Quadrature phase shift keying (QPSK)-based high-order modulation carrier phase recovery method, device and program product

Abstract

The invention provides a QPSK (Quadrature Phase Shift Keying)-based high-order modulation carrier phase recovery method and device and a program product, and belongs to the technical field of communication. The method comprises the following steps: extracting n QPSK signals from a target signal; constructing a target error function based on the kth QPSK signal and a preset error function; sequentially inputting preset test phases into the target error function, outputting a group of error function values of the kth QPSK signal, and determining the test phase corresponding to the minimum value as the phase noise value of the kth QPSK signal; taking the obtained n phase noise values as sampling points of corresponding QPSK signals, performing phase estimation on a high-order modulation signal block between two adjacent QPSK signal sampling points, and generating an interpolation of continuous phase change; and respectively carrying out carrier phase recovery on each high-order modulation signal block in the target signal through interpolation. The problem that an existing high-order modulation coherent light communication system is difficult in phase recovery under the condition of large phase noise can be solved. The complexity of phase recovery is reduced, and the bit error rate performance is improved.

Description

Technical Field

[0001] The present invention relates to the field of communication technologies, and in particular, to a method, apparatus, and program product for high-order modulation carrier phase recovery based on QPSK. Background Art

[0002] In recent years, with the rapid development of new services such as high-definition video, Internet, and cloud computing, the bandwidth capacity demand of the backbone network has increased exponentially. Traditional intensity modulation and direct detection optical fiber communication systems can no longer meet the demand. High-speed coherent optical communication systems, with the advantages of high-order modulation, coherent detection, and digital signal processing technologies, have become an important technology to meet the large bandwidth demand. Coherent optical communication systems improve spectral efficiency and transmission capacity through high-order modulation, and at the same time use digital signal processing technologies such as I, Q orthogonality and dispersion compensation to cope with the damage caused by dispersion and phase noise during signal transmission. High-order modulation is highly sensitive to frequency offset and phase noise. Especially for high-order M-QAM modulation formats, due to the dense constellation points, the distance between constellation points is reduced, reducing the tolerance of the system to laser phase noise. Therefore, researching carrier phase recovery algorithms with low complexity and high precision is crucial for realizing high-order modulation.

[0003] With the increase in the bandwidth demand of the core optical network and the progress of coherent detection technology, high-order modulation formats have been widely concerned due to their high spectral efficiency and high-speed transmission potential. However, although the increase in the modulation order improves the bandwidth utilization rate, it also increases the impact of laser phase noise on the system. At the same time, high-complexity algorithms increase the hardware burden, bringing greater computational pressure, and there is a problem that it is difficult to recover the phase in high-order modulation coherent optical communication systems under the condition of large phase noise. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide a method, apparatus, and program product for high-order modulation carrier phase recovery based on QPSK to eliminate or improve one or more defects existing in the prior art. It can solve the problem that it is difficult to recover the phase in existing high-order modulation coherent optical communication systems under the condition of large phase noise.

[0005] One aspect of the present invention provides a method for high-order modulation carrier phase recovery based on QPSK, the method comprising the following steps:

[0006] In response to the received target signal, extract n QPSK signals from the target signal; the target signal is obtained by the transmitting-end device embedding n QPSK signals in the high-order modulation signal; n is an integer greater than 1;

[0007] Based on the k-th QPSK signal and a preset error function, a target error function is constructed; the target error function is used to measure the phase error of the k-th QPSK signal at the input preset test phase; k takes positive integers from 1 to n in sequence;

[0008] The preset test phase is input into the target error function in sequence, a set of error function values corresponding to the k-th QPSK signal is output, and the test phase corresponding to the minimum value among them is determined as the phase noise value corresponding to the k-th QPSK signal;

[0009] When k is equal to n, the obtained n phase noise values are used as sampling points of the corresponding QPSK signals, and phase estimation is performed on the high-order modulation signal blocks between the sampling points of two adjacent QPSK signals to generate an interpolation with continuous phase change;

[0010] Carrier phase recovery is performed on each high-order modulation signal block in the target signal through interpolation.

[0011] In some embodiments of the present invention, the selection range of the preset test phase is [-π / 4, π / 4]; the preset error function is expressed as:

[0012]

[0013] In the formula, φ test represents the preset test phase; r k represents the k-th QPSK signal; Re() represents the function for extracting the real part; Im() represents the function for extracting the imaginary part; j represents the imaginary unit.

