RU2625804C1 - Method of estimating navigation signal phase on background of interfering reflections of multipath distribution and navigation receiver with device for suppressing interfering reflections in phase estimation - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: receiver contains a master oscillator, an RF transducer, a multi-channel digital correlator, a multichannel digital correlation signal processing unit, a receiver timeline generator and a navigation processor. Each channel of the digital correlator comprises a device for suppressing interfering reflections in the phase estimation, and each digital correlation signal processing unit comprises a phase measurement generating unit. The device for suppressing interfering reflections in the phase estimation comprises a weight register, a shift copy register, a plurality of M code-mixers, M accumulators, M multipliers and an M-input combiner, at the output of which the phase estimation of the forward navigation signal is generated.

EFFECT: eliminating the errors in the phase estimation of the direct navigation signal caused by interfering reflected multipath signals.

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Description

The invention relates to the field of radio navigation, and in particular to signal receivers of satellite radio navigation systems GLONASS (Russia) [1], GPS (USA) [2], Galileo (EU) [3] and BeiDou (China) [4], which simultaneously receives signals these systems and intended for use in precision differential phase systems [5] positioning.

A solution to the problem of receiving navigation signals in multipath conditions is known, i.e. with interfering effects of reflected signals. This solution is based on the selection of the leading edge of the direct signal using narrow discriminator gates. Various modifications of this method have been developed at present, such as those described in [6] ... [9]. A drawback common to these solutions is the fact that, although they provide an increase in the accuracy of pseudorange measurements, they are ineffective in measuring the phase of the carrier, while the distortion of the phase of the carrier of the navigation signal in multipath conditions is the main source of errors in precision differential phase positioning systems [10].

For example, a receiver is known [9], comprising a series-connected radio frequency converter, a sampler, a multi-channel correlator, and a microprocessor. In Fig. 1 shows a simplified functional diagram of a navigation receiver-analogue 10, which reflects only the main essential functional blocks. The signal received by the antenna 11 is fed to a radio frequency converter 12, which amplifies it, filters it, and performs conversion to lower frequencies.

The radio frequency Converter 12 has several radio frequency paths and, accordingly, several outputs, each of which corresponds to a specific navigation system and a specific frequency range. The output of each RF path is converted to digital form in the corresponding analog-to-digital converter (ADC) 14 (only one ADC is shown in Fig. 1) and fed to the input of the multi-channel correlator 16 (only one channel is shown in Fig. 1).

Each correlation processing channel contains a mixer 25, multipliers 26, a carrier frequency generator 22, a code generator 24 and batteries 28. A mixer 25 multiplies the complex input signal by a complex conjugate reference frequency signal coming from the carrier frequency generator 22. Multipliers 26 multiply the signal by three copies pseudo-random code Early, Punctual, Late (EPL) corresponding to the selected satellite and delayed by a certain amount relative to each other. Copies of the pseudo-random code are generated by the code generator 24. The outputs of the multipliers 26 are integrated in the batteries 28. The direct (Punctual) output of the battery 28 (I, Q) _P is fed to the input of the phase discriminator 52, and a signal is generated in the discriminator of the code 54, depending on the phase error of the signal code and Punctual copy code phases.

The output of the phase discriminator 52 is processed in the filter of the Phase Tracking System (CCF, PLL) 60, and the output of the code discriminator 54 is processed in the filter of the System for Tracking Delay (CVD, DLL) 62. The full phase at the output of the CCF is used in the CVD to increase accuracy and reliability tracking delay.

The reflected signal suppression system includes a combination of accumulator registers 32 and a multipath suppression processor 50 (Multipath Mitigation Technique, MMT). In the register-accumulators 32, the complex signal is accumulated from the output of the Early 28 multiplier in the gates formed by the code generator 24 and tied to different phases of the code symbol. The processor MMT 50 analyzes the signals accumulated in the register-accumulators 32, highlighting the level jumps of the in-phase and quadrature components corresponding to the edges of the reflected signals. Based on the calculated values of the amplitudes and phases of the reflected signals, the MMT processor calculates the corrections to the measurements of the delay and the phase of the carrier, which it introduces into the loop for tracking the delay and phase using the adders 58 and 56, respectively.

