Peak-to-average power ratio suppression method for high energy-efficiency visible light FBMC system

Abstract

The present invention discloses a peak-to-average power ratio suppression method for a high-efficiency visible light FBMC system. First, user binary data or pseudo-random binary sequences are grouped and pulse amplitude modulated and mapped, and then multiplied with a real number precoding matrix, and then phase shifted, conjugated symmetric and N Point inverse fast Fourier transform, the upper branch IFFT output signal is processed by asymmetric limiting and the lower branch IFFT output signal is processed by multiphase network, and then multiplied by their respective power factors for power adjustment. N After a 1 / 2 data delay, the signal is added to the power-adjusted upper branch signal to generate a real baseband FBMC signal. Finally, after digital-to-analog conversion and electro-optical conversion, a high-efficiency optical FBMC signal is obtained. The real precoding technology of the present invention has lower computational complexity, reduces the signal's peak-to-average power ratio, and equalizes the data subcarrier signal-to-noise ratio, thus reducing system hardware implementation complexity and improving system performance.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a peak-to-average power ratio suppression method applied to a high-energy-efficiency visible light FBMC system. Background Art

[0002] Visible light communication (VLC) utilizes visible light in the 380nm to 780nm wavelength range as an information carrier. Its advantages include wide bandwidth, strong anti-interference capabilities, and immunity to electromagnetic interference. It holds broad application prospects in aerospace, deep-sea exploration, medical communications, and other fields. By adding data transmission auxiliary functions to LED lighting, a VLC wireless communication system can be constructed, enabling high-speed wireless information transmission. However, the narrow modulation bandwidth of conventional commercial LEDs limits the system's transmission rate. To fully utilize this limited bandwidth and increase the system's transmission rate, high-spectral-efficiency multi-carrier modulation formats have become a research hotspot.

[0003] Among various physical layer modulation technologies, orthogonal frequency-division multiplexing (OFDM) and filter bank multi-carrier (FBMC) modulation have attracted widespread attention due to their high spectral efficiency and robustness against multipath interference. Compared to OFDM, FBMC utilizes filters with superior time-frequency focusing properties to effectively reduce inter-subcarrier interference and adjacent channel leakage, while also improving spectral efficiency by saving cyclic prefixes.

[0004] Visible light FBMC systems mainly exist in the following two forms: direct current biased optical FBMC (DCO-FBMC) and asymmetrically clipped optical FBMC (ACO-FBMC). The DCO-FBMC system has high spectral efficiency but low energy efficiency; while the ACO-FBMC system has high energy efficiency but the disadvantage of low spectral efficiency. In order to balance spectral efficiency and improve the energy efficiency of the system, a high-energy-efficiency visible light FBMC scheme based on asymmetric clipping was proposed. For details, see the literature: S.Niu, P.Wang, S.Chi, Z.Liu, W.Pang and L.Guo, Enhanced Optical OFDM / OQAM for Visible Light Communication Systems, IEEE Wireless Communications Letters, vol.10, no.3, pp.614-618, 2021. However, the system still suffers from high peak-to-average power ratio (PAPR) problems and uneven signal-to-noise ratio (SNR) distribution on data subcarriers due to the limited LED modulation bandwidth, which affects the transmission performance of the high-efficiency visible light FBMC system.

[0005] Precoding technology can effectively suppress the PAPR of FBMC signals while equalizing the SNR on data subcarriers, significantly improving the receiver's bit error rate performance. However, traditional precoding techniques typically use complex precoding matrices, which have high computational complexity. Furthermore, due to the inconsistent number of digital subcarriers in the upper and lower branches of high-efficiency visible light FBMC systems, traditional complex precoding or low-complexity real precoding techniques cannot be directly applied to these systems. Therefore, exploring low-complexity real precoding techniques for high-efficiency visible light FBMC systems to reduce symbol PAPR and equalize data subcarrier SNR, thereby reducing system hardware implementation complexity and improving system performance, has certain application value. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a peak-to-average power ratio suppression method for a high-energy-efficiency visible light FBMC system with a simple algorithm.

