Joint Estimation Method for Terminal Pose and Time-Varying Channel Based on 6G Visible Light Communication

Abstract

The present invention proposes a method for joint estimation of terminal pose and time-varying channel based on 6G visible light communication, which relates to the technical field of visible light communication. Considering the small-scale attenuation in line-of-sight transmission, based on the orthogonal frequency division multiplexing technology, different frequency bands are assigned to different LED transmitters. The photodiode PD in the target terminal UD system demodulates the signals sent by the LED transmitters, and different LED transmitters are modulated on their respective frequency carriers. A joint estimation function of terminal pose and time-varying channel is constructed and solved, and the channel is effectively estimated through frequency-domain diversity, avoiding the interference problem brought to terminal positioning after the visible light communication signal experiences small-scale attenuation, thereby realizing the joint estimation of position and attitude and the channel, and improving the accuracy of terminal positioning.

Description

Technical Field

[0001] The present invention relates to the technical field of visible light communication, and more specifically, to a method for jointly estimating the terminal pose and time-varying channel based on 6G visible light communication. Background Art

[0002] Visible light communication (VLC, also known as LiFi) is an important supplement to 6G short-distance communication and is envisioned as an important technology for 6G wireless communication to improve indoor communication quality. In a visible light communication system, a light-emitting diode (LED) is the signal light source, visible light waves are the communication carriers, and free space is the transmission channel. Visible light communication has many advantages such as high speed, low cost, and environmental friendliness due to the characteristics of the LED itself, such as its bandwidth, low energy consumption, and low price. Visible light communication is suitable for many indoor scenarios, such as healthcare facilities, airports and railway stations, factories and logistics, shopping malls, and other indoor public places. However, the basis of visible light transmission is to accurately obtain the position and orientation of the user terminal. VLC is highly sensitive to distance and angle. Therefore, it is necessary to consider simultaneous position and orientation estimation (SPO) based on visible light. The current research on SPO mainly solves the five-dimensional problem, that is, three-dimensional position and two-dimensional direction (the direction is represented by a unit vector). However, in the application scenarios of visible light positioning, the six-dimensional positioning problem is more practical. The basis of visible light transmission is to accurately obtain the position and orientation of the user. Since the reliability of transmission is sensitive to the position and orientation of the user, it is necessary to study visible light positioning (VLP) based on VLC.

[0003] At present, there have been many research works on VLC-based positioning using various measurement signals. However, most of the research is based on known prior information about the user's direction. For example, it is assumed that the direction is vertically upward or the direction vectors of the transmitter and the receiver are parallel, etc. There are still certain limitations in the research on user direction estimation. An effective SPO algorithm has been proposed in the prior art to jointly estimate the user's position and direction through this algorithm. However, in this research, the receiver direction is represented by the normal vector, which actually has only 2 degrees of freedom and cannot achieve the estimation of the attitude in three-dimensional space. Compared with this scheme, another scheme considers a more general direction representation - the rotation matrix, which can achieve the estimation of the three directions of the attitude. However, the considered scenario is relatively simple, and it is assumed that the line-of-sight transmission channel is a perfect channel without any attenuation. The channel gain is only limited by the position and attitude of the receiver to be estimated, as well as constants such as the transmit power and filter gain. However, these assumptions are too ideal. In an actual short-distance communication system, due to the scattering, diffraction, and reflection of light waves, the received waveform at the receiving end is actually a composite waveform of multiple path waveforms. These multipath components with randomly distributed amplitudes, phases, and incident angles are vectorially combined by the receiver antenna into a signal with rapidly changing amplitudes and phases, resulting in fading distortion of the received signal. This kind of fading caused by multipath propagation is called multipath fading, which belongs to small-scale fading and cannot achieve accurate positioning of the terminal's pose. Summary of the Invention

[0004] To solve the interference problem brought by the small-scale fading of visible light communication signals to terminal positioning in visible light communication-based positioning, the present invention proposes a method for jointly estimating the terminal's pose and time-varying channel based on 6G visible light communication, considering the small-scale attenuation problem in line-of-sight transmission, and realizing the joint estimation of the terminal's position and attitude and the time-varying channel.

[0005] To achieve the above technical effects, the technical solution of the present invention is as follows:

[0006] A method for jointly estimating the terminal's pose and time-varying channel based on 6G visible light communication, the method comprising the following steps:

[0007] S1. Establish a VLP system composed of several LED transmitters and a target terminal UD system equipped with several photodiodes PD;

[0008] S2. Establish a line-of-sight channel gain model between the LED transmitter and the photodiode PD, and considering the small-scale fading coefficient of the line-of-sight transmission channel, improve the line-of-sight channel gain model;

[0009] S3. Based on the orthogonal frequency division multiplexing technology, the photodiode PD in the target terminal UD system demodulates the signal sent by the LED transmitter to obtain the demodulated subcarrier frequency band and time delay;

[0010] S4. Consider the observations between different LED transmitters and the photodiode PD, combine the subcarrier frequency band and time delay, obtain the signal vector transmitted by the LED transmitter received by the photodiode PD, and based on the received signal vector, obtain the observation vector;

[0011] S5. Combine the observation vector, construct a joint estimation function of the terminal pose and the time-varying channel, and solve the joint estimation function after considering the improved LOS channel gain model to achieve the joint estimation of the channel and pose in the visible light communication system.

