阅读说明：本技术 一种基于判决反馈的载波相位误差鉴别方法 (Carrier phase error identification method based on decision feedback ) 是由 史学森 王永庆 申宇瑶 沈人豪 于 2021-08-25 设计创作，主要内容包括：本发明提供一种基于判决反馈的载波相位误差鉴别方法,通过倍频、选点的方式得到载波相位误差,且倍频后的信号降低了调制阶数,初步减小了符号判决次数；然后,本发明将倍频后的星座图顺时针旋转90度,位于X轴上的星座点相当于多组幅度不同的BPSK调制,因此选择位于X轴上的星座点,有利于进行相干积分和相位误差的提取,并能够进一步减小符号判决次数；相比于常规的判决反馈环载波相位误差鉴别器,本发明所提改进的判决反馈环载波相位误差鉴别器旋转操作不会带来额外的计算,只增加了倍频带来的乘法运算,但不需要提取接收信号相位,也不需要对多种调制相位进行判决和相位旋转,极大地减小了判决次数和总运算量。(The invention provides a carrier phase error identification method based on decision feedback, which obtains the carrier phase error in a frequency multiplication and point selection mode, reduces the modulation order of a frequency multiplied signal, and preliminarily reduces the symbol decision times; then, the frequency-doubled constellation diagram is rotated by 90 degrees clockwise, and the constellation points on the X axis are equivalent to a plurality of sets of BPSK modulation with different amplitudes, so that the selection of the constellation points on the X axis is beneficial to extraction of coherent integration and phase errors, and the symbol decision frequency can be further reduced; compared with the conventional decision feedback loop carrier phase error discriminator, the improved decision feedback loop carrier phase error discriminator provided by the invention does not bring extra calculation, only increases multiplication operation brought by frequency multiplication, but does not need to extract the phase of a received signal, and does not need to carry out decision and phase rotation on various modulation phases, thereby greatly reducing decision times and total operation amount.)

1. A carrier phase error identification method based on decision feedback is characterized by comprising the following steps:

s1: will 2^MI branch signal s of APSK synchronous signal of bit_I(k) And Q branch signal s_Q(k) After mixing with local carrier, the mixed signal is frequency-doubled to obtain I-path frequency-doubled signal x_{I_2}(k) And Q-path frequency multiplication signal x_{Q_2}(k) Wherein M is at least 4;

s2: multiplying the I path frequency signal x_{I_2}(k) And Q-path frequency multiplication signal x_{Q_2}(k) Rotating the corresponding constellation diagram by 90 degrees clockwise to obtain a rotated constellation diagram;

s3: dividing each constellation point on the rotating constellation diagram into M-2 data rings, and acquiring the constellation points belonging to the X-axis neighborhood range on the rotating constellation diagram according to each data ring;

s4: the phase error estimates for each data loop are obtained as follows:

wherein the content of the first and second substances,phase error estimate, θ, for the first data loop at the center₁For the phase extraction result of the first data loop, i 2,3, M-2,phase error estimation results for the 2 nd to M-2 nd data loops, θ_iPhase extraction results for the 2 nd to M-2 nd data loops, M_iThe number of constellation points of the 2 nd to M-2 nd data rings is represented by round {. DEG } which is rounded up;

s5: the average of the phase error estimates for each data loop is taken as 2^MPhase estimation error of the APSK synchronization signal of the bits.

2. The method for discriminating carrier phase error based on decision feedback according to claim 1, wherein the method for obtaining constellation points belonging to the X-axis neighborhood range on the rotated constellation diagram is as follows:

s31: judging whether the amplitude rho of the constellation point is smaller than a first judgment thresholdWherein the content of the first and second substances,andrespectively representing the radius of the first data ring and the second data ring, if the radius is smaller than the first radius, the constellation point belongs to the X-axis neighborhood range; if not, go to step S32;

s32: for amplitudes rho not less than a first decision threshold D₁Respectively judging whether the ratio | Q |/| I | between the projection | Q | of each constellation point on the Y axis and the projection | I | on the X axis is less than tan (2 pi/2M)_i) Wherein M is_iIf the number of the constellation points is smaller than the number of the constellation points of the data ring to which the constellation points belong, the constellation points belong to the X-axis neighborhood range; if not, the constellation point does not belong to the X-axis neighborhood range.

