An adaptive receiving method for partial response encoding of an optical fiber communication system

Abstract

The application provides a kind of partial response encoding adaptive receiving method of optical fiber communication system, and relates to the field of optical fiber communication system.The method comprises: using adaptive partial response hybrid feed structure, signal is carried out hybrid feed filter processing;According to adaptive algorithm, filter tap coefficient is updated with large step, and filter tap coefficient corresponding to partial response encoding coefficient is calculated;With small step, the tap coefficient calculated is updated, and the received signal is carried out adaptive partial response removal algorithm;Partial response encoding after the signal is removed is directly decoded to obtain original information.The application embodiment provided by the method is used to receive partial response encoding signal, can effectively reduce the influence of noise and inter-symbol interference in optical fiber channel, reduce the complexity of partial response encoding reception, and improve the performance of maximum likelihood detection algorithm.

Description

Technical Field

[0001] This invention relates to the field of optical communication, and in particular to an adaptive reception method for partially coded signals in optical fiber communication systems. Background Technology

[0002] With the rapid development of emerging businesses such as big data and cloud computing, network traffic has surged, and optical communication urgently needs to increase transmission rates to cope with the ever-growing bandwidth demands. Due to channel quality limitations, high-order modulation formats are difficult to apply in practical systems; therefore, the simplest and most common approach is to increase the symbol rate. However, according to the Nyquist theorem, devices need to meet sampling rates higher than twice the symbol rate to achieve inter-symbol interference-free transmission, which increases the complexity and performance requirements of the equipment. Therefore, how to achieve high symbol rate transmission with limited sampling rates using existing equipment is one of the research hotspots in the field. This is beneficial for reducing the system's requirements on analog-to-digital and digital-to-analog conversion rates of transceivers, and for controlling networking costs.

[0003] To address the aforementioned issues, partial response coding (PSC) technology has been widely adopted. By introducing controllable inter-symbol interference through source coding, it concentrates signal energy in the low-frequency region, compressing the signal spectrum and thus achieving high-speed signal transmission at limited sampling rates. At the receiving end, the PSC signal is received through the reverse process corresponding to the transmitting end. However, current PSC transmission systems mostly employ fixed PSC coefficients for transmission and reception, lacking flexibility and failing to adjust the coefficients based on signal characteristics during transmission to achieve better signal transmission performance. Therefore, adaptive reception of PSC signals is necessary.

[0004] This invention mainly designs an adaptive reception method for partially responsive encoded signals in optical fiber communication systems. The proposed method is implemented using an adaptive partially responsive mixed-feed structure and an adaptive partially responsive removal algorithm. Based on the adaptive reception of partially responsive encoded signals, it improves the signal reception effect and reduces the limitation of signal transmission rate imposed by equipment in optical transmission systems. Summary of the Invention

[0005] The purpose of this invention is to provide an adaptive reception method for partially coded signals in an optical fiber communication system, so as to solve the problems of signal detection, reception and decoding at the receiving end after partial response coding, as well as the noise and inter-symbol interference introduced during transmission in optical fiber.

[0006] To address the above problems, embodiments of the present invention provide an adaptive reception method for partially coded signals in an optical fiber communication system, comprising two stages:

[0007] In the coarse estimation stage, a signal of a certain length is filtered, and at the same time, a coarse estimate is made for the filter taps corresponding to some response coding coefficients. The calculation of the error function and the updating of the taps are both performed by calculating and averaging the signal of a certain length.

[0008] In the fine estimation stage, partial response codes of the signal are removed and the original signal is recovered.

[0009] The rough estimation stage includes:

[0010] Filtering: Filtering of a signal of a certain length is performed using an adaptive partial response mixed-feed structure;

[0011] Partial response coefficient calculation: Based on the maximum likelihood estimation principle, update the filter tap coefficients and calculate the filter tap coefficients corresponding to the partial response coding coefficients;

[0012] The filtering process includes the following steps:

[0013] The tap coefficients of the feedforward and feedback filters in the adaptive partial response mixed-feed structure are defined, and the received signal is filtered according to the mixed-feed structure and the filter tap coefficients. The mixed-feed structure consists of a feedforward filter, a feedback filter, an adder, and an adaptive module. The feedforward filter processes the received signal, the feedback filter processes the signal output from the feedforward filter, and the adder sums the two filter outputs to obtain the final output. Furthermore, filtering is only performed on the sign of the filter tap coefficients at the corresponding time points; signs exceeding the specified length do not affect the output.

