A layered orthogonal LACO-OFDM method and system for wireless optical communication

Abstract

The present invention discloses a wireless optical communication hierarchical orthogonal LACO-OFDM method and system, which allocates QAM symbols to the subcarriers of each layer and performs symmetry. After symmetry, an inverse transform operation is performed to obtain the time-domain signal of the layer; according to the time-domain signal of the layer, a cyclic preprocessing operation is adopted to calculate the preprocessed time-domain signal of the layer; according to the time-domain signal of the first layer and the preprocessed time-domain signal of the layer, a clipping operation is performed and superposed for transmission to obtain a hierarchical orthogonal LACO-OFDM signal; the hierarchical orthogonal LACO-OFDM signal is subjected to digital-to-analog conversion, and after generating an analog signal, an LED is driven to emit a visible light signal. The present invention has a lower peak-to-average ratio and no error propagation problem, effectively improving the transmission bit error rate performance in the non-linear case and having higher transmission reliability.

Description

Technical Field

[0001] The invention relates to a wireless optical communication layered orthogonal LACO-OFDM method and system, belonging to the technical field of wireless optical communication. Background Art

[0002] Wireless optical communication (OWC) has attracted more and more attention in the field of wireless communication in recent years due to its advantages such as rich spectrum resources, high security, and low electromagnetic interference. However, OWC systems still face many technical challenges in practical applications, such as inter-symbol interference (ISI) caused by optical multipath effects, limited modulation bandwidth, and low optical power utilization. In order to solve these bottlenecks, orthogonal frequency division multiplexing (OFDM) technology came into being. As an efficient multi-carrier modulation technology, OFDM effectively reduces inter-subcarrier interference (ICI) through orthogonal subcarrier transmission, while significantly improving spectrum utilization efficiency and anti-multipath capability, making it one of the key technologies in OWC systems.

[0003] In OWC, intensity modulation direct detection (IM / DD) technology is usually used, which requires that the signal detected at the receiving end must be non-negative and real-valued. To meet this requirement, researchers have proposed a variety of optical orthogonal frequency division multiplexing (O-OFDM) technologies, including DC biased optical OFDM (DCO-OFDM) and asymmetric confined optical OFDM (ACO-OFDM). However, these two methods have the disadvantages of low power efficiency and limited spectrum utilization, which restricts their application in efficient optical communication systems.

[0004] In order to further optimize O-OFDM technology, researchers have proposed more efficient improvement schemes, such as hybrid ACO-OFDM (HACO-OFDM), absolute value layered ACO-OFDM (ALACO-OFDM), and layered ACO-OFDM (LACO-OFDM). Among them, LACO-OFDM can make full use of subcarrier resources compared to other schemes, and its spectrum efficiency can approach DCO-OFDM. At the same time, LACO-OFDM still maintains the power efficiency advantage of ACO-OFDM. Therefore, it has received widespread attention from researchers and is a modulation technology with broad application prospects.

[0005] However, in LACO-OFDM, the limiting noise of each layer of the signal will interfere with the transmission symbols of the subsequent layers, resulting in layered non-orthogonal transmission. Therefore, the receiver needs to use serial interference elimination to detect the signal layer by layer, resulting in higher reception complexity and processing delay. More importantly, the LACO-OFDM transmission method will lead to error propagation problems, especially in nonlinear conditions, which will cause serious deterioration of transmission performance. Although there are some frequency domain preprocessing methods to remove inter-layer interference, frequency domain preprocessing requires high-complexity FFT operations, resulting in a sharp increase in the complexity of the transmitter. Summary of the invention

[0006] Purpose: In order to overcome the mutual interference between layers in the prior art, it is necessary to realize signal detection layer by layer with the help of serial interference elimination, resulting in higher reception complexity and processing delay. At the same time, there is an error propagation problem, which leads to the deterioration of transmission performance under nonlinear conditions. The present invention provides a layered orthogonal LACO-OFDM method and system for wireless optical communication, which adopts a low-complexity time domain preprocessing method to remove inter-layer interference, realize layered orthogonal transmission, significantly reduce the reception complexity of LACO-OFDM, and at the same time, improve the transmission reliability under nonlinear transmission conditions.

