ONU online registration method and system for P2MP system

Abstract

The invention provides a method and a system for online registration of an ONU (Optical Network Unit) of a P2MP (Point to Multipoint) system. The ONU randomly selects a sequence from the sequence code set, carries out analog intensity modulation on the sequence, then moves a registration signal to a frequency band protection interval, and sends the registration signal to the OLT together with a service signal. After the OLT receives the signals, the signals are subjected to frequency shift and filtering to extract registration signals. The method comprises the following steps of: performing resampling operation on a registration signal, performing simulation square detection, removing a direct current component in the registration signal, combining two polarized signals, performing multiple periodic averaging, performing cyclic cross-correlation operation on the processed signal and a local sequence code set, and detecting an obtained peak value; and if the peak value is detected to exceed a preset judgment threshold value, indicating that the sequence code is activated, and estimating the time delay of the sequence code. According to the invention, high frequency offset estimation and time delay estimation precision can be realized, and the designed registration signal has small influence on the performance of the service signal; registration signal power is allowed to be far smaller than service signals.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a method and system for online registration of an optical network unit (ONU) in a point-to-multipoint (P2MP) system. Background Art

[0002] In today's era of rapid technological development, cutting-edge technologies such as the Internet of Things, edge computing, and 5G / 6G are emerging at a very fast pace, bringing new demands and challenges to various fields. Against this backdrop, passive optical networks have also ushered in a rapid development opportunity.

[0003] As technology continues to evolve, service providers have not only put forward unprecedentedly high requirements for passive optical networks in terms of network capacity and speed, but are also actively seeking innovative solutions that can effectively reduce transmission costs, power consumption and latency, while also hoping to further enhance the scalability and flexibility of services.

[0004] At present, as coherent optical technology gradually penetrates downward, coherent passive optical network (Passive Optical Network, PON) is replacing the traditional direct-adjustment and direct-detection passive optical network with its own advantages and becoming the mainstream development trend of the industry. At the same time, the flexible, scalable and cost-effective P2MP transmission mode is gradually emerging and becoming an important evolution direction of traditional point-to-point transmission optical network.

[0005] An effective way to achieve P2MP coherent PON is to use Digital Subcarrier Multiplexing (DSCM) technology, which divides a large-bandwidth single-carrier signal into multiple small-bandwidth independent subcarrier signals for transmission in the digital domain. This innovative measure successfully eliminates the electrical aggregation process in traditional point-to-point (P2P) networks, significantly reduces the number of transceivers, and effectively reduces equipment costs.

[0006] Compared with single-carrier transmission, DSCM transmission has many advantages, including large dispersion compensation tolerance, high nonlinear tolerance, and flexible bandwidth allocation. It is precisely because of these unique advantages that the DSCM-based P2MP coherent PON architecture has received extensive attention and research. However, in this new architecture, due to the fundamental change in the way channel multiplexing has taken place, a series of new problems have arisen that need to be solved.

[0007] Through searching patent documents, it was found that the patent with publication number CN107342973B discloses a registration method, device and passive optical network system for a passive optical network. The patent includes: the optical line terminal OLT receives the registration information continuously sent by the optical network unit ONU through a preset wavelength, and the registration information is continuously sent to the OLT after random delay by the ONU; the OLT performs registration processing according to the received registration information. The patent does not solve the problem of effectively distinguishing when multiple users access the network at the same time, and how to quickly complete the uplink synchronization.

[0008] In summary, in view of the above problems in the prior art, studying a method and system for online registration of ONUs in a P2MP system has become a key task that needs to be solved urgently. Summary of the invention

[0009] In view of the defects in the prior art, the object of the present invention is to provide a method and system for online registration of an optical network unit (ONU) in a point-to-multipoint (P2MP) system.

[0010] According to the present invention, a method for online registration of an ONU in a P2MP system includes the following steps:

[0011] Step S1, ONU initialization: The ONU to be put online completes basic configuration, completes the frequency deviation correction of the local laser through downlink synchronization, and obtains the ONU that has completed the frequency deviation correction;

[0012] Step S2, sequence code set construction: using the sequence to construct the registered sequence code set;

[0013] Step S3, ONU selects a registration sequence: the ONU that has completed frequency offset correction randomly selects a sequence from the sequence code set as the registration sequence;

[0014] Step S4, modulation of the registration signal: the ONU that has completed frequency deviation correction upsamples the registration sequence to the DAC sampling rate, then adds direct current, and then performs a square root operation to generate a registration signal;

[0015] Step S5, frequency shift and transmission of the registration signal: frequency shift the registration signal to the frequency band protection interval and send it to the OLT end together with other service signals;

[0016] Step S6, extraction of registration signal: The OLT first performs IQ front-end correction on the received signal to compensate for IQ skew and IQ imbalance, and filters out the registration signal by frequency shifting and filtering;

[0017] Step S7, processing of service signals: performing signal recovery and quality assessment on the service signals remaining after the registration signals are extracted, and finally calculating the bit error rate and signal-to-noise ratio;

[0018] Step S8, processing of the registration signal: square the registration signal, remove the DC component, perform analog strength detection on the registration signal, merge the signals on the two polarizations, improve the signal-to-noise ratio of the received registration signal by superimposing and averaging multiple signal segments, and finally perform cyclic cross-correlation with the local code set to detect the registration sequence and the corresponding delay information.

