Light-operated visible light high-correlation MIMO system based on CWDM

Abstract

The invention provides a light-operated visible light high-correlation MIMO system based on CWDM. The light-operated visible light high-correlation MIMO system 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 (SMDSP), 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), and the PI control block and the MZM unit are used for carrying out concentrated light control on the LED transmitting power in the LED AP unit; each MZM unit comprises a laser device LD and an MZM module; 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 method is reasonable in conception, takes the CWDM technology as the background of an access network, mainly aims to reduce the correlation of visible light communication, and constructs a visible light MIMO system with low energy consumption and high performance based on a centralized optical signal processing theory.

Description

Technical Field

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

[0002] At present, the mainstream solutions to high channel correlation mainly include photodetector angle diversity technology, image sensor reception and power imbalance method. Photodetection diversity technology and image sensor technology are mainly concentrated in the receiving end, which greatly increases the complexity of reception. In terms of photodetection technology, non-patent documents 1 and 2 reduce the channel correlation of visible light MIMO by controlling the receiving angle of the photodetector, thereby improving the channel capacity. At the same time, non-patent document 3 is based on angle diversity technology and adopts the method of grouping LEDs to further reduce the correlation of the visible light MIMO system. In addition, non-patent document 4 considers the angle control capability of the photodetector for multiple reception schemes, thereby improving the flexible and robust performance of the system. In terms of image sensors, non-patent document 5 comprehensively analyzes the visible light MIMO communication performance based on image sensors for different modulation formats, and obtains the optimal modulation format under different spatial distribution conditions. The above photodetection diversity technology and image sensor technology reduce the correlation of the visible light MIMO system at the cost of increasing the user-end signal processing module, which is extremely unfriendly to lightweight Internet of Things 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 by controlling the power distribution of each LED, the optimal power allocation coefficient is derived to reduce 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 densely distributed 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, around the above challenges, the technical problems to be solved by the present invention are as follows:

[0005] Channel correlation mitigation mechanism for low-energy visible light MIMO system: For the study of visible light MIMO correlation, the traditional power imbalance method uses the access end power controller module to control the power of the LED. How to reduce the complexity and high energy consumption of the access end is the basic premise to ensure low complexity and high transmission efficiency. For user mobile scenarios, the optimal power allocation coefficient changes with the LED spacing and the user's mobile position. How to achieve centralized, efficient and low-energy allocation of the optimal allocated power is the main difficult problem solved by this patent.

[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 view of 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, which has a reasonable concept, takes CWDM technology as the access network background, takes reducing the correlation of visible light communication as the main purpose, and constructs a low-energy consumption and high-performance visible light MIMO system based on centralized optical signal processing theory.

[0016] In order 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 through 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 is used together with the MZM unit to centrally control the LED transmission power 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 RF power amplifier PA respectively; the MZM module is electrically connected to the corresponding RF power amplifier PA, and is connected to the corresponding laser LD and the CWDM multiplexer through an optical fiber;

[0018] The LED AP unit comprises 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;

[0019] The outdoor access network data is transmitted through the spatial modulation digital signal processor SM DSP to generate DB signal and CB signal in SM; the DB signal is modulated by carrier wave and is up-regulated to the carrier wave with the RF center frequency of f1, 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, each frequency band MZM modulated optical signal 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 photoelectric 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 optically controlled visible light high-correlation MIMO system based on CWDM, wherein: before the optical modulation of the MZM unit, 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 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 independent variable.

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

[0024]

[0025] In the above formula (2), represents 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 RF signal output by the RF power amplifier PA is simultaneously modulated to the optical signals on both sides of the optical carrier, and after photoelectric modulation, the RF 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 an LED driving RF signal, which only contains the frequency

[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: from the formula (4), it can be known that 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 optically controlled visible light high-correlation MIMO system based on CWDM, 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 represent 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 optically controlled visible light high-correlation MIMO system based on CWDM, 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 coefficients are 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] The optically controlled visible light high-correlation MIMO system based on CWDM, wherein: 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 for 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 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;

[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, the H value in the formula is changed to gain element 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 reasonably conceived and has the following advantages or characteristics:

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

[0050] Aiming at the high channel correlation of visible light MIMO communication, the present invention is based on CWDM optical network architecture, utilizes the relationship between MZM modulation index and output optical power, removes the high energy consumption power control module of indoor room LED access point, and adopts centralized optical network framework to control LED power, thus realizing low energy consumption and low complexity power imbalance control room 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 view of the change of 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, compared with the prior art, the present invention also has the following characteristics:

[0056] Passive Optical Networks (PON) is the current mainstream access optical network, with low energy consumption, simplified deployment, centralized signal processing and other characteristics. The CWDM-based access optical network module in the present invention belongs to a centralized optical network and is suitable for the WDM-PON architecture. In addition, the present invention can be used as an indoor application technology of the WDM-PON network, focusing on solving the high correlation problem of indoor visible light.

