Method and apparatus for correcting tfdm-pon system

Abstract

A TFDM-PON system correction method and device, including OLT receiving ONU based on time division multiplexing or time-frequency division multiplexing sends double polarization signal, it includes target signal sequence corresponding with X / Y polarization, and target signal sequence is IQ period complex signal and its I road and Q road are single tone signal of first frequency and second frequency respectively;Based on the Fourier transform of double polarization signal and frequency domain symmetry, calculate target parameters including target transceiver frequency offset, target transmitting terminal, receiving terminal IQ delay and target power deviation between each ONU, make ONU correct frequency, delay and power according to target parameters, eliminate subcarrier crosstalk caused by frequency offset in TFDM uplink burst transmission, image crosstalk caused by IQ imbalance and performance degradation caused by subcarrier power imbalance, reduce bit error rate, improve system robustness.

Description

Technical Field

[0001] This application relates to the field of optical communication technology, specifically to a TFDM-PON system calibration method and apparatus. Background Technology

[0002] With the rapid growth of global data traffic (driven by cloud computing, 5G / 6G, and the Internet of Things), optical access networks require higher bandwidth, lower latency, and greater flexibility. Future PON (Passive Optical Network) technologies need higher spectral efficiency to support multiple users and high capacity. Current intensity modulation and direct detection (IM / DD) technologies are limited to intensity modulation and struggle to utilize other signal information. Compared to traditional incoherent optical communication, coherent optical communication enables polarization diversity and multidimensional modulation, improving transmission capacity. It also boasts a higher power budget, enabling long-distance communication and wider coverage. Furthermore, its flexible bandwidth allocation and low latency are more suitable for multi-user scenarios and support point-to-multipoint (PtMP) architectures (such as TFDM-PON), adapting to scenarios such as metropolitan area networks, access networks, and data center interconnections, providing large-scale connectivity and flexibility. Notably, coherent communication technology is gradually becoming the most promising technology for future high-capacity access networks, better meeting customer needs.

[0003] Among them, TFDM (Time-Frequency Division Multiplexing) technology is an advanced technology based on DSCM (Digital Subcarrier Multiplexing), which has attracted much attention in coherent passive optical networks (PON). It achieves flexible bandwidth scheduling and low-latency access by efficiently dividing and allocating signals in the time and frequency domains and utilizing multiple subcarriers to transmit data in parallel. Specifically, IQ modulation achieves complex-domain modulation of the optical carrier by manipulating the amplitude and phase of the optical signal.

[0004] However, in TFDM systems, parameters such as frequency offset, power imbalance, and IQ delay can affect the communication quality of PON systems. First, IQ delay disrupts the orthogonality of subcarrier signals, generating mirror signals at frequency symmetry positions. This prevents the conjugate mirror components of the subcarriers from effectively canceling each other, leading to image interference and an increased bit error rate. Second, in coherent passive optical networks based on digital subcarrier multiplexing, power imbalance can cause some subcarriers to have excessively low signal power, reducing their SNR (Signal-to-Noise Ratio). In higher-order modulation, a low SNR makes constellation points harder to distinguish, leading to demodulation errors at the receiver and significantly increasing the bit error rate. Conversely, excessively powerful subcarriers may induce nonlinear effects (such as fiber nonlinear distortion), similarly degrading signal quality. Furthermore, in DSCM systems, frequency offset can cause the frequency center of the subcarriers to shift, resulting in overlapping spectra of adjacent subcarriers and causing ICI (Inter-Carrier Interference). Therefore, in order to address the interference factors present in the communication system, it is necessary to correct non-ideal factors such as frequency offset, power imbalance, and IQ delay in the TFDM-PON system in order to improve system performance. Summary of the Invention

[0005] This application provides a TFDM-PON system correction method and apparatus, which can calculate and correct frequency offset, power imbalance and IQ delay in TFDM-PON system, so as to eliminate the performance degradation caused by subcarrier crosstalk, image crosstalk and power imbalance between subcarriers in TFDM uplink burst transmission, reduce bit error rate and improve system robustness.

[0006] In a first aspect, embodiments of this application provide a TFDM-PON system calibration method, the method being applied to an OLT, the method comprising:

[0007] Receive dual-polarization signals transmitted by the ONU based on time-division multiplexing or time-frequency-division multiplexing. The dual-polarization signals include target signal sequences corresponding to X-polarization or Y-polarization. The target signal sequences are IQ periodic complex signals, with I-channel being a single-tone signal of the first frequency and Q-channel being a single-tone signal of the second frequency.

[0008] The target parameters are calculated based on the Fourier transform of the dual-polarization signal and frequency domain symmetry. The target parameters include the target transceiver frequency offset, the target transmitter IQ delay, the target receiver IQ delay, and the target power deviation between each ONU.

[0009] The target parameters are sent to the ONU so that the ONU can correct the frequency, delay, and power based on the target parameters.

[0010] In conjunction with the first aspect, in one implementation, the calculation of the target parameters based on the Fourier transform of the dual-polarization signal and frequency domain symmetry includes:

[0011] The dual-polarization signal is coherently demodulated based on the local oscillator light, and the coherent demodulation result is converted into the target digital signal through an analog-to-digital converter (ADC).

[0012] Perform Fourier transform processing on the target digital signal to obtain the Fourier transform result;

[0013] The target transceiver frequency offset between the ONU carrier and the local oscillator is calculated based on the Fourier transform results and frequency domain symmetry.

[0014] The target transmitter IQ delay and the target receiver IQ delay are calculated based on the Fourier transform results, the number of frequency points corresponding to the single tone signal, and the location of the single tone signal.

[0015] The target power deviation between each ONU is calculated using the Fourier transform results and the total number of ONUs.

[0016] In conjunction with the first aspect, in one implementation, calculating the target transceiver frequency offset between the ONU carrier and the local oscillator light based on the Fourier transform result and frequency domain symmetry includes:

[0017] Based on frequency domain symmetry, the first actual frequency corresponding to the actual position of the first frequency f1, the first actual negative frequency corresponding to the first frequency -f1 corresponding to the actual position of the first negative frequency, or the second actual frequency corresponding to the actual position of the second frequency f2 and the second actual negative frequency corresponding to the second frequency -f2 corresponding to the actual position of the second negative frequency are determined from the Fourier transform results.

