CN110380789B - Signal processing method and device - Google Patents

Signal processing method and device Download PDF

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CN110380789B
CN110380789B CN201810327240.0A CN201810327240A CN110380789B CN 110380789 B CN110380789 B CN 110380789B CN 201810327240 A CN201810327240 A CN 201810327240A CN 110380789 B CN110380789 B CN 110380789B
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volterra
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CN110380789A (en
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涂芝娟
郭琦
鞠诚
张治国
陈彦旭
陈雪
张俊文
黄新刚
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ZTE Corp
Beijing University of Posts and Telecommunications
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
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    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
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    • H04B10/616—Details of the electronic signal processing in coherent optical receivers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H04B10/612—Coherent receivers for optical signals modulated with a format different from binary or higher-order PSK [X-PSK], e.g. QAM, DPSK, FSK, MSK, ASK

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Abstract

The embodiment of the invention discloses a signal processing method, which is used for a communication system equivalent to the condition that channel nonlinear damage acts in front and IQ imbalance acts in back, and comprises the following steps: performing combined modeling on linear damage of a series Volterra channel model and IQ imbalance of a receiving front end to obtain a coefficient of backward inverse equalization processing of variant Volterra; at a receiving end of the communication system, compensation processing is carried out on linear damage of signals and IQ imbalance of the receiving end through a generalized linear equalizer obtained by first-order modification of a Volterra backward inverse equalizer, and compensation processing is carried out on nonlinear damage of the signals through a high-order operator of the modified Volterra backward inverse equalization processing. The embodiment of the invention also discloses a signal processing device and a computer readable storage medium.

Description

Signal processing method and device
Technical Field
The present invention relates to the field of impairment suppression in communication technologies, and in particular, to a signal processing method and apparatus, and a computer-readable storage medium.
Background
The concept and theory of the Volterra series was first proposed by the spanish mathematician Vito Volterra in 1959. The mathematician Norbert Wiener applies the Volterra series theory to nonlinear system analysis modeling, and Wiener applies the theory to analyze a series of nonlinear system problems. Since the conference of OFC and ECOC in 2013, Volterra theory is applied to the DSB-IMDD OFDM system to inhibit beat frequency interference damage. The current beat frequency interference suppression algorithm mainly comprises an injury suppression algorithm based on an iterative idea and a nonlinear equalizer based on a Volterra theory. Compared with an iterative impairment suppression algorithm, the complexity and the system cost of the second-order and third-order time domain nonlinear filters based on the Volterra theory are lower, because the iterative impairment suppression algorithm needs to acquire channel characteristic values including a modulator chirp value, the total dispersion amount of the optical fiber and a modulator nonlinear transmission curve in advance, so as to assist in reconstructing beat frequency interference impairment, and the tap coefficient of the Volterra filter based on the time domain is obtained by adopting LMS or RLS adaptive calculation.
In recent years, coherent detection has attracted considerable interest as a key technology for the development of long-range, high-rate, and high-spectral-efficiency optical networks. By restoring the electric field in both polarization directions of the fiber, a coherent receiver can allow information to be encoded in all degrees of freedom of the fiber, including amplitude, phase, and polarization. Thus, coherent reception can improve signal power and spectral efficiency of the system. The structure of coherent detection is more complex than that of direct detection. It needs a local oscillation laser at the local receiving end, and performs beat frequency with the received signal light through the emitted light of the local oscillation laser to realize signal demodulation. The balanced receiver adopts four groups and eight PDs for receiving, while the unbalanced receiver adopts four groups and four PDs for receiving signals, and because the signal output by one branch is abandoned, unbalanced detection can bring beat frequency interference, and IQ imbalance damage of a receiving end is also avoided.
In the prior art, a direct detection system receives a transmission signal through a photoelectric detector, the system complexity is low, IQ (in-phase and quadrature) imbalance damage can be caused at the receiving front end in the direct detection system containing I/Q signals, and meanwhile, when the system speed and the transmission distance of the traditional intensity modulation direct detection scheme are simultaneously increased, the influence of beat frequency interference nonlinear damage can be encountered. For a coherent detection system, balanced detection can avoid introducing beat interference damage, but eight PDs receive signals, which increases the complexity of hardware; and the unbalanced detection adopts single PD reception, which can reduce the hardware cost of the system, but can introduce beat frequency interference nonlinear damage.
Disclosure of Invention
In order to solve the existing technical problem, embodiments of the present invention provide a signal processing method, apparatus, and computer readable storage medium, which effectively suppress IQ imbalance and channel nonlinear damage of a direct detection system or a coherent system receiver, and reduce hardware cost of a coherent receiving system.
