Odd-even subcarrier self-adaptive weighted merging method in asymmetric amplitude limiting orthogonal frequency division multiplexing system

Abstract

The invention discloses a self-adaptive weighted merging method for odd and even subcarriers in an asymmetric amplitude-limiting orthogonal frequency division multiplexing system, the method comprises two parts, namely a transmitting end process and a receiving end process, and the transmitting end comprises the following steps of: performing asymmetric amplitude-limiting orthogonal frequency division multiplexing modulation on data and then transmitting the data through a light-emitting component; a receiving end comprises the following steps: firstly, removing a cyclic prefix from a training sequence, and then obtaining frequency domain data through a Fourier transform module; secondly, respectively extracting data of odd and even subcarriers, re-importing the data into the inverse Fourier transform module to obtain time domain data, recovering data from even subcarrier information through the positive and negative characteristics of odd subcarrier time domain information, then transferring the data to a frequency domain through the Fourier transform module, and carrying out weighted merging on the data and odd subcarrier frequency domain data; thirdly, after the weighting coefficients are traversed, correlation coefficients of the combined data and the known training sequence are solved, and beta corresponding to the maximum correlation coefficient is taken out; and finally, extracting information source data to be demodulated, and using a weighting coefficient beta solved through a training sequence when even subcarrier data and odd subcarrier data are merged. According to the method, the optimal weighting coefficient in the current signal-to-noise ratio environment can be adaptively obtained, so that the asymmetric amplitude limiting orthogonal frequency division multiplexing system has high flexibility and low bit error rate.

Description

Technical Field

[0001] The invention belongs to the field of wireless optical communication, and in particular relates to an adaptive weighted combining method for odd and even subcarriers in an asymmetric limited orthogonal frequency division multiplexing system. Background Art

[0002] In recent years, as an emerging communication technology, wireless optical communication has gradually become a research hotspot in the field of communication due to its advantages such as rich spectrum resources and strong confidentiality. In order to improve the communication rate of wireless optical communication systems, orthogonal frequency division multiplexing technology is introduced. However, in asymmetric limited-amplitude orthogonal frequency division multiplexing systems, how to reduce the system bit error rate is an important issue.

[0003] In the traditional asymmetric limited-amplitude orthogonal frequency division multiplexing system, the bit data stream at the transmitter is first subjected to orthogonal amplitude modulation and then to Hermitian conjugate symmetric transformation. Next, the data is assigned to the odd subcarriers, and the even subcarriers are filled with zeros. Thereafter, the data is converted into a real signal through inverse Fourier transform, and then the signal is adjusted to a positive real number through limiting processing. Finally, after D / A digital-to-analog conversion, the signal is transmitted through the light-emitting element. The receiving end obtains the demodulated data after photoelectric conversion, amplification and A / D analog-to-digital conversion of the optical modulated signal, extracts and utilizes the information on the even subcarrier, and combines it with the information on the odd subcarrier through a fixed weighting coefficient to restore the original signal. However, this method of fixed weighting coefficients has certain limitations, especially in different signal-to-noise ratio environments, it cannot flexibly adapt to channel changes, resulting in a high bit error rate and affecting communication quality. Summary of the invention

[0004] The main problem solved by the present invention is that the receiving end of the asymmetric limited-orthogonal frequency division multiplexing system previously used a fixed weighting coefficient to combine the information on the odd and even subcarriers, which is not suitable for a variable channel environment. Therefore, the present invention proposes a method for adaptively changing the weighting coefficient, so that the receiving end can select the optimal value in different signal-to-noise ratio environments to perform weighted combination of odd and even subcarrier information, thereby achieving the effect of reducing the system bit error rate.

[0005] The present invention adopts the following technical solution:

[0006] Compared with the traditional method, the proposed solution adds training sequence modulation at the transmitter. The difference is that the orthogonal amplitude modulation is replaced by binary phase shift keying modulation, and the other processes are the same. The following will focus on the method of adaptively selecting the optimal weighting coefficient at the receiver through the training sequence. The specific steps are as follows:

[0007] (1) The received training sequence data is stripped of the cyclic prefix and subjected to Fourier transform. The information on the odd and even subcarriers is extracted and then sent to inverse Fourier transform to obtain the time domain signal. The even subcarrier information is corrected for its own positive or negative properties by the positive or negative properties of the odd subcarrier information.

