Dual-layer bit loading method and device based on channel state and clipping distortion constraint

Abstract

The application discloses a double-layer bit loading method and system based on channel state and clipping distortion constraint, comprising the following steps: demodulating and channel estimating a received signal to obtain channel state parameters of each subcarrier, and feeding back the channel state parameters and historical channel state information to a sending end; generating channel state reliability parameters corresponding to each subcarrier according to the channel state parameters and the historical channel state information; generating a clipping distortion constraint quantity according to system hardware constraint; performing double-layer division on data subcarriers according to the channel state parameters, the channel state reliability parameters and the clipping distortion constraint quantity, and performing differentiated bit loading rules on subcarriers of different layers; and verifying and correcting an initial bit loading result according to the clipping distortion constraint quantity to generate a transmitting signal. The application solves the technical problems of poor adaptability caused by bit loading relying on instantaneous channel state and insufficient system stability caused by separation of bit allocation and a nonlinear distortion control process in the prior art.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and in particular to a two-layer bit loading method and apparatus based on channel state and clipping distortion constraints. Background Technology

[0002] Multi-carrier modulation techniques (such as OFDM and DMT) divide a broadband channel into multiple narrowband subcarriers, allowing data to be transmitted independently under near-flat fading conditions. They are widely used in digital subscriber lines, optical wireless communications, and high-speed wired serial links. To improve spectrum utilization, existing technologies typically employ bit-loading techniques. This involves allocating higher-order modulation to subcarriers with good channel conditions and lower-order modulation or no modulation to subcarriers with poor channel conditions, based on the instantaneous channel state information (CSI) or signal-to-interference-plus-noise ratio (SINR) of each subcarrier.

[0003] However, existing technologies have the following drawbacks in practical applications:

[0004] First, the stability of channel state information is not effectively utilized; most existing bit loading schemes are directly based on instantaneous CSI for allocation. When the channel changes rapidly, there is feedback delay or estimation error, the accuracy of instantaneous CSI will drop significantly, resulting in poor adaptability of bit allocation decisions based on unstable channel states, which can easily cause drastic fluctuations in system performance.

[0005] Secondly, the hardware nonlinear distortion constraint is separated from the bit loading process. In multicarrier systems, an excessively high peak-to-average power ratio (PAPR) can cause the transmitter amplifier to enter the nonlinear region, resulting in clipping distortion and severely affecting the bit error rate. Existing technologies typically complete bit allocation first and then handle clipping noise through subsequent bias adjustment or power backoff, lacking a constraint mechanism that can directly incorporate the clipping distortion boundary into the subcarrier-level bit allocation decision.

[0006] Finally, the coordination between the hierarchical structure and bit allocation is insufficient. Although there are two-layer Optical OFDM structures in the existing technology, they mainly focus on the subcarrier arrangement and activation factor adjustment between layers, and fail to make full use of the differences in "channel reliability" and "distortion sensitivity" of subcarriers for targeted layer loading, resulting in limited utilization efficiency of the hierarchical structure.

[0007] For example, patent document CN202610172308.7 discloses an HPLC signal processing method based on bit loading, but it does not solve the aforementioned technical problems. Therefore, there is an urgent need to propose a two-layer bit loading method and apparatus based on channel state and clipping distortion constraints to solve the technical problems in the prior art where bit loading only depends on the instantaneous channel state, resulting in poor adaptability, and where the separation of the bit allocation process and the nonlinear distortion control process leads to insufficient system stability. Summary of the Invention

[0008] The main objective of this invention is to propose a two-layer bit loading method and apparatus based on channel state and clipping distortion constraints, aiming to solve the technical problems in the prior art where bit loading relies only on instantaneous channel state, resulting in poor adaptability, and where the separation of bit allocation process and nonlinear distortion control process leads to insufficient system stability.

[0009] To achieve the above objectives, the present invention provides a two-layer bit loading method based on channel state and clipping distortion constraints, wherein the two-layer bit loading method based on channel state and clipping distortion constraints includes the following steps:

[0010] S1. The receiving end demodulates and estimates the channel of the received signal, obtains the channel state parameters of each subcarrier, and feeds back the channel state parameters and historical channel state information to the transmitting end.

