Implementation method of rate-adaptive multi-input single-output visible light communication system

Abstract

The invention discloses an implementation method of a rate-adaptive multi-input single-output visible light communication system, the visible light communication system comprises a plurality of transmitting ends and a receiving end, binary transmitting data streams in one-to-one correspondence with the transmitting ends are respectively modulated to a constellation diagram, and the receiving end is connected with the receiving end. All the transmitting constellations are loaded to the signal generator after being subjected to digital signal processing, the signal generator outputs analog signals of the corresponding number, the analog signals are amplified through the electric amplifier and then coupled with the direct current through the bias device, and electric signals obtained through coupling are converted into optical signals through the light sources in one-to-one correspondence with the transmitting ends. Probabilistic shaping is performed on all transmitting constellations, so that the transmitting constellations conform to MB distribution of a QAM constellation; and geometric shaping is carried out on all transmitting constellations at the same time, so that the transmitting signal power of each transmitting end is equal. According to the invention, bandwidth and space resources can be fully utilized, and a flexible high data rate close to channel capacity is provided for each user.

Description

Technical Field

[0001] The present invention relates to visible light communication, and in particular to a method for realizing a rate-adaptive multi-input single-output visible light communication system, belonging to the technical field of wireless optical communication. Background Art

[0002] With the surge in emerging services and the expansion of ultra-large-scale interconnection, the rapid growth of mobile network data traffic and the increasingly scarce radio frequency (RF) spectrum have formed a sharp contradiction. Visible light communication (VLC) has many advantages such as abundant and unregulated spectrum resources, no electromagnetic interference, high efficiency and energy saving, and is considered to be a key enabling technology for 6G mobile networks.

[0003] VLC systems in point-to-multipoint (PtMP) networks can serve multiple mobile or fixed user terminals while providing the same bandwidth and lighting resources. PtMP VLC systems using a single modulation format suffer from inefficient bandwidth utilization. Switching modulation formats based on the user's signal-to-noise ratio (SNR) budget can only partially solve this problem because there is still a large SNR gap between adjacent conventional quadrature amplitude modulation (R-QAM) formats. Probabilistic shaping (PS) rate adaptive single-input single-output (SISO) VLC systems can flexibly provide data rates close to the channel capacity for different users. Increasing the transmitted optical power is an effective way to improve the SNR and thus the achievable data rate for users. However, the transmitted optical power of VLC systems is limited by the nonlinear effects of light-emitting diodes (LEDs). Therefore, the system design with a single transmitter limits the overall achievable data rate for all users.

[0004] The nonlinear constraints of LEDs can be alleviated by increasing the number of parallel transmitters. The multiple-input single-output (MISO) VLC system in a multipoint-to-multipoint network can not only serve multiple user terminals, but also obtain considerable spatial diversity gain. However, the optical front end of the VLC system uses intensity modulation / direct detection (IM / DD) technology, which makes the MISO VLC channel always highly correlated. The small difference in channel gain leads to channel matrix rank deficiency, and the MISO demultiplexing method in the RF communication system cannot be directly applied to the VLC system.

[0005] Superposition coded modulation (SCM) is robust to highly correlated MISO VLC channels. The power ratio (PR) between transmitted signals determines the minimum Euclidean distance (MED) of the superimposed constellation at the receiving end and is an important factor affecting the performance of the SCM VLC system. A power ratio PR of 1 is optimal. Deviation from 1 will cause high-power signals to fall into the nonlinear range of the LED more easily and cause power competition at the photodetector (PD). Geometric shaping (GS) can make the optimal power ratio PR of the SCM scheme 1, but a universal geometric shaping GS method has not yet been proposed. In addition, if the transmitted signals are not equivalent, the optimal power ratio PR will change with the change of the probability shaping factor (PSF).

[0006] Therefore, it is urgent to propose an implementation method of a rate adaptive MISO VLC system to solve the above problems and improve the utilization efficiency of bandwidth and space resources. Summary of the invention

[0007] In view of the problem of low bandwidth and space resource utilization efficiency of existing modulation format single-input single-output visible light communication systems, the purpose of the present invention is to propose a method for realizing a rate-adaptive multi-input single-output visible light communication system. The present invention fully utilizes bandwidth and space resources through a hybrid geometric-probabilistic shaping (GPS) rate-adaptive multi-input single-output visible light communication MISO VLC system based on SCM, and provides each user with a flexible high data rate close to the channel capacity.