[0014] The calculation of the partial response coefficients includes the following steps:

[0015] In the adaptive module, the average error of the filtered signal is calculated based on the maximum likelihood estimation principle. The filter tap coefficients are updated using a larger step size, and the filter tap coefficients corresponding to the partial response coding coefficients are calculated. Specifically, the tap coefficients of the feedforward and feedback filters are updated according to the following expression:

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

[0022] Where w is the forgetting factor, Let K be the vector of the input signal and the decision feedback signal. N (n) is the Kalman gain vector, P N (n) is the update matrix. These are the filter tap coefficients. After the tap coefficients are updated, the final tap coefficients are used as the partial response coding coefficients of the signal.

[0023] The coarse estimation stage filters a certain length of signal, calculates the average error of that segment, and updates the filter tap coefficients with a relatively large step size. This yields filter tap coefficients that roughly correspond to the partial response coding coefficients. Since it's an average of a certain length of signal, its error function reflects the overall characteristics of that segment, aiming to make the signal converge towards the characteristics after removing the partial response coding. Based on this, the fine estimation stage fine-tunes the filter. In this stage, filtering is performed on individual symbols, and the instantaneous error of that symbol is calculated. The filter tap coefficients are updated with a smaller step size. The goal is to remove as much inter-symbol interference as possible introduced by the partial response coding. Because the step size is small, it prevents convergence failure due to sudden errors in a single symbol.

[0024] The detailed estimation stage includes:

[0025] Adaptive partial response removal algorithm: Update the filter tap coefficients with a small step size to obtain the signal after partial response removal and encoding;

[0026] Viterbi decoding algorithm: Perform Viterbi decoding on the signal after removing part of the response encoding to recover the original signal.

[0027] The adaptive partial response removal algorithm described above includes the following steps:

[0028] The algorithm is initialized based on the filter tap coefficients calculated in the coarse estimation stage. The filter tap coefficients are then updated with small step sizes. The filters are used to filter a single signal, and the output signal after removing part of the response coding is obtained based on the characteristic differences between the received signal and the modulation format. The tap coefficients of the feedforward and feedback filters are updated according to the following expression:

[0029]

[0030] w err (n) = d(i),

[0031]

[0032]

[0033] in, Let e(n) be the different amplitude values ​​of the original signal's standard modulation format, e(n) be a single signal of the filtered output, μ be the step size, and w be the amplitude value of the signal. err (n) represents the error.

[0034] The Viterbi algorithm described above includes the following steps:

[0035] To avoid the influence of partial response coding on the signal, the signal with partial response coding removed is directly Viterbi decoded. A state transition table and state transition diagram are established based on the original signal. Survivor paths are calculated based on the state transition table. Finally, the original signal is recovered by backtracking the survivor paths.

[0036] Beneficial effects of the embodiments of the present invention:

[0037] The method provided in this invention enables the reception of partially coded response signals, which reduces the requirements for the sampling rate of transceiver devices, thus reducing device complexity and performance. By adaptively receiving partially coded response signals, the system can more flexibly select different partial coding techniques, improving transmission performance. At the same time, by updating the tap coefficients in two stages of coarse estimation and fine estimation, the partial response coding is removed, reducing the complexity of receiving partially coded response signals. Attached Figure Description

[0038] The accompanying drawings, which are included to provide a further understanding of the invention, form part of this invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute a limitation thereof.

[0039] In the attached diagram:

[0040] Figure 1 This is a flowchart of the partial response encoding signal receiving method in this invention.

[0041] Figure 2 This is a block diagram of the partial response-encoded signal receiving method in this invention. Detailed Implementation

[0042] Referring to the accompanying drawings, the foregoing and other features of the embodiments of the present invention will become apparent from the following description. These embodiments are merely exemplary and not intended to limit the invention. To enable those skilled in the art to readily understand the principles and implementation methods of the present invention, the embodiments of the present invention are described below. Figure 1 The working principle of this invention will be explained using the partial response coding signal receiving method shown as an example.

[0043] Example 1:

[0044] In the partial response coding system of PAM-4 fiber optic communication system, the receiver uses, for example... Figure 1The adaptive reception method for partial response coding shown includes the following steps S101-S108.

[0045] S101: Perform initialization, setting the filter order N, tap coefficients C, forgetting factor λ, and update matrix P. The partial response coding adaptive receiver structure is as follows: Figure 2 As shown, the adaptive partial response mixed-feed structure consists of a feedforward filter, a feedback filter, an adder, and an adaptive module. The feedforward filter processes the received signal, the feedback filter processes the signal output from the feedforward filter, and the adder adds the output signals of the two filters to obtain the final output.

