An orthogonal frequency division multiplexing transmission method based on dirty paper coding

Abstract

This invention discloses an orthogonal frequency division multiplexing (OFDM) transmission method based on dirty paper coding, belonging to the field of wireless communication technology. At the transmitting end, at least two layers of frequency domain symbols to be transmitted are generated. A first-layer OFDM signal is generated from the first-layer frequency domain symbols and non-negatively clipped in the time domain to generate first-layer clipped noise. The cumulative clipped noise from the first layer to the (h-1)th (h≥2)th layer is used as interference signal to perform dirty paper coding pre-coding on the h-th layer of the frequency domain symbols to be transmitted, generating pre-coded frequency domain symbols, and then generating the h-th layer OFDM signal. The OFDM signals of each layer are superimposed and transmitted. At the receiving end, after performing a fast Fourier transform on the received signal, the received frequency domain symbols of each layer are extracted from the received frequency domain signal and decoded independently. This invention eliminates deterministic interference between layered signals through dirty paper coding pre-coding at the transmitting end, eliminating the need for serial interference cancellation at the receiving end, avoiding error propagation problems, and significantly reducing the computational complexity at the receiving end.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and specifically to an orthogonal frequency division multiplexing transmission method based on dirty paper coding. Background Technology

[0002] OFDM (Orthogonal Frequency Division Multiplexing) is a high-speed communication technology suitable for small-size, power-constrained scenarios. In IM / DD (Intensity Modulation / Direct Demodulation) optical systems, light sources such as LEDs (Light Emitting Diodes) require the transmitted signal to be a non-negative real number. The bipolar complex signal generated by traditional electrical domain OFDM cannot directly drive LEDs, thus requiring modification of the OFDM signal. To address this issue, various optical orthogonal frequency division multiplexing schemes have been proposed. Among them, DCO-OFDM (Direct Current Optical Orthogonal Frequency Division Multiplexing) is one of the most direct solutions, satisfying the non-negative constraint by superimposing a sufficient DC bias onto the bipolar OFDM signal. This method is simple to implement, all subcarriers can be used for data transmission, and it has high spectral efficiency. However, the DC bias itself does not carry information, resulting in low system power efficiency, and the bias magnitude needs to be dynamically adjusted according to the signal amplitude, leading to some power waste.

[0003] To improve power efficiency, ACO-OFDM (Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing) was proposed. This scheme uses only odd-numbered subcarriers to transmit data, performing non-negative clipping on the time-domain signal. Since the clipping noise is distributed only on even-numbered subcarriers and remains orthogonal to the data subcarriers, the receiver can directly recover the data without additional processing. ACO-OFDM has relatively ideal power efficiency, but its spectral efficiency is halved, with only 50% of the subcarriers available for data transmission, making it difficult to meet the demands of high-speed communication.

[0004] To achieve a better balance between spectral efficiency and power efficiency, ADO-OFDM (Asymmetrically Clipped Direct Current Optical Orthogonal Frequency Division Multiplexing) was proposed. ADO-OFDM combines ACO-OFDM and DCO-OFDM, where the ACO (Asymmetrically Clipped Optical) branch uses odd-numbered subcarriers, and the DCO (Direct Current Optical) branch uses even-numbered subcarriers. The receiver needs to employ serial interference cancellation technology to first decode the ACO branch signal, reconstruct and eliminate its interference with the DCO branch, and then decode the DCO branch. This scheme improves spectral efficiency while maintaining high power efficiency. Building on this, LACO-OFDM (Layered Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing) further extends the multi-layer structure. LACO-OFDM superimposes multiple layers of ACO-OFDM signals, with each layer using an orthogonal set of subcarriers. The first layer uses odd-numbered subcarriers, the second layer uses subcarriers with indices divisible by 2 but not by 4, and so on. The receiver requires multi-stage SIC (Successive Interference Cancellation), decoding layer by layer starting from the first layer. After decoding each layer, the signal of that layer is reconstructed and removed from the received signal to reduce interference to subsequent layers. LACO-OFDM further improves spectral efficiency and outperforms DCO-OFDM in power efficiency.

