A receiver for transmitter quality parameter determination

Abstract

The disclosure relates to communication based on pulse amplitude modulation (PAM). The disclosure proposes a receiver and a corresponding method for operating the receiver. The receiver is configured to obtain a signal, wherein the signal is based on a PAM signal that comprises N PAM signal levels and is sent by a transmitter over a channel to the receiver, equalize the signal using a Duobinary feed forward equalizer (DB FFE) with a plurality of taps to generate an equalized signal comprising 2N-1 signal levels; and determine a transmitter quality parameter of the transmitter based on the equalized signal.

Description

[0001] A RECEIVER FOR TRANSMITTER QUALITY PARAMETER DETERMINATION

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to communication based on pulse amplitude modulation. The disclosure proposes a receiver and a corresponding method for operating the receiver. The receiver determines a transmitter quality parameter in a new kind of way.

[0004] BACKGROUND

[0005] Conventional high-performance optical interconnects used in data communications deploy a 4-level pulse amplitude modulation format (PAM4). One of the main system-level signal quality metrics is transmitter dispersion eye closure quaternary (TDECQ). The transmitter eye closure quaternary (TECQ) is also used for channels without chromatic dispersion (CD). The difference between TDECQ and TECQ values provides CD penalties.

[0006] The TDECQ quantifies penalties coming from impairments that are equalizable or nonequalizable using a reference receiver. TDECQ is a measure of each optical transmitter's vertical eye closure when transmitted through a worst-case optical channel, as measured through an optical-to-electrical converter (O / E) and oscilloscope with the combined frequency response and equalized with the reference equalizer. The reference receiver and equalizer may be implemented in software or may be part of an oscilloscope.

[0007] SUMMARY

[0008] In view of the above, an objective of this disclosure is to improve transmitter quality determination. Another objective is to enhance equalization performance. Another objective to relax the requirement on transmitter components.

[0009] This and other objectives are achieved by the solutions of this disclosure as described in the independent claims. Advantageous implementations are further described in the dependent claims.

[0010] The solutions of this disclosure are based on the following considerations.

[0011] A first aspect of this disclosure provides a receiver for pulse amplitude modulation (PAM) signals, the receiver being configured to: obtain a signal, wherein the signal is based on a PAM signal that comprises N PAM signal levels and is sent by a transmitter, for example, an optical transmitter or an Radio Frequency (RF) transmitter, over a channel to the receiver, wherein N is an integer larger than 1 ; equalize the signal using a Duobinary feed forward equalizer (DB FFE) with a plurality of taps to generate an equalized signal comprising 2N-1 signal levels; and determine a transmitter quality parameter of the transmitter based on the equalized signal.

[0012] For example, the signal may be or comprise the PAM signal or the signal may be an electrical signal based on the PAM signal, whereas the PAM signal may be an optical signal. The transmitter quality parameter may represent a quality of the transmitter. For example, the transmitter quality parameter may represent how the transmitter performs in transmitting the signal. The DB FFE may provide improved performance in, for example, bandwidth-limited systems. The receiver provides improved transmitter quality parameter calculation. For example, the receiver device can calculate an accurate transmitter quality parameter. In an implementation form of the first aspect, the receiver is configured to: generate a histogram based on the equalized signal, determine, for example, in an initial iteration, a first noise deviation based on the histogram, the plurality of taps, and a target signal error rate (TSER), wherein a signal error rate (SER) of the histogram reaches the TSER if noise based on the first noise deviation is added to the histogram, and determine the transmitter quality parameter based on the first noise deviation and the TSER. The TSER may be predetermined. Generating the histogram may be performed in an initial iteration. A first input referred receiver noise deviation may be based on the first noise deviation. A SER of the histogram may reach the TSER if noise having the first input referred receiver noise deviation is added to the histogram.

