EVM-based visible light real-time communication positioning method and system

Abstract

The application provides a visible light real-time communication positioning method and system based on EVM, which is based on a DCO-OFDM system and comprises the following steps: modulating communication information and preset positioning information onto corresponding subcarriers according to a preset resource allocation scheme; performing data processing on the subcarriers carrying the communication information and the preset positioning information; emitting a visible light signal by driving an LED with the subcarriers after data processing; receiving the visible light signal by a PD receiving end and converting the visible light signal into an electrical signal; converting the time domain signal of the electrical signal into a frequency domain signal, and performing equalization processing on the frequency domain signal; performing error vector magnitude calculation on the frequency domain signal after equalization processing, obtaining a new resource allocation scheme, extracting the communication information and the positioning information of the PD receiving end, replacing the new resource allocation scheme with the preset resource allocation scheme, and then repeating the execution in the next cycle; and decrypting the positioning information of the PD receiving end by a positioning algorithm module and outputting the positioning information.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of communication technology, and particularly relates to a VLC real-time communication positioning method and system based on EVM. BACKGROUND

[0002] With the rapid development of 5G network, the research on the next generation of wireless communication has been put on the agenda. Visible light communication (VLC) has become one of the hotspots of wireless communication research due to its low cost, low power consumption, high anti-interference ability and other advantages. In addition, its rich bandwidth resources are one of the effective solutions to the shortage of current wireless spectrum resources. The application of orthogonal frequency division multiplexing technology (OFDM) in visible light communication can reduce the inter-symbol interference caused by the transmission link multipath and improve the system transmission rate. The visible light OFDM communication mode includes direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) and asymmetrically clipped optical-orthogonal frequency division multiplexing (ACO-OFDM). For the problem of resource allocation of VLCP system, the existing technology uses OFDM to realize visible light communication and positioning in the same frequency band, uses the power of data sequence as a measure to estimate the transmission distance, thereby reducing the positioning error. In addition, the existing technology also proposes a low complexity subcarrier method, and uses the sequential quadratic programming (SQP) method to solve the nonlinear power allocation problem, which can effectively improve the rate and positioning accuracy of the VLCP system. However, the focus of these works is mainly on optimizing the resource allocation of the VLC system and the VLP system, and there is no further improvement on the rationality of channel estimation, so the effect of improvement is limited. SUMMARY

[0003] To solve the above problems, the application provides a visible light real-time communication positioning method and system based on EVM, and the system adopts a DCO-OFDM modulation mode. In addition to communication, visible light is also widely used in indoor positioning. Visible light positioning (VLP) has the characteristics of low cost, low power consumption, high stability and high precision, and can also take into account the lighting function. The integrated visible light system that integrates the communication function and the positioning function is closer to the actual application scene. Among them, the VLCP system is to integrate the VLC system and the VLP system, and to realize the optimization of the communication performance and the positioning performance through reasonable allocation of resources, specifically including:

[0004] A visible light real-time communication positioning method based on EVM, which is realized based on a visible light real-time communication positioning system based on EVM, and the visible light real-time communication positioning system based on EVM includes a sending end and a PD receiving end; the method includes the following steps:

[0005] S1, the sending end modulates the communication information and the preset positioning information onto the corresponding subcarriers according to the preset resource allocation scheme;

[0006] S2, the sending end performs data processing on the subcarriers carrying the communication information and the preset positioning information, and the data-processed subcarriers emit a visible light signal through direct current bias driving LED;

[0007] S3, the PD receiving end receives the visible light signal and converts the visible light signal into an electrical signal;

[0008] S4, the PD receiving end converts the time domain signal of the electrical signal into a frequency domain signal and performs equalization processing on the frequency domain signal;

[0009] S5, the PD receiving end performs error vector magnitude calculation on the equalization-processed frequency domain signal to obtain a new resource allocation scheme, and extracts the communication information and the positioning information of the PD receiving end;

[0010] S6, the PD receiving end replaces the new resource allocation scheme with the preset resource allocation scheme, and then repeatedly executes S1;

[0011] Meanwhile, the PD receiving end decrypts the positioning information through a positioning algorithm module and outputs it.

[0012] Preferably, the sending end of S1 modulates the communication information and the preset positioning information onto the corresponding subcarriers according to the preset resource allocation scheme, which includes:

[0013] S101, judging whether the communication information is initial communication information, if yes, performing 4QAM modulation on the communication information and preset positioning information, otherwise, performing modulation on the communication information and preset positioning information according to a preset resource allocation scheme;

[0014] S102, performing Hermite symmetry on the modulated communication information and preset positioning information;

[0015] S103, modulating the communication information after Hermite symmetry onto corresponding subcarriers through inverse fast Fourier algorithm;

[0016] modulating the preset positioning information after Hermite symmetry onto corresponding subcarriers through inverse fast Fourier algorithm.

[0017] Preferably, the sending end of S2 performs data processing on the subcarriers carrying the communication information and preset positioning information, and the subcarriers after data processing emit visible light signals through direct current bias driving LED, including:

[0018] S201, performing digital-to-analog conversion on the data of the subcarriers carrying the communication information and preset positioning information, converting digital signals into analog signals;

[0019] S202, the subcarriers carrying the analog signals emit visible light signals through direct current bias driving LED.

[0020] Preferably, the PD receiving end of S3 includes a horizontal PD0 and an inclined PD i (i = 1, 2, 3, 4);

[0021] The layout method of the PD receiving end includes:

[0022] The horizontal PD0 is set as the center position of the PD receiving end, the position coordinates of the horizontal PD0 are set as (x R , y R , z R ), and the position coordinates of the inclined PD i are set as (x Ri , y Ri , z Ri ),

[0023] Wherein, x Ri = x R + l cosαcosω i , y Ri = y R + l cosαsinω i , z Ri = z R + lsinα;

[0024] Wherein, by PD i the line through the center and perpendicular to the x-axis is p, and l represents the PD i the line segment from the center to the line p parallel to the inclined plane, and a represents the elevation angle of the PD i (0°≤a<90°), ω i represents the included angle between the projection of the line connecting the PD0 and the PD i in the xoy plane and the positive direction of the x-axis, wherein ω1=0°, ω2=90°, ω3=180°, and ω4=270°.