In order to achieve the above purpose, the technical solution of the embodiment of the present invention is realized as follows:
a signal processing method, applied to a communication system, where the communication system is equivalent to a system with channel nonlinear impairments acting before and IQ imbalances acting after, the method comprising:
performing combined modeling on linear damage of a series Volterra channel model and IQ imbalance of a receiving front end to obtain a coefficient of backward inverse equalization processing of variant Volterra;
at a receiving end of the communication system, compensation processing is carried out on linear damage of signals and IQ imbalance of the receiving end through a generalized linear equalizer obtained by first-order modification of a Volterra backward inverse equalizer, and compensation processing is carried out on nonlinear damage of the signals through a high-order operator of the modified Volterra backward inverse equalization processing.
Further, before the jointly modeling the linear impairment of the series-connected Volterra channel model and the receive front-end IQ imbalance, the method includes:
modeling a transmission channel of the communication system according to a Volterra theory to obtain a parallel Volterra channel model, wherein an operator of the parallel Volterra channel model system is G, GiIs an i-order Volterra operator, G, in channel modeling1[D(ω)]A valid signal representing the influence of linear damage to the channel after photoelectric conversion,
Figure BDA0001626973640000021
representing the nonlinear damage of the second order and above, D (omega) is an input signal;
converting the parallel Volterra channel model into a serial Volterra channel model according to a Volterra theory, wherein the serial Volterra channel model comprises: a high-order operator F and a first-order operator S, wherein the first-order Volterra operator F in the high-order operator F 11, the first order operator S comprises only the first order Volterra operator S1，S1≡G1。
Further, the jointly modeling the linear impairment of the series-connected Volterra channel model and the receive front-end IQ imbalance includes:
and performing combined modeling on the first-order channel linear damage and the receiving end IQ imbalance damage in the series Volterra channel model.
Further, the method further comprises:
the IQ imbalance caused by analog receiving front end is expressed by adopting a generalized linear model in a complex value form, in order to completely compensate the linear distortion introduced by a communication system and the IQ imbalance of a receiving end, an operator Q of an IQ imbalance system is required to completely compensate the linear distortion and the IQ imbalance introduced by the communication system, and an operator mu in a complex value operator W of a generalized linear equalizer obtained by a first-order modification of a Volterra backward inverse equalizereAnd veThe conditions met include:
Figure BDA0001626973640000031
and
Figure BDA0001626973640000032
wherein μ (ω) ═ μr(ω)G1(ω)，
Figure BDA0001626973640000033
μr(ω) and vr(ω) is the IQ imbalance caused by the analog receive front end, and the input-output relationship is: w (ω) ═ μe(ω)Q(ω)+ve(ω)Q*(-. omega.), Q (omega) is the received signal affected by IQ imbalance.
Further, a first-order operator K of the variant Volterra backward inverse equalization process1，K1≡1，
Second-order operator K for variant Volterra backward inverse equalization processing2，K2＝-K1H2K1＝-H2；
Third-order operator K for variant Volterra backward reverse equalization processing3，K3＝K1[-H3+H2(1+K1H2)-H2K1H2-H2]K1＝-H3+H2(1+H2)-H2H2-H2；
Wherein H2For second order Volterra operators, H3Is a third order Volterra operator.
Further, the first-order operator of the variant Volterra backward inverse equalization processing is K1，K1≡W，
The second-order operator of the variant Volterra backward inverse equalization processing is K2，K2＝-K1H2K1；
The third-order operator of the variant Volterra backward reverse equalization processing is K3，K3＝K1[-H3+H2(1+K1H2)-H2K1H2-H2]K1；
Wherein H2For second order Volterra operators, H3Is a third order Volterra operator, W ═ mue+ve。
The embodiment of the invention provides a signal processing device, which is applied to a communication system with equivalent channel nonlinear damage acting in front and IQ imbalance acting in back; the signal processing apparatus includes: a modeling unit, a processing unit, wherein,
the modeling unit is used for carrying out combined modeling on linear damage of a series Volterra channel model and IQ imbalance of a receiving front end to obtain a coefficient of variant Volterra backward inverse equalization processing;
the processing unit is used for compensating linear damage of the signal and IQ imbalance of the receiving end by a generalized linear equalizer obtained by first-order modification of a Volterra backward inverse equalizer at the receiving end of the communication system, and compensating nonlinear damage of the signal by a high-order operator of the modified Volterra backward inverse equalization processing.
Further, the modeling unit is further configured to model a transmission channel of the communication system according to a Volterra theory to obtain a parallel Volterra channel model, where an operator of the parallel Volterra channel model system is G and GiIs an i-order Volterra operator, G, in channel modeling1[D(ω)]A valid signal representing the influence of linear damage to the channel after photoelectric conversion,
Figure BDA0001626973640000041
representing the nonlinear damage of the second order and above, D (omega) is an input signal;
the processing unit is further configured to convert the parallel-form Volterra channel model into a serial-form Volterra channel model according to a Volterra theory, where the serial-form Volterra channel model includes: a high-order operator F and a first-order operator S, wherein the first-order Volterra operator F in the high-order operator F 11 ≡ 1, first order operationThe symbol S comprises only first order Volterra operators S1，S1≡G1。
Further, the modeling unit is further configured to jointly model a first-order channel linear impairment and a receiving-end IQ imbalance impairment in the series-form Volterra channel model.
