CN114928521A - High-order QAM signal transmission method, general filtering multi-carrier system and passive optical network - Google Patents
High-order QAM signal transmission method, general filtering multi-carrier system and passive optical network Download PDFInfo
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Abstract
The invention provides and experimentally verifies that 30-km SSMF transmission of truncated probability shape 1024-QAM signals in an IM/DD UFMC system has serious oscillation of the signal-to-noise ratio of the 1024-QAM UFMC signals compared with 64/256-QAM signals, which is caused by serious intersubband interference. Because the optimized probability distribution has higher degree of dependence on the signal-to-noise ratio, in order to reduce the influence of the signal-to-noise ratio change on probability shaping, the invention utilizes orthogonal cyclic transformation and constant amplitude zero autocorrelation pre-coding technology to balance the signal-to-noise ratio envelope of the data subcarriers. The precoding technique improves the error rate performance to within the soft-decision forward error correction threshold. Compared with the OCT scheme, the CAZAC scheme suppresses the peak-to-average power ratio at the same time, increasing the receiver sensitivity by 2dB again.
Description
Technical Field
The present invention relates to the field of communications technologies, and in particular, to a high-order QAM signal transmission method and apparatus, a general filtering multi-carrier system, and a passive optical network.
Background
With the rapid development of communication technology, 5G networks have been commercialized on a large scale. New communication service types are continuously emerging, such as mobile medical, smart home electronics and automotive interconnection, which will drive the explosive growth of Internet of Things (IoT) applications, and a large number of terminal devices will access the network. In order to maintain high capacity transmission of IoT networks, Passive Optical Network (PON) based edge computing platforms become critical. Meanwhile, the multi-carrier modulation technology has a wide application prospect in the PON due to the high Spectrum Efficiency (SE) and the robustness to the dispersion of the transmission optical fiber. Universal Filtered Multi-Carrier (UFMC) is a Filtered Multi-Carrier Modulation technique that has better performance than traditional Orthogonal Frequency-division Multiplexing (OFDM) because UFMC has lower out-of-band leakage, higher SE, and higher robustness to time-Frequency offset in UFMC systems where the entire data band is divided into several subbands, each subband is Filtered separately Experimental verification of transmission of PS 16384-QAM signals with effective information entropy of 10 bits/symbol on 2.4-km Standard Single Mode Fiber (SSMF) in a Modulation Direct-Detection (IM/DD) OFDM system. However, the application scenario of PON requires longer distance SSMF transmission, so UFMC PON is more competitive. Although the performance of PS 64-QAM signals has been evaluated in UFMC PONs, high-order QAM signals have different signal-to-noise ratio behavior, so it is very important to find out the performance bottleneck of high-order QAM applications.
A Universal Filtered Multi-Carrier (UFMC) Passive Optical Network (PON) can provide high-capacity data communication for an edge computing center, and is an effective way to implement high-speed short-distance Optical interconnection. Compared with 64/256-QAM signals, symbols with larger amplitude in PS1024-QAM UFMC signals are easily affected by various noises, the interference between subbands is significantly increased, and the signal-to-noise ratio curve of the whole data subcarrier severely oscillates, so how to reduce the influence of the signal-to-noise ratio on the transmission of high-order QAM signals, thereby improving the transmission performance of the high-order signals in the UFMC, is a problem to be solved at present.
Disclosure of Invention
Therefore, the technical problem to be solved by the present invention is to overcome the influence of the signal-to-noise ratio on the transmission performance of high-order signals in the prior art.
In order to solve the above technical problem, the present invention provides a high-order QAM signal transmission method, including:
utilizing a truncation probability shaping technology to truncate symbols exceeding a preset threshold value in a constellation diagram to obtain a truncated QAM signal;
pre-coding the truncated QAM signal by using a pre-coding technology to obtain a pre-coded QAM signal;
and modulating and transmitting the pre-coded QAM signal into a standard single-mode optical fiber.
Preferably, the precoding the truncated QAM signal using a precoding technique to obtain a precoded QAM signal includes:
and multiplying the truncated QAM signal by a precoding matrix to obtain a precoded QAM signal.