3. The method for discriminating the carrier phase error based on the decision feedback as claimed in claim 2, wherein the method for determining the data ring to which each constellation point belongs is:

if the amplitude rho of the constellation point is smaller than a first decision threshold D₁If yes, the constellation point belongs to the first data ring;

if the amplitude rho of the constellation point satisfies D_i-1≤ρ＜D_iIf the constellation point belongs to the ith data ring, and the ith ring decision threshold Andthe radii of the (i + 1) th data ring and the ith data ring are respectively.

4. The decision feedback-based carrier phase error discrimination method as claimed in claim 1, wherein the phase extraction result obtaining method of each data loop is as follows:

wherein, theta_jIs the phase extraction result for each data ring, and j ═ 1, 2., M-2, x'_{I_2}(k) Is an I-line frequency multiplication signal x 'rotated by 90 degrees clockwise'_{Q_2}(k) Sign (·) is a sign function for the Q-path frequency multiplication signal rotated by 90 degrees clockwise.

5. A decision feedback based carrier phase error discrimination method as claimed in claim 1, wherein if M is 4, then the phase error estimation results of the first data loop and the second data loop are as follows:

meanwhile, the phase estimation error of the APSK synchronous signal of 16 bits

Technical Field

The invention belongs to the field of aerospace measurement and control communication, and particularly relates to a carrier phase error identification method based on decision feedback.

Background

The satellite-ground data transmission communication technology is used as a communication means between the heaven and the earth, and has been expanded to high-speed services such as image, video and video call on the basis of meeting the traditional voice call service. With the high-resolution and high-multispectral resolution technology of the video images of the remote sensing equipment becoming mature, a large amount of information such as ultra-high-definition video images and the like needs to be transmitted in real time, and the data rate of satellite-ground link transmission is higher and higher. Higher and higher data transmission rates present a problem with spectral spreading, which is exacerbated if classical low order modulation is still selected, resulting in a dramatic increase in transmission bandwidth. Therefore, high-order modulation combining amplitude and phase is selected as the trend of the development of a high-speed data transmission signal modulation system. The Amplitude Phase Shift Keying (APSK) signal constellation diagram presents a circular distribution, the Amplitude is limited on a plurality of circles in a certain proportion, the signal envelope variation is smaller, and the Amplitude Phase Shift Keying (APSK) signal constellation diagram is more suitable for being transmitted in a satellite-ground link with nonlinear transmission characteristics. In the satellite-ground high-speed data transmission, due to the relative motion of satellite-ground equipment, a data transmission signal sent by a satellite and received by a ground station has Doppler frequency shift, and the Doppler estimation is completed by carrier synchronization through a carrier synchronization technology. The good and bad synchronization performance of the satellite-ground high-speed communication system is related to whether data can be accurately demodulated, the satellite-ground communication quality is directly influenced, and the satellite-ground high-speed communication system is a crucial link for ensuring the normal operation of the satellite-ground high-speed communication system.

As shown in fig. 1, the carrier phase estimation method based on closed-loop feedback generally employs a phase-locked loop, which is widely used due to its high interference rejection, high synchronization accuracy, and easy integration. Common phase-locked loops are classified as Costas loops, depending on the phase detector^[72]M power ring^[73]And a decision feedback loop^[74]. For multilevel constellation signals such as APSK, the amplitude and the phase both contain modulation information, so that the phase discriminator in a common phase-locked loop needs to be improved, the modulation phase is stripped, the influence of the modulation phase is removed, and then the carrier phase error is extracted. The Costas loop eliminates the modulation phase by means of phase compensation and filtering, the phase extraction precision is affected by noise, and when the signal modulation order is too high, the loop structure is numerous and complicated, and the resource-limited satellite-ground high-number data transmission comesIt is not suitable. The M-power ring eliminates the modulation phase in a frequency multiplication mode, the requirement of phase difference extraction can be met only by multiple times of frequency multiplication for high-order modulation, the noise item is enhanced by the multiple times of frequency multiplication, and the sensitivity of a receiver is reduced. The decision feedback loop firstly carries out symbol decision on a received signal, eliminates the influence of modulation information, extracts phase error information, has the same performance as a maximum likelihood method under the condition of small bit timing error, but a target symbol needing to be decided is related to the number of constellation points, and when the number of the constellation points is too high, a large amount of calculation is needed to judge which position of the constellation is the received signal, so that the calculation amount is increased rapidly.

For satellite-ground high-speed data transmission, the relative motion speed of the transceiver is high, the dynamic range of signals is large, the signal power is limited, the received signal-to-noise ratio is low, and the real-time requirement on carrier error estimation is high. The carrier synchronization precision is mainly determined by the precision of the phase discriminator for extracting the carrier error, and the precision and the operand of the existing phase discriminator still have improved space.