[0011] S2. The transmitting end generates channel state reliability parameters for each subcarrier based on the channel state parameters and historical channel state information.

[0012] S3. The sending end generates clipping distortion constraint based on system hardware constraints;

[0013] S4. The transmitting end divides the data subcarriers into two layers according to the channel state parameters, channel state reliability parameters and clipping distortion constraints, and performs differentiated bit loading rules on the subcarriers of different layers.

[0014] S5. The transmitting end verifies and corrects the initial bit loading result according to the clipping distortion constraint, and generates a transmission signal.

[0015] In one preferred embodiment, the channel state reliability parameter is used to characterize the stability and availability of the channel state parameters within the current scheduling period.

[0016] In one preferred embodiment, step S2 generates channel state reliability parameters corresponding to each subcarrier, specifically as follows:

[0017] The transmitting end combines historical channel state information within a continuous observation window to calculate the channel state fluctuation of each subcarrier;

[0018] For subcarriers whose channel state fluctuations are within the first threshold range and whose mean deviation between the current measurement and historical channel state information is less than the second threshold, the reliability score of the subcarrier is increased; for subcarriers whose channel state fluctuations are within the third threshold range and whose mean deviation between the current measurement and historical channel state information is greater than the second threshold, the reliability score of the subcarrier is decreased.

[0019] In one preferred embodiment, the system hardware constraints include at least one of the following: LED power constraints, DC bias range, target bit error rate, allowable clipping ratio, peak-to-average power ratio limit, or device dynamic range.

[0020] In one preferred embodiment, the clipping distortion constraint is used to characterize the nonlinear distortion boundary that the system can withstand under the current loading conditions.

[0021] In one preferred embodiment, step S4 involves performing a two-layer division of the data subcarriers, specifically as follows:

[0022] Based on the channel quality, channel state reliability, and distortion sensitivity of each subcarrier, the data subcarriers are divided into first-layer subcarriers and second-layer subcarriers.

[0023] The first layer of subcarriers is used to carry subcarriers with high channel quality and channel state reliability; the second layer of subcarriers is used to carry subcarriers with low channel quality and channel state reliability.

[0024] In one preferred embodiment, step S4 applies differentiated bit loading rules to subcarriers of different layers, specifically as follows:

[0025] The first-layer subcarriers are modulated using a high-bit loading method;

[0026] The second-layer subcarriers are modulated using a low-bit loading method.

[0027] In one preferred embodiment, step S5 involves the transmitting end verifying and correcting the initial bit loading result based on the clipping distortion constraint, specifically as follows:

[0028] Calculate the expected peak-to-average power ratio or clipping ratio corresponding to the initial bit loading result;

[0029] Determine whether the predicted peak-to-average power ratio or clipping ratio meets the clipping distortion constraint.

[0030] If the expected distortion exceeds the limit, reduce the number of bits in the second-layer subcarriers, or re-layer some boundary subcarriers until the target bit error rate and clipping distortion constraints are met.

[0031] In one preferred embodiment, step S5, which generates the transmission signal, further includes:

[0032] The time-domain signal after double-layer superposition is positiveized.

[0033] The loading results are verified by combining the allowable clipping ratio of the current system, and the DC bias is adaptively adjusted.

[0034] An apparatus including the aforementioned two-layer bit loading method based on channel state and clipping distortion constraints, comprising:

[0035] The receiving module is used to acquire the channel state parameters of each subcarrier;

[0036] The reliability assessment module is used to generate channel state reliability parameters for each subcarrier based on channel state parameters and historical channel state information.

[0037] The constraint generation module is used to generate clipping distortion constraint quantities based on system hardware constraints.

[0038] The layered loading module is used to perform two-layer partitioning of data subcarriers and execute differentiated bit loading based on channel state parameters, channel state reliability parameters, and clipping distortion constraints.

[0039] The verification and correction module is used to verify and correct the loading result based on the clipping distortion constraint amount, and output the transmission signal.