[0019] Preferably, in step S2, the sequence is an m-sequence or a Gold sequence.

[0020] Preferably, step S4 comprises:

[0021] The registration sequence randomly selected from the sequence code set by the sender registration signal is denoted as x u (n), n=0,…,N-1. Then upsample to the DAC sampling rate to get the signal x ′ u (n), by adding DC and square root operation to simulate intensity modulation, and then shifting the frequency to the guard interval of the frequency band, the signal x is sent T (n) is expressed as formula (1), u dc is the added DC component, f c is the carrier frequency of the registration signal, N T is the length of the sent signal,

[0022]

[0023] Preferably, step S6 comprises:

[0024] At the receiving end, the OLT receives signals in the entire frequency domain through a coherent receiver, and the received X and Y polarization signals It is expressed as formula (2), where Δt represents the transmission delay, Δf represents the residual frequency offset, represents the transmitted X-polarization and Y-polarization service signals, n0(n) represents the system noise,

[0025]

[0026] Select the registered signal at the protection interval through frequency shifting and filtering operations It is expressed as formula (3), n′0(n) represents the influence of business signal and system noise on registration signal, u dc is the added DC component, N T is the length of the sent signal,

[0027]

[0028] Preferably, in step S7, signal recovery and quality assessment include: dispersion compensation, multi-input multi-output equalization based on a multi-mode algorithm, fourth-power frequency offset estimation and compensation, symbol synchronization and carrier phase recovery based on a phase-locked loop.

[0029] Preferably, step S8 includes the following sub-steps:

[0030] Step S8.1, estimate the residual frequency deviation Δf: square the signal to remove the DC component, complete the analog strength detection of the registered signal, and obtain the signal It is expressed as formula (4), ignoring the signal amplitude damage, n″0(n) represents the cumulative noise impact, including the impact of the business signal on the registration signal,

[0031]

[0032] Step S8.2, signal Perform peak detection to obtain delay information;

[0033] Step S8.3, combine the signals on the two polarizations to obtain the signal x r′ (n), expressed as formula (8)

[0034]

[0035] Step S8.4, perform multi-segment superposition and averaging of the registered signal in the time domain, and finally perform cyclic cross-correlation detection with the local code set, as shown in formula (9), x i (n) is the i-th registration sequence code in the code set, thereby detecting the registration sequence selected by the registration signal, and calculating the delay according to the position corresponding to the maximum correlation peak, completing the processing and analysis of the registration signal,

[0036] x e (n) = IFFT {FFT (x r′ (n))FFT(x i (n))} (9)

[0037] Preferably, in step S8.2, there are two detection modes for peak detection, namely normalized absolute peak detection and peak-to-average ratio detection.

[0038] Preferably, in the normalized absolute peak detection, the cyclic cross-correlation result of the registration sequences a(n) and b(n) is assumed to be (5), where FFT refers to fast Fourier transform, IFFT refers to inverse fast Fourier transform,

[0039] R(n)=|{IFFT{FFT{a(n)}FFT{b(n)}}}| (5)

[0040] The normalized absolute peak value is shown in formula (6), where ||a|| represents the modulus of the registration sequence a(n),

[0041]

[0042] The peak position d = argmax n M(n) is the delay information.

[0043] Preferably, the peak-to-average ratio detection, as shown in formula (7), is the ratio of the maximum value to the average value of the correlation result,

[0044]

[0045] The peak position d = argmax n M(n) is the delay information.

[0046] The present invention also provides a system for online registration of ONUs in a P2MP system, comprising:

[0047] Module M1, ONU initialization: The ONU to be put online completes basic configuration, completes the frequency deviation correction of the local laser through downlink synchronization, and obtains the ONU that has completed the frequency deviation correction;

[0048] Module M2, sequence code set construction: Use sequences to construct registered sequence code sets;

[0049] Module M3, ONU selects registration sequence: the ONU that has completed frequency offset correction randomly selects a sequence from the sequence code set as the registration sequence;

[0050] Module M4, modulation of registration signal: the ONU that has completed frequency deviation correction upsamples the registration sequence to the DAC sampling rate, then adds DC, and then performs a square root operation to generate a registration signal;

[0051] Module M5, frequency shift and transmission of registration signal: frequency shift the registration signal to the frequency band protection interval and send it to the OLT end together with other service signals;

[0052] Module M6, registration signal extraction: The OLT first performs IQ front-end correction on the received signal to compensate for IQ skew and IQ imbalance, and filters out the registration signal by frequency shifting and filtering;

[0053] Module M7, service signal processing: for the service signal remaining after the registration signal is extracted, signal recovery and quality assessment are performed, and finally the bit error rate and signal-to-noise ratio are calculated;

[0054] Module M8, registration signal processing: square the registration signal, remove the DC component, perform analog strength detection on the registration signal, merge the signals on the two polarizations, improve the signal-to-noise ratio of the received registration signal by superimposing and averaging multiple signal segments, and finally perform cyclic cross-correlation with the local code set to detect the registration sequence and the corresponding delay information.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] 1. In the present invention, the generation and detection of the registration signal are compatible with the existing coherent transceiver, and the complexity of the transceiver algorithm is low.