[0008] The technical solution of the present invention is achieved in this way:

[0009] A method for implementing a rate-adaptive multi-input single-output visible light communication system, the visible light communication system comprising a transmitting end and a receiving end, wherein the transmitting end is multiple and the receiving end is one, thereby forming a multi-input single-output visible light communication system; each transmitting end corresponds to a light source; binary transmission data streams corresponding to the transmitting end are modulated onto a constellation diagram to increase spectrum efficiency, thereby obtaining a transmission constellation, all transmission constellations are loaded onto a signal generator after digital signal processing, the signal generator outputs a corresponding number of analog signals, and the analog signals are amplified by an electrical amplifier and then coupled to a direct current through a bias device, the coupled electrical signals are converted into optical signals by the light source corresponding to the transmitting end, and the receiving end is used to receive the optical signal;

[0010] All transmit constellations are probability shaped to conform to the Maxwell-Boltzmann distribution of the QAM constellation; at the same time, all transmit constellations are geometrically shaped to make the transmit signal power of each transmitter equal.

[0011] Furthermore, during probability shaping, the transmit constellation is probability shaped using the constant component matching distribution. When there are two transmitters, the probability distribution of the QAM signal with a modulation order of M is:

[0012]

[0013] Among them, X i represents the complex coordinate set of the i-th low-order M-QAM constellation at the transmitter, X = {x0, x1, ..., x M-1}; x and x' represent constellation symbols; v is the probability shaping factor that controls the source entropy SE, and its value is between 0 and 1; there is a one-to-one mapping relationship between the source entropy SE and the probability shaping factor v.

[0014] Furthermore, the source entropy SE is determined as follows,

[0015] 1) Establish a lookup table of the relationship between normalized generalized mutual information, signal-to-noise ratio and source entropy;

[0016] 2) determining the threshold of the normalized generalized mutual information as the value of the normalized generalized mutual information for searching;

[0017] 3) The signal-to-noise ratio is obtained by estimation, and based on the lookup table in step 1), the maximum source entropy SE of each scheme that can meet the normalized generalized mutual information threshold is determined.

[0018] Furthermore, during geometric shaping, the optimal geometric shaping factor is solved in advance, and then the transmit constellation is geometrically shaped based on the obtained optimal geometric shaping factor. The optimal geometric shaping factor is defined as the geometric shaping factor when the power ratio of each transmit signal is equal to 1 and the superimposed constellation at the receiving end is evenly distributed.

[0019] Furthermore, the optimal geometric shaping factor is determined as follows:

[0020] a) adding geometric shaping factors to the in-phase and quadrature components of the two transmitted signals respectively;

[0021] b) Presetting the optimal power ratio of the two transmitted signals to 1, and obtaining a symbol set of a superimposed constellation at the receiving end;

[0022] c) the elements of the symbol set constitute an arithmetic progression whose common difference is the minimum Euclidean distance;

[0023] d) establishing a set of equations about the geometric shaping factor based on the arithmetic progression in step c), and the geometric shaping factor obtained by solving the set of equations is the optimal geometric shaping factor.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. Compared with the existing conventional modulation format switching rate adaptive SISO VLC and probability shaping rate adaptive SISO VLC technologies, the SCM-based hybrid GPS rate adaptive multi-input single-output visible light communication MISO VLC system proposed in the present invention can provide each user with a flexible and fine-grained net data rate (NDR) while improving the overall NDR performance of all users.

[0026] 2. Compared with the traditional SISO system, the present invention disperses the total power to multiple LEDs through a multi-transmitter setting, reducing the risk of nonlinear distortion of LEDs under the same total power budget, improving the maximum transmission power tolerance of the system, and thus improving the receiving signal-to-noise ratio.