[0040] In the above-described technical solution of the present invention, the two-layer bit loading method based on channel state and clipping distortion constraints includes the following steps: the receiving end demodulates and estimates the channel of the received signal, obtains the channel state parameters of each subcarrier, and feeds back the channel state parameters and historical channel state information to the transmitting end; the transmitting end generates channel state reliability parameters corresponding to each subcarrier based on the channel state parameters and historical channel state information; the transmitting end generates clipping distortion constraints based on system hardware constraints; the transmitting end performs two-layer partitioning of the data subcarriers based on the channel state parameters, channel state reliability parameters, and clipping distortion constraints, and executes differentiated bit loading rules for subcarriers in different layers; the transmitting end verifies and corrects the initial bit loading result based on the clipping distortion constraints, and generates a transmit signal. The present invention solves the technical problems in the prior art where bit loading relies solely on instantaneous channel state, leading to poor adaptability, and where the separation of the bit allocation process and the nonlinear distortion control process leads to insufficient system stability.

[0041] In this invention, the integration of dual-layer subcarriers, adaptive bias, and differentiated bit recording allows high-quality and high-reliability subcarriers to prioritize higher bit loading, while restricted subcarriers carry data in a more conservative manner. This improves the allocation targeting without changing the basic orthogonal frequency division multiplexing transceiver framework. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of a two-layer bit loading method based on channel state and clipping distortion constraints according to an embodiment of the present invention.

[0044] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0045] 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 a part of the embodiments of the present invention, and not all of them. 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.

[0046] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0047] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0048] See Figure 1 According to one aspect of the present invention, a two-layer bit loading method based on channel state and clipping distortion constraints is provided, wherein the two-layer bit loading method based on channel state and clipping distortion constraints includes the following steps:

[0049] S1. The receiving end demodulates and estimates the channel of the received signal, obtains the channel state parameters of each subcarrier, and feeds back the channel state parameters and historical channel state information to the transmitting end.

[0050] S2. The transmitting end generates channel state reliability parameters for each subcarrier based on the channel state parameters and historical channel state information.

[0051] S3. The sending end generates clipping distortion constraint based on system hardware constraints;

[0052] S4. The transmitting end divides the data subcarriers into two layers according to the channel state parameters, channel state reliability parameters and clipping distortion constraints, and performs differentiated bit loading rules on the subcarriers of different layers.

[0053] S5. The transmitting end verifies and corrects the initial bit loading result according to the clipping distortion constraint, and generates a transmission signal.

[0054] Specifically, in this embodiment, the channel state reliability parameter is used to characterize the stability and availability of the channel state parameters within the current scheduling period.

[0055] Specifically, in this embodiment, step S2 generates the channel state reliability parameters corresponding to each subcarrier, specifically as follows:

[0056] The transmitting end combines historical channel state information within a continuous observation window to calculate the channel state fluctuation of each subcarrier;

[0057] For subcarriers whose channel state fluctuations are within the first threshold range and whose mean deviation between the current measurement and historical channel state information is less than the second threshold, the reliability score of the subcarrier is increased; for subcarriers whose channel state fluctuations are within the third threshold range and whose mean deviation between the current measurement and historical channel state information is greater than the second threshold, the reliability score of the subcarrier is decreased.

[0058] Specifically, in this embodiment, the system hardware constraints include at least one of LED power constraints, DC bias range, target bit error rate, allowable clipping ratio, peak-to-average power ratio limit, or device dynamic range.

[0059] Specifically, in this embodiment, the clipping distortion constraint is used to characterize the nonlinear distortion boundary that the system can withstand under the current loading conditions.

[0060] Specifically, in this embodiment, step S4 performs a two-layer division of the data subcarriers, specifically as follows:

[0061] Based on the channel quality, channel state reliability, and distortion sensitivity of each subcarrier, the data subcarriers are divided into first-layer subcarriers and second-layer subcarriers.

[0062] The first layer of subcarriers is used to carry subcarriers with high channel quality and channel state reliability; the second layer of subcarriers is used to carry subcarriers with low channel quality and channel state reliability.