[0005] Although the LACO-OFDM scheme achieves a good balance between spectral efficiency and power efficiency, the SiC (Sequential Injection) technology commonly used in its receivers has inherent drawbacks. First, SiC suffers from error propagation; decoding errors in previous layers propagate to all subsequent layers, severely degrading system reliability, especially in low signal-to-noise ratio (SNR) or multi-layer stacking scenarios, where bit error rate performance deteriorates significantly. Second, the SiC receiver requires multiple Fast Fourier Transform (FFT) and interference reconstruction operations, with the computational burden increasing significantly with the number of layers, making it unbearable for mobile terminals or low-power devices. Furthermore, SiC relies on accurate interference reconstruction and is extremely sensitive to channel estimation and synchronization errors; in real-world multi-user or mobile scenarios, fluctuations in channel conditions further worsen SiC performance. Finally, the receiver requires a complete interference estimation and cancellation link, increasing hardware implementation complexity and power consumption.

[0006] In summary, there is an urgent need in this field for an orthogonal frequency division multiplexing transmission method that can maintain high spectral efficiency while avoiding error propagation and reducing the computational complexity of the receiver. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides an orthogonal frequency division multiplexing transmission method based on dirty paper coding. By precoding known clipping noise at the transmitting end, deterministic interference between layered signals is eliminated, allowing the receiving end to independently decode each layer of signals without serial interference cancellation. This avoids error propagation, significantly reduces the computational complexity at the receiving end, and maintains high spectral efficiency.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention proposes an orthogonal frequency division multiplexing transmission method based on dirty paper coding, comprising:

[0010] At the transmitting end, at least two layers of frequency domain symbols to be transmitted are generated. The first layer of frequency domain symbols to be transmitted is subjected to inverse fast Fourier transform (IFFT) to generate the first layer of OFDM signal. The first layer of OFDM signal is non-negatively truncated in the time domain to generate the first layer of truncated noise.

[0011] For the The frequency domain symbols to be transmitted are from the first layer to the second layer. The accumulated trimming noise of the layer is used as an interference signal for dirty paper coding precoding to generate the first layer. The precoded frequency domain symbols corresponding to the layer are used to generate the first layer. Layer OFDM signal;

[0012] The OFDM signals from each layer are superimposed and then transmitted.

[0013] At the receiving end, after performing a fast Fourier transform on the received signal, a frequency domain received signal is obtained. The received frequency domain symbols of each layer are extracted from the frequency domain received signal, and each layer of received frequency domain symbols is decoded independently.

[0014] Furthermore, the dirty paper coding precoding includes:

[0015] Construct auxiliary variables based on the frequency domain symbols to be transmitted and the interference signals;

[0016] The auxiliary variable is moduloed according to a preset modulus, and mapped to a preset basic region to obtain an integer offset.

[0017] The precoded frequency domain symbol is generated based on the integer offset and the interference signal.

[0018] Furthermore, the integer offset is calculated using the following formula:

[0019]

[0020]

[0021]

[0022] In the formula, Integer offset The offset is the integer part of the real part. The imaginary part is the integer offset. as auxiliary variables The real part, as auxiliary variables The imaginary part, For the preset modulus, To round down, The imaginary unit, For absolute values, It is a symbolic function.

[0023] Furthermore, the preset basic area is:

[0024]

[0025] in For the preset basic area, Let be any complex number in the complex plane. for The real part, for The imaginary part, For the preset modulus, It is an absolute value.

[0026] Furthermore, the preset modulus is calculated using the following formula:

[0027]

[0028] In the formula, For the preset modulus, The minimum Euclidean distance for modulating constellations. This represents the modulation order.

[0029] Furthermore, the method is used for ADO-OFDM transmission:

[0030] The frequency domain symbols to be transmitted on the ACO branch are used as the first layer of frequency domain symbols to be transmitted. The ACO branch uses subcarriers with odd indices. The OFDM signal of the ACO branch is non-negatively clipped to generate the first layer of clipped noise.

[0031] The frequency domain symbols to be transmitted in the DCO branch are used as the second-layer frequency domain symbols to be transmitted. The DCO branch uses subcarriers with even-numbered indices and uses the frequency domain components of the first-layer clipped noise on the even-numbered subcarriers as interference signals to perform dirty paper coding precoding on the second-layer frequency domain symbols to be transmitted.