[0012] In this technical solution, considering the small-scale attenuation in LOS transmission, based on the orthogonal frequency division multiplexing technology, different frequency bands are allocated to different LED transmitters. The photodiode PD in the target terminal UD system demodulates the signals transmitted by the LED transmitters. Different LED transmitters are modulated on their respective frequency carriers. A joint estimation function of the terminal pose and the time-varying channel is constructed and solved. The channel is effectively estimated through frequency-domain diversity, avoiding the interference problem brought to terminal positioning after the visible light communication signal experiences small-scale attenuation, thereby realizing the joint estimation of the position and attitude and the channel, and improving the accuracy of terminal positioning.

[0013] Preferably, assume that there are N L LED transmitters in the VLP system, and the target terminal UD system is equipped with N P photodiodes PD, that is, N L LED transmitters transmit signals, and N P photodiodes PD receive signals. Let and respectively represent the position and direction vectors of the known i-th LED transmitter, where m = 1, 2,..., N L , and all the photodiodes PD are deployed on the target terminal UD. As the target terminal UD synchronously translates and rotates, the relative distances and relative directions of all the photodiodes PD remain unchanged.

[0014] Preferably, when the coordinates and direction vectors of the photodiode PD are defined in the receiver coordinate system where the target terminal UD system is located, assume that the centroid of the receiver is the coordinate origin of the current receiver coordinate system. The coordinates of the j-th photodiode PD are represented by a relative distance vector , and its direction is defined by a known rotation matrix Rp,j ∈ SO(3). SO(3) is the three-dimensional rotation group, that is, the space where the rotation matrix is located. The direction of the j-th photodiode PD relative to the direction n0 of the receiver coordinate system is n P，j，0 = Rp,jn0, where n0 = [0, 0, 1] T ;

[0015] In the system coordinate system where the VLP system and the target terminal UD system are located as a whole, the position and orientation of the receiver are represented by and \(R\in SO(3)\) respectively. Among them, the normal vector of the receiver is represented by \(n\), that is, \(n = Rn_0\). The coordinate vector of the \(j\)-th photodiode PD is represented by \(r\) j , \(r\) j \(= r + d\) j , where \(d\) j \(= Rd\) j，0 , and the direction vector is represented by \(n\) j , \(n\) j \(= Rn\) P，j，0 .

[0016] Preferably, let represent the radiation vector of the line-of-sight transmission channel between the \(m\)-th LED transmitter and the \(j\)-th light-emitting diode PD. The expression is:

[0017]

[0018] Solve for the angle between the direction vector \(v\) m of the \(m\)-th LED transmitter and the radiation vector \(e\) 0，j，m , and the included angle between the direction vector \(n\) j of the \(j\)-th light-emitting diode PD and the radiation vector \(e\) 0，j，m . The expressions are respectively:

[0019]

[0020] \(\theta\) 0，j，m \(= \arccos(-e\) 0，j，m T \(n\) j )

[0021] Suppose that all the light-emitting diodes PD have the same received signal range All the LED transmitters have the same transmitted signal range \(\theta\) FOV . For the \(m\)-th LED and the \(j\)-th PD, the line-of-sight channel gain model between the LED transmitter and the photodiode PD is:

[0022]

[0023] where \(\psi\) R is a known quantity, depends on the transmission power \(W\) of the LED transmitter T ; Considering the small-scale fading coefficient of the line-of-sight transmission channel, the improved line-of-sight channel gain model is expressed as:

[0024] \(h\) 0，j，m \(= \alpha\) 0，j，m \(g\)0，j，m

[0025] Converted to:

[0026]

[0027] Where, α 0，j，m ∈ [0, 1), represents the small-scale fading coefficient of the line-of-sight transmission channel from the m-th LED transmitter to the j-th PD, and r j = r + Rd j，0 , and n j = Rn P，j，0 , r and R represent the unknown position and direction of the receiver to be determined.

[0028] Here, for the m-th LED transmitter and the j-th photodiode PD, if and Then it is determined that the PD will be able to receive the LOS (line-of-sight) signal sent by the LED, where |·| is the absolute value.