[0027] 3. The geometric-probabilistic hybrid shaping strategy proposed in the present invention enhances the robustness of the system against non-ideal factors such as nonlinear distortion, high channel correlation, power competition, and dynamic changes in power ratio. The general method for solving the optimal geometric shaping factor GSF provides a technical paradigm for designing superimposed even-order constellations. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 - Schematic diagram of the GS SCM scheme of the present invention; wherein (a) MISO-GS (4,4); (b) MISO-GS (8,8); (c) MISO-GS (16,16);

[0029] Figure 2 - Schematic diagram of probability distribution of the hybrid GPS SCM scheme of the present invention; where (a) MISO-GS (4,4), H = 3.9 bit / symbol; (b) MISO-GS (8,8), H = 5.9 bit / symbol; (c) MISO-GS (16,16), H = 7.9 bit / symbol;

[0030] Figure 3 - Schematic representation of the NGMI lookup of the hybrid GPS SCM solution of the present invention; wherein (a) MISO-GS (4,4); (b) MISO-GS (8,8); (c) MISO-GS (16,16);

[0031] Figure 4 -System block diagram and experimental device diagram of the hybrid GPS rate adaptive MISO VLC system based on SCM of the present invention;

[0032] Figure 5 -Characteristics of the VLC experimental system of the present invention; wherein (a) frequency response; (b) amplitude-amplitude response in the linear region; (c) amplitude-amplitude response in the nonlinear region;

[0033] Figure 6- NGMI performance comparison chart under different situations of the present invention; (a) different Vpp total (a) NGMI performance of MISO-GS(16,16) and MISO-R(16,16) schemes under different Vpp1; (b) NGMI performance of MISO-GPS(16,16) and MISO-PS(16,16) schemes under different Vpp1; (c) Constellation diagram of the marker points;

[0034] Figure 7 -Different Vpp of the present invention total Performance diagram of the MISO-GS(16,16) and SISO-R(256) schemes; (a) NDR and NGMI; (b) AIR and GMI;

[0035] Figure 8 -Different Vpp of the present invention total Performance diagram of the MISO-GPS (16,16) and SISO-PS (256) schemes; (a) NDR and NGMI; (b) AIR and GMI;

[0036] Fig. 9 -Different Vpp of the present invention total The following is a comparison chart of NDR and NGMI performance of various rate adaptive VLC systems;

[0037] Fig.10 -NDR performance comparison chart of various rate adaptive VLC systems at different distances of the present invention. DETAILED DESCRIPTION

[0038] The present invention provides a method for implementing a rate-adaptive multi-input single-output visible light communication system, wherein the visible light communication system includes a transmitting end and a receiving end, wherein there are multiple transmitting ends, each of which corresponds to a light source, and there is one receiving end, thereby forming a multi-input single-output visible light communication system. Binary transmission data streams corresponding to the transmitting ends are modulated onto a constellation diagram to increase the spectrum efficiency, thereby obtaining a transmission constellation, and all transmission constellations are loaded onto a signal generator after digital signal processing, and the signal generator outputs a corresponding number of analog signals and amplifies them through an electrical amplifier and then couples them with a DC through a bias device, and the coupled electrical signals are converted into optical signals through the light source corresponding to the transmitting end, and the receiving end is used to receive the optical signal.

[0039] The present invention distributes the total power to multiple LEDs, reduces the risk of nonlinear distortion of LEDs under the same total power budget, improves the maximum transmission power tolerance of the system, and further improves the receiving signal-to-noise ratio.

[0040] The present invention performs probability shaping on all transmission constellations to make them conform to the Maxwell-Boltzmann distribution of the QAM constellation; at the same time, all transmission constellations are geometrically shaped to make the transmission signal power of each transmitting end equal. The present invention enhances the robustness of the system against non-ideal factors such as nonlinear distortion, high channel correlation, power competition, and dynamic changes in power ratio through a geometric-probabilistic hybrid shaping strategy.

[0041] The SCM-based hybrid GPS rate adaptive multi-input single-output visible light communication (MISO VLC) system proposed in the present invention can provide each user with a flexible and fine-grained net data rate (NDR) while improving the overall NDR performance of all users.

[0042] In order to better understand the implementation principle and solution of the present invention, the specific implementation scheme of the present invention is described in detail below with reference to the accompanying drawings.

[0043] In order to clearly illustrate the technical solution and the main points of the invention, a naming convention is first established: AB (M1, M2). "A" represents MISO or SISO, representing the type of VLC system. "B" represents GPS, GS, PS or R, R means no shaping, representing the type of constellation. "M1" and "M2" represent the modulation orders of the two transmitted signals. When "A" is SISO, "M2" is omitted. For example, MISO-GPS (16, 16) represents a MISO VLC system in which both transmitted signals are GPS-16QAM, and SISO-PS (256) represents a SISO VLC system in which the transmitted signal is PS-16QAM.

