CWDM-based optical control visible light high-correlation MIMO system

Abstract

The application provides a CWDM-based light-controlled visible light high-correlation MIMO system, which comprises an RG optical module and an LED AP unit connected with the RG optical module through an optical fiber; the RG optical module comprises a spatial modulation digital signal processor (SM DSP), a carrier modulation module, a PI control block, a CWDM multiplexer and at least one MZM unit; the PI control block comprises at least one radio frequency power amplifier (PA) which is used for centralized light control of LED emission power in the LED AP unit together with the MZM unit; each MZM unit comprises a laser (LD) and a MZM module; the LED AP unit comprises a CWDM demultiplexer, at least one photoelectric converter (PD), at least one band-pass filter (BPF) and at least one LED. The application is reasonable in concept, takes the CWDM technology as the access network background, takes reducing the correlation of visible light communication as the main purpose, constructs a low-energy-consumption high-performance visible light MIMO system based on the centralized light signal processing theory.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a CWDM-based optically controlled visible light high-correlation MIMO system. Background Art

[0002] Currently, mainstream solutions to address high channel correlation include photodetector angle diversity, image sensor reception, and power imbalance methods. Photodetection diversity and image sensor technologies primarily focus on the receiving end, significantly increasing reception complexity. Regarding photodetection technology, non-patent documents 1 and 2 reduce visible light MIMO channel correlation by controlling the photodetector's receiving angle, thereby increasing channel capacity. Furthermore, non-patent document 3, based on angle diversity, further reduces the correlation of visible light MIMO systems by employing a grouping LED approach. Furthermore, non-patent document 4 addresses a multi-receiver solution by considering the individual angle control capabilities of the photodetector, improving the system's flexibility and robustness. Regarding image sensors, non-patent document 5 comprehensively analyzes the performance of image sensor-based visible light MIMO communications for different modulation formats, identifying the optimal modulation format for different spatial distribution scenarios. These photodetection diversity and image sensor technologies reduce visible light MIMO system correlation at the expense of additional user-side signal processing modules, making them extremely unsuitable for lightweight IoT scenarios.

[0003] Therefore, visible light MIMO based on the power imbalance method can effectively reduce the correlation of the visible light MIMO system without sacrificing the complexity of the user end. Non-patent document 6 is based on the visible light MIMO system and derives the optimal power allocation coefficient by controlling the power distribution of each LED, thereby reducing the channel correlation. Then, for indoor systems with dense distribution of multiple LEDs, non-patent document 7 further uses convex optimization to optimize the power allocation of each LED signal to improve system throughput and spectrum efficiency. By controlling the power size of each LED, the power imbalance method can effectively reduce the impact of channel correlation. However, the optimal power allocation coefficient in this method is strongly related to the LED spacing and the user's mobile position, and a complex and energy-consuming power controller is required at the LED access end. At the same time, in indoor application scenarios with dense distribution of LEDs and multiple houses, the energy consumption and complexity of the power distribution control system will increase linearly.

[0004] In the context of indoor mobile users, based on the power imbalance method in the high-correlation visible light MIMO system, the high-performance power controller at the LED access end faces the challenges of high energy consumption and high complexity. Therefore, in view of the above challenges, the technical problems to be solved by this invention are as follows:

[0005] Channel Correlation Mitigation Mechanism for Low-Energy Visible Light MIMO Systems: Regarding visible light MIMO correlation research, traditional power imbalance methods use access-side power controller modules to control LED power. Reducing access-side complexity and high energy consumption is a fundamental prerequisite for ensuring low-complexity, high-efficiency transmission. In user mobility scenarios, the optimal power allocation coefficient varies with LED spacing and user location. This patent addresses the key challenge of achieving centralized, efficient, and low-energy distribution of optimally allocated power.

[0006] Prior art literature

[0007] Non-patent document 1: Nuwanpriya Asanka, Ho Siu-Wai, Chen Chung Shue, "Indoor MIMOVisible Light Communications: Novel Angle Diversity Receivers for Mobile Users", IEEE Journal on Selected Areas in Communications, 2015, 33(9), 1780-1792, DOI: 10.1109 / JSAC.2015.2432514.