[0007] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is:

[0008] In a first aspect, the present invention provides a layered orthogonal LACO-OFDM method for wireless optical communication, specifically comprising:

[0009] Step 1: Assign QAM symbols to the serial numbers in each layer. The subcarriers are symmetrically transformed and then the inverse transformation is performed to obtain the Tier The ACO-OFDM time domain signal of sampling points is expressed as ,in , , , Indicates the total number of subcarriers, Indicates the number of layers.

[0010] Step 2: According to Tier ACO-OFDM time domain signal with sampling points , using a loop preprocessing operation, calculate the Layer Preprocessing ACO-OFDM Time Domain Signal ,in, l ̂ ∈ [ 2 , L ] .

[0011] Step 3: Based on the first layer ACO-OFDM time domain signal with sampling points and Layer Preprocessing ACO-OFDM Time Domain Signal Perform limiting operation and superposition transmission to obtain layered orthogonal LACO-OFDM signal .

[0012] Step 4: Layered orthogonal LACO-OFDM signal After performing digital-to-analog conversion and generating analog signals, the LED is driven to emit visible light signals.

[0013] As a preferred solution, it also includes: Step 5: converting the visible light signal into an electrical signal, performing analog-to-digital conversion on the electrical signal to generate a digital signal, performing FFT operation on the digital signal to generate a frequency domain signal, performing QAM symbol detection on the frequency domain signal, and obtaining the transmitted information.

[0014] In a second aspect, a wireless optical communication layered orthogonal LACO-OFDM system includes a transmitter.

[0015] The transmitting end performs the following steps:

[0016] Step 1: Assign QAM symbols to the serial numbers in each layer. The subcarriers are symmetrically transformed and then the inverse transformation is performed to obtain the Tier The ACO-OFDM time domain signal of sampling points is expressed as ,in , , , Indicates the total number of subcarriers, Indicates the number of layers.

[0017] Step 2: According to Tier ACO-OFDM time domain signal with sampling points , using a loop preprocessing operation, calculate the Layer Preprocessing ACO-OFDM Time Domain Signal ,in, l ̂ ∈ [ 2 , L ] .

[0018] Step 3: Based on the first layer ACO-OFDM time domain signal with sampling points and Layer Preprocessing ACO-OFDM Time Domain Signal Perform limiting operation and superposition transmission to obtain layered orthogonal LACO-OFDM signal .

[0019] Step 4: Layered orthogonal LACO-OFDM signal After performing digital-to-analog conversion and generating analog signals, the LED is driven to emit visible light signals.

[0020] As a preferred solution, a transmitting end is also included.

[0021] The transmitting end performs the following steps:

[0022] Step 5: Convert the visible light signal into an electrical signal, perform analog-to-digital conversion on the electrical signal to generate a digital signal, perform FFT operation on the digital signal to generate a frequency domain signal, perform QAM symbol detection on the frequency domain signal, and obtain the transmitted information.

[0023] Beneficial effects: The present invention provides a layered orthogonal LACO-OFDM method and system for wireless optical communication. In the method of the present invention, the preprocessing process of the transmitting end does not require the use of additional FFT operations, thereby avoiding a sharp increase in the complexity of the transmitting end and maintaining a low transmission complexity. More importantly, the receiving end does not need to use a serial interference elimination method for signal detection, which effectively reduces the receiving complexity and processing delay compared to the original LACO-OFDM.

[0024] Compared with the original LACO-OFDM method, the method of the present invention has a lower peak-to-average ratio (PAPR) and no error propagation problem, effectively improving the transmission bit error rate performance under nonlinear conditions and having higher transmission reliability. The spectrum utilization of the present invention is close to that of DCO-OFDM, which is significantly better than the traditional ACO-OFDM method. At the same time, its power efficiency is better than that of DCO-OFDM. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The figure is a block diagram of the transmitter of a layered orthogonal LACO-OFDM method for wireless optical communication.

[0026] Figure 2 The figure is a receiving end block diagram of a layered orthogonal LACO-OFDM method for wireless optical communication.

[0027] Figure 3 It is a schematic diagram of complementary cumulative distribution function curves of the peak-to-average ratio (PAPR) of the method of the present invention and the prior art.

[0028] Figure 4 The optical bit energy to noise power ratio of the method of the present invention is different from that of the prior art. Schematic diagram of the nonlinear transmission bit error rate performance curve under . DETAILED DESCRIPTION

[0029] The following is a clear and complete description of the technical solutions in the examples of the present invention in conjunction with the accompanying drawings in the examples of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the protection scope of the present invention.