Preferably, the precoding matrix is a constant amplitude zero autocorrelation coding matrix, and assuming that there are N data subcarriers, the constant amplitude zero autocorrelation coding matrix CAZAC is represented as:
the element in the precoding matrix CAZAC is c m,s ＝c m+N ·(s-1)＝c k ,m,s＝1,2,L,N：
Wherein L is the length of the CAZAC sequence, and L is N 2 A is a constant, k is a subscript representing an element,
is c k+l J represents the imaginary part, the square of j being-1.
Preferably, the precoding matrix is an orthogonal cyclic transformation precoding matrix, and it is assumed that N data sub-carriers orthogonal cyclic transformation precoding matrices OCT are expressed as:
the elements of the OCT precoding matrix are:
t u (u＝1,2,…,N)
wherein L is the length of the OCT sequence, and L is N 2 Where a is a constant, u is a subscript of the sequence t, n is an arbitrarily selected integer, the calculation formula for tu is selected based on the parity of n, j represents an imaginary component, and j has a square of-1.
Preferably, the truncating the symbol errors exceeding the preset threshold in the constellation diagram by using a truncating probability shaping technique to obtain a truncated QAM signal comprises:
and intercepting symbols smaller than 8.8 multiplied by 10 < -4 > in the probability density function PMF graph to obtain truncated QAM signals.
Preferably, the modulating and transmitting the precoded QAM signal into a standard single-mode fiber comprises:
converting the pre-coded QAM signal after filtering into a path of real number signal by utilizing a time domain juxtaposition technology;
loading the real number signal to an arbitrary waveform generator and converting the real number signal into an electric signal;
the Mach-Zehnder modulator converts the electrical signals into optical signals through a continuous wavelength laser;
launching the optical signal into the standard single mode optical fiber.
Preferably, after modulating and transmitting the precoded QAM signal into a standard single-mode fiber, the method further includes:
controlling the noise level by using a variable optical attenuator and an erbium-doped fiber amplifier;
on the receiver side, converting the received optical signal into an electrical signal by using a photodetector;
and acquiring data of the off-line DSP by using the real-time oscilloscope, and realizing opposite operation on the transmitter.
The invention also provides a device for transmitting the high-order QAM signal, which comprises:
the signal interception module is used for truncating symbols exceeding a preset threshold value in the constellation diagram by utilizing a truncation probability shaping technology to obtain truncated QAM signals;
the pre-coding module is used for pre-coding the truncated QAM signal by utilizing a pre-coding technology to obtain a pre-coded QAM signal;
and the modulation module is used for modulating the pre-coded QAM signal and transmitting the pre-coded QAM signal to a standard single mode optical fiber.
The invention also provides a general filtering multi-carrier system comprising a high order QAM signal transmission apparatus as claimed in claim 8.
The invention also provides a passive optical network characterized in that it comprises a generic filtering multi-carrier system as claimed in claim 9.
Compared with the prior art, the technical scheme of the invention has the following advantages:
although the probability shaping technology reduces the occurrence probability of a symbol with higher amplitude, the outer layer constellation point has a symbol with high amplitude level, and still has great influence on the whole SER of the system, therefore, the invention uses truncation probability shaping to discard the symbol of which PMF exceeds an expected threshold value, and the truncated probability shape QAM signal is transmitted by a standard single-mode optical fiber in the UFMC system, thereby enhancing the tolerance to nonlinear noise and simultaneously inhibiting the PAPR; because the optimized probability distribution has higher degree of dependence on the signal-to-noise ratio, in order to reduce the influence of the signal-to-noise ratio change on probability shaping, the signal-to-noise ratio envelope of a data subcarrier is balanced by using a pre-coding technology, and the error rate performance is improved within a soft-decision forward error correction threshold value by using the pre-coding technology.
