CN110113282B - Probability PAPR (peak-to-average power ratio) inhibition method based on polarization code assistance - Google Patents

Abstract

The invention provides a method for restraining probability PAPR based on polarization code assistance, which can solve the problem that the performance of the system is influenced by the inevitably over-high PAPR of the existing OFDM system. The invention relates to a probability PAPR restraining method based on polarization code assistance, which comprises the following steps: dividing a signal to be encoded into a plurality of blocks; coding the divided blocks by using a polarization code to obtain a plurality of transmission signals; and calculating the peak-to-average power ratio of the transmission signals, and selecting the transmission signal with the lowest peak-to-average power ratio for transmission.

Description

Probability PAPR (peak-to-average power ratio) inhibition method based on polarization code assistance

Technical Field

The invention relates to a method for restraining probability PAPR based on polarization code assistance.

Background

With the popularization of various data services, particularly video services, the demand for access network capacity is increasing, and the transmission rate is 40/100 Gbps. An Orthogonal Frequency Division Multiplexing (OFDM) -PON system has the characteristics of strong dispersion resistance, high spectrum efficiency, flexible bandwidth allocation, strong expansibility and the like, and thus becomes one of the research hotspots of next-generation PONs. Compared with coherent light detection, the OFDM-PON direct detection system has the advantage of low cost.

However, since OFDM is a multi-carrier technology, the superimposed transmission of each carrier will result in a higher peak-to-average power ratio (PAPR), which will require a wider linear range of the network device, thereby increasing the cost of the system.

Therefore, it is imperative to suppress PAPR so that the OFDM-PON can operate stably and safely. Many scholars invest in studies to suppress PAPR. For example, clipping, coding, probability-based methods.

The clipping technique is the simplest method to implement, but the method is to perform nonlinear processing on the signal, so that in-band interference and out-of-band radiation are caused, and the error rate performance of the system is deteriorated.

The basic idea of the encoding method is to calculate the PAPRs of all code groups generated by different encoding methods, compare the PAPRs with each other, remove the code group with the larger PAPR, and select the code group with the lower PAPR as the allowable code group for signal transmission, thereby avoiding the occurrence of larger signal amplitude. The processing process of the method is a linear process, which does not cause signal distortion, but causes the problem of broadband utilization rate due to the reduction of the coding rate. In addition, to search for the best code word, the PAPR of all code groups needs to be calculated, and a large number of lookup tables for storing encoding and decoding are needed, so that the calculation complexity is high, and meanwhile, the encoding and decoding processes are complex, and the influence on the information transmission rate is large, so that the method is only suitable for being used in signals with a small number of subcarriers and is not suitable for being used in signals with a large number of subcarriers.

The probabilistic techniques do not suppress amplitude peaks of a signal, but improve PAPR performance of a system by reducing the probability of peak occurrence. Selecting a mapping technology (SLM) to be divided into several groups of information multiplied by phase factors, and then selecting a peak signal to be relatively low through IFFT; partial transmission sequence technique (PTS) groups information of IFFT and then reduces PAPR by adjusting phase factors, multiplying the information by the phase factors, respectively. Compared with the former two methods, the complexity of the method is higher, and the requirement on the accuracy of sideband information is higher.

Referring to fig. 1, in a structure of a conventional SLM algorithm, signals are subjected to Quadrature Amplitude Modulation (QAM), multiplied by U different phase sequences, then IFFT operations are performed and PAPR is calculated, and a group of signals with the smallest PAPR is selected for transmission. The SLM algorithm has a good suppression effect on PAPR, but it needs to transmit additional phase information, thereby reducing the transmission efficiency of the system. However, the SLM algorithm has high redundancy information, which reduces the universality of the use of the SLM algorithm.