[0030] The present invention will be further described below in conjunction with specific embodiments.

[0031] Embodiment 1:

[0032] This embodiment introduces a layered orthogonal LACO-OFDM method for wireless optical communication. Figure 1 As shown in the figure, it can be seen that the preprocessing process does not require additional FFT operations and has lower complexity than the traditional frequency domain preprocessing process. Specifically, it includes:

[0033] Step 1: The total number of subcarriers is expressed as , the number of stratification layers used is recorded as , in In the layers, the serial number is The subcarriers will be used to transmit data, where . Allocate QAM symbols to each layer with sequence number The subcarriers are processed and Hermitian matrix (Hermitian symmetry) is performed, and the time domain signal is obtained by the fast Fourier transform (IFFT) operation. Tier The ACO-OFDM time domain signal of sampling points is expressed as , ,in .

[0034] Step 2: According to Tier ACO-OFDM time domain signal with sampling points , using a loop preprocessing operation, calculate the Layer Preprocessing ACO-OFDM Time Domain Signal ,in, l ̂ ∈ [ 2 , L ] .

[0035] Step 3: Based on the first layer ACO-OFDM time domain signal with sampling points and Layer Preprocessing ACO-OFDM Time Domain Signal Perform limiting operation and superposition transmission to obtain layered orthogonal LACO-OFDM signal .

[0036] Step 4: Layered orthogonal LACO-OFDM signal After performing digital-to-analog conversion and generating analog signals, the LED is driven to emit visible light signals.

[0037] Furthermore, the step 2 specifically includes:

[0038] Step 2.1, according to the first layer ACO-OFDM time domain signal with sampling points , calculate the limiting noise of the first layer ACO-OFDM signal .

[0039] Step 2.2, based on the limiting noise of the first layer ACO-OFDM signal Decompose the first layer of ACO-OFDM signal to obtain the Limiting Noise of ACO-OFDM Signal , the first layer ACO-OFDM signal is for the The limiting noise of all subsequent ACO-OFDM signals in the layer .

[0040] Step 2.3, according to , and Calculate the Layer Preprocessing ACO-OFDM Time Domain Signal .

[0041] Step 2.4, As the initial value, traverse Execute loop operation and output ,in, .

[0042] Step 2.4.1, calculate the Layer Preprocessing ACO-OFDM Time Domain Signal ,when , go to step 2.4.2, otherwise, exit the loop.

[0043] Step 2.4.2, according to Layer Preprocessing ACO-OFDM Time Domain Signal , generating Limiting Noise of ACO-OFDM Signal .

[0044] Step 2.4.3, let Using loop operation, calculate the Layer ACO-OFDM signal pair Clipping noise of the first - layer ACO - OFDM signal , and the clipping noise of the first - layer ACO - OFDM signal on the subsequent all - layer ACO - OFDM signals of the layer. When , output , where represents the clipping noise of the first - layer ACO - OFDM signal on the layer ACO - OFDM signal, represents the clipping noise of the second - layer ACO - OFDM signal on the layer ACO - OFDM signal, represents the clipping noise of the layer ACO - OFDM signal on the layer ACO - OFDM signal.

[0045] Step 2.4.4, let , and return to Step 2.4.1.

[0046] Furthermore, the layered orthogonal LACO - OFDM signal has the following expression:

[0047]

[0048] where .

[0049] Furthermore, the clipping noise of the first - layer ACO - OFDM signal has the following expression:

[0050]

[0051] where represents the absolute - value operation, represents the ACO - OFDM time - domain signal at the th sampling point of the first layer.

[0052] Furthermore, the clipping noise of the first - layer ACO - OFDM signal with respect to the layer ACO - OFDM signal has the following expression:

[0053]

[0054] where represents the floor operation, represents the clipping noise of the first - layer th ACO - OFDM signal, Indicates the first layer The limiting noise of an ACO-OFDM signal. express about The remainder operation.

[0055] The first layer ACO-OFDM signal is for the The limiting noise of all subsequent ACO-OFDM signals in the layer The expression is as follows:

[0056]

[0057] Furthermore, the Layer Preprocessing ACO-OFDM Time Domain Signal The expression is as follows:

[0058]

[0059] in, Indicates Tier ACO-OFDM time domain signal with sampling points, Indicates Layer ACO-OFDM signal pair Limiting noise of layer ACO-OFDM signal.