Drawings
In order that the present disclosure may be more readily and clearly understood, reference is now made to the following detailed description of the present disclosure taken in conjunction with the accompanying drawings, in which:
fig. 1 is a flow chart of an implementation of a high-order QAM signal transmission method of the present invention;
FIG. 2(a) is a graph of a probability density function for a PS1024-QAM UFMC signal;
FIG. 2(b) is a graph of the symbol error rate distribution of a PS1024-QAM UFMC signal;
FIG. 3 is a constellation diagram of a PS/TPS 1024-QAM signal transmitting end;
FIG. 4 is a CCDF plot of a PS/TPS 1024-QAM UFMC signal;
FIG. 5 is a power spectral density plot of a UFMC baseband signal;
FIG. 6 is a schematic diagram of an experimental setup for IM-DD precoded TPS1024-QAM UFMC transmission over 30 km-SSMF;
FIG. 7 is a plot of experimentally measured data subcarrier signal-to-noise ratios for PS 64-QAM/256-QAM/1024-QAM UFMC signals;
FIG. 8 is a graph of experimentally measured signal-to-noise ratios of data subcarriers of a PS1024-QAM UFMC signal with or without precoding;
FIG. 9 is a graph of experimentally measured signal-to-noise ratios of data subcarriers of a PS1024-QAM UFMC signal with or without precoding;
FIG. 10 is a graph of measured error rate for pre-coded TPS1024-QAM UFMC, and uniform 512-QAM UFMC signals at different received optical powers.
Detailed Description
The core of the invention is to provide a high-order QAM signal transmission method, a device, a general filtering multi-carrier system and a passive optical network, which reduce the influence of signal-to-noise ratio on the transmission of high-order QAM signals and improve the transmission performance of the high-order QAM signals in a UFMC system.
In order that those skilled in the art will better understand the disclosure, reference will now be made in detail to the embodiments of the disclosure as illustrated in the accompanying drawings. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
Referring to fig. 1, fig. 1 is a flowchart illustrating an implementation of a high-order QAM signal transmission method according to the present invention; the specific operation steps are as follows:
s101, utilizing a truncation probability shaping technology to truncate symbols exceeding a preset threshold value in a constellation diagram to obtain a truncated QAM signal;
in an Additive White Gaussian Noise (AWGN) channel, a Probability density Function (PMF) graph obtained by simulation is shown in fig. 2(a), and a Symbol Error rate distribution (SER) graph is shown in fig. 2 (b);
it is clear that the outermost constellation point, i.e. the symbol with a high amplitude level, is prone to generate non-linear noise and therefore it has a higher SER. Although the probability shaping technique reduces the probability of occurrence of the higher amplitude symbols, these constellation points still have a large influence on the SER of the system as a whole. Therefore, Truncated Probability Shaping (TPS) is typically used to discard symbols with PMFs exceeding a desired threshold, the distance of a constellation point to the origin is a key factor in the TPS scheme, since constellation points with larger distances have higher SER;
FIG. 3 shows a constellation diagram of PS1024-QAM and TPS1024-QAM transmitting terminals;
since a final transmission signal is generated by overlapping a plurality of subcarriers, a Peak-to-Average Power Ratio (PAPR) is also very important for a multicarrier communication system. If the same phase subcarrier signals are added, a larger peak occurs, and conversely a lower value valley occurs. Thus, the amplitude of the multi-carrier signal fluctuates frequently, and larger amplitude peaks may saturate the power amplifier and cause non-linear effects. Thus, as shown in the following equation:
PAPR(dB)＝10log 10 (max{|x(t)| 2 }/E{|x(t)| 2 })
PAPR is defined as the ratio of the maximum instantaneous power to the average power, and is often used to evaluate the performance of a multi-carrier system.
If the PAPR is too high, the system performance and transmission reliability will be improved, and a Complementary Cumulative Distribution Function (CCDF) is generally used to represent the statistical characteristics of the PAPR. Fig. 4 shows CCDFs curves for a PS1024-QAM UFMC signal and a TPS1024-QAM UFMC signal. In contrast, in the TPS scheme, the PAPR of the UFMC signal is suppressed at the same time after symbols with higher amplitude levels are discarded, as shown in the black circular labeled curve of fig. 4. The TPS signal achieved a PAPR suppression of 0.5-dB as compared to the PS1024-QAM UFMC signal, as shown by the black triangle and the circled plot in FIG. 4. In summary, the TPS UFMC signal enhances tolerance to nonlinear noise while also suppressing PAPR.
S102, precoding the truncated QAM signal by utilizing a precoding technology to obtain a precoded QAM signal;
and multiplying the truncated QAM signal by a precoding matrix to obtain a precoded QAM signal.
And S103, modulating the pre-coded QAM signal and transmitting the signal to a standard single mode fiber.