[0014] In some embodiments of the present invention, the target signal includes the amplitude information and phase information of the signal; correspondingly, the k-th QPSK signal includes the amplitude information and the current phase information of the k-th QPSK signal, expressed as: r k = Re jφ ;

[0015] According to r k = Re jφ and Euler's formula, the preset error function is simplified to obtain:

[0016] J(φ test ) = (-R 4 ) × [cos(φ - φ test ) × sin(φ - φ test )] 2

[0017] In the formula, φ test represents the preset test phase; R represents the amplitude information of the k-th QPSK signal, and φ represents the current phase information of the k-th QPSK signal.

[0018] In some embodiments of the present invention, when the preset test phases are 0, -π / 4, and -π / 8, the amplitude expression form in the simplified preset error function is abstracted into three variables, resulting in:

[0019] J(φ test ) = A 1 cos(4φ test + A 2 ) + A 3 ;

[0020] Wherein, φ test represents the preset test phase; A 1 , A 2 , and A 3 represent the three variables abstracted from the amplitude expression form;

[0021] Sequentially inputting the preset test phase into the target error function further includes:

[0022] Substituting the preset test phase into the target error function and solving to obtain A 1 , A 2 , and A 3 ;

[0023] Determining -A 2 / 4 as the phase noise value corresponding to each QPSK signal.

[0024] In some embodiments of the present invention, when k is less than n, let k = k + 1, and perform the step of constructing a target error function based on the k-th QPSK signal and the preset error function; the target error function is used to measure the phase error of the k-th QPSK signal at the input preset test phase.

[0025] In some embodiments of the present invention, the generation method of the target signal includes:

[0026] Performing channel estimation on the high-order modulation signal to obtain a channel estimation result;

[0027] Calculating the current signal-to-noise ratio of the high-order modulation signal based on the channel estimation result;

[0028] Calculating a signal-to-noise ratio adjustment factor based on the current signal-to-noise ratio and the signal-to-noise ratio of the QPSK signal, and adjusting the amplitude of the QPSK signal through the signal-to-noise ratio adjustment factor;

[0029] Embedding the adjusted QPSK signal into the high-order modulation signal at a preset signal interval to obtain the target signal.

[0030] In some embodiments of the present invention, extracting n QPSK signals from the target signal includes:

[0031] Locate the frame header of the target signal to determine the starting position of the QPSK signal in the target signal;

[0032] Starting from the starting position, extract n QPSK signals from the target signal at a preset signal interval.

[0033] Another aspect of the present invention provides a device for high-order modulation carrier phase recovery based on QPSK, including a processor, a memory, and computer programs / instructions stored on the memory. The processor is used to execute the computer programs / instructions, and when the computer programs / instructions are executed, the device implements the steps of the aforementioned high-order modulation carrier phase recovery method based on QPSK.

[0034] Another aspect of the present invention provides a computer-readable storage medium with computer programs / instructions stored thereon. When the computer programs / instructions are executed by a processor, the steps of the aforementioned high-order modulation carrier phase recovery method based on QPSK are implemented.

[0035] Another aspect of the present invention provides a computer program product, including computer programs / instructions. When the computer programs / instructions are executed by a processor, the steps of the aforementioned high-order modulation carrier phase recovery method based on QPSK are implemented.

[0036] The high-order modulation carrier phase recovery method and device based on QPSK of the present invention can solve the problem of difficult phase recovery in existing high-order modulation coherent optical communication systems under the condition of large phase noise; the transmitting-end device inserts a QPSK signal into the high-order modulation signal to achieve a preliminary phase reference mark for the high-order modulation signal; the receiving-end device performs phase estimation on the received target signal based on the constructed target error function to obtain the phase information of the accurate QPSK signal, uses the target error function to recover the phase offset of the QPSK signal, and then performs linear interpolation on the estimated QPSK phase noise value to construct a phase compensation function to accurately compensate the phase offset of the high-order modulation signal. By introducing the QPSK signal mark, the complexity of phase recovery is reduced; at the same time, the target error function is used to optimize the phase estimation accuracy, and the phase recovery accuracy of the high-order modulation signal is improved through phase interpolation compensation, which can effectively improve the bit error rate performance.