[0057] 2. The online registration scheme of the present invention has high ranging accuracy.

[0058] 3. The registration signal of the present invention has little influence on the performance of the service signal and can also support a larger optical distribution network (ODN) power difference, thus having a high practical use value. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0060] Figure 1 It is a flowchart of a method for online registration of an ONU in a P2MP system according to an embodiment of the present invention;

[0061] Figure 2 It is a generation and detection scheme of a registration signal in an embodiment of the present invention;

[0062] Figure 3 is a schematic diagram of the relationship between the frequency spectrum positions of a registration signal and a service signal in an embodiment of the present invention;

[0063] Figure 4 It is a schematic diagram of the experimental scheme in an embodiment of the present invention;

[0064] Figure 5 It is a power spectrum diagram of the registration signal and the service signal sent on the X and Y polarizations in the embodiment of the present invention;

[0065] Figure 6 DSP flow chart for processing receiving end service signals and registration signals in an embodiment of the present invention;

[0066] Figure 7 The power spectrum of the received signal when the relative service signal power of the position 3 registration in the embodiment of the present invention is (a) 15dB, (b) 20dB, (c) 25dB, and (d) 30dB smaller;

[0067] Figure 8 The Gaussian distribution is selected for distribution fitting and parameter estimation in the embodiment of the present invention, and the result diagram of the best detection threshold bestTh, false detection rate Pe, missed detection rate Pmiss and false alarm rate Pfalse is obtained (Gold sequence, using normalized absolute peak detection, the registration signal at position 3 is smaller than the service signal power by (a) 15dB, (b) 20dB, (c) 25dB, (d) 30dB, the best detection threshold bestTh, false detection rate Pe, missed detection rate Pmiss and false alarm rate Pfalse results);

[0068] Fig. 9 The Gold sequence in the embodiment of the present invention uses peak-to-average ratio detection. When the power of the registration signal at position 3 is (a) 15 dB, (b) 20 dB, (c) 25 dB, and (d) 30 dB smaller than the power of the service signal, the best detection threshold value bestTh, the false detection rate Pe, the missed detection rate Pmiss, and the false alarm rate Pfalse are shown in the figure;

[0069] Fig.10 The normalized absolute peak detection is used for the Gold sequence in the embodiment of the present invention. When the power of the registration signal at position 3 is (a) 15 dB, (b) 20 dB, (c) 25 dB, and (d) 30 dB smaller than the service signal, the delay estimation error result diagram in 200 detections, where the cross indicates that no detection or detection error occurs;

[0070] Fig.11 The result diagram of the delay estimation error in 200 detections when the peak-to-average ratio detection is used for the Gold sequence in the embodiment of the present invention, and the power of the registration signal at position 3 is (a) 15 dB, (b) 20 dB, (c) 25 dB, and (d) 30 dB smaller than the service signal power, wherein the cross indicates that no detection or detection error occurs;

[0071] Fig.12 This is a graph showing the X and Y polarization frequency offset estimation error results of 100 experiments in an experiment of measuring the influence of different frequency offsets on detection performance in an embodiment of the present invention;

[0072] Fig.13 Result diagram of the false detection rate Pe, missed detection rate Pmiss and false alarm rate Pfalse under different frequency offsets in the embodiment of the present invention;

[0073] Fig.14 1 is a graph showing the delay estimation error results corresponding to different frequency offsets in an embodiment of the present invention (the Gold sequence uses normalized absolute peak detection, and the registration signal frequency offset at position 3 is (a) -500MHz, (b) -250MHz, (c) 250MHz, and (d) 500MHz, and the delay estimation error in 200 detections);

[0074] Fig.15 The graph is a curve showing the variation of X and Y polarization BER of ONU (ONU-2) at position 2 with ROP when there is no registration signal (w / o register signal) in the embodiment of the present invention and the frequency deviation is -500MHz, -250MHz, 0MHz, 250MHz, and 500MHz;

[0075] Fig.16 1 is a curve showing the variation of X and Y polarization BER of ONU No. 3 (ONU-3) with ROP when there is no registration signal (w / o register signal) in the embodiment of the present invention and the frequency deviation is -500MHz, -250MHz, 0MHz, 250MHz, and 500MHz. DETAILED DESCRIPTION

[0076] At present, as coherent optical technology continues to expand into wider fields, the P2MP coherent PON architecture based on DSCM has attracted much attention and in-depth research due to its unique advantages. Under this new architecture, the channel multiplexing method has undergone a significant change, from traditional time division multiple access to time-frequency division multiple access. This change has forced us to explore a new online registration mechanism that is compatible with it to ensure that system data transmission can be carried out efficiently and orderly.