[0029] Preferably, based on the orthogonal frequency division multiplexing technology, when the photodiode in the target terminal UD system demodulates the signal sent by the LED transmitter, each light-emitting diode PD can distinguish signals with different carrier frequencies from different LED transmitters. For the information stream to be transmitted, its front end contains the pilot signal of the LED transmitter, that is, the information known in advance at the receiving end. After serial input, it is converted from serial to parallel to obtain a parallel signal, which is carried on each subcarrier of the LED transmitter and undergoes an inverse Fourier transform to obtain a parallel time-domain signal, which is then converted to serial output, and finally through digital-to-analog conversion, the final transmitted signal a k is expressed as:

[0030]

[0031] Where, i = √(-1), T s is the symbol period length, and the demodulated signal of the j-th light-emitting diode PD at the receiving end for the signal sent by the m-th LED is expressed as:

[0032]

[0033] Where, X j，m [n] is the symbol on the n-th subcarrier sent by the m-th LED transmitter to the j-th light-emitting diode PD, and f n，m is the n-th subcarrier frequency band of the m-th LED.

[0034] Preferably, the expression of the n-th subcarrier frequency band of the m-th LED is: Time delay τ j，mThe time of flight from the m-th LED emitter to the j-th light emitting diode PD, defined as:

[0035]

[0036] Preferably, let denote the characteristic parameters of the rotation matrix defining the receiver direction, including the pitch angle, heading angle, and roll angle, denote the unknown position and orientation parameters of the receiver to be determined, i.e., the pose information, β is related to the time of flight of the received signal and the angle gain. For the signal vector of the m-th LED received by the j-th PD:

[0037] y j，m =G j，m (β)α 0，j，m

[0038] where, denote the signal received by the j-th PD from the m-th LED;

[0039]

[0040] denote an N×1 dimensional complex column vector. When considering the observations of different LED and PD pairs, the received signal is expressed as,

[0041] y=G(β)h

[0042] where,

[0043]

[0044]

[0045]

[0046] Based on the received signal vector, the observation vector is obtained:

[0047] z=G(β)h+∈

[0048] where, is the measurement noise vector. Let the noise follow a zero-mean complex Gaussian distribution, i.e., is its covariance matrix.

[0049] Preferably, combining the observation vector, the joint estimation function of the terminal pose and the time-varying channel is constructed and expressed as:

[0050]

[0051] where G(β) is a non-linear function of β and the variable h to be estimated, and is non-convex with respect to β and h, and R is an arbitrary 3×3 matrix.

[0052] Preferably, after considering the improved line-of-sight channel gain model, when solving the joint estimation function of the terminal pose and the time-varying channel, the channel estimation and the terminal pose estimation are alternately iterated until both the channel estimation and the pose estimation converge.

[0053] Preferably, the specific process of solving the joint estimation function of the terminal pose and the time-varying channel is as follows:

[0054] S51. Set the initial pose as

[0055] S52. At t = 0, perform channel estimation, and the estimation expression is: Obtain the estimation of the channel under the current pose, where represents the pseudo-inverse operation, represents the current pose, represents the current channel;

[0056] S53. Through and obtain the pose estimation of the next iteration under the current pose and channel;

[0057] The objective function is a non-convex function with respect to the receiver position and orientation. Perform the first-order Taylor expansion of G(β)h under the current pose and channel as follows:

[0058]

[0059] where is the gradient at the current pose,

[0060]

[0061]

[0062] S54. Repeat S52 and S53 until the estimations of the terminal pose and the time-varying channel converge.

[0063] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0064] The present invention proposes a method for joint estimation of terminal pose and time-varying channel based on 6G visible light communication. Considering the small-scale attenuation in line-of-sight transmission and based on orthogonal frequency division multiplexing technology, different frequency bands are assigned to different LED transmitters. The photodiode PD in the target terminal UD system demodulates the signals sent by the LED transmitters, and different LED transmitters are modulated on their respective frequency carriers. A joint estimation function of terminal pose and time-varying channel is constructed and solved, and the channel is effectively estimated through frequency-domain diversity, avoiding the interference problem brought to terminal positioning after the visible light communication signal experiences small-scale attenuation, thereby realizing the joint estimation of position and attitude and the channel, and improving the accuracy of terminal positioning. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is a schematic flow chart showing the method for joint estimation of terminal pose and time-varying channel based on 6G visible light communication proposed in Embodiment 1 of the present invention;

[0066] Figure 2 It is a schematic diagram of the receiver coordinate system proposed in Embodiment 1 of the present invention;

[0067] Figure 3 It is a schematic diagram of the system coordinate system proposed in Embodiment 1 of the present invention;

[0068] Figure 4 It is a schematic diagram of the line-of-sight transmission channel between the m-th LED transmitter and the j-th photodiode PD proposed in Embodiment 1 of the present invention;

[0069] Figure 5 It is a modulation block diagram of the LED transmitter end based on orthogonal frequency division multiplexing technology proposed in Embodiment 2 of the present invention;

[0070] Figure 6 It is a demodulation block diagram of the photodiode PD end based on orthogonal frequency division multiplexing technology proposed in Embodiment 2 of the present invention;