[0044] About Geometry Shaping

[0045] The geometric shaping criterion ensures that the optimal power ratio of the hybrid GPSSCM scheme is 1, reducing the risk of nonlinear distortion caused by the LED and power competition caused by the photodetector.

[0046] GSSCM program Figure 1 As shown. The gray dotted circles indicate the initial positions of the constellation points, and the colored solid circles indicate the positions of the constellation points after geometric shaping. The color composition of the superimposed constellation points details the superposition mechanism of each scheme. The two transmitted signals of the MISO-GS(4,4) scheme are 4QAM located in the in-phase (I) and quadrature (Q) components, respectively. The transmitted signals of the MISO-GS(8,8) and MISO-GS(16,16) schemes are two GS-8QAM and two GS-16QAM, respectively. The optimal power ratio of all GSSCM schemes is 1. The two transmitted signals of each GSSCM scheme have the same amplitude and different phases. Since the IM / DD, VLC system transmits amplitude information through optical intensity, the two transmitted signals can be regarded as equivalent.

[0047] Before power normalization, the minimum Euclidean distance MED of the transmitted signal is equal to 2. Therefore, the two transmitted signals without geometric shaping are expressed as:

[0048]

[0049] Among them, N1, N2, N3 and N4 are all positive even numbers.

[0050] The superposition constellation can be regarded as the linear superposition of two transmit constellations on the I and Q components, expressed as:

[0051]

[0052] Wherein, p1 and p2 represent the power coefficients of the two transmitted signals respectively.

[0053] Without loss of generality, the MISO-GS (16,16) scheme is used as an example to illustrate the method of solving the optimal geometric shaping factor. N1, N2, N3 and N4 are all 4. Therefore, equation (1) can be rewritten as:

[0054]

[0055] Given the target power ratio is 1, p1 and p2 are both set to 1. Then equation (2) is rewritten as:

[0056] I' y ,Q' y ∈{0,±2,±4,±6} (4)

[0057] According to equation (4), the I and Q components of the superposition constellation have only 7 levels. The system performance of SCMMISOVLC will be significantly deteriorated due to the serious overlap of the superposition constellation points.

[0058] The SCM scheme is optimized by geometric shaping. The optimal geometric shaping factor is defined as the geometric shaping factor when the power ratio is equal to 1 and the superimposed constellation at the receiving end is evenly distributed. Figure 1 As shown in (c), two geometric shaping factors a1 and a2 are introduced into the Q and I components of the two transmitted signals, respectively, where a2 ≥ a1 ≥ 0. The signal levels of the two GS-16QAM constellations are expressed as:

[0059]

[0060] Set p1 and p2 to 1, that is, the power ratio is 1, and solve for the optimal geometric shaping factor. At this time, the signal level of the superimposed constellation is expressed as:

[0061]

[0062] Without power normalization, the minimum Euclidean distance of the superimposed constellation is equal to 2. The signal level should be an arithmetic progression with a tolerance of 2. Therefore, the following set of equations is established:

[0063]

[0064] The solution is a1=3, a2=9.

[0065] By analogy with the MISO-GS (16,16) scheme, the optimal geometric shaping factors of the MISO-GS (4,4) and MISO-GS (8,8) schemes are 0 and 3, respectively. Since the two transmitted signals are equivalent, power normalization does not change the optimal power ratio.

[0066] About Hybrid GPS Strategy

[0067] The strategy solves the problem that the optimal power ratio varies dynamically with the probability shaping factor, and applies probability shaping to the two transmitted signals to maximize the probability shaping gain.

[0068] Apply probability shaping to Figure 1 The GSSCM scheme shown is a hybrid GPSSCM scheme. Compared with the probability shaping at the receiving end, the probability shaping at the transmitting end is more robust to the peak voltage (Vpp) and has a larger driving Vpp dynamic range. Therefore, the constant component matching distribution (CCDM) is used to probability shape the transmit constellation to make it conform to the optimal probability distribution of the QAM constellation - the Maxwell-Boltzmann (MB) distribution. Both equal-order M-QAM signals of the hybrid GPSSCM scheme must be probability shaped. The probability distribution of the probability shaped M-QAM following the MB distribution is:

[0069]

[0070] Among them, X i represents the complex coordinate set of the i-th low-order M-QAM constellation at the transmitter, X = {x0, x1, ..., x M-1}. x and x' represent constellation symbols. v is the probability shaping factor that controls the source entropy (SE), and its value is between 0 and 1.