[0018] The target transceiver frequency offset between the ONU carrier and the local oscillator is calculated using the first actual frequency and the first actual negative frequency or the second actual frequency and the second actual negative frequency.

[0019] In conjunction with the first aspect, in one implementation, the target originating IQ delay And target receiver IQ latency The calculation formulas are as follows:

[0020]

[0021]

[0022]

[0023]

[0024]

[0025] In the formula, This indicates the IQ delay at the transmitting end in either X-polarization or Y-polarization. This represents the transmitter IQ delay calculated using the received X-polarized or Y-polarized I-channel data. This represents the IQ delay at the transmitting end calculated using the received X-polarized or Y-polarized Q-channel data. N represents the Fourier transform length, n represents the number of frequency points around the single-tone signal, k1 and k2 represent the positions of the single-tone signal at the first frequency f1 and the second frequency f2, respectively, N1 represents the number of frequency points between the first negative frequency -f1 and f1 corresponding to the first frequency f1, and N2 represents the number of frequency points between the second negative frequency -f2 and f2 corresponding to the second frequency f2. The Fourier transform representing the real part of the X-polarized or Y-polarized received signal. The Fourier transform represents the imaginary part of the X-polarized or Y-polarized received signal. This indicates the IQ delay at the receiving end in X-polarization or Y-polarization. This represents the IQ delay at the receiver calculated using data near the first frequency f1 of the received X-polarized or Y-polarized signal. This represents the IQ delay at the receiver calculated using data near the second frequency f2 of the received X-polarized or Y-polarized signal.

[0026] In conjunction with the first aspect, in one implementation method, the formula for calculating the target power deviation is:

[0027]

[0028]

[0029]

[0030] In the formula, This represents the target power deviation between the i-th ONU and the average power. This represents the power of the i-th ONU, and M represents the total number of ONUs. This represents the average power of M ONUs. This represents the Fourier transform of the signal with frequency f1 in the X-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f2 in the X-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f1 in the Y-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f2 in the Y-polarized received signal corresponding to the i-th ONU. This indicates the operation of taking the average.

[0031] Secondly, embodiments of this application provide a TFDM-PON system calibration method, which is applied to an ONU, and the method includes:

[0032] A dual-polarization signal is generated, the dual-polarization signal including a target signal sequence corresponding to X polarization or Y polarization, the target signal sequence being an IQ periodic complex signal with its I channel being a single-tone signal of a first frequency and its Q channel being a single-tone signal of a second frequency;

[0033] Based on time-division multiplexing or time-frequency-division multiplexing, dual-polarization signals are transmitted to the OLT, so that the OLT can calculate the target parameters based on the Fourier transform of the dual-polarization signals and frequency domain symmetry. The target parameters include the target transmit / receive frequency offset, the target transmit IQ delay, the target receive IQ delay, and the target power deviation between each ONU.

[0034] Upon receiving the target parameters sent by the OLT, the frequency, delay, and power are corrected based on the target parameters.

[0035] Thirdly, embodiments of this application provide a TFDM-PON system calibration device, the device including an OLT, the OLT being used for:

[0036] Receive dual-polarization signals transmitted by the ONU based on time-division multiplexing or time-frequency-division multiplexing. The dual-polarization signals include target signal sequences corresponding to X-polarization or Y-polarization. The target signal sequences are IQ periodic complex signals, with I-channel being a single-tone signal of the first frequency and Q-channel being a single-tone signal of the second frequency.

[0037] The target parameters are calculated based on the Fourier transform of the dual-polarization signal and frequency domain symmetry. The target parameters include the target transceiver frequency offset, the target transmitter IQ delay, the target receiver IQ delay, and the target power deviation between each ONU.

[0038] The target parameters are sent to the ONU so that the ONU can correct the frequency, delay, and power based on the target parameters.

[0039] In conjunction with the third aspect, in one implementation, the OLT is specifically used for:

[0040] The dual-polarization signal is coherently demodulated based on the local oscillator light, and the coherent demodulation result is converted into the target digital signal through an analog-to-digital converter (ADC).

[0041] Perform Fourier transform processing on the target digital signal to obtain the Fourier transform result;

[0042] The target transceiver frequency offset between the ONU carrier and the local oscillator is calculated based on the Fourier transform results and frequency domain symmetry.

[0043] The target transmitter IQ delay and the target receiver IQ delay are calculated based on the Fourier transform results, the number of frequency points corresponding to the single tone signal, and the location of the single tone signal.

[0044] The target power deviation between each ONU is calculated using the Fourier transform results and the total number of ONUs.

[0045] In conjunction with the third aspect, in one implementation, the OLT is further used for:

[0046] Based on frequency domain symmetry, the first actual frequency corresponding to the actual position of the first frequency f1, the first actual negative frequency corresponding to the first frequency -f1 corresponding to the actual position of the first negative frequency, or the second actual frequency corresponding to the actual position of the second frequency f2 and the second actual negative frequency corresponding to the second frequency -f2 corresponding to the actual position of the second negative frequency are determined from the Fourier transform results.

[0047] The target transceiver frequency offset between the ONU carrier and the local oscillator is calculated using the first actual frequency and the first actual negative frequency or the second actual frequency and the second actual negative frequency.

[0048] Fourthly, embodiments of this application provide a TFDM-PON system calibration device, the device including an ONU, the ONU being used for:

[0049] A dual-polarization signal is generated, the dual-polarization signal including a target signal sequence corresponding to X polarization or Y polarization, the target signal sequence being an IQ periodic complex signal with its I channel being a single-tone signal of a first frequency and its Q channel being a single-tone signal of a second frequency;

[0050] Based on time-division multiplexing or time-frequency-division multiplexing, a dual-polarization signal is transmitted to the OLT, so that the OLT can calculate the target parameters based on the Fourier transform of the dual-polarization signal and the frequency domain symmetry. The target parameters include the target transmit / receive frequency offset, the target transmit IQ delay, the target receive IQ delay, and the target power deviation.

[0051] Upon receiving the target parameters sent by the OLT, the frequency, delay, and power are corrected based on the target parameters.