[0060] Further, Limiting Noise of ACO-OFDM Signal The expression is as follows:

[0061]

[0062] Among them, , Indicates Layer ACO-OFDM signal for the first The clipping noise after all subsequent layered ACO-OFDM signals.

[0063] Furthermore, the step 2.4.3 specifically includes:

[0064] Step 2.4.3.1, let ,calculate ,in, The expression is as follows:

[0065]

[0066] in, Indicates Tier The ACO-OFDM signal is targeted at The clipping noise of all subsequent layers of the layer, Indicates Tier The ACO-OFDM signal is targeted at Layer clipping noise for all subsequent layers.

[0067] Step 2.4.3.2, calculate the The nth ACO-OFDM signal of the layer is Clipping noise of all subsequent layers ,in, The expression is as follows:

[0068]

[0069] Step 2.4.3.3, let ,when , go to step 2.4.3.1, otherwise, exit the loop and output .

[0070] Furthermore, it also includes: Step 5: converting the visible light signal into an electrical signal through an optoelectronic device, performing analog-to-digital conversion on the electrical signal to generate a digital signal, performing FFT operation on the digital signal to generate a frequency domain signal, performing QAM symbol detection on the frequency domain signal, and obtaining the transmitted information.

[0071] like Figure 2 As shown in the figure, it can be seen that since the layered orthogonal LACO-OFDM method proposed in the present invention adopts a preprocessing method to remove the interference between layers, the receiving end does not need to adopt the serial interference elimination method in the original LACO-OFDM method to perform signal detection, and can directly adopt a low-complexity standard OFDM receiver structure.

[0072] Embodiment 2:

[0073] This embodiment introduces a wireless optical communication layered orthogonal LACO-OFDM system, including a transmitting end.

[0074] The transmitting end performs the following steps:

[0075] Step 1: The total number of subcarriers is expressed as , the number of stratification layers used is recorded as , in In the layers, the serial number is The subcarriers will be used to transmit data, among which . Allocate QAM symbols to each layer with sequence number The subcarriers are processed and Hermitian matrix (Hermitian symmetry) is performed, and the time domain signal is obtained by the fast Fourier transform (IFFT) operation. Tier The ACO-OFDM time domain signal of sampling points is expressed as , ,in .

[0076] Step 2: According to Tier ACO-OFDM time domain signal with sampling points , using a loop preprocessing operation, calculate the Layer Preprocessing ACO-OFDM Time Domain Signal ,in, l ̂ ∈ [ 2 , L ] .

[0077] Step 3: Based on the first layer ACO-OFDM time domain signal with sampling points and Layer Preprocessing ACO-OFDM Time Domain Signal Perform limiting operation and superposition transmission to obtain layered orthogonal LACO-OFDM signal .

[0078] Step 4: Layered orthogonal LACO-OFDM signal After performing digital-to-analog conversion and generating analog signals, the LED is driven to emit visible light signals.

[0079] Furthermore, the step 2 specifically includes:

[0080] Step 2.1, according to the first layer ACO-OFDM time domain signal with sampling points , calculate the limiting noise of the first layer ACO-OFDM signal .

[0081] Step 2.2, based on the limiting noise of the layer 1 ACO-OFDM signal Decompose the first layer of ACO-OFDM signal to obtain the Limiting Noise of ACO-OFDM Signal , the first layer ACO-OFDM signal is for the The limiting noise of all subsequent ACO-OFDM signals in the layer .

[0082] Step 2.3, according to , and Calculate the preprocessed ACO - OFDM time - domain signal of the layer .

[0083] Step 2.4, take as the initial value, traverse to perform loop operations, and output , where .

[0084] Step 2.4.1, calculate the preprocessed ACO - OFDM time - domain signal of the layer , when , enter Step 2.4.2, otherwise, jump out of the loop.

[0085] Step 2.4.2, according to the preprocessed ACO - OFDM time - domain signal of the layer , generate the clipping noise of the ACO - OFDM signal of the layer .

[0086] Step 2.4.3, let Adopt loop operations to calculate the clipping noise of the ACO - OFDM signal of the layer on the ACO - OFDM signal of the layer , and the clipping noise of the ACO - OFDM signal of the layer on all subsequent hierarchical ACO - OFDM signals of the layer , when , output , where represents the clipping noise of the ACO - OFDM signal of the first layer on the ACO - OFDM signal of the layer, represents the clipping noise of the ACO - OFDM signal of the second layer on the ACO - OFDM signal of the layer, represents the clipping noise of the ACO - OFDM signal of the layer on the ACO - OFDM signal of the layer.