[0037] The additional advantages, objectives, and features of the present invention will be partially elaborated in the following description, and will become partially obvious to those of ordinary skill in the art after studying the following text, or can be learned through the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures specifically pointed out in the specification and the drawings.

[0038] Those skilled in the art will understand that the objectives and advantages achievable by the present invention are not limited to those specifically described above, and the above and other objectives achievable by the present invention will be more clearly understood from the following detailed description. Description of the Drawings

[0039] The drawings described herein are used to provide a further understanding of the present invention, form a part of this application, and do not limit the present invention. In the drawings:

[0040] Figure 1 It is a flowchart of a high-order modulation carrier phase recovery method based on QPSK provided by an embodiment of the present invention.

[0041] Figure 2 It is a schematic diagram of a high-order modulation carrier phase recovery method based on QPSK provided by an embodiment of the present invention.

[0042] Figure 3 It is a schematic diagram of finding the minimum value of an error function provided by an embodiment of the present invention.

[0043] Figure 4 It is a comparison diagram of simulation results before and after phase recovery of a high-order adjustment signal provided by an embodiment of the present invention. Detailed Embodiments

[0044] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the embodiments and the drawings. Herein, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but do not limit the present invention.

[0045] Here, it should also be noted that in order to avoid obscuring the present invention due to unnecessary details, only the structures and / or processing steps closely related to the solution of the present invention are shown in the drawings, while other details less related to the present invention are omitted.

[0046] It should be emphasized that the term "including / comprising" when used herein refers to the presence of features, elements, steps, or components, but does not exclude the presence or addition of one or more other features, elements, steps, or components.

[0047] Here, it should also be noted that if not otherwise specified, the term "connection" in this document can refer not only to a direct connection but also to an indirect connection with an intermediate.

[0048] In the following, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

[0049] Some terms related to this application will be described below.

[0050] High-order modulation signal: It refers to a communication signal modulated by a high-order modulation method. In this modulation method, data is transmitted through more symbols, and each symbol carries more bit information. Therefore, more information can be transmitted under the same bandwidth. These high-order modulation techniques are widely used in digital communications, especially in fields such as wireless communication systems and optical fiber communication systems. Common high-order modulation methods include: 16-QAM (16 Quadrature Amplitude Modulation), 64-QAM (64 Quadrature Amplitude Modulation), and 256-QAM (256 Quadrature Amplitude Modulation), etc.

[0051] Quadrature Phase Shift Keying (QPSK) signal: It is a digital modulation technique that uses four different phases to represent different binary data patterns. QPSK is a phase modulation technique. Compared with traditional binary modulation (such as BPSK), QPSK transmits more bit information in each symbol, thus improving the spectral efficiency.

[0052] Bit Error Rate (BER): The bit error rate refers to the proportion of data bits received incorrectly during the communication process. It represents the proportion of incorrect bits among all the received bits. In short, the bit error rate measures the reliability of the communication system. The lower the BER, the higher the reliability of data transmission.

[0053] Signal-to-Noise Ratio (SNR): The signal-to-noise ratio is the ratio of the signal strength to the noise strength, used to measure the quality of the signal. In communication, the higher the SNR, the stronger the signal relative to the noise, and the better the communication quality.

[0054] The following provides a detailed introduction to the high-order modulation carrier phase recovery method based on QPSK provided by this application.

[0055] In some embodiments of the present invention, the execution subject of the high-order modulation carrier phase recovery method based on QPSK provided by this application is the receiver device (Receiver). This receiver device can be a wireless communication device (such as a mobile phone, a tablet computer, etc.), a satellite receiver, a modem, or a base station receiving device, etc. The device type of the receiver device is not limited in this embodiment.

[0056] This embodiment provides a high-order modulation carrier phase recovery method based on QPSK, as Figure 1As shown, the method at least includes steps S101 to S105:

[0057] Step S101, in response to a received target signal, extracting n QPSK signals from the target signal.

[0058] In some embodiments of the present invention, the target signal is obtained after the transmitting end device embeds n QPSK signals in a high-order modulation signal; n is an integer greater than 1.

[0059] The transmitting device is a device that interacts with the receiving device and is used to generate and send a high-order modulated signal with an embedded QPSK signal. The transmitting device can be a wireless base station (such as an LTE or 5G base station), a satellite ground station, a modem (such as a DSL modem), a radio transmission device, or a Wi-Fi router, etc. This embodiment does not limit the type of the transmitting device.