[0025] Preferably, the PD receiving end of S6 replaces the new resource allocation scheme with the preset resource allocation scheme, and then repeatedly executes S1, and the PD receiving end decrypts the positioning information through the positioning algorithm module and outputs the positioning information, including:

[0026] S601, determining a QAM grid table according to a target BER;

[0027] The receiving end performs EVM calculation once for each group of OFDM symbols, wherein each group of OFDM symbols includes N b ×1000 OFDM symbols;

[0028] Wherein, N b is the total number of blocks of each OFDM symbol, N b =K / b, N b is an integer, and if it is not an integer, it is rounded up to an integer;

[0029] Wherein, K is the total number of subcarriers in the DCO-OFDM system, and b is the number of subcarriers per block;

[0030] S602, QAM modulation allocation is performed according to the EVM condition of each subcarrier block and the determined QAM table, and the lowest frequency subcarrier in the EVM-optimized subcarrier block is allocated to the positioning algorithm for calculation;

[0031] S603, the selected positioning subcarrier and the determined QAM modulation condition form a new resource allocation scheme, and the new resource allocation scheme replaces the preset resource allocation scheme of the last period;

[0032] The positioning algorithm module decrypts the received lowest frequency subcarrier in the EVM-optimized subcarrier block, and outputs the positioning information.

[0033] Preferably, the S601 of determining a QAM grid table according to a target BER includes:

[0034] In the case of meeting the target BER, the threshold value of EVM is determined according to different modulation modes, and the allocation table is obtained as the QAM grid table.

[0035] An EVM-based visible light real-time communication positioning system for implementing an EVM-based visible light real-time communication positioning method, comprising a sending end and a PD receiving end:

[0036] The sending end modulates the communication information and the preset positioning information onto corresponding subcarriers according to a preset resource allocation scheme, performs data processing on the subcarriers carrying the communication information and the preset positioning information, and drives an LED to emit a visible light signal through direct current biasing of the subcarriers after data processing;

[0037] The PD receiving end receives the visible light signal and converts the visible light signal into an electrical signal, converts a time domain signal of the electrical signal into a frequency domain signal, performs equalization processing on the frequency domain signal, performs error vector magnitude calculation on the frequency domain signal after equalization processing, obtains a new resource allocation scheme, extracts the communication information and the positioning information of the PD receiving end, replaces the new resource allocation scheme for the preset resource allocation scheme, and then repeats S1;

[0038] Meanwhile, the PD receiving end decrypts the positioning information through a positioning algorithm module and outputs the positioning information.

[0039] Preferably, the sending end comprises:

[0040] A judgment unit for judging whether the communication information is initial communication information, and if so, performing 4QAM modulation on the communication information and the preset positioning information, otherwise, performing modulation on the communication information and the preset positioning information according to the preset resource allocation scheme in step S6;

[0041] A Hermite symmetry unit for performing Hermite symmetry on the modulated communication information and the preset positioning information;

[0042] An information processing and modulation unit for modulating the communication information after Hermite symmetry onto corresponding subcarriers through inverse fast Fourier algorithm;

[0043] The preset positioning information after Hermite symmetry is modulated onto corresponding subcarriers through inverse fast Fourier algorithm.

[0044] Preferably, the sending end further comprises:

[0045] A digital-to-analog conversion unit for performing digital-to-analog conversion on data of the subcarriers carrying the communication information and the preset positioning information, and converting digital signals into analog signals;

[0046] A driving unit for driving the LED to emit a visible light signal through direct current biasing of the subcarriers carrying the analog signals.

[0047] Preferably, the PD receiving end comprises: a horizontal PD0 and an inclined PD i (i = 1, 2, 3, 4);

[0048] The layout method of the PD receiving end comprises:

[0049] The horizontal PD0 is set as the center position of the PD receiving end, the position coordinates of the horizontal PD0 are set as (x R , y R , z R ), and the position coordinates of the horizontal PD i are set as (x Ri , y Ri , z Ri ),

[0050] wherein x Ri = x R + lcosαcosω i , y Ri = y R + lcosαsinω i , z Ri = z R + lsina;

[0051] wherein a straight line through the PD i center and perpendicular to the x axis is p, l represents a line segment from the PD i center to the straight line p and parallel to the inclined plane, a represents the elevation angle of the PD i (0°≤a<90°), ω i represents the included angle between the projection of the line connecting the PD0 and the PD i in the xoy plane and the positive direction of the x axis, wherein ω1=0°, ω2=90°, ω3=180°, and ω4=270°.

[0052] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0053] The method is the first to propose a resource allocation method based on EVM for the resource allocation problem in the VLCP system. Compared with the algorithm using SNR for resource allocation, the EVM parameter can more directly reflect the deviation of the received signal from the ideal signal, so that a more reasonable resource allocation result is obtained. Compared with the algorithm using the BER standard for resource allocation, EVM can give the performance measurement of the channel before demodulation, which can avoid the BER calculation of a large amount of data, and the method of subcarrier blocking can improve the accuracy of EVM while also reducing a certain amount of calculation. The simulation results under the Lambert radiation model and the visible light low communication channel environment show that, compared with the fixed modulation algorithm, the new allocation algorithm can adjust the communication and positioning allocation scheme in time with the change of the channel environment, and can improve the channel utilization rate by 30% on average, the positioning error of the effective area in the indoor environment of 7m*7m*2.5m is kept within 25cm, which can meet the basic positioning demand. BRIEF DESCRIPTION OF DRAWINGS

[0054] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0055] Figure 1 The flow chart of the visible light real-time communication positioning method based on EVM provided by the embodiment of the present application;

[0056] Figure 2 The flow chart of the visible light real-time communication positioning method based on EVM provided by the embodiment of the present application;

[0057] Figure 3 The structure diagram of the PD receiving end provided by the embodiment of the present application;

[0058] Figure 4 The EVM threshold value EVM EVM under different M th order modulation;

[0059] Figure 5 The EVM situation and QAM modulation distribution under different distances provided by the embodiment of the present application;

[0060] Figure 6 The channel utilization rate comparison of different algorithms provided by the embodiment of the present application;

[0061] Figure 7 The average error under three different allocation modes provided by the embodiment of the present application;

[0062] Figure 8 This is a schematic diagram of the visible light real-time communication and positioning system based on EVM provided in the embodiment.