[0071] Figure 7 It is a schematic diagram of carrier allocation under orthogonal frequency division multiplexing technology proposed in Embodiment 2 of the present invention;

[0072] Figure 8 It is a schematic diagram of channel estimation error in the case of no noise proposed in Embodiment 3 of the present invention;

[0073] Figure 9 It is a schematic diagram of position estimation error in the case of no noise proposed in Embodiment 3 of the present invention;

[0074] Figure 10 It is a schematic diagram of attitude estimation error in the case of no noise proposed in Embodiment 3 of the present invention;

[0075] Figure 11It shows the comparison diagram of position estimation errors when small-scale fading is considered and not considered under the condition of 80 dB noise in Embodiment 3 of the present invention;

[0076] Figure 12 It shows the comparison diagram of direction estimation errors when small-scale fading is considered and not considered under the condition of 80 dB noise in Embodiment 3 of the present invention; Specific implementation manners

[0077] The accompanying drawings are only for illustrative purposes and should not be construed as limitations on this patent;

[0078] In order to better illustrate this embodiment, some parts of the accompanying drawings will be omitted, enlarged or reduced, which do not represent the actual size;

[0079] For those skilled in the art, it is understandable that some well-known content descriptions in the accompanying drawings may be omitted.

[0080] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0081] The description of the positional relationship in the accompanying drawings is only for illustrative purposes and should not be construed as limitations on this patent;

[0082] Embodiment 1

[0083] As Figure 1 shown, this embodiment proposes a joint estimation method for the pose and time-varying channel of a terminal based on 6G visible light communication. Refer to Figure 1 , this method includes the following steps:

[0084] S1. Establish a VLP system composed of several LED transmitters and a target terminal UD system equipped with several photodiodes PD;

[0085] S2. Establish a line-of-sight channel gain model between the LED transmitter and the photodiode PD, and consider the small-scale fading coefficient of the line-of-sight transmission channel to improve the line-of-sight channel gain model;

[0086] S3. Based on the orthogonal frequency division multiplexing technology, the photodiode PD in the target terminal UD system demodulates the signal sent by the LED transmitter to obtain the demodulated subcarrier frequency band and time delay;

[0087] S4. Consider the observations between different LED transmitters and photodiodes PD, combine the subcarrier frequency band and time delay to obtain the signal vector sent by the LED transmitter received by the photodiode PD, and based on the received signal vector, obtain the observation vector;

[0088] S5. Combine the observation vectors to construct a joint estimation function for the terminal pose and the time-varying channel, and solve the joint estimation function considering the improved LOS channel gain model to achieve the joint estimation of the channel and the pose in the visible light communication system.

[0089] Overall, this embodiment aims at the problem that the VLC signal transmission causes interference to the terminal positioning after experiencing small-scale fading. First, consider the small-scale fading in the LOS transmission. Based on the orthogonal frequency division multiplexing technology, different frequency bands are allocated to different LED transmitters. The photodiode PD in the target terminal UD system demodulates the signals sent by the LED transmitters. Different LED transmitters are modulated on their respective frequency carriers. A joint estimation function for the terminal pose and the time-varying channel is constructed and solved. The channel is effectively estimated through frequency-domain diversity, avoiding the interference problem caused by the visible light communication signal experiencing small-scale fading to the terminal positioning, thereby realizing the joint estimation of the position and attitude and the channel, and improving the accuracy of the terminal positioning.

[0090] In this embodiment, assume that there are N L LED transmitters in the VLP system, and the target terminal UD system is equipped with N P photodiodes PD, that is, N L LED transmitters send signals, and N P photodiodes PD receive signals. Let and respectively represent the known position and direction vectors of the i-th LED transmitter, where m = 1, 2,..., N L , and all the photodiodes PD are deployed on the target terminal UD. As the target terminal UD synchronously translates and rotates, the relative distances and relative directions of all the photodiodes PD remain unchanged. In this way, the coordinates and direction vectors of the photodiodes PD are first defined in the coordinate system of the receiver, and then converted to the system coordinate system for positioning estimation.

[0091] Specifically, when the coordinates and direction vectors of the photodiode PD are defined in the coordinate system of the receiver where the target terminal UD system is located, as Figure 2 shown, assume that the centroid of the receiver is the coordinate origin of the current receiver coordinate system. The coordinate of the j-th photodiode PD is represented by a relative distance vector , and its direction is defined by a known rotation matrix Rp,j ∈ SO(3). SO(3) is the three-dimensional rotation group, that is, the space where the rotation matrix is located. The direction of the j-th photodiode PD relative to the direction n0 of the receiver coordinate system is n P，j，0 = Rp,jn0, where n0 = [0, 0, 1] T .