[0032] Furthermore, the method is used for LACO-OFDM transmission:

[0033] The first layer OFDM signal is generated using the ACO-OFDM method. The first layer OFDM signal is then non-negatively clipped to generate the first layer clipping noise.

[0034] For the The frequency domain symbols to be transmitted in the first layer to the second layer are... The cumulative clipping noise of the layer, in its frequency domain component on the corresponding subcarrier, is used as an interference signal for dirty paper coding precoding, where the first... Layers are used from the first layer to the second layer. A set of subcarriers that are orthogonal to the layer.

[0035] Furthermore, the cumulative clipping noise is calculated using the following formula:

[0036]

[0037] In the formula, To accumulate cutting noise, For the first Layer cutting noise, This is the index for the sampling points.

[0038] Furthermore, the independent decoding includes:

[0039] For subcarriers with odd indices, their corresponding received frequency domain symbols are directly demodulated;

[0040] For subcarriers with even indices, their corresponding received frequency domain symbols are demodulated after modulo operations.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] (1) This invention treats the clipping noise generated by the layered signal as known interference at the transmitter and uses dirty paper coding precoding to eliminate inter-layer deterministic interference at the transmitter. Since the interference cancellation process is completed at the transmitter, the receiver does not need to perform serial interference cancellation, and each layer signal can be decoded independently and in parallel, fundamentally avoiding the problem of backward propagation of decoding errors from the previous layer in traditional serial interference cancellation methods. At the same time, the receiver only needs one fast Fourier transform and symbol-by-symbol modulo operation, without the need for multiple transformations and interference reconstruction, transferring the main computational task to the transmitter, which significantly reduces the complexity of the receiver and the power consumption of the user equipment.

[0043] (2) The present invention adopts a layered structure, with each layer using an orthogonal set of subcarriers, making full use of subcarrier resources and achieving a high subcarrier utilization rate. At the same time, inter-layer interference is eliminated by dirty paper coding precoding at the transmitting end, and the signals of each layer can be decoded independently at the receiving end, avoiding the error propagation problem caused by serial interference cancellation in traditional methods, and achieving high reliability transmission while maintaining high spectral efficiency.

[0044] (3) In this invention, the frequency domain symbols are pre-coded with dirty paper coding at the transmitting end, and the pre-coded frequency domain symbols are converted into time domain signals by inverse fast Fourier transform. Since dirty paper coding pre-coding constrains the transmitted symbols during the modulus operation, the amplitude distribution of the time domain signal is more uniform, thereby effectively reducing the peak-to-average power ratio of the system, alleviating the pressure on the nonlinear devices at the transmitting end, and improving the overall stability of the system. Attached Figure Description

[0045] Figure 1 A flowchart of the orthogonal frequency division multiplexing transmission method based on dirty paper coding provided by the present invention;

[0046] Figure 2 A comparison of the receiving constellation diagrams of the DCO branch in the traditional ADO-OFDM transmission method and the transmission method provided in Embodiment 1 of the present invention is shown, wherein (a) is the receiving constellation diagram of the DCO branch in the traditional ADO-OFDM transmission method, and (b) is the receiving constellation diagram of the DCO branch in the transmission method provided in Embodiment 1 of the present invention.

[0047] Figure 3 A comparison chart of the bit error rate performance between the traditional ADO-OFDM transmission method and the transmission method provided in Embodiment 1 of the present invention;

[0048] Figure 4A comparison of the receiving constellation diagrams of each layer in the traditional LACO-OFDM transmission method and the transmission method provided in Embodiment 2 of the present invention is shown, wherein (a)-(c) are the receiving constellation diagrams of the second to fourth layers in the traditional LACO-OFDM transmission method, and (d)-(f) are the receiving constellation diagrams of the second to fourth layers in the transmission method provided in Embodiment 2 of the present invention.

[0049] Figure 5 This is a comparison chart of the bit error rate performance of each layer in the traditional LACO-OFDM transmission method and the transmission method provided in Embodiment 2 of the present invention. Detailed Implementation

[0050] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] Example 1

[0052] This embodiment provides an orthogonal frequency division multiplexing transmission method based on dirty paper coding for ADO-OFDM transmission.