The method comprises the steps of converting a pre-coded QAM signal after filtering into a path of real signal by using a time domain juxtaposition technology, loading the real signal to an arbitrary waveform generator to be converted into an electric signal, converting the electric signal into an optical signal by a continuous wavelength laser through a Mach-Zehnder modulator, transmitting the optical signal to the standard single-mode optical fiber, controlling the noise level by using a variable optical attenuator and an erbium-doped optical fiber amplifier, converting the received optical signal into the electric signal by using an optical detector on one side of a receiver, acquiring data of an offline DSP by using a real-time oscilloscope, and realizing the opposite operation on the transmitter.
The invention abandons the symbols of PMF exceeding the expected threshold value by using truncation probability shaping, and outputs the transmission of truncation probability shape QAM signals in a standard single-mode optical fiber in a UFMC system, thereby enhancing the tolerance to nonlinear noise and simultaneously inhibiting PAPR; because the optimized probability distribution has higher degree of dependence on the signal-to-noise ratio, in order to reduce the influence of the signal-to-noise ratio change on probability shaping, the signal-to-noise ratio envelope of a data subcarrier is balanced by using a pre-coding technology, and the error rate performance is improved within a soft-decision forward error correction threshold value by using the pre-coding technology.
Based on the above embodiment, step S102 is further described in detail as follows:
fig. 5 shows the Power Spectral Density (PSD) of the UFMC baseband signal generated at the transmitter side, where 128 data subcarriers are divided into 8 equal-sized subbands. The band pass filters in UFMC systems distort the signal at the sub-band boundaries severely, resulting in a reduction of the corresponding signal-to-noise ratio. The 1024-QAM UFMC signal is prone to non-linear noise compared to the signal-to-noise envelope of a 64-QAM UFMC signal with less fluctuation, and therefore the degradation of inter-subband interference results in a larger variation of the signal-to-noise ratio. Multicarrier systems widely use precoding techniques to equalize the signal-to-noise ratio and suppress PAPR of frequency domain fading channels. The OCT and CAZAC pre-coding matrix with constant amplitude characteristics obtained by the Zadoff-Chu (ZC) sequence can make the signal-to-noise ratio envelope of 1024-QAM UFMC signals smoother, and the obtained uniform signal-to-noise ratio is more suitable for a PS scheme. Further, the ZC sequence has a low correlation, and when the cyclic shift is set to a non-zero value, the autocorrelation is zero. Therefore, elements in the OCT/CAZAC matrix can form a recognition sequence with synchronous clock, and the method is very suitable for the application of a multi-user asynchronous UFMC transmission scene.
In the precoding scheme, a non-uniform 1024-QAM signal is multiplied by a specific precoding matrix to obtain a precoded signal. Subsequently, the precoding signal is loaded on each data subcarrier, and the size of the precoding matrix is determined by the size of the data subcarrier. Assuming N data subcarriers, N waves, the precoding matrix is nxn.
The CAZAC precoding matrix may be represented as:
in the formula (1), c m,s ＝c m+N·(s-1) ＝c k M, s-1, 2, L, N, the precoding matrix is orthogonal so it satisfies CAZACHCAZAC-I. The elements in the precoding matrix CAZAC can be calculated from equation (2):
in formula (3), L is the length of the CAZAC sequence, and L ═ N 2 A is a constant, k is a subscript representing an element,
is c k+l J denotes the imaginary part, the square of j is-1, and for simplicity, a is chosen to be 1. As shown in equation (3), the CAZAC sequence has good periodic autocorrelation and all non-zero cyclic shifts have zero autocorrelation. Therefore, the precoding matrix formed by the CAZAC sequence can reduce the correlation between input symbols.
The OCT precoding matrix is an orthogonal circulant matrix whose matrix dimension depends on the number N of data subcarriers, and can be expressed as:
matrix elements [ t1, t2, …, t N ]Also from the ZC sequence, the element tu (u ═ 1,2, …, N) of the OCT precoding matrix is calculated from equation (5):
wherein L is the length of the OCT sequence, L is N 2 Where a is a constant, u is a subscript of the sequence t, n is an arbitrarily selected integer, and the formula for tu is selected based on the parity of n, j represents an imaginary component, and the square of j is-1, and similarly, where a is also selected to be 1.