Further, the modeling unit is further configured to represent the IQ imbalance caused by the analog receiving front end by using a generalized linear model in a complex form, and to fully compensate the linear distortion introduced by the communication system and the IQ imbalance of the receiving front end, an operator μ in a complex operator W of the generalized linear equalizer obtained by first-order modification of the Volterrra backward inverse equalizereAnd veThe conditions met include:
Figure BDA0001626973640000042
and
Figure BDA0001626973640000043
wherein μ (ω) ═ μr(ω)G1(ω)，
Figure BDA0001626973640000044
μr(ω) and vr(ω) is the IQ imbalance caused by the analog receive front end, and the input-output relationship is: w (ω) ═ μe(ω)Q(ω)+ve(ω)Q*(-. omega.), Q (omega) is the received signal affected by IQ imbalance.
Further, a first-order operator K of the variant Volterra backward inverse equalization process1，K1≡1，
Second-order operator K for variant Volterra backward inverse equalization processing2，K2＝-K1H2K1＝-H2；
Third-order operator K for variant Volterra backward reverse equalization processing3，K3＝K1[-H3+H2(1+K1H2)-H2K1H2-H2]K1＝-H3+H2(1+H2)-H2H2-H2；
Wherein H2For second order Volterra operators, H3Is a third order Volterra operator.
Further, the first-order operator of the variant Volterra backward inverse equalization processing is K1，K1≡W，
The second-order operator of the variant Volterra backward inverse equalization processing is K2，K2＝-K1H2K1；
The third-order operator of the variant Volterra backward reverse equalization processing is K3，K3＝K1[-H3+H2(1+K1H2)-H2K1H2-H2]K1；
Wherein H2For second order Volterra operators, H3Is a third order Volterra operator, W ═ mue+ve。
Embodiments of the present invention also provide a computer readable storage medium storing one or more programs, which are executable by one or more processors to implement the steps of the method as described in any above.
The embodiment of the invention provides a signal processing method, a device and a computer readable storage medium, wherein the method is applied to a communication system which is equivalent to that a channel nonlinear damage acts in front and an IQ imbalance acts in back, and comprises the following steps: performing combined modeling on linear damage of a series Volterra channel model and IQ imbalance of a receiving front end to obtain a coefficient of backward inverse equalization processing of variant Volterra; at a receiving end of the communication system, compensation processing is carried out on linear damage of signals and IQ imbalance of the receiving end through a generalized linear equalizer obtained by first-order modification of a Volterra backward inverse equalizer, and compensation processing is carried out on nonlinear damage of the signals through a high-order operator of the modified Volterra backward inverse equalization processing. According to the signal processing method, the signal processing device and the computer readable storage medium provided by the embodiment of the invention, a Volterra model is utilized to model a transmission channel, a signal is subjected to channel nonlinear damage first and then to IQ imbalance damage, and a modified Volterra backward inverse equalizer is utilized at a receiving end to simultaneously inhibit the signal nonlinear damage and the IQ imbalance damage, so that IQ imbalance and channel nonlinear damage of a direct detection system or a coherent system receiver can be effectively inhibited, and the hardware cost of a coherent receiving system is reduced.
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In the drawings, which are not necessarily drawn to scale, like reference numerals may describe similar components in different views. Like reference numerals having different letter suffixes may represent different examples of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed herein.
Fig. 1 is a schematic flow chart of a signal processing method according to an embodiment of the present invention;
fig. 2 is a transmission system parallel-mode Volterra channel model and a modified serial-mode Volterra channel model provided in an embodiment of the present invention;
FIG. 3 is a schematic block diagram of a cascade configuration provided by an embodiment of the present invention;
FIG. 4 is a schematic block diagram of a parallel form provided by an embodiment of the present invention;
FIG. 5 is a schematic diagram of an implementation of a direct detection system according to an embodiment of the present invention;
fig. 6 is a schematic diagram of an implementation of an unbalanced coherent detection system according to an embodiment of the present invention;
fig. 7 is a schematic structural diagram of a signal processing apparatus according to an embodiment of the present invention.
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
An embodiment of the present invention provides a signal processing method, where the method is used in a communication system, where the communication system is equivalent to a system in which channel nonlinear impairments are acting before and IQ imbalance is acting after, as shown in fig. 1, the method may include:
step 101, modeling a transmission channel of a communication system according to a Volterra theory to obtain a parallel Volterra channel model, and converting the parallel Volterra channel model into a serial Volterra channel model according to the Volterra theory.