[0087] Step 2.4.4, let , and return to Step 2.4.1.

[0088] Furthermore, the hierarchical orthogonal LACO - OFDM signal has the following expression:

[0089]

[0090] in, .

[0091] Furthermore, the limiting noise of the first layer ACO-OFDM signal The expression is as follows:

[0092]

[0093] in, Indicates the absolute value operation. Indicates the first layer ACO-OFDM time domain signal with sampling points.

[0094] Further, the first layer ACO-OFDM signal is for the Limiting Noise of ACO-OFDM Signal The expression is as follows:

[0095]

[0096] in, Indicates a round-down operation. Indicates the first layer The limiting noise of an ACO-OFDM signal, Indicates the first layer The limiting noise of an ACO-OFDM signal. express about The remainder operation.

[0097] The first layer ACO-OFDM signal is for the The limiting noise of all subsequent ACO-OFDM signals in the layer The expression is as follows:

[0098]

[0099] Furthermore, the Layer Preprocessing ACO-OFDM Time Domain Signal The expression is as follows:

[0100]

[0101] in, Indicates Tier ACO-OFDM time domain signal with sampling points, Indicates Layer ACO-OFDM signal pair Limiting noise of layer ACO-OFDM signal.

[0102] Further, Limiting Noise of ACO-OFDM Signal The expression is as follows:

[0103]

[0104] Among them, , Indicates Layer ACO-OFDM signal for the first The clipping noise after all subsequent layered ACO-OFDM signals.

[0105] Furthermore, the step 2.4.3 specifically includes:

[0106] Step 2.4.3.1, let ,calculate ,in, The expression is as follows:

[0107]

[0108] in, Indicates Tier The ACO-OFDM signal is targeted at The clipping noise of all subsequent layers of the layer, Indicates Tier The ACO-OFDM signal is targeted at Layer clipping noise for all subsequent layers.

[0109] Step 2.4.3.2, calculate the The nth ACO-OFDM signal of the layer is Clipping noise of all subsequent layers ,in, The expression is as follows:

[0110]

[0111] Step 2.4.3.3, let ,when , go to step 2.4.3.1, otherwise, exit the loop and output .

[0112] Furthermore, it also includes a transmitting end.

[0113] The transmitting end performs the following steps:

[0114] Step 5: Convert the visible light signal into an electrical signal through an optoelectronic device, perform analog-to-digital conversion on the electrical signal to generate a digital signal, perform FFT operation on the digital signal to generate a frequency domain signal, perform QAM symbol detection on the frequency domain signal to obtain the transmitted information.

[0115] Embodiment 3:

[0116] This embodiment uses the layered orthogonal LACO-OFDM method of the present invention to conduct a comparative experiment with the existing LACO method, and the following conclusions are obtained.

[0117] Figure 3 is the complementary cumulative distribution function curve of the peak-to-average ratio (PAPR) of the method of the present invention, that is, the signal PAPR is greater than the threshold PAPR 0 Probability , it can be seen from the results that and When the PAPR of the layered orthogonal LACO-OFDM of the present invention is greater than the threshold PAPR 0 =10, respectively and , in contrast, and When the PAPR of LACO-OFDM is greater than the threshold PAPR 0 =10, respectively and Therefore, when using the same number of layers In the case of the present invention, the PAPR is greater than the threshold PAPR 0 The probability of is significantly lower than that of the original LACO-OFDM method, indicating that the method of the present invention has a lower PAPR and, therefore, has a better ability to resist nonlinear distortion.

[0118] Figure 4 The optical bit energy to noise power ratio of the method of the present invention is The nonlinear transmission bit error rate performance curve under the condition of When layered orthogonal LACO-OFDM and LACO-OFDM are The bit error rates at dB are and , when the nonlinear limiting ratio When layered orthogonal LACO-OFDM and LACO-OFDM are The bit error rates at dB are and Therefore, at the same nonlinear clipping ratio In this case, the layered orthogonal LACO-OFDM method proposed in the present invention has a lower bit error rate than the original LACO-OFDM method, indicating that the method of the present invention can better combat nonlinear distortion and improve the transmission reliability under nonlinear conditions.