[0013] The term “reaching a TSER” may refer to the absolute value of the difference between the SER and the TSER being below a threshold and / or the SER being larger than the TSER and / or a selected SER of a set of SERs being the closest SER to the TSER. For example, a TDECQ algorithm, which may be connected to the receiver, may find the largest input referred receiver noise deviation (OG) that causes a SER equal to the TSER.

[0014] In a single iteration, for example, the initial iteration or an iteration of the one or more iterations, the receiver may be configured to scan noise until determining a noise with a certain noise deviation that reaches the TSER. For example, the receiver may be configured to start with a small noise deviation and estimate an intermediate SER, for example, based on equations using cumulative distributions. If said intermediate SER is smaller than the TSER, the noise deviation of the noise is increased until the TSER is crossed / reached. The receiver may be configured to repeat this procedure until the added noise difference is below some small value or threshold. For example, in a single iteration, the receiver may be configured to vary the noise deviation 1000 times in small steps. The noise that produces a SER that is closest to TSER may be selected. The one or more iterations may not comprise the initial iteration.

[0015] In a further implementation form of the first aspect, for each iteration of one or more iterations, the receiver is further configured to: add noise, for example, Additive White Gaussian Noise (AWGN), having a previously determined noise deviation at an input of the DB FFE to the signal, wherein the previously determined noise deviation is the first noise deviation or an updated noise deviation of a directly preceding iteration of the one or more iterations, update the plurality of taps with the equalizer based on the signal and the added noise having the previously determined noise deviation, determine an updated noise deviation of the iteration based on the histogram, the updated plurality of taps of the iteration, and the TSER, wherein a SER of the histogram reaches the TSER if noise based on the updated noise deviation of the iteration is added to the histogram, wherein the receiver is configured to calculate the transmitter quality parameter based on the updated noise deviation of a last iteration of the one or more iterations and the TSER.

[0016] An updated input referred receiver noise deviation may be based on the updated noise deviation. A SER of the histogram may reach the TSER if noise having the updated input referred receiver noise deviation is added to the histogram. Each iteration may be used to determine more accurate / updated taps and a more accurate / updated noise deviation.

[0017] An initial iteration may include generating the histogram and determining the first noise deviation. For each iteration of the one or more iterations, AWGN with the previously determined noise deviation may be added to the samples before the DB FFE. The DB FFE may change the plurality of taps due to added noise. The updated plurality of taps may be used to determine the updated noise deviation. For example, the updated plurality of taps may be used to calculate an updated noise enhancement factor, wherein the updated noise enhancement factor may be used to calculate the updated noise deviation.

[0018] In a further implementation form of the first aspect, the receiver is configured to: calculate a first noise enhancement factor based on the plurality of taps, calculate a plurality of cumulative distribution functions (CFs) based on the histogram, determine the first noise deviation based on the first noise enhancement factor, the plurality of cumulative distribution functions, and the TSER, wherein the SER of the histogram reaches the TSER if noise based on the first noise deviation is added to the histogram. The first noise deviation may be further determined based on the histogram. The first input referred receiver noise deviation may be based on the first noise deviation and the first noise enhancement factor.

[0019] In a further implementation form of the first aspect, for each iteration of one or more iterations, the receiver is configured to: calculate an updated noise enhancement factor of the iteration based on the updated plurality of taps, determine the updated noise deviation of the iteration based on the updated noise enhancement factor of the iteration, the plurality of cumulative distribution functions, and the TSER. The updated noise deviation of the iteration may be further determined based on the histogram. The updated input referred receiver noise deviation may be based on the updated noise deviation and the updated noise enhancement factor. Each iteration may be used to determine a more accurate / updated noise enhancement factor.

[0020] In a further implementation form of the first aspect, the plurality of CFs are 2N-2 CFs.

[0021] In a further implementation form of the first aspect, the first noise deviation fulfills an equation that is based on at least one of: a sum over M>1 bins of the histogram; a sum over the plurality of CFs; the first noise enhancement factor; the TSER.