The disadvantages of the analog receiver [9] (Fig. 1) are:

- the lack of means of forming raw phase measurements suitable for use in differential-phase systems, including, there is no exact determination of the moment of phase digitization;

- phase estimation based on using only the part of the signal falling into the strobe, i.e. contained in a small part of the code symbol is characterized by an increased random error compared to devices using the full signal contained in the whole code symbol;

- due to the limited bandwidth of the radio frequency path, the edges of the direct and reflected signals are not perfectly steep, which also leads to an increase in random errors in the phase estimation.

The closest known solution is the method (prototype) [11] (Fig. 2), in which the formation of the correlation vector of the input signal with a set of reference transmitted signals overlapping the region of possible moments of the appearance of the direct and reflected signals is carried out. The suppression of reflected signals is carried out by subtracting copies of the reflected signals from the input mixture, and obtaining these copies is based on a joint assessment of the set of random parameters of the entire input signal, presented in the form

Here A is the complex amplitude of the direct signal,

τ is the moment of arrival of the signal (delay of the direct signal),

α _i are the complex amplitudes of the individual components of the reflected signal having delays i⋅Δ, and Δ is the minimum distinguishable delay between the components, taken equal to the sampling period of the signal;

n (t) is the internal noise of the receiver.

According to the synthesis of the optimal algorithm, the best mean-square estimate of the vector α, composed of the weights of the reflected signals α _i i = 1 ... L, obtained for each value of τ from the uncertainty range for a fixed value of A, is

where K is a matrix of coefficients of size L × L, determined by the waveform, the level of internal noise and a priori information about the magnitude of the complex amplitudes of the direct and reflected signals,

q _τ is a vector of length L containing the signal samples at the output of the correlator calculated for the corresponding signal delay values τ + Δ, ..., τ + L⋅Δ.

Thus, the vector of complex amplitudes of the reflected signals in [11] is obtained in the form of a linear combination of L consecutive delay outputs of the correlator, and the algorithm for estimating the signal delay is reduced to finding the maximum functional

where q ₀ - reference signal at the output of the correlator for the delay τ,

a is a vector of length L, taking into account the mutual correlation of the direct and reflected signals with delays Δ, ..., L⋅Δ relative to the direct,

To ₀ is the weight coefficient.

The disadvantages of the prototype are:

- to calculate the matrix K and estimate the reflected signals by the formula (2), and then to estimate the delay of the direct signal by the formula (3), a priori information is needed on the magnitude of the complex amplitudes of the direct and reflected signals;

- to calculate the vector a and further for estimating the delay of the direct signal according to formula (3), a priori information is needed on the mutual correlation of the direct and reflected signals;

- the search for the maximum of functional (3) is carried out using iterative procedures, which are associated with large expenditures of time and computing resources;

- in the algorithm of Fig. 2 there is no formation of raw measurements of the direct signal phase, which is required for differential phase measurements of the location.

The present invention solves the problem of optimal non-iterative estimation of the direct signal phase and the formation of crude phase measurements necessary for differential-phase positioning systems under the influence of noise and interfering reflections without the need for a priori information about the magnitude of the complex amplitudes of the direct and reflected signals and their mutual correlation. To achieve this technical result, a new method is proposed for estimating the phase of the navigation signal, based on the application of the maximum likelihood method [12], which reduces to minimizing the functional:

where x (t) is the complex signal at the output of the radio frequency part of the proposed receiver (Fig. 3), which is an additive mixture of the direct navigation signal, reflected signals and Gaussian noise;

r (t-τ _k ) ⋅e ^{j (ωt + ϕ)} is the replica of the signal at the input of the k-th subchannel of the correlator;

w _k , k = 0, ... L are the unknown complex amplitudes of the signals arriving with delays τ _k , and w ₀ corresponds to the direct navigation signal.

In addition to the above-mentioned new method, the present invention proposes a device for its implementation, which contains a register of weighting coefficients, a shift register of the copy, the input of which is connected to the output of the leading copy of the rangefinder code generator, a set of M code mixers, each of which has a first input connected to a signal input interfering reflection suppression devices, and the second input of the mth code mixer is connected to the mth cell of the shift register, the set M of accumulating adders, the input of the mth accumulating the adder is connected to the output of the m-th code mixer, the set of M multipliers, the first input of the m-th multiplier connected to the output of the m-th accumulating adder, and the second input of the m-th multiplier connected to the output of the m-th register of the weight coefficients, and M-input adder, the inputs of which are connected to the outputs of the multipliers, and the output is the output of the device for suppressing interfering reflections when evaluating the phase.