[0052] The beneficial effects of the technical solutions provided in this application include:

[0053] The OLT (Optical Line Terminal) receives dual-polarization signals transmitted by the ONU (Optical Network Unit) based on time-division multiplexing or time-frequency-division multiplexing. These dual-polarization signals include target signal sequences corresponding to X-polarization or Y-polarization, and the target signal sequence is an IQ periodic complex signal with a single-tone signal at a first frequency on the I channel and a single-tone signal at a second frequency on the Q channel. Based on the Fourier transform of the dual-polarization signals and frequency domain symmetry, target parameters are calculated, including target transmit / receive frequency offset, target transmit IQ delay, target receive IQ delay, and target power deviation between ONUs. This allows the ONUs to correct frequency, delay, and power according to the target parameters. Therefore, this application can calculate and correct frequency offset, power imbalance, and IQ delay in a TFDM-PON system, eliminating subcarrier crosstalk caused by frequency offset in TFDM uplink burst transmission, image crosstalk caused by IQ imbalance, and performance degradation caused by power imbalance between subcarriers, while reducing the bit error rate and improving system robustness. Attached Figure Description

[0054] Figure 1 This is a flowchart illustrating the first embodiment of the TFDM-PON system calibration method of this application;

[0055] Figure 2 This is a schematic diagram of the system architecture of TFDM-PON involved in the embodiments of this application;

[0056] Figure 3 This is a schematic diagram of the dual-polarization signal involved in the embodiments of this application;

[0057] Figure 4 This is a flowchart illustrating the second embodiment of the TFDM-PON system calibration method of this application.

[0058] Figure 5 This is a schematic diagram illustrating the specific process of parameter correction and data transmission involved in the embodiments of this application. Detailed Implementation

[0059] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0060] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0061] In a first aspect, embodiments of this application provide a TFDM-PON system calibration method.

[0062] In one embodiment, reference is made to Figure 1 , Figure 1 This is a flowchart illustrating the first embodiment of the TFDM-PON system calibration method of this application. It should be understood that, for optical communication systems, the designed TFDM-PON uplink transmission system architecture is as follows... Figure 2 As shown, this embodiment takes the dual-polarization modulation transceiver used on both the OLT and ONU ends as an example. Specifically, there are multiple ONUs in the TFDM-PON system. Each ONU consists of a light source, an IQ modulator, a DAC (Digital-to-Analog Converter), and a transmitting end (Tx end) DSP (Digital Signal Processing). In addition, the OLT on the other side consists of a LO (Local Oscillator), a coherent receiver, an ADC (Analog-to-Digital Converter), and a receiving end (Rx end) DSP. Understandably, the transmitting DSP at the ONU generates the digital signal to be transmitted. This digital signal is converted into an analog signal by the DAC, modulated by the IQ modulator, and then transmitted to the optical link. The signals from multiple ONUs are coupled together by an optical coupler and finally transmitted to the coherent receiver on the OLT side via optical fiber (such as standard single-mode fiber). At the receiving end of the OLT, the local oscillator light emitted by the LO is used by the coherent receiver to demodulate the signal light, which is then converted into a digital signal by the ADC. This digital signal data will be processed in the receiving DSP.

[0063] like Figure 1 As shown, the TFDM-PON system calibration method is applied to the OLT, and the method includes:

[0064] Step S10: Receive the dual-polarization signal transmitted by the ONU based on time-division multiplexing or time-frequency-division multiplexing. The dual-polarization signal includes a target signal sequence corresponding to X-polarization or Y-polarization. The target signal sequence is an IQ periodic complex signal, and its I channel is a single-tone signal of the first frequency and its Q channel is a single-tone signal of the second frequency.

[0065] As an example, in this embodiment, the TFDM-PON system is first put into correction mode, and on the ONU side, selective transmission is performed on X-polarization and Y-polarization as follows: Figure 3The dual-polarization signal shown includes a specially designed target signal sequence TS, which is an IQ periodic complex signal. Its I channel is a single-tone signal with a first frequency of f1 and its Q channel is a single-tone signal with a second frequency of f2. It should be noted that the first frequency f1 is preferably greater than the second frequency f2, for example, f1=R / 2 and f2=R / 4, where R represents the baud rate.

[0066] It is worth noting that when the ONU sends dual-polarization signals to the OLT, it will do so using either time-division multiplexing or time-frequency multiplexing; for details, see [link to documentation]. Figure 3 As shown, at time t1, the ONU transmits an X-polarized TS signal, but does not transmit a Y-polarized signal. At time t2, the ONU transmits a Y-polarized TS signal, but does not transmit a X-polarized signal. The signal is transmitted continuously and periodically according to this pattern. Thus, the coherent receiver on the OLT side will receive the dual-polarized signal from the ONU.

[0067] Step S20: Calculate the target parameters based on the Fourier transform of the dual-polarization signal and frequency domain symmetry. The target parameters include the target transmit / receive frequency offset, the target transmit IQ delay, the target receive IQ delay, and the target power deviation.

[0068] Specifically, the calculation of the target parameters based on the Fourier transform of the dual-polarization signal and frequency domain symmetry includes:

[0069] The dual-polarization signal is coherently demodulated based on the local oscillator light, and the coherent demodulation result is converted into the target digital signal through an analog-to-digital converter (ADC).

[0070] Perform Fourier transform processing on the target digital signal to obtain the Fourier transform result;

[0071] The target transceiver frequency offset between the ONU carrier and the local oscillator is calculated based on the Fourier transform results and frequency domain symmetry.

[0072] The target transmitter IQ delay and the target receiver IQ delay are calculated based on the Fourier transform results, the number of frequency points corresponding to the single tone signal, and the location of the single tone signal.

[0073] The target power deviation between each ONU is calculated using the Fourier transform results and the total number of ONUs.