[0053] In this embodiment, the system parameters are set as follows:

[0054] Total number of subcarriers : , ,Right now ;

[0055] Exclude DC subcarriers and Nyquist subcarriers;

[0056] Modulation method: 16QAM, modulation order M=16, minimum Euclidean distance of constellation =2;

[0057] Cyclic prefix length: 64 sampling points;

[0058] DC bias coefficient: Take 3 times the maximum signal value to ensure linear operating range.

[0059] The transmission method provided in this embodiment is performed according to the following steps:

[0060] At the sending end:

[0061] S1, transfer the frequency domain symbols to be transmitted on the ACO branch. As the first layer of frequency domain symbols to be transmitted, The index of the frequency domain symbol to be transmitted. The frequency domain symbols to be transmitted Mapped to subcarriers with odd indices:

[0062]

[0063] In the formula, Indicates that the index is The frequency domain symbol sequence on the subcarrier. Factor 2 is used to compensate for the 3dB power loss in the ACO-OFDM system caused by subsequent non-negative clipping.

[0064] S2. To ensure that a real signal is obtained after IFFT, the frequency domain symbol sequence is... By applying conjugate symmetry conditions, a frequency domain symbol sequence satisfying conjugate symmetry is obtained. That is, frequency domain symbol sequence satisfy:

[0065]

[0066] At the same time, the DC subcarrier and Nyquist subcarrier are set to zero:

[0067] , ;

[0068] Other unassigned subcarriers remain at zero.

[0069] In the formula, for . conjugate.

[0070] S3. For frequency domain symbol sequences that satisfy conjugate symmetry Perform IFFT to obtain the OFDM signal of the ACO branch. :

[0071]

[0072] In the formula, For time-domain sampling point index, It is the imaginary unit.

[0073] S4. To meet the requirement of non-negativity of signals for light sources such as LEDs, OFDM signals... Non-negative clipping generates clipping noise. :

[0074]

[0075]

[0076] In the formula, This is the signal after non-negative clipping.

[0077] Clipping noise using FFT Transform to the frequency domain to obtain the signal :

[0078]

[0079] S5. Transfer the frequency domain symbols to be transmitted on the DCO branch. As the second layer of frequency domain symbols to be transmitted, For subcarrier index, -2;

[0080] With signal Frequency domain components on even-numbered subcarriers As an interference signal, the second-layer frequency domain symbols to be transmitted are pre-coded using dirty paper coding. The specific process is as follows:

[0081] S501, Based on the frequency domain symbol to be transmitted Interference signals Constructing auxiliary variables :

[0082]

[0083] S502, according to the preset module For auxiliary variables Perform modular arithmetic to map it to a preset basic region. Within, obtain the integer offset. :

[0084]

[0085]

[0086]

[0087]

[0088]

[0089] In the formula, Let be any complex number in the complex plane. for The real part, for The imaginary part, The offset is the integer part of the real part. The imaginary part is the integer offset. For symbolic functions, For absolute values, To round down, as auxiliary variables The real part, as auxiliary variables The imaginary part, The imaginary unit, The minimum Euclidean distance for modulating constellations. This represents the modulation order.

[0090] S503, Based on integer offset Interference signals Generate precoded frequency domain symbols :

[0091]

[0092] S6. Convert the pre-encoded frequency domain symbols Mapped to subcarriers with even indices:

[0093]

[0094] In the formula, Indicates that the index is The frequency domain symbol sequence on the subcarrier.

[0095] To ensure that a real signal is obtained after IFFT, the frequency domain symbol sequence is... By applying conjugate symmetry conditions, a frequency domain symbol sequence satisfying conjugate symmetry is obtained. That is, frequency domain symbol sequence satisfy:

[0096] ;

[0097] At the same time, the DC subcarrier and Nyquist subcarrier are set to zero:

[0098] , ;

[0099] Other unassigned subcarriers remain at zero.

[0100] In the formula, for . conjugate.

[0101] S7. For frequency domain symbol sequences that satisfy conjugate symmetry Perform IFFT to obtain the OFDM signal of the DCO branch. :

[0102]

[0103] In the formula, For time-domain sampling point index, It is the imaginary unit.