In addition, the present invention provides a satellite navigation receiver in which the aforementioned device is used for phase estimation with suppression of interfering multipath reflections, and which comprises a master oscillator, a timeline generator, the input of which is connected to the output of the master oscillator, a radio frequency converter connected in series, an input which forms the signal input of the receiver, multi-channel digital correlator, multi-channel device for digital processing of correl samples and a navigation processor, the input of which is connected to the output of a multi-channel device for digital processing of correlation samples, each channel of the digital correlator contains a carrier generator, carrier mixer, code generator, code mixer and integrator, and each channel of a multi-channel device for digital processing of correlation samples contains a tracking system delay, phase discriminator and phase tracking system, characterized in that in each channel of the multichannel correlator an additional but an interfering reflection suppression device is introduced when evaluating the phase, the first input of which is a signal input and connected to the output of the carrier mixer, the second input is connected to the output of the leading copy of the ranging code generator, and the output is connected to the input of the phase discriminator of the multichannel device for digital processing of correlation samples, and in each the channel of the multichannel device for digital processing of correlation samples is additionally introduced a module for generating phase measurements, the first input of which is connected to zovym output by phase tracking system, a second input connected to the output frequency of the phase of the tracking system, a third input coupled to the output time of digitizing the phase of a tracking system, a fourth input connected to the output of the receiver timeline generator, and an output coupled to the input of navigation processor.

In the proposed method, the functional (4) is represented in the form:

Where:

The minimum condition for functional (5):

Equation (8) is represented as:

Where:

R = {R _km } is the Toeplitz matrix corresponding to the autocorrelation function of the rangefinder code;

w = {w _k } is the vector of unknown complex signal amplitudes;

ρ = {ρ _k } is the vector of the complex output signals of the correlator subchannels, and its average value is equal to R⋅w.

Optimal according to the criterion of maximum likelihood, an estimate of the complex amplitudes of the signals is determined from (9) as:

Where

The vector element w with index k = 0 represents the complex amplitude of the direct navigation signal. From (10) follows the formula for its calculation:

where q is the first row of the matrix Q, i.e. q _m = Q _0m , m = 0, ..., L.

, т.е. равна

. С другой стороны, ковариационная матрица оценки вектора w из (10) равна R^-1, т.е. оценка (10) имеет минимальную дисперсию среди несмещенных оценок, т.е. является наиболее точной среди всех возможных оценок.The argument ϕ of the complex value w ₀ = r⋅е ^jϕ calculated according to (12) is the phase value of the direct navigation signal that was to be determined. The proposed method for forming an estimate of the complex amplitude (12) does not require a priori information about the magnitude of the complex amplitudes of the direct and reflected signals and their mutual correlation. The proposed method does not require any iteration to form an estimate of the complex amplitudes of the signals. Estimates (10), (12) are unbiased, i.e. in the absence of random noise, the estimate of the direct signal (12) is exactly equal to the true complex amplitude of the direct signal, regardless of the intensity of the reflected signals. In addition, in the presence of random noise, the Fisher information matrix [13] of the probability distribution of the vector ρ with the parameter w is equal to I = R, as follows from (7), therefore, as is known from [13], the lower bound of the variance of the estimate of the parameter w ₀ is

, i.e. is equal to

. On the other hand, the covariance matrix for estimating the vector w from (10) is equal to R ^-1 , i.e. estimate (10) has minimal variance among unbiased estimates, i.e. is the most accurate of all possible estimates.

In Fig. 3 ... 7 shows an example of the formation of an estimate of the phase of a direct navigation signal against a background of an interfering reflected signal under the following conditions:

- the passband of the radio frequency path is wide enough in comparison with the spectrum of the navigation signal, so that the autocorrelation function of the navigation signal is considered an ideal triangle;

- delay panorama step = 0.1 symbol duration of the GPS ranging code (GPS chip duration);

- the number of parallel subchannels by delay L + 1 = 26;

- delay of the reflected signal relative to the direct = 0.1 chip duration;

- amplitude of the reflected signal = 0.8 of the amplitude of the direct;

- phase of the direct signal = 0.2 cycle = 72 °;

- phase of the reflected signal = 0.45 cycles = 162 °.