[0008] Non-patent document 2: D.Zheng, H.Zhang and J.Song, "Spatial Multiplexing MIMOVisible Light Communications With Densely Distributed LEDs and PDs", IEEEPhotonics Journal, vol.12, no.5, Oct.2020, Art no.7905807, DOI:10.1109 / JPHOT.2020.3029185.

[0009] Non-patent literature 3: X.Gao, Q.Bai, P.Gong, D.Wu, "Design and Performance Analysis of LED-Grouping Based Spatial Modulation in the Visible Light Communication System", IEEE Transactions on Vehicular Technology, vol.69, no.7, pp.7317-7324, July 2020, DOI:10.1109 / TVT.2020.2990102.

[0010] Non - Patent Document 4: AU Khan, Y Celik, SA Colak, “Capacity Variation of an Indoor MIMO VLC System for a Pyramid Receiver”, Conference: 2020 28th Signal Processing and Communications Applications Conference (SIU), October 2020,

[0011] DOI: 10.1109 / SIU49456.2020.9302226.

[0012] Non - Patent Document 5: Amit Kumar Gupta, Ananthanarayanan Chockalingam, “Performance of MIMO Modulation Schemes With Imaging Receivers in Visible Light Communication”, Lightwave Technology, Journal of. 2018, 36(10), 1912 - 1927, DOI: 10.1109 / JLT.2018.2795698.

[0013] Non - Patent Document 6: Fath T, Haas H, “Performance comparison of MIMO techniques for optical wireless communications in indoor environments”, IEEE Transactions on Communications, 2013, 61(2):733 - 742, DOI: 10.1109 / TCOMM.2012.120512.110578.

[0014] Non-patent literature 7: C.Wang, Y.Yang, Z.Yang, C.Feng, J.Cheng, C.Guo, "Joint SIC-based Precoding and Sub-connected Architecture Design for MIMO VLC Systems", IEEE Transactions on Communications, vol. 71, no. 2, pp. 1044-1058, Feb. 2023, DOI: 10.1109 / TCOMM.2022.3231635. Summary of the Invention

[0015] In response to the technical problems existing in the above-mentioned background technology, the present invention proposes a CWDM-based optically controlled visible light high-correlation MIMO system. The system has a reasonable concept, takes CWDM technology as the access network background, and aims to reduce the correlation of visible light communication. Based on the theory of centralized optical signal processing, it constructs a low-energy, high-performance visible light MIMO system.

[0016] To solve the above technical problems, the present invention provides a CWDM-based optically controlled visible light high-correlation MIMO system, which specifically includes an RG optical module and an LED AP unit connected to the RG optical module via an optical fiber;

[0017] The RG optical module includes a spatial modulation digital signal processor (SM DSP), a carrier modulation module, a PI control block, a CWDM multiplexer, and at least one MZM unit. The PI control block includes at least one RF power amplifier (PA), which, together with the MZM unit, is used to centrally control the LED transmit power in the LED AP unit. Each MZM unit includes a laser (LD) and an MZM module. The signal input end of the spatial modulation digital signal processor (SM DSP) is connected to network data, and the signal output end is electrically connected to the carrier modulation module and the RF power amplifier (PA). The MZM modules are electrically connected to the corresponding RF power amplifiers (PA), and are connected to the corresponding lasers (LD) and the CWDM multiplexer via optical fibers.

[0018] The LED AP unit includes a CWDM demultiplexer, at least one photoelectric converter PD, at least one bandpass filter BPF, and at least one LED; the CWDM demultiplexer is connected to the CWDM multiplexer via an optical fiber; the input end of each photoelectric converter PD is connected to the CWDM demultiplexer via an optical fiber, and the output end is electrically connected to the corresponding bandpass filter BPF; each bandpass filter BPF is electrically connected to the corresponding LED;

[0019] The outdoor access network data is transmitted through the spatial modulation digital signal processor SM DSP to generate the DB signal and CB signal in the SM; the DB signal is up-regulated to the carrier with the RF center frequency f1 through carrier modulation, and the CB signal transmits the carrier modulation signal to the corresponding MZM unit according to the control bit information; each MZM unit is responsible for the electro-optical conversion in each CWDM band; then, the MZM modulated optical signal of each frequency band is coupled to the CWDM multiplexer to form a CWDM signal; at the indoor LED AP unit end, the wavelength division multiplexing signal is separated according to the band through optical fiber transmission and the CWDM demultiplexer, and then the single band is restored to the RF signal through the optical-to-electrical converter PD; after the RF signal is filtered to remove noise interference, the corresponding SM signal is transmitted to the corresponding LED for visible light MIMO transmission.