[0063] Specifically, in this embodiment, step S4 applies differentiated bit loading rules to subcarriers of different layers, specifically as follows:

[0064] The first-layer subcarriers are modulated using a high-bit loading method;

[0065] The second-layer subcarriers are modulated using a low-bit loading method.

[0066] Specifically, in this embodiment, step S5, where the transmitting end verifies and corrects the initial bit loading result based on the clipping distortion constraint, specifically involves:

[0067] Calculate the expected peak-to-average power ratio or clipping ratio corresponding to the initial bit loading result;

[0068] Determine whether the predicted peak-to-average power ratio or clipping ratio meets the clipping distortion constraint.

[0069] If the expected distortion exceeds the limit, reduce the number of bits in the second-layer subcarriers, or re-layer some boundary subcarriers until the target bit error rate and clipping distortion constraints are met.

[0070] Specifically, in this embodiment, step S5, generating the transmission signal, further includes:

[0071] The time-domain signal after double-layer superposition is positiveized.

[0072] The loading results are verified by combining the allowable clipping ratio of the current system, and the DC bias is adaptively adjusted.

[0073] Specifically, in this embodiment, after obtaining the initial bit loading result, the transmitting end verifies the loading result in conjunction with the clipping distortion constraint, and adjusts the DC bias, clipping distortion constraint, or inter-layer subcarrier allocation ratio as needed. When the expected distortion exceeds the limit, the number of bits of some subcarriers in the second layer is reduced, or some boundary subcarriers are re-layered until the target bit error rate and distortion constraint requirements are met. Finally, the transmitting end completes constellation mapping, subcarrier loading, IFFT, bias addition, and transmit waveform generation based on the corrected bit loading result, and drives the optical transmitter to complete signal transmission. The receiving end updates the error statistics information based on the reception result, so that the channel state reliability assessment and bit loading adjustment can continue in the next transmission cycle.

[0074] Specifically, in this embodiment, based on dual-layer optical orthogonal frequency division multiplexing (hereinafter referred to as optical OFDM), this embodiment uses a forced modulation / direct detection visible light communication system. The transmitting end adopts a dual-layer optical OFDM transmission structure, and the receiving end adopts a corresponding photoelectric detection and OFDM demodulation structure. The system sets up a first-layer subcarrier and a second-layer subcarrier. The inter-layer division is controlled by the subcarrier activation factor. The first-layer subcarrier adopts a high-bit-loaded modulation method, and the second-layer subcarrier adopts a low-bit-loaded modulation method, that is, a relatively conservative modulation method. In this invention, the subcarrier activation factor can be set to three values: 0.3, 0.5, and 0.7, to cover three working states: low activation, medium activation, and high activation. The receiving end uses the current OFDM... After completing channel estimation, the symbol feeds back the channel state parameters of each subcarrier to the transmitter. The transmitter, combining the historical channel state information from the most recent few frames, calculates the channel state reliability parameter of each subcarrier. The reliability parameter can be calculated using a continuous scoring method or a discrete level method. In this invention, reliability thresholds are set to 0.3, 0.6, and 0.9, where 0.3 corresponds to a lower reliability threshold, 0.6 corresponds to an intermediate threshold, and 0.9 corresponds to a higher reliability threshold. After completing the reliability calculation, the transmitter performs a two-layer partitioning based on subcarrier channel quality and channel state reliability. Subcarriers with better channel quality and higher reliability are preferentially assigned to the first layer of subcarriers, while subcarriers with average channel quality or lower reliability are assigned to the next layer. The second layer subcarrier is then loaded, and bit loading is performed on both layers separately: the first layer subcarrier is allowed to use a higher number of bits, while the second layer uses a lower number of bits to reduce sensitivity to clipping distortion and hardware dynamic range. After the initial allocation is completed, the transmitter introduces an adaptive DC bias to positively process the time-domain signal after the two layers are superimposed, and verifies the loading result in combination with the current system's allowable clipping ratio. If the expected clipping noise is too large, the number of bits of the second layer local subcarrier is reduced, or the number of active second layer subcarriers is reduced. If the current distortion risk is low, the original loading result is maintained. Using the method described in this invention, channel state reliability + two-layer partitioning + adaptive bias correction can be achieved in the same transmission link.