[0092] As Figure 3As shown, in the system coordinate system where the VLP system and the target terminal UD system are located as a whole, the position and orientation of the receiver are represented by and \(R\in SO(3)\) respectively. Among them, the normal vector of the receiver is represented by \(n\), that is, \(n = Rn_0\). The coordinate vector of the \(j\)th photodiode PD is represented by \(r\) j denoted as \(r\) j \(=r + d\) j where \(d\) j \(= Rd\) j，0 The direction vector is represented by \(n\) j denoted as \(n\) j \(= Rn\) P，j，0 .

[0093] See Figure 4 the line-of-sight transmission channel between the \(m\)th LED transmitter and the \(j\)th light-emitting diode PD shown in the figure. Let represent the radiation vector of the line-of-sight transmission channel between the \(m\)th LED transmitter and the \(j\)th light-emitting diode PD. The expression is:

[0094]

[0095] Solve for the angle between the direction vector \(v\) m of the \(m\)th LED transmitter and the radiation vector \(e\) 0，j，m , and the angle between the direction vector \(n\) j of the \(j\)th light-emitting diode PD and the radiation vector \(e\) 0，j，m . The expressions are respectively:

[0096]

[0097] \(\theta\) 0，j，m \(=\arccos(-e\) 0，j，m T \(n\) j )

[0098] Assume that all the light-emitting diodes PD have the same received signal range All the LED transmitters have the same transmitted signal range \(\theta\) FOV . For the \(m\)th LED transmitter and the \(j\)th photodiode PD, if and Then it is determined that this PD will be able to receive the LOS (line-of-sight) signal sent by this LED. Among them, \(|\cdot|\) is the absolute value. For the \(m\)th LED and the \(j\)th PD, the line-of-sight channel gain model between the LED transmitter and the photodiode PD is:

[0099]

[0100] where \(\psi\) R is a known quantity. depending on the emission power W of the LED emitter T ; in this embodiment, let the aperture be φ R , the optical filter gain be G R , the condenser gain be Γ R , θ m ∈ [0, θ FOV , is the reflection index of the receiving end filter gain, usually G R = 1, φ R = 1 [cm 2 , θ FOV = π / 2. The radiation angle of the LED is usually described by the Lambertian sequence in the Lambertian model where is the half angle of the half power of the LED lamp. Usually, r = 1. Π(·) is the rectangle function

[0101]

[0102] then considering the small-scale attenuation experienced by the line-of-sight signal, substituting the radiation vector into the small-scale fading coefficient of the line-of-sight transmission channel, the improved line-of-sight channel gain model is expressed as:

[0103] h 0，j，m = α 0，j，m g 0，j，m

[0104] is transformed into:

[0105]

[0106] where α 0，j，m ∈ [0, 1), representing the small-scale fading coefficient of the line-of-sight transmission channel from the mth LED emitter to the jth PD, and r j = r + Rd j，0 , and n j = Rn P，j，0 , r and R represent the unknown position and direction of the receiver to be determined

[0107] This line-of-sight channel model includes the large-scale gain of visible light (g 0，j，m ) and the small-scale attenuation of the channel (α 0，j，m )

[0108] Embodiment 2

[0109] In this embodiment, as Figure 5 and Figure 6As shown, based on the orthogonal frequency division multiplexing technology, when the photodiode in the target terminal UD system demodulates the signal sent by the LED transmitter, each light-emitting diode PD can distinguish signals with different carrier frequencies from different LED transmitters. For the information flow to be transmitted, its front end includes the pilot signal of the LED transmitter, that is, the information known in advance at the receiving end. After serial input, it is converted from serial to parallel through serial-to-parallel conversion to obtain a parallel signal, which is carried on each subcarrier of the LED transmitter and undergoes inverse Fourier transform to obtain a parallel time-domain signal, which is then converted to serial output. Finally, through digital-to-analog conversion, to ensure that the transmitted signal is real, the transmitted signal needs to satisfy the Hermitian symmetry condition, that is:

[0110]

[0111] So the final transmitted signal a is obtained k , which is expressed as:

[0112]

[0113] where \(i = \sqrt{-1}\), \(T\) s is the symbol period length. The signal transmission is mainly determined by the angular gain model of traditional visible light transmission, but it will be affected by small-scale attenuation and time delay. The demodulated signal of the \(j\)-th photodiode PD at the receiving end for the signal sent by the \(m\)-th LED is expressed as:

[0114]

[0115] where \(X\) j，m [n] is the symbol on the \(n\)-th subcarrier sent from the \(m\)-th LED transmitter to the \(j\)-th photodiode PD, and \(f\) n，m is the \(n\)-th subcarrier frequency band of the \(m\)-th LED. The subcarrier allocation situation is shown in Figure 7 , there are a total of \(N\) L LEDs, and at most \(N\) subcarriers are allocated to each LED, so there are a total of \(NN\) L subcarriers. The expression for the \(n\)-th subcarrier frequency band of the \(m\)-th LED is: The time delay \(\tau\) j，m is the flight time from the \(m\)-th LED transmitter to the \(j\)-th photodiode PD, which is defined as:

[0116]