[0077] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0078] The present invention provides a method and system for online registration of ONUs in a P2MP system. The ONU randomly selects a sequence from a sequence code set, performs analog intensity modulation on the sequence code, and then moves the registration signal to the frequency band protection interval, and then sends it to the optical line terminal (OLT) together with the service signal. When the OLT receives these signals, it first performs frequency shifting and filtering on the signal to extract the registration signal. For the registration signal, a resampling operation is first performed, and then an analog square detection is performed to remove the DC component therein, and then the two polarized signals are merged, and multiple periodic averages are performed, and the processed signal is subjected to a cyclic cross-correlation operation with the local sequence code set, and the obtained peak value is detected. If the peak value detected exceeds a preset decision threshold, it indicates that the sequence code is activated, and its delay is estimated. The present invention can achieve higher frequency deviation estimation and delay estimation accuracy, and the designed registration signal has little impact on the performance of the service signal; the registration signal power is allowed to be much smaller than the service signal.

[0079] Embodiment 1:

[0080] Figure 1 The present invention is a flowchart of a method for online registration of an ONU in a P2MP system according to an embodiment of the present invention.

[0081] like Figure 1 As shown, this embodiment provides a method for online registration of an ONU in a P2MP system, comprising the following steps:

[0082] Step S1, ONU initialization: The ONU to be put online completes basic configuration, completes the frequency offset correction of the local laser through downlink synchronization, and obtains an ONU that has completed the frequency offset correction.

[0083] Step S2, sequence code set construction: Use the sequence to construct the registered sequence code set.

[0084] Specifically, the sequence is an m-sequence or a Gold sequence.

[0085] Step S3, ONU selects a registration sequence: the ONU that has completed frequency offset correction randomly selects a sequence from the sequence code set as the registration sequence.

[0086] Step S4, modulation of the registration signal: the ONU that has completed the frequency offset correction upsamples the registration sequence to the DAC (digital to analogue counter) sampling rate, then adds direct current, and then performs a square root operation to generate a registration signal.

[0087] Figure 2 This is a registration signal generation and detection scheme in an embodiment of the present invention.

[0088] like Figure 2 As shown, step S4 includes:

[0089] The registration sequence randomly selected from the sequence code set by the sender registration signal is denoted as x u (n), n = 0, ..., N-1, and then up-sampled to the DAC sampling rate to obtain the signal x′u(n), simulated intensity modulation by adding DC and square root operation, and then frequency shifted to the guard interval of the frequency band.

[0090] Figure 3 It is a schematic diagram of the relationship between the frequency spectrum positions of the registration signal and the service signal in the embodiment of the present invention.

[0091] Register signal location Figure 3 shown.

[0092] Send signal x T (n) is expressed as formula (1), u dc is the added DC component, f c is the carrier frequency of the registration signal, NT In order to transmit the signal length, intensity modulation is used to generate the registration signal to avoid the influence of frequency deviation on the registration signal detection performance.

[0093]

[0094] Step S5, frequency shift and sending of the registration signal: the registration signal is frequency shifted to the frequency band guard interval and sent to the OLT end together with other service signals.

[0095] Step S6, extraction of registration signal: The OLT first performs IQ (In-phase and Quadrature) front-end correction on the received signal to compensate for IQ skew and IQ imbalance, and filters out the registration signal by frequency shifting and filtering.

[0096] Specifically, step S6 includes:

[0097] like Figure 2 As shown, at the receiving end, the OLT receives signals in the entire frequency domain through a coherent receiver, and the received X and Y polarization signals It is expressed as formula (2), where Δt represents the transmission delay, Δf represents the residual frequency offset, represents the transmitted X-polarization and Y-polarization service signals, n0(n) represents the system noise,

[0098]

[0099] Select the registered signal at the protection interval through frequency shifting and filtering operations It is expressed as formula (3), n′0(n) represents the influence of business signal and system noise on registration signal, u dc is the added DC component, N T is the length of the sent signal,

[0100]

[0101] Step S7, processing of service signals: for the service signals remaining after the registration signals are extracted, signal recovery and quality assessment are performed, and finally the bit error rate (BER) and signal-to-noise ratio (SNR) are calculated.

[0102] Specifically, signal recovery and quality assessment include: dispersion compensation, Multiple-Input Multiple-Output equalization based on Multi-ModulusAlgorithm (MMA-MIMO), fourth-power frequency offset estimation and compensation, symbol synchronization, and carrier phase recovery based on a phase-locked loop.

[0103] Step S8, processing of the registration signal: performing signal preprocessing, signal merging, signal-to-noise ratio enhancement and key information detection on the registration signal to obtain a registration sequence and corresponding delay information.