[0075] Specifically, in this embodiment, the present invention incorporates LED power constraints into the bit loading decision process. Before performing double-layer bit loading, the transmitting end first generates a clipping distortion constraint for the current transmission cycle based on the available luminous power of each LED, the total transmit power limit, and the target frequency band usage range. The clipping distortion constraint can be expressed as a system-level constraint or further refined into a spatial stream-level or subcarrier-level constraint. In this embodiment, the maximum allowed number of bits for each layer can be set to multiple example point values ​​for testing. For example, the maximum number of bits for the first-layer subcarrier can be set to 4 bits, 5 bits, and 6 bits, and the maximum number of bits for the second-layer subcarrier can be set to 1 bit, 2 bits, and 3 bits. For each subcarrier to be loaded, the transmitter evaluates the candidate bit count set step by step: if the corresponding bit count can still meet the reliability threshold and target bit error rate requirements under the current LED power constraint, the loading is accepted; if not, the bit count is reduced by one level until the conditions are met; if the lowest bit count still cannot meet the constraints, the subcarrier can be temporarily not allocated service data. This invention introduces the LED power constraint, which is originally used for back-end power control, into the bit loading stage in advance, so that the inter-layer partitioning and subcarrier allocation consider the channel availability and device boundaries at the time of formation. This makes the invention closer to the actual working conditions of optical wireless systems.

[0076] Specifically, in this embodiment, the participation of clipping distortion constraints in bit loading correction is as follows: the transmitter calculates the expected peak-to-average power ratio (PAPR) of the initial double-layer bit loading result and determines whether the current loading result will cause significant clipping distortion based on the target clipping distortion constraint. For further explanation, the clipping distortion constraint or equivalent PAPR control point can be set to three example values: 10 dB, 12.3 dB, and 14 dB, where 10 dB corresponds to a tighter constraint, 12.3 dB corresponds to the intermediate operating point, and 14 dB corresponds to the intermediate operating point. dB corresponds to a relatively loose constraint. When the system operates under a low clipping distortion constraint, the transmitter prioritizes compressing the loading strength of the second-layer subcarrier to avoid bit error rate deterioration due to clipping. When the system operates under a high clipping distortion constraint, although clipping distortion is reduced, bit error rate performance may still be affected due to the decrease in effective SNR. In this case, the high-order loading of the boundary subcarriers in the first layer is prioritized. When the system is at an intermediate operating point, the current allocation results of the two layers are kept unchanged, or only a small offset adjustment is made. The clipping distortion constraint in this invention is not a simple post-processing condition, but can be directly used as the basis for backoff of bit loading. By comparing different values ​​of the clipping distortion constraint, a more suitable inter-layer loading ratio and offset adjustment strategy can be determined.

[0077] Specifically, in this embodiment, the transmitting end does not rely entirely on the instantaneous channel state information of a single frame, but combines the statistical characteristics of channel state information from several historical frames to generate a reliability score for each subcarrier. For subcarriers whose channel state fluctuations are within a first threshold range and whose current measurement value deviates from the mean of historical channel state information by less than a second threshold, their reliability score is increased. For subcarriers whose channel state fluctuations are within a third threshold range and whose current measurement value deviates from the mean of historical channel state information by more than a second threshold, their reliability score is decreased. Subsequently, this score result and the current channel quality parameters are used together as the basis for the two-layer division. The reliability in this invention is not required to be limited to the output of a certain prediction model, but can be generated by the stability of statistical channel state information, historical error information, or other indicators reflecting the reliability of the state, thereby expanding the scope of application of this invention.