[0046] S102: Based on the initial settings of the tap coefficients of the feedforward and feedback filters in the adaptive partial response mixed-feed structure, the received signal is filtered. Only the symbols corresponding to the tap coefficients at specific moments are considered for filtering; symbols exceeding the specified length do not affect the output.

[0047] S103: In the adaptive module, based on the maximum likelihood estimation principle, the average error of the filtered signal is calculated. The filter tap coefficients are updated using a larger step size. The updated tap coefficients are returned to S102, and the filtering process is repeated until all symbols participate in the tap coefficient update. Finally, the filter tap coefficients corresponding to the partial response coding coefficients are transmitted to the fine estimation stage.

[0048] S104: Determine whether the filter tap coefficients have been updated for all symbols. If yes, end the calculation of the above variables and proceed to step S105; otherwise, proceed to step S102.

[0049] S105: Initialize the filter tap coefficients based on the filter tap coefficients calculated in the coarse estimation stage, and set the PAM-4 signal amplitude value. The range is [-3, -1, 1, 3]. A single signal is filtered and output, the difference between the square of the amplitude of the standard modulation format and the square of the signal is calculated, the minimum absolute value of the difference is taken as the error, the tap coefficients are updated according to the error, and finally the signal after removing the partial response coding is obtained.

[0050] S106: After removing the partial response coding, the signal is directly subjected to Viterbi decoding to avoid adjusting the Viterbi decoding algorithm based on the partial response coding coefficients. A state transition table and state transition diagram are established based on the PAM-4 signal. Survivor paths are calculated based on the state transition table, and finally, the original signal is recovered by backtracking the survivor paths.

[0051] S107: Determine whether all symbols have completed partial response encoding removal and Viterbi decoding. If yes, end the calculation of the above variables and proceed to step S108; otherwise, proceed to step S105.

[0052] S108: Output the recovered signal and end the process.

Claims

1. An adaptive receiving method of partial response encoding for optical fiber communication systems, characterized by, include: Coarse estimation stage: A signal of a certain length is selected, and the signal is mixed-feed filtered using an adaptive partial response mixed-feed structure. The average error of the mixed-feed filtered signal is calculated, and the filter tap coefficients are updated according to the average error. The filter tap coefficients corresponding to the partial response coding coefficients are also calculated. The adaptive partial response mixed-feed structure is characterized by comprising: a feedforward filter, a feedback filter, an adder, and an adaptive module. The feedforward filter is connected to the feedback filter, the adder, and the adaptive module, respectively, and is used to filter the input signal according to the tap coefficients set by the adaptive module, and output the filtering result to the feedback filter and the adder. The feedback filter is connected to the feedforward filter... The system is connected to an adder and an adaptive module. The adder filters the output signal of the feedforward filter according to the tap coefficients set by the adaptive module, and outputs the filtered result to the adder. The adder is connected to the feedforward filter, the feedback filter, and the adaptive module respectively. It sums the output signals of the feedforward filter and the feedback filter at the same time, and outputs the summation result to the adaptive module. The adaptive module calculates the average error of the signal segment based on the output of the adder, according to the maximum likelihood estimation principle. Based on the average error, it updates the tap coefficients of the feedforward filter and the feedback filter with a larger step size, and calculates the filter tap coefficients corresponding to the partial response coding coefficients. Fine estimation stage: Based on the calculated filter tap coefficients, an adaptive partial response removal algorithm is applied to the original signal to obtain the signal after partial response removal encoding. This signal is then directly decoded to obtain the original information. The adaptive partial response removal algorithm is characterized by including: initializing the tap coefficients based on the filter tap coefficients obtained in the coarse estimation stage; filtering a single input signal each time to obtain a filtered output signal, and calculating an error function and updating the tap coefficients; calculating the difference between the square of the amplitude of the standard modulation format and the square of the filtered output signal, and using the minimum absolute value of each difference as the error function value; updating the tap coefficients based on the error function value, the input signal, and the filtered output signal, using a step size smaller than the update step size of the coarse estimation stage.

2. The adaptive receiving method of claim 1, wherein, The detailed estimation stage includes: Adaptive partial response removal algorithm: The algorithm is initialized based on the filter tap coefficients calculated in the coarse estimation stage, the instantaneous error of the signal is calculated, and the filter tap coefficients are updated with a small step size to obtain the signal after partial response removal encoding. Viterbi decoding algorithm: The signal after partial response coding is directly decoded by Viterbi, thus avoiding the need to adjust the Viterbi decoding algorithm according to the partial response coefficients and reducing the implementation complexity.

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