[0119] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A layered orthogonal LACO-OFDM method for wireless optical communication, characterized by: Specifically include: Step 1: Assign QAM symbols to the sequence number 2 in each layer l-1 The ACO-OFDM time domain signal of the nth sampling point in the lth layer is obtained by inverse transformation. Where n=0,1,…,N-1,l=1,2,···,L,i=0,1,···,N / 2 l+1 -1, N represents the total number of subcarriers, and L represents the number of hierarchical layers; Step 2: Based on the ACO-OFDM time domain signal of the nth sampling point in the lth layer Using the loop preprocessing operation, calculate the Layer Preprocessing ACO-OFDM Time Domain Signal in, Step 3: Based on the ACO-OFDM time domain signal of the nth sampling point in layer 1 and Layer Preprocessing ACO-OFDM Time Domain Signal Perform limiting operation and superposition transmission to obtain layered orthogonal LACO-OFDM signal Step 4: Layered orthogonal LACO-OFDM signal After performing digital-to-analog conversion and generating analog signals, the LED is driven to emit visible light signals; The step 2 specifically includes: Step 2.1, based on the ACO-OFDM time domain signal of the nth sampling point in layer 1 Calculate the limiting noise of the layer 1 ACO-OFDM signal Step 2.2, based on the limiting noise of the first layer ACO-OFDM signal Decompose the limiting noise of the first layer ACO-OFDM signal to the second layer ACO-OFDM signal The limiting noise of the ACO-OFDM signal in the first layer for all subsequent ACO-OFDM signals in the second layer Step 2.3, according to and Calculate the Layer Preprocessing ACO-OFDM Time Domain Signal Step 2.4, As the initial value, traverse Execute loop operation and output in, Step 2.4.1, calculate the Layer Preprocessing ACO-OFDM Time Domain Signal when When , go to step 2.4.2, otherwise, jump out of the loop; Step 2.4.2, according to Layer Preprocessing ACO-OFDM Time Domain Signal Generate Limiting Noise of ACO-OFDM Signal Step 2.4.3, let g = 1 and use the loop operation to calculate the g-th layer ACO-OFDM signal for the Limiting Noise of ACO-OFDM Signal and the g-th layer ACO-OFDM signal to the The limiting noise of all subsequent ACO-OFDM signals in the layer when Output in, Indicates the first layer of ACO-OFDM signal The limiting noise of the ACO-OFDM signal is Indicates the second layer of ACO-OFDM signal The limiting noise of the ACO-OFDM signal is Indicates Layer ACO-OFDM signal pair Limiting noise of ACO-OFDM signal; Step 2.4.4, let Return to step 2.4.1; The step 2.4.3 specifically includes: Step 2.4.3.1, let g = 1, calculate in, The expression is as follows: in, Indicates the gth layer The ACO-OFDM signal is targeted at The clipping noise of all subsequent layers of the layer, Indicates the gth layer The ACO-OFDM signal is targeted at The clipping noise of all subsequent layers of the layer; Step 2.4.3.2, calculate the nth ACO-OFDM signal of the gth layer for the Clipping noise of all subsequent layers of the layer in, The expression is as follows: Step 2.4.3.3, let g = g + 1, when When , go to step 2.4.3.1, otherwise, jump out of the loop and output 2. A layered orthogonal LACO-OFDM method for wireless optical communication according to claim 1, characterized in that: Also includes: Step 5: Convert the visible light signal into an electrical signal, perform analog-to-digital conversion on the electrical signal to generate a digital signal, perform FFT operation on the digital signal to generate a frequency domain signal, perform QAM symbol detection on the frequency domain signal, and obtain the transmitted information.

3. A layered orthogonal LACO-OFDM method for wireless optical communication according to claim 1, characterized in that: The layered orthogonal LACO-OFDM signal The expression is as follows: in, 4. A layered orthogonal LACO-OFDM method for wireless optical communication according to claim 1, characterized in that: The clipping noise of the layer 1 ACO-OFDM signal The expression is as follows: Among them, |*| represents the absolute value operation. Represents the ACO-OFDM time domain signal of the nth sampling point in layer 1.