[0063] Figure 9 A schematic diagram of the structure of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0065] This application optimizes the channel utilization of OFDM systems by optimizing the system resource allocation algorithm for visible light OFDM communication. It provides a real-time visible light communication and positioning method and system based on EVM, employing DCO-OFDM modulation. Besides communication, visible light is widely used for indoor positioning. Visible Light Positioning (VLP) features low cost, low power consumption, high stability, and high accuracy, and can also provide illumination. An integrated visible light system combining communication and positioning functions is more suitable for practical applications. Specifically, the VLCP system integrates VLC and VLP systems, optimizing communication and positioning performance through rational resource allocation.

[0066] like Figure 1 As shown, a visible light real-time communication positioning method based on EVM is presented, and a visible light real-time communication positioning system based on EVM is implemented. The method employs DCO-OFDM modulation, estimating the channel based on the EVM of the received symbols in the visible light communication positioning system. The channel state is then incorporated as an influencing factor into the resource allocation optimization objective problem, resulting in a more reasonable allocation. Compared to directly using the signal-to-noise ratio (SNR) as an influencing factor, EVM can more directly reflect the deviation between the received symbols and the original symbols, effectively improving subcarrier allocation efficiency and channel utilization. For positioning, the optimal subcarrier obtained according to the novel allocation algorithm is used for positioning calculation. Simultaneously, a multi-PD receiver with a symmetrical structure is used to maximize positioning accuracy. This improves the performance of the integrated communication and positioning system.

[0067] Includes the following steps:

[0068] S1, the sending end modulates the communication information and the preset positioning information onto corresponding subcarriers according to a preset resource allocation scheme;

[0069] S2, the sending end performs data processing on the subcarriers carrying the communication information and the preset positioning information, and the data-processed subcarriers emit visible light signals through direct current bias driving of LEDs;

[0070] S3, the PD receiving end receives the visible light signals and converts the visible light signals into electrical signals;

[0071] S4, the PD receiving end converts the time domain signals of the electrical signals into frequency domain signals and performs equalization processing on the frequency domain signals;

[0072] S5, the PD receiving end performs error vector magnitude calculation on the equalization-processed frequency domain signals, obtains a new resource allocation scheme, and extracts the communication information and the positioning information of the PD receiving end;

[0073] S6, the PD receiving end replaces the new resource allocation scheme with the preset resource allocation scheme, and then repeatedly executes S1;

[0074] Meanwhile, the PD receiving end decrypts the positioning information through a positioning algorithm module and outputs the positioning information.

[0075] The specific principles of the steps of the application include:

[0076] As shown in Figure 2 , in the sending end, a data stream flows into the system, and the data stream includes communication information, and the system carries a preset positioning information value.

[0077] S1 of the sending end includes:

[0078] S101, determining whether the communication information is initial communication information, if the communication information is initial communication information, performing 4QAM modulation on the communication information and the preset positioning information, otherwise, modulating the communication information and the preset positioning information according to the preset resource allocation scheme in step S6;

[0079] The reason for determining whether it is initial communication information is that if the data stream is first transmitted into the system, the modulation rule is according to 4QAM modulation, but if the data stream is not first transmitted into the system, the modulation scheme is according to the new resource allocation scheme calculated in the last period S6.

[0080] S102, performing Hermite symmetry on the modulated communication information and the preset positioning information;

[0081] S103. The communication information after Hermitian symmetry is modulated onto the corresponding subcarrier using the inverse fast Fourier algorithm; the preset positioning information after Hermitian symmetry is modulated onto the corresponding subcarrier using the inverse fast Fourier algorithm.

[0082] Then, the transmitting end of S2 processes the data of the subcarrier carrying communication information and preset positioning information. The processed subcarrier drives the LED to emit visible light signals through DC bias, including:

[0083] S201. Perform digital-to-analog conversion on the data of the subcarrier carrying communication information and preset positioning information, converting the digital signal into an analog signal;

[0084] S202. The subcarrier carrying the analog signal drives the LED to emit a visible light signal through DC bias.

[0085] Steps S1 and S2 mainly involve the sending end processing the received data stream, which can be summarized as follows:

[0086] At the transmitting end, if the data stream enters the system first, it is 4QAM modulated according to the preset resource allocation algorithm to obtain the preset allocation scheme. Otherwise, the resource allocation scheme obtained in the previous cycle is executed. Then, the communication information and positioning information are Hermitian symmetric and modulated onto the corresponding subcarriers by the inverse fast Fourier algorithm. Then, the digital signal is converted into an analog signal by digital-to-analog conversion. Finally, a DC bias is added to drive the LED light source on the roof.

[0087] like Figure 3 As shown, in a preferred embodiment, the PD receiver of S3 includes: a horizontal PD0 and a tilted PD. i (i = 1, 2, 3, 4);

[0088] The layout methods for PD receivers include:

[0089] Set the horizontal PD0 to the center position of the PD receiver, and set the position coordinates of the horizontal PD0 as (x... R y R , z R ), set tilt PD i The position coordinates are (x Ri y Ri , z Ri ),

[0090] Where, x Ri =x R +l cosαcosω i y Ri =y R +l cosαsinω i , zRi = z R + l sin a;

[0091] wherein the PD i center and perpendicular to the x-axis is p, and l represents the PD i center to the line segment parallel to the inclined plane and the line p, and a represents the elevation angle (0°≤a<90°) of the PD i , and w i represents the included angle between the projection of the connecting line of the PD0 and the PD i in the xoy plane and the positive direction of the x-axis, wherein w1=0°, w2=90°, w3=180°, and w4=270°.

