). For example, the bit error rate ER 3 × ^{10 -4} (i.e., alpha = 3 and N = 4), When the 5, CW size _{CW size} error FEC symbol number sE _{5440, T CW} 625 _{becomes, E CW} is It becomes 204.

Further, the CW timing control unit 25f calculates n, m, and p described above according to the following equations (5) to (7).

ここで、ｍｏｄ（Ｔ_ＣＷ／Ｅ_ＣＷ）は、Ｔ_ＣＷをＥ_ＣＷで割ったときの余りである。このようにして、ｎ、ｍ、及びｐを算出することにより、Ｔ_ＣＷ個のＦＥＣコードワードの中に、ほぼ均等にＥ_ＣＷ個の誤りＦＥＣコードワードを配置することができる。

Here, mod(T _CW /E _CW ) is the remainder when T _CW is divided by E _CW . By calculating n, m, and p in this way, it is possible to arrange E _CW error FEC codewords almost evenly in T _CW FEC codewords.

In the case of the above example in which the bit error rate ER is 3×10 ⁻⁴ , the number of error FEC symbols sE is 5, the CW size CW _size is 5440, the _TCW is 625, and the _ECW is 204, equations (5) to (7) are used. ), n=3, m=191, and p=13. That is, as shown in FIG. 2, for 573 (=n×m) of 625 FEC codewords, one error FEC codeword (shown in black) is provided for every three FEC codewords. The included pattern is repeated 191 times. Further, for 52 (=(n+1)×p) of 625 FEC codewords, a pattern including one error FEC codeword for every four FEC codewords is repeated 13 times. Within each error FEC codeword, there are 5 consecutive error FEC symbols (ie, burst FEC symbol errors). The same applies to the 626th and subsequent FEC codewords.

In the example shown in FIG. 2, in the 625 consecutive FEC codewords, the pattern for every three FEC codewords is repeated, and then the pattern for every four FEC codewords is repeated. However, the present invention is not limited to this. For example, the pattern for every three FEC codewords and the pattern for every four FEC codewords may be arranged in a random order.

The CW timing control unit 25f gives an error to the MSB and/or the LSB of the PAM4 signal output from the PAM4 processing unit 13 at a predetermined bit interval according to the appearance timing of the error FEC codeword obtained as described above. A timing signal for adding is generated. For example, focusing on one error FEC codeword, when the number of error FEC symbols sE is 2, as shown in black in FIG. Is added twice. The location to which the error is added may be the LSB or both the MSB and the LSB.

Hereinafter, an example of the process of the FEC error adding method using the FEC error adding device 20 will be described with reference to the sequence diagram of FIG.

First, various parameters are input by the user operating the operation unit 27 (input step S1). These parameters include the bit error rate ER of the test signal, the number sE of error FEC symbols included in the error FEC codeword, the number bE of error bits included in the error FEC symbol, the CW size CW _{size, and the} like. Be done.

Next, the CW number calculation unit 25e determines the FEC codeword required to realize the desired bit error rate based on the parameters such as the bit error rate and the number of error FEC symbols input in the input step S1. The minimum number and the number of error FEC codewords included in this minimum number of FEC codewords are calculated (CW number calculation step S2).

Next, the CW timing control unit 25f starts the output of the timing signal that controls the timing of the error signal output from the error signal generation unit 22 (step S3).

Next, the error signal generator 22 starts outputting an error signal for continuously adding an error to MSB and/or LSB of the PAM4 signal output from the divider 21 at predetermined bit intervals (error). Signal generation step S4). This error signal is for generating a test signal in which the minimum number of consecutive FEC codewords calculated in the CW number calculation step S2 includes the number of erroneous FEC codewords calculated in the CW number calculation step S2. is there.

On the other hand, the division unit 21 starts the process of dividing the PAM4 signal output from the PAM4 signal output unit 10 into MSB and LSB (division step S5).

Next, the error adding unit 23 performs an XOR operation on a bit-by-bit basis between the MSB and LSB of the PAM4 signal output from the dividing step S5 and the error signal output from the error signal generating step S4, and obtains the operation result as the operation result. The output of the bit string to be generated is started (error adding step S6).

Next, the synthesizing section 24 synthesizes the MSB and LSB bit strings output from the error adding step S6 to generate an error-added PAM4 signal, and outputs the error-added PAM4 signal as a test signal. The process is started (compositing step S7).

As described above, the FEC error adding apparatus 20 according to the present exemplary embodiment allows the user to specify parameters such as the bit error rate of the test signal and the number of error FEC symbols, so that the FEC of the DUT 200 that receives the PAM4 signal. A test signal can be generated to test the function. The FEC error adding apparatus 20 according to the present embodiment can easily generate a test signal that can or cannot be error-corrected by the FEC decoder of the DUT 200 by changing these parameters.

By the way, conventionally, in error rate measurement, a test signal whose error has a Poisson distribution may be used. However, when a test signal whose error is Poisson distribution is used, there is a problem that the test time becomes long. Furthermore, when the bit rate exceeds 100 Gbit/s, if a logic circuit such as an FPGA is used to generate a test signal whose error is Poisson distribution, the circuit implementation scale becomes enormous, and as a result it becomes impossible to implement. There is a problem of becoming.