Wherein, the operator of the parallel Volterra channel model system is G, GiIs an i-order Volterra operator, G, in channel modeling1[D(ω)]A valid signal representing the influence of linear damage to the channel after photoelectric conversion,
Figure BDA0001626973640000061
the nonlinear impairments of the second order and above are shown in the communication system, and D (ω) is the input signal.
Wherein the series-form Volterra channel model comprises: a high-order operator F and a first-order operator S, wherein the first-order Volterra operator F in the high-order operator F 11, the first order operator S comprises only the first order Volterra operator S1，S1≡G1。
Specifically, the method provided by the embodiment of the invention is suitable for a system with channel nonlinear damage acting in front and IQ imbalance acting in back in a system channel model; meanwhile, a system with interaction of nonlinear damage and IQ imbalance damage can be equivalently that the nonlinear damage acts in front and the IQ imbalance acts in back after decomposition, and the system model is also suitable.
As shown in fig. 2, the upper part of fig. 2 is a parallel-type Volterra channel model of the transmission system, and the lower part of fig. 2 is a modified serial-type Volterra channel model. The system shown above in figure 2 and below in figure 2 is fully equivalent according to Volterra theory.
As shown in fig. 2, the input signal is D (ω), D (ω) passes through the parallel Volterra channel model, the output signal is I (ω),
Figure BDA0001626973640000062
wherein, the system operator of the parallel Volterra channel model is G, GiIs a Volterra operator of order i. G1[D(ω)]A valid signal representing the influence of linear damage to the channel after photoelectric conversion,
Figure BDA0001626973640000063
representing the second and above-second order nonlinear damage suffered by the system.
As shown in fig. 2, the input signal is D (ω), D (ω) passes through the series-type Volterra channel model, and the output signal is I (ω). The series Volterra channel model comprises a high-order part and a first-order part, wherein a first-order Volterra operator F in operators F of the high-order part 11 ≡ 1. The first order part S of the concatenated Volterra channel model, containing only first order Volterra operators S1And S is1≡G1. And jointly modeling a first-order part S of the Volterra channel model and IQ imbalance Q caused by the analog receiving front end.
And 102, performing combined modeling on linear damage of a series Volterra channel model and IQ imbalance of a receiving front end to obtain a coefficient of backward inverse equalization processing of the variant Volterra.
Specifically, the signal processing device performs joint modeling on the first-order channel linear damage and the receiving end IQ imbalance damage in the series-form Volterra channel model, so as to obtain a coefficient of the variant Volterra backward inverse equalization processing.
103, at a receiving end of the communication system, compensating linear damage of the signal and IQ imbalance of the receiving end by a generalized linear equalizer obtained by first-order modification of a Volterra backward inverse equalizer, and compensating nonlinear damage of the signal by a high-order operator of the modified Volterra backward inverse equalization.
It should be noted that the first-order modification of the Volterra backward inverse equalizer results in a generalized linear equalizer, and the generalized linear equalizer and the high-order part of the Volterra backward inverse equalizer are combined to perform modified Volterra backward inverse equalization processing. The high-order part of the generalized linear equalizer and the Volterra backward inverse equalizer is a serial relation. The first order Volterra operator of the higher order part of the Volterra backward inverse equalizer is 1. The coefficients of the modified Volterra backward inverse equalizer process include coefficients of a generalized linear equalizer and coefficients of a higher order part of the Volterra backward inverse equalizer.
Possible implementationIn the present mode, a first-order operator K for the Volterra backward inverse equalization processing is modified1，K1Equivalence 1, second-order operator K for variant Volterra backward inverse equalization processing2，K2＝-K1H2K1＝-H2(ii) a Third-order operator K for variant Volterra backward reverse equalization processing3，K3＝K1[-H3+H2(1+K1H2)-H2K1H2-H2]K1＝-H3+H2(1+H2)-H2H2-H2(ii) a Wherein H2For second order Volterra operators, H3Is a third order Volterra operator.
As shown in fig. 3, embodiments of the present invention provide a block diagram representation of a tandem form operator. The communication system of fig. 3 includes an input signal, a transmission channel, an analog receive front end, a generalized linear equalizer derived from a first order variant of the Volterra backward inverse equalizer, a variant Volterra backward inverse equalizer, and an output signal. The channel model corresponding to the photoelectric conversion process from the sending end can be represented as a series connection form of operational characters F and S of a Volterra system, and the system H is a system obtained by channel linear damage, namely joint modeling of a first-order part S of the Volterra channel model and IQ imbalance Q of the receiving front end.