[0022] In a further implementation form of the first aspect, for each iteration of the one or more iterations, the updated noise deviation of the iteration fulfills an equation that is based on at least one of: a sum over M>1 bins of the histogram; a sum over the plurality of CFs; the updated noise enhancement factor of the iteration; the TSER.

[0023] In a further implementation form of the first aspect, the receiver is configured to determine the transmitter quality parameter (TQP) based on TQP = 101oglO(OMA / 12 / Q / o), and Q = Q-1(TSER-8 / l 5), wherein Q1is the inverse function of Q, wherein OMA is an optical modulation amplitude of the signal, and wherein o is the first noise deviation or the updated noise deviation if present. For example, OMA may be the difference between the highest amplitude level and the lowest amplitude level.

[0024] In a further implementation form of the first aspect, the receiver is configured to determine 2N-1 signal levels and / or 2N-2 thresholds of the histogram based on the histogram, and determine the first noise deviation further based on the determined 2N-1 signal levels and / or 2N-2 thresholds.

[0025] In a further implementation form of the first aspect, for each iteration of the one or more iterations, the receiver is configured determine the updated noise deviation of the iteration further based on the determined 2N-1 signal levels and / or 2N-2 thresholds.

[0026] In a further implementation form of the first aspect, the receiver is configured to apply a hard slicer on the equalized signal to obtain one or more 2N-1 level symbols. For example, the receiver may be configured to apply the hard slicer on the equalized signal based on the determined 2N-1 signal levels and / or the determined 2N-2 thresholds.

[0027] In a further implementation form of the first aspect, the receiver is configured decode each symbol of the one or more 2N-1 level symbols based on a value of the symbol modulo N. Each symbol of the one or more 2N- 1 level symbols may be converted to a N level symbol based on the value of the symbol modulo N. Thus, decoding may be more efficient and / or the complexity of decoding may be reduced. The DB FFE may form a Duobinary encoder for the receiver. The receiver may not comprise another Duobinary encoder for the one or more symbols. An output of the Duobinary encoder may provide the one or more 2N-1 level symbols. In this disclosure, a “N’ level symbol” is considered to be a symbol having one respective signal level of N’ signal levels, wherein N’ is an integer larger than 1. For example, each symbol of the one or more 2N-1 level symbols may have one respective signal level of 2N-1 signal levels.

[0028] In a further implementation form of the first aspect, the receiver is configured to determine a respective transmitter quality parameter by using a respective equalized signal for each sampling phase of two or more sampling phases.

[0029] In a further implementation form of the first aspect, the transmitter quality parameter is a transmitter dispersion eye closure multinary (TDECM) or a transmitter dispersion eye closure quaternary (TDECQ).

[0030] In a further implementation form of the first aspect, N is 4 and the one or more modulated signals are modulated according to a 4-level pulse amplitude modulation format, PAM4.

[0031] A second aspect of this disclosure provides a method of operating a receiver for PAM signals, the method comprising: obtaining a signal, wherein the signal is based on a PAM signal that comprises N PAM signal levels and is sent by a transmitter over a channel to the receiver, wherein N is an integer larger than 1 ; equalizing the signal using a DB FFE with a plurality of taps to generate an equalized signal comprising 2N-1 signal levels; and determining a transmitter quality parameter of the transmitter based on the equalized signal.

[0032] The method of the second aspect may have implementation forms that correspond to the implementation forms of the receiver of the first aspect. The method of the second aspect and its implementation forms achieve the advantages and effects described above for the receiver of the first aspect and its respective implementation forms. Further, in this disclosure, the term “symbol error rate” and “signal error rate” may be used interchangeably. Further, in this disclosure, a first element and a second element are considered to be different components, if not explicitly mentioned otherwise.

[0033] It has to be noted that all devices, elements, units and means described in the disclosure could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the disclosure as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities.