[0007] The technical solution of the present invention to solve the above technical problems is: a method for suppressing the peak-to-average power ratio applied to a high-efficiency visible light FBMC system, comprising the following steps:

[0008] S1: In the FBMC baseband transmitter, the user binary data or pseudo-random binary sequence is divided into two groups, the upper branch and the lower branch, and mapped into corresponding frequency domain symbols according to the pulse amplitude modulation (PAM) method;

[0009] S2: After further grouping the mapped frequency domain symbols according to the number of valid data subcarriers in the upper and lower branches, they are multiplied by the predefined M-order real precoding matrix corresponding to the upper branch and the 2M-order real precoding matrix corresponding to the lower branch, respectively, to complete the real precoding operation;

[0010] S3: Phase shift, conjugate symmetry, and N-point inverse fast Fourier transform (IFFT) are performed on the precoded symbols of the upper and lower branches respectively; the upper branch IFFT output signal is subjected to asymmetric limiting processing and then to polyphase network processing together with the lower branch IFFT output signal;

[0011] S4: The upper and lower branch signals output by the multiphase network processing are multiplied by their respective power factors to achieve power adjustment. The power-adjusted lower branch signal is added to the power-adjusted upper branch signal after N / 2 data delays to generate a real baseband FBMC signal. After digital-to-analog conversion and electro-optical conversion, a high-efficiency visible light FBMC signal is obtained.

[0012] In the peak-to-average power ratio suppression method for a high-efficiency visible light FBMC system, in step S1, in the FBMC baseband transmitter, the serial user binary data or pseudo-random binary sequence is divided into two groups, the upper branch and the lower branch, and mapped into frequency domain symbols by pulse amplitude modulation. and and are the mth frequency domain symbols in the upper and lower branches respectively.

[0013] The peak-to-average power ratio suppression method applied to the high-efficiency visible light FBMC system, in step S2, the number of valid data subcarriers in the upper branch is M, the number of valid data subcarriers in the lower branch is 2M, and the column vector corresponding to each group of M frequency domain symbols after the upper branch is grouped is X u , after the lower branch is grouped, the column vector corresponding to each group of 2M frequency domain symbols is X l :

[0014]

[0015] Where T is the matrix transpose operation;

[0016] X u The M-order real number precoding matrix P corresponding to the predefined upper branch M×M Multiply to get the upper branch pre-coded symbol Y u , X lThe 2M-order real precoding matrix P corresponding to the lower branch 2M×2M Multiply to get the symbol Y of the lower branch precoding l , complete the real number precoding operation, Y u and Y l They are:

[0017]

[0018] The peak-to-average power ratio suppression method for a high-efficiency visible light FBMC system is applied to step S2. In the step S2, the real number precoding technology includes Walsh-Hadamard transform WHT, discrete cosine transform DCT and Hartley transform DHT. The precoding matrix used in WHT precoding is the Hadamard matrix, and the element located in the rth row and the cth column in the W-order precoding matrix used in DCT and DHT precoding is and Respectively expressed as:

[0019]

[0020] In the above-mentioned peak-to-average power ratio suppression method applied to a high-efficiency visible light FBMC system, in step S3, the pre-coded symbols on the upper and lower branches are phase-shifted to meet the real-domain orthogonality requirement of the FBMC modulation format. The specific operations are as follows:

[0021]

[0022] In the formula χ and η are the phase shift factor vectors of the upper and lower branches respectively, Z u With Z l are the matrix signals after phase shift of the upper and lower branches respectively, Represents the Hadamard product of two matrices.

[0023] The peak-to-average power ratio suppression method for the high-efficiency visible light FBMC system is applied to the step S3. After the pre-coded symbols on the upper and lower branches are phase-shifted, the upper and lower branches respectively perform conjugate symmetry and N-point inverse fast Fourier transform on the phase-shifted data. The IFFT output signal matrix of the kth group of upper branches is The IFFT output signal matrix of the kth group of lower branches for:

[0024]

[0025] In the formula is a matrix For every n elements in is a matrix The nth element in the array, where n ranges from 0 to N-1.