In this example, the noise at the receiver input is not taken into account to make the effect of the interfering reflected signal clearer.

The real and imaginary components of the mixture of direct and reflected signals at the output of the correlator, as well as the module of the complex signal at the output of the correlator are shown in Fig. 3a in Fig. Figure 4 shows the same complex signal in the form of a module and a phase; it shows significant distortions in the phase of correlation samples (up to 0.1 cycles or more). In Fig. Figure 5 shows the matrix Q calculated according to (11), and Fig. 6 - its first line q, which is used in (12).

The calculation results according to (10) are presented in Fig. 7, from which it can be seen that the phase estimate corresponding to τ _k = 0 is exactly equal to the true phase of the direct signal, despite the significant phase distortions of the raw correlation integrals (up to 0.1 cycles or more), which are visible in Fig. 4. Thus, the distorting effect of the reflected signal on the estimation of the phase of the direct signal is completely eliminated and the proposed method provides an accurate optimal non-iterative estimation of the phase of the direct signal in the presence of noise and interfering reflections without the need for a priori information about the magnitude of the complex amplitudes of the direct and reflected signals and their mutual correlations.

A phase estimator with suppression of interfering reflections that implements the method proposed above is shown in Fig. 8. The input signal x (t) ⋅e ^-jωt in L + 1 multipliers 103 is multiplied by a copy of the pseudo-random rangefinder code r (t-τ _m ), m = 0, ..., L, obtained on the shift register 102 from the code r (t ) corresponding to the direct navigation signal. The accumulators 104 form the values of the complex correlation integrals ρ _m (5), m = 0, ..., L, which in the multipliers 105 are multiplied by the actual coefficients q _m stored in the registers 106, and the results of the multiplications q _m ⋅ρ _m are summed in the adder 107 Thus, the most plausible estimate of the complex amplitude of the direct signal is obtained at the output of the adder 107 in accordance with (12), and the argument of the complex amplitude at the output of the adder 107 is an estimate of the phase of the direct navigation signal, “cleared” of interfering reflections Nij multipath.

The proposed satellite navigation receiver 201 with a device for suppressing interfering reflections of multipath propagation during phase estimation (Fig. 9) contains a series-connected radio frequency converter 204, a multichannel correlator 211 (only one correlator channel is shown in Fig. 9), and digital correlation data processing units 220 (on Fig. 9 shows only one such unit) and the navigation processor 232, and the operation of all components is synchronized from one master oscillator 203. In addition, the receiver has a gene ator timeline 231, the output of which is used to digitize the time points, which include raw measurements and navigation data definitions. The receiver operates as follows. The signal received by the antenna 202 is supplied to a radio frequency unit 204, which amplifies it, filters it, performs conversion to lower frequencies and digitizes it. All of the above operations in the receiver 201 are completely similar to those performed in the receiver-analogue and receiver-prototype. The digitized signal is subjected to correlation processing in the multi-channel correlator 211.

Each channel of the multi-channel correlator can be tuned to the frequency and code of one satellite in the same frequency range. For this, the input time-discrete complex signal x (t) in the multiplier 207 is multiplied by the complex reference signal e- ^jωt , the frequency of which is accurately aligned with the frequency of the direct navigation signal of this satellite. The resulting signal y (t) = x (t) ⋅ e ^-jωt is multiplied by the rangefinder code of this satellite in the multiplier 208 and integrated into the battery 209, the output of which is normally processed and filtered in the delay tracking system 221 in the digital correlation processing unit data 220 of this satellite, and the filtered data controls the code generator 206, providing closed loop feedback tracking delay. In parallel with this, the signal y (t) = x (t) ⋅ e ^-jωt is supplied to the input of the phase estimator 101, to the other input of which there is a signal of a copy of the ranging code from the code generator 206. The output complex signal of block 101, "cleared" from interfering reflections is processed in the phase discriminator 222, according to the results of which, in the phase 223 tracking system, smooth estimates of the phase ϕ and frequency ω are generated. The smoothed frequency ω is used in the usual way to control the carrier generator 205, providing closed feedback of the carrier phase tracking loop.

