A method for clock synchronization of a mobile communication network against Doppler effect

Abstract

The application provides a mobile communication network clock synchronization method for Doppler effect, and relates to the technical field of mobile target synchronization positioning. In the current combined synchronization positioning method, the Doppler effect influence on the target when receiving signals cannot be eliminated, and the real-time mobile target synchronization positioning precision is poor. The mobile target synchronization positioning model containing an unknown mobile target node and an anchor node is established, the anchor node is provided with a transmitter, the unknown mobile target node is provided with a receiver, then the synchronization positioning is performed by using the transmission and reception signal waveforms of the transmitter and the receiver, and the information transmitted between the transmitter and the receiver is processed by a signal transmission model. Further, the unknown mobile target node is combined with synchronization, positioning, lateral, speed measurement and transmission channel gain estimation, the influence of the Doppler effect on the clock synchronization and position estimation of the mobile target is eliminated, and the mobile target synchronization positioning precision is effectively improved.

Description

Technical Field

[0001] This invention relates to the technical field of mobile target synchronization and positioning, and in particular to a clock synchronization method for mobile communication networks that addresses the Doppler effect. Background Technology

[0002] Synchronization and positioning are key components of wireless sensor networks. Synchronization technology research is conducted from the perspective of protocol design, while positioning technology research is conducted from the perspective of signal processing. In traditional wireless sensor network research, synchronization and positioning technologies have been studied separately, neglecting the relationship between them. In fact, synchronization and positioning are closely related.

[0003] Currently, with the development of science and technology, synchronous positioning technology has been widely applied. Most joint synchronous positioning methods utilize known transmit and receive timestamps for target localization. For example, the directional frame timing synchronization proposed by Dalin Zhu et al. in broadband millimeter-wave systems, when using transmit and receive timestamps for vehicle synchronous positioning, suffers from clock drift even after clock calibration due to the influence of the minimum time frame interval. Moreover, in practical applications, the transmit and receive timestamps are unknown quantities, estimated using the waveforms of the transmitted and received signals. This estimation method itself contains errors and cannot accurately achieve target synchronous positioning. Existing technology discloses a joint synchronous positioning method that calculates the target node's velocity and direction using estimates of the target node's joint synchronous positioning at different times. On the one hand, the calculated speed is the average speed rather than the real-time speed, and the calculated direction of motion is not the real-time displacement direction. That is, when facing non-uniform linear motion, the calculation accuracy of the target node's speed and direction is poor, resulting in poor synchronization positioning accuracy. On the other hand, the target node in real-time motion is subject to the Doppler effect when receiving signals. The Doppler effect refers to the fact that the received frequency of the wave increases when the wave source moves towards the observer and decreases when the wave source moves away from the observer. The movement of the target node is prone to causing carrier frequency offset, thereby affecting the clock synchronization and position estimation of the moving target. Summary of the Invention

[0004] To address the problem of poor real-time moving target synchronization accuracy caused by the inability to eliminate the Doppler effect on the target when receiving signals in current joint synchronization positioning methods, this invention proposes a mobile communication network clock synchronization method to address the Doppler effect. This method eliminates the impact of the Doppler effect on the clock synchronization and position estimation of moving targets, effectively improving the synchronization positioning accuracy of moving targets.

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

[0006] A method for clock synchronization in mobile communication networks to address the Doppler effect includes the following steps:

[0007] S1. Establish a synchronous positioning model for a moving target. The synchronous positioning model for a moving target includes an unknown moving target node to be positioned and multiple anchor nodes for transmitting signals. Each anchor node is equipped with a transmitter, and the unknown moving target node is equipped with a receiver. Both the transmitter and the receiver are equipped with antennas.

[0008] S2. The unknown moving target node sends a location request to one of the anchor nodes;

[0009] S3. Upon receiving the positioning request, the anchor node uses a transmitter to send a first frequency domain signal and data parameters containing the anchor node's position, the transmitter's antenna direction, and the anchor node's local clock parameters to the unknown moving target node.

[0010] S4. Construct a signal transmission model. The signal transmission model uses the anchor node's position, the transmitter's antenna direction, and the anchor node's local clock parameters in the first frequency domain signal and data parameters to convert the first frequency domain signal transmitted to the unknown moving target node into a second frequency domain signal.

[0011] S5. The position of the receiver of the unknown moving target node, the antenna direction of the receiver, the speed of the unknown moving target node, the direction of movement of the unknown moving target node, the local clock parameters of the unknown target node, and the transmission channel gain between the transmitter and the receiver are recorded as the parameters to be estimated. Calculate the initial estimated value and the initial error value of the parameters to be estimated.