[0071] There is a one-to-one mapping between source entropy and probability shaping factor. For a given M-QAM signal, its information rate can be flexibly adjusted by changing the probability shaping factor. The average power of the transmit constellation decreases as the probability of the outer constellation points decreases. After power normalization, the constellation points of transmit constellations with different source entropies have different positions. If two transmit constellations are equivalent, their constellation points change synchronously. In this case, the optimal power ratio does not change with the change of the probability shaping factor. This feature reduces the complexity of the SCMMISOVLC system.

[0072] The probability distribution of the superposition constellation at the receiving end is determined by the superposition mechanism of each superposition scheme. Since both transmit constellations are of order M, the probability distribution of the superposition constellation is:

[0073]

[0074] Where X' is the high-order M at the receiving end 2 -The set of complex coordinates of the QAM constellation,

[0075] The source entropy of the superposition constellation is expressed as:

[0076] H=-Σ x∈X' P X' (x)log2(P X' (x))(10)

[0077] When the power ratio is 1, the probability distribution of the transmission constellation and superposition constellation of each hybrid GPSSCM scheme is shown as follows: Figure 2 shown.

[0078] On the Hybrid GPS Rate Adaptive MISOVLC System Based on SCM

[0079] In order to maximize the signal-to-noise ratio budget of each user and avoid bandwidth waste, modulation format switching and probability shaping are applied to the transmitter to achieve rate adaptation, so that each user can achieve a data rate close to the channel capacity. In addition, MISO can further improve the channel capacity of the VLC system. The hybrid GPS rate adaptive MISO VLC system based on SCM can improve the achievable data rate of all users while achieving flexible data rates.

[0080] First, a mathematical model of the 2×1SCMVLC system is established. The transmit signal is defined as:

[0081] x(t)=[x1(t),x2(t)] Τ (11)

[0082] Here, x1 and x2 represent the signals emitted from the first LED (LED1) and the second LED (LED2), respectively.

[0083] The superposition constellation at the receiving end is expressed as:

[0084]

[0085] Among them, h i (t) represents the channel response. i is the index of the LED. n i (t) is the noise.

[0086] The power ratio between LED1 and LED2 is defined as α, which is expressed as:

[0087]

[0088] Wherein, Vpp1 and Vpp2 represent the signal Vpp applied to LED1 and LED2 respectively. When α is taken as the optimal power ratio, the performance of the SCMMISOVLC system is optimal.

[0089] Generalized mutual information (GMI) can accurately reflect the performance of the transmitted signal and is defined as:

[0090]

[0091] Among them, b k,i ∈{0,1} is the i-th bit of the k-th transmitted symbol. The i-th bit is b k,i The QAM conforms to the set. The modulation order of the superimposed constellation is M 2 , m = log2(M 2 ). Y represents a received sequence of length N. is the channel probability mass function. 2 is the noise variance.

[0092] Normalized generalized mutual information (NGMI) can accurately predict the bit error rate performance of forward error correction (FEC). The NGMI calculation method for R-QAM and PS-QAM signals is:

[0093]

[0094] m refers to the number of bits transmitted per symbol; H refers to the source entropy; FEC code rate R c There is a corresponding relationship between and NGMI threshold. c , when the NGMI measurement value is higher than the corresponding NGMI threshold, FEC error-free transmission can be achieved. c It is fixed at 9 / 10 to avoid multiple FEC codewords and different frame structures, and its corresponding NGMI threshold is 0.92. An NGMI lookup table is constructed for the SCM-based hybrid GPS rate adaptive MISOVLC system, as shown in Figure 3 As shown. The lookup table provides the relationship between NGMI, signal-to-noise ratio SNR and source entropy SE. Based on this lookup table and the estimated signal-to-noise ratio SNR, the maximum source entropy SE that can meet the NGMI threshold for each solution can be determined.