[0104] Specifically, the registration signal is squared and the DC component is removed. The registration signal is subjected to analog strength detection, and the signals on the two polarizations are combined. The signal-to-noise ratio of the received registration signal is improved by superimposing and averaging multiple signal segments. Finally, a cyclic cross-correlation is performed with the local code set to detect the registration sequence and the corresponding delay information.

[0105] More specifically, step S8 includes the following sub-steps:

[0106] Step S8.1, estimate the residual frequency deviation Δf: square the signal to remove the DC component, complete the analog strength detection of the registered signal, and obtain the signal It can be expressed as formula (4), ignoring the signal amplitude damage, n″0(n) represents the cumulative noise impact, including the impact of the business signal on the registration signal,

[0107]

[0108] Step S8.2, signal Perform peak detection to obtain delay information.

[0109] Specifically, there are two detection modes for peak detection, namely normalized absolute peak detection and peak-to-average ratio detection.

[0110] In normalized absolute peak detection, the cyclic cross-correlation result of the registered sequences a(n) and b(n) is assumed to be (5)

[0111] R(n)=|{IFFT{FFT{a(n)}FFT{b(n)}}}|(5)

[0112] The normalized absolute peak value is shown in formula (6), where ||a|| represents the modulus of the registration sequence a(n),

[0113]

[0114] The peak position d = argmax nM(n) is the delay information.

[0115] Peak-to-average ratio detection, as shown in formula (7), is the ratio of the maximum value to the average value of the correlation result.

[0116]

[0117] The peak position d = argmax n M(n) is the delay information.

[0118] Step S8.3, combine the signals on the two polarizations to obtain the signal x r′ (n), expressed as formula (8)

[0119]

[0120] Step S8.4, perform multi-segment superposition and averaging of the registration signal in the time domain to improve the signal-to-noise ratio of the received registration signal and improve the detection performance. Finally, perform cyclic cross-correlation detection with the local code set, as shown in formula (9), x i (n) is the i-th registration sequence code in the code set, thereby detecting the registration sequence selected by the registration signal, and calculating the delay according to the position corresponding to the maximum correlation peak, completing the processing and analysis of the registration signal,

[0121] x e (n) = IFFT {FFT (x r′ (n))FFT(x i (n))} (9)

[0122] Embodiment 2:

[0123] This embodiment is a preferred example of Embodiment 1.

[0124] In order to verify the effectiveness and feasibility of the scheme, a P2MP system ONU online registration signal experiment was conducted. The schematic diagram of the experimental scheme is shown in the figure. Figure 4 As shown in the figure, six 10GBaud DP-16QAM signals are generated in the electrical domain to simulate the service signals of different ONUs. The registration signal uses an m / Gold sequence with a length of 127 and a rate of 200MHz, which is modulated to the right 1 / 3 of the subcarrier guard interval. The relative position of the registration signal and the service signal is shown in the figure. Figure 3As shown. The registration signal is modulated together with the service signal through a coherent transmitter (CDM), and a 1550nm external cavity tunable semiconductor laser (ECL) is used as the modulated light source. After the modulated signal is amplified by an erbium-doped fiber amplifier (EDFA), it enters a 20km standard single-mode fiber (SSMF) for transmission. At the receiving end, the adjustable optical attenuator (VOA) adjusts the received optical power, and the 1550nm ECL is used as the local oscillator (LO). An integrated coherent receiver is used to perform coherent detection on the signal. After sampling by the analog-to-digital converter (ADC), the registration signal detection and service signal recovery are completed by the digital signal processing (DSP) at the receiving end.

[0125] At the transmitting end, the power of the six service signals is set to be the same, all 2.02dBm, so the output of the EDFA is set to 9.8dBm. The power spectra of the registration signal and service signal sent on X and Y polarization are shown in the figure below: Figure 5 As shown, the registration signal is located at 1 / 3 of the guard interval on the left side of the service signal. For example, for the nth ONU, let its center frequency be f n , then the corresponding registration signal center frequency f r：n =f n -1 / 2(R Data +α)-1 / 3F Guard , where R Data is the service signal baud rate, i.e. 10GBuad, α is the root raised cosine roll-off coefficient, i.e. 0.0625, F Guard is the protection interval, i.e. 600MHz. Figure 3 In the figure, the test registration signal at position 3 is 15dB less than the service signal power.

[0126] The receiving DSP process of registration signal detection and service signal recovery is as follows Figure 6 As shown in the figure, for the received signal, IQ front-end correction is first performed to compensate for IQ skew and IQ imbalance. Then the registration signals are filtered out separately. For the service signal, after resampling to 2 sample points per symbol (2sps), dispersion compensation, MMA-MIMO equalization, fourth-power frequency offset estimation and compensation, symbol synchronization, and carrier phase recovery based on a phase-locked loop are performed, and finally BER and SNR are calculated. For the registration signal, it is resampled to 2sps, analog square detection is performed, the DC component is removed, the two polarization signals are merged, averaged for 5 cycles, and cyclic cross-correlated with the local sequence code set is performed. The peak is detected. If it exceeds the decision threshold, it means that the sequence code is activated, and its delay is estimated.