The above coding method can find that all code groups need to be calculated, so that the coding method is only suitable for signals with a small number of carriers, the complexity of a system with a large number of carriers is extremely high, and in addition, the used code groups are screened, so that certain redundancy is increased. Although the probability algorithm does not limit its use due to the number of carriers, it generates an extra sideband signal, and the information of the extra sideband is very important for recovering the signal, so that it costs much extra information to transmit the signal.

The optimal situation of the methods is that no distortion is generated on the signal, and the error correction cannot be carried out on the signal.

Disclosure of Invention

Aiming at the technical problems in the prior art, the invention provides a probability PAPR suppression method based on polarization code assistance, which can effectively reduce the excessive PAPR in a system and reduce the error rate of the system.

The technical scheme adopted for solving the technical problem of the invention is a probability PAPR inhibition method based on polarization code assistance, which comprises the following steps:

dividing a signal to be encoded into a plurality of blocks;

coding the divided blocks by using a polarization code to obtain a plurality of transmission signals;

and calculating the peak-to-average power ratio of the transmission signals, and selecting the transmission signal with the lowest peak-to-average power ratio for transmission.

Optionally, the dividing the signal to be encoded into a plurality of blocks includes:

determining whether the length of the signal to be encoded is odd or even,

if the number of the signals to be coded is an even number, dividing the signals to be coded into a first block and a second block, wherein the length sizes of the first block and the second block are equal;

and if the number is odd, equally dividing the signal into a third block and a fourth block, wherein the length dimension of the third block is larger than the length dimension of the fourth block by one unit dimension.

Optionally, the encoding the signal to be encoded by using a polarization code includes:

and carrying out parallel U-time coding on the signal to be coded, carrying out amplitude modulation QAM (quadrature amplitude modulation) and Inverse Fast Fourier Transform (IFFT), and sequencing a plurality of transmission signals in sequence, wherein U is a positive integer.

Optionally, the method further includes a step of decoding the transmission signal, including:

receiving a signal sequence, formulated as

For each y_iCalculating

y_iRepresenting recipient information;

this formula is the ratio of the probability of a signal appearing 0 and 1;

sequentially calculating likelihood value of ith bit of sending end

Indicating that the receiving end is encoding the transmitting end before

The evaluation sequence of (a) is:

if it is

Then

Otherwise

The probability PAPR restraining method based on polarization code assistance has the following advantages:

the PAPR of the signals is calculated respectively, a signal with the lowest PAPR is selected for transmission, and the PAPR suppression condition of the signals is analyzed in a simulation mode. And through a direct detection OFDM system as an experimental system to carry out experiments and analyze information correction conditions, traditional OFDM signals after back-to-back and optical fiber transmission are respectively compared, and through an SLM algorithm and an FPC (50%, 20%) error rate FPC algorithm, under the condition of 50% redundancy, 4.2dB is improved compared with the SLM algorithm, and 1 dB is also improved when the FPC redundancy is 20%.

Drawings

FIG. 1 is a diagram illustrating an SLM algorithm;

FIG. 2 is a 2 nd order polar code structure;

FIG. 3 is a diagram of an Nth order polar code encoding;

FIG. 4 is a diagram of a PC suppression algorithm;

FIG. 5 is a PC block coding;

FIG. 6 is a flow chart of a method for probability-based PAPR suppression based on polarization code assistance;

FIG. 7 is a verification structure diagram of a polar code assisted PAPR suppression algorithm; flexible block coding of FPC; QAM quadrature amplitude modulation; S/P serial/parallel conversion; IFFT inverse Fourier transform; CP cyclic redundancy; AWG arbitrary waveform generator; an EDFA erbium-doped fiber amplifier; a VOA variable optical attenuator; an SSMF standard fiber amplifier; a PD photodetector; BER bit error rate;

FIG. 8 is a cumulative distribution function and signal;

FIG. 9a is a graph showing the variation of the bit error rate curves in different blocking modes when the redundancy of the simulation analysis is 20%;

FIG. 9b is a graph showing the variation of the bit error rate curves in different blocking modes when the redundancy of the simulation analysis is 50%;

FIG. 10 is a plot of the bit error rate after back-to-back and fiber optic transmission of conventional signals, SLM, FPC.