[0104] S8, transfer the OFDM signal of the ACO branch. OFDM signal of DCO branch Superposition yields the superimposed signal. :

[0105]

[0106] To ensure the transmitted signal is non-negative, the superimposed signal is... Add DC bias :

[0107]

[0108] In the formula, To transmit signals;

[0109] To ensure a linear work area, .

[0110] To transmit signals After adding a cyclic prefix, drive the LED array to emit.

[0111] At the receiving end:

[0112] Step 1: After the photodetector at the receiving end receives the signal transmitted by the transmitting end, it removes the cyclic prefix and DC bias to obtain the time-domain received signal. .

[0113] Step 2: Receive the signal in the time domain. Perform an FFT transform to obtain the frequency domain received signal. .

[0114] Step 3: Receive signal from the frequency domain Extract the received frequency domain symbols from each layer:

[0115] For subcarriers with odd indices, extract their frequency domain symbols as the first-layer received frequency domain symbols;

[0116] For subcarriers with even indices, extract their frequency domain symbols as the second-layer received frequency domain symbols.

[0117] Step 4: Decode the received frequency domain symbols of each layer independently:

[0118] The first layer received frequency domain symbols are directly demodulated using 16QAM to recover the ACO tributary data;

[0119] Perform modulo operations on the second-layer received frequency domain symbols to map them to the basic region; detect the minimum distance and recover the DCO branch data.

[0120] Example 2

[0121] This embodiment provides an orthogonal frequency division multiplexing transmission method based on dirty paper coding for LACO-OFDM transmission.

[0122] In this embodiment, the parameters are set as follows:

[0123] Total number of subcarriers : , ,Right now ;

[0124] Total number of floors H: H=4;

[0125] Exclude DC subcarriers and Nyquist subcarriers;

[0126] Modulation method: 64QAM, modulation order M=64, minimum Euclidean distance of constellation =2;

[0127] Subcarrier allocation:

[0128] The first layer uses subcarriers with odd-numbered indices, with the index set K1={1,3,5,...,F-1};

[0129] The second layer uses subcarriers whose indices are divisible by 2 but not by 4, with the index set K2={2,6,10,...,F-2};

[0130] The third layer uses subcarriers whose indices are divisible by 4 but not by 8, with the index set K3={4,12,20,...,F-4}.

[0131] The fourth layer uses subcarriers whose indices are divisible by 8 but not by 16, with the index set K4={8,24,40,...,F-8};

[0132] The subcarriers of each layer are orthogonal;

[0133] Cyclic prefix length: 128 sampling points;

[0134] DC bias coefficient: Take 3 times the maximum signal value to ensure linear operating range.

[0135] The transmission method provided in this embodiment is performed according to the following steps:

[0136] At the sending end:

[0137] S1, First Layer Processing

[0138] S101. In this embodiment, the first layer is the ACO branch, which transmits the frequency domain symbols of the first layer. As the first layer of frequency domain symbols to be transmitted, The index of the frequency domain symbol to be transmitted. The frequency domain symbols to be transmitted Mapped to subcarriers with odd indices:

[0139]

[0140] In the formula, Indicates that the index is The frequency domain symbol sequence on the subcarrier. Factor 2 is used to compensate for the 3dB power loss in the ACO-OFDM system caused by subsequent non-negative clipping.

[0141] S102. To ensure that a real signal is obtained after IFFT, the frequency domain symbol sequence is... By applying conjugate symmetry conditions, a frequency domain symbol sequence satisfying conjugate symmetry is obtained. That is, frequency domain symbol sequence satisfy:

[0142]

[0143] At the same time, the DC subcarrier and Nyquist subcarrier are set to zero:

[0144] , ;

[0145] Other unassigned subcarriers remain at zero.

[0146] In the formula, for . conjugate.

[0147] S103, For frequency domain symbol sequences that satisfy conjugate symmetry Perform IFFT to obtain the first layer OFDM signal. :

[0148]

[0149] In the formula, For time-domain sampling point index, It is the imaginary unit.

[0150] S104. To meet the requirement of non-negativity of signals for light sources such as LEDs, OFDM signals... Perform non-negative clipping, generating the first layer of clipping noise. :

[0151]

[0152]

[0153] In the formula, This is the signal after non-negative clipping.