[0127] During the experiment, we randomly selected the registration sequence code for each registration signal, and conducted experimental tests in the following manner. Each case was tested 200 times, and finally statistical analysis was performed:

[0128] (1) Send a registration signal at position 3 and change its relative power value so that the registration signal power is different dB lower than the service signal power. Observe the changes in the false detection rate, false alarm rate, and missed detection rate as well as the delay estimation.

[0129] (2) Add different frequency offsets to the registration signal at position 3 to observe changes in detection performance and the impact on service signals;

[0130] When testing the effect of different signal powers on detection performance, a registration signal is sent at position 3, and its power is set to be 15dB, 20dB, 25dB, and 30dB lower than the power of the service signal. The false detection rate, missed detection rate, false alarm rate, and delay estimation are compared. When the registration signal sent at position 3 is 15dB, 20dB, 25dB, and 30dB lower than the power of the service signal, the power spectrum of the received signal is as follows: Figure 7 shown.

[0131] When verifying the detection performance of the Gold sequence, the registration signal uses the Gold sequence, the receiving end uses normalized absolute peak detection, and the test registration signal at position 3 is set to be 15dB, 20dB, 25dB and 30dB smaller than the service signal power, respectively. 200 experiments are conducted. According to the distribution of the peak value of the registration signal at position 3 related to the correct sequence code and the peak value related to other sequence codes, Gaussian distribution is selected for distribution fitting and parameter estimation, and the best detection threshold bestTh, false detection rate Pe, missed detection rate Pmiss and false alarm rate Pfalse are obtained. The results are shown in the figure. Figure 8 As shown. When the Gold sequence receiver uses peak-to-average ratio detection, the registration signal is 15dB, 20dB, 25dB and 30dB smaller than the service signal power, respectively. 200 experiments are conducted. According to the distribution of the peak value of the registration signal at position 3 related to the correct sequence code and the peak value related to other sequence codes, Gaussian distribution is selected for distribution fitting and parameter estimation, and the best detection threshold bestTh, false detection rate Pe, missed detection rate Pmiss and false alarm rate Pfalse are obtained. The results are shown in Fig. 9 As shown. It can be seen that the performance of the Gold sequence using peak-to-average ratio detection is much worse than that using normalized absolute peak detection. When the registration signal is -15dB smaller than the service signal, the false detection rate Pe of the peak-to-average ratio detection is 0.0138, and the corresponding best detection threshold bestTh is 3.9718. For delay estimation, when the registration signal power at position 3 is -15dB, -20dB, -25dB and -30dB smaller than the service signal power, the delay estimation errors using normalized absolute peak detection and peak-to-average ratio detection are as follows: Fig.10 and Fig.11As shown in the figure, the cross indicates that the registration signal was not detected this time or the detection was an incorrect sequence, because the correlation peak between the registration signal and the correct sequence is less than the detection threshold or the correlation peak with other sequences exceeds the threshold. Fig.10 and Fig.11 It can be seen that when the correct registration sequence code is detected, the estimation error is less than or equal to ±1 Sample, that is, less than ±2.5ns.

[0132] When verifying the impact of different frequency offsets on detection performance, a dual-fiber bidirectional architecture is used. The ONU's transmitted light and local oscillator light come from the same laser. Therefore, frequency synchronization is first performed in the downstream direction. The operation is to sweep the broadcast signal in the downstream direction to adjust the ONU's receiving laser to the target frequency position, and then send a registration signal for ranging to complete the delay estimation. Therefore, for frequency offset estimation, we select two different subcarriers for fourth-power FFT frequency offset estimation and calculate the relative error. The X and Y polarization frequency offset estimation errors statistically obtained from 100 experiments are shown in the figure below. Fig.12 As shown, the error is less than ±0.5MHz. When the registration signal has different frequency offsets, it will overlap with the service signal, resulting in a decrease in the signal-to-noise ratio of the registration signal and deterioration of the detection performance. The registration signal uses the Gold sequence, and the detection scheme uses normalized absolute peak detection. The registration signal at position 3 is set to be -15dB smaller than the service signal power. The registration signal is set to have different frequency offsets in the electrical domain, namely -500MHz, -250MHz, 250MHz, and 500MHz, to evaluate the detection performance. The results of the false detection rate Pe, missed detection rate Pmiss, and false alarm rate Pfalse under different frequency offsets are shown in the figure below. Fig.13 As shown in the figure, since the registration signal is closer to the service signal on the right at the 600MHz guard interval, when the frequency offset is 250MHz and 500MHz, the false detection rate and other indicators will be significantly degraded, from the order of magnitude of about 1e-74 to the order of magnitude of 1e-44 and 1e-31, but still meet the false detection rate requirement of 1e-15. The corresponding delay estimation error results under different frequency offsets are shown in the figure below. Fig.14 As shown, the error range is still less than or equal to ±2.5ns.