Detailed Description

In order to make those skilled in the art better understand the technical solution of the present invention, a display unit, a display substrate, a driving method thereof, and a display device provided by the present invention are described in further detail below with reference to the accompanying drawings and the detailed description.

Example 1:

the embodiment provides a method for probability PAPR suppression based on polarization code assistance, which comprises the following steps:

dividing a signal to be encoded into a plurality of blocks;

coding the divided blocks by using a polarization code to obtain a plurality of transmission signals;

and calculating the peak-to-average power ratio of the transmission signals, and selecting the transmission signal with the lowest peak-to-average power ratio for transmission.

Referring to fig. 6, the specific process of the method includes:

step1 first initializes the information, the length N of PC code encoding, the length K before encoding, the number of parallel encoding times is U, and the position P of the starting point.

Step2 PC encodes the two separated blocks and saves the start point location

Step3 respectively calculating PAPR values of OFDM signals at different starting point positions

Step4 picks the minimum PAPR and saves the start point location

The polarization code is the only theoretical proof at present to reach the Shannon limit, and has clear and simple coding and decoding algorithms. The core of the polar code structure is that through the processing of 'channel polarization', at the encoding end, the encoding method is adopted to make each sub-channel present different reliability, when the code length continuously increases, one part of the channel tends to the perfect channel (without error code) with the capacity close to 1, the other part of the channel tends to the pure noise channel with the capacity close to 0, and the channel with the capacity close to 1 is selected to directly transmit information to approach the channel capacity. At the decoding end, the polarized channel can obtain the performance similar to the maximum natural decoding with low realization complexity by a simple successive interference cancellation decoding (SC) method.

Alternatively, for any given code length of a polar code, its code length N is specified to satisfy a power of 2 due to its regular butterfly elementary unit transform. As the code length N approaches infinity, the channel is polarization transformed into equivalent perfectly noise-free virtual subchannels and perfectly noise virtual subchannels. Therefore, the information bit is transmitted on the channel with good channel quality, and the known fixed bit of the transmitting end is transmitted on the channel with poor channel quality, so that the Shannon tolerance is reached as far as possible. The generator matrix GN plays a crucial decisive role in the coding of the polarization code. Referring to fig. 2 and 3, a basic transform unit includes a two-input modulo two addition operation, which is equivalent to an input matrix undergoing a regular matrix transformation, and the equivalent inputs are:

one transform unit represents the smallest coding unit of the polar code coding. The information block signal is generated after being partitioned. The information blocks may occur prior to encoding.

(u₁,u₂)(x₁，x₂)＝(u₁,u₂)G₂

Wherein G2 is a generator matrix:

for a generator matrix of order N:

where ≧ is the tensor product, RN is a flip matrix.

Alternatively, referring to fig. 5, for an initial OFDM signal, the signal is directly divided into two parts, Block1 and Block 2. Assuming that the length of the OFDM signal is K, assuming that the signal length is an even number, the length of Block1 is K/2 and the length of Block2 is K/2, so that the signal is divided into two on average. The initial signal can be expressed as:

S＝{B₁,B₂}

wherein B is₁＝{χ₁,χ₂...χ_K/2},B₂＝{χ_K/2+1,χ_K/2+2...χ_K}

The Block1 signal is defined to be divided into 2 parts by Block 2. As shown, Bolck2 can be slid back and forth to obtain L/2 different signal combinations. Then

S'＝{B_p1,B₂,B_p2}

Wherein B is_p1＝{χ₁,χ₂...χ_P}，B_p2＝{χ_P+K/2+1,χ_P+K/2+1...χ_K}，B₁＝{χ_P+1,χ_P+2...χ_P+K/2}

The first data of Block2 at each position has its position K reserved, K is in the range of 1,2, 1, L/2-1, and then the signal divided into two blocks is encoded by PC code, and for the encoded data, it is specified that the encoded data of Block1 is placed in front of the encoded data, and the encoded data of Block2 is placed in the back of the encoded data. Then

Encode(S)＝{Encode([B_p1,B_p2]),Encode(B_p2)}

Wherein Encode represents polar code encoding.