Disclosure of Invention

In order to solve the above problems, the present invention provides a carrier phase error identification method based on decision feedback, which can reduce the modulation order and greatly reduce the decision times and the total computation.

A carrier phase error identification method based on decision feedback comprises the following steps:

s1: will 2^MI branch signal s of APSK synchronous signal of bit_I(k) And Q branch signal s_Q(k) After mixing with local carrier, the mixed signal is frequency-doubled to obtain I-path frequency-doubled signal x_{I_2}(k) And Q-path frequency multiplication signal x_{Q_2}(k) Wherein M is at least 4;

s2: multiplying the I path frequency signal x_{I_2}(k) And Q-path frequency multiplication signal x_{Q_2}(k) Rotating the corresponding constellation diagram by 90 degrees clockwise to obtain a rotated constellation diagram;

s3: dividing each constellation point on the rotating constellation diagram into M-2 data rings, and acquiring the constellation points belonging to the X-axis neighborhood range on the rotating constellation diagram according to each data ring;

s4: the phase error estimates for each data loop are obtained as follows:

wherein the content of the first and second substances,phase error estimate, θ, for the first data loop at the center₁For the phase extraction result of the first data loop, i 2,3, M-2,phase error estimation results for the 2 nd to M-2 nd data loops, θ_iPhase extraction results for the 2 nd to M-2 nd data loops, M_iThe number of constellation points of the 2 nd to M-2 nd data rings is represented by round {. DEG } which is rounded up;

s5: the average of the phase error estimates for each data loop is taken as 2^MPhase estimation error of the APSK synchronization signal of the bits.

Further, the method for obtaining the constellation points belonging to the X-axis neighborhood range on the rotated constellation diagram is as follows:

s31: judging whether the amplitude rho of the constellation point is smaller than a first judgment thresholdWherein the content of the first and second substances,andrespectively representing the radius of the first data ring and the second data ring, if the radius is smaller than the first radius, the constellation point belongs to the X-axis neighborhood range; if not, go to step S32;

s32: for amplitudes rho not less than a first decision threshold D₁Respectively judging whether the ratio | Q |/| I | between the projection | Q | of each constellation point on the Y axis and the projection | I | on the X axis is less than tan (2 pi/2M)_i) Wherein M is_iIf the number of the constellation points is smaller than the number of the constellation points of the data ring to which the constellation points belong, the constellation points belong to the X-axis neighborhood range; if not, the constellation point does not belong to the X-axis neighborhood range.

Further, the method for determining the data ring to which each constellation point belongs is as follows:

if the amplitude rho of the constellation point is smaller than a first decision threshold D₁If yes, the constellation point belongs to the first data ring;

if the amplitude rho of the constellation point satisfies D_i-1≤ρ＜D_iIf the constellation point belongs to the ith data ring, and the ith ring decision threshold Andthe radii of the (i + 1) th data ring and the ith data ring are respectively.

Further, the phase extraction result obtaining method of each data ring is as follows:

wherein, theta_jIs the phase extraction result for each data ring, and j ═ 1, 2., M-2, x'_{I_2}(k) Is an I-line frequency multiplication signal x 'rotated by 90 degrees clockwise'_{Q_2}(k) Sign (·) is a sign function for the Q-path frequency multiplication signal rotated by 90 degrees clockwise.

Further, if M is 4, the phase error estimation results of the first data loop and the second data loop are as follows:

meanwhile, the phase estimation error of the APSK synchronous signal of 16 bits

Has the advantages that:

1. the invention provides a carrier phase error identification method based on decision feedback, wherein an improved decision feedback loop carrier phase error identifier obtains a carrier phase error in a frequency multiplication and point selection mode, and a frequency multiplied signal reduces a modulation order and preliminarily reduces symbol decision times; then, the frequency-doubled constellation diagram is rotated by 90 degrees clockwise, and the constellation points on the X axis are equivalent to a plurality of sets of BPSK modulation with different amplitudes, so that the selection of the constellation points on the X axis is beneficial to extraction of coherent integration and phase errors, and the symbol decision frequency can be further reduced; compared with the conventional decision feedback loop carrier phase error discriminator, the improved decision feedback loop carrier phase error discriminator provided by the invention does not bring extra calculation, only increases multiplication operation brought by frequency multiplication, but does not need to extract the phase of a received signal, and does not need to carry out decision and phase rotation on various modulation phases, thereby greatly reducing decision times and total operation amount.