[0133] During the online registration process, we do not want the registration signal to have a significant impact on the communication quality of the business signal. Therefore, the impact of the registration signal on the business signal is evaluated. During the experiment, the registration signal frequency deviation is changed, and the bit error rate changes of the adjacent business signals are compared with when the registration signal is not sent.

[0134] In the experiment, six service signals of equal power are generated in the electrical domain. Each service signal is DP-16QAM with 65536 symbols. The output working setting of EDFA is 9.8dBm. The received optical power ROP is changed from -16dBm to -10dBm. The BER of two polarizations of ONUs at positions 2 and 3 is recorded. The registration signal selects the Gold sequence and sets its power to be 15dB less than the service signal. Then the ROP is adjusted. The X and Y polarization BER curves of ONUs at positions 2 (ONU-2) and 3 (ONU-3) with ROP are compared with the frequency deviation of -500MHz, -250MHz, 0MHz, 250MHz, and 500MHz without registration signal. Fig.15 and Fig.16 As shown in the figure, it can be seen that the impact of different frequency offset registration signals on business signals is within 0.2dB.

[0135] Embodiment 3:

[0136] This embodiment provides a system for online registration of ONUs in a P2MP system. The system for online registration of ONUs in a P2MP system can be implemented by executing the process steps of the method for online registration of ONUs in a P2MP system. That is, those skilled in the art can understand the method for online registration of ONUs in a P2MP system as a preferred implementation of the system for online registration of ONUs in a P2MP system.

[0137] Specifically, the system includes:

[0138] Module M1, ONU initialization: The ONU to be put online completes basic configuration, completes the frequency deviation correction of the local laser through downlink synchronization, and obtains the ONU that has completed the frequency deviation correction;

[0139] Module M2, sequence code set construction: Use sequences to construct registered sequence code sets;

[0140] Module M3, ONU selects registration sequence: the ONU that has completed frequency offset correction randomly selects a sequence from the sequence code set as the registration sequence;

[0141] Module M4, modulation of registration signal: the ONU that has completed frequency deviation correction upsamples the registration sequence to the DAC sampling rate, then adds DC, and then performs a square root operation to generate a registration signal;

[0142] Module M5, frequency shift and transmission of registration signal: frequency shift the registration signal to the frequency band protection interval and send it to the OLT end together with other service signals;

[0143] Module M6, registration signal extraction: The OLT first performs IQ front-end correction on the received signal to compensate for IQ skew and IQ imbalance, and filters out the registration signal by frequency shifting and filtering;

[0144] Module M7, service signal processing: for the service signal remaining after the registration signal is extracted, signal recovery and quality assessment are performed, and finally the bit error rate and signal-to-noise ratio are calculated;

[0145] Module M8, registration signal processing: square the registration signal, remove the DC component, perform analog strength detection on the registration signal, merge the signals on the two polarizations, improve the signal-to-noise ratio of the received registration signal by superimposing and averaging multiple signal segments, and finally perform cyclic cross-correlation with the local code set to detect the registration sequence and the corresponding delay information.

[0146] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0147] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for online registration of ONU in a P2MP system, characterized in that: The steps include: Step S1, ONU initialization: The ONU to be put online completes basic configuration, completes the frequency deviation correction of the local laser through downlink synchronization, and obtains the ONU that has completed the frequency deviation correction; Step S2, sequence code set construction: using the sequence to construct the registered sequence code set; Step S3, ONU selects a registration sequence: the ONU that has completed frequency offset correction randomly selects a sequence from the sequence code set as a registration sequence; Step S4, modulation of the registration signal: the ONU that has completed the frequency offset correction upsamples the registration sequence to the DAC sampling rate, then adds direct current, and then performs a square root operation to generate a registration signal; Step S5, frequency shift and sending of the registration signal: frequency shift the registration signal to the frequency band protection interval, and send it to the OLT end together with other service signals; Step S6, extraction of registration signal: the OLT first performs IQ front-end correction on the received signal to compensate for IQ skew and IQ imbalance, and filters out the registration signal by frequency shifting and filtering; Step S7, processing of service signals: performing signal recovery and quality assessment on the service signals remaining after extracting the registration signal, and finally calculating the bit error rate and signal-to-noise ratio; Step S8, processing of the registration signal: squaring the registration signal, removing the DC component, performing analog strength detection on the registration signal, and merging the signals on the two polarizations, improving the signal-to-noise ratio of the received registration signal by superimposing and averaging multiple signal segments, and finally performing cyclic cross-correlation with the local code set to detect the registration sequence and the corresponding delay information.

2. The method for online registration of an ONU in a P2MP system according to claim 1, characterized in that: In the step S2, the sequence is an m-sequence or a Gold sequence.