[0034] Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

[0035] BRIEF DESCRIPTION OF DRAWINGS

[0036] The above-described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which

[0037] FIG. 1 shows a receiver according to this disclosure.

[0038] FIG. 2 shows a SER associated with a FR FFE and a SER associated with a DB FFE.

[0039] FIG. 3a shows an exemplary receiver according to this disclosure implemented in an optical transmission system.

[0040] FIG. 3b shows a PAM4 eye diagram of a conventional FR FEE.

[0041] FIG. 4a shows a Duobinary system including a DB FFE according to this disclosure. FIG. 4b shows a conventional Duobinary system including a FR FFE.

[0042] FIG. 5 shows an exemplary Duobinary histogram according to this disclosure.

[0043] FIG. 6 shows a respective SER obtained using DT and OT according to this disclosure.

[0044] FIG. 7 shows an exemplary Duobinary histogram according to this disclosure.

[0045] FIG. 8 shows a method according to this disclosure.

[0046] DETAILED DESCRIPTION OF EMBODIMENTS

[0047] FIG. 1 shows a receiver 100 according to this disclosure. The receiver 100 is for PAM signals. The receiver 100 is configured to obtain a signal 104, wherein the signal 104 is based on a PAM signal that comprises N PAM signal levels, and is sent by a transmitter 101, for example, an optical transmitter or a RF transmitter, over a channel 102 to the receiver 100. For example, the signal 104 may be or comprise the PAM signal. For example, the receiver 100 may be configured to receive the signal 104 from the transmitter 101 over the channel 102. Alternatively, the signal 104 may be an electrical signal based on the PAM signal, whereas the PAM signal may be an optical signal. N is an integer larger than 1.

[0048] The receiver 100 is further configured to equalize the signal 104 using a DB FFE 103 with a plurality of taps to generate an equalized signal 105 comprising 2N-1 signal levels; and determine a transmitter quality parameter 106 of the transmitter 101 based on the equalized signal 105. Determining the transmitter quality parameter 106 may comprise performing one or more iterations to update the plurality of taps and / or update a noise deviation.

[0049] The transmitter quality parameter may represent a quality of the transmitter. For example, the transmitter quality parameter may represent how the transmitter performs in transmitting the signal. For example, the transmitter quality parameter may be a transmitter TDECM or a TDECQ. The transmitter quality parameter 106 may include any transmission scenario and any modulation format. Thus, the receiver 100 may be used to estimate the quality of the transmitter 101, for example, an optical transmitter 101. The receiver 100 may support standardization and transmitter 101 selection.

[0050] A person skilled in the art will appreciate that the method disclosed herein can be applied to any PAM (Pulse Amplitude Modulation) modulation format without loss of generality.

[0051] The following embodiments exemplary focus on the PAM4 modulation format.

[0052] FIG. 2 shows a SER associated with a FR FFE and a SER associated with a DB FFE 103. High-speed optical interconnects suffer from channel 102 bandwidth limitations. Especially, limitations based on electrical connections between pluggable modules and switches may be critical. Their limited bandwidth, which depends on electrical link length, may significantly degrade performance. For example, for three selected channels 102 a full response full response feedforward equalizer (FR FFE) may not cross a SER=le-2, while a DB FFE 103 may improve the performance significantly, as shown in FIG. 2.

[0053] The receiver 100 comprises a DB FFE 103 and may be configured to perform corresponding steps to calculate the transmitter quality parameter 106, for example, TDECQ, wherein a conventional receiver may instead comprise a FR FFE. This may include Duobinary precoding and decoding, specific SER calculation, and specific FFE target output levels.