[0012] S6. Use the first frequency domain signal and the second frequency domain signal to update the initial estimated value and the initial error value of the parameter to be estimated in turn until the update process converges, and obtain the joint estimated value of the parameter to be estimated.

[0013] S7. Set the joint estimate of the parameters to be estimated as the synchronous positioning result of the unknown moving target node.

[0014] In this technical solution, a synchronous positioning model for a moving target, including an unknown moving target node and an anchor node, is first established. The anchor node is equipped with a transmitter, and the unknown moving target node is equipped with a receiver. Synchronous positioning is achieved by using the transmitted and received signal waveforms of the transmitter and receiver, avoiding the use of transmit and receive timestamps for synchronous positioning and ensuring the accuracy of synchronous positioning. After receiving a positioning request from the unknown moving target node, the anchor node sends information for synchronous positioning. This information is processed by a signal transmission model and then transmitted to the unknown moving target node to prevent carrier frequency offset caused by the Doppler effect. Furthermore, the position of the receiver of the unknown moving target node, the antenna direction of the receiver, the movement speed of the unknown moving target node, the movement direction of the unknown moving target node, the local clock parameters of the unknown target node, and the transmission channel gain between the transmitter and receiver are set as parameters to be estimated. The values ​​of the parameters to be estimated are then jointly estimated to obtain the joint estimated values ​​of the parameters. This achieves joint synchronization, positioning, lateral movement, velocity measurement, and transmission channel gain estimation for the unknown moving target node, eliminating the influence of the Doppler effect on the clock synchronization and position estimation of the moving target, and effectively improving the synchronous positioning accuracy of the moving target.

[0015] Preferably, the number of anchor nodes is M, and the number of antennas of the transmitter is N. BS Each antenna is oriented according to its direction. The antennas of the receiver are arranged in an array of N. MS Root, each antenna is arranged according to The antenna spacing of the receiver and the transmitter are both d. a .

[0016] Preferably, in step S3, let the first frequency domain signal be x[m,n], and the specific expression of the first frequency domain signal x[m,n] is:

[0017]

[0018] Among them, M t The number of samples is represented by m, where m represents the signal transmitted by the m-th transmitter (m = 1, ..., M) and n represents the n-th subcarrier (n = 1, ..., N).

[0019] The specific expression for the anchor node position is:

[0020]

[0021] Where, q m Indicates the position of the m-th anchor node;

[0022] The anchor node local clock parameters include the bias α of the m-th transmitter clock. BS and the bias θ of the m-th transmitter clock BSThe local time t of the m-th transmitter clock BS The calculation expression is:

[0023] t BS =α BS t+θ BS

[0024] Where t is the standard time.

[0025] Preferably, in the process of converting the first frequency domain signal transmitted to the unknown moving target node into a second frequency domain signal, the position of the receiver of the unknown moving target node is set using a uniformly random generation method. The antenna direction of the receiver is b. MS The bias of the receiver clock of the unknown moving target node is α. MS The bias θ of the receiver clock of the unknown moving target node MS Given the transmission channel gain between the transmitter and receiver as h, and the local time t of the receiver at the unknown mobile target node. MS The calculation expression is:

[0026] t MS =α MS t+θ MS

[0027] Where, α MS and θ MS The local clock parameters of the nodes constituting the unknown moving target; the transmitter of the m-th anchor node at a specific local time R. m Sending information, the receiver of the unknown mobile target node at a specific local time T m Upon receiving this information, the transmission speed is c. Let the second frequency domain signal be y[m,n]. The specific expression for the second frequency domain signal y[m,n] is:

[0028]

[0029] When the transmitter sends a signal to the receiver, the observation error ε[m,n] of the signal is considered as follows:

[0030]

[0031] Where, ε l [m,n] are independent and identically distributed according to a Gaussian distribution with zero mean and N0, l=1,...,N M .