[0020] The CWDM-based optically controlled visible light high-correlation MIMO system, wherein: before the MZM unit optical modulation, the carrier modulation module is electrically connected to the PI control block; the PI control block is composed of a radio frequency power amplifier PA; the relationship between the optical modulation index of the MZM unit and the LED transmission power is given to achieve optical control of power imbalance; the unmodulated optical signal E output by the laser LD in (t) are as follows:

[0021]

[0022] In the above formula (1), P Laser is the laser light power, is the optical carrier angular frequency, e is the base of the natural logarithm, j is the imaginary unit in the complex number, and t is the time variable.

[0023] The CWDM-based optically controlled visible light high-correlation MIMO system, wherein: if the MZM module operates at the orthogonal bias point, its output light field is:

[0024]

[0025] In the above formula (2), Indicates the center angle frequency of the SM signal driving the modulator; V π is the modulator half-wave voltage; V dr It is the amplitude of the radio frequency signal, and the amplitude is determined by each of the radio frequency power amplifiers PA.

[0026] The optically controlled visible light high correlation MIMO system based on CWDM, wherein: the radio frequency signal output by the radio frequency power amplifier PA is modulated simultaneously to the optical signals on both sides of the optical carrier, and after photoelectric modulation, the radio frequency signal contains a frequency of and its harmonics The ingredients can be expressed as:

[0027]

[0028] In the above formula (3), η is the responsivity of the photoelectric converter PD, represents the (2N-1)th order Bessel function of the first kind, is the modulation index of the MZM module, n represents the accumulator numerator in formula (3), and t is the time independent variable; then, the RF signal output by the photoelectric converter PD passes through the bandpass filter BPF to generate the LED driving RF signal, which only contains the frequency of

[0029]

[0030] In the above formula (4), J1 represents a first-order Bessel function of the first kind, and α represents a signal attenuation coefficient generated by the bandpass filter BPF.

[0031] The optically controlled visible light high-correlation MIMO system based on CWDM, wherein: According to the formula (4), the photoelectric converter PD restores the optical signal to the RF signal amplitude and modulation index of the electrical signal Related; if ηαP Laser Normalized, the formula (4) can be further expressed as:

[0032]

[0033] The CWDM-based optically controlled visible light high-correlation MIMO system, wherein: the LED can be regarded as a directly modulated laser, and its output power working in the linear range is:

[0034]

[0035] In the centralized SM mechanism, in each time slot, only one MZM unit performs optical double-sideband transmission, so formula (6) can express the LED power activated in each time slot. The LED power can be controlled by the modulation index of the MZM unit, and each LED can be controlled independently.

[0036] The CWDM-based optically controlled visible light high-correlation MIMO system, wherein: the MIMO system uses multiple LEDs to construct a MIMO signal based on the visible light frequency band as a visible light MIMO channel, and uses LEDs to transmit optically controlled SM signals. The visible light spatial modulation channel can be expressed as:

[0037] Y = βHX + N (7);

[0038] In the above formula (7), H represents N r×N t The visible light MIMO channel matrix, where N r 、N t They are the number of users and the number of transmission LEDs, respectively. The matrix coefficient is the signal gain h from the jth LED to the i-th user. ij represents; β represents the optical fiber link loss coefficient, which comes from phase noise, nonlinearity and dispersion effects; X=[s1,s2,…,s n ] represents the SM signal at the transmitting end, and N represents additive white Gaussian noise.