[0054] FIG. 3a shows an exemplary receiver 100 according to this disclosure implemented in an optical transmission system. The system shown in FIG. 3a comprises a receiver 100 and an optical transmitter 101. The receiver 100 may, for example, be denoted a TDECQ tester. The receiver 100 may comprise a positive intrinsic negative based photo detector (PIN), a filter, for example, a fourth-order Bessel-Thomson (BT4) filter, and a DB FFE 103. The optical transmitter 101 may be configured to transmit an optical PAM signal though an optical channel 102, which may be considered to be a worst-case optical channel, to the PIN. The PIN may be configured to convert the optical PAM signal to an electrical signal 104. The obtained electrical signal 104 may be filtered by the filter, for example, the BT4 filter, of the receiver 100, and the filtered signal output by the filter may be equalized by a DB FFE 103.

[0055] The receiver may 100 be configured to determine the transmitter quality parameter 106, for example, TDECQ, based on adding a noise having a noise deviation and / or a noise enhancement factor. For example, FIG. 3a depicts reference points for adding noise OG based on o and a noise enhancement factor Ceq. A transmitter quality parameter algorithm or a TDECQ algorithm may find the largest input referred receiver noise deviation (OG) that causes a SER equal to the TSER.

[0056] FIG. 3b shows a PAM4 eye diagram of a conventional FR FEE. As shown in FIG. 3b, the FFE may sample at two sampling points at a distance of 0.1UI, and the best sampling phase (where the transmitter quality parameter 106 or TDECQ is smallest) may be found. There may be two sampling phases and the TDECQ with the worst value may be selected.

[0057] A PAM4 eye diagram of a DB FEE may have 7 levels and form 6 eyes instead of 4 levels and 3 eyes as shown in FIG. 3b. The DB FFE 103 may sample at two sampling points, for example, at a distance of 0.1UI, and the best sampling phase (where the transmitter quality parameter 106 or TDECQ is smallest) may be found. There may be two sampling phases and the TDECQ with the worst value may be selected.

[0058] FIG. 4a shows a Duobinary system including a DB FFE 103 according to this disclosure.

[0059] FIG. 4b shows a conventional Duobinary system including a FR FFE.

[0060] Conventional systems comprising a FR FFE may include a Duobinary precoder at the transmitter side to protect the error propagation in severe bandwidth-limited systems. The Duobinary precoder may not modify the signal spectrum. Additionally, conventional systems comprising a FR FFE may compensate the channel imperfections with the FR FFE after precoding. As the channel conditions may be bad, the decision errors after the FR FFE may be critical with long error bursts. These error bursts can be improved after the Duobinary precoding but the SER may still be significant. Additionally, FR FFE noise amplification may become critical in severe bandwidth-limited systems leading to very high SER.

[0061] A DB FFE 103 may enhance equalization performance as shown in FIG. 2. The receiver 100 may be for transmission quality estimation in PAM4 systems and include a DB FFE 103 that uses 7-level FFE output to calculate the TDECQ. The receiver 100 may enable to relax the requirements on transmission components of the transmitter 101. Thus, the flexibility and / or the cost of the system may be further improved. Further, fair comparison of different transmitters 101 may be enabled to fulfill future standards.

[0062] In a system or receiver 100 including a DB FFE 103 the DB FFE 103 may perform equalization and Duobinary precoding at the same time. Additionally, or alternatively, the DB FFE 103 noise amplification may be negligible in severe bandwidthlimited systems enabling improved DB FFE 103 SER compared to FR FFE SER.

[0063] A DB FFE 103 SER formula for a Duobinary precoded signal 104 can be used for TDECQ evaluation. The DB FFE 103 may output a signal with 2N-1 levels, for example, seven signal levels L(i), i=0,l,...,6 where OMA=L(6)-L(0). Thus, a level probability may be p(i)=(l / 162 / 16 3 / 16 4 / 16 3 / 162 / 162 / 16); and thresholds may be denoted by T(i),i=0,l,...,5. The receiver may or may not set optimum thresholds between the 2N-1 levels. The optimum thresholds may depend on the amount of noise and level probabilities. Assuming Gaussian noise, the optimum threshold (OT) between levels L(i) and L(i+1) may be calculated based on: p(i)exp(-(OT(i)-L(i))2 / 2 / o2)= p(i+l)exp(-(OT(i)-L(i+l))2 / 2 / o2). The optimum thresholds may be OT(i)=DT(i)+o2 / (L(i+l)-L(i))log(p(i) / p(i+l)), where the default thresholds (DT)may be equal

[0064] DT(i)=0.5(L(i)+L(i+l)). SER may be calculated by: where Q represents a Q function defined by Q(x) = x=f"' exp (— x2 / 2).