[0032] Preferably, in step S4, the specific expression of the signal transmission model y is:

[0033] y=G(ζ)h+ε

[0034] in

[0035]

[0036]

[0037]

[0038]

[0039]

[0040] Where v represents the velocity of the unknown moving target node, and u represents the direction of movement of the unknown moving target node. This represents a vector consisting of y[m,n] arranged in ascending order of n. This represents the vector ε[m,n] arranged in order of magnitude of n. Let g[m,n] be a vector formed by arranging n in ascending order. The expression for calculating g[m,n] is:

[0041] g[m,n]=H[m,n]F[m,n]x[m,n]

[0042] in, Let H[m,n] represent the beamforming matrix, satisfying the following relationship:

[0043]

[0044] Indicates a R The conjugate transpose of [m,n], a R The specific expression for [m,n] is:

[0045]

[0046] a T The specific expression for [m,n] is:

[0047]

[0048] Among them, a R [i,m,n] represents the transmit angle gain, where i represents the signal received by the i-th antenna of the receiver, i = 1,…,N M a T [k,m,n] represents the angle of arrival gain, k represents the signal transmitted by the k-th antenna of the transmitter, k=1,…,N B a S [m,n] represents the loss caused by transmission distance, a D[m,n] represents the gain caused by the Doppler frequency shift.

[0049] Preferably, in step S5, the position p of the receiver of the unknown moving target node and the antenna direction b of the receiver are set. MS The unknown moving target node's velocity v, the unknown moving target node's direction u, and the unknown target node's local clock parameter α. MS θ MS The transmission channel gain h between the transmitter and receiver is taken as the parameter to be estimated, and the calculation is performed with p and b. MS v, u, α MS θ MS The specific process for obtaining the initial estimates and initial error values ​​of the joint estimation parameters ζ and transmission channel gain h for the components is as follows:

[0050] S51. Obtain the initial value of the parameter ζ to be jointly estimated as ζ. (0) The initial value of the transmission channel gain h is h (0) ;

[0051] in,

[0052] h (0) =[h1 (0) , ..., h M (0) ] T ;

[0053] S52. Will v (0) u (0) α MS (0) θ MS (0) By performing joint estimation, we obtain the initial estimate G(ζ) of the parameter to be estimated. (0) );

[0054] S53. Based on G(ζ) (0) ) and h (0) Solve for the initial error value r of the parameter to be estimated. (0) r (0) The specific solution expression is as follows:

[0055] r (0) =yG(ζ (0) )h (0) .

[0056] Preferably, in step S6, the specific steps of the update are as follows:

[0057] S61. Setting r (-1) For N MAn M*N dimensional zero vector, where t is 0, the cutoff threshold is δ, and the number of cutoffs is N. T ;

[0058] S62. Determine if ||r (t) -r (t-1) Is ||2 less than δ, or is t greater than or equal to N? T If so, then let the estimated values ​​of ζ and h be ζ ​​and h, respectively. (t) and h (t) Output joint estimate Otherwise, let t+1, and execute step S63;

[0059] S63. Update the value of the parameter ζ to be estimated using gradient descent to obtain ζ. (t) Execute step S64;

[0060] S64. Calculate the estimated value G(ζ) after the t-th iteration update. (t) The estimated value of h is updated using linear regression, and h is updated to h0. (t) ;

[0061] S65. G(ζ) obtained based on S64 (t) ), calculate the error value r after the t-th iteration. (t) =yG(ζ (t) )h (t) Return to step S62.

[0062] Preferably, in step S62, the joint estimate is... The calculation expression is:

[0063]

[0064] Preferably, during the gradient descent process, the components p,b of ζ MS ,v,u,α MS ,θ MS The update expressions are as follows:

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071] Where, p (t), v (t) , α MS (t) ,θ MS (t) Let p and b represent respectively. MS ,v,u,α MS ,θ MS The value after the t-th iteration update, where β represents the step size of gradient descent. p (t-1) gradient, b MS (t-1) gradient, Indicates v (t-1) gradient, Indicate u (t-1) gradient, Represents α MS (t-1) gradient, Represents θ MS (t-1) The gradient;

[0072] For b MS Updated The value is normalized. The normalization calculation expression is:

[0073]

[0074] Updated for u The value is normalized. The normalization calculation expression is:

[0075]

[0076] Preferably, in step S64, the calculation expression for updating the parameter h to be estimated using linear regression is:

[0077] h (t) =(G(ζ) (t) ) T G (ζ (t) )) -1 G(ζ (t) ) T y.