[0074] Exemplary, see Figure 2As shown, the coherent receiver receives the dual-polarized signal from the ONU and uses the signal light (i.e., local oscillator light) of the LO to coherently demodulate the received signal (i.e., the dual-polarized signal). The ADC converts the demodulated data into a target digital signal, which is used in the receiving-end DSP to calculate the IQ delay, power offset, and frequency offset of each ONU, as well as the IQ delay of the OLT. In other words, the receiving-end DSP performs Fourier transform processing on the target digital signal to obtain the Fourier transform result, and then uses this Fourier transform result to calculate the power offset, frequency offset, and IQ delay. It should be noted that the specific implementation methods and working principles of coherent demodulation, analog-to-digital conversion, Fourier transform, etc., are common knowledge in this field, and will not be elaborated here for the sake of simplicity. In addition, the Fourier transform can preferably be a Fast Fourier Transform to effectively reduce computational complexity.

[0075] It is worth noting that this embodiment can calculate power deviation, frequency offset, and IQ delay using the TS sequence. Specifically, when calculating the frequency offset at the transceiver end, since the LO has a frequency offset from the transmitting light source, the single-tone signal at frequency f1 / f2 is offset compared to the expected frequency. Therefore, the offset frequency can be calculated using the symmetry of the frequency domain, that is, the estimated frequency offset between the ONU carrier and the local oscillator light (i.e., the target transceiver frequency offset) is calculated using the Fourier transform result and the frequency domain symmetry. When calculating the IQ delay at the transceiver end, the power deviation, frequency offset, and IQ delay are calculated using the Fourier transform of the real and imaginary parts of the X / Y polarized received signal, the position of the single-tone signal at the first frequency f1 and the second frequency f2, and the first negative frequency -f1 (i.e., the target transceiver frequency offset). The estimated values ​​of the IQ delay at the transmitting and receiving ends (i.e., the target transmitting end IQ delay and the target receiving end IQ delay) are calculated by using the number of frequency points between the negative frequency corresponding to the positive frequency f1 and f1, the number of frequency points between the second negative frequency -f2 (i.e., the negative frequency corresponding to the positive frequency f2) and f2, the number of frequency points around the single-tone signal, and the Fourier transform length. For power imbalance between signals transmitted by different ONUs, the estimated value of the power deviation of each ONU (i.e., the target power deviation) is calculated by using the Fourier transform of the signals with frequencies f1 / f2 in the X / Y polarized received signals transmitted by each ONU and the total number of ONUs.

[0076] Further, in one embodiment, the step of calculating the target transceiver frequency offset between the ONU carrier and the local oscillator light based on the Fourier transform result and frequency domain symmetry includes:

[0077] Based on frequency domain symmetry, the first actual frequency corresponding to the actual position of the first frequency f1, the first actual negative frequency corresponding to the first frequency -f1 corresponding to the actual position of the first negative frequency, or the second actual frequency corresponding to the actual position of the second frequency f2 and the second actual negative frequency corresponding to the second frequency -f2 corresponding to the actual position of the second negative frequency are determined from the Fourier transform results.

[0078] The target transceiver frequency offset between the ONU carrier and the local oscillator is calculated using the first actual frequency and the first actual negative frequency or the second actual frequency and the second actual negative frequency.

[0079] As an example, in this embodiment, based on frequency symmetry, the frequency offset is estimated according to the actual position of either the first set of frequencies (i.e., the first frequency f1 and the first negative frequency -f1) or the second set of frequencies (i.e., the second frequency f2 and the second negative frequency -f2):

[0080] (1)

[0081] In the formula, This represents the frequency offset between the current ONU carrier and the local oscillator light of the OLT, calculated in X-polarization or Y-polarization (i.e., the target transceiver frequency offset). This represents the actual frequency corresponding to the actual position of the first negative frequency -f1 (i.e., the first actual negative frequency, or -f1+Δf, which can be directly measured, where Δf represents the frequency deviation between the local oscillator and the emitting light source) or the actual frequency corresponding to the actual position of the second negative frequency -f2 (i.e., the second actual negative frequency, or -f2+Δf); simultaneously This represents the actual frequency (i.e., the first actual frequency, or f1+Δf) corresponding to the actual position of the first frequency f1 of X-polarization or Y-polarization, or the actual frequency (i.e., the second actual frequency, or f2+Δf) corresponding to the actual position of the second frequency f2.

[0082] It should be noted that since the calculation methods and principles for frequency offset on X-polarization and Y-polarization are the same, the same calculation formula is used for characterization for the sake of simplicity, and X / Y is used to distinguish between X-polarization and Y-polarization. Similarly, the calculation methods and principles for IQ delay and power deviation on X-polarization and Y-polarization are also the same. Therefore, for the sake of simplicity, the same calculation formula is used in subsequent embodiments to characterize IQ delay and power deviation respectively, and X / Y is used to distinguish between X-polarization and Y-polarization.

[0083] Furthermore, in one embodiment, the target transmitter IQ delay And target receiver IQ latency The calculation formulas are as follows:

[0084]

[0085]

[0086]

[0087]

[0088]

[0089] In the formula, This indicates the IQ delay at the transmitting end in either X-polarization or Y-polarization. This represents the transmitter IQ delay calculated using the received X-polarized or Y-polarized I-channel data. This represents the IQ delay at the transmitting end calculated using the received X-polarized or Y-polarized Q-channel data. N represents the Fourier transform length, n represents the number of frequency points around the single-tone signal, k1 and k2 represent the positions of the single-tone signal at the first frequency f1 and the second frequency f2, respectively, N1 represents the number of frequency points between the first negative frequency -f1 and f1 corresponding to the first frequency f1, and N2 represents the number of frequency points between the second negative frequency -f2 and f2 corresponding to the second frequency f2. The Fourier transform representing the real part of the X-polarized or Y-polarized received signal. The Fourier transform represents the imaginary part of the X-polarized or Y-polarized received signal. This indicates the IQ delay at the receiving end in X-polarization or Y-polarization. This represents the IQ delay at the receiver calculated using data near the first frequency f1 of the received X-polarized or Y-polarized signal. This represents the IQ delay at the receiver calculated using data near the second frequency f2 of the received X-polarized or Y-polarized signal.