[0092] The receiving end adopts a multi-PD structure, converts the optical signal into an electrical signal through the multi-PD, performs fast Fourier transform (FFT) after analog-digital conversion and cyclic prefix removal, converts the time-domain signal into a frequency-domain signal, and performs EVM calculation on the data after equalization processing.

[0093] In a preferred embodiment, the PD receiving end of S6 replaces the new resource allocation scheme with the preset resource allocation scheme, and then repeatedly executes S1;

[0094] Meanwhile, the PD receiving end decrypts the positioning information through the positioning algorithm module and outputs the following information:

[0095] S601, determining a QAM grid table according to a target BER;

[0096] The receiving end performs EVM calculation once for each group of OFDM symbols, wherein each group of OFDM symbols includes N b ×1000 OFDM symbols;

[0097] wherein N b is the total number of blocks of each OFDM symbol, N b =K / b, N b is an integer, and if it is not an integer, the integer is rounded up;

[0098] wherein K is the total number of subcarriers in the DCO-OFDM system, and b is the number of subcarriers per block;

[0099] S602, performing QAM modulation allocation according to the EVM condition of each subcarrier block and the determined QAM table, and assigning the lowest frequency subcarrier in the subcarrier block with the optimal EVM condition to the positioning algorithm for calculation;

[0100] S603, forming a new resource allocation scheme from the selected positioning subcarrier and the determined QAM modulation condition, and replacing the preset resource allocation scheme of the previous period with the new resource allocation scheme;

[0101] The positioning algorithm module decrypts the lowest frequency subcarrier in the received EVM optimal subcarrier block and outputs the positioning information.

[0102] The QAM grid table according to the target BER in S601 includes:

[0103] In the case of meeting the target BER, the threshold value of EVM is determined according to different modulation modes, and an allocation table is obtained, which is determined as the QAM grid table.

[0104] Specifically, in order to expand the symbol set for calculating EVM, at the receiving end, EVM is calculated every N b ×1000 OFDM symbols, and the EVM of each group is calculated, wherein the symbol set can be expanded or reduced as appropriate. At this time, the number of symbol sets for calculating EVM in each block is EVM num = b × 1000, and according to the EVM of each subcarrier block and the determined QAM table, QAM modulation allocation is performed, and the lowest frequency subcarrier in the EVM optimal subcarrier block is taken to be allocated to the positioning algorithm for calculation.

[0105] According to the EVM, the resource allocation scheme of the positioning subcarrier and the communication subcarrier in the next period is obtained and fed back to the sending end. At the same time, the communication information and the positioning information are extracted, and the decoding mapping module and the positioning algorithm module are respectively implemented to realize visible light communication and visible light positioning.

[0106] As shown in Figures 2 to 5 , the present application considers a single lamp and multiple PD communication positioning scene, assuming that the size of the room is 7m × 7m × 2.5m, and the scene and system structure are as shown in Figure 1 , a high-power LED is arranged at the center of the ceiling as a light source, and a multiple PD receiver is used as a receiving device at the receiving end. The indoor visible light channel model is divided into a direct link (Line of Sight, LOS) and a non-direct link (Non Line of Sight, NLOS). Since the proportion of the impulse response of the non-direct link in the optical channel is extremely low, this paper only considers the direct link optical channel. The optical channel gain H Los is expressed by formula (1) as:

[0107]

[0108] Wherein, A is the physical receiving area of the photoelectric detector, m is the number of Lambert radiation mode, the value of m is related to the half-power half-angle Φ 1 / 2where d is the linear distance from the light emitting diode (LED) light source to the PD, Φ is the radiation angle of the LED relative to the receiving end of the PD, ψ is the light incidence angle of the receiving end of the PD, ψ c is the receiving field of view (FOV) of the detector, T(ψ) is the gain of the optical filter, and G(ψ) is the gain of the optical concentrator, where T(ψ) = G(ψ) = 1.

[0109] Since the bandwidth of the optical device is generally low-pass, the high frequency attenuates fast. Therefore, the visible light channel can also be regarded as a low-pass channel. The amplitude-frequency response of the visible light channel is shown in FIG. 3. Figure 3

[0110] At the transmitting end, the data stream is first modulated by 4QAM according to the default resource allocation algorithm to obtain an allocation scheme. After Hermite symmetry of the communication information and the positioning information, the communication information and the positioning information are respectively modulated onto corresponding subcarriers by an inverse fast Fourier algorithm. Then, the digital signal is converted into an analog signal by digital-to-analog conversion, and finally, a direct current bias is added for driving the LED light source on the roof. The receiving end adopts a multi-PD structure, converts the optical signal into an electrical signal by the multi-PD, and performs fast Fourier transform (FFT) after analog-to-digital conversion and cyclic prefix removal, so as to convert the time domain signal into a frequency domain signal. After equalization processing, the data is subjected to EVM calculation. In order to expand the symbol set for calculating EVM, N b ×1000 OFDM symbols are received at the receiving end for EVM calculation, and the EVM of each group is calculated. (The symbol set can be expanded or reduced as appropriate.) At this time, the number of symbol sets for calculating EVM in each block is EVM num = b × 1000. According to the EVM of each subcarrier block and the determined QAM table, QAM modulation allocation is performed, and the lowest frequency subcarrier in the subcarrier block with the optimal EVM is allocated to the positioning algorithm for calculation.

[0111] The resource allocation scheme of the positioning subcarrier and the communication subcarrier in the next period is obtained according to the EVM and is fed back to the transmitting end. At the same time, the communication information and the positioning information are extracted and subjected to a decoding mapping module and a positioning algorithm module, respectively.