[0117] Let represent the characteristic parameters of the rotation matrix defining the receiver direction, including pitch angle, heading angle, and roll angle, represent the unknown position and direction parameters of the receiver to be solved, that is, the pose information. \(\beta\) is related to the flight time and angular gain of the received signal. For the signal vector of the \(m\)-th LED received by the \(j\)-th PD:

[0118] y j，m = G j，m (β)α 0，j，m

[0119] where represents the signal received by the j-th PD from the m-th LED;

[0120]

[0121] represents an N×1 dimensional complex column vector. When considering the observations of different LED and PD pairs, the received signal is expressed as,

[0122] y = G(β)h

[0123] where

[0124]

[0125]

[0126]

[0127] Based on the received signal vector, the observation vector is obtained:

[0128] z = G(β)h + ∈

[0129] where is the measurement noise vector, and it is assumed that the noise follows a zero-mean complex Gaussian distribution, that is is its covariance matrix.

[0130] Combined with the observation vector, the joint estimation function of the terminal pose and the time-varying channel is constructed and expressed as:

[0131]

[0132] where G(β) is a non-linear function of β and the variable h to be estimated, and it is non-convex with respect to β and h, and R is an arbitrary 3×3 matrix.

[0133] After considering the improved line-of-sight channel gain model, when solving the joint estimation function of the terminal pose and the time-varying channel, the channel estimation and the terminal pose estimation are alternately iterated until both the channel estimation and the pose estimation converge.

[0134] The specific process of solving the joint estimation function of the terminal pose and the time-varying channel is as follows:

[0135] S51. Let the initial pose be

[0136] At t = 0, channel estimation is performed, and the estimation expression is: Obtain the estimation of the channel under the current pose, where represents the pseudo-inverse operation, represents the current pose, represents the current channel;

[0137] S53. Through and Obtain the pose estimation of the next iteration under the current pose and channel;

[0138] The objective function is a non-convex function with respect to the position and orientation of the receiver. Perform the first-order Taylor expansion of G(β)h under the current pose and channel as follows:

[0139]

[0140] where is the gradient under the current pose,

[0141]

[0142]

[0143] S54. Repeat S52 and S53 until the estimation of the terminal pose and the time-varying channel converges.

[0144] The specific solution process is to jointly estimate the position, orientation of the photodiode PD in the target terminal UD system and the small-scale fading of the channel. For the joint estimation function of the terminal pose and the time-varying channel, the main difficulty in solving it lies in G(β). Since G(β) is a non-linear function with respect to β, the above problem is a non-convex problem with respect to β and cannot be directly solved. In addition, R is not an arbitrary 3×3 matrix, so we cannot directly obtain its gradient direction through differentiation. For the first challenge, the Gauss-Newton method is used to approximate the original function through a continuous approximation function to overcome the non-convex problem. For the second challenge, the parameters R can be estimated by optimizing the manifold. Specifically:

[0145] (1) Channel estimation. The objective function is a convex function with respect to the variable h to be estimated. Given the current estimate of the pose β its current least-squares estimation solution can be directly obtained.

[0146] (2) Pose estimation. Perform the first-order Taylor expansion of G(β)h under the current pose and channel as follows, and further structure it as follows,

[0147]

[0148]

[0149]

[0150]

[0151] In the above formula, β only depends on g 0，j，m (β) and are related. Therefore, the key is to determine the derivatives of these two parts with respect to β. The first part in β is the position vector r of the receiver, and its derivative can be directly calculated in the Euclidean space. The second part in β is the parameter γ of the position vector R of the receiver. Obtaining the gradient of the direction is one of the difficulties in this study. The method adopted here is to introduce an infinitesimal left perturbation exp(ω × ), mapping the rotation matrix R ∈ SO(3) to the direction dimension. By calculating the gradient of the tangent space (rotation direction) and finally mapping it back to the space where the rotation matrix is located. The specific calculation is as follows:

[0152]

[0153]

[0154] where is a constant. The left perturbation variable exp(ω × ) ∈ SO(3) is mapped from the three-dimensional parameter vector ω = [ω x , ω y , ω z T , and the mapping function is as follows:

[0155]

[0156] exp(·) represents the matrix exponential function, and (·) × represents converting the direction vector into the form of an anti-symmetric matrix. Finally, the derivative of exp(-i2πf n，m τ j，m ) with respect to β can be obtained:

[0157]

[0158] where q j，m = r + Rd j，0 - p m . Similarly, the derivative of g 0，j，m with respect to β can also be obtained.

[0159]

[0160] Therefore, given the current pose and channel estimation ​Under the following circumstances, the gradient direction with respect to β is

[0161]

[0162] Δ β = [Δ r , Δ γ , different from the standard Gauss-Newton algorithm, our direction iteration is carried out on the manifold, and the iteration formulas for position and direction are given by the following formula

[0163]

[0164]

[0165] where δ is the iteration step size.