[0060] Specifically, the transmitting device first obtains a suitable high-order modulation transposition (such as 16-QAM, 64-QAM, etc.) and an input signal (such as a randomly generated bit stream) and generates a high-order modulation signal according to the bandwidth and bit error rate requirements of the system (higher-order modulation methods require larger bandwidths and usually have higher bit error rates). After the randomly generated bit stream is mapped to different modulation symbols, these symbols are converted into time domain signals to obtain a high-order modulation signal. The bit stream is mapped to the four symbols of QPSK (for example, 00->+1, 01->+j, 10->-1, 11->-j), these symbols are mapped to time domain signals, which are converted into complex signals to obtain QPSK signals; the QPSK signal is inserted into the high-order modulation signal to generate the target signal and send it to the receiving device.

[0061] In actual implementation, due to the possible differences in signal amplitude and signal-to-noise ratio between the high-order modulated signal and the QPSK signal, the bit error rate of the QPSK signal may be higher than that of the high-order modulated signal at the receiving end, especially in the case of strong noise or non-ideal channels. The mismatch in signal-to-noise ratio will make the QPSK signal more susceptible to interference and noise during the demodulation process, thereby affecting the accuracy of its phase recovery and the performance of the overall system. Based on this, in order to improve the phase recovery performance and anti-noise capability, it is also necessary to adjust the amplitude of the QPSK signal according to the channel estimation result of the high-order modulated signal so that the signal-to-noise ratio of the QPSK signal matches that of the high-order modulated signal.

[0062] Specifically, the generation method of the target signal includes: performing channel estimation on a high-order modulation signal to obtain a channel estimation result; calculating the current signal-to-noise ratio of the high-order modulation signal based on the channel estimation result; calculating a signal-to-noise ratio adjustment factor based on the current signal-to-noise ratio and the signal-to-noise ratio of the QPSK signal, and adjusting the amplitude of the QPSK signal through the signal-to-noise ratio adjustment factor; embedding the adjusted QPSK signal into the high-order modulation signal at a preset signal interval to obtain the target signal.

[0063] After the receiving-end device receives the target signal, it extracts the embedded QPSK signal part from the target signal for subsequent phase offset estimation reference.

[0064] In some embodiments of the present invention, the transmitting-end device embeds the QPSK signal into the QPSK signal at a preset signal interval. Wherein, the preset signal interval is the number of high-order modulation signal intervals set in advance, including 15, 20, or 30, etc. The present embodiment does not limit the value of the preset signal interval. For example: when the value of the preset signal interval is 20, the transmitting-end device inserts a QPSK signal every 20 high-order modulation signals.

[0065] Correspondingly, after the receiving-end device determines the starting position of the QPSK signal in the target signal through frame header positioning, it extracts the QPSK signal from the target signal at a preset signal interval. Wherein, frame header positioning refers to a method for determining the position of the frame header in data transmission or data frames, including but not limited to fixed-length frame headers, identifier positioning, or dynamic frame headers.

[0066] For example: when the value of the preset signal interval is 20, the corresponding QPSK signal is extracted every 20 QAM symbols to achieve the complete extraction of the QPSK signal.

[0067] Specifically, extracting n QPSK signals from the target signal includes: performing frame header positioning on the target signal to determine the starting position of the QPSK signal in the target signal; starting from the starting position, extracting n QPSK signals from the target signal at a preset signal interval.

[0068] Step S102, constructing a target error function based on the k-th QPSK signal and a preset error function. Wherein, the target error function is used to measure the phase error of the k-th QPSK signal at a preset test phase input; k takes positive integers from 1 to n in sequence.

[0069] In some embodiments of the present invention, the target signal includes amplitude information and phase information of the signal. However, during actual transmission, the target signal also includes phase fluctuations caused by the laser linewidth. Taking the actual phase θ of the target signal m as an example, refer to Figure 2, due to the influence of phase fluctuations caused by the laser linewidth, the actual phase of the received target signal also includes phase noise and additive white Gaussian noise (AWGN), denoted as θ m +φ noise .

[0070] Based on this, in order to compensate for the phase fluctuations caused by the laser linewidth and ensure that all symbols in the high-order modulation signal can accurately reflect their original phase information, as Figure 2 shown, after extracting n QPSK signals, it is also necessary to recover the QPSK signals, calculate the phase noise values corresponding to the n QPSK signals, and then perform linear interpolation on the phase noise values to correctly compensate the phase of the target signal, so as to reduce errors and improve signal quality and transmission performance.