[0008] (2) The time domain odd and even subcarrier data is converted back to the frequency domain through Fourier transform, and the weight ratio is β i The odd subcarrier data and weight ratio is (1-β i ), where i = 1, 2, 3, ..., M, and M represents the number of possible values ​​of β.

[0009] (3) Traverse β i The obtained data are combined with different weights and the correlation coefficient is calculated with the known training sequence, and the corresponding weight coefficient β′ when the correlation coefficient is the largest is found and waited for use.

[0010] In order to overcome the limitations of the traditional fixed weighting coefficient method, the present invention introduces an adaptive weighting coefficient method. In this method, the weighted combination coefficients of odd and even subcarriers are dynamically adjusted so as to select the optimal weighting value according to different channel conditions. The advantage of the adaptive weighting coefficient method is that it can flexibly adapt to different channel conditions, and can achieve more efficient signal recovery in both low signal-to-noise ratio and high signal-to-noise ratio environments.

[0011] The technical features and significant effects of the present invention are as follows:

[0012] The present invention proposes for the first time an adaptive weighted combination method for odd and even subcarriers in an asymmetric limited orthogonal frequency division multiplexing system, which can be applied to environments with different signal-to-noise ratios, has good flexibility, and can reduce the system bit error rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a flow chart of asymmetric limiting orthogonal frequency division multiplexing system.

[0014] Figure 2 It is a schematic diagram of the algorithm for adaptively calculating the weight coefficient β.

[0015] Figure 3 It can be seen that under different signal-to-noise ratio conditions, the bit error rate is lower after adding the adaptive algorithm than the traditional method. DETAILED DESCRIPTION

[0016] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0017] Example:

[0018] like Figure 1As shown in the figure, the transmitter process is that the source data undergoes orthogonal amplitude modulation and training sequence, undergoes binary phase shift keying modulation, Hermitian conjugate symmetry transformation, inverse Fourier transform, and adds a cyclic prefix before being limited to obtain a positive real signal, which is finally emitted through a light-emitting component. The receiver performs photoelectric conversion, amplification, A / D analog-to-digital conversion, and removes the cyclic prefix on the optical signal to obtain the data to be demodulated.

[0019] The source data to be demodulated uses the weighting coefficients selected by the adaptive algorithm to combine the odd and even subcarriers. Figure 2 As shown, data processing is performed in two parts.

[0020] Part 1: Using training sequences to find the optimal weighting coefficients.

[0021] S1, the training sequence is subjected to 64-point Fourier transform to extract the odd and even subcarrier information, where the odd subcarrier information is marked as Y odd =[0,Y1,0,Y3,…,0,Y 63 ], even subcarrier information is marked as Y even =[Y0,0,Y2,0,…,Y 62 ,0].

[0022] S2, put Y odd and Y even Input into the 64-point inverse Fourier transform to obtain the time domain signal y odd =[0,y1,0,y3,…,0,y 63 ] and y even =[y0,0,y2,0,…,y 62 ,0], then y even By y odd The positive and negative properties of the

[0023] S3, the parity subcarrier information after positive and negative correction is returned to the frequency domain through 64-point Fourier transform and combined by weighting coefficient β, as shown in the following formula

[0024] Y=β·Y odd +(1-β)·Y even

[0025] S4, divide β into nine possibilities. Traversing the weighted coefficient β, we can get nine weighted combined sequences. The correlation coefficients of different sequences and the known training sequence of length 16 X = [-1,-1,-1,1,-1,-1,1,1,-1,1,-1,1,1,1,-1] are calculated by the following formula, where and is the mean of each sequence. The β′ corresponding to the maximum correlation coefficient is saved for demodulation of the source data.

[0026]

[0027] Part 2: Use the β-weighted combined signal source obtained from the training sequence to obtain the parity subcarrier information of the demodulated data.

[0028] S1, the source data to be demodulated is subjected to 64-point Fourier transform to extract the odd and even subcarrier information, where the odd subcarrier information is marked as Y′ odd =[0,Y1′,0,Y3′,…,0,Y′ 63 ], the even subcarrier information is marked as Y′ even =[Y0′,0,Y2′,0,…,Y′ 62 ,0].