[0166] Embodiment 3

[0167] In this embodiment, combined with specific simulations, the method proposed in this application is verified and illustrated. The number of LEDs is set to 4, the ceiling height is 3m, and the x and y coordinates of each LED are 1m apart. The transmission power is set to 2.2W, and the signal transmission range is set to π / 2. The number of PDs on the receiver is set to 4, one of which is distributed in the center, and the remaining three are distributed in a pyramid shape around the central PD. The receiving range of the receiver PD is π / 2, the filter gain is 1, and the aperture area is 1cm 2 . The visible light center frequency is set to 100MHz, and the number of subcarriers allocated to each LED is 6, so there are a total of 24 subcarrier frequency bands.

[0168] The initial position is set within the 0.01 noise variance of the true position, the true direction is set such that the angle between the x-axis of the receiver coordinate system and the system coordinate system differs by 30°, the y-axis and z-axis coincide, and the initial direction is set with a 5° variance in the x-axis. Figure 8 It shows the schematic diagram of the channel estimation error in the noise-free case. Figure 9 and Figure 10 respectively show the schematic diagrams of the position estimation error and the attitude estimation error in the noise-free case. It can be seen that in the noise-free environment, the proposed algorithm realizes the joint estimation of the channel and the pose, and can achieve an error level of 10^ (-13) ; Figure 11 and Figure 12 respectively show the comparison of the position estimation error and the direction estimation error considering small-scale fading and not considering small-scale fading at different receiver signal-to-noise ratios. From Figure 11 and Figure 12 it can be seen that when there is noise, compared with the pose estimation algorithm that does not consider small-scale, the proposed algorithm can achieve good positioning performance, while the algorithm that does not consider small-scale cannot achieve accurate pose positioning.

[0169] Obviously, the above embodiments of the present invention are only examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for joint estimation of terminal pose and time-varying channel based on 6G visible light communication, characterized in that, The method includes the following steps: S1. Establish a VLP system composed of a number of LED transmitters and a target terminal UD system equipped with a number of photodiodes PD; S2. Establish a line-of-sight channel gain model between the LED transmitter and the photodiode PD, and consider the small-scale fading coefficient of the line-of-sight transmission channel to improve the line-of-sight channel gain model; S3. Based on the orthogonal frequency division multiplexing technology, the photodiode PD in the target terminal UD system demodulates the signal sent by the LED transmitter to obtain the demodulated subcarrier frequency band and time delay; S4. Consider the observations between different LED transmitters and photodiodes PD, combine the subcarrier frequency band and time delay to obtain the signal vector sent by the LED transmitter received by the photodiode PD, and based on the received signal vector, obtain the observation vector; S5. Combine the observation vector, construct a joint estimation function of the terminal pose and the time-varying channel, and solve the joint estimation function after considering the improved line-of-sight channel gain model to realize the joint estimation of the channel and the pose in the visible light communication system.

2. The joint estimation method of terminal pose and time-varying channel based on 6G visible light communication according to claim 1, characterized in that Suppose there are N LED transmitters in the VLP system L and the target terminal UD system is equipped with N P photodiodes PD, that is, N L LED transmitters emit signals and N P photodiodes PD receive signals. Let and respectively represent the position and direction vector of the known m-th LED transmitter, where m = 1, 2, …, N L , and all photodiodes PD are deployed on the target terminal UD. As the target terminal UD moves and rotates synchronously, the relative distances and relative directions of all photodiodes PD remain unchanged.

3. The method for jointly estimating the terminal pose and time-varying channel based on 6G visible light communication according to claim 2, wherein When the coordinates and direction vectors of the photodiode PD are defined in the receiver coordinate system where the target terminal UD system is located, let the centroid of the receiver be the origin of the current receiver coordinate system. The coordinates of the j-th photodiode PD are represented by a relative distance vector and its direction is defined by a known rotation matrix R j ∈ SO(3), where SO(3) is the three-dimensional rotation group, that is, the space where the rotation matrix is located. The direction of the j-th photodiode PD relative to the direction n0 of the receiver coordinate system is n j,0 = R j n0, where n0 = [0, 0, 1] T ; In the system coordinate system where the VLP system and the target terminal UD system are located as a whole, the position and orientation of the receiver are represented by and R ∈ SO(3) respectively. Among them, the normal vector of the receiver is represented by n, that is, n = Rn0, and the coordinate vector of the j-th photodiode PD is represented by r j , r j = r + d j , where d j = Rd j,0 , and the direction vector is represented by n j , n j = Rn j,0 .