2. The invention provides a carrier phase error identification method based on decision feedback, which can be expanded and applied to higher-order APSK signals, such as 32-APSK signals, and has stronger applicability and wider application range.

Drawings

FIG. 1 is a carrier synchronization loop based on closed loop feedback;

fig. 2 is a decision feedback based carrier phase error discriminator provided by the present invention;

FIG. 3 is a 16-APSK signal constellation;

FIG. 4 is a constellation diagram of a multiplied 16-APSK signal;

FIG. 5 is a 16-APSK signal constellation after frequency multiplication and rotation;

FIG. 6 is a 32-APSK signal constellation diagram after frequency multiplication;

FIG. 7 is a 32-APSK signal constellation after frequency multiplication and rotation.

Detailed Description

In order to make the technical solutions better understood by those skilled in the art, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.

The invention relates to a carrier phase error identification method based on decision feedback, which obtains the carrier phase error in a frequency multiplication and point selection mode, wherein the frequency multiplication reduces the modulation order of each ring signal, preliminarily reduces the symbol decision frequency, selects the constellation points of each data ring signal on a straight line on a constellation diagram for phase discrimination, does not need to extract the phase of a received signal, and further reduces the symbol decision frequency.

As shown in fig. 2, a method for identifying a carrier phase error based on decision feedback includes the following steps:

s1: will 2^MI branch signal s of APSK synchronous signal of bit_I(k) And Q branch signal s_Q(k) After mixing with local carrier, the mixed signal is frequency-doubled to obtain I-path frequency-doubled signal x_{I_2}(k) And Q-path frequency multiplication signal x_{Q_2}(k) Wherein M is at least 4.

Further, the APSK synchronization signal is expressed as:

where ρ (k) represents the amplitude of the kth signal sample point, w_dIs the carrier doppler frequency at which the carrier signal is transmitted,unknown phases introduced for carrier offset and phase jitter,indicating the modulation phase, N_I(k) And N_Q(k) Is gaussian noise. s_I(k) And s_Q(k) The signal obtained after mixing with the local carrier is:

wherein, Δ ω_dWhich represents the frequency offset of the carrier wave,indicating carrier phase offset, n_I(k) And n_Q(k) Is a noise term.

To s_I(k) And s_Q(k) The local constellation diagram obtained by signal-to-noise ratio estimation is represented as

Wherein the content of the first and second substances,is the estimated signal amplitude. The carrier phase error discriminator compares x_I(k)、x_Q(k) And X_I(k)、X_Q(k) The phase error is estimated and then the phase of the local carrier is adjusted by low pass filtering and a voltage controlled oscillator. The invention researches a carrier phase error discriminator.

Performing 2 frequency multiplication on the received signals after frequency mixing to obtain frequency-multiplied signals:

wherein n is_{I_2}(k) And n_{Q_2}(k) Is a noise term. If a 16-APSK signal is taken as an example, a constellation diagram of the 16-APSK signal before frequency multiplication is shown in fig. 3, and a signal constellation diagram after frequency multiplication is shown in fig. 4, it can be seen that an inner ring signal after frequency multiplication is equivalent to BPSK modulation, an outer ring signal is equivalent to 6-PSK modulation, and the modulation order is effectively reduced.

S2: multiplying the I path frequency signal x_{I_2}(k) And Q-path frequency multiplication signal x_{Q_2}(k) And rotating the corresponding constellation diagram by 90 degrees clockwise to obtain a rotated constellation diagram.

It should be noted that the constellation diagram is rotated by 90 degrees clockwise, which is convenient for phase extraction, and the rotated signal is

It can be seen that constellation rotation is equivalent to exchanging I, Q two signals, and no extra calculation is added; the rotated constellation is shown in fig. 5; it can be seen that the phase difference between the received signal constellation and the local constellation before frequency multiplication is relative to the x-axis, and the phase difference after frequency multiplication is relative to the y-axis, which is inconvenient for extracting the phase difference; after the constellation diagram rotates, the phase difference between the received signal constellation diagram and the local constellation diagram becomes relative to the x axis, and coherent integration and phase extraction are better facilitated.

S3: and dividing each constellation point on the rotating constellation diagram into M-2 data rings, and acquiring the constellation points belonging to the X-axis neighborhood range on the rotating constellation diagram according to each data ring.