[0026] The peak-to-average power ratio suppression method for the high energy efficiency visible light FBMC system is applied. In step S3, the upper branch IFFT output signal is subjected to asymmetric limiting processing, i.e. AC processing to improve the energy efficiency of the system. The upper branch k-th group n-th point discrete signal after AC is Written as:

[0027]

[0028] The peak-to-average power ratio suppression method for the high-efficiency visible light FBMC system is applied to the step S3. After the AC upper branch signal is processed by the multiphase network, the dth output discrete signal is: After the IFFT output signal of the lower branch is processed by the multiphase network, the dth output discrete signal is and They are:

[0029]

[0030] Where h(n) is the impulse response sequence of the prototype filter, and d%N represents the remainder of d divided by N.

[0031] In the peak-to-average power ratio suppression method for a high-efficiency visible light FBMC system, in step S4, the power factors α and β are used to adjust the power of the upper and lower branch multiphase network output signals, respectively, to optimize system performance; the adjusted lower branch signal is added to the power-adjusted upper branch signal after N / 2 data delays to generate a real baseband FBMC signal s d for:

[0032]

[0033] Define the power ratio PR as 20log 10 (α / β), in dB. The generated real baseband FBMC signal undergoes digital-to-analog conversion and electro-optical conversion to obtain a high-efficiency visible light FBMC signal. After transmission through the visible light channel, it undergoes optical-to-electrical conversion and analog-to-digital conversion at the receiving end, and finally uses the receiver digital signal processing algorithm to recover the transmitted binary data.

[0034] The beneficial effects of the present invention are as follows: the present invention first groups user binary data or pseudo-random binary sequences in an FBMC baseband transmitter and performs pulse amplitude modulation mapping, then multiplies the data with a real precoding matrix, and then undergoes phase shifting, conjugate symmetry, and N-point inverse fast Fourier transform (IFFT). The upper branch IFFT output signal is processed by asymmetric limiting (AC) and the lower branch IFFT output signal is processed by a polyphase network (PPN). Then, the upper branch IFFT output signal is multiplied by its respective power factors for power adjustment. The power-adjusted lower branch signal is delayed by N / 2 data times and then added to the power-adjusted upper branch signal to generate a real baseband FBMC signal. Finally, a high-efficiency optical FBMC signal is obtained after digital-to-analog conversion and electro-optical conversion. Compared with traditional precoding technology that uses a complex precoding matrix (i.e., the matrix elements are complex numbers), the real precoding technology has lower computational complexity and can reduce symbol PAPR and equalize data subcarrier SNR, thereby reducing system hardware implementation complexity and improving system performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flowchart of the overall process of the present invention.

[0036] Figure 2 2 is a comparison diagram of PAPR complementary cumulative distribution function curves in an embodiment of the present invention.

[0037] Figure 3 4 is a signal-to-noise ratio comparison diagram in an embodiment of the present invention.

[0038] Figure 4 2 is a comparison diagram of bit error rates in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] like Figure 1 As shown, a peak-to-average power ratio suppression method for a high-efficiency visible light FBMC system includes the following steps:

[0041] S1: In the FBMC baseband transmitter, the user binary data or pseudo-random binary sequence is divided into two groups, the upper branch and the lower branch, and mapped into corresponding frequency domain symbols according to the pulse amplitude modulation (PAM) method.

[0042] In step S1, in the FBMC baseband transmitter, the serial user binary data or pseudo-random binary sequence is divided into two groups, upper and lower branches, and mapped into frequency domain symbols by pulse amplitude modulation. and and are the mth frequency domain symbols in the upper and lower branches respectively.

[0043] S2: After further grouping the mapped frequency domain symbols according to the number of valid data subcarriers in the upper and lower branches, they are multiplied by the predefined M-order real precoding matrix corresponding to the upper branch and the 2M-order real precoding matrix corresponding to the lower branch to complete the real precoding operation.