4. The method for jointly estimating the terminal pose and time-varying channel based on 6G visible light communication according to claim 3, wherein Let denote the radiation vector of the line-of-sight transmission channel between the m-th LED transmitter and the j-th photodiode PD, and the expression is: Solve for the direction vector v of the m-th LED emitter m and the radiation vector e 0,j,m The angle between the two, the direction vector n of the j-th light-emitting diode PD j and the radiation vector e 0,j,m The included angles between them are expressed as follows: θ 0,j,m = arccos(-e 0,j,m T n j ) Assume that all the light-emitting diodes PD have the same received signal range All LED transmitters have the same transmission signal range θ FOV , for the m-th LED and the j-th PD, the line-of-sight channel gain model between the LED transmitter and the photodiode PD is as follows: where ψ R is a known quantity, which depends on the transmission power W of the LED transmitter T ; considering the small-scale fading coefficient of the line-of-sight transmission channel, the improved line-of-sight channel gain model is expressed as: h 0,j,m = α 0,j,m g 0,j,m Converted to: Among them, α 0,j,m ∈ [0, 1), represents the small-scale fading coefficient of the LOS transmission channel from the m-th LED transmitter to the j-th PD, and r j = r + Rd j,0 , and n j = Rn j,0 , r and R represent the unknown position and orientation of the receiver to be determined.

5. The method for jointly estimating the terminal pose and time-varying channel based on 6G visible light communication according to claim 4, wherein Based on the orthogonal frequency division multiplexing technology, when the photodiode in the target terminal UD system demodulates the signal sent by the LED transmitter, each light-emitting diode PD can distinguish signals with different carrier frequencies from different LED transmitters. For the information stream to be transmitted, its front end contains the pilot signal of the LED transmitter, that is, the information known in advance at the receiving end. After serial input, it is converted from serial to parallel to obtain a parallel signal, which is carried on each subcarrier of the LED transmitter and undergoes an inverse Fourier transform to obtain a parallel time-domain signal, which is then converted to serial output, and finally through digital-to-analog conversion, the final transmitted signal a is obtained. k , expressed as: Among them, T s is the symbol period length, and the demodulation signal of the j-th photodiode PD at the receiving end for the signal transmitted by the m-th LED is expressed as: Among them, X j,m [n] is the symbol on the nth subcarrier sent from the mth LED transmitter to the jth light-emitting diode PD, f n,m is the nth subcarrier frequency band of the mth LED; τ j,m is the flight time from the mth LED transmitter to the jth light-emitting diode PD.

6. The method for joint estimation of terminal pose and time-varying channel based on 6G visible light communication according to claim 5, wherein The expression for the nth subcarrier frequency band of the mth LED is as follows: Time delay τ j,m Is the flight time from the mth LED transmitter to the jth light-emitting diode PD, defined as: Where c represents the speed of light.

7. The method for jointly estimating the terminal pose and time-varying channel based on 6G visible light communication according to claim 6, wherein Let represent the characteristic parameters of the rotation matrix defining the receiver direction, including the pitch angle, heading angle, and roll angle, represent the unknown position and direction parameters of the receiver to be determined, i.e., the pose information. β is related to the flight time and angle gain of the received signal. For the signal vector of the m-th LED received by the j-th PD: y j,m = G j,m (β)α 0,j,m Among them, represents the signal received by the j-th PD from the m-th LED; Denote an N×1 dimensional complex column vector; when considering the observations of different LED and PD pairs, the received signal is expressed as, y = G(β)h Where Based on the received signal vector, obtain the observation vector: z = G(β)h + ∈ Among them, is the measurement noise vector. Assume that the noise follows a zero-mean complex Gaussian distribution, that is is its covariance matrix.

8. The joint estimation method of terminal pose and time-varying channel based on 6G visible light communication according to claim 7, characterized in that Combining the observation vector, the joint estimation function of the terminal pose and the time-varying channel is expressed as: Where β = [r, γ] are the unknown position and direction parameters of the receiver to be solved, h is the channel small-scale fading coefficient, and G(β) is a non-linear function of β and the variable h to be estimated, which is non-convex with respect to β and h.

9. The method for jointly estimating the terminal pose and time-varying channel based on 6G visible light communication according to claim 8, wherein After considering the improved line-of-sight channel gain model, when solving the joint estimation function of the terminal pose and the time-varying channel, the channel estimation and the terminal pose estimation are alternately iterated until both the channel estimation and the pose estimation converge.

10. The method for jointly estimating the terminal pose and time-varying channel based on 6G visible light communication according to claim 9, wherein The specific process of solving the joint estimation function of the terminal pose and the time-varying channel is: S51. Set the initial pose as At t = 0, channel estimation is performed, and the estimation expression is: Obtain the estimation of the channel in the current pose, where represents the pseudo-inverse operation, represents the current pose, represents the current channel; S53. By and obtain the pose estimate for the next iteration at the current pose and channel; The objective function is a non-convex function with respect to the position and orientation of the receiver. Perform the first-order Taylor expansion of \(G(\beta)\mathbf{h}\) at the current pose and channel as follows: Among them, is the gradient at the current pose, S54. Repeat S52 and S53 until the estimation of the terminal pose and the time-varying channel converges.

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