[0078] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0079] This invention proposes a clock synchronization method for mobile communication networks to address the Doppler effect. First, a mobile target synchronization and positioning model is established, including an unknown mobile target node and an anchor node. The anchor node is equipped with a transmitter, and the unknown mobile target node is equipped with a receiver. Synchronization and positioning are performed using the transmitted and received signal waveforms of the transmitter and receiver, avoiding the use of transmit and receive timestamps and ensuring the accuracy of synchronization and positioning. After receiving a positioning request from the unknown mobile target node, the anchor node sends information for synchronization and positioning. This information is processed by a signal transmission model before being transmitted to the unknown mobile target node, preventing carrier frequency offset caused by the Doppler effect. Furthermore, the location of the receiver of the unknown mobile target node, the antenna direction of the receiver, the movement speed of the unknown mobile target node, the movement direction of the unknown mobile target node, the local clock parameters of the unknown target node, and the transmission channel gain between the transmitter and receiver are set as parameters to be estimated. The values ​​of these parameters are then jointly estimated to obtain joint estimated values. This achieves joint synchronization, positioning, lateral movement, speed measurement, and transmission channel gain estimation for the unknown mobile target node, eliminating the impact of the Doppler effect on the clock synchronization and position estimation of the mobile target, and effectively improving the accuracy of mobile target synchronization and positioning. Attached Figure Description

[0080] Figure 1 This is a flowchart illustrating a mobile communication network clock synchronization method for dealing with the Doppler effect proposed in an embodiment of the present invention.

[0081] Figure 2 A structural diagram representing a moving target synchronous localization model;

[0082] Figure 3 A schematic diagram showing the antenna receiving signals at the receiver;

[0083] Figure 4 A CDF plot showing the position estimation error at 20 dB noise;

[0084] Figure 5 CDF plot representing the azimuth estimation error at 20dB noise;

[0085] Figure 6 A CDF plot showing the motion velocity error at 20dB noise;

[0086] Figure 7 The CDF plot representing the motion direction error at 20dB noise;

[0087] Figure 8 A CDF plot representing the clock offset estimation error of an unknown moving target node at 20dB noise;

[0088] Figure 9The CDF plot representing the clock skewness estimation error of an unknown moving target node at 20dB noise;

[0089] Figure 10 The CDF plot representing the root mean square error of the transmission channel gain estimation at 20dB noise;

[0090] Figure 11 A comparison graph showing the squared error of the position estimation method of the present invention with the position estimation error of the method that does not consider the Doppler effect;

[0091] Figure 12 This represents a traditional static model for synchronous positioning of a target. Detailed Implementation

[0092] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent.

[0093] To better illustrate this embodiment, some parts of the accompanying drawings may be omitted, enlarged, or reduced, and do not represent actual dimensions. The descriptions of directions such as "up" and "down" are not intended to limit this patent.

[0094] It is understandable to those skilled in the art that some well-known details may be omitted from the accompanying drawings;

[0095] The positional relationships depicted in the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent.

[0096] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0097] Example 1

[0098] like Figure 1 As shown, this embodiment proposes a clock synchronization method for mobile communication networks to address the Doppler effect, including the following steps:

[0099] S1. Establish a synchronous positioning model for a moving target. The synchronous positioning model for a moving target includes an unknown moving target node to be positioned and multiple anchor nodes for transmitting signals. Each anchor node is equipped with a transmitter, and the unknown moving target node is equipped with a receiver. Both the transmitter and the receiver are equipped with antennas.

[0100] In step S1, see Figure 1 and Figure 2 The number of anchor nodes is M, the number of nodes is M, and the number of transmitter antennas is N. BS Each antenna is oriented according to its direction. The antennas of the receiver are arranged in an array of N. MS Root, each antenna is arranged according to The antenna spacing of the receiver and the transmitter are both d.a .

[0101] S2. The unknown moving target node sends a location request to one of the anchor nodes;

[0102] S3. Upon receiving the positioning request, the anchor node uses a transmitter to send a first frequency domain signal and data parameters containing the anchor node's position, the transmitter's antenna direction, and the anchor node's local clock parameters to the unknown moving target node.

[0103] In step S3, see Figure 1 and Figure 3 In step S3, let the first frequency domain signal be x[m,n], and the specific expression of the first frequency domain signal x[m,n] is as follows:

[0104]

[0105] Among them, M t The number of samples is represented by m, where m represents the signal transmitted by the m-th transmitter (m = 1, ..., M) and n represents the n-th subcarrier (n = 1, ..., N).

[0106] The specific expression for the anchor node position is:

[0107]

[0108] Where, q m Indicates the position of the m-th anchor node;

[0109] The anchor node local clock parameters include the bias α of the m-th transmitter clock. BS and the bias θ of the m-th transmitter clock BS The local time t of the m-th transmitter clock BS The calculation expression is:

[0110] t BS =α BS t+θ BS

[0111] Where t is the standard time.