[0065] FIG. 5 shows an exemplary Duobinary histogram 107 according to this disclosure. Assuming equidistant signal levels and thresholds, for example, A=L(i+l)-L(i), T(i)= L(i)+ A / 2, and A / 2=OMA / 12, it may follow that SER= 15 / 8Q(A / 2 / o) and Q=Q' '(SER*8 / 15), where Q1is the inverse Q function. Equidistant signal levels and thresholds are exemplary shown in FIG. 5 for seven signal levels L(i). The equidistant thresholds may be denoted DT.

[0066] FIG. 6 shows a respective SER obtained using DT and OT according to this disclosure. The SERs obtained using DT and OT may be similar. For example, FIG. 6 shows less than a 0.03dB error between the respective SER obtained using DT and OT. Thus, the SER approximation formula for DT may be used.

[0067] One or more decoded symbols (dsym) may be obtained, for example, if a conventional differential precoder is used at the transmitter 101 side, based on mod(dsym,4), where dsym may be a 7-level symbol after a hard slicer. The dsym symbol error probability may almost be identical to dsym symbol error probability and the previous equation can be used to calculate the symbol error probability of the differentially precoded PAM4 signal.

[0068] The transmitter quality parameter 106 or TDECQ may be calculated according to the IEEE Standard for Ethernet (IEEE Std. 802.3, 2018).

[0069] A receiver 100 comprising a DB FFE 103 may be configured to perform the following steps:

[0070] 1. Collect data after data / signal transmission.

[0071] 2. Calculate TDECQ at two sampling phases and select the worst value, wherein at each sampling phase, for example, left and right, at least one of the following steps may be executed: a) The DB FFE 103 with a plurality of taps and a target 7-level Duobinary PAM4 signal may generate an equalized histogram 107 with 7 levels. b) Determine signal levels and thresholds of the histogram. c) Calculate a plurality of cumulative distribution functions. d) Calculate a noise enhancement factor (Ceq), for example, as defined in the IEEE Standard for Ethernet (IEEE Std. 802.3, 2018), but with 7-level signal 104. e) Find a noise deviation (a) to reach the TSER. f) Repeat at least the steps d) and e) several times to determine a more accurate Ceq value. g) Calculate the TDECQ. The DB FFE 103 may be configured to reconstruct a received signal 104 by using a plurality of linear taps. The DB FFE 103 output may be used to obtain a histogram 107 indicating 2N-1 levels, for example, 7 levels. For example, 2N-1 levels L can be determined by searching the histogram 107 maxima locations. 2N-2, for example, 6, thresholds can be determined by searching the histogram 107 minima locations between the L signal levels.

[0072] FIG. 7 shows an exemplary Duobinary histogram 107 according to this disclosure. If minimum locations cannot be found (more than one minima or low noise), minima locations can be approximated by the middle value between two levels, e.g., T(l)=(L(0)+L(l)) / 2, as shown in FIG. 7.