[0112] In order to improve the positioning accuracy, a multi-PD receiving end with a symmetrical structure as shown in FIG. 4 is adopted in this paper. Figure 3 The PD receiving end includes horizontal PD0 and tilted PDs i (i = 1, 2, 3, 4), which are equivalent to four tilted PDs, i.e., tilted PD1, PD2, PD3, and PD4.

[0113] The layout method of the PD receiving end includes: ​

[0114] Set the horizontal PD0 to the center position of the PD receiver, and set the position coordinates of the horizontal PD0 as (x... R y R , z R ), set tilt PD i The position coordinates are (x Ri y Ri , z Ri ),

[0115] Where, x Ri =x R +l cosαcosω i y Ri =y R +l cosαsinω i , z Ri =z R +lsinα;

[0116] Among them, through PD i Let p be the line centered on and perpendicular to the x-axis, and l represent PD. i The line segment from the center to the line p parallel to the inclined plane, α represents PD. i The angle of elevation (0°≤α<90°), ω i Indicates PD0 and PD i The angle between the projection of the line connecting the x and y axes onto the xoy plane and the positive x-axis, where ω1 = 0°, ω2 = 90°, ω3 = 180°, and ω4 = 270°.

[0117] For a tilted PD0, the cosine of the incident angle is cosψ = ​​cosφ = h / d, where h represents the vertical height from the light source to the PD. For the PD... i The cosine of the incident angle is given in formula (2):

[0118]

[0119] Among them, (x t ,y t ,z t ) represents the LED coordinates, β i The azimuth angles of the tilted PD (β1 = 180°, β2 = 270°, β3 = 0°, β4 = 90°) and the emitted optical power P t and received optical power P r The relationship between them is expressed by formula (3):

[0120] P r =P t ×H LOS (3)

[0121] Therefore, when the received power P rThe distance d between the horizontal PD0 and the light source can be obtained by the layout method of the PD receiving end and formulas (2) and (3), and the calculation formula is as formula (4):

[0122]

[0123] In addition, since the method is used for real-time positioning of the entity by visible light, the cycle stopping condition of steps S6 to S1 is that the positioning of the target object is stopped, and when manual intervention is performed and the target object is not monitored in real time, the cycle can be stopped at any step and at any time, wherein the receiving end is arranged on the target object.

[0124] Here, the design principle of the resource allocation scheme based on EVM includes:

[0125] The algorithm proposed in the application aims to maximize the system channel utilization and positioning accuracy under the premise of meeting the quality of service requirements. In order to meet the quality of service of the system, according to the conversion relationship between EVM and bit error rate (BER), the threshold value of EVM (expressed in percentage) is determined according to different modulation modes under the condition of meeting the system BER, and the allocation table is obtained. According to the number of subcarriers, the subcarriers are blocked. The EVM value in each subcarrier block is calculated, and the selection of positioning subcarriers and the determination of the number of QAM modulation points M EVM in each block are performed according to the EVM condition.

[0126] The conversion relationship between the bit error rate BER and the EVM is shown in formula (5):

[0127]

[0128] Wherein, L is the number of levels in each dimension of the M EVM modulation mode. Q[.] is the Gaussian complementary error function, and the specific expression of Q[.] is shown in formula (6):

[0129]

[0130] Wherein, BER=3.8×10 -3 , the EVM threshold EVM EVM under different M th order modulations is calculated, as shown in the following table 1:

[0131] Table 1

[0132]

[0133] EVM is the root mean square value of the difference between the received symbol and the ideal symbol set, in order to get the EVM value can accurately reflect the channel situation, must ensure that the data set for calculating EVM is large enough, for this paper adopts the block subcarrier and cross cycle decision idea, in order to expand the symbol set for calculating EVM, according to the order of subcarrier, the subcarrier is divided into blocks, the same block is used for the same modulation mode and the calculation of EVM value, at the same time, every several receiving cycle is distributed scheme update. Because of the similar channel characteristics of adjacent subcarriers in OFDM, the block method can ensure the effectiveness of the allocation algorithm and greatly reduce the calculation amount. For the resource allocation between VLC and VLP system, in order to improve the positioning accuracy of the system as much as possible, according to the EVM calculation of each group, the subcarrier block with the optimal EVM is selected for positioning subcarrier allocation. Because of the low pass characteristics of visible light channel, the higher frequency subcarrier attenuates fast, so the lowest frequency subcarrier of the corresponding subcarrier block is selected for the calculation of positioning algorithm.

[0134] As shown in Figure 2 , the method and system are verified, and the indoor environment of single lamp and single communication terminal is simulated as shown in Figure 2 . The LED emission power is 10 W, and the receiving end adopts multi PD structure. The indoor simulation environment of 7 m x 7 m x 2.5 m is established, the transmitting end is placed on the ceiling of (3.5 m, 3.5 m, 2.5 m), and the simulation system parameters are shown in the following table 2:

[0135] Table 2

[0136]

[0137] As shown in Figure 5 , the number of subcarriers K of the simulated DCO-OFDM system in this embodiment is set to 128. Since the first subcarrier is a direct current signal and does not carry information, and the first half of the subcarriers and the second half of the subcarriers are conjugate symmetric relationship, the number of subcarriers carrying information is 63. The 63 subcarriers are divided into 9 subblocks, each block includes 7 subcarriers, and the EVM value and QAM modulation of each block under different distances obtained by the allocation algorithm are shown in Figure 5 .

[0138] As shown in Figure 5 , with the increase of the distance between the receiver and the transmitter, the EVM value of the same channel gradually increases, and the QAM modulation order of the subcarrier block continuously decreases, which indicates that the channel condition is deteriorating. Looking horizontally, due to the influence of the characteristics of the visible light channel, the EVM increases with the increase of the frequency, and the low frequency subcarrier can always adopt a higher order modulation mode than the high frequency subcarrier, which shows that the allocation algorithm can effectively adapt to the change of the channel environment and change the modulation mode of the channel in real time according to the change of the channel condition.