[0154] Clipping noise using FFT Transform to the frequency domain to obtain the signal :

[0155]

[0156] S2, Second Layer Processing

[0157] S201, with signal Frequency domain components on the second layer subcarrier As an interference signal, the second layer of frequency domain symbols to be transmitted Perform dirty paper coding and precoding:

[0158] S2011, Based on the frequency domain symbols to be transmitted Interference signals Construct the auxiliary variables corresponding to the second layer :

[0159]

[0160]

[0161] S2012, According to the preset module For auxiliary variables Perform modular arithmetic to map it to a preset basic region. Within, obtain the integer offset. :

[0162]

[0163]

[0164]

[0165] In the formula, Let be any complex number in the complex plane. for The real part, for The imaginary part, For symbolic functions, For absolute values, To round down, as auxiliary variables The real part, as auxiliary variables The imaginary part, The imaginary unit, This represents the minimum Euclidean distance for the modulated constellation.

[0166] S2013, Based on the integer offset Interference signals Generate precoded frequency domain symbols :

[0167]

[0168] S202, convert the pre-encoded frequency domain symbols Mapped to the second-layer subcarrier:

[0169]

[0170] In the formula, Indicates that the index is The frequency domain symbol sequence on the subcarrier.

[0171] To ensure that a real signal is obtained after IFFT, the frequency domain symbol sequence is... By applying conjugate symmetry conditions, a frequency domain symbol sequence satisfying conjugate symmetry is obtained. That is, frequency domain symbol sequence satisfy:

[0172] ;

[0173] At the same time, the DC subcarrier and Nyquist subcarrier are set to zero:

[0174] , ;

[0175] Other unassigned subcarriers remain at zero.

[0176] In the formula, for . conjugate.

[0177] S203, For frequency domain symbol sequences that satisfy conjugate symmetry Perform IFFT to obtain the second-layer OFDM signal. :

[0178]

[0179] In the formula, For time-domain sampling point index, It is the imaginary unit.

[0180] S204, OFDM signal Non-negative clipping generates clipping noise. :

[0181]

[0182]

[0183] In the formula, This is the signal after non-negative clipping.

[0184] Clipping noise using FFT Transform to the frequency domain to obtain the signal :

[0185]

[0186] S3, Third Layer Processing

[0187] S301, Reduce the cumulative noise from the first and second layers. Frequency domain components on the third-layer subcarrier As an interference signal, the third-layer frequency domain symbol to be transmitted Perform dirty paper coding and precoding:

[0188] S3011, Based on the frequency domain symbols to be transmitted Interference signals Construct the auxiliary variables corresponding to the third layer :

[0189]

[0190]

[0191]

[0192] S3012, According to the preset module For auxiliary variables Perform modular arithmetic to map it to a preset basic region. Within, obtain the integer offset. :

[0193]

[0194] In the formula, For symbolic functions, For absolute values, To round down, as auxiliary variables The real part, as auxiliary variables The imaginary part.

[0195] S3013, Based on the integer offset Interference signals Generate precoded frequency domain symbols :

[0196]

[0197] S302. Generate the third-layer OFDM signal in the same manner as the second layer. and cutting noise ;

[0198] Clipping noise using FFT Transform to the frequency domain to obtain the signal .

[0199] S4, Fourth Layer Processing

[0200] S401, Reduce the cumulative clipping noise from the first to the third layer. Frequency domain components on the fourth-layer subcarrier As an interference signal:

[0201]

[0202]

[0203] Following the same method as the second and third layers, the frequency domain symbols to be transmitted in the fourth layer are processed. Perform dirty paper coding precoding to generate precoded frequency domain symbols. .

[0204] S402. Generate the fourth layer OFDM signal in the same manner as the second and third layers. .

[0205] S5. Superimpose the OFDM signals from the first to the fourth layer to obtain the superimposed signal. :

[0206]

[0207] For the superimposed signal Add DC bias :

[0208]

[0209] In the formula, To transmit signals;

[0210]

[0211] To transmit signals After adding a cyclic prefix, drive the LED array to emit.