In order to facilitate the representation of signals, a generalized linear model in a complex value form is adopted to represent IQ imbalance caused by a simulation receiving front end, an operator Q of an IQ imbalance system is composed of an upper branch and a lower branch, linear distortion and IQ imbalance introduced by the system S and the system Q are completely compensated, and an operator mu in a complex value system operator W of a generalized linear equalizer obtained by a first-order modification of a Volterra backward inverse equalizer is required to be completely compensatedeAnd veThe conditions need to be satisfied:
Figure BDA0001626973640000081
and
Figure BDA0001626973640000082
wherein μ (ω) ═ μr(ω)G1(ω)，
Figure BDA0001626973640000083
W(ω)＝μe(ω)Q(ω)+ve(ω)Q*(-. omega.), Q (omega) refers to the signal coming out of the receive front-end, i.e., the received signal affected by IQ imbalance.
When the above conditions are satisfied, the system H, which is formed by connecting S, Q and W in series, is a distortion-free system, i.e., the input and output are completely equal. Therefore, the generalized linear equalizer obtained by the first-order modification of the Volterra backward inverse equalizer can ideally inhibit the channel linear damage and the IQ imbalance damage.
At this time, the system is only affected by nonlinear distortion caused by chromatic dispersion and square rate detection, and as shown in fig. 3, a parallel Volterra backward inverse equalizer can be used to suppress channel nonlinear damage, where K is an operator of the system corresponding to the Volterra backward inverse equalizer, and K is an operator of the system corresponding to the Volterra backward inverse equalizeriIs a Volterra operator of order i. Under the realization of the algorithm in a tandem form, because the linear distortion of a channel is already inhibited by a generalized linear equalizer, a first-order Volterra backward inverse equalizer operator K 11 ≡ 1. According to the Volterra theory, the frequency domain operator expression of the second-order and third-order Volterra backward inverse equalizer is as follows:
K2＝-K1H2K1＝-H2
K3＝K1[-H3+H2(1+K1H2)-H2K1H2-H2]K1
＝-H3+H2(1+H2)-H2H2-H2
wherein H2For second order Volterra operators, H3The method is a third-order Volterra operator, and specific parameter values can be obtained through a DD-LMS and other adaptive algorithms.
It should be noted that the operator G is a system operator of the Volterra channel model used in channel modeling; the operator K is an operator of a variant Volterra backward inverse equalizer; operator H refers to a Volterra series operator.
In one possible implementation, the first-order operator of the modified Volterra backward inverse equalization processing is K1，K1W, K is the second order operator of the variant Volterra backward inverse equalization process2，K2＝-K1H2K1(ii) a The third-order operator of the variant Volterra backward reverse equalization processing is K3，K3＝K1[-H3+H2(1+K1H2)-H2K1H2-H2]K1(ii) a Wherein H2For second order Volterra operators, H3Is a third order Volterra operator, W ═ mue+ve。
As shown in fig. 4, a block diagram representation of a parallel form operator is provided by an embodiment of the present invention. The communication system of fig. 4 includes an input signal, a transmission channel, an analog receive front end, a modified Volterra backward inverse equalizer, and an output signal. The corresponding channel model from the transmitting end to the photoelectric conversion process can be represented as a concatenation of the Volterra system operators F and S. The system H is a system obtained by channel linear damage, namely a first-order part S of a Volterra channel model and IQ imbalance Q joint modeling of a receiving front end.
The first-order part of the Volterra backward inverse equalizer is used for inhibiting linear damage and IQ imbalance, and the second order and the third order are used for inhibiting nonlinear damage. Volterra equalizer first order operator K1W is identical to the original content. According to the Volterra theory, the frequency domain operator expression of the second-order and third-order Volterra backward inverse equalizer is as follows:
K2＝-K1H2K1
K3＝K1[-H3+H2(1+K1H2)-H2K1H2-H2]K1
wherein H2For second order Volterra operators, H3Is a third order Volterra operator, W ═ mue+veThe specific parameter value can be obtained by a DD-LMS and other adaptive algorithms.
Specifically, the method provided by the embodiment of the present invention models the transmission system according to the Volterra theory, jointly models the linear damage of the Volterra channel model and the IQ imbalance caused by the receiving front end, suppresses the linear damage and the IQ imbalance of the receiving end by using the generalized linear equalizer obtained by the first-order modification of the Volterra backward inverse equalizer, and suppresses the nonlinear damage by using the high-order modification of the Volterra backward inverse equalizer.
For example, the method provided by the embodiment of the present invention is implemented in a Nyquist-16QAM scheme, as shown in fig. 5, after a signal is transmitted to a photodetector PD through an optical fiber, the signal is detected by the PD and then divided into two I/Q paths, and the two I/Q paths of signals are input to the method provided by the embodiment of the present invention after passing through an analog-to-digital converter ADC, so that the signal can be compensated, specifically, a generalized linear equalizer obtained by a first-order variation of a Volterra backward inverse equalizer suppresses a linear damage of a channel and an IQ imbalance damage caused by a receiving front end, and a second-order and a third-order of the Volterra backward inverse equalizer suppresses a nonlinear damage of the channel.