[0139] As Figure 6 The adaptive algorithm and the system channel utilization rate of the fixed modulation method are compared in the case of different transmission distances. The horizontal axis is the distance from the PD receiving end to the transmitting end, and the vertical axis is the channel utilization rate of the DCO-OFDM system. In order to ensure that the system error rate is below a given value, if the EVM value of the channel exceeds the threshold value of the minimum modulation method determined in the table, no data allocation is performed. As can be seen from the figure, as the distance between the transmitting and receiving ends increases, the channel utilization rate of the fixed modulation method algorithm continuously decreases and gradually approaches 0, indicating that the channel condition at this time is very poor and cannot guarantee data transmission under a given service quality.

[0140] Therefore, compared with the fixed modulation method, the adaptive subcarrier allocation algorithm can adjust the corresponding QAM modulation method according to the channel condition, and always maintains a high channel utilization rate. As Figure 6 shown, at this time, the channel utilization rate of the adaptive algorithm presents a slow decline, and does not appear a sharp decline as in the fixed modulation algorithm. And it is better than the fixed modulation method in any case. As can be seen, the algorithm can effectively improve the channel utilization rate of the indoor visible light DCO-OFDM system, and verifies the effectiveness of the algorithm.

[0141] The positioning results are compared and analyzed:

[0142] The single light source positioning method is adopted in the present application. The single light source positioning algorithm is the basic algorithm for positioning in the present application. The related positioning algorithm is relatively mature, and therefore will not be described again. In order to more reasonably balance the resource allocation between communication and positioning, the present application compares the communication system utilization rate and the positioning error under three different selection methods of positioning subcarriers. Method one is to select the lowest frequency subcarrier in the subcarrier block with the minimum EVM value as the positioning subcarrier, which is the selected method of the present application; method two is to select the middle subcarrier in the subcarrier block with the EVM value in the middle position; and method three is to select the highest frequency subcarrier in the subcarrier block with the maximum EVM value. The comparison of the system channel utilization rate and the average positioning error under the three methods is shown in Figure 7 .

[0143] As Figure 7 can be seen, since the influence of a single subcarrier on the overall communication performance of the system is limited, the channel utilization rates under the three different selection methods of the positioning subcarrier are very small and can be almost ignored. For the positioning performance, the selection of the positioning subcarrier has a very large influence. Due to the influence of the visible light low communication channel, the EVM value of the subcarrier with a higher frequency decreases greatly compared with the subcarrier with a lower frequency, which greatly increases the positioning error. Therefore, in order to ensure the overall performance of the system, method one is a suitable allocation scheme.

[0144] The selection of the positioning sub-carrier is determined according to the allocation algorithm, and input to the positioning algorithm to determine the position information of the receiving end. It can be known from theoretical analysis and simulation that when the receiver is located directly below the light source, the error component offset by the symmetrical structure is large, and at this time, the positioning error is minimum. With the increasing distance between the transmitting end and the receiving end, the positioning error also increases. Since the simulated indoor environment is 7m*7m*2.5m, and the positioning error in most areas is maintained within 25cm, the basic positioning requirements can be met. The rationality of the new allocation algorithm for positioning sub-carrier selection is indicated, and the effectiveness of the positioning performance of the method is verified.

[0145] The method first proposes an EVM-based resource allocation method for resource allocation in the VLCP system. Compared with the current SNR-based resource allocation algorithm, the EVM parameter can more directly reflect the deviation of the received signal from the ideal signal, thereby obtaining a more reasonable resource allocation result. Compared with the BER standard-based resource allocation algorithm, EVM can give a performance measurement of the channel before demodulation, which can avoid BER calculation on a large amount of data, and the method of sub-carrier blocking can improve the accuracy of EVM while reducing the calculation amount. The simulation results under the Lambert radiation model and the visible light communication channel environment show that compared with the fixed modulation algorithm, the new allocation algorithm can adjust the communication and positioning allocation scheme in time with the change of the channel environment, and can improve the channel utilization rate by 30% on average. In a 7m*7m*2.5m indoor environment, the positioning error in the effective area is maintained within 25cm, which can meet the basic positioning requirements.

[0146] As Figure 8 , another aspect of the present application provides an EVM-based visible light real-time communication positioning system for implementing the above-mentioned EVM-based visible light real-time communication positioning method, specifically based on the DCO-OFDM modulation method, comprising: a receiving end 100 and a PD transmitting end 200.

[0147] The receiving end 100 is used for modulating the communication information and the preset positioning information onto the corresponding sub-carriers according to the preset resource allocation scheme, performing data processing on the sub-carriers carrying the communication information and the preset positioning information, and emitting a visible light signal through a direct current bias driving LED after the data processing of the sub-carriers;

[0148] The PD receiving end 300 is configured to receive the visible light signal and convert the visible light signal into an electrical signal, convert the time domain signal of the electrical signal into a frequency domain signal, perform equalization processing on the frequency domain signal, perform error vector magnitude calculation on the equalization-processed frequency domain signal, obtain a new resource allocation scheme, extract communication information and positioning information of the PD receiving end, replace the new resource allocation scheme with the preset resource allocation scheme, and then repeat the execution of S1; meanwhile, the positioning information of the PD receiving end is decrypted by the positioning algorithm module and output.

[0149] In an embodiment, the receiving end comprises a judgment unit, a Hermite symmetry unit, an information processing and modulation unit, a digital-to-analog conversion unit, and a driving unit.

[0150] The judgment unit is configured to determine whether the communication information is initial communication information, and if so, perform 4QAM modulation on the communication information and the preset positioning information, otherwise, perform modulation on the communication information and the preset positioning information according to the preset resource allocation scheme in step S6.

[0151] The Hermite symmetry unit is configured to perform Hermite symmetry on the modulated communication information and the preset positioning information.

[0152] The communication information after Hermite symmetry by the information processing and modulation unit is modulated onto the corresponding subcarrier by an inverse fast Fourier algorithm, and the preset positioning information after Hermite symmetry by the information processing and modulation unit is modulated onto the corresponding subcarrier by the inverse fast Fourier algorithm.