[0090] As an example, in this embodiment, the TS sequence is still used to calculate the IQ time delay at the transceiver end. Specifically, it is assumed that... The two-way polarization delay of the transmitter's IQ (i.e., the IQ delay of the transmitter in X polarization or Y polarization). Given the two-way polarization delay of IQ at the receiving end (i.e., the IQ delay at the receiving end in X-polarization or Y-polarization), after receiving the signal, the IQ delays of the ONU transmitter and OLT receiver in X / Y polarization at the receiving end can be expressed as follows:

[0091] (2)

[0092] (3)

[0093] (4)

[0094] (5)

[0095] (6)

[0096] (7)

[0097] In the formula, This represents the transmitter IQ delay calculated using the received X-polarized or Y-polarized I-channel data. This represents the IQ delay at the transmitting end calculated using the received X-polarized or Y-polarized Q-channel data. N represents the Fourier transform length, n represents the number of frequency points around the single-tone signal, k1 and k2 represent the positions of the single-tone signal at the first frequency f1 and the second frequency f2, respectively, N1 represents the number of frequency points between the first negative frequency -f1 and f1 corresponding to the first frequency f1, and N2 represents the number of frequency points between the second negative frequency -f2 and f2 corresponding to the second frequency f2. The Fourier transform representing the real part of the X-polarized or Y-polarized received signal. The Fourier transform represents the imaginary part of the X-polarized or Y-polarized received signal. This represents the IQ delay at the receiver calculated using data near the first frequency f1 of the received X-polarized or Y-polarized signal. This represents the IQ delay at the receiver calculated using data near the second frequency f2 of the received X-polarized or Y-polarized signal. It should be noted that parameters such as N, n, k1, k2, N1, and N2 can be obtained directly through measurement or directly output by the system.

[0098] Furthermore, in one embodiment, the formula for calculating the target power deviation is:

[0099]

[0100]

[0101]

[0102] In the formula, This represents the target power deviation between the i-th ONU and the average power. This represents the power of the i-th ONU, and M represents the total number of ONUs. This represents the average power of M ONUs. This represents the Fourier transform of the signal with frequency f1 in the X-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f2 in the X-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f1 in the Y-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f2 in the Y-polarized received signal corresponding to the i-th ONU. This indicates the operation of taking the average.

[0103] As an example, in this embodiment, the TS sequence is also used to calculate the power imbalance (i.e., power deviation) between signals transmitted by different ONUs:

[0104] (8)

[0105] (9)

[0106] (10)

[0107] in, This represents the Fourier transform of the signal with frequency f1 in the X-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f2 in the X-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f1 in the Y-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f2 in the Y-polarized received signal corresponding to the i-th ONU. This indicates the operation of taking the average. This represents the power of the i-th ONU, and M represents the total number of ONUs. This represents the average power of M ONUs. This represents the target power deviation between the i-th ONU and the average power.

[0108] Step S30: Send the target parameters to the ONU so that the ONU can correct the frequency, delay and power based on the target parameters.

[0109] As an example, in this embodiment, after the calculation is completed using the above algorithm, the calculated target transceiver frequency offset, target power deviation, target transmitter IQ delay, and target receiver IQ delay results for each ONU in the system are sent back to the corresponding ONU for correction. After the ONU has completed the correction, the system switches to data mode, and the ONU transmits normal data in burst mode for data transmission, while the OLT receives the data. It can be seen that, for a TFDM uplink burst transmission system, this embodiment can calculate the frequency offset, power imbalance, and IQ delay of the TFDM-PON system and correct the system, improving the overall system performance. Furthermore, it does not require the addition of specially designed preambles or training sequences during data transmission, thus improving data transmission efficiency.

[0110] In summary, this embodiment addresses the issues of frequency offset between ONUs and OLTs, power imbalance among ONUs, and IQ imbalance in signals generated by individual ONUs during uplink burst transmission, which degrade signal quality and affect system performance. By designing special sequences and corresponding signal processing algorithms, it estimates frequency offset, power imbalance, and IQ delay, and corrects them based on the estimation results to effectively improve system performance.

[0111] Secondly, embodiments of this application also provide a TFDM-PON system calibration device.

[0112] In one embodiment, the TFDM-PON system calibration device includes an OLT, the OLT being used for:

[0113] Receive dual-polarization signals transmitted by the ONU based on time-division multiplexing or time-frequency-division multiplexing. The dual-polarization signals include target signal sequences corresponding to X-polarization or Y-polarization. The target signal sequences are IQ periodic complex signals, with I-channel being a single-tone signal of the first frequency and Q-channel being a single-tone signal of the second frequency.

[0114] The target parameters are calculated based on the Fourier transform of the dual-polarization signal and frequency domain symmetry. The target parameters include the target transceiver frequency offset, the target transmitter IQ delay, the target receiver IQ delay, and the target power deviation between each ONU.

[0115] The target parameters are sent to the ONU so that the ONU can correct the frequency, delay, and power based on the target parameters.

[0116] Furthermore, in one embodiment, the OLT is specifically used for:

[0117] The dual-polarization signal is coherently demodulated based on the local oscillator light, and the coherent demodulation result is converted into the target digital signal through an analog-to-digital converter (ADC).

[0118] Perform Fourier transform processing on the target digital signal to obtain the Fourier transform result;

[0119] The target transceiver frequency offset between the ONU carrier and the local oscillator is calculated based on the Fourier transform results and frequency domain symmetry.

[0120] The target transmitter IQ delay and the target receiver IQ delay are calculated based on the Fourier transform results, the number of frequency points corresponding to the single tone signal, and the location of the single tone signal.

[0121] The target power deviation between each ONU is calculated using the Fourier transform results and the total number of ONUs.

[0122] Furthermore, in one embodiment, the OLT is specifically used for:

[0123] Based on frequency domain symmetry, the first actual frequency corresponding to the actual position of the first frequency f1, the first actual negative frequency corresponding to the first frequency -f1 corresponding to the actual position of the first negative frequency, or the second actual frequency corresponding to the actual position of the second frequency f2 and the second actual negative frequency corresponding to the second frequency -f2 corresponding to the actual position of the second negative frequency are determined from the Fourier transform results.

[0124] The target transceiver frequency offset between the ONU carrier and the local oscillator is calculated using the first actual frequency and the first actual negative frequency or the second actual frequency and the second actual negative frequency.