[0044] In step S2, the number of valid data subcarriers in the upper branch is M, the number of valid data subcarriers in the lower branch is 2M, and the column vector corresponding to each group of M frequency domain symbols after the upper branch is grouped is X u , after the lower branch is grouped, the column vector corresponding to each group of 2M frequency domain symbols is X l :

[0045]

[0046] Where T is the matrix transpose operation;

[0047] X u The M-order real number precoding matrix P corresponding to the predefined upper branch M×M Multiply to get the upper branch pre-coded symbol Y u , X l The 2M-order real precoding matrix P corresponding to the lower branch 2M×2M Multiply to get the symbol Y of the lower branch precoding l , complete the real number precoding operation, Y u and Y l They are:

[0048]

[0049] Real number precoding technologies include Walsh-Hadamard transform (WHT), discrete cosine transform (DCT), and Hartley transform (DHT). The precoding matrix used by WHT precoding is the Hadamard matrix, while the elements in the rth row and cth column of the W-order precoding matrix used by DCT and DHT precoding are and Respectively expressed as:

[0050]

[0051] S3: Phase shift, conjugate symmetry and N-point inverse fast Fourier transform IFFT are performed on the symbols pre-coded by the upper and lower branches respectively; the upper branch IFFT output signal is processed by asymmetric limiting and then subjected to polyphase network processing together with the lower branch IFFT output signal.

[0052] In step S3, the precoded symbols on the upper and lower branches are phase-shifted to meet the real domain orthogonality requirement of the FBMC modulation format. The specific operation is as follows:

[0053]

[0054] In the formula χ and η are the phase shift factor vectors of the upper and lower branches respectively, Z u With Z l are the matrix signals after phase shift of the upper and lower branches respectively, Represents the Hadamard product of two matrices.

[0055] After phase shifting the pre-coded symbols on the upper and lower branches, the upper and lower branches perform conjugate symmetry and N-point inverse fast Fourier transform on the phase-shifted data respectively. The IFFT output signal matrix of the kth group of upper branches is The IFFT output signal matrix of the kth group of lower branches for:

[0056]

[0057] In the formula is a matrix For every n elements in is a matrix The nth element in the array, where n ranges from 0 to N-1.

[0058] The upper branch IFFT output signal is processed by asymmetric limiting, that is, AC processing to improve the energy efficiency of the system. The upper branch k-th group n-th discrete signal after AC Written as:

[0059]

[0060] After the AC upper branch signal is processed by the multiphase network, the dth output discrete signal is After the IFFT output signal of the lower branch is processed by the multiphase network, the dth output discrete signal is and They are:

[0061]

[0062] Where h(n) is the impulse response sequence of the prototype filter, and d%N represents the remainder of d divided by N.

[0063] S4: The upper and lower branch signals output by the multiphase network processing are multiplied by their respective power factors to achieve power adjustment. The power-adjusted lower branch signal is added to the power-adjusted upper branch signal after N / 2 data delays to generate a real baseband FBMC signal. After digital-to-analog conversion and electro-optical conversion, a high-efficiency visible light FBMC signal is obtained.

[0064] In step S4, the power factors α and β are used to adjust the power of the upper and lower branch multiphase network output signals respectively to optimize the system performance; the adjusted lower branch signal is added to the power-adjusted upper branch signal after N / 2 data delays to generate a real baseband FBMC signal s d for:

[0065]

[0066] Define the power ratio PR as 20log 10 (α / β), in dB. The generated real baseband FBMC signal undergoes digital-to-analog conversion and electro-optical conversion to obtain a high-efficiency visible light FBMC signal. After transmission through the visible light channel, it undergoes optical-to-electrical conversion and analog-to-digital conversion at the receiving end, and finally uses the receiver digital signal processing algorithm to recover the transmitted binary data.