[0071] In some embodiments of the present invention, for any one of the n QPSK signals, the corresponding phase noise value is calculated by using the error function minimization method. The specific steps include: constructing the target error function corresponding to the k-th QPSK signal, setting a preset test phase, calculating the error function values of the k-th QPSK signal at each preset test phase, and selecting the preset test phase corresponding to the minimum error function value as the phase noise value of the k-th QPSK signal.

[0072] In the existing technical solutions, the error function is usually designed as a function that can measure the difference between the current phase of the signal and the correct phase, so as to reflect the "error" or "mismatch" degree of the current phase estimation. At the correct phase angle, the error function should obtain an extreme value (usually the minimum value), because this means that the currently estimated phase is closest to the true phase. A common form of the existing error function is:

[0073]

[0074] In the formula, represents the phase angle; r(k) represents the received target signal; s(k) represents the actual signal; j represents the imaginary unit.

[0075] As Figure 3 shown, Figure 3 is a schematic diagram of finding the minimum value of the error function. When the error function is the smallest, it means that the currently estimated phase is closest to the true phase. That is to say, when the phase angle makes the error function take the minimum value, the phase angle at this time can be regarded as the phase noise value.

[0076] In some embodiments of the present invention, the target error function is used to measure the phase error magnitude of the k-th QPSK signal under various preset test phase rotations, and the k-th QPSK signal is represented as r k ; The target error function can be expressed as:

[0077]

[0078] In the formula, φ test represents the preset test phase; r k represents the k-th QPSK signal; Re() represents the function for extracting the real part; Im() represents the function for extracting the imaginary part; j represents the imaginary unit; the real part and the imaginary part respectively represent the phase components after rotation of the k-th QPSK signal.

[0079] Due to the inherent characteristics of the QPSK signal, that is, the correct QPSK signal coordinates should be (0, ±1) or (±1, 0), this characteristic ensures that one of the real part or the imaginary part of the signal is zero. Therefore, when the preset test phase makes the recovered QPSK signal accurate, the value of the target error function will reach the minimum value of 0, thus realizing the accurate estimation of the phase error.

[0080] In addition, through squaring processing, the influence of the imaginary unit in the imaginary part can be effectively eliminated, enabling the target error function to directly reflect the deviation degree of the QPSK signal phase, and improving the accuracy and reliability in the phase recovery process.

[0081] Through the target error function, the k-th QPSK signal is rotated with different test phases, the target error function values of the k-th QPSK signal under different preset test phases are calculated, and the phase noise value of the k-th QPSK signal is estimated by minimizing the target error function, so as to compensate the carrier phase offset with the minimum point of the phase fluctuation.

[0082] In some embodiments of the present invention, three groups of preset test phases are designed, and the selection range of the preset test phase is [-π / 4, π / 4].

[0083] Since the QPSK signal has complete phase information within the range of [-π / 4, π / 4], therefore, by selecting three representative test phases within this range, it can be ensured that the target error function can cover all possible phase error situations, thereby improving the accuracy of the phase error estimation. By calculating the error values under each preset test phase, a set of error function values can be obtained.

[0084] In actual implementation, the target signal includes the amplitude information and phase information of the signal; accordingly, the k-th QPSK signal includes the amplitude information and the current phase information of the k-th QPSK signal, which is expressed as: k =Re jφ Based on this, the error function can be rewritten as: According to Euler's formula jθ =cosθ+jsinθ The rewritten objective error function can be simplified to obtain:

[0085] J(φ test )=(-R 4 )×[cos(φ-φ test )×sin(φ-φ test )] 2

[0086] In the formula, φ test represents the preset test phase; R represents the amplitude information of the kth QPSK signal; φ represents the current phase information of the kth QPSK signal.

[0087] Step S103, input the preset test phases into the target error function in sequence, output a set of error function values ​​corresponding to the kth QPSK signal, and determine the test phase corresponding to the minimum value as the phase noise value corresponding to the kth QPSK signal.