[0153] The digital-to-analog conversion unit is configured to perform digital-to-analog conversion on the data of the subcarriers carrying the communication information and the preset positioning information, and convert the digital signal into an analog signal.

[0154] The driving unit is configured to drive the subcarriers carrying the analog signal to emit a visible light signal by the LED.

[0155] In an embodiment, the PD receiving end comprises a horizontal PD0 and an inclined PD1. i (i = 1, 2, 3, 4).

[0156] The layout method of the PD receiving end comprises:

[0157] The horizontal PD0 is set as the center position of the PD receiving end, the position coordinates of the horizontal PD0 are set as (x0, y0, z0), and the position coordinates of the horizontal PD1 are set as (x1, y1, z1). R R R i Ri Ri Ri

[0158] wherein, x​​​​​​​Ri = x R + l cos alpha cos omega i , y Ri = y R + l cos alpha sin omega i , z Ri = z R + l sin alpha

[0159] wherein the straight line through the center of the PD and perpendicular to the x-axis is p, l represents the line segment from the center of the PD to the line p parallel to the inclined plane, alpha represents the elevation angle of the PD (0° <= alpha < 90°), omega represents the angle between the projection of the line connecting the PD0 and the PD in the xoy plane and the positive direction of the x-axis, wherein omega1 = 0°, omega2 = 90°, omega3 = 180°, and omega4 = 270°. i i i i i

[0160] The system first proposes an EVM-based resource allocation method for the resource allocation problem in the VLCP system. Compared with the algorithm using SNR for resource allocation, the EVM parameter can more directly reflect the deviation degree of the received signal from the ideal signal, so that a more reasonable resource allocation result is obtained. Compared with the algorithm using the BER standard for resource allocation, EVM can give the performance measurement of the channel before demodulation, can avoid the BER calculation on a large amount of data, and at the same time, the method of subcarrier blocking can improve the accuracy of EVM while also reducing a certain amount of calculation. The simulation results under the Lambert radiation model and the visible light low communication channel environment show that, compared with the fixed modulation algorithm, the new allocation algorithm can timely adjust the communication and positioning allocation scheme according to the change of the channel environment, and can improve the channel utilization rate by 30% on average, the positioning error of the effective area in the indoor environment of 7m*7m*2.5m can be kept within 25cm, and the basic positioning demand can be met.

[0161] Figure 9 is a structural schematic diagram of an electronic device 700 provided by an embodiment of the application. The electronic device 600 can be different in configuration or performance and can have relatively large differences, and can include one or more processors (central processing units, CPUs) 710 and one or more memories 720, wherein the memory 720 stores at least one instruction, the at least one instruction is loaded and executed by the processor 710 to realize the steps of the above-mentioned EVM-based visible light real-time communication positioning method.

[0162] ​​​​​In the exemplary embodiments, a computer readable storage medium, such as a memory including instructions executable by a processor in a terminal to perform the above-mentioned EVM-based visible light real-time communication positioning method, is also provided. For example, the computer readable storage medium can be a ROM, a random access memory (RAM), a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like.

[0163] The above embodiments are not limited to the technical solutions of the embodiments themselves, and the embodiments can be combined with each other to form new embodiments. The above embodiments are only used to illustrate the technical solutions of the present application and not to limit them, and any modification or equivalent replacement without departing from the spirit and scope of the present application should be covered within the scope of the technical solutions of the present application.

Claims

1. A method for EVM-based visible light real-time communication positioning, characterized in that, The EVM-based visible light real-time communication positioning method is implemented based on an EVM-based visible light real-time communication positioning system, which comprises a sending end and a PD receiving end; the method comprises the following steps: S1, the sending end modulates the communication information and the preset positioning information onto corresponding subcarriers according to a preset resource allocation scheme; S2, the sending end performs data processing on the subcarriers carrying the communication information and the preset positioning information, and the data-processed subcarriers emit visible light signals through direct current bias driving LEDs; S3, the PD receiving end receives the visible light signals and converts the visible light signals into electrical signals; S4, the PD receiving end converts the time domain signals of the electrical signals into frequency domain signals and performs equalization processing on the frequency domain signals; S5, the PD receiving end performs error vector magnitude calculation on the equalization-processed frequency domain signals, obtains a new resource allocation scheme, and extracts the communication information and the positioning information of the PD receiving end; S6, the PD receiving end replaces the new resource allocation scheme with the preset resource allocation scheme, and then repeatedly executes S1; Meanwhile, the PD receiving end decrypts the positioning information through a positioning algorithm module and outputs the positioning information; S601, determining a QAM grid table according to a target BER; The EVM calculation is performed once per set of OFDM symbols received by the receiving end, where each set of OFDM symbols includes N b x 1000 OFDM symbols. where N b is the total number of OFDM symbols, N b = K / b, N b is an integer, and if not an integer, then rounded up. wherein K is the total number of subcarriers in the DCO-OFDM system, and b is the number of subcarriers of each block; S602, performing QAM modulation allocation according to the EVM condition of each subcarrier block and the determined QAM table, and assigning the lowest frequency subcarrier in the EVM-optimal subcarrier block to the positioning algorithm for calculation; S603, forming a new resource allocation scheme by combining the selected positioning subcarriers and the determined QAM modulation condition, and replacing the new resource allocation scheme with the preset resource allocation scheme of the previous period; The positioning algorithm module decrypts the lowest frequency subcarrier in the EVM-optimal subcarrier block and outputs the positioning information.

2. The EVM-based visible light real-time communication positioning method according to claim 1, wherein, The sending end of S1 modulates the communication information and the preset positioning information onto corresponding subcarriers according to a preset resource allocation scheme, which comprises: S101, determining whether the communication information is initial communication information, if so, performing 4QAM modulation on the communication information and the preset positioning information, otherwise, modulating the communication information and the preset positioning information according to the preset resource allocation scheme; S102, performing Hermite symmetry on the modulated communication information and the preset positioning information; S103, modulating the Hermite-symmetry communication information onto corresponding subcarriers through inverse fast Fourier algorithm; modulating the Hermite-symmetry preset positioning information onto corresponding subcarriers through inverse fast Fourier algorithm.

