Transmission method of LED-OAM multiplexing MIMO visible light communication system based on LMS equalization algorithm

Abstract

The invention provides a transmission method of an LED-OAM multiplexing MIMO visible light communication system based on an LMS equalization algorithm, which belongs to the technical field of visible light communication and comprises the steps of construction of the LED-OAM multiplexing MIMO visible light communication system, signal multiplexing and transmission, received signal demultiplexing, channel modeling and signal compensation and dynamic parameterization. According to the method, the problems of inter-mode crosstalk, nonlinear distortion, channel interference and the like in the prior art are solved, the transmission efficiency and stability of a system are improved, the multiplexing characteristic of an OAM light beam, the transmission advantage of an MIMO technology and the balancing capacity of an LMS algorithm are combined, and a new thought and a new technical means are provided for development of the visible light communication field.

Description

Technical Field

[0001] The present invention relates to the field of visible light communication, and particularly to an improved technology for signal processing in an LED-OAM multiplexed MIMO (Multiple-Input Multiple-Output) visible light communication system. Background Art

[0002] In the field of visible light communication, with the increasing demand for data transmission, how to improve the transmission efficiency and stability of communication systems has become a research hotspot. Traditional visible light communication systems mainly rely on intensity modulation and direct detection (IM / DD) technology. However, this technology often struggles to ensure high-quality communication when facing challenges such as multipath effects, atmospheric turbulence interference, and nonlinear distortion.

[0003] In recent years, due to its unique helical phase structure, the orbital angular momentum (OAM) beam has shown great application potential in free space optical communication (FSO). By using the OAM beam as an information transmission medium, signal multiplexing can be achieved, thus greatly enriching the transmission capacity of visible light communication systems. At the same time, the introduction of multiple-input multiple-output (MIMO) technology further improves the transmission performance and stability of the system. However, LED-OAM multiplexed MIMO visible light communication systems still face many challenges in practical applications. Problems such as intermodal crosstalk, nonlinear distortion, and channel interference caused by atmospheric turbulence seriously restrict the performance of the system. To solve these problems, researchers have proposed various equalization algorithms, and among them, the least mean square (LMS) adaptive equalization algorithm has attracted much attention due to its simple implementation and fast convergence speed.

[0004] The LMS algorithm is based on the least mean square error criterion. By dynamically adjusting the weight parameters of the adaptive filter, precise equalization of the received signal can be achieved. In an LED-OAM multiplexed MIMO visible light communication system, adopting the LMS algorithm with training sequences based on deep learning can effectively compensate for the linear and nonlinear distortions suffered by the signal during channel transmission, thereby improving the transmission performance and stability of the system.

[0005] In addition, related research shows that the helical phase structure of the OAM beam can still maintain good stability when experiencing atmospheric turbulence, which makes the OAM modulation technology have potential application value in long-distance optical communication. At the same time, the introduction of MIMO technology further enhances the anti-interference ability and transmission capacity of the system.

[0006] For the above reasons, the present invention proposes a transmission method for an LED-OAM multiplexed MIMO visible light communication system based on the LMS equalization algorithm. Summary of the Invention

[0007] The purpose of the present invention is to solve problems such as inter-modal crosstalk, non-linear distortion, and channel interference existing in the prior art, where the transmission efficiency and stability of the system are insufficient, and a transmission method for an LED-OAM multiplexing MIMO visible light communication system based on the LMS equalization algorithm is proposed.

[0008] A transmission method for an LED-OAM multiplexing MIMO visible light communication system based on the LMS equalization algorithm includes the following steps:

[0009] S1: Construct an LED-OAM multiplexing MIMO visible light communication system, including

[0010] Configure multiple LED light sources at the transmitting end, and each light source generates OAM beams carrying different topological charge values through optical elements;

[0011] Configure multiple receiving antennas at the receiving end for capturing the OAM beams transmitted through the free space optical channel;

[0012] S2: Signal multiplexing and transmission: Modulate each user signal onto OAM beams with different topological charge values for parallel transmission;

[0013] S3: Demultiplexing of received signals: Utilize the orthogonality of OAM modes to separate independent signals in the superimposed state beam through a spatial light modulator;

[0014] S4: Channel modeling and signal compensation, including:

[0015] Establish a channel impulse response model including the effects of atmospheric turbulence;

[0016] Perform adaptive equalization processing on the received signals based on the LMS algorithm;

[0017] S5: Dynamic parameter optimization: Use a training sequence to drive the LMS algorithm to update the MIMO equalizer weight coefficients in real time and minimize the mean square error of the output signal..

[0018] In the above-mentioned transmission method for an LED-OAM multiplexing MIMO visible light communication system based on the LMS equalization algorithm, the generation of the OAM beam in step S1 includes:

[0019] S1: Assign a unique topological charge value to each LED light source through a phase modulator;

[0020] S2: Ensure that different OAM beams maintain modal orthogonality during spatial propagation.