[0095] After removing the forward error correction coding FEC overhead, the net transmission spectrum efficiency (NTSE) is expressed as:

[0096] NTSE=H-(1-R c )·m(16)

[0097] The net data rate NDR is expressed as:

[0098] NDR=NTSE·B(17)

[0099] Where B represents the modulation bandwidth of the system.

[0100] The achievable information rate characterizes the transmission capacity of the system and is expressed as:

[0101] AIR=GMI·B(18)

[0102] In order to clearly describe the implementation method of the SCM-based hybrid GPS rate adaptive MISO VLC system, the following embodiments are given to comprehensively evaluate GS, PS, MISO and the SCM-based hybrid GPS rate adaptive MISO VLC system.

[0103] A 2×1MISO VLC system was built for concept verification. The system block diagram and experimental setup are shown in Figure 4 As shown. Discrete Fourier transform spread spectrum orthogonal frequency division multiplexing (DFT-s-OFDM) is applied to suppress the peak-to-average power ratio and inter-symbol interference. First, the two binary data streams are modulated into PS-QAM signals through CCDM. Then, the DFT spread spectrum signal is generated by discrete Fourier transform DFT. After inserting the training sequence, Hermitian symmetry and upsampling are performed. The real-valued OFDM signal is obtained by inverse fast Fourier transform (IFFT). Subsequently, a cyclic prefix (CP) is added before each OFDM time domain frame to resist multipath interference. Digital signal processing (DSP) at the transmitter is performed by MATLAB.

[0104] The transmission data stream generated offline is loaded into an arbitrary waveform generator (AWG: UNI-T UTG9604T) and output. Subsequently, the analog signal is amplified by an electrical amplifier (EA: Mini-Circuits ZHL-6A-S+) and coupled to direct current (DC) through a bias tee (Mini-circuits ZFBT-4R2GWFT+). The electrical signal is converted into an optical signal by two commercial red LEDs (Cree XLampXPE-2). After propagating in free space, the optical signal is detected by an avalanche photodiode (APD: Hamamatsu C12702-11) and converted into an electrical signal. A lens is placed in front of the APD to focus the light to increase the received optical power. The electrical signal is sampled and recorded by an oscilloscope (OSC: Tektronix MDO3034) and forwarded to offline processing.

[0105] After synchronization and CP removal, OFDM demodulation is performed by fast Fourier transform (FFT) and downsampling. Channel distortion is compensated by frequency domain channel estimation and equalization. Time domain symbols are obtained by inverse discrete Fourier transform (IDFT). SCM decoding and PS-QAM demodulation are performed based on the concept of superposition constellation demapping. Finally, performance indicators are calculated.

[0106] The specific experimental parameters are as follows: DFT points are 122, FFT points are 256, and CP length is 8. The 6 low-frequency subcarriers are filled with 0 due to poor EA response. The upsampling factor is 2. The AWG sampling rate is 25MSa / s. The DC is 100mA. The LED spacing is 40cm. The transmission distance is between 65cm and 185cm. The effective bandwidth of the system is about 5.96MHz. Figure 5 The experimental system characteristics such as frequency response and amplitude-amplitude response are demonstrated. Figure 5 (a) shows the frequency response; Figure 5 (b) shows the magnitude-amplitude response in the linear region; Figure 5 (c) shows the magnitude-amplitude response in the nonlinear region.

[0107] First, the MISO-GS (16,16) and MISO-GPS (16,16) schemes are used as examples to verify the superiority of GS. Figure 6 The traditional MISO-R (16,16) and MISO-PS (64,4) schemes are introduced for comparison.

[0108] Figure 6 (a) describes the NGMI performance of the MISO-GS(16,16) and MISO-R(16,16) schemes at different total Vpp (Vpptotal), Vpptotal = Vpp1 + Vpp2. The two equivalent transmission signals of each scheme are sent by two LEDs respectively. The optimal PRs of the MISO-GS(16,16) and MISO-R(16,16) schemes are 1 and 4, respectively. In the experiments, all schemes maintain the optimal PR. Therefore, for the MISO-GS(16,16) scheme, Vpp1 = Vpp2. For the MISO-R(16,16) scheme, Vpp2 / Vpp1 = 4. Thanks to the balanced power distribution, the NGMI performance of the MISO-GS(16,16) scheme is always better than that of the MISO-R(16,16) scheme, and has a driving Vpptotal dynamic range of about 540mV. The experimental results demonstrate the significant advantages of GS.