[0039] In the CWDM-based optically controlled visible light high-correlation MIMO system, the signal model from the LED AP unit to the indoor user adopts the Lambertian radiation model, so the visible light MIMO channel matrix coefficient can be written as:

[0040] h ij =TRεG ij (8);

[0041] In the above formula (8), T represents the gain of the CWDM demultiplexer to the optical signal; R represents the photoelectric receiving responsivity of the indoor user end; ε is the electro-optical conversion efficiency of the LED; G ij represents the visible light channel gain from the jth LED to the i-th user in the Lambertian radiation model, which can be expressed as:

[0042]

[0043] In the above formula (9), L represents the order of Lambertian radiation; d ij The distance from the i-th LED to the j-th LED; Φ and ψ ij A represents the exit angle and incident angle of the channel from the jth LED to the ith LED respectively; R and ψ FoV are the detection range and half angle of the field of view of the photoelectric detector at the user receiving end respectively; From formula (9), we can know that if the LED is not within the field of view, G ij =0;

[0044] The signal is recovered by using the maximum detection method through the following formula (10)

[0045]

[0046] In the above formula (10), A represents the set of all transmitted symbols; Represents the square of the 2-norm; the power imbalance method is used to reduce the h correlation, that is, to change the H value in the formula. The gain element is changed from h ij becomes γh ij, thereby reducing the probability of decision error; γ represents the optical control gain, which is directly generated by the optical control module in the RG optical module.

[0047] By adopting the above technical solution, the present invention has the following beneficial effects:

[0048] The optically controlled visible light high-correlation MIMO system based on CWDM of the present invention is well-conceived and has the following advantages or characteristics:

[0049] (1) Low-energy centralized optical control power imbalance

[0050] To address the high channel correlation in visible light MIMO communication, this invention, based on the CWDM optical network architecture, utilizes the relationship between the MZM modulation index and the output optical power. By removing the high-energy-consuming power control module at the indoor LED access point, a centralized optical network framework is adopted to control the LED power, thus achieving a low-energy and low-complexity power imbalance control mechanism.

[0051] (2) Low-cost optical spatial modulation

[0052] In order to reduce the radio frequency link of visible light MIMO, the present invention optimizes spatial modulation in the optical domain based on traditional spatial modulation MIMO transmission, and realizes low-cost visible light MIMO transmission through the mapping relationship between CWDM band and LED index.

[0053] (3) Efficient power distribution

[0054] In response to the changes in the optimal coefficient of power imbalance in user mobility scenarios, the present invention adopts a centralized optically controlled visible light MIMO module to dynamically and centrally allocate the coefficient, effectively providing efficient multi-user power allocation capabilities and improving the visible light MIMO multi-user channel capacity.

[0055] At the same time, the present invention has the following characteristics compared with the prior art:

[0056] Passive Optical Networks (PONs) are currently the mainstream access optical network, offering low energy consumption, simplified deployment, and centralized signal processing. The CWDM-based access optical network module in this invention belongs to a centralized optical network and is suitable for the WDM-PON architecture. Furthermore, this invention can be used as an indoor application technology for WDM-PON networks, focusing on addressing the high correlation of visible light indoors.

[0057] Centralized Radio Access Networks (C-RAN) are currently the predominant access architecture for cellular networks. Future mobile networks will integrate outdoor cellular networks with indoor communication networks. The network architecture of this invention can be used to separate functional modules within C-RAN, further simplifying the complexity of indoor access points and enhancing centralized and flexible allocation capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0059] Figure 1 Schematic diagram of the structure of the optically controlled visible light high-correlation MIMO system based on CWDM ( Figure 1 In the network, the home interface, namely the RG optical module, acts as a gateway to connect the external outdoor network and indoor users);

[0060] Figure 2 This is a schematic diagram of the structural connection principle of the CWDM-based high-correlation optically controlled visible light MIMO system of the present invention;

[0061] Figure 3 Schematic diagram of spectrum evolution involved in the CWDM-based high-correlation optically controlled visible light MIMO system of the present invention. DETAILED DESCRIPTION

[0062] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0063] The present invention will be further explained below with reference to specific embodiments.