The present invention also provides a QAM signal transmission apparatus, comprising:
a signal interception module 100, configured to truncate symbols that exceed a preset threshold in a constellation diagram by using a truncation probability shaping technique to obtain a truncated QAM signal;
a pre-coding module 200, configured to pre-code the truncated QAM signal by using a pre-coding technique to obtain a pre-coded QAM signal;
and a modulation module 300, configured to modulate the precoded QAM signal and transmit the precoded QAM signal to a standard single-mode fiber.
A QAM signal transmission apparatus of this embodiment is configured to implement the foregoing QAM signal transmission method, and thus a specific implementation manner of a QAM signal transmission apparatus may be seen in the foregoing embodiments of a QAM signal transmission method, for example, the signal interception module 100, the pre-coding module 200, and the modulation module 300 are respectively configured to implement steps S101, S102, and S103 in the foregoing QAM signal transmission method, so that the specific implementation manner thereof may refer to descriptions of corresponding embodiments of each part, and is not described herein again.
The invention also provides a general filtering multi-carrier system which comprises the QAM signal transmission device.
Based on the above embodiments, the present embodiment is an experimental setup and parameters of an IM/DD precoding TPS1024-QAM UFMC system on a 30-km SSMF transmission link, as shown in fig. 6:
first, an off-line Digital Signal Processor (DSP) at the transmitter side processes the original bit information into a precoded TPS1024-QAM UFMC Signal. Meanwhile, the filtered complex signal is converted into a path of real signal by utilizing a time domain juxtaposition technology. The 12.5-GBd UFMC signal would then be loaded into an Arbitrary Waveform Generator (AWG) with an AWG sampling rate of 50-GSa/s and a 3-dB bandwidth of about 11 GHz. Then, a Mach-Zehnder Modulator (MZM) converts the electrical signal output from the AWG into an optical signal by a Continuous Wavelength (CW) laser, and the output power of the Modulator is about 5.8 dBm. And then transmitting the modulated pre-coded TPS1024-QAM UFMC optical signal into a 30 km-SSMF. The BER is then measured using a Variable Optical Attenuator (VOA) and an Erbium-Doped Fiber Amplifier (EDFA) to control the noise level. The Optical signal Power entering the EDFA is defined as the Received Optical Power (ROP) in the error rate measurement. On the receiver side, a Photo Detector (PD) with a 10-GHz bandwidth converts the received optical signal into an electrical signal. Then, a real-time oscilloscope with a sampling rate of 50-GSa/s acquires data of the off-line DSP, the opposite operation is realized on a transmitter, and finally, the error rate is calculated.
FIG. 7 is a plot of the signal-to-noise ratio of experimentally measured 12.5GBaud PS 64-QAM/256-QAM/1024-QAM UFMC signals. It is clear that the signal-to-noise ratio curve for the PS 64-QAM UFMC signal has 8 subbands with similar signal-to-noise ratio variations, as shown by the black triangle labeled curve in fig. 7. The signal-to-noise ratio distribution of the different subbands corresponds to 8 subbands in the PSD of the UFMC transmit signal in fig. 5. The PS 256-QAM UFMC signal has a similar signal-to-noise ratio curve as the PS 64-QAM UFMC signal if shown by the black triangle and square labeled curves. In contrast, the signal-to-noise ratio of the PS1024-QAM UFMC signal fluctuates greatly, as shown by the diamond-labeled curve in fig. 7. In the PS1024-QAM UFMC signal, symbols with larger amplitude are susceptible to various noises, so the subband boundary distortion caused by the band pass filter is more serious. Therefore, in the PS1024-QAM UFMC system, inter-subband interference increases significantly, and the signal-to-noise ratio curve of the entire data subcarrier oscillates severely. In a PS1024-QAM UFMC system, the maximum variation of the signal-to-noise ratio of all data subcarriers is about 15 dB. In order to realize higher AIR, subcarriers with different signal-to-noise ratios are collocated with non-uniform QAM signals with different probability distributions, however, a large number of distribution matchers greatly increase the system complexity. Without considering a plurality of distribution matchers, the method introduces a simple precoding technology based on OCT and CAZAC to smooth the signal-to-noise ratio envelope, thereby using a single distribution matcher for all data subcarriers.