[0067] Compared with the complex precoding matrix of traditional precoding technology (i.e., the matrix elements are complex numbers), real precoding technology has lower computational complexity, and can reduce symbol PAPR and equalize data subcarrier SNR, reduce system hardware implementation complexity and improve system performance.

[0068] To verify the effectiveness of the present invention, a digital signal processing algorithm at the FBMC transmitter end was implemented based on software programming, and numerical simulation analysis was performed. The FBMC signal parameters are as follows: the number of IFFT points is 256, the number of valid data subcarriers in the upper and lower branches is 48 and 96 respectively, and the other subcarriers are set to zero. The PPN uses the PHYDYAS prototype filter.

[0069] Figure 2 The complementary cumulative distribution function curve of the peak-to-average power ratio of the signal obtained by statistically analyzing 100,000 randomly generated FBMC symbols after 4 times oversampling. -4 When using precoding technology, the peak-to-average power ratio of the signal can be reduced by up to 4dB compared to not using precoding technology.

[0070] To further evaluate the subcarrier signal-to-noise ratio equalization capability of the present invention, a first-order low-pass filter is used to simulate a bandwidth-limited LED model (-3dB bandwidth is 50MHz). Signal transmission only considers the additive white Gaussian noise channel, the signal bandwidth is 375MHz, and the SNR is set to 25dB. Figure 3 The figure shows the SNR distribution of different data subcarriers estimated by the receiver after a frame of FBMC signal (including 1000 FBMC symbols) is transmitted through the channel when the PR is 4dB. Figure 3It can be seen that when precoding is not used, the two branches have a signal-to-noise ratio fluctuation of about 15dB due to frequency selective power fading caused by the limited bandwidth of the LED. The precoding technology of the present invention can reduce the signal-to-noise ratio fluctuation to below 3dB, achieving a better subcarrier SNR equalization effect.

[0071] Figure 4 The figure shows the distribution of the bit error rate (BER) calculated for a frame of FBMC signal after transmission through the channel as a function of the power ratio (PR) of the upper and lower branch signals. This shows that the real precoding technology proposed in this invention can significantly reduce the BER. When the PR is 4 dB, the BER of the FBMC signal generated using real precoding is reduced by approximately an order of magnitude compared to the signal without precoding.

[0072] In summary, the present invention can not only effectively reduce the peak-to-average power ratio of the signal in the high-efficiency visible light FBMC system, thereby reducing nonlinear distortion, but also balance the signal-to-noise ratio distribution on the data subcarriers and improve the bit error rate performance of the system.

Claims

1. A peak-to-average power ratio suppression method for a high-efficiency visible light FBMC system, characterized in that: The following steps are involved: S1: In the FBMC baseband transmitter, the user binary data or pseudo-random binary sequence is divided into two groups, the upper branch and the lower branch, and mapped into corresponding frequency domain symbols according to the pulse amplitude modulation (PAM) method; S2: After further grouping the mapped frequency domain symbols according to the number of valid data subcarriers in the upper and lower branches, they are multiplied by the predefined M-order real precoding matrix corresponding to the upper branch and the 2M-order real precoding matrix corresponding to the lower branch, respectively, to complete the real precoding operation; S3: Phase shift, conjugate symmetry, and N-point inverse fast Fourier transform (IFFT) are performed on the precoded symbols of the upper and lower branches respectively; the upper branch IFFT output signal is subjected to asymmetric limiting processing and then to polyphase network processing together with the lower branch IFFT output signal; S4: The upper and lower branch signals output by the multiphase network processing are multiplied by their respective power factors to achieve power adjustment. The power-adjusted lower branch signal is added to the power-adjusted upper branch signal after N / 2 data delays to generate a real baseband FBMC signal. After digital-to-analog conversion and electro-optical conversion, a high-efficiency visible light FBMC signal is obtained.