[0064] like Figure 1As shown in the figure, since visible light communication signals are mainly transmitted in the line-of-sight channel, MIMO signals have a relatively high correlation. Controlling the power of each LED, namely the power imbalance method (PI), can effectively reduce the impact of channel correlation on the channel capacity of the visible light MIMO system. Since the traditional power imbalance signal processing module is located in the LED AP, in order to reduce the complexity of the LED end, this invention will propose a CWDM-based optical control visible light high-correlation MIMO system, which will effectively improve the high channel correlation problem in the visible light MIMO system. Its specific functional structure is shown in the figure. Figure 2 As shown, it includes RG optical module and LED AP unit.

[0065] The RG optical module includes a spatial modulation digital signal processor SM DSP, a carrier modulation module, a PI control block, a CWDM multiplexer and at least one MZM unit; the PI control block contains at least one power amplifier PA, which, together with the MZM unit, is used to centrally optically control the transmission power of the LED in the LED AP unit; each of the MZM units includes a laser LD and an MZM module; the signal input end of the spatial modulation digital signal processor SM DSP is connected to network data, and the signal output end is electrically connected to the carrier modulation module and the power amplifier PA respectively; the MZM module is electrically connected to the corresponding power amplifier PA, and is connected to the corresponding laser LD and the CWDM multiplexer through optical fiber.

[0066] The LED AP unit includes a CWDM demultiplexer, at least one photoelectric converter PD, at least one bandpass filter BPF and at least one LED; wherein, the LED AP unit includes a CWDM demultiplexer, at least one photoelectric converter PD, at least one bandpass filter BPF and at least one LED; the CWDM demultiplexer is connected to the CWDM multiplexer through an optical fiber; the input end of each photoelectric converter PD is connected to the CWDM demultiplexer through an optical fiber, and the output end is electrically connected to the corresponding bandpass filter BPF; each bandpass filter BPF is electrically connected to the corresponding LED.

[0067] Figure 2 The RG optical module and LED AP unit correspond to Figure 1Corresponding module. In order to further simplify the RG optical module, the present invention adopts spatial modulation (SM) as the MIMO transmission technology, which is commonly used in visible light MIMO communication. In the traditional SM (spatial modulation) system, SM divides the signal into a data bit (DB) signal and a control bit (CB) signal. The control bit controls the index of the transmitting LED, and only one LED is transmitting information at the same time. At the same time, at the SM receiving end, the control bit and the data bit will be decoded simultaneously to achieve the purpose of spatial multiplexing.

[0068] Different from the traditional LED-based SM mechanism, e.g. Figure 2 As shown, the present invention utilizes RG optical modules and adopts optical radio frequency communication technology to implement centralized optical control (PI) technology for SM. Specifically, the outdoor access network data is transmitted through the spatial modulation digital signal processor (SM DSP) in the RG optical module to generate the DB and CB signals in the SM. The DB signal is then modulated by the carrier and up-regulated to a carrier with a radio frequency center frequency of f1. The CB signal transmits the carrier modulation signal to the corresponding MZM unit based on the control bit information. Each MZM unit is responsible for the transmission of the signal in each CWDM band (λ1, λ2…λ n ) electro-optical conversion, including power amplifier (PA), laser diode (LD) and MZM module (Mach-Zehnder Modulator); then, each band MZM unit modulates the optical signal and couples it to the CWDM multiplexer (CWDM Multiplexer) to form a CWDM signal. At the indoor LED AP unit end, through optical fiber transmission and CWDM demultiplexer, the wavelength division multiplexing signal is divided into different wavelengths (λ1, λ2…λ n ) is separated; then the single band is restored to the RF signal through the photoelectric converter (Photo Detector, PD); after the RF signal is filtered to remove noise interference, the corresponding SM signal is transmitted to the corresponding LED using visible light MIMO transmission.

[0069] Based on the above optical transmission system, the present invention can realize SM transmission in the optical domain. For example, if a 4×4 MIMO signal is realized, the present invention needs to transmit a 4-WDM signal, that is, a wavelength division multiplexing signal composed of 4 waves. Figure 2In the RG optical module, the SM control bits "00", "01", "10" and "11" respectively indicate that the 1st, 2nd, 3rd or 4th MZM unit is connected to the carrier modulation module, and at the same time ensure that only one MZM unit can be connected in a time slot. In addition, the present invention adopts low-energy centralized optical signal processing, and combines the optical double-sideband modulation technology of the Mach-Zehnder external modulator to realize the mapping of LED transmission power-optical modulator modulation index. If in time slot T1, the SM control bit is "00", then the first MZM unit will transmit the carrier modulation signal, and the corresponding Figure 2 The spectrum evolution process ①-⑦ in different optical transmission stages is as follows: Figure 3 shown.