In each block of digital processing of correlation data 220, there is also a phase measurement generation module (IFFI) 224 (Fig. 10), in which, based on smoothed estimates of the phase ϕ, frequency ω, digitized value of the moment of reading the correlation data t _i and using data from the scale generator receiver time t _r 231, a measurement of the phase of the carrier ψ is produced, reduced to a given moment t _r on the receiver's time scale. All data obtained at the output of the digital correlation data processing unit 220 is transmitted to the navigation processor 232, in which the navigation problem is solved and messages are transmitted to the consumer containing coordinates, components of the velocity vector of navigation definitions and raw measurements of pseudorange and pseudo-Doppler phases.

The inventive receiver and a phase estimator with suppression of interfering reflections consist of functional blocks, the device of which is widely known in the field of satellite navigation. For example, various implementation methods of the RF converter 204 are described in [14], [15] and [16], any of the circuits described in [15] can be used in the inventive receiver. CVD devices 221 and SSF 223 are also well known from [14], and various methods for generating phase measurements in block 224 are discussed in detail in [5]. As the navigation processor 232, for example, various microprocessor cores developed by ARM Limited can be used. As the master oscillator 203, any of the TLCO chips or crystal oscillators produced by various companies can be used, as a generator of the timeline 231, any of the binary counters produced by the electronics industry can be used.

The proposed satellite navigation receiver with a phase estimator with suppression of interfering reflections provides a solution to the technical problem of eliminating phase measurement errors caused by reflected signals, without spending time and resources on iterative processes and without the need for a priori information about the magnitude of the complex amplitudes of the direct and reflected signals and their cross-correlation.

In Fig. 1 shows a functional diagram of a receiver-analogue.

In Fig. 2 presents a functional diagram of the receiver of the prototype.

In Fig. Figure 3 presents an example of a mixture of direct and reflected signals at the output of the correlator, the real part, imaginary part and module.

In Fig. Figure 4 presents the same mixture of direct and reflected signals as in Fig. 3, but in the form of a module and an argument of complex correlation integrals.

In Fig. 5 shows the matrix R ^{-1 of the} considered example.

In Fig. Figure 6 shows the vector of weights q = {q _m } of the considered example.

In Fig. 7 presents the results of calculating the estimates of the modulus and argument of the complex amplitudes of the direct (at k = 0) and reflected signals.

In Fig. 8 presents a functional diagram of the inventive device for suppressing interfering reflections during phase evaluation.

In Fig. 9 is a functional diagram of the inventive satellite navigation receiver with a device for suppressing interfering reflections during phase estimation.

In Fig. 10 is an example of a functional diagram of a phase measurement forming unit.

Information sources

1. "Global Navigation Satellite System - GLONASS. Interface control document (version 5.1). RNIIKP 2008"

2. Interface Specification IS-GPS-200, rev. H, 2013.

3.Galileo Open Service Signal In Space Interface Control Document, issue 1.1, Sept. 2010.

4. BDS-SIS-ICD-B1I-1.0, Dec.2012.

5. Povalyaev A.A. Satellite radio navigation systems: time, clock readings, formation of measurements and determination of relative coordinates. - M.: Radio Engineering, 2008.

6. Garin L., Van Diggelen F. and Rousseau J.M. "Strobe and Edge Correlator Multipath Mitigation for Code", proceedings of ION GPS-96, Kansas City, September 17-20.

7. Garin L. and Rousseau J.M. Enhanced Strobe Correlator, Proceedings of ION GPS-97, Kansas City, September 16-19.

8. Townsend, B., et al, (1995) "Performance evaluation of the multipath estimating delay lock loop," Navigation: Journal of the Institute of Navigation, vol 42, no 3, Fall, pp. 503-514.

9. Fenton P.C., Apparatus for and Method of Making Pulse-Shape Measurements. US Pat. No. 8,467,433 B2, Jun. 18, 2013.

10. J.k. Ray, M.E. Cannon. Characterization of GPS Carrier Phase Multipath. ION NTM-99, San Diego, January 25-27.

11. Moon Wang Jin (KR), Dongwook Kim (KR), Jae Cheng Chang (KR), Kharisov V.N. (RU), Efimenko B.C. (RU), Bulavsky N.T. (RU), Ivanov V.I. (RU), Yemets S.V. (RU), Tretyakov A.N. (RU). A method of synchronizing a radio signal. RF patent No. 2278470 C2, 06.20.2006.