[0029] S2, put Y′ odd and Y′ even Input into the 64-point inverse Fourier transform to obtain the time domain signal y′ odd =[0,y1′,0,y3′,…,0,y′ 63 ] and y′ even =[y0′,0,y2′,0,…,y′ 62 ,0], then y′ even Through y′ odd The positive and negative properties of the

[0030] S3, the parity subcarrier information after positive and negative correction is returned to the frequency domain through Fourier transform, and the weighting coefficient β′ is calculated by the first part of the receiving end for merging, as shown in the following formula

[0031] Y′=β′·Y′ odd +(1-β′)·Y′ even

[0032] S4, demodulate Y′ using 4-QAM constellation diagram to get the original bit information. Figure 3 As shown, the system bit error rate after adding the adaptive algorithm has a lower bit error rate than the traditional method.

[0033] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for adaptively weighting and combining odd and even subcarriers in an asymmetric limited orthogonal frequency division multiplexing system, characterized in that: Receiving process part: (1) The photodetector receives the light signal, which is amplified and converted into analog-to-digital data to obtain the data to be demodulated. (2) After the cyclic prefix is ​​removed from the training sequence and the demodulated data of the source data, they are sent to the Fourier transform module respectively. (3) Extract the data using the even subcarrier and perform weighted combination with the odd subcarrier information. (4) Using the training sequence, an adaptive weighting coefficient algorithm is used to obtain the optimal weighting coefficient β′ under the current signal-to-noise ratio environment. (5) After the source data is Fourier transformed, the weight coefficient β′ obtained in step (4) is used to perform weighted combination of the odd and even subcarrier data, and the obtained data is sent to the constellation diagram for demodulation to restore the original information.

2. The method for adaptively weighting and combining odd and even subcarriers in an asymmetric limited-amplitude orthogonal frequency division multiplexing system according to claim 1, characterized in that: Step (4) comprises: S1, the training sequence is subjected to 64-point Fourier transform to extract the odd and even subcarrier information, where the odd subcarrier information is marked as Y odd =[0,Y1,0,Y3,…,0,Y 63 ], even subcarrier information is marked as Y even =[Y0,0,Y2,0,…,Y 62 ,0]. S2, put Y odd and Y even Input into the 64-point inverse Fourier transform to obtain the time domain signal y odd =[0,y1,0,y3,…,0,y 63 ] and y even =[y0,0,y2,0,…,y 62 ,0], then y even By y odd The positive and negative properties of the S3, the parity subcarrier information after positive and negative correction is returned to the frequency domain through 64-point Fourier transform and combined by weighting coefficient β, as shown in the following formula Y=β·Y odd +(1-β)·Y even S4, divide β into nine possibilities. Traversing the weighted coefficient β, we can get nine weighted combined sequences. The correlation coefficients of different sequences and the known training sequence of length 16 X = [-1,-1,-1,1,-1,-1,1,1,-1,1,-1,1,1,1,-1] are calculated by the following formula, where and is the mean of each sequence. The β′ corresponding to the maximum correlation coefficient is saved for demodulation of the source data.

3. The method for adaptively weighting and combining odd and even subcarriers in an asymmetric limited-amplitude orthogonal frequency division multiplexing system according to claim 1, characterized in that: Step (5) comprises: S1, the source data to be demodulated is subjected to 64-point Fourier transform to extract the odd and even subcarrier information, where the odd subcarrier information is marked as Y′ odd =[0,Y1′,0,Y3′,…,0,Y′ 63 ], the even subcarrier information is marked as Y′ even =[Y0′,0,Y2′,0,…,Y′ 62 ,0]. S2, put Y′ odd and Y′ even Input into the 64-point inverse Fourier transform to obtain the time domain signal y′ odd =[0,y′1,0,y′3,…,0,y′ 63 ] and y′ even =[y′0,0,y′2,0,…,y′ 62 ,0], then y′ even Through y′ odd The positive and negative properties of the S3, the parity subcarrier information after positive and negative correction is returned to the frequency domain through Fourier transform, and the weighting coefficient β′ is calculated by the first part of the receiving end for merging, as shown in the following formula Y′=β′·Y′ odd +(1-β′)·Y′ even S4, demodulate Y′ using 4-QAM constellation diagram to obtain the original bit information.

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