[0088] In addition, when the test phases are preset to 0, -π / 4, and -π / 8, the amplitude expression in the simplified target error function can be abstracted into three undetermined parameters, making the expression of the error function more concise, which helps to minimize the error more efficiently in the actual calculation process. At the same time, the setting of the three undetermined variables can more flexibly adapt to signals of different amplitudes and achieve precise control of the phase error. Specifically, after abstracting the amplitude expression in the simplified target error function into three undetermined parameters, we get:

[0089] J(φ test )=A 1 cos(4φ test +A 2 )+A 3 ;

[0090] In the formula, φ test Indicates the preset test phase; A 1 , A 2 and A 3 Represents three undetermined parameters obtained by abstracting the amplitude expression; the specific values ​​of these undetermined parameters are solved through 0, -π / 4 and -π / 8.

[0091] In the implementation process of the present invention, specific preset test phases 0, π / 4, and -π / 8 are used to optimize the solution accuracy and calculation efficiency of three undetermined parameters. Selecting 0 and π / 4 in the preset test phases aims to simplify the calculation process of the error function. These two phase values can effectively reduce the complexity in the calculation, making the solution process of the three undetermined parameters A 1 、A 2 and A 3 more efficient, thereby improving the accuracy and stability of phase estimation.

[0092] Selecting -π / 8 as the third test phase is based on the fact that this value is negative, which can expand the range span of the preset test phases, making the distribution of the three preset test phases more uniform, facilitating the discovery of the minimum value of the error function, and thus accurately determining the optimal phase compensation value. In addition, -π / 4 is not selected as the test phase because the cos function has the property of an even function, and for symmetric positive and negative phase values, its function values are the same, which cannot provide additional effective information, so it is not conducive to the uniqueness and accuracy of the parameter solution. After the preset test phases 0, π / 4, and -π / 8, the solution is as follows:

[0093]

[0094] Since A 1 is always greater than zero, the minimum value of the target error function will appear at the point where cos(4φ test +A 2 ) reaches its minimum value. According to the properties of trigonometric functions, when 4φ test +A 2 =π, cos(4φ test +A 2 )=-1 obtains the minimum value. Therefore, the test phase at this time is solved as -A 2 / 4, and the target error function takes the minimum value, and this test phase is the phase noise value.

[0095] Specifically, when the preset test phases are successively input into the target error function, it also includes: substituting the preset test phases into the target error function to solve for A 1 、A 2 and A 3 ; determining -A 2 / 4 as the phase noise value corresponding to each QPSK signal.

[0096] Step S104, when k is equal to n, using the obtained n phase noise values as the sampling points of the corresponding QPSK signals, performing phase estimation on the high-order modulation signal blocks between the sampling points of adjacent two QPSK signals, and generating an interpolation with continuous phase change.

[0097] In some embodiments of the present invention, linear interpolation is performed on the sampling points of any two adjacent QPSK signals to generate a phase compensation sequence for the corresponding high-order modulation signal block, so as to smoothly transition the recovered QPSK phase information to the entire QAM symbol sequence, construct a phase mapping relationship with the high-order modulation signal block, and ensure that all symbols in the high-order modulation signal obtain corresponding high-precision phase compensation.

[0098] Specifically, first, after the phase noise value corresponding to each QPSK signal extracted by the receiving device is obtained through the target error function, these phase noise values are used as known sampling points. On this basis, a linear interpolation algorithm is used to estimate the phase of the high-order modulation signal block between two adjacent sampling points, generating an interpolation with continuous phase change. Through this interpolation, the phase error of the high-order modulation signal within the interpolation interval is compensated, so that the phase offset of all high-order modulation signals is corrected.

[0099] For the a-th QPSK signal, its phase noise value is denoted as θ a , and the phase noise value of the (a - 1)-th QPSK signal is denoted as θ a-1 . The length of the high-order modulation signal block between the a-th QPSK signal and the (a - 1)-th QPSK signal is N; the phase noise value of the b-th high-order modulation signal between the a-th QPSK signal and the (a - 1)-th QPSK signal can be expressed by the following formula:

[0100]

[0101] In addition, when k is less than n, let k = k + 1, and perform the step of constructing the target error function based on the k-th QPSK signal and the preset error function.

[0102] Step S105, carrier phase recovery is performed on each high-order modulation signal block in the target signal through interpolation.