[0073] A histogram 107 may comprise M values y taken on M bins x. The sum of all bins may be equal to 1. Cumulative distribution functions (CF) may be calculated according to: for i=0:M-l for n=0:5 ifx(i)<T(n)

[0074] CF (n,i)=sum(y(i: cc(n))); else

[0075] CF(n,i)=sum(y(cc(n):i)); end end end where for i=l :M-l for n=0:5 end end

[0076] Conventional receivers may use 3 CFs (N-l for PAM-N), for example in the IEEE Standard for Ethernet (IEEE Std. 802.3, 2018), for PAM4 system to determine the TDECQ. The receiver 100 may use 2N-2, for example, 6 CFs, to determine the TDECQ. The TDECQ may be calculated by TDECQ=10*loglO(OMA / 12 / Q / o), where OMA=L(6)-L(0). The parameter Q may be defined by Q=Q-1(TSER*8 / 15) and may depend on the TSER. The standard deviation or noise deviation o of noise, wherein the noise enhancement factor Ceq multiplied with the noise deviation o defines a noise that can be added to the reconstructed histogram 107 to reach the TSER, may fulfill the following equation:

[0077] The standard deviation or noise deviation may be scanned within a specified range and SER may be calculated for each value. The closest SER to TSER may indicate the correct noise deviation value o. The noise with the calculated noise deviation value r> may be added to the FFE input and updated FFE taps may be calculated. These taps may be used to calculate an updated Ceq value and the equation for TSER based on o may again be used to determine a further updated noise deviation o value. This procedure may be repeated several times, e.g. 5 times, and the final TDECQ value 106 can be calculated based on the updated parameters. The receiver 100 may comprise a processor. Generally, the processor may be configured to perform, conduct or initiate the various operations of the receiver 100 described herein. The processor may comprise hardware and / or may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or multi-purpose processors. The receiver 100 may further comprise memory circuitry, which stores one or more instruction(s) that can be executed by the processor, in particular under control of the software. For instance, the memory circuitry may comprise a non- transitory storage medium storing executable software code which, when executed by the processor, causes the various operations of the receiver 100 to be performed. In one embodiment, the receiver 100 may comprises one or more processors and a non-transitory memory connected to the one or more processors. The non-transitory memory may carry executable program code which, when executed by the one or more processors, causes the receiver 100 to perform, conduct or initiate the operations or methods described herein.

[0078] FIG. 8 shows a method 200 according to this disclosure. The method 200 is a method of operating a receiver 100 for PAM signals 104. The method 200 comprises a step 201 of obtaining a signal 104, wherein the signal 104 is based on a PAM signal that comprises N PAM signal levels and is sent by a transmitter 101 over a channel 102 to the receiver 100. Further, the method 200 comprises a step 202 of equalizing the signal 104 using a DB FFE 103 with a plurality of taps to generate an equalized signal 105 comprising 2N-1 signal levels. Further, the method 200 comprises a step 203 of determining a transmitter quality parameter 106 of the transmitter 101 based on the equalized signal 105. N is an integer larger than 1.

[0079] The disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

CLAIMS1. A receiver (100) for pulse amplitude modulation, PAM, signals (104), the receiver (100) being configured to: obtain a signal (104), wherein the signal (104) is based on a PAM signal that comprises N PAM signal levels and is sent by a transmitter (101) over a channel (102) to the receiver (100), wherein N is an integer larger than 1; equalize the signal (104) using a Duobinary feed forward equalizer, DB FFE (103), with a plurality of taps to generate an equalized signal (105) comprising 2N-1 signal levels; and determine a transmitter quality parameter (106) of the transmitter (101) based on the equalized signal (105).

2. The receiver (100) according to claim 1, wherein the receiver (100) is configured to: generate a histogram (107) based on the equalized signal (105), determine a first noise deviation based on the histogram (107), the plurality of taps, and a target signal error rate, TSER, wherein a signal error rate, SER, of the histogram (107) reaches the TSER, if noise based on the first noise deviation is added to the histogram (107), and determine the transmitter quality parameter (106) based on the first noise deviation and the TSER.