Information length after table-algorithm processing

Type of algorithm	C_OFDM	SLM	FPC
				Length (information)	K/M	K/M+K/(M+E)	K/M+(N-K)/M+(log2(k/2)/E

Where (log2(K/2)/E is much smaller than the length of K/(M + E), so ignoring this small redundancy, assuming both algorithms have the same redundancy, it can be expressed as:

from the above formula, it can be seen that the redundancy of the signal has a close relationship with the modulation method used by the safety channel transmission signal.

When the secure channel adopts E equal to 1, E/(E +1) equal to 0.5, and when the coding redundancy of the PC code is 50%, the redundancy is the same as that of the traditional SLM algorithm. When E is 4, E/(E +1) is 0.8, and when the coding redundancy of the PC code is 20%, the same redundancy as that of the conventional SLM algorithm is obtained.

For PC codes, the signal is changed by encoding, and the signal before and after encoding is regular, so that the signal can be recovered by calculation without additional side information. Compared with the traditional SLM algorithm, a large amount of redundant information is not needed. Compared with the encoding mode, all code groups do not need to be calculated, and only the required code group needs to be found. Referring to fig. 4, which is a basic flow of the FPC algorithm, it can be found that the conventional SLM algorithm modulates first, then multiplies the modulated signal by U different phase sequences, and then calculates the phase sequence with the minimum PAPR. The FPC algorithm firstly carries out parallel multi-time coding on an original signal for the same U times, then carries out QAM modulation operation and IFFT, and then calculates the minimum PAPR value in the code groups to be used as a transmitting end signal for transmitting.

Optionally, the decoding process comprises:

suppose that

Indicates the sequence obtained at the receiving end, for each y_iCan calculate

Sequentially calculating likelihood value of ith bit of sending end

Indicating that the receiving end is encoding the transmitting end before

The evaluation sequence of (a) is:

if it is

Then

Otherwise

Compared with the prior art, the following method for analyzing probability PAPR suppression based on polarization code assistance in the scheme is compared in a simulation mode:

referring to fig. 7, in an experimental structure of a PAPR suppression algorithm assisted by a polarization code, at a transmitting end of OFDM, a signal of a PRBS15 is used as information source, as an initial signal, and then an algorithm-related algorithm for PAPR suppression is applied to suppress PAPR of the signal, a modulation mode adopts 16QAM where the number of carriers of the signal is 512 and the effective data carrier is 128, after all the above operations are processed offline, an electrical signal is generated by a 12.5 Arbitrary Waveform Generator (AWG), and modulated to an optical carrier by a mach-zehnder modulator (MZM), and an External Cavity Laser (ECL) is used, and the wavelength is 1552 nm. An amplifier and a variable optical attenuator are used to control the input fiber power prior to the fiber link. The power of the optical fiber entering the scheme is 6.5dBm, the optical fiber link is a standard single-mode optical fiber with the length of 30km, and the attenuation is 0.2dB per kilometer at 1550 nm. A noise control module consisting of an attenuator and an amplifier at an OFDM receiving end can adjust the signal-to-noise ratio of the system, and is convenient for testing the relation between the bit error rate and the optical signal-to-noise ratio. The input power to the photodetector is then controlled by a fixed optical attenuator. And finally, transmitting the signal to a 50G sampling oscilloscope, and performing signal processing on the obtained signal. And calculates the bit error rate by a series of digital signal processing operations, such as fourier transform, channel estimation, FPC removal, modulation, etc., mirrored at the transmitting end, and comparing the transmitted and received signals.