[0103] The phase offset of the QAM signal is adjusted through interpolation, so as to recover the phase information of the high-order modulation signal. The phase noise values of all signals included in the target signal together constitute the phase noise value of the target signal. Compensating the high-order modulation signal with the obtained phase noise value of the target signal can achieve accurate carrier phase recovery. Refer to Figure 4 , Figure 4 is a comparison diagram of the simulation results before (left figure) and after (right figure) the phase recovery of the high-order adjustment signal of 64QAM.

[0104] The traditional Blind Phase Search (BPS) algorithm requires a large amount of hardware resources to perform addition, multiplication, comparison, and decision operations. It is relatively complex in hardware implementation. It is suitable for environments with strong noise, but the hardware consumption is large. As shown in Table 1, the BPS algorithm modulation requires a large number of addition operations, which may be used for operations such as signal combination or inverse modulation. Therefore, 739 real number adders are needed. At the same time, since the BPS algorithm may involve operations such as signal amplitude adjustment and phase adjustment, multipliers are also widely used, and 768 real number multipliers are required. During the demodulation process of the BPS algorithm, 128 comparators are needed to determine the phase of the signal and judge the binary information of 0 or 1, and 128 decision operation units make decisions based on the signal to judge the output bit (0 or 1).

[0105]

[0106] Table 1

[0107] The high-order modulation carrier phase recovery method based on QPSK provided in this application is more efficient in hardware implementation. The required hardware resources are much lower than those of the blind phase search algorithm. It can achieve efficient modulation and demodulation through fewer calculations. Therefore, it has advantages in resource-constrained systems. As shown in Table 1, compared with the blind phase search algorithm, the method provided in this application is more efficient in operation, and the number of adders and real number multipliers required is greatly reduced. Only 13 real number adders and 16 real number multipliers are needed. The requirements for comparators and decision operation units are also much lower than those of BPSK, only 2 comparators and 1 decision operation unit are needed.

[0108] In summary, the high-order modulation carrier phase recovery method based on QPSK provided in this embodiment extracts n QPSK signals from the target signal in response to the received target signal; constructs a target error function based on the k-th QPSK signal and a preset error function; sequentially inputs the preset test phases into the target error function, outputs a set of error function values corresponding to the k-th QPSK signal, and determines the test phase corresponding to the minimum value as the phase noise value corresponding to the k-th QPSK signal; uses the obtained n phase noise values as sampling points of the corresponding QPSK signals, estimates the phase of the high-order modulation signal block between the sampling points of two adjacent QPSK signals, and generates an interpolation with continuous phase change; and performs carrier phase recovery on each high-order modulation signal block in the target signal through the interpolation. It can solve the problem of difficult phase recovery in existing high-order modulation coherent optical communication systems under the condition of large phase noise; the transmitting device inserts QPSK signals into the high-order modulation signal to achieve a preliminary phase reference mark for the high-order modulation signal; the receiving device performs phase estimation on the received target signal based on the constructed target error function to obtain the accurate phase information of the QPSK signal, uses the target error function to recover the phase offset of the QPSK signal, and then performs linear interpolation on the estimated QPSK phase noise value to construct a phase compensation function to accurately compensate the phase offset of the high-order modulation signal. By introducing QPSK signal markers, the complexity of phase recovery is reduced; at the same time, the target error function is used to optimize the phase estimation accuracy, and the phase recovery accuracy of the high-order modulation signal is improved through phase interpolation compensation, effectively improving the bit error rate performance.

[0109] Another aspect of the present invention provides an apparatus for a high-order modulation carrier phase recovery method based on QPSK, including a processor, a memory, and a computer program / instructions stored on the memory. The processor is configured to execute the computer program / instructions, and when the computer program / instructions are executed, the device implements the steps of the foregoing high-order modulation carrier phase recovery method based on QPSK. The present application also provides a computer-readable storage medium in which a program is stored, and the program is loaded and executed by the processor to implement the high-order modulation carrier phase recovery method based on QPSK in the above method embodiment.

[0110] The present application also provides a computer program product, including computer program / instructions, and when the computer program / instructions are executed by the processor, the high-order modulation carrier phase recovery method based on QPSK in the above method embodiment is implemented.

[0111] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0112] Obviously, the embodiments described above are only a part of the embodiments of the present application, rather than all of them. Based on the embodiments in the present application, those of ordinary skill in the art can make other different forms of changes or variations without making creative efforts, and all of them should fall within the scope of protection of the present application.