[0112] Let the transmitter position be Q, and the specific expression for Q is:

[0113]

[0114] The transmitter's clock parameters are as follows:

[0115] S4. Construct a signal transmission model. The signal transmission model uses the anchor node's position, the transmitter's antenna direction, and the anchor node's local clock parameters in the first frequency domain signal and data parameters to convert the first frequency domain signal transmitted to the unknown moving target node into a second frequency domain signal.

[0116] S5. The position of the receiver of the unknown moving target node, the antenna direction of the receiver, the speed of the unknown moving target node, the direction of movement of the unknown moving target node, the local clock parameters of the unknown target node, and the transmission channel gain between the transmitter and the receiver are recorded as the parameters to be estimated. Calculate the initial estimated value and the initial error value of the parameters to be estimated.

[0117] In step S5, the possibility of deviations in the local clock parameters of the unknown target node and the inaccuracy of the given prior transmission channel gain are considered. These two parameters and other parameters to be estimated are jointly estimated to reduce the deviations caused by the inaccuracy of the local clock parameters of the unknown target node and the prior channel gain, thereby improving the positioning accuracy.

[0118] S6. Use the first frequency domain signal and the second frequency domain signal to update the initial estimated value and the initial error value of the parameter to be estimated in turn until the update process converges, and obtain the joint estimated value of the parameter to be estimated.

[0119] S7. Set the joint estimate of the parameters to be estimated as the synchronous positioning result of the unknown moving target node.

[0120] In the embodiments, see Figure 2First, a synchronous positioning model for a moving target is established, including an unknown moving target node and an anchor node. The anchor node is equipped with a transmitter, and the unknown moving target node is equipped with a receiver. Synchronous positioning is achieved using the transmitted and received signal waveforms of the transmitter and receiver, avoiding the use of transmission and reception timestamps and ensuring the accuracy of synchronous positioning. After receiving a positioning request from the unknown moving target node, the anchor node sends information for synchronous positioning. This information is processed by a signal transmission model before being transmitted to the unknown moving target node. This prevents carrier frequency offset caused by the Doppler effect. Since the received waveform is affected by the angle of arrival, departure angle, the antenna spacing being much smaller than the distance between the transmitter and receiver, and channel gain, the transmitted signal can be considered to arrive at each antenna in parallel, adjacent to each other. The transmission distance between antennas can be considered as the difference between the antenna spacing and the cosine of the included angle. Therefore, the included angle can be estimated for direction finding. Furthermore, the position of the receiver of the unknown moving target node, the antenna direction of the receiver, the speed of the unknown moving target node, the direction of movement of the unknown moving target node, the local clock parameters of the unknown target node, and the transmission channel gain between the transmitter and the receiver are set as parameters to be estimated. The values ​​of the parameters to be estimated are then jointly estimated to obtain the joint estimated values ​​of the parameters to be estimated. This realizes the joint synchronization, positioning, lateral direction finding, speed measurement, and transmission channel gain estimation of the unknown moving target node, eliminates the influence of the Doppler effect on the clock synchronization and position estimation of the moving target, and effectively improves the synchronization and positioning accuracy of the moving target.

[0121] Example 2

[0122] See Figure 1 and Figure 3 In step S2, during the process of converting the first frequency domain signal transmitted to the unknown mobile target node into a second frequency domain signal, the position of the receiver of the unknown mobile target node is set to a uniformly random generation method. The antenna direction of the receiver is b. MS The bias of the receiver clock of the unknown moving target node is α. MS The bias θ of the receiver clock of the unknown moving target node MS Given the transmission channel gain between the transmitter and receiver as h, and the local time t of the receiver at the unknown mobile target node. MS The calculation expression is:

[0123] t MS =α MS t+θ MS

[0124] Where, α MS and θ MSThe local clock parameters of the nodes constituting the unknown moving target; the transmitter of the m-th anchor node at a specific local time R. m Sending information, the receiver of the unknown mobile target node at a specific local time T m Upon receiving this information, the transmission speed is c. Let the second frequency domain signal be y[m,n]. The specific expression for the second frequency domain signal y[m,n] is:

[0125]

[0126] When the transmitter sends a signal to the receiver, the observation error ε[m,n] of the signal is considered as follows:

[0127]

[0128] Where, ε l [m,n] are independent and identically distributed according to a Gaussian distribution with zero mean and N0, l=1,...,N M .