12. B.R. Levin. Theoretical foundations of statistical radio engineering. M., Sov. radio, 1968.

13. M. Kendall, A. Stewart. Statistical conclusions and relationships. M., Science, 1973.

14. Van Dierendonck, A.J., “GPS Receivers,” in: Global Positioning System: Theory and Applications, Vol I, Parkinson, B.W. and Spilker, J.J. Jr., eds., American Institute of Aeronautics and Astronautics, Washington, 1996, pp. 329-407.

15. D.K. Shaeffer, T.H. Lee The Design and Implementation of Low-Power CMOS Radio Receivers. Kluwer Academic Publishers, Boston / Dordrecht / London, 1999.

16. Raymond A. Eastwood "An Integrated GPS / Glonass receiver". - "Navigation" (USA), 1990, 2, - pp. 141-151.

Claims (4)

1. The method of estimating the phase of the navigation signal with the suppression of interfering reflections of multipath propagation, based on the maximum likelihood (MP) method in such a way that the complex amplitude w _{0 of the} direct signal is formed as the sum of correlations ρ _{m of the} complex input signal with the range of copies of the rangefinder, weighted with weights q _m code r (t-τ _m ), m = 0, ..., L, overlapping the region of possible delays of the reflected signals relative to the direct navigation signal, i.e. w ₀ = q⋅ρ = Σ, q _m ⋅ρ _m , where q is the first row of the matrix Q, previously calculated as Q = R ^-1 , where R = {R _km } is the Toeplitz matrix corresponding to the autocorrelation function of the rangefinder code taken at points {τ _m }, and the phase estimate, not distorted by interfering reflections, is formed as an argument of the complex number w ₀ . 2. A satellite navigation receiver with an interfering reflection suppression device for phase estimation, comprising a master oscillator, a timeline generator, the input of which is connected to the output of the master oscillator, a radio frequency converter connected in series, the input of which forms the signal input of the receiver, a multi-channel digital correlator, and a multi-channel digital processing device correlation samples and a navigation processor, the input of which is connected to the output of a multi-channel digital processing unit relational samples, each channel of the digital correlator containing a carrier generator, carrier mixer, code generator, code mixer and integrator, and each channel of a multi-channel device for digital processing of correlation samples contains a delay tracking system, a phase discriminator and a phase tracking system, characterized in that in each channel of the multichannel correlator, an interfering reflection suppression device is additionally introduced when evaluating the phase, the first input of which is a signal and is connected to the output m of the carrier mixer, the second input is connected to the output of the leading copy of the rangefinder code generator, and the output is connected to the input of the phase discriminator of the multichannel device for digital processing of correlation samples, and a phase measurement module is additionally introduced into each channel of the multichannel device for digital processing of correlation samples, the first input of which is connected with the phase output of the phase tracking system, the second input is connected to the frequency output of the phase tracking system, the third input is connected to by the output of the time tracking phase monitoring system, the fourth input is connected to the output of the receiver timeline generator, and the output is connected to the input of the navigation processor. 3. The receiver according to claim 2, in which the interfering reflection suppression device for phase evaluation comprises a weighting register, a shift register of the copy, the input of which is connected to the output of the leading copy of the rangefinder code generator, a set of M code mixers, each of which has a first input connected to the signal input of the device for suppressing interfering reflections, and the second input of the mth mixer of the code is connected to the mth cell of the shift register, the set M of accumulating adders, the input of the mth accumulating adder is connected to by the mth code mixer, the set of M multipliers, the first input of the mth multiplier connected to the output of the mth accumulating adder, and the second input of the mth multiplier connected to the output of the mth cell of the weight register, and the M-input adder the inputs of which are connected to the outputs of the multipliers, and the output is the output of the device for suppressing interfering reflections when evaluating the phase. 4. The receiver according to claim 3, in which the phase measurement generating module comprises a subtraction unit, the first input of which is connected to the third input of the module, and the second input is connected to the fourth input of the module, a multiplier, the first input of which is connected to the second input of the module, and the second input connected to the output of the subtraction unit, and an adder, the first input of which is connected to the first input of the module, the second input is connected to the output of the multiplier, and the output is the output of the phase measurement forming module.

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