Claims

1. A QPSK-based high-order modulation carrier phase recovery method, characterized in that: The method comprises the following steps: In response to the received target signal, n QPSK signals are extracted from the target signal; the target signal is obtained after the transmitting end device embeds the n QPSK signals in the high-order modulation signal; n is an integer greater than 1; Based on the k-th QPSK signal and the preset error function, a target error function is constructed; the target error function is used to measure the phase error of the k-th QPSK signal under the input preset test phase; k is a positive integer from 1 to n in sequence; Input the preset test phases into the target error function in sequence, output a set of error function values ​​corresponding to the k-th QPSK signal, and determine the test phase corresponding to the minimum value as the phase noise value corresponding to the k-th QPSK signal; When k is equal to n, the obtained n phase noise values ​​are used as sampling points of the corresponding QPSK signal, and the phase of the high-order modulation signal block between the sampling points of two adjacent QPSK signals is estimated to generate an interpolation of continuous phase changes; Carrier phase recovery is performed on each high-order modulation signal block in the target signal through the interpolation.

2. The QPSK-based high-order modulation carrier phase recovery method according to claim 1, characterized in that: The selection range of the preset test phase is [-π / 4, π / 4]; the preset error function is expressed as: J(φ test )=(Re(r k e -jφ test )) 2 ×(I(r k e -jφ test )) 2 In the formula, the φ test represents the preset test phase; the r k represents the kth QPSK signal; the Re() represents a function for extracting the real part; the Im() represents a function for extracting the imaginary part; and the j represents an imaginary unit.

3. The QPSK-based high-order modulation carrier phase recovery method according to claim 2, characterized in that: The target signal includes the amplitude information and phase information of the signal; accordingly, the k-th QPSK signal includes the amplitude information and the current phase information of the k-th QPSK signal, which is expressed as: k =Re jφ ; According to the k =Re jφ The preset error function is simplified by using the Euler formula to obtain: J(φ test )=(-R 4 )×[cos(φ-φ test )×sin(φ-φ test )] 2 In the formula, the φ test represents the preset test phase; the R represents the amplitude information of the k-th QPSK signal, and the φ represents the current phase information of the k-th QPSK signal.

4. The QPSK-based high-order modulation carrier phase recovery method according to claim 3, characterized in that: When the preset test phase is 0, -π / 4 and -π / 8, the amplitude expression in the simplified preset error function is abstracted into three variables, and the following is obtained: J(φ test )=A1cos(4φ test +A2)+A3; In the formula, the φ test represents the preset test phase; the A1, the A2 and the A3 represent three variables abstracted from the amplitude expression form; The step of sequentially inputting the preset test phases into the target error function further includes: Substituting the preset test phase into the target error function, and solving to obtain A1, A2 and A3; -A2 / 4 is determined as the phase noise value corresponding to each QPSK signal.

5. The QPSK-based high-order modulation carrier phase recovery method according to claim 1, characterized in that: When k is less than n, let k=k+1, and execute the step of constructing a target error function based on the kth QPSK signal and the preset error function.

6. The QPSK-based high-order modulation carrier phase recovery method according to claim 1, characterized in that: The target signal is generated in the following manner: Performing channel estimation on the high-order modulated signal to obtain a channel estimation result; Calculating a current signal-to-noise ratio of the high-order modulation signal based on the channel estimation result; Calculate a signal-to-noise ratio adjustment factor based on the current signal-to-noise ratio and the signal-to-noise ratio of the QPSK signal, and adjust the amplitude of the QPSK signal by the signal-to-noise ratio adjustment factor; The adjusted QPSK signal is embedded into the high-order modulation signal according to a preset signal interval to obtain the target signal.

7. The QPSK-based high-order modulation carrier phase recovery method according to claim 6, characterized in that: The step of extracting n QPSK signals from the target signal comprises: Performing frame header positioning on the target signal to determine the starting position of the QPSK signal in the target signal; Starting from the starting position, the n QPSK signals are extracted from the target signal according to the preset signal interval.

8. A QPSK-based high-order modulation carrier phase recovery method and device, comprising a processor, a memory, and a computer program / instruction stored in the memory, characterized in that: The processor is used to execute the computer program / instructions. When the computer program / instructions are executed, the device implements the steps of the method according to any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program / instruction stored thereon, characterized in that: When the computer program / instructions are executed by a processor, the steps of the method as claimed in any one of claims 1 to 7 are implemented.

10. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instructions are executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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