[0109] Figure 6(b) shows the NGMI performance of the MISO-GPS(16,16) and MISO-PS(64,4) schemes at different Vpptotal. The two equivalent GPS-16QAM signals of the MISO-GPS(16,16) scheme are sent by two LEDs respectively. The PS-64QAM and R-4QAM signals of the MISO-PS(64,4) scheme are sent by LED1 and LED2 respectively. In the experiment, Vpp2 was fixed at 350mV. PR gradually decreases with the increase of Vpp1. The distribution of constellation points of the superimposed constellation changes with the change of PR. When Vpp2 / Vpp1 achieves the optimal PR, the superimposed constellation is evenly distributed and has the largest MED, and the NGMI reaches the peak. Figure 6 This is confirmed by the constellation diagram shown in (c). When the PSF changes, the MISO-GPS (16,16) scheme always achieves the best NGMI performance when the PR is 1, while the NGMI peak point of the MISO-PS (64,4) scheme is constantly changing. The dynamically changing optimal PR will introduce additional complexity to the SCM-based MISO VLC system. The experimental results demonstrate the advantage of designing two equivalent GS transmission signals.

[0110] Then, taking the MISO-GS(16,16) and SISO-R(256) schemes as examples, the advantages of multi-transmitter systems over single-transmitter systems in resisting nonlinear effects are verified, such as Figure 7 As shown. The R-256QAM signal of the SISO-R(256) scheme is sent by LED1, and Vpptotal = Vpp1. Figure 7 As shown in (a), the nonlinearity of both MISO and SISO VLC systems increases with the increase of Vpptotal. The SCM-based MISO VLC system enters the nonlinear region later than the SISO VLC system by evenly distributing Vpptotal on two LEDs, and significantly improves the tolerance to high Vpptotal. Therefore, the NGMI and NDR performance of the MISO-GS (16,16) scheme is always better than that of the SISO-R (256) scheme. Figure 7 (b) further describes the AIR and GMI performance of the MISO-GPS (16,16) and MISO-PS (64,4) schemes. The MISO-GPS (16,16) scheme has higher signal transmission quality and achieves considerable AIR and GMI gains.

[0111] Then, the MISO-GPS (16,16) and SISO-PS (256) schemes are taken as examples to verify the performance gain brought by PS, such as Figure 8 As shown. For the MISO-GPS (16,16) solution, Vpp1 = Vpp2. Figure 8(a) shows, with Figure 7 (a) Compared with MISO-GS(16,16) and SISO-R(256) without PS, MISO-GPS(16,16) and SISO-PS(256) achieve NGMI values ​​above the post-FEC error-free transmission threshold at all driving Vpptotal. PS brings significant shaping gain by improving the MED of the superimposed constellation and improving the robustness to nonlinear distortion. Although PS significantly enhances the performance of SISO-PS(256), MISO-GPS(16,16) still achieves considerable NDR gain.

[0112] The PS depth of the SISO-PS(256) scheme is greater, resulting in greater SE loss. Figure 7 (b) and Figure 8 (b), After applying PS, the AIR and GMI gains of the MISO-GPS (16,16) scheme are improved.

[0113] Finally, the advantages of the SCM-based hybrid GPS rate adaptive MISO VLC system (MISO-GPS-AdaptiveMod.) are verified. The existing R-QAM modulation format switching SISO VC system (SISO-R-Adaptive Mod.) and PS-QAM modulation format switching SISO VLC system (SISO-PS-Adaptive Mod.) are introduced for comparison.

[0114] Fig. 9 The NDR and NGMI performances of three rate-adaptive VLC systems at different Vpptotals are described. Under all Vpptotal values, the MISO-GPS-Adaptive Mod. and SISO-PS-AdaptiveMod. systems can reach the NGMI threshold and achieve flexible and fine-grained NDR by adjusting the PSF and modulation format. At high Vpptotal values, the MISO-GPS-Adaptive Mod. system suffers from less nonlinearity and outperforms the SISO-PS-Adaptive Mod. system. The SISO-R-Adaptive Mod. system can only adjust the rate by switching the modulation format, so it can only achieve two discrete NDRs. When the NGMI value is higher than 0.92, the bandwidth resources of the SISO-R-Adaptive Mod. system are not fully utilized.