Further, the method for obtaining the constellation points belonging to the X-axis neighborhood range on the rotated constellation diagram is as follows:

s31: judging whether the amplitude rho of the constellation point is smaller than a first judgment thresholdWherein the content of the first and second substances,andrespectively representing the radius of the first data ring and the second data ring, if the radius is smaller than the first radius, the constellation point belongs to the X-axis neighborhood range; if not, the step S32 is executed to further judge the constellation point whose amplitude is not less than the first decision threshold;

s32: for amplitudes rho not less than a first decision threshold D₁Respectively judging whether the ratio | Q |/| I | between the projection | Q | of each constellation point on the Y axis and the projection | I | on the X axis is less than tan (2 pi/2M)_i) Wherein M is_iIf the number of the constellation points is smaller than the number of the constellation points of the data ring to which the constellation points belong, the constellation points belong to the X-axis neighborhood range; if not, the constellation point does not belong to the X-axis neighborhood range.

Meanwhile, the method for determining the data ring to which each constellation point belongs is as follows:

that is, if the amplitude ρ of the constellation point is smaller than the first decision threshold D₁If the constellation point belongs to the first data ring, the constellation point is judged to be a point on the X axis; if the amplitude rho of the constellation point satisfies D_i-1≤ρ＜D_iIf the constellation point belongs to the ith data ring, and the ith ring decision threshold Andthe radii of the (i + 1) th data ring and the ith data ring are respectively.

For example, taking a 16-APSK signal as an example, how to determine whether a constellation point on a constellation belongs to a point near the X axis will be described in detail. As shown in fig. 3, the constellation points on the constellation diagram corresponding to the 16-APSK signal are divided into an inner ring and an outer ring, where s12, s13, s14 and s15 are inner ring points, and the others are outer ring points; as shown in fig. 6 and 7, the 32-APSK signal constellation after frequency multiplication and rotation is shown, and it can be seen that the constellation after frequency multiplication and rotation has 3 rings, which are defined as a first ring, a second ring and a third ring from inside to outside.

Further, continue toReferring to fig. 5, when the constellation point is a point on the inner ring, then this point must be a point near the X-axis. When the constellation point is a point on the outer ring, the point may be a point near the X axis or a point near the Y axis; so firstly, whether the constellation belongs to the inner ring point is judged, D is defined₁Represents an inner loop decision threshold, andwhereinAndrepresenting the radii of the inner and outer rings. Defining the amplitude rho < D of the sampling point of the signal₁Judging the constellation point as the point on the inner ring; otherwise, it is a point on the outer ring. When a certain constellation point is a point on the outer ring, whether the point is close to the X axis is judged by using | Q |/| I |, wherein if yes, the point is judged to be close to the X axisThe constellation point is judged to be a point near the X axis, otherwise, the constellation point is a point far away from the X axis.

S4: the phase error estimates for each data loop are obtained as follows:

wherein the content of the first and second substances,phase error estimate, θ, for the first data loop at the center₁For the phase extraction result of the first data loop, i 2,3, M-2,phase error estimation results for the 2 nd to M-2 nd data loops, θ_iPhase extraction results for the 2 nd to M-2 nd data loops, M_iIs 2 nd to M thConstellation points for 2 data rings, round {. cndot } denotes rounding.

It should be noted that the phase error estimation includes two steps of coherent integration and phase extraction; let theta_jRepresents the phase extraction result in the s-th phase coherent integration period of the j-th ring, then theta_jThe calculation is as follows:

wherein, theta_jIs the phase extraction result for each data ring, and j ═ 1, 2., M-2, x'_{I_2}(k) Is an I-line frequency multiplication signal x 'rotated by 90 degrees clockwise'_{Q_2}(k) Sign (·) is a sign function for the Q-path frequency multiplication signal rotated by 90 degrees clockwise.

E.g., still using a 16-APSK signal as an example, then θ₁And theta₂For the phase extraction results of the inner and outer rings, the pair θ₁And theta₂The frequency multiplication and phase ambiguity removing operations are carried out to obtain phase error estimates of the inner ring and the outer ring

S5: averaging the phase error estimates for each data loopAs 2^MPhase estimation error of the APSK synchronization signal of the bits.

So far, the invention completes the pair 2 based on the judgment feedback^MCarrier phase error discrimination of the APSK synchronization signal of the bits.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it will be understood by those skilled in the art that various changes and modifications may be made herein without departing from the spirit and scope of the invention as defined in the appended claims.