[0212] At the receiving end:

[0213] Step 1: After the photodetector at the receiving end receives the signal transmitted by the transmitting end, it removes the cyclic prefix and DC bias to obtain the time-domain received signal. .

[0214] Step 2: Receive the signal in the time domain. Perform an FFT transform to obtain the frequency domain received signal. .

[0215] Step 3: Receive signal from the frequency domain Extract the received frequency domain symbols from each layer:

[0216] For index The subcarriers are used to extract the frequency domain symbols on them as the first layer of received frequency domain symbols.

[0217] For index The subcarriers are used to extract the frequency domain symbols on them as the second-layer received frequency domain symbols.

[0218] For index The subcarriers are used to extract the frequency domain symbols on them as the third-layer received frequency domain symbols.

[0219] For index The subcarriers are used to extract the frequency domain symbols on them as the fourth layer received frequency domain symbols;

[0220] Step 4: Decode the received frequency domain symbols at each layer:

[0221] The first-layer received frequency domain symbols are directly demodulated using 64QAM to recover the first-layer data.

[0222] Perform modulo operations on the second-layer received frequency domain symbols to map them to the basic region; detect the minimum distance and recover the second-layer data;

[0223] Perform modulo operations on the received frequency domain symbols of the third layer to map them to the basic region; detect the minimum distance and recover the third layer data;

[0224] Perform modulo operations on the received frequency domain symbols of the fourth layer to map them to the basic region; detect the minimum distance and recover the fourth layer data;

[0225] To verify the performance of the transmission method proposed in this invention, numerical simulations were performed. The simulations compared the traditional ADO-OFDM transmission method (Method 1) with the transmission method (Method 2) provided in Embodiment 1 of this invention, and compared the traditional LACO-OFDM transmission method (Method 3) with the transmission method (Method 4) provided in Embodiment 2 of this invention. Method 3 employs a 4-layer transmission structure, while the receiving ends of Methods 1 and 3 use serial interference cancellation.

[0226] The simulation parameters are shown in Table 1.

[0227] Table 1 Simulation Parameters

[0228]

[0229] The comparison results are as follows:

[0230] Figure 2 This section presents a comparison of the receiver constellation diagrams for the DCO branch in Method 1 and Method 2. From... Figure 2 As can be seen from the data, in Method 1, the DCO branch is affected by clipped noise, and the constellation points are severely diverged; in Method 2, the received constellation diagram of the DCO branch is restored to a clear state, and the interference is effectively eliminated.

[0231] Figure 3 The comparison of bit error rate performance between Method 1 and Method 2 is presented. From Figure 3 As can be seen, under the same signal-to-noise ratio, the bit error rate of the DCO branch in Method 2 is lower than that of the DCO branch in Method 1.

[0232] Figure 4 This demonstrates a comparison of the receiver constellation diagrams for each layer in Method 3 and Method 4. From Figure 4 As can be seen, in Method 3, the receiving constellation diagrams from the second to the fourth layer show a trend of gradual diffusion; in Method 4, the receiving constellation diagrams from the second to the fourth layer are all restored to a clear constellation distribution, and the performance of each layer is basically the same.

[0233] Figure 5 The bit error rate performance of each layer in methods 3 and 4 is demonstrated. From Figure 5 It can be seen that the bit error rate performance of each layer in Method 4 is basically the same, indicating that the present invention effectively avoids the problem of inter-layer interference accumulation; while the bit error rate performance of each layer in Method 3 is significantly different.

[0234] Table 2 shows a comparison of the peak-to-average ratio (PAPR) for each method.

[0235] Table 2 PAPR Comparison

[0236]

[0237] As can be seen from Table 2, the transmission method provided by the present invention has a significantly lower PAPR than the traditional method.

[0238] The verification results above show that:

[0239] (1) The present invention eliminates the clipping noise interference between layered signals by precoding dirty paper at the transmitting end, effectively avoiding the problem of inter-layer interference accumulation, and the bit error rate performance of each layer is basically consistent.

[0240] (2) The present invention adopts a layered structure, and each layer uses an orthogonal set of subcarriers, which maintains a high spectral efficiency.