[0078] Specifically, in this embodiment, the present invention is not only applicable to modulation / direct detection visible light communication systems, but can also be extended to other multi-carrier communication systems. When loading bits, the bit allocation result is no longer determined solely based on the channel quality parameters of each subcarrier, but rather the channel state reliability and the system's tolerable clipping distortion constraints are considered simultaneously. Based on this, the data subcarriers are divided into two layers, and then differentiated bit allocation is performed separately, thereby taking into account spectral efficiency, bit error rate performance, and hardware implementation constraints. This technical approach is aligned with publicly available research directions such as dual-layer optical OFDM, adaptive DC bias, LED power constraints, and clipping distortion constraint optimization.

[0079] According to another aspect of the present invention, the present invention provides a two-layer bit loading device based on channel state and clipping distortion constraints, comprising:

[0080] The receiving module is used to acquire the channel state parameters of each subcarrier;

[0081] The reliability assessment module is used to generate channel state reliability parameters for each subcarrier based on channel state parameters and historical channel state information.

[0082] The constraint generation module is used to generate clipping distortion constraint quantities based on system hardware constraints.

[0083] The layered loading module is used to perform two-layer partitioning of data subcarriers and execute differentiated bit loading based on channel state parameters, channel state reliability parameters, and clipping distortion constraints.

[0084] The verification and correction module is used to verify and correct the loading result based on the clipping distortion constraint amount, and output the transmission signal.

[0085] Specifically, in this embodiment, by introducing a channel state reliability parameter during the bit loading process, bit allocation no longer relies solely on the subcarrier channel quality parameters themselves, but further considers the stability and availability of channel state information. Thus, when there are channel fluctuations, feedback delays, or deviations in channel state information, the allocation results can be constrained and corrected based on reliability, thereby improving the adaptability and allocation stability of the bit loading results. After introducing clipping distortion constraints into the bit loading decision stage, subcarrier bit allocation is not only constrained by channel conditions but also by hardware-side nonlinear distortion boundary constraints. Due to factors such as peak-to-average power ratio, clipping distortion constraints, transmitter offset, and... The dynamic range of the devices collectively affects the balance between signal-to-noise ratio and bit error rate. Therefore, incorporating distortion constraints in advance during the allocation phase helps reduce performance fluctuations caused by clipping, saturation, or power limitations under high loading conditions, and facilitates a balance between throughput and bit error rate. The dual-layer subcarrier processing mechanism eliminates the uniform bit loading rule for different subcarriers, instead allowing for differentiated processing based on channel state reliability and distortion sensitivity. Subcarriers with better conditions can handle higher bit loading, while those with relatively limited conditions adopt a more conservative loading method, making the allocation results more targeted and improving the utilization efficiency of the hierarchical structure. This approach aligns with the engineering approach in dual-layer optical OFDM, which involves hierarchically arranging subcarriers and combining adaptive offset to handle clipping noise. Compared to processing bit loading, offset adjustment, and clipping control separately, the above scheme incorporates channel state reliability, dual-layer subcarrier partitioning, and clipping distortion constraints into the same decision-making process, enabling coordinated processing of channel adaptability and hardware constraints within the same stage. This approach helps reduce subsequent compensation and redundant adjustments, facilitates the formation of a unified control strategy, and allows for joint trade-offs between target bit error rate, target spectral efficiency, and device constraints. Based on existing orthogonal frequency division multiplexing, discrete multi-tone, and intensity modulation / direct detection multi-carrier systems, this invention primarily adds processing steps such as channel state reliability assessment, two-layer allocation, and distortion constraint control. It does not require changes to the system's basic modulation and transmission framework, thus exhibiting good compatibility. For systems with LED power constraints, clipping noise control requirements, or dynamic channel adaptation needs, it provides a new bit loading implementation path while maintaining the existing transceiver structure essentially unchanged, thus possessing significant engineering application value.

[0086] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A two-layer bit loading method based on channel state and clipping distortion constraints, characterized in that, Includes the following steps: S1. The receiving end demodulates and estimates the channel of the received signal, obtains the channel state parameters of each subcarrier, and feeds back the channel state parameters and historical channel state information to the transmitting end. S2. The transmitting end generates channel state reliability parameters for each subcarrier based on the channel state parameters and historical channel state information. S3. The transmitting end generates clipping distortion constraint based on system hardware constraints; S4. The transmitting end divides the data subcarriers into two layers according to the channel state parameters, channel state reliability parameters and clipping distortion constraints, and performs differentiated bit loading rules on the subcarriers of different layers. S5. The transmitting end verifies and corrects the initial bit loading result according to the clipping distortion constraint, and generates a transmission signal.