3. The EVM-based visible light real-time communication positioning method of claim 1, wherein, The sending end of S2 performs data processing on the subcarriers carrying the communication information and the preset positioning information, and the data-processed subcarriers emit visible light signals through direct current bias driving LEDs, which comprises: S201, performing digital-to-analog conversion on the data of the subcarriers carrying the communication information and the preset positioning information, and converting digital signals into analog signals; S202, the subcarriers carrying analog signals pass through direct current bias to drive the LED to emit a visible light signal.

4. The EVM-based visible light real-time communication positioning method of claim 1, wherein, The PD receiving end of the S3 includes a horizontal PD0 and a tilted PD i i = 1, 2, 3, 4; The layout method of the PD receiving end comprises: The horizontal PD0 is set as the center position of the PD receiving end, the position coordinates of the horizontal PD0 are set as (x R , y R , z R ), and the position coordinates of the inclined PD i are set as (x Ri , y Ri , z Ri ), wherein x Ri = x R + l cos α cos ω i , y Ri = y R + l cos α sin ω i , z Ri = z R + l sin α Among them, through PD i Let p be the line centered on and perpendicular to the x-axis, and l represent PD. i The line segment from the center to the line p that is parallel to the inclined plane. Indicates PD i The angle of elevation is , Indicates PD0 and PD i The projection of the line connecting them onto the xoy plane and The included angles in the positive direction of the axis, where ω1=0°, ω2=90°, ω3=180°, and ω4=270°.

5. The EVM-based visible light real-time communication positioning method according to claim 4, wherein, The QAM grid table determined according to the target BER in S601 comprises: In the case of meeting the target BER, the threshold value of EVM is determined according to different modulation modes, and a distribution table is obtained, which is determined as the QAM grid table.

6. An EVM based visible light real-time communication positioning system, characterized by, A visible light real-time communication positioning method based on EVM is implemented, comprising a sending end and a PD receiving end: The sending end modulates the communication information and the preset positioning information onto corresponding subcarriers according to a preset resource allocation scheme, performs data processing on the subcarriers carrying the communication information and the preset positioning information, and drives the LED to emit a visible light signal through direct current bias after the data processing of the subcarriers; The PD receiving end receives the visible light signal and converts the visible light signal into an electrical signal, converts the time domain signal of the electrical signal into a frequency domain signal, performs equalization processing on the frequency domain signal, performs error vector magnitude calculation on the equalization-processed frequency domain signal, obtains a new resource allocation scheme, extracts the communication information and the positioning information of the PD receiving end, replaces the new resource allocation scheme with the preset resource allocation scheme, and then repeats S1; Meanwhile, the PD receiving end decrypts the positioning information through a positioning algorithm module and outputs the positioning information; The replacement of the new resource allocation scheme with the preset resource allocation scheme comprises: The EVM calculation is performed once per set of OFDM symbols received by the receiving end, where each set of OFDM symbols includes N b x 1000 OFDM symbols. where N b is the total number of OFDM symbols, N b = K / b, N b is an integer, and if not an integer, then rounded up. K is the total number of subcarriers in the DCO-OFDM system, and b is the number of subcarriers in each block. QAM modulation and distribution are performed according to the EVM condition of each subcarrier block and the determined QAM table, and the lowest frequency subcarrier in the EVM-optimal subcarrier block is allocated to the positioning algorithm for calculation. The selected positioning subcarrier and the determined QAM modulation condition form a new resource allocation scheme, and the new resource allocation scheme replaces the preset resource allocation scheme of the previous period. The positioning algorithm module decrypts the lowest frequency subcarrier in the EVM-optimal subcarrier block and outputs the positioning information.

7. The EVM based visible light real-time communication positioning system as claimed in claim 6, wherein, The sending end comprises: A judgment unit is configured to judge whether the communication information is initial communication information, and if so, to perform 4QAM modulation on the communication information and the preset positioning information, otherwise, to modulate the communication information and the preset positioning information according to the preset resource allocation scheme. A Hermitian symmetry unit is configured to perform Hermitian symmetry on the modulated communication information and the preset positioning information. An information processing and modulation unit is configured to modulate the communication information after Hermitian symmetry to corresponding subcarriers through inverse fast Fourier algorithm. The preset positioning information after Hermitian symmetry is modulated to corresponding subcarriers through inverse fast Fourier algorithm.

8. The EVM based visible light real-time communication positioning system according to claim 7, wherein, The sending end further comprises: An analog-to-digital conversion unit is configured to perform analog-to-digital conversion on the data of the subcarriers carrying the communication information and the preset positioning information, and convert the digital signal into an analog signal. A driving unit is configured to drive the subcarriers carrying the analog signal to emit a visible light signal through direct current bias.

9. The EVM based visible light real-time communication positioning system as claimed in claim 7, wherein, The PD receiving end comprises a horizontal PD0 and a tilted PD i i = 1, 2, 3, 4; The layout method of the PD receiving end comprises: The horizontal PD0 is set as the center position of the PD receiving end, the position coordinates of the horizontal PD0 are set as (x R , y R , z R ), and the position coordinates of the inclined PD i are set as (x Ri , y Ri , z Ri ). wherein x Ri = x R + l cos α cos ω i , y Ri = y R + l cos α sin ω i , z Ri = z R + l sin α wherein the PD i The straight line through the center and perpendicular to the x-axis is p, and l represents the PD i The straight line through the center and perpendicular to the x-axis is p, and l represents the PD The straight line through the center and perpendicular to the x-axis is p, and l represents the PD i The elevation angle of the PD , The straight line through the center and perpendicular to the x-axis is p, and l represents the PD i The straight line through the center and perpendicular to the x-axis is p, and l represents the PD The straight line through the center and perpendicular to the x-axis is p, and l represents the PD

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