[0125] Furthermore, in one embodiment, the target transmitter IQ delay And target receiver IQ latency The calculation formulas are as follows:

[0126]

[0127]

[0128]

[0129]

[0130]

[0131] In the formula, This indicates the IQ delay at the transmitting end in either X-polarization or Y-polarization. This represents the transmitter IQ delay calculated using the received X-polarized or Y-polarized I-channel data. This represents the IQ delay at the transmitting end calculated using the received X-polarized or Y-polarized Q-channel data. N represents the Fourier transform length, n represents the number of frequency points around the single-tone signal, k1 and k2 represent the positions of the single-tone signal at the first frequency f1 and the second frequency f2, respectively, N1 represents the number of frequency points between the first negative frequency -f1 and f1 corresponding to the first frequency f1, and N2 represents the number of frequency points between the second negative frequency -f2 and f2 corresponding to the second frequency f2. The Fourier transform representing the real part of the X-polarized or Y-polarized received signal. The Fourier transform represents the imaginary part of the X-polarized or Y-polarized received signal. This indicates the IQ delay at the receiving end in X-polarization or Y-polarization. This represents the IQ delay at the receiver calculated using data near the first frequency f1 of the received X-polarized or Y-polarized signal. This represents the IQ delay at the receiver calculated using data near the second frequency f2 of the received X-polarized or Y-polarized signal.

[0132] Furthermore, in one embodiment, the formula for calculating the target power deviation is:

[0133]

[0134]

[0135]

[0136] In the formula, This represents the target power deviation between the i-th ONU and the average power. This represents the power of the i-th ONU, and M represents the total number of ONUs. This represents the average power of M ONUs. This represents the Fourier transform of the signal with frequency f1 in the X-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f2 in the X-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f1 in the Y-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f2 in the Y-polarized received signal corresponding to the i-th ONU. This indicates the operation of taking the average.

[0137] The function of the OLT in the above-mentioned TFDM-PON system calibration device corresponds to each step in the above-mentioned TFDM-PON system calibration method embodiment, and its function and implementation process will not be described in detail here.

[0138] Thirdly, embodiments of this application provide another method for TFDM-PON system calibration.

[0139] In one embodiment, reference is made to Figure 4 , Figure 4 This is a flowchart illustrating the second embodiment of the TFDM-PON system calibration method of this application.

[0140] like Figure 4 As shown, the TFDM-PON system calibration method is applied to the ONU, and the method includes:

[0141] N10: Generate a dual-polarization signal, the dual-polarization signal including a target signal sequence corresponding to X polarization or Y polarization, the target signal sequence being an IQ periodic complex signal with its I channel being a single-tone signal of the first frequency and its Q channel being a single-tone signal of the second frequency.

[0142] As an example, in this embodiment, a dual-polarization signal needs to be generated on the ONU side for the OLT side to calculate frequency offset, power deviation, and IQ delay. Specifically, the system is put into correction mode, and the ONU side constructs a specially designed target signal sequence TS on the X-polarization and Y-polarization sides. That is, the TS sequence is an IQ periodic complex signal, with its I path being a single-tone signal with a frequency of f1 (i.e., the first frequency) and its Q path being a single-tone signal with a frequency of f2 (i.e., the second frequency).

[0143] N20: Transmits a dual-polarization signal to the OLT based on time-division multiplexing or time-frequency-division multiplexing, so that the OLT can calculate the target parameters based on the Fourier transform of the dual-polarization signal and frequency domain symmetry. The target parameters include the target transmit / receive frequency offset, the target transmit IQ delay, the target receive IQ delay, and the target power deviation between each ONU.

[0144] As an example, in this embodiment, the ONU side transmits the dual-polarization signal to the OLT end via time-division multiplexing or time-frequency-division multiplexing, i.e., see [reference needed]. Figure 3 As shown, at time t1, the transmitting end sends an X-polarized TS signal and does not send a Y-polarized signal, while at time t2, the transmitting end sends a Y-polarized TS signal and does not send a X-polarized signal. This pattern is repeated periodically to send signals to the OLT, allowing the OLT to calculate target parameters based on the received dual-polarized signals, Fourier transform, and frequency domain symmetry. These parameters include the target transceiver frequency offset, the target transmitter IQ delay, the target receiver IQ delay, and the target power deviation between each ONU. It should be noted that the specific calculation methods and principles of the target parameters are detailed in the first embodiment described above and will not be repeated here.

[0145] N30: When the target parameters are received from the OLT, the frequency, delay and power are corrected based on the target parameters.

[0146] In this exemplary embodiment, after the OLT completes the target transceiver frequency offset, target power deviation, target transmitter IQ delay, and target receiver IQ delay results for each ONU, it sends them back to the corresponding ONU for correction. That is, the ONU corrects the frequency, power, and delay based on the received target transceiver frequency offset, target power deviation, target transmitter IQ delay, and target receiver IQ delay. It should be noted that the methods and principles for correcting frequency, power, and delay based on the calculated frequency offset, power deviation, and IQ delay are common knowledge in the art and will not be elaborated here for the sake of brevity. After the ONU correction is complete, the system switches to data mode. The ONU sends normal data in burst mode for data transmission, and the OLT receives and processes the data. Therefore, for a TFDM uplink burst transmission system, this embodiment can calculate the frequency offset, power imbalance, and IQ delay of the TFDM-PON system and correct the system, improving the overall system performance. Furthermore, it does not require a specially designed preamble or training sequence during data transmission, thus improving data transmission efficiency.

[0147] It is worth noting that the overall operation process of this embodiment is as follows: Figure 5 As shown, firstly, the system is put into correction mode. At the ONU transmitting end, a specially designed TS signal is generated and transmitted after DAC and optical modulation. Transmitted through the communication system, at the OLT receiving end, the coherent receiver receives the signal, and the ADC converts the demodulated data into a digital signal. This signal is used in the DSP to calculate the IQ delay, power deviation, and frequency offset of each ONU, as well as the IQ delay of the OLT. The calculated estimates are then sent back to the corresponding ONU for correction. After correction, the system switches to normal data transmission mode, allowing the ONU to transmit normal data signals, while the OLT receives and processes them. This correction method significantly improves the communication quality of the TFDM uplink burst transmission system.