Fig. 8 shows the signal-to-noise ratio curve of data subcarriers of PS1024-QAM UFMC signals obtained by experimental measurement with or without OCT/CAZAC precoding. OCT and CAZAC precoding suppresses large signal-to-noise ratio fluctuations as shown by the black curves of the triangle and square markers in fig. 8. The signal-to-noise ratio of the PS1024-QAM UFMC signal without any precoding fluctuates frequently between 15dB and 30dB, compared to the UFMC signal with CAZAC and OCT precoding with a relatively smooth envelope of signal-to-noise ratios, with an average signal-to-noise ratio of about 25 dB.
The PAPR has an important meaning in the UFMC system, and in order to evaluate the influence of OCT and CAZAC precoding on the PAPR, fig. 9 plots the CCDF curves of PS1024-QAM UFMC signals before and after OCT/CAZAC precoding. The vectors in the CAZAC matrix have zero autocorrelation, which reduces the probability of in-phase and opposite phase subcarrier signals adding, thereby avoiding large peaks and valleys. Thus, as shown by the black square and diamond-marked curve in fig. 9, CAZAC precoding suppresses PAPR of PS1024-QAM UFMC signals by approximately 2-dB. However, since OCT is a circulant matrix, the vector does not have the characteristics of zero autocorrelation. Therefore, we cannot effectively suppress PAPR by OCT precoding, as shown by the curves of black diamond and circular marks.
FIG. 10 plots the measured error rate curves of OCT/CAZAC TPS1024-QAM, TPS1024-QAM and uniform 512-QAM UFMC signals, with the effective information entropy of all 9 bits/symbol. Here, the solid and dashed lines represent BERs measured in BTB and 30-km SSMF transmissions, respectively. It is clear that UFMC signals increase the resilience to fiber dispersion, so 30-km SSMF transmission has a negligible impact on the bit error rate performance.
The dashed line in fig. 10 represents the soft decision FEC threshold, i.e. 2 x 10-2. Although the uniform 512-QAM UFMC signal and the PS1024-QAM UFMC have the same effective information entropy, probability shaping improves the error rate performance of 1024-QAM signals, as shown by the curves marked by black squares and circles in fig. 10. However, their bit error rate is still outside the soft-decision FEC threshold. As shown by the curve marked by the upward triangle in the black direction, in the OCT TPS1024-QAM UFMC system, the error rate performance is improved by using OCT to equalize the signal-to-noise ratio over the entire data band and truncating constellation points with a higher SER based on a truncation probability shaping technique, and approaches the soft-decision FEC threshold when ROP is-6 dBm. In addition, CAZAC precoding can not only equalize the signal-to-noise envelope but also suppress PAPR at the same time. Therefore, we observed a greater performance improvement in the CAZAC TPS1024-QAM UFMC system. As shown by the curve of the triangle mark with the black direction down, at the soft decision FEC threshold, the receiver sensitivity using the CAZAC precoding scheme is improved by 2-dB compared to OCT. The performance differences between OCT and CAZAC schemes are consistent with the theoretical analysis described above.
The invention also provides a passive optical network which comprises the general filtering multi-carrier system.
The UFMC PON is an effective method for connecting an edge computing platform and maintaining a high-speed Internet of things and an MTC network. Meanwhile, the high-order QAM signal with high spectral efficiency has wide application prospect in a high-speed PON system. However, high order QAM signals are more susceptible to noise and performance bottlenecks have prevented their practical application. In the research of the PS-1024QAM UFMC signal with the actual entropy of 9 bits/symbol, the signal-to-noise ratio of the PS1024-QAM UFMC signal is observed to be greatly changed, and the peripheral constellation points have a large influence on the transmission quality of the signal as a whole. In order to improve the performance of a high-order PS scheme and not introduce more complexity, a system scheme of OCT/CAZAC TPS1024-QAM UFMC is provided by combining truncation probability shaping and a precoding technology. Researches find that the truncation probability shaping technology can simultaneously reduce nonlinear noise and reduce PAPR; in addition to the performance similarity in equalizing the signal-to-noise ratio, the CAZAC precoding matrix can also reduce the PAPR of the UFMC signal. The transmission effects of uniform 512-QAM, PS1024-QAM and OCT/CAZAC TPS1024-QAM UFMC signals on a 12.5-GBd IM/DD system are verified and compared through experiments. The experimental result verifies the theoretical research, compared with uniform 512-QAM and PS1024-QAM, the error rate of the OCT/CAZAC TPS1024-QAM UFMC signal can be reduced to be within the soft-decision FEC threshold range, and larger performance gain can be obtained by using the CAZAC TPS1024-QAM UFMC scheme.