2. The two-layer bit loading method based on channel state and clipping distortion constraints according to claim 1, characterized in that, The channel state reliability parameter is used to characterize the stability and availability of the channel state parameters within the current scheduling period.

3. The two-layer bit loading method based on channel state and clipping distortion constraints according to any one of claims 1-2, characterized in that, Step S2 generates channel state reliability parameters for each subcarrier, specifically as follows: The transmitting end combines historical channel state information within a continuous observation window to calculate the channel state fluctuation of each subcarrier; For subcarriers whose channel state fluctuations are within the first threshold range and whose mean deviation between the current measurement and historical channel state information is less than the second threshold, the reliability score of the subcarrier is increased; for subcarriers whose channel state fluctuations are within the third threshold range and whose mean deviation between the current measurement and historical channel state information is greater than the second threshold, the reliability score of the subcarrier is decreased.

4. The two-layer bit loading method based on channel state and clipping distortion constraints according to any one of claims 1-2, characterized in that, The system hardware constraints include at least one of the following: LED power constraints, DC bias range, target bit error rate, allowable clipping ratio, peak-to-average power ratio limit, or device dynamic range.

5. The two-layer bit loading method based on channel state and clipping distortion constraints according to any one of claims 1-2, characterized in that, The clipping distortion constraint is used to characterize the nonlinear distortion boundary that the system can withstand under the current loading conditions.

6. The two-layer bit loading method based on channel state and clipping distortion constraints according to any one of claims 1-2, characterized in that, Step S4 involves a two-layer division of the data subcarriers, specifically as follows: Based on the channel quality, channel state reliability, and distortion sensitivity of each subcarrier, the data subcarriers are divided into first-layer subcarriers and second-layer subcarriers. The first layer of subcarriers is used to carry subcarriers with high channel quality and channel state reliability; the second layer of subcarriers is used to carry subcarriers with low channel quality and channel state reliability.

7. The two-layer bit loading method based on channel state and clipping distortion constraints according to claim 6, characterized in that, Step S4 applies differentiated bit loading rules to subcarriers of different layers, specifically as follows: The first-layer subcarriers are modulated using a high-bit loading method; The second-layer subcarriers are modulated using a low-bit loading method.

8. The two-layer bit loading method based on channel state and clipping distortion constraints according to any one of claims 1-2, characterized in that, In step S5, the transmitting end verifies and corrects the initial bit loading result based on the clipping distortion constraint, specifically as follows: Calculate the expected peak-to-average power ratio or clipping ratio corresponding to the initial bit loading result; Determine whether the predicted peak-to-average power ratio or clipping ratio meets the clipping distortion constraint. If the expected distortion exceeds the limit, reduce the number of bits in the second-layer subcarriers, or re-layer some boundary subcarriers until the target bit error rate and clipping distortion constraints are met.

9. The two-layer bit loading method based on channel state and clipping distortion constraints according to any one of claims 1-2, characterized in that, Step S5, which generates the transmission signal, further includes: The time-domain signal after double-layer superposition is positiveized. The loading results are verified by combining the allowable clipping ratio of the current system, and the DC bias is adaptively adjusted.

10. An apparatus comprising the two-layer bit loading method based on channel state and clipping distortion constraints as described in any one of claims 1-9, characterized in that, include: The receiving module is used to acquire the channel state parameters of each subcarrier; The reliability assessment module is used to generate channel state reliability parameters for each subcarrier based on channel state parameters and historical channel state information. The constraint generation module is used to generate clipping distortion constraint quantities based on system hardware constraints; The layered loading module is used to perform two-layer partitioning of data subcarriers and execute differentiated bit loading based on channel state parameters, channel state reliability parameters, and clipping distortion constraints. The verification and correction module is used to verify and correct the loading result based on the clipping distortion constraint amount, and output the transmission signal.

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