[0148] In summary, this system first sends a special signal sequence at the ONU end, then uses a corresponding algorithm at the OLT end to calculate the estimated values ​​of frequency offset, power imbalance, and IQ delay for the TFDM system, and sends them back to the ONU end for correction. After correction, the system then transmits data. Therefore, this embodiment proposes a method for estimating and correcting frequency offset, power imbalance, and IQ delay in a TFDM-PON system. This method aims to eliminate subcarrier crosstalk caused by frequency offset in TFDM uplink burst transmission, image crosstalk caused by IQ imbalance, and performance degradation caused by power imbalance between subcarriers, thereby reducing the bit error rate and improving the system's robustness.

[0149] Fourthly, embodiments of this application also provide another TFDM-PON system calibration device.

[0150] In one embodiment, the TFDM-PON system calibration device includes an ONU, the ONU being used for:

[0151] A dual-polarization signal is generated, the dual-polarization signal including a target signal sequence corresponding to X polarization or Y polarization, the target signal sequence being an IQ periodic complex signal with its I channel being a single-tone signal of a first frequency and its Q channel being a single-tone signal of a second frequency;

[0152] Based on time-division multiplexing or time-frequency-division multiplexing, a dual-polarization signal is transmitted to the OLT, so that the OLT can calculate the target parameters based on the Fourier transform of the dual-polarization signal and the frequency domain symmetry. The target parameters include the target transmit / receive frequency offset, the target transmit IQ delay, the target receive IQ delay, and the target power deviation.

[0153] Upon receiving the target parameters sent by the OLT, the frequency, delay, and power are corrected based on the target parameters.

[0154] The functions of the ONU in the above-mentioned TFDM-PON system calibration device correspond to the steps in the above-mentioned TFDM-PON system calibration method embodiment, and their functions and implementation processes will not be described in detail here.

[0155] It should be noted that the sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0156] The terms "comprising" and "having," and any variations thereof, in the specification, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus. The terms "first," "second," and "third," etc., are used to distinguish different objects, etc., and do not indicate a sequence, nor do they limit "first," "second," and "third" to different types.

[0157] In the description of the embodiments of this application, terms such as "exemplary," "for example," or "for instance" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as "exemplary," "for example," or "for instance" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary," "for example," or "for instance" is intended to present the relevant concepts in a concrete manner.

[0158] In the description of the embodiments of this application, unless otherwise stated, " / " means "or". For example, A / B can mean A or B. The "and / or" in the text is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, in the description of the embodiments of this application, "multiple" means two or more.

[0159] In some processes described in the embodiments of this application, multiple operations or steps are included in a specific order. However, it should be understood that these operations or steps may not be executed in the order they appear in the embodiments of this application, or they may be executed in parallel. The sequence number of the operation is only used to distinguish the different operations, and the sequence number itself does not represent any execution order. In addition, these processes may include more or fewer operations, and these operations or steps may be executed sequentially or in parallel, and these operations or steps may be combined.

[0160] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) as described above, and includes several instructions to cause a terminal device to execute the methods described in the various embodiments of this application.

[0161] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A calibration method for a TFDM-PON system, characterized in that, The method is applied to an OLT, and the method includes: Receive dual-polarization signals transmitted by the ONU based on time-division multiplexing or time-frequency-division multiplexing. The dual-polarization signals include target signal sequences corresponding to X-polarization or Y-polarization. The target signal sequences are IQ periodic complex signals, with I-channel being a single-tone signal of the first frequency and Q-channel being a single-tone signal of the second frequency. The target parameters are calculated based on the Fourier transform of the dual-polarization signal and frequency domain symmetry. The target parameters include the target transceiver frequency offset, the target transmitter IQ delay, the target receiver IQ delay, and the target power deviation between each ONU. The target parameters are sent to the ONU so that the ONU can correct the frequency, delay, and power based on the target parameters. The calculation of target parameters based on the Fourier transform of dual-polarization signals and frequency domain symmetry includes: The dual-polarization signal is coherently demodulated based on the local oscillator light, and the coherent demodulation result is converted into the target digital signal through an analog-to-digital converter (ADC). Perform Fourier transform processing on the target digital signal to obtain the Fourier transform result; The target transceiver frequency offset between the ONU carrier and the local oscillator is calculated based on the Fourier transform results and frequency domain symmetry. The target transmitter IQ delay and the target receiver IQ delay are calculated based on the Fourier transform results, the number of frequency points corresponding to the single tone signal, and the location of the single tone signal. The target power deviation between each ONU is calculated using the Fourier transform results and the total number of ONUs.

2. The TFDM-PON system calibration method as described in claim 1, characterized in that, The calculation of the target transceiver frequency offset between the ONU carrier and the local oscillator light based on the Fourier transform result and frequency domain symmetry includes: Based on frequency domain symmetry, the first actual frequency corresponding to the actual position of the first frequency f1, the first actual negative frequency corresponding to the first frequency -f1 corresponding to the actual position of the first negative frequency, or the second actual frequency corresponding to the actual position of the second frequency f2 and the second actual negative frequency corresponding to the second frequency -f2 corresponding to the actual position of the second negative frequency are determined from the Fourier transform results. The target transceiver frequency offset between the ONU carrier and the local oscillator is calculated using the first actual frequency and the first actual negative frequency or the second actual frequency and the second actual negative frequency.

3. The TFDM-PON system calibration method as described in claim 1, characterized in that, The target originating IQ delay And target receiver IQ latency The calculation formulas are as follows: In the formula, This indicates the IQ delay at the transmitting end in either X-polarization or Y-polarization. This represents the transmitter IQ delay calculated using the received X-polarized or Y-polarized I-channel data. This represents the IQ delay at the transmitting end calculated using the received X-polarized or Y-polarized Q-channel data. N represents the Fourier transform length, n represents the number of frequency points around the single-tone signal, k1 and k2 represent the positions of the single-tone signal at the first frequency f1 and the second frequency f2, respectively, N1 represents the number of frequency points between the first negative frequency -f1 and f1 corresponding to the first frequency f1, and N2 represents the number of frequency points between the second negative frequency -f2 and f2 corresponding to the second frequency f2. The Fourier transform representing the real part of the X-polarized or Y-polarized received signal. The Fourier transform represents the imaginary part of the X-polarized or Y-polarized received signal. This indicates the IQ delay at the receiving end in X-polarization or Y-polarization. This represents the IQ delay at the receiver calculated using data near the first frequency f1 of the received X-polarized or Y-polarized signal. This represents the IQ delay at the receiver calculated using data near the second frequency f2 of the received X-polarized or Y-polarized signal.