The Cumulative Distribution Function (also called Distribution Function) is an integral of the probability density Function, and can completely describe the probability Distribution of a real random variable X. The CCDF of different algorithms is calculated to judge the suppression situation of the algorithm to the PAPR of the OFDM signal. Wherein 10000 OFDM symbols are used to simulate different algorithms. The results are shown in FIG. 8. Wherein the pink line represents the C-OFDM signal, and the corresponding PAPR value is 13.5dB when CCDF is 10^ -3. Wherein the red curve, the green curve and the blue curve respectively represent the curves corresponding to the cumulative distribution functions of the FPC and the SLM algorithm at the random times of 50,100,150. As can be seen from the figure, when the random number is constant, the suppression capabilities of the SLM algorithm and the FPC algorithm are nearly coincident with each other. In addition, referring to fig. 8, a signal diagram of algorithms under different algorithms is drawn, and from top to bottom, the third bar represents a conventional OFDM signal, and it is obvious that the signal has many prominent peaks. The first graph and the second graph show the OFDM signals after being suppressed by the SLM algorithm and the FPC algorithm, so that the signals are more average, and high peak signals are obviously suppressed.

Referring to fig. 9, an initial length of 410 (20%) and 256 (50%) signals, where the length after PC coding is 512, are used as initial signals, in order to test the FPC Block structure proposed herein to an optimal structure, the length 410 herein simulates 40%, 45% and 50% of Block1, the remaining 60%, 55% and 50% of Block2, the red line indicates 50% of Block1, the green line indicates 45% of Block1, and the blue line indicates 40% of Block 1. From the simulation results, it can be found that the solution occupying 50% is the optimal solution. Meanwhile, when the initial length is 256, three schemes (30%, 70%), (40%, 60%), (50% ) are also designed, and the average allocation scheme has an optimal solution.

Referring to fig. 10, a comparison shows the comparison results after the SLM algorithm and the PC algorithm suppress the SLM algorithm for both algorithms. Two pink lines represent the BER curve of a conventional OFDM signal, and a red line represents the BER curve of a signal after the SLM algorithm. Blue and green represent the BER curves of the signal at 20% and 50% FPC redundancy, respectively. In addition, the circle indicates the signal of BTB, and the square indicates the signal after passing through the 80Km optical fiber. It is clear from the figure that the SLM algorithm has only 0.5dB gain at 10-3, while the FPC algorithm proposed herein has 4dB gain at 20% redundancy and 6.5dB gain at 0.5 redundancy.

It will be understood that the above embodiments are merely exemplary embodiments taken to illustrate the principles of the present invention, which is not limited thereto. It will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the spirit and substance of the invention, and these modifications and improvements are also considered to be within the scope of the invention.

Claims (2)

1. A method for probability PAPR suppression based on polarization code assistance is characterized by comprising the following steps:

dividing a signal to be encoded into a plurality of blocks;

coding the divided blocks by using a polarization code to obtain a plurality of transmission signals;

calculating the peak-to-average power ratio of the transmission signals, and selecting a transmission signal with the lowest peak-to-average power ratio for transmission;

wherein the dividing of the signal to be encoded into a plurality of blocks comprises:

determining whether the length of the signal to be encoded is odd or even,

if the number of the signals to be coded is an even number, dividing the signals to be coded into a first block and a second block, wherein the length sizes of the first block and the second block are equal;

and if the number is odd, equally dividing the signal into a third block and a fourth block, wherein the length dimension of the third block is larger than the length dimension of the fourth block by one unit dimension.

2. The method for probability PAPR suppression based on polarization code assistance according to claim 1, wherein the encoding the signal to be encoded by using polarization code comprises:

and carrying out parallel U-time coding on the signal to be coded, carrying out amplitude modulation QAM (quadrature amplitude modulation) and Inverse Fast Fourier Transform (IFFT), and sequencing a plurality of transmission signals in sequence, wherein U is a positive integer.

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