3. The receiver (100) according to claim 2, wherein, for each iteration of one or more iterations, the receiver (100) is further configured to: add noise having apreviously determined noise deviation at an input of the DB FFE (103) to the signal (104), wherein the previously determined noise deviation is the first noise deviation or an updated noise deviation of a directly preceding iteration of the one or more iterations, update the plurality of taps with the equalizer based on the signal (104) and the added noise having the previously determined noise deviation, determine an updated noise deviation of the iteration based on the histogram (107), the updated plurality of taps of the iteration, and the TSER, wherein a SER of the histogram (107) reaches the TSER if noise based on the updated noise deviation of the iteration is added to the histogram (107), wherein the receiver (100) is configured to calculate the transmitter quality parameter (106) based on the updated noise deviation of a last iteration of the one or more iterations and the TSER.

4. The receiver (100) according to claim 2 or 3, wherein the receiver (100) is configured to: calculate a first noise enhancement factor based on the plurality of taps, calculate a plurality of cumulative distribution functions, CFs, based on the histogram (107),determine the first noise deviation based on the first noise enhancement factor, the plurality of cumulative distribution functions, and the TSER, wherein the SER of the histogram (107) reaches the TSER if noise based on the first noise deviation is added to the histogram (107).

5. The receiver (100) according to claim 4, wherein, for each iteration of one or more iterations, the receiver (100) is configured to: calculate an updated noise enhancement factor of the iteration based on the updated plurality of taps, determine the updated noise deviation of the iteration based on the updated noise enhancement factor of the iteration, the plurality of cumulative distribution functions, and the TSER.

6. The receiver (100) according to claim 4 or 5, wherein the plurality of CFs are 2N-2 CFs.

7. The receiver (100) according to any one of the claims 2 to 6, wherein the first noise deviation fulfills an equation that is based on at least one of: a sum over M>1 bins of the histogram (107); a sum over the plurality of CFs; the first noise enhancement factor; the TSER.

8. The receiver (100) according to any one of the preceding claims, wherein the receiver (100) is configured to determine the transmitter quality parameter (106), TQP, based on TQP = 101oglO(OMA / 12 / Q / o), and Q = Q-1(TSER-8 / 15), wherein Q1is the inverse function of Q, wherein OMA is an optical modulation amplitude of the signal (104), and wherein o is the first noise deviation or the updated noise deviation if present.

9. The receiver (100) according to any one of the preceding claims, wherein the receiver (100) is configured to apply a hard slicer on the equalized signal (105) to obtain one or more 2N-1 level symbols.

10. The receiver (100) according to claim 9, wherein the receiver (100) is configured to decode each symbol of the one or more 2N-1 level symbols based on a value of the symbol modulo N.

11. The receiver (100) according to any one of the claims 2 to 10,wherein the receiver (100) is configured to determine 2N-1 signal levels and / or 2N-2 thresholds of the histogram (107) based on the histogram (107), and determine the first noise deviation further based on the determined 2N-1 signal levels and / or 2N-2 thresholds.

12. The receiver (100) according to any one of the preceding claims, wherein the receiver (100) is configured to determine a respective transmitter quality parameter (106) by using a respective equalized signal (105) for each sampling phase of two or more sampling phases.

13. The receiver (100) according to any one of the preceding claims, wherein the transmitter quality parameter (106) is a transmitter dispersion eye closure multinary, TDECM or a transmitter dispersion eye closure quaternary, TDECQ.

14. The receiver (100) according to any one of the preceding claims, wherein N is 4 and the one or more modulated signals (104) are modulated according to a 4-level pulse amplitude modulation format, PAM4.

15. A method of operating a receiver ( 100) for pulse amplitude modulation, PAM, signals ( 104), the method comprising : obtaining a signal (104), wherein the signal (104) is based on a PAM signal that comprises N PAM signal levels and is sent by a transmitter (101) over a channel (102) to the receiver (100), wherein N is an integer larger than 1; equalizing the signal (104) using a duobinary feed forward equalizer, DB FFE (103), with a plurality of taps to generate an equalized signal (105) comprising 2N-1 signal levels; and determining a transmitter quality parameter (106) of the transmitter (101) based on the equalized signal (105).

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