3. The method for online registration of an ONU in a P2MP system according to claim 1, characterized in that: The step S4 comprises: The registration sequence randomly selected from the sequence code set by the sender registration signal is denoted as x u (n), n=0,…,N-1, and then upsample to the DAC sampling rate to obtain the signal x′ u (n), by adding DC and square root operation to simulate intensity modulation, and then shifting the frequency to the guard interval of the frequency band, the signal x is sent T (n) is expressed as formula (1), u dc is the added DC component, f c is the carrier frequency of the registration signal, N T is the length of the sent signal, 4. The method for online registration of an ONU in a P2MP system according to claim 1, characterized in that: The step S6 comprises: At the receiving end, the OLT receives signals in the entire frequency domain through a coherent receiver, and receives X and Y polarization signals. It is expressed as formula (2), where Δt represents the transmission delay, Δf represents the residual frequency offset, represents the transmitted X-polarization and Y-polarization service signals, n0(n) represents the system noise, (2) Select the registered signal at the protection interval through frequency shifting and filtering operations It is expressed as formula (3), n′0(n) represents the influence of business signal and system noise on registration signal, u dc is the added DC component, N T is the length of the sent signal, 5. The method for online registration of an ONU in a P2MP system according to claim 1, characterized in that: In step S7, the signal recovery and quality assessment include: dispersion compensation, multi-input multi-output equalization based on a multi-mode algorithm, fourth-power frequency offset estimation and compensation, symbol synchronization and carrier phase recovery based on a phase-locked loop.

6. The method for online registration of an ONU in a P2MP system according to claim 1, characterized in that: The step S8 includes the following sub-steps: Step S8.1, estimate the residual frequency deviation Δf: square the signal to remove the DC component, complete the analog strength detection of the registered signal, and obtain the signal It is expressed as formula (4), ignoring the signal amplitude damage, n″0(n) represents the cumulative noise impact, including the impact of the business signal on the registration signal, Step S8.2, the signal Perform peak detection to obtain delay information; Step S8.3, combine the signals on the two polarizations to obtain the signal x r′ (n), expressed as formula (8) Step S8.4, perform multi-segment superposition and averaging of the registered signal in the time domain, and finally perform cyclic cross-correlation detection with the local code set, as shown in formula (9), x i (n) is the i-th registration sequence code in the code set, thereby detecting the registration sequence selected by the registration signal, and calculating the delay according to the position corresponding to the maximum correlation peak, completing the processing and analysis of the registration signal, x e (n)=IFFT{FFT(x r′ (n))FFT(x i (n))} (9) 7. The method for online registration of an ONU in a P2MP system according to claim 6, characterized in that: In step S8.2, there are two detection modes for peak detection, namely normalized absolute peak detection and peak-to-average ratio detection.

8. The method for online registration of an ONU in a P2MP system according to claim 7, characterized in that: In the normalized absolute peak detection, the cyclic cross-correlation result of the registration sequences a(n) and b(n) is assumed to be (5), where FFT refers to fast Fourier transform, IFFT refers to inverse fast Fourier transform, T(n)=|{IFFT{FFT{a(n)}FFT{b(n)}}}| (5) The normalized absolute peak value is shown in formula (6), where ‖a‖ represents the modulus of the registration sequence a(n), The peak position d = argmax n M(n) is the delay information.

9. The method for online registration of an ONU in a P2MP system according to claim 7, characterized in that: The peak-to-average ratio detection, as shown in formula (7), is the ratio of the maximum value to the average value of the correlation result. The peak position d = argmax n M(n) is the delay information.

10. A system for online registration of ONU in a P2MP system, characterized in that: include: Module M1, ONU initialization: The ONU to be put online completes basic configuration, completes the frequency deviation correction of the local laser through downlink synchronization, and obtains the ONU that has completed the frequency deviation correction; Module M2, sequence code set construction: Use sequences to construct registered sequence code sets; Module M3, ONU selects registration sequence: the ONU that has completed frequency offset correction randomly selects a sequence from the sequence code set as the registration sequence; Module M4, modulation of registration signal: the ONU that has completed frequency deviation correction upsamples the registration sequence to the DAC sampling rate, then adds direct current, and then performs a square root operation to generate a registration signal; Module M5, frequency shift and transmission of registration signal: frequency shift the registration signal to the frequency band protection interval and send it to the OLT end together with other service signals; Module M6, extraction of registration signal: the OLT first performs IQ front-end correction on the received signal to compensate for IQ skew and IQ imbalance, and filters out the registration signal by frequency shifting and filtering; Module M7, service signal processing: for the service signal remaining after the registration signal is extracted, signal recovery and quality assessment are performed, and finally the bit error rate and signal-to-noise ratio are calculated; Module M8, processing of registration signal: square the registration signal, remove the DC component, perform analog strength detection on the registration signal, merge the signals on the two polarizations, improve the signal-to-noise ratio of the received registration signal by superimposing and averaging multiple signal segments, and finally perform cyclic cross-correlation with the local code set to detect the registration sequence and the corresponding delay information.

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