Illustratively, the method provided by the embodiment of the invention is extended to the implementation in the unbalanced coherent system. As shown in fig. 6, after the received optical signal is subjected to polarization beam splitting and detected by using four groups of single PDs, the method provided by the embodiment of the present invention is used for each polarization state, specifically, after the signal is transmitted to the photodetector PD through an optical fiber, the signal is input into the method provided by the embodiment of the present invention after passing through an analog-to-digital converter ADC, the generalized linear equalizer obtained by the first-order modification of the Volterra backward inverse equalizer suppresses the channel linear damage and the IQ imbalance damage caused by the receiving front end, and the Volterra backward inverse equalizer suppresses the channel nonlinear damage by the second-order and the third-order. In an unbalanced coherent detection system, beat frequency interference damage can be generated after photoelectric detection, and the method provided by the embodiment of the invention can ideally inhibit damage caused by unbalanced detection. Compared with the balanced detection, the four groups of unbalanced detection detectors adopt single PD for detection, the system cost can be reduced, and meanwhile, the damage caused by adopting single PD for detection can be compensated by using the invention.
For a coherent detection system, although beat frequency interference nonlinear damage can be introduced by adopting single PD reception for unbalanced detection, the hardware cost of the system can be reduced, and by adopting the method provided by the invention after the unbalanced detection ADC, the beat frequency interference nonlinear damage and IQ imbalance damage of a receiving end can be completely inhibited theoretically, and the system performance of unbalanced reception is improved. For a direct detection system, the method provided by the embodiment of the invention can simultaneously inhibit IQ imbalance and channel nonlinear damage of a receiver.
According to the signal processing method provided by the embodiment of the invention, a Volterra model is utilized to model a transmission channel, a signal is subjected to channel nonlinear damage first and then to IQ imbalance damage, and a modified Volterra backward inverse equalizer is utilized at a receiving end to simultaneously inhibit the signal nonlinear damage and the IQ imbalance damage, so that IQ imbalance and channel nonlinear damage of a direct detection system or a coherent system receiver can be effectively inhibited, and hardware cost of a coherent receiving system is reduced.
An embodiment of the present invention provides a signal processing apparatus 20, as shown in fig. 7, where the signal processing apparatus is applied to a communication system that is equivalent to a communication system in which a channel nonlinear impairment is acted before and an IQ imbalance is acted after; the signal processing apparatus includes: a modeling unit 201, a processing unit 202, wherein,
the modeling unit 201 is configured to perform joint modeling on linear impairments of a series-connected Volterra channel model and IQ imbalance of a receiving front end to obtain a coefficient of backward inverse equalization processing of the variant Volterra;
the processing unit 202 is configured to, at a receiving end of the communication system, perform compensation processing on linear damage of a signal and IQ imbalance of the receiving end by using a generalized linear equalizer obtained by a first-order modification of a Volterra backward inverse equalizer, and perform compensation processing on nonlinear damage of the signal by using a high-order operator of the modified Volterra backward inverse equalization processing.
Further, the modeling unit 201 is further configured to model a transmission channel of the communication system according to a Volterra theory to obtain a parallel Volterra channel model, where an operator of the parallel Volterra channel model system is G, and G is an operator of the parallel Volterra channel model systemiIs an i-order Volterra operator, G, in channel modeling1[D(ω)]Means for indicating influence of linear damage of channel after photoelectric conversionThe effect signal is a signal that is, or is,
Figure BDA0001626973640000101
representing the nonlinear damage of the second order and above, D (omega) is an input signal;
the processing unit 202 is further configured to convert the parallel-form Volterra channel model into a serial-form Volterra channel model according to a Volterra theory, where the serial-form Volterra channel model includes: a high-order operator F and a first-order operator S, wherein the first-order Volterra operator F in the high-order operator F 11, the first order operator S comprises only the first order Volterra operator S1，S1≡G1。
Further, the modeling unit 201 is further configured to perform joint modeling on the first-order channel linear impairment and the receiving-end IQ imbalance impairment in the series-form Volterra channel model.
Further, the modeling unit 201 is further configured to use a generalized linear model in a complex form to represent IQ imbalance caused by the analog receiving front end, to completely compensate for linear distortion and IQ imbalance introduced by the communication system, and an operator μ in a complex operator W of a generalized linear equalizer obtained by a first-order transformation of a Volterra backward inverse equalizereAnd veThe conditions met include:
Figure BDA0001626973640000111
and
Figure BDA0001626973640000112
wherein μ (ω) ═ μr(ω)G1(ω)，
Figure BDA0001626973640000113
μr(ω) and vr(ω) is the IQ imbalance caused by the analog receive front end, and the input-output relationship is: w (ω) ═ μe(ω)Q(ω)+ve(ω)Q*(-. omega.), Q (omega) is the received signal affected by IQ imbalance.