The sequence in CAZAC matrix has good periodic autocorrelation, and besides the equalization of signal-to-noise ratio and suppression of PAPR, it can also be used as a preamble identification sequence of UFMC signal, which can generate very sharp correlation peak when synchronous recovery is carried out. In addition, the UFMC system has strong time-frequency offset resistance, so the CAZAC TPS1024-QAM UFMC scheme provided by the method has great application potential in PONs of high-speed multi-user asynchronous transmission.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. This need not be, nor should it be exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.
Claims (10)
1. A method for high order QAM signal transmission, comprising:
utilizing a truncation probability shaping technology to truncate symbols exceeding a preset threshold value in a constellation diagram to obtain a truncated QAM signal;
pre-coding the truncated QAM signal by using a pre-coding technology to obtain a pre-coded QAM signal;
and modulating and transmitting the pre-coded QAM signal into a standard single-mode optical fiber.
2. The method for transmitting a high-order QAM signal according to claim 1, wherein said pre-coding said truncated QAM signal using a pre-coding technique to obtain a pre-coded QAM signal comprises:
and multiplying the truncated QAM signal by a precoding matrix to obtain a precoded QAM signal.
3. A method according to claim 2, wherein the precoding matrix is a constant amplitude zero autocorrelation coding matrix, and assuming that there are N data subcarriers, the constant amplitude zero autocorrelation coding matrix CAZAC is expressed as:
the element in the precoding matrix CAZAC is c m,s ＝c m+N·(s-1) ＝c k ,m,s＝1,2,L,N：
Wherein L is the length of the CAZAC sequence, and L is N 2 A is a constant, k is a subscript representing an element,
is c k+l J denotes the imaginary part, the square of j is-1.
4. The method according to claim 2, wherein the precoding matrix is an orthogonal cyclic transform precoding matrix, and assuming that there are N data subcarriers, the orthogonal cyclic transform precoding matrix OCT is expressed as:
the elements of the OCT precoding matrix are:
t u (u＝1,2,…,N)
wherein L is the length of the OCT sequence, L is N 2 Where a is a constant, u is a subscript of the sequence t, n is an arbitrarily selected integer, the calculation formula for tu is selected based on the parity of n, j represents an imaginary component, and j has a square of-1.
5. The method according to claim 1, wherein said truncating said truncated QAM signals by truncating said symbols exceeding a predetermined threshold from said constellation using a truncating probability shaping technique comprises:
and intercepting symbols smaller than 8.8 multiplied by 10 < -4 > in the probability density function PMF graph to obtain the truncated QAM signal.
6. The method of claim 1, wherein said modulating and transmitting said precoded QAM signal into a standard single mode fiber comprises:
converting the pre-coded QAM signal after filtering into a path of real number signal by utilizing a time domain juxtaposition technology;
loading the real number signal to an arbitrary waveform generator and converting the real number signal into an electric signal;
the Mach-Zehnder modulator converts the electric signal into an optical signal through a continuous wavelength laser;
launching the optical signal into the standard single mode optical fiber.
7. The method for transmitting high-order QAM signals according to claim 6, wherein said modulating and transmitting said pre-coded QAM signals into a standard single-mode optical fiber further comprises:
controlling the noise level by using a variable optical attenuator and an erbium-doped fiber amplifier;
on the receiver side, converting the received optical signal into an electrical signal by using a photodetector;
and acquiring data of the off-line DSP by using the real-time oscilloscope, and realizing opposite operation on the transmitter.
8. A high order QAM signal transmission device, comprising:
the signal interception module is used for truncating symbols exceeding a preset threshold value in the constellation diagram by utilizing a truncation probability shaping technology to obtain truncated QAM signals;
the pre-coding module is used for pre-coding the truncated QAM signal by utilizing a pre-coding technology to obtain a pre-coded QAM signal;
and the modulation module is used for modulating the pre-coded QAM signal and transmitting the pre-coded QAM signal to a standard single mode optical fiber.
9. A general filtering multi-carrier system, characterized in that it comprises a high order QAM signal transmission apparatus according to claim 8.
10. A passive optical network comprising the general filtering multi-carrier system according to claim 9.
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