[0057] Centralized Radio Access Networks (C-RAN) are the main access architecture of cellular networks at present. In the future, mobile networks will integrate outdoor cellular networks with indoor communication networks. The network architecture of the present invention can be used for the functional segmentation module in C-RAN, further simplifying the complexity of indoor access points and improving the centralized flexible allocation capability. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0059] Figure 1 The 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, i.e., the RG optical module, acts as a gateway to connect the external outdoor network with 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 It is a 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 described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0063] The present invention is further explained below in conjunction with specific implementation modes.

[0064] like Figure 1As shown in the figure, since visible light communication signals are mainly transmitted in line-of-sight channels, 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 of the visible light MIMO system on the channel capacity. Since the traditional power imbalance signal processing module is in the LED AP, in order to reduce the complexity of the LED end, the present 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 as follows: Figure 2 As shown, it includes an RG optical module and an 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 includes at least one power amplifier PA, which is used together with the MZM unit 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 in the 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 transmission 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, such as Figure 2 As shown, the present invention uses RG optical module and optical radio frequency communication technology to realize the centralized optical control PI technology of 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 DB and CB signals in SM; then, the DB signal is modulated by the carrier and is up-regulated to the carrier with the RF center frequency f1, 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 each CWDM band (λ1,λ2…λ n ) electro-optical conversion, including power amplifier (PA), laser diode (LD) and MZM module (Mach-zenhder 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 according to the wavelength band (λ1,λ2…λ n ) are 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 LED transmission power-optical modulator modulation index mapping. 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 the figure, in time slot T1, only LED1 has a driving RF signal, i.e., the RF signal f1 in ④. The driving frequency of other LEDs is 0 as shown in 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 It is shown that through the CWDM structure and the passive filter module in the LED AP unit, the SM control bit in the RG optical module can realize low-energy centralized MIMO control. In addition, based on centralized MIMO processing, in order to solve the problems of visible light MIMO correlation and power imbalance and high energy consumption, the present invention introduces a power amplifier PA in the RG optical module, derives the mapping relationship between LED transmission power and optical modulator modulation index, and proposes an optical control power imbalance technology.

[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 gives the relationship between the MZM unit optical modulation index and the LED emission power to achieve power imbalance optical control. 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), represents 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 through photoelectric modulation. 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

[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 photoelectric converter PD that restores the optical signal to the electrical signal 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, in each time slot, only one MZM unit performs optical double-sideband transmission, so formula (6) can represent the LED power activated in each time slot, which can be controlled by the modulation index of the MZM unit, and each LED can be controlled independently. Below, the present invention will be described with respect to 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 frequency 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 jth LED to the i-th user. ij 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.

[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 on 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] 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 denote the exit angle and incident angle of the channel from the jth LED to the ith LED, respectively, and 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 signal is restored by the maximum detection method through formula (10):

[0094]

[0095] Wherein, in the above formula (10), A represents the set of all transmission symbols; It is known from formula (10) that when the h values ​​of some channels are similar, because the maximum likelihood algorithm is an exhaustive method, it is possible to make Therefore, the present invention adopts the power imbalance method 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 error. Different from the traditional power controller where the power imbalance is at the LED end, the γ in the present invention represents the size of 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned 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 is used together with the MZM unit to centrally control the LED transmission power 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 RF power amplifier PA respectively; the MZM module is electrically connected to the corresponding RF power amplifier PA, and is connected to the corresponding laser LD and the CWDM multiplexer through an optical fiber; The LED AP unit comprises 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; The outdoor access network data is transmitted through the spatial modulation digital signal processor SM DSP to generate DB signal and CB signal in SM; the DB signal is modulated by carrier wave and is up-regulated to the carrier wave with the RF center frequency of f1, 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, each frequency band MZM modulated optical signal 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 photoelectric 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 power imbalance optical control; the unmodulated optical signal E output by the laser LD in (t) are as follows: 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.

3. The CWDM-based optically controlled visible light high-correlation MIMO system according to claim 1, characterized in that: If the MZM module operates at the orthogonal bias point, its output light field is: In the above formula (2), represents 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.

4. The CWDM-based optically controlled visible light high-correlation MIMO system according to claim 1, 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: 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 an LED driving RF signal, which only contains the frequency 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.

5. The CWDM-based optically controlled visible light high-correlation MIMO system according to claim 4, characterized in that: It can be seen from the formula (4) that 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:

6. The CWDM-based optically controlled visible light high-correlation MIMO system according to claim 3, characterized in that: The LED can be regarded as a directly modulated laser, and its output power in the linear range is: In the centralized SM mechanism, in each time slot, only one MZM unit performs optical double-sideband transmission, so formula (6) can represent 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: Y = βHX + N (7); 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 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.

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: h ij =TRεG ij (8); In the above formula (8), T represents the gain of the CWDM demultiplexer for 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: 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 They are the detection range and half angle of the field of view 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; The signal is recovered by using the maximum detection method through the following formula (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, the H value in the formula is changed to gain element 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.

Images