[0070] like Figure 3 As shown in Figure 4, in time slot T1, only LED1 has a driving RF signal, i.e., the RF signal f1 in Figure 4. The driving frequencies of other LEDs are 0 as shown in Figure 7. Similarly, if in time slot T2, the SM control bit is "01", then the second MZM unit will transmit the carrier modulation signal, and only LED2 will transmit the driving RF signal. Therefore, Figure 3 This study demonstrates that, through the CWDM architecture and passive filtering modules within the LED AP unit, the SM control bits within the RG optical module can achieve low-energy centralized MIMO control. Furthermore, based on centralized MIMO processing, this paper addresses the issues of visible light MIMO correlation and high energy consumption due to power imbalance by introducing a power amplifier (PA) into the RG optical module, deriving the mapping between LED transmit power and optical modulator modulation index, and proposing an optically controlled power imbalance technique.

[0071] like Figure 2 As shown, before the MZM unit optical modulation, the carrier modulation module is connected to the PI control block. The PI control block is composed of a radio frequency power amplifier PA. Based on the optical double-sideband modulation technology of the MZM unit, the present invention provides the relationship between the MZM unit optical modulation index and the LED transmission power to achieve optical control of power imbalance. Therefore, the unmodulated optical signal E output by the laser LD is in (t) are as follows:

[0072]

[0073] In the above formula (1), P Laser is the laser light power, is the optical carrier angular frequency, e is the base of the natural logarithm, j is the imaginary unit in the complex number, and t is the time independent variable; then, if the MZM module operates at the orthogonal bias point, its output optical field is:

[0074]

[0075] In the above formula (2), Indicates the center angle frequency of the SM signal driving the modulator; V π is the modulator half-wave voltage; V dr The amplitude of the RF signal is determined by each RF power amplifier PA. The RF signal output by the RF power amplifier PA is modulated to the optical signal on both sides of the optical carrier. After the optical signal is photoelectrically modulated, the RF signal contains a frequency of and its harmonics The ingredients can be expressed as:

[0076]

[0077] In the above formula (3), η is the responsivity of the photoelectric converter PD, represents the (2N-1)th order Bessel function of the first kind, is the modulation index of the MZM module, n represents the numerator of the accumulator in formula (3), and t is the time independent variable. Then, the RF signal output by the photoelectric converter PD passes through the bandpass filter BPF to generate the LED driving RF signal, which only contains the frequency of

[0078]

[0079] In the above formula (4), J1 represents the first-order Bessel function of the first kind, and α represents the signal attenuation coefficient generated by the bandpass filter BPF. Therefore, it can be seen from formula (4) that the RF signal amplitude and modulation index of the optical signal restored by the photoelectric converter PD to the electrical signal are If ηαP Laser Normalized, formula (4) can be further expressed as:

[0080]

[0081] Finally, since the LED can be regarded as a directly modulated laser, its output power in the linear range is:

[0082]

[0083] So, if Figure 2 In the centralized SM mechanism, only one MZM unit performs optical double-sideband transmission in each time slot. Therefore, Equation (6) represents the LED power activated in each time slot. This LED power can be controlled by the modulation index of the MZM unit, and each LED can be independently controlled. The following describes the system transmission model.

[0084] S200, system transmission model

[0085] The present invention uses multiple LEDs to construct a MIMO signal based on the visible light band as a visible light MIMO channel, and uses LEDs to transmit light-controlled SM signals. The visible light spatial modulation channel (i.e., visible light-SM channel) can be expressed as:

[0086] Y = βHX + N (7);

[0087] In the above formula (7), H represents N r ×N t The visible light MIMO channel matrix, where N r 、N t They are the number of users and the number of transmission LEDs, respectively. The matrix coefficients are the signal gain h from the j-th LED to the i-th user. ij β represents the optical fiber link loss coefficient, which comes from phase noise, nonlinearity and dispersion effects. n ] represents the SM signal at the transmitting end, and N represents additive white Gaussian noise.