Further, a first-order operator K of the variant Volterra backward inverse equalization process1，K1≡1，
Second-order operator K for variant Volterra backward inverse equalization processing2，K2＝-K1H2K1＝-H2；
Third-order operator K for variant Volterra backward reverse equalization processing3，K3＝K1[-H3+H2(1+K1H2)-H2K1H2-H2]K1＝-H3+H2(1+H2)-H2H2-H2；
Wherein H2For second order Volterra operators, H3Is a third order Volterra operator.
Further, the first-order operator of the variant Volterra backward inverse equalization processing is K1，K1≡W，
The second-order operator of the variant Volterra backward inverse equalization processing is K2，K2＝-K1H2K1；
The third-order operator of the variant Volterra backward reverse equalization processing is K3，K3＝K1[-H3+H2(1+K1H2)-H2K1H2-H2]K1；
Wherein H2For second order Volterra operators, H3Is a third order Volterra operator, W ═ mue+ve。
Specifically, for understanding of the signal processing apparatus provided in the embodiment of the present invention, reference may be made to the description of the signal processing method embodiment described above, and details of the embodiment of the present invention are not repeated herein.
The signal processing device provided by the embodiment of the invention utilizes a Volterra model to model a transmission channel, a signal is subjected to channel nonlinear damage first and then to IQ imbalance damage, and a modified Volterra backward inverse equalizer is utilized at a receiving end to simultaneously inhibit the signal nonlinear damage and the IQ imbalance damage, so that IQ imbalance and channel nonlinear damage of a direct detection system or a coherent system receiver can be effectively inhibited, and the hardware cost of a coherent receiving system is reduced.
Embodiments of the present invention also provide a computer readable storage medium storing one or more programs, which are executable by one or more processors to implement the steps of the method as described above.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of a hardware embodiment, a software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention.

Claims (11)

1. A signal processing method applied to a communication system, wherein the communication system is equivalent to a system with channel nonlinear impairments acting before and IQ imbalance acting after, the method comprising:
performing combined modeling on linear damage of a series Volterra channel model and IQ imbalance of a receiving front end to obtain a coefficient of backward inverse equalization processing of variant Volterra;
at a receiving end of the communication system, a generalized linear equalizer obtained by first-order modification of a Volterra backward inverse equalizer compensates linear damage of a signal and IQ imbalance of the receiving end, and a high-order operator of the modified Volterra backward inverse equalization processes compensates nonlinear damage of the signal;
the method further comprises the following steps:
the IQ imbalance caused by analog receiving front end is expressed by adopting a generalized linear model in a complex value form, in order to completely compensate the linear distortion introduced by a communication system and the IQ imbalance of a receiving end, an operator Q of an IQ imbalance system is required to completely compensate the linear distortion and the IQ imbalance introduced by the communication system, and an operator mu in a complex value operator W of a generalized linear equalizer obtained by a first-order modification of a Volterra backward inverse equalizereAnd veThe conditions met include:
Figure FDA0003363968090000011
and
Figure FDA0003363968090000012
wherein μ (ω) ═ μr(ω)G1(ω)，
Figure FDA0003363968090000013
μr(ω) and vr(ω) is the IQ imbalance caused by the analog receive front end, and the input-output relationship is: w (ω) ═ μe(ω)Q(ω)+ve(ω)Q*(-. omega.), Q (omega) is the received signal affected by IQ imbalance.
2. The method of claim 1, wherein prior to jointly modeling linear impairments of a series-formed Volterra channel model and receive front-end IQ imbalance, comprising:
modeling a transmission channel of the communication system according to a Volterra theory to obtain a parallel Volterra channel model, wherein an operator of the parallel Volterra channel model system is G, GiIs an i-order Volterra operator, G, in channel modeling1[D(ω)]A valid signal representing the influence of linear damage to the channel after photoelectric conversion,
Figure FDA0003363968090000021
representing the nonlinear damage of the second order and above, D (omega) is an input signal;
converting the parallel Volterra channel model into a serial Volterra channel model according to a Volterra theory, wherein the serial Volterra channel model comprises: a high-order operator F and a first-order operator S, wherein the first-order Volterra operator F in the high-order operator F11, the first order operator S comprises only the first order Volterra operator S1，S1≡G1。
3. The method of claim 2, wherein jointly modeling linear impairments of a series-formed Volterra channel model and receive front-end IQ imbalance comprises:
and performing combined modeling on the first-order channel linear damage and the receiving end IQ imbalance damage in the series Volterra channel model.