On the other hand, since the FEC error adding apparatus 20 according to the present embodiment continuously adds errors to MSB and LSB of the PAM4 signal at predetermined bit intervals, the FEC codeword including a burst error is almost time-wise. It can be generated at even intervals. As a result, the FEC error adding apparatus 20 according to the present embodiment can generate a test signal that enables efficient error rate measurement in a short time.

10 PAM4 signal output unit 11 MAC frame data output unit 12 FEC encoder 13 PAM4 processing unit 20 FEC error addition device 21 division unit 22 error signal generation unit 23 error addition unit 24 synthesis unit 25 control unit 25a bit error rate input unit 25b error FEC Symbol number input unit 25c Error bit number input unit 25d CW size input unit 25e CW number calculation unit 25f CW timing control unit 26 Display unit 27 Operation unit 100 Test signal generator 200 DUT

Claims (5)

An FEC error adding device (20) for adding an error to a PAM4 signal including a plurality of FEC codewords each including a plurality of FEC symbols,
A division unit (21) for dividing the PAM4 signal into MSB and LSB;
An error signal generator (22) for generating an error signal for continuously adding the error to one or both of the MSB and the LSB at a predetermined bit interval;
An error addition unit (23) that performs an exclusive OR operation of the MSB and the LSB and the error signal in bit units, and outputs a bit string obtained as a result of the operation,
A combining unit (24) that combines the MSB and LSB bit strings output from the error adding unit to generate the error-added PAM4 signal and outputs the error-added PAM4 signal as a test signal. When,
A bit error rate input unit (25a) to which the bit error rate of the test signal is input;
An error FEC symbol to which the number of the error FEC symbols included in the FEC codeword having an error FEC symbol, which is the FEC symbol to which the error is added, among the plurality of FEC codewords included in the test signal is input. A number input section (25b),
An error bit number input unit (25c) for inputting the number of error bits included in the error FEC symbol,
A CW size input unit (25d) into which the number of bits forming the FEC codeword is input;
The bit error rate input to the bit error rate input unit, the number of error FEC symbols input to the error FEC symbol number input unit, the number of error bits input to the error bit number input unit, and , The minimum number of the FEC codewords required to realize the bit error rate based on the number of the bits input to the CW size input unit, and the minimum number of FEC codewords included in the FEC codewords. A CW number calculation unit (25e) for calculating the number of FEC codewords having erroneous FEC symbols,
The error signal generation unit generates an FEC codeword in which the minimum number of continuous FEC codewords calculated by the CW number calculation unit has the number of the error FEC symbols calculated by the CW number calculation unit. An FEC error adding apparatus, which outputs the error signal for generating the test signal including the FEC error adding apparatus. The error signal generator repeats a pattern including an FEC codeword having one error FEC symbol for every n FEC codewords m times in the minimum number of consecutive FEC codewords in the test signal. The error signal is generated so that a pattern including an FEC codeword having one error FEC symbol for every n+1 FEC codewords is repeated p times. FEC error adding device. An FEC error adding device (20) according to claim 1 or 2,
A PAM4 signal output unit (10) for outputting a PAM4 signal including a plurality of FEC codewords each including a plurality of FEC symbols to the division unit of the FEC error adding device, the test signal generating device. A FEC error adding method for adding an error to a PAM4 signal including a plurality of FEC codewords each including a plurality of FEC symbols,
A dividing step (S5) of dividing the PAM4 signal into MSB and LSB;
An error signal generating step (S4) of generating an error signal for continuously adding the error to one or both of the MSB and the LSB at a predetermined bit interval;
An error addition step (S6) of performing an exclusive OR operation of the MSB and the LSB and the error signal on a bit-by-bit basis and outputting a bit string obtained as a result of the operation.
A combining step (S7) of combining the bit strings of the MSB and the LSB output from the error adding step to generate a PAM4 signal added with the error and outputting the PAM4 signal added with the error as a test signal. When,
A bit error rate input step (S1) in which the bit error rate of the test signal is input,
An error FEC symbol to which the number of the error FEC symbols included in the FEC codeword having an error FEC symbol, which is the FEC symbol to which the error is added, among the plurality of FEC codewords included in the test signal is input. A number input step (S1),
An error bit number input step (S1) for inputting the number of error bits included in the error FEC symbol;
A CW size input step (S1) in which the number of bits forming the FEC codeword is input;
The bit error rate input in the bit error rate input step, the number of error FEC symbols input in the error FEC symbol number input step, the number of error bits input in the error bit number input step, and , A minimum number of the FEC codewords required to achieve the bit error rate based on the number of the bits input to the CW size input step, and the minimum number of FEC codewords included in the FEC codewords. A CW number calculation step (S2) for calculating the number of FEC codewords having an erroneous FEC symbol, and
In the error signal generating step, the minimum number of consecutive FEC codewords calculated in the CW number calculating step are FEC codewords having the number of the error FEC symbols calculated in the CW number calculating step. An FEC error adding method comprising outputting the error signal for generating the test signal including the error signal. In the error signal generating step, a pattern including an FEC codeword having one error FEC symbol for every n FEC codewords is repeated m times in the minimum number of consecutive FEC codewords in the test signal. At the same time, the error signal is generated such that a pattern including an FEC codeword having one error FEC symbol for every n+1 FEC codewords is repeated p times. FEC error addition method.

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