[0088] In addition, the signal model from the LED AP unit to indoor users adopts the Lambertian radiation model; therefore, the visible light MIMO channel matrix coefficients can be written as:

[0089] h ij =TRεG ij (8);

[0090] In the above formula (8), T represents the gain of the CWDM demultiplexer to the optical signal; R represents the photoelectric receiving response of the indoor user end; ε is the electro-optical conversion efficiency of the LED. In addition, G ij represents the visible light channel gain from the jth LED to the i-th user in the Lambertian radiation model, which can be expressed as:

[0091]

[0092] Where, L in the above formula (9) represents the order of Lambertian radiation, d ij The distance from the i-th LED to the j-th LED, Φ and ψ ij are the exit angle and incident angle of the channel from the jth LED to the ith LED, A R and ψ FoV are the detection range and half angle of the photoelectric detector at the user receiving end. From formula (9), we can see that if the LED is not within the field of view, G ij =0.

[0093] Then, the maximum detection method is used to recover the signal through formula (10)

[0094]

[0095] Wherein, A in the above formula (10) represents the set of all transmitted symbols; It is known from formula (10) that when the h values ​​of some channels are similar, since the maximum likelihood algorithm is an exhaustive method, it is possible to make Therefore, the present invention adopts the method of power imbalance to reduce the h correlation, that is, to change the H value gain element in the formula from h ij becomes γh ij , thereby reducing the probability of decision errors. Unlike the traditional power controller where the power imbalance is at the LED end, the γ in the present invention represents the optical control gain, which is directly generated by the optical control module in the RG optical module.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A CWDM-based optically controlled visible light high-correlation MIMO system, characterized by: The MIMO system specifically includes an RG optical module and an LED AP unit connected to the RG optical module via an optical fiber; The RG optical module includes a spatial modulation digital signal processor (SM DSP), a carrier modulation module, a PI control block, a CWDM multiplexer, and at least one MZM unit. The PI control block includes at least one RF power amplifier (PA), which, together with the MZM unit, is used to centrally control the LED transmit power in the LED AP unit. Each MZM unit includes a laser (LD) and an MZM module. The signal input end of the spatial modulation digital signal processor (SM DSP) is connected to network data, and the signal output end is electrically connected to the carrier modulation module and the RF power amplifier (PA). The MZM modules are electrically connected to the corresponding RF power amplifiers (PA), and are connected to the corresponding lasers (LD) and the CWDM multiplexer via optical fibers. The LED AP unit includes a CWDM demultiplexer, at least one photoelectric converter PD, at least one bandpass filter BPF, and at least one LED; the CWDM demultiplexer is connected to the CWDM multiplexer via an optical fiber; the input end of each photoelectric converter PD is connected to the CWDM demultiplexer via an optical fiber, and the output end is electrically connected to the corresponding bandpass filter BPF; each bandpass filter BPF is electrically connected to the corresponding LED; The outdoor access network data is passed through the spatial modulation digital signal processor SM DSP to generate the DB signal and CB signal in the SM; the DB signal is modulated by the carrier and is raised to the RF center frequency of On the carrier, the CB signal transmits the carrier modulated signal to the corresponding MZM unit according to the control bit information; each MZM unit is responsible for the electro-optical conversion in each CWDM band; then, the MZM modulated optical signal of each frequency band is coupled to the CWDM multiplexer to form a CWDM signal; at the indoor LED AP unit end, through optical fiber transmission and the CWDM demultiplexer, the wavelength division multiplexing signal is separated according to the band, and then the single band is restored to the RF signal through the optical-to-electrical converter PD; After the RF signal is filtered to remove noise interference, the corresponding SM signal is transmitted to the corresponding LED for visible light MIMO transmission.

2. The CWDM-based optically controlled visible light high-correlation MIMO system according to claim 1, characterized in that: Before the MZM unit optical modulation, the carrier modulation module is electrically connected to the PI control block; the PI control block is composed of a radio frequency power amplifier PA; the relationship between the optical modulation index of the MZM unit and the LED emission power is given to achieve optical control of power imbalance; the unmodulated optical signal output by the laser LD as follows: （1）； In the above formula (1), is the laser light power, is the optical carrier angular frequency, e is the base of the natural logarithm, j is the imaginary unit in the complex number, and t is the time variable.