4. The method according to any one of claims 1 to 3,
first-order operator K for variant Volterra backward reverse equalization processing1，K1≡1，
Second-order operator K for variant Volterra backward inverse equalization processing2，K2＝-K1H2K1＝-H2；
Third-order operator K for variant Volterra backward reverse equalization processing3，K3＝K1[-H3+H2(1+K1H2)-H2K1H2-H2]K1＝-H3+H2(1+H2)-H2H2-H2；
Wherein H2For second order Volterra operators, H3Is a third order Volterra operator.
5. The method according to any one of claims 1 to 3,
the first-order operator of the variant Volterra backward inverse equalization processing is K1，K1≡W，
The second-order operator of the variant Volterra backward inverse equalization processing is K2，K2＝-K1H2K1；
The third-order operator of the variant Volterra backward reverse equalization processing is K3，K3＝K1[-H3+H2(1+K1H2)-H2K1H2-H2]K1；
Wherein H2For second order Volterra operators, H3Is a third order Volterra operator, W ═ mue+ve。
6. A signal processing apparatus, wherein the signal processing apparatus is applied to a communication system equivalent to a channel nonlinear impairment before and IQ imbalance after; the signal processing apparatus includes: a modeling unit, a processing unit, wherein,
the modeling unit is used for carrying out combined modeling on linear damage of a series Volterra channel model and IQ imbalance of a receiving front end to obtain a coefficient of variant Volterra backward inverse equalization processing;
the processing unit is used for compensating linear damage of a signal and IQ imbalance of the receiving end by a generalized linear equalizer obtained by first-order modification of a Volterra backward inverse equalizer at the receiving end of the communication system, and compensating nonlinear damage of the signal by a high-order operator of the modified Volterra backward inverse equalization;
the modeling unit is further configured to represent the IQ imbalance caused by the analog receiving front end by using a generalized linear model in a complex value form, and to fully compensate for the linear distortion introduced by the communication system and the IQ imbalance of the receiving front end, an operator mu in a complex-value operator W of a generalized linear equalizer obtained by a first-order variation of a Volterrra backward inverse equalizereAnd veThe conditions met include:
Figure FDA0003363968090000031
and
Figure FDA0003363968090000032
wherein μ (ω) ═ μr(ω)G1(ω)，
Figure FDA0003363968090000033
μr(ω) and vr(ω) is the IQ imbalance caused by the analog receive front end, and the input-output relationship is: w (ω) ═ μe(ω)Q(ω)+ve(ω)Q*(-. omega.), Q (omega) is the received signal affected by IQ imbalance.
7. The apparatus of claim 6,
the modeling unit is further configured to model a transmission channel of the communication system according to a Volterra theory to obtain a parallel Volterra channel model, where an operator of the parallel Volterra channel model system is G and GiIs an i-order Volterra operator, G, in channel modeling1[D(ω)]A valid signal representing the influence of linear damage to the channel after photoelectric conversion,
Figure FDA0003363968090000034
representing the nonlinear damage of the second order and above, D (omega) is an input signal;
the processing unit is further configured to convert the parallel-form Volterra channel model into a serial-form Volterra channel model according to a Volterra theory, where the serial-form Volterra channel model includes: a high-order operator F and a first-order operator S, wherein the first-order Volterra operator F in the high-order operator F11, the first order operator S comprises only the first order Volterra operator S1，S1≡G1。
8. The apparatus of claim 7, wherein the modeling unit is further configured to jointly model a first-order channel linear impairment and a receiving-end IQ imbalance impairment in the series-form Volterra channel model.
9. The apparatus according to any one of claims 6 to 8,
first-order operator K for variant Volterra backward reverse equalization processing1，K1≡1，
Second-order operator K for variant Volterra backward inverse equalization processing2，K2＝-K1H2K1＝-H2；
Third-order operator K for variant Volterra backward reverse equalization processing3，K3＝K1[-H3+H2(1+K1H2)-H2K1H2-H2]K1＝-H3+H2(1+H2)-H2H2-H2；
Wherein H2For second order Volterra operators, H3Is a third order Volterra operator.
10. The apparatus according to any one of claims 6 to 8,
the first-order operator of the variant Volterra backward inverse equalization processing is K1，K1≡W，
The second-order operator of the variant Volterra backward inverse equalization processing is K2，K2＝-K1H2K1；
The third-order operator of the variant Volterra backward reverse equalization processing is K3，K3＝K1[-H3+H2(1+K1H2)-H2K1H2-H2]K1；
Wherein H2For second order Volterra operators, H3Is a third order Volterra operator, W ═ mue+ve。
11. A computer readable storage medium, characterized in that the computer readable storage medium stores one or more programs which are executable by one or more processors to implement the steps of the method as claimed in any one of claims 1 to 5.
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