[0129] In step S4, the specific expression of the signal transmission model y is:

[0130] y=G(ζ)h+ε

[0131] in

[0132]

[0133]

[0134]

[0135]

[0136]

[0137] Where v represents the velocity of the unknown moving target node, and u represents the direction of movement of the unknown moving target node. This represents a vector consisting of y[m,n] arranged in ascending order of n. This represents the vector ε[m,n] arranged in order of magnitude of n. Let g[m,n] be a vector formed by arranging n in ascending order. The expression for calculating g[m,n] is:

[0138] g[m,n]=H[m,n]T[m,n]x[m,n]

[0139] in, Let H[m,n] represent the beamforming matrix, satisfying the following relationship:

[0140]

[0141] Indicates a R The conjugate transpose of [m,n], a R The specific expression for [m,n] is:

[0142]

[0143] a T The specific expression for [m,n] is:

[0144]

[0145] Among them, a R [i,m,n] represents the transmit angle gain, where i represents the signal received by the i-th antenna of the receiver, i = 1,…,N M a T [k,m,n] represents the angle of arrival gain, k represents the signal transmitted by the k-th antenna of the transmitter, k=1,…,N B a S [m,n] represents the loss caused by transmission distance, a D [m,n] represents the gain caused by the Doppler frequency shift, and the emission angle gain a. R The expression for calculating [i,m,n] is:

[0146]

[0147] in, The transmission angle is the direction of the line-of-sight path from the m-th anchor node to the target node and the direction the transmitter of the m-th anchor node is facing. BS The included angle, λ n It is the signal wavelength of the nth subcarrier. The calculation expression is:

[0148]

[0149] Where, q m Indicates the position of the m-th anchor node;

[0150] λ n The calculation expression is:

[0151]

[0152] Where c is the signal transmission speed. f is the sampling period. c B is the carrier frequency, and B is the bandwidth.

[0153] Angle of arrival gain a T [k,m,n]

[0154]

[0155] Where, φ m This represents the angle of arrival, which is the direction of the line-of-sight path from the m-th anchor node to the target node and the direction the target node's receiver is facing (b). MS The included angle;

[0156] cosφ m The calculation expression is:

[0157]

[0158] a S The expression for calculating [m,n] is:

[0159]

[0160] Where, τ m Transmission time;

[0161] a D The expression for calculating [m,n] is:

[0162]

[0163] Where, ψ m This indicates the angle between the line connecting the receiver and the wave source and the direction of velocity.

[0164] cosψ m The calculation expression is:

[0165]

[0166] In step S5, let the position p of the receiver of the unknown moving target node and the antenna direction b of the receiver be set. MS The unknown moving target node's velocity v, the unknown moving target node's direction u, and the unknown target node's local clock parameter α. MS θ MS The transmission channel gain h between the transmitter and receiver is taken as the parameter to be estimated, and the calculation is performed with p and b. MS v, u, α MS θ MS The specific process for obtaining the initial estimates and initial error values ​​of the joint estimation parameters ζ and transmission channel gain h for the components is as follows:

[0167] S51. Obtain the initial value of the parameter ζ to be jointly estimated as ζ. (0) The initial value of the transmission channel gain h is h (0) ;

[0168] in,

[0169] h (0) =[h1 (0) , ..., h M (0) ] T ;

[0170] S52. Will v (0) u (0) α MS (0) θ MS (0) By performing joint estimation, we obtain the initial estimate G(ζ) of the parameter to be estimated. (0) );

[0171] S53. Based on G(ζ) (0) ) and h (0) Solve for the initial error value r of the parameter to be estimated. (0) r (0) The specific solution expression is as follows:

[0172] r (0) =yG(ζ (0) )h (0) .

[0173] Example 3

[0174] See Figure 2 and Figure 3 Consider a 100m × 100m location. Establish a synchronous positioning model for a moving target that addresses the Doppler effect within this location. In the synchronous positioning model for the moving target, refer to Table 1, and set the carrier frequency f. c =60GHz, bandwidth B=100MHz, signal transmission speed c=3×10 8 m / s, number of transmitter antennas N B =5, Number of receiver antennas N B =5, the number of anchor nodes M=5, and the direction of the anchor nodes, i.e. the direction of the transmitter antenna arrangement, is b. m =(0,1) T m = 1, ..., M, where d is the distance between two adjacent antennas of the transmitter and receiver. a =0.005m, x[m,n] represents the randomly generated transmitted signal, the number of subcarriers N=5, and x is processed by beamforming to obtain w[m,n]=F[m,n]x[m,n]; transmitter clock parameter α q =1 M θ q =0 MThis means that the transmitter clock time is set to standard time in the simulation experiment; considering that the signal-to-noise ratio of the frequency domain signal received by the receiver is 20dB, noise is randomly generated, and the actual and initial values ​​of the transmitter position Q and the target node receiver position p are uniformly and randomly generated in a 100m×100m area, and the direction b is uniformly and randomly generated on the unit circle. p The true and initial values ​​of the motion velocity parameter v are uniformly and randomly generated in the range [0,1]. The true and initial values ​​of the orientation parameter u are uniformly and randomly generated on the unit circle. The clock parameter α is uniformly and randomly generated in the range [0,1]. p The actual and initial values ​​are used to uniformly and randomly generate the clock parameter θ in the range [0.95, 1.05]. p The actual and initial values, and the component h of the transmission channel gain h between the transmitter and the target receiver. m The actual and initial values ​​are uniformly and randomly generated in the range [0.8, 0.95]; the specific expression for the transmitter position Q is:

[0175]

[0176] Table 1

[0177]

[0178]

[0179] See Figure 1 And as shown in Table 1, the specific steps for updating in step S6 are as follows:

[0180] S61. Setting r (-1) For N M An M*N dimensional zero vector, where t is 0, the cutoff threshold is δ, and the number of cutoffs is N. T ;

[0181] S62. Determine if ||r (t) -r (t-1) Is ||2 less than δ, or is t greater than or equal to N? T If so, then let the estimated values ​​of ζ and h be ζ ​​and h, respectively. (t) and h (t) Output joint estimate Otherwise, let t+1, and execute step S63;

[0182] In step S62,

[0183] S63. Update the value of the parameter ζ to be estimated using gradient descent to obtain ζ. (t) Execute step S64;

[0184] In step S63, during gradient descent, the step size is set to β = 5. For the t-th iteration, the error of the t-th iteration is calculated:

[0185]

[0186]

[0187] in, express The conjugate transpose of . The specific expression is:

[0188]

[0189] The emission angle gain in the t-th iteration:

[0190]

[0191] Gain of arrival angle in the t-th iteration:

[0192]

[0193] The gain caused by the corrected transmission distance in the t-th iteration:

[0194]

[0195] The gain caused by the Doppler effect in the t-th iteration:

[0196]

[0197] The cosine value of the emission angle in the t-th iteration:

[0198]

[0199] The cosine value of the angle reached in the t-th iteration:

[0200]

[0201] The cosine of the angle between the direction of motion and the direction of signal transmission in the t-th iteration:

[0202]

[0203] Calculate S (t-1) Regarding p (t-1) ,b MS (t-1) ,v (t-1) ,u (t-1) ,α MS (t-1) ,θ MS (t-1) gradient For each component p, b of ζ MS ,v,u,α MS ,θ MS The update is performed, and the update expressions are as follows:

[0204]

[0205]

[0206]

[0207]

[0208]

[0209]

[0210] Where, p (t) , v (t) , α MS (t) ,θ MS (t) Let p and b represent respectively. MS ,v,u,α MS ,θ MS The value after the t-th iteration update.

[0211] The values ​​of each component are as follows:

[0212]

[0213]

[0214]

[0215]

[0216]

[0217]

[0218] in, The calculation expression is:

[0219]

[0220] The calculation expression is:

[0221]

[0222] The calculation expression is:

[0223]

[0224] The calculation expression is:

[0225]

[0226] The calculation expression is:

[0227]

[0228] The calculation expression is:

[0229]

[0230] The calculation expression is:

[0231]

[0232] The calculation expression is:

[0233]

[0234] The calculation expression is:

[0235]

[0236] The calculation expression is:

[0237]

[0238] The calculation expression is:

[0239]

[0240] The calculation expression is:

[0241]

[0242] The calculation expression is:

[0243]

[0244] For b MS Updated The value is normalized. The normalization calculation expression is:

[0245]

[0246] Updated for u The value is normalized. The normalization calculation expression is:

[0247]

[0248] S64. Calculate the estimated value G(ζ) after the t-th iteration update. (t) The estimated value of h is updated using linear regression, and h is updated to h0. (t) ;

[0249] In step S64, the calculation expression for updating the estimated parameter h using linear regression is as follows:

[0250]

[0251] S65. G(ζ) obtained based on S64 (t) ), calculate the error value r after the t-th iteration. (t) =yh(ζ (t) )h (t) Return to step S62.