[0241] (3) The method of the present invention significantly reduces PAPR compared with the traditional serial interference cancellation method, thus alleviating the pressure on the nonlinear devices at the transmitting end.

[0242] The specific embodiments of the present invention are provided to enable those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

[0243] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. An orthogonal frequency division multiplexing transmission method based on dirty paper coding, characterized in that, include: At the transmitting end, at least two layers of frequency domain symbols to be transmitted are generated. The first layer of frequency domain symbols to be transmitted is subjected to inverse fast Fourier transform to generate the first layer of OFDM signal. The first layer of OFDM signal is non-negatively truncated in the time domain to generate the first layer of truncated noise. For the first The frequency domain symbols to be transmitted are from the first layer to the second layer. The accumulated trimming noise of the layer is used as an interference signal for dirty paper coding precoding to generate the first layer. The precoded frequency domain symbols corresponding to the layer are used to generate the first layer. Layer OFDM signal; The dirty paper encoding precoding includes: constructing auxiliary variables based on the frequency domain symbols to be transmitted and interference signals; The auxiliary variable is subjected to a modulo operation based on a preset modulus, and mapped to a preset basic region to obtain an integer offset; a precoded frequency domain symbol is generated based on the integer offset and the interference signal. The preset basic region is: in For the preset basic area, Let be any complex number in the complex plane. for The real part, for The imaginary part, For the preset modulus, It is the absolute value; The OFDM signals from each layer are superimposed and then transmitted. At the receiving end, after performing a fast Fourier transform on the received signal, a frequency domain received signal is obtained. The received frequency domain symbols of each layer are extracted from the frequency domain received signal, and each layer of received frequency domain symbols is decoded independently.

2. The orthogonal frequency division multiplexing transmission method based on dirty paper coding according to claim 1, characterized in that, The integer offset is calculated using the following formula: In the formula, Integer offset The offset is the integer part of the real part. The imaginary part is the integer offset. as auxiliary variables The real part, as auxiliary variables The imaginary part, For the preset modulus, To round down, The imaginary unit, For absolute values, It is a symbolic function.

3. The orthogonal frequency division multiplexing transmission method based on dirty paper coding according to claim 1, characterized in that, The preset modulus is calculated using the following formula: In the formula, For the preset modulus, The minimum Euclidean distance for modulating constellations. This represents the modulation order.

4. The orthogonal frequency division multiplexing transmission method based on dirty paper coding according to claim 1, characterized in that, For ADO-OFDM transmission: The frequency domain symbols to be transmitted on the ACO branch are used as the first layer of frequency domain symbols to be transmitted. The ACO branch uses subcarriers with odd indices. The OFDM signal of the ACO branch is non-negatively clipped to generate the first layer of clipped noise. The frequency domain symbols to be transmitted in the DCO branch are used as the second-layer frequency domain symbols to be transmitted. The DCO branch uses subcarriers with even-numbered indices and uses the frequency domain components of the first-layer clipped noise on the even-numbered subcarriers as interference signals to perform dirty paper coding precoding on the second-layer frequency domain symbols to be transmitted.

5. The orthogonal frequency division multiplexing transmission method based on dirty paper coding according to claim 1, characterized in that, For LACO-OFDM transmission: The first layer OFDM signal is generated using the ACO-OFDM method. The first layer OFDM signal is then non-negatively clipped to generate the first layer clipping noise. For the first The frequency domain symbols to be transmitted in the first layer to the second layer are... The cumulative clipping noise of the layer, in its frequency domain component on the corresponding subcarrier, is used as an interference signal for dirty paper coding precoding, where the first... Layers are used from the first layer to the second layer. A set of subcarriers that are orthogonal to the layer.

6. The orthogonal frequency division multiplexing transmission method based on dirty paper coding according to claim 5, characterized in that, The cumulative clipping noise is calculated using the following formula: In the formula, To accumulate cutting noise, For the first Layer cutting noise, This is the index for the sampling points.

7. The orthogonal frequency division multiplexing transmission method based on dirty paper coding according to claim 1, characterized in that, The independent decoding includes: For subcarriers with odd indices, their corresponding received frequency domain symbols are directly demodulated; For subcarriers with even indices, their corresponding received frequency domain symbols are demodulated after modulo operations.

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