[0021] In the above-mentioned transmission method for an LED-OAM multiplexing MIMO visible light communication system based on the LMS equalization algorithm, the construction of the channel impulse response model in step S4 includes:

[0022] Calculate the signal strength attenuation in a single - reflection scenario;

[0023] Quantify the crosstalk effect between OAM modes caused by atmospheric turbulence.

[0024] In the above - mentioned transmission method of the LED - OAM multiplexing MIMO visible - light communication system based on the LMS equalization algorithm, the MIMO equalizer in step S4 is of a transversal filter structure, and the dimension of its system function matrix matches the number of transceiver antennas, satisfying the M×N matrix relationship.

[0025] In the above - mentioned transmission method of the LED - OAM multiplexing MIMO visible - light communication system based on the LMS equalization algorithm, the iterative process of the LMS algorithm in step S5 includes:

[0026] S1: Initialize the filter coefficient vector;

[0027] S2: Read the received signal and the training sequence reference value at the current moment;

[0028] S3: Calculate the equalization output signal error value;

[0029] S4: Dynamically update the weight coefficient matrix according to the step - size factor.

[0030] Compared with the existing technologies, the advantages of the present invention are as follows:

[0031] Functionally speaking:

[0032] 1. Improve system performance: By introducing the OAM beam multiplexing technology, an additional multiplexing dimension is provided for visible - light communication, enhancing system stability. An adaptive equalizer based on the LMS algorithm can achieve precise equalization of the received signal, effectively reducing the impact of environmental factors such as atmospheric turbulence on system performance, and improving the stability and reliability of the system.

[0033] 2. Reduce the bit - error rate: Through simulation experiments, it is verified that the transmission method proposed by the present invention can significantly reduce the bit - error rate of the system in different intensities of atmospheric turbulence environments, improving the communication quality.

[0034] 3. Optimize the delay characteristics: Through equalization processing, the present invention reduces the root - mean - square delay spread of the system, optimizes the inter - symbol interference situation, and further improves the communication quality of the system;

[0035] 4. The transmitter, receiver, and adaptive equalizer of this system all adopt modular design, which is convenient for maintenance and upgrade. At the same time, it also provides convenience for the expansion and integration of the system. Brief Description of the Drawings

[0036] Figure 1This is the system block diagram in the transmission method of an LED-OAM multiplexing MIMO visible light communication system based on the LMS equalization algorithm proposed by the present invention.

[0037] Figure 2 This is the communication system diagram of the multiple-input multiple-output visible light communication system MIMO-VLC proposed by the present invention.

[0038] Figure 3 This is the schematic diagram of the adaptive equalizer.

[0039] Figure 4 This is the iterative process diagram of the LMS algorithm. Specific implementation manner

[0040] Refer to Figures 1-4 A transmission method of an LED-OAM multiplexing MIMO visible light communication system based on the LMS equalization algorithm includes the following parts

[0041] P1: Construct an LED-OAM multiplexing MIMO visible light communication system. The specific steps include:

[0042] Set the room size as (x×y×z) m 3 , and adopt a (M×N) MIMO transceiver communication system;

[0043] Among them, M LED light sources are used at the transmitting end;

[0044]

[0045] X represents the original user signal. Each transmitter sends 1 signal, and the user information sent can be expressed as

[0046] x j (t) j∈[1,M]

[0047] t represents that at different times, each LED light source generates OAM beams with different topological charges through specific optical elements (such as phase plates or spiral phase plates). These OAM beams serve as carriers for information transmission, and unique information signals are loaded on each carrier.

[0048] While at the receiving end, the system deploys N receiving antennas to receive the OAM beams transmitted through the free space FSO optical communication channel. The received signals recover the original information signals through appropriate separation methods;

[0049] P2: OAM beam multiplexing and demultiplexing

[0050] At the transmitting end, by adjusting the parameters of the optical elements, OAM beams with different topological charges can be generated. These beams form orthogonal modes in space, achieving signal multiplexing. The OAM beam multiplexing signal is:

[0051]

[0052] Two independent pieces of information are respectively encoded in two OAM beams with different topological charges and transmitted separately. Then the two OAM beams are respectively:

[0053] U x1 (r, θ, t) = x1(t)A1(r)exp(-il1θ)

[0054] U x2 (r, θ, t) = x2(t)A2(r)exp(-il2θ)

[0055] At the receiving end, by using the orthogonality of OAM beams and through a specific demodulation technique, signals of different modes can be separated to achieve signal demultiplexing. The two OAM beams pass through a spatial light modulator that can generate an additional phase factor exp(i(l1 + l2) θ .

[0056] The information loaded on the OAM states respectively becomes:

[0057] U x ′1(r, θ, t) = x2(t)A2(r)exp(-il1θ)

[0058] U x ′2(r, θ, t) = x1(t)A1(r)exp(-il2θ)

[0059] P3: Construct a channel model, simulate the atmospheric turbulence channel, and calculate the system impulse response.