4. The TFDM-PON system calibration method as described in claim 1, characterized in that, The formula for calculating the target power deviation is: In the formula, This represents the target power deviation between the i-th ONU and the average power. This represents the power of the i-th ONU, and M represents the total number of ONUs. This represents the average power of M ONUs. This represents the Fourier transform of the signal with frequency f1 in the X-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f2 in the X-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f1 in the Y-polarized received signal corresponding to the i-th ONU. This represents the Fourier transform of the signal with frequency f2 in the Y-polarized received signal corresponding to the i-th ONU. This indicates the operation of taking the average.

5. A calibration method for a TFDM-PON system, characterized in that, The method is applied to an ONU, and the method includes: A dual-polarization signal is generated, the dual-polarization signal including a target signal sequence corresponding to X polarization or Y polarization, the target signal sequence being an IQ periodic complex signal with its I channel being a single-tone signal of a first frequency and its Q channel being a single-tone signal of a second frequency; Based on time-division multiplexing or time-frequency-division multiplexing, dual-polarization signals are transmitted to the OLT, so that the OLT can calculate the target parameters based on the Fourier transform of the dual-polarization signals and frequency domain symmetry. The target parameters include the target transmit / receive frequency offset, the target transmit IQ delay, the target receive IQ delay, and the target power deviation between each ONU. Upon receiving the target parameters sent by the OLT, the frequency, delay, and power are corrected based on the target parameters; The calculation of target parameters based on the Fourier transform of dual-polarization signals and frequency domain symmetry includes: The dual-polarization signal is coherently demodulated based on the local oscillator light, and the coherent demodulation result is converted into the target digital signal through an analog-to-digital converter (ADC). Perform Fourier transform processing on the target digital signal to obtain the Fourier transform result; The target transceiver frequency offset between the ONU carrier and the local oscillator is calculated based on the Fourier transform results and frequency domain symmetry. The target transmitter IQ delay and the target receiver IQ delay are calculated based on the Fourier transform results, the number of frequency points corresponding to the single tone signal, and the location of the single tone signal. The target power deviation between each ONU is calculated using the Fourier transform results and the total number of ONUs.

6. A TFDM-PON system calibration device, characterized in that, The device includes an OLT, the OLT being used for: Receive dual-polarization signals transmitted by the ONU based on time-division multiplexing or time-frequency-division multiplexing. The dual-polarization signals include target signal sequences corresponding to X-polarization or Y-polarization. The target signal sequences are IQ periodic complex signals, with I-channel being a single-tone signal of the first frequency and Q-channel being a single-tone signal of the second frequency. The target parameters are calculated based on the Fourier transform of the dual-polarization signal and frequency domain symmetry. The target parameters include the target transceiver frequency offset, the target transmitter IQ delay, the target receiver IQ delay, and the target power deviation between each ONU. The target parameters are sent to the ONU so that the ONU can correct the frequency, delay, and power based on the target parameters. Specifically, the OLT is used for: The dual-polarization signal is coherently demodulated based on the local oscillator light, and the coherent demodulation result is converted into the target digital signal through an analog-to-digital converter (ADC). Perform Fourier transform processing on the target digital signal to obtain the Fourier transform result; The target transceiver frequency offset between the ONU carrier and the local oscillator is calculated based on the Fourier transform results and frequency domain symmetry. The target transmitter IQ delay and the target receiver IQ delay are calculated based on the Fourier transform results, the number of frequency points corresponding to the single tone signal, and the location of the single tone signal. The target power deviation between each ONU is calculated using the Fourier transform results and the total number of ONUs.

7. The TFDM-PON system calibration device as described in claim 6, characterized in that, The OLT is also specifically used for: Based on frequency domain symmetry, the first actual frequency corresponding to the actual position of the first frequency f1, the first actual negative frequency corresponding to the first frequency -f1 corresponding to the actual position of the first negative frequency, or the second actual frequency corresponding to the actual position of the second frequency f2 and the second actual negative frequency corresponding to the second frequency -f2 corresponding to the actual position of the second negative frequency are determined from the Fourier transform results. The target transceiver frequency offset between the ONU carrier and the local oscillator is calculated using the first actual frequency and the first actual negative frequency or the second actual frequency and the second actual negative frequency.

8. A TFDM-PON system calibration device, characterized in that, The device includes an ONU, the ONU being used for: A dual-polarization signal is generated, the dual-polarization signal including a target signal sequence corresponding to X polarization or Y polarization, the target signal sequence being an IQ periodic complex signal with its I channel being a single-tone signal of a first frequency and its Q channel being a single-tone signal of a second frequency; Based on time-division multiplexing or time-frequency-division multiplexing, a dual-polarization signal is transmitted to the OLT, so that the OLT can calculate the target parameters based on the Fourier transform of the dual-polarization signal and the frequency domain symmetry. The target parameters include the target transmit / receive frequency offset, the target transmit IQ delay, the target receive IQ delay, and the target power deviation. Upon receiving the target parameters sent by the OLT, the frequency, delay, and power are corrected based on the target parameters; The calculation of target parameters based on the Fourier transform of dual-polarization signals and frequency domain symmetry includes: The dual-polarization signal is coherently demodulated based on the local oscillator light, and the coherent demodulation result is converted into the target digital signal through an analog-to-digital converter (ADC). Perform Fourier transform processing on the target digital signal to obtain the Fourier transform result; The target transceiver frequency offset between the ONU carrier and the local oscillator is calculated based on the Fourier transform results and frequency domain symmetry. The target transmitter IQ delay and the target receiver IQ delay are calculated based on the Fourier transform results, the number of frequency points corresponding to the single tone signal, and the location of the single tone signal. The target power deviation between each ONU is calculated using the Fourier transform results and the total number of ONUs.

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