2. The peak-to-average power ratio suppression method for a high-efficiency visible light FBMC system according to claim 1, characterized in that: In step S1, in the FBMC baseband transmitter, the serial user binary data or pseudo-random binary sequence is divided into two groups, upper and lower branches, and mapped into frequency domain symbols by pulse amplitude modulation. and and are the mth frequency domain symbols in the upper and lower branches respectively.

3. The peak-to-average power ratio suppression method for a high-efficiency visible light FBMC system according to claim 1, characterized in that: In step S2, the number of valid data subcarriers in the upper branch is M, the number of valid data subcarriers in the lower branch is 2M, and the column vector corresponding to each group of M frequency domain symbols after the upper branch is grouped is X u , after the lower branch is grouped, the column vector corresponding to each group of 2M frequency domain symbols is X l : Where T is the matrix transpose operation; X u The M-order real number precoding matrix P corresponding to the predefined upper branch M×M Multiply to get the upper branch pre-coded symbol Y u , X l The 2M-order real precoding matrix P corresponding to the lower branch 2M×2M Multiply to get the symbol Y of the lower branch precoding l , complete the real number precoding operation, Y u and Y l They are:

4. The peak-to-average power ratio suppression method for a high-efficiency visible light FBMC system according to claim 3, characterized in that: In step S2, the real number precoding technology includes Walsh-Hadamard transform WHT, discrete cosine transform DCT and Hartley transform DHT, wherein the precoding matrix used by WHT precoding is Hadamard matrix, and the element located in the rth row and cth column of the W-order precoding matrix used by DCT and DHT precoding is and Respectively expressed as:

5. The peak-to-average power ratio suppression method for a high-efficiency visible light FBMC system according to claim 3, characterized in that: In step S3, the precoded symbols on the upper and lower branches are phase-shifted to meet the real domain orthogonality requirement of the FBMC modulation format. The specific operation is as follows: In the formula χ and η are the phase shift factor vectors of the upper and lower branches respectively, Z u With Z l are the matrix signals after phase shift of the upper and lower branches respectively, Represents the Hadamard product of two matrices.

6. The peak-to-average power ratio suppression method for a high-efficiency visible light FBMC system according to claim 5, characterized in that: In step S3, after the pre-coded symbols on the upper and lower branches are phase-shifted, the upper and lower branches respectively perform conjugate symmetry and N-point inverse fast Fourier transform on the phase-shifted data, and the kth group of upper branch IFFT output signal matrix The IFFT output signal matrix of the kth group of lower branches for: In the formula is a matrix The nth element in is a matrix The nth element in the array, where n ranges from 0 to N-1.

7. The peak-to-average power ratio suppression method for a high-efficiency visible light FBMC system according to claim 6, characterized in that: In step S3, the upper branch IFFT output signal is processed by asymmetric limiting, that is, AC processing to improve the energy efficiency of the system. The upper branch k-th group n-th point discrete signal after AC Written as:

8. The peak-to-average power ratio suppression method for a high-efficiency visible light FBMC system according to claim 7, characterized in that: In step S3, after the AC-passed upper branch signal is processed by a multiphase network, the dth output discrete signal is: After the IFFT output signal of the lower branch is processed by the multiphase network, the dth output discrete signal is and They are: Where h(n) is the impulse response sequence of the prototype filter, and d%N represents the remainder of d divided by N.

9. The peak-to-average power ratio suppression method for a high-efficiency visible light FBMC system according to claim 8, characterized in that: In step S4, the power factors α and β are used to adjust the power of the upper and lower branch multiphase network output signals respectively to optimize the system performance; the adjusted lower branch signal is added to the power-adjusted upper branch signal after N / 2 data delays to generate a real baseband FBMC signal s d for: Define the power ratio PR as 20log 10 (α / β), in dB. The generated real baseband FBMC signal undergoes digital-to-analog conversion and electro-optical conversion to obtain a high-efficiency visible light FBMC signal. After transmission through the visible light channel, it undergoes optical-to-electrical conversion and analog-to-digital conversion at the receiving end, and finally uses the receiver digital signal processing algorithm to recover the transmitted binary data.

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