[0060] In a given indoor visible light communication (VLC), the positions of the light source S and the receiver R remain constant. With the increase in the number of reflections, the intensity of the signal gradually attenuates when it reaches the receiving end. Only focusing on the scenario where the signal reaches the receiving end through a single reflection, the expression form of the system impulse response:

[0061]

[0062] When the OAM multiplexed beam is transmitted in free space, it will be affected by the atmospheric disturbance channel, thus generating a crosstalk effect. The channel matrix of the OAM state multiplexed visible light communication system; the interference signal received at the receiving end can be expressed as:

[0063]

[0064] The signal expressions of N receiving end users are:

[0065]

[0066] P4: The signal passes through the MIMO equalizer

[0067] When the OAM multiplexed beam distorted by atmospheric turbulence reaches the receiving end, it needs to be detected and separated to extract the distorted user information rj(t) of each path from the superimposed optical path. The distorted user information of each path

[0068]

[0069] Adopting the LMS adaptive equalization algorithm with training sequences based on deep learning, an MIMO (M×N) equalizer is designed. W is the MIMO equalization system function, and the matrix representation of the weighting coefficient W is:

[0070]

[0071] The signal output after passing through the MIMO equalizer can be expressed as:

[0072] Y = W × R.

[0073] P5: The LMS algorithm updates the filter coefficients

[0074] In the MIMO equalizer, the LMS algorithm is used to adjust the coefficients of the equalizer to minimize the mean square error of the output signal. Using the training sequence as a reference, it is compared and analyzed with the received signal, thereby adjusting and updating the coefficients of the filter;

[0075] The iterative process of the LMS algorithm is: initialize w(t); read r(t) and d(t); calculate the output value of the equalizer:

[0076]

[0077] Calculate the error:

[0078] e(t) = d(t) - y(t) = d(t) - w(t)r(t)

[0079] Calculate the step size factor:

[0080]

[0081] Update the weight (transversal filter coefficient):

[0082] w(t + 1) = w(t) + 2μ(t)e(t)r(t).

[0083] As is known by common technical knowledge, the present invention can be implemented by other embodiments that do not depart from its spiritual essence or essential features. Therefore, the above-disclosed embodiments are illustrative in all aspects and not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are encompassed by the present invention.

Claims

1. A transmission method for an LED-OAM multiplexing MIMO visible light communication system based on the LMS equalization algorithm, characterized in that, It includes the following steps: S1: Construct an LED-OAM multiplexing MIMO visible light communication system, including A. Configure multiple LED light sources at the transmitter, and each light source generates OAM beams carrying different topological charge values through optical elements; B. Configure multiple receiving antennas at the receiver to capture the OAM beams transmitted through the free space optical channel; S2: Signal multiplexing and transmission: Modulate each user signal onto OAM beams with different topological charge values for parallel transmission; S3: Demultiplexing of received signals: Utilize the orthogonality of OAM modes to separate independent signals in the superimposed state beam through a spatial light modulator; S4: Channel modeling and signal compensation, including: A. Establish a channel impulse response model including atmospheric turbulence effects; B. Perform adaptive equalization processing on the received signal based on the LMS algorithm; S5: Dynamic parameter optimization: Use the training sequence to drive the LMS algorithm to update the MIMO equalizer weight coefficients in real time and minimize the mean square error of the output signal.

2. The transmission method of the LED-OAM multiplexing MIMO visible light communication system based on the LMS equalization algorithm according to claim 1, characterized in that, The generation of the OAM beam in step S1 includes: S1: Assign a unique topological charge value to each LED light source through a phase modulator; S2: Ensure that different OAM beams maintain modal orthogonality during spatial propagation.

3. The transmission method of the LED-OAM multiplexing MIMO visible light communication system based on the LMS equalization algorithm according to claim 1, characterized in that, The construction of the channel impulse response model described in step S4 includes: Calculate the signal intensity attenuation in the single reflection scenario; Quantify the crosstalk effect between OAM modes caused by atmospheric turbulence.

4. The transmission method of the LED-OAM multiplexing MIMO visible light communication system based on the LMS equalization algorithm according to claim 1, characterized in that, The MIMO equalizer described in step S4 has a transversal filter structure, and the dimension of its system function matrix matches the number of transceiver antennas, satisfying the M×N matrix relationship.

5. The transmission method of the LED-OAM multiplexing MIMO visible light communication system based on the LMS equalization algorithm according to claim 1, characterized in that The iterative process of the LMS algorithm described in step S5 includes: S1: Initialize the filter coefficient vector; S2: Read the received signal and the training sequence reference value at the current moment; S3: Calculate the equalization output signal error value; S4: Dynamically update the weight coefficient matrix according to the step size factor.

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