[0115] Fig.10The NDR performance of three distance-based multi-user rate-adaptive VLC systems is described. In the experiment, Vpptotal is fixed at 1000mV. Compared with the SISO-PS-Adaptive Mod. system, the MISO-GPS-Adaptive Mod. system achieves approximately 19% and 105% NDR gains for near-end users and far-end users, respectively. Compared with the SISO-R-AdaptiveMod. system, the MISO-GPS-Adaptive Mod. system not only achieves considerable NDR gain but also enables flexible rate adjustment. Under the 30Mbps NDR constraint, the MISO-GPS-Adaptive Mod. system increases the maximum transmittable distance of the SISO-PS-AdaptiveMod. and SISO-R-AdaptiveMod. systems by approximately 24.5% and 111%, respectively.

[0116] Finally, it should be noted that the above examples of the present invention are merely examples for illustrating the present invention, and are not intended to limit the embodiments of the present invention. Although the applicant has described the present invention in detail with reference to the preferred embodiments, for those of ordinary skill in the art, other different forms of changes and modifications can be made based on the above description. It is impossible to list all the embodiments here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for implementing a rate-adaptive multi-input single-output visible light communication system, the visible light communication system comprising a transmitting end and a receiving end, characterized in that: There are multiple transmitting ends and one receiving end, thereby forming a multi-input single-output visible light communication system; each transmitting end corresponds to a light source; the binary transmission data streams corresponding to the transmitting ends are modulated onto the constellation diagram to increase the spectrum efficiency, thereby obtaining a transmission constellation, and all the transmission constellations are loaded onto the signal generator after digital signal processing, the signal generator outputs a corresponding number of analog signals and amplifies them through an electrical amplifier and then couples them with a DC through a bias device, and the coupled electrical signals are converted into optical signals through the light source corresponding to the transmitting end, and the receiving end is used to receive the optical signal; All transmit constellations are probability shaped to conform to the Maxwell-Boltzmann distribution of the QAM constellation; at the same time, all transmit constellations are geometrically shaped to make the transmit signal power of each transmitter equal.

2. The method for implementing a rate adaptive multi-input single-output visible light communication system according to claim 1, characterized in that: During probability shaping, the transmit constellation is probability shaped using the constant component matching distribution. When there are two transmitters, the probability distribution of the QAM signal with a modulation order of M is: Among them, X i represents the complex coordinate set of the i-th low-order M-QAM constellation at the transmitter, X = {x0, x1, ..., x M-1 }; x and x' represent constellation symbols; v is the probability shaping factor that controls the source entropy SE, and its value is between 0 and 1; there is a one-to-one mapping relationship between the source entropy SE and the probability shaping factor v.

3. The method for implementing a rate adaptive multi-input single-output visible light communication system according to claim 2, characterized in that: Determine the source entropy SE as follows: 1) Establish a lookup table of the relationship between normalized generalized mutual information, signal-to-noise ratio and source entropy; 2) determining the threshold of the normalized generalized mutual information as the value of the normalized generalized mutual information for searching; 3) The signal-to-noise ratio is obtained by estimation, and based on the lookup table in step 1), the maximum source entropy SE of each scheme that can meet the normalized generalized mutual information threshold is determined.

4. The method for implementing a rate adaptive multi-input single-output visible light communication system according to claim 1, characterized in that: During geometric shaping, the optimal geometric shaping factor is solved in advance, and then the transmit constellation is geometrically shaped based on the obtained optimal geometric shaping factor. The optimal geometric shaping factor is defined as the geometric shaping factor when the power ratio of each transmit signal is equal to 1 and the superimposed constellation at the receiving end is evenly distributed.

5. The method for implementing a rate adaptive multi-input single-output visible light communication system according to claim 4, characterized in that: The optimal geometric shaping factor is determined as follows: a) adding geometric shaping factors to the in-phase and quadrature components of the two transmitted signals respectively; b) Presetting the optimal power ratio of the two transmitted signals to 1, and obtaining a symbol set of a superimposed constellation at the receiving end; c) the elements of the symbol set constitute an arithmetic progression whose common difference is the minimum Euclidean distance; d) establishing a set of equations about the geometric shaping factor based on the arithmetic progression in step c), and the geometric shaping factor obtained by solving the set of equations is the optimal geometric shaping factor.

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