5. The layered orthogonal LACO-OFDM method for wireless optical communication according to claim 1, characterized in that: The first layer ACO-OFDM signal is a limiting noise of the second layer ACO-OFDM signal. The expression is as follows: in, Indicates a round-down operation. represents the limiting noise of the mod(n,N / 4)th ACO-OFDM signal in layer 1, represents the limiting noise of the mod(n,N / 4)+N / 4th ACO-OFDM signal in the first layer; mod(n,N / 4) represents the modulo operation of n with respect to N / 4; The first layer of ACO-OFDM signal is the limiting noise of all subsequent layered ACO-OFDM signals in the second layer. The expression is as follows:

6. A layered orthogonal LACO-OFDM method for wireless optical communication according to claim 1, characterized in that: The said Layer Preprocessing ACO-OFDM Time Domain Signal The expression is as follows: in, Indicates The ACO-OFDM time domain signal of the nth sampling point of the layer, Indicates the ACO-OFDM signal of layer 1 to layer 2 Limiting noise of layer ACO-OFDM signal.

7. A wireless optical communication layered orthogonal LACO-OFDM method according to claim 1, characterized in that: No. Limiting Noise of ACO-OFDM Signal The expression is as follows: Among them, Indicates Layer ACO-OFDM signal for the first The clipping noise after all subsequent layered ACO-OFDM signals.

8. A wireless optical communication layered orthogonal LACO-OFDM system, characterized by: Including the transmitter; The transmitting end performs the following steps: Step 1: Assign QAM symbols to the sequence number 2 in each layer l-1 The ACO-OFDM time domain signal of the nth sampling point in the lth layer is obtained by inverse transformation. Where n=0,1,…,N-1,l=1,2,···,L,i=0,1,···,N / 2 l+1 -1, N represents the total number of subcarriers, and L represents the number of hierarchical layers; Step 2: Based on the ACO-OFDM time domain signal of the nth sampling point in the lth layer Using the loop preprocessing operation, calculate the Layer Preprocessing ACO-OFDM Time Domain Signal in, Step 3: Based on the ACO-OFDM time domain signal of the nth sampling point in layer 1 and Layer Preprocessing ACO-OFDM Time Domain Signal Perform limiting operation and superposition transmission to obtain layered orthogonal LACO-OFDM signal Step 4: Layered orthogonal LACO-OFDM signal After performing digital-to-analog conversion and generating analog signals, the LED is driven to emit visible light signals; The step 2 specifically includes: Step 2.1, based on the ACO-OFDM time domain signal of the nth sampling point in layer 1 Calculate the limiting noise of the layer 1 ACO-OFDM signal Step 2.2, based on the limiting noise of the first layer ACO-OFDM signal Decompose the limiting noise of the first layer ACO-OFDM signal to the second layer ACO-OFDM signal The limiting noise of the ACO-OFDM signal in the first layer for all subsequent ACO-OFDM signals in the second layer Step 2.3, according to and Calculate the Layer Preprocessing ACO-OFDM Time Domain Signal Step 2.4, As the initial value, traverse Execute loop operation and output in, Step 2.4.1, calculate the Layer Preprocessing ACO-OFDM Time Domain Signal when When , go to step 2.4.2, otherwise, jump out of the loop; Step 2.4.2, according to Layer Preprocessing ACO-OFDM Time Domain Signal Generate Limiting Noise of ACO-OFDM Signal Step 2.4.3, let g = 1 and use the loop operation to calculate the g-th layer ACO-OFDM signal for the Limiting Noise of ACO-OFDM Signal and the g-th layer ACO-OFDM signal to the The limiting noise of all subsequent ACO-OFDM signals in the layer when Output in, Indicates the first layer of ACO-OFDM signal The limiting noise of the ACO-OFDM signal is Indicates the second layer of ACO-OFDM signal The limiting noise of the ACO-OFDM signal is Indicates Layer ACO-OFDM signal pair Limiting noise of ACO-OFDM signal; Step 2.4.4, let Return to step 2.4.1; The step 2.4.3 specifically includes: Step 2.4.3.1, let g = 1, calculate in, The expression is as follows: in, Indicates the gth layer The ACO-OFDM signal is targeted at The clipping noise of all subsequent layers of the layer, Indicates the gth layer The ACO-OFDM signal is targeted at The clipping noise of all subsequent layers of the layer; Step 2.4.3.2, calculate the nth ACO-OFDM signal of the gth layer for the Clipping noise of all subsequent layers of the layer in, The expression is as follows: Step 2.4.3.3, let g = g + 1, when When , go to step 2.4.3.1, otherwise, jump out of the loop and output

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