3. The CWDM-based optically controlled visible light high-correlation MIMO system according to claim 2, characterized in that: If the MZM module operates at the quadrature bias point, its output light field is: （2）； In the above formula (2), represents the center angular frequency of the SM signal driving the modulator; is the modulator half-wave voltage; It is the amplitude of the radio frequency signal, and the amplitude is determined by each of the radio frequency power amplifiers PA.

4. The CWDM-based optically controlled visible light high-correlation MIMO system according to claim 3, characterized in that: The RF signal output by the RF power amplifier PA is modulated to the optical signals on both sides of the optical carrier at the same time. After photoelectric modulation, the RF signal contains a frequency of and its harmonics The ingredients can be expressed as: （3）； In the above formula (3), is the responsivity of the photoelectric converter PD, represents the (2N-1)th order Bessel function of the first kind, is the modulation index of the MZM module, n represents the numerator of the accumulator in formula (3), and t is the time independent variable; Then, the RF signal output by the photoelectric converter PD passes through the bandpass filter BPF to generate an LED driving RF signal, which only contains the frequency : （4）； In the above formula (4) represents the first-order Bessel function of the first kind, represents the signal attenuation coefficient produced by the bandpass filter BPF.

5. The CWDM-based optically controlled visible light high-correlation MIMO system according to claim 4, characterized in that: From the formula (4), it can be seen that the photoelectric converter PD restores the optical signal to the RF signal amplitude and modulation index of the electrical signal Related; if Normalized, the formula (4) can be further expressed as: （5）。 6. The CWDM-based optically controlled visible light high-correlation MIMO system according to claim 5, characterized in that: The LED can be regarded as a directly modulated laser, and its output power in the linear range is: （6）； In the centralized SM mechanism, in each time slot, only one MZM unit performs optical double-sideband transmission, so formula (6) can express the LED power activated in each time slot. The LED power can be controlled by the modulation index of the MZM unit, and each LED can be controlled independently.

7. The CWDM-based optically controlled visible light high-correlation MIMO system according to claim 1, characterized in that: The MIMO system uses multiple LEDs to construct a MIMO signal based on the visible light band as a visible light MIMO channel, and uses LEDs to transmit light-controlled SM signals. The visible light spatial modulation channel can be expressed as: （7）； In the above formula (7) express The visible light MIMO channel matrix is They are the number of users and the number of transmission LEDs, respectively. The matrix coefficients are the signal gain from the jth LED to the i-th user. express; Represents the optical fiber link loss coefficient, which comes from phase noise, nonlinearity and dispersion effects; Indicates the SM signal at the sending end, represents additive white Gaussian noise.

8. The CWDM-based optically controlled visible light high-correlation MIMO system according to claim 7, characterized in that: The signal model from the LED AP unit to the indoor user adopts the Lambertian radiation model, so the visible light MIMO channel matrix coefficient can be written as: （8）； In the above formula (8) Indicates the gain of the CWDM demultiplexer on the optical signal; Indicates the photoelectric receiving response of the indoor user end; is the electro-optical conversion efficiency of the LED; represents the visible light channel gain from the jth LED to the i-th user in the Lambertian radiation model, which can be expressed as: (9)； In the above formula (9), L represents the order of Lambertian radiation; The distance from the i-th LED to the j-th LED; and denote the exit angle and incident angle of the channel from the jth LED to the ith LED respectively; and are the detection range and half angle of the photoelectric detector at the user receiving end respectively; From formula (9), we can see that if the LED is not within the field of view, ; The signal is recovered by using the maximum detection method through the following formula (10) : （10）； In the above formula (10), A represents the set of all transmitted symbols; Represents the square of the 2-norm; the power imbalance method is used to reduce the h correlation, that is, to change the H value in the formula. The gain element is becomes , thereby reducing the probability of judgment errors; Indicates the optical control gain, which is directly generated by the optical control module in the RG optical module.

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