[0252] This embodiment conducted 3000 experiments at a signal-to-noise ratio of 20dB, obtaining the cumulative distribution function graphs of the root mean square errors for the unknown moving target node's position estimation, orientation estimation, velocity estimation, direction of motion, clock offset estimation, clock skew estimation, and transmission channel gain estimation. (See attached graph). Figure 4 The position estimation error is generally below 0.2m; see [link / reference]. Figure 5 The azimuth estimation error is generally below 0.06 rad; see [link / reference]. Figure 6 The velocity estimation error is generally below 0.2 m / s; see [link / reference]. Figure 7 The error in estimating the direction of motion is generally below 0.05m; see [link / reference]. Figure 8 The clock parameter offset estimation error is generally below 0.5 ns; see [link / reference]. Figure 9 The clock parameter skewness estimation error is generally below 0.005; see [link / reference]. Figure 10 The root mean square error of the transmission channel gain estimation is generally below 0.05.

[0253] See Figure 11This embodiment also compares the squared error of the position estimation method with the error of the position estimation method that does not consider the Doppler effect. The horizontal axis represents the number of iterations, and the vertical axis represents the error of position estimation. Figure 11 It can be seen that the positioning accuracy considering the Doppler effect is significantly better than that without it. This indicates that if the Doppler effect is not compensated for, and the traditional synchronous positioning model is used to jointly estimate the moving target node, and the carrier frequency offset caused by the Doppler effect is considered as part of the sampling frequency offset caused by clock inaccuracy, the sampling frequency offset of the unknown moving target node will be larger than the true value, leading to an increase in the error of the joint estimation. Therefore, this embodiment eliminates the impact of the Doppler effect on the clock synchronization and position estimation of the moving target, effectively improving the synchronous positioning accuracy of the moving target. Since the signal transmission speed from the anchor node to the unknown target node is extremely fast, generally the signal transmission speed is the speed of light c = 3 × 10⁻⁶. 8 The signal transmission speed is m / s, which is much greater than the movement speed of the unknown target node. Therefore, the change in the position of the unknown target node between the time the anchor node transmits the signal and the time the unknown target node receives the signal can be ignored. It can be assumed that the unknown target node is stationary during this time. See [link / reference]. Figure 12 Therefore, traditional methods use static models to synchronously locate and estimate the position of unknown moving target nodes and their local clock parameters. By estimating the position of the target node multiple times, the speed and direction of the target node's movement can be estimated. However, due to the Doppler effect of the moving target node, there will be a carrier frequency offset in the received signal. If a static model is still used to estimate the target node of the moving model, the carrier frequency offset caused by the Doppler effect will be regarded as a sampling frequency offset caused by clock inaccuracy, which will increase the sampling frequency offset caused by clock inaccuracy, thereby increasing the error of positioning and clock synchronization estimation. Therefore, this embodiment uses a dynamic model to synchronously locate the moving target, which can effectively make up for the shortcomings of the traditional static model.

[0254] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A clock synchronization method for mobile communication networks to address the Doppler effect, characterized in that, Includes the following steps: S1. Establish a synchronous positioning model for a moving target. The synchronous positioning model for a moving target includes an unknown moving target node to be positioned and multiple anchor nodes for transmitting signals. Each anchor node is equipped with a transmitter, and the unknown moving target node is equipped with a receiver. Both the transmitter and the receiver are equipped with antennas. S2. The unknown moving target node sends a location request to one of the anchor nodes; S3. Upon receiving the positioning request, the anchor node uses a transmitter to send a first frequency domain signal and data parameters containing the anchor node's position, the transmitter's antenna direction, and the anchor node's local clock parameters to the unknown moving target node. S4. Construct a signal transmission model. The signal transmission model uses the anchor node's position, the transmitter's antenna direction, and the anchor node's local clock parameters in the first frequency domain signal and data parameters to convert the first frequency domain signal transmitted to the unknown moving target node into a second frequency domain signal. S5. The position of the receiver of the unknown moving target node, the antenna direction of the receiver, the speed of the unknown moving target node, the direction of movement of the unknown moving target node, the local clock parameters of the unknown target node, and the transmission channel gain between the transmitter and the receiver are recorded as the parameters to be estimated. Calculate the initial estimated value and the initial error value of the parameters to be estimated. S6. Use the first frequency domain signal and the second frequency domain signal to update the initial estimated value and the initial error value of the parameter to be estimated in turn until the update process converges, and obtain the joint estimated value of the parameter to be estimated. S7. Set the joint estimate of the parameters to be estimated as the synchronous positioning result of the unknown moving target node; In the process of converting the first frequency domain signal transmitted to the unknown moving target node into a second frequency domain signal, the position of the receiver of the unknown moving target node is set to be uniformly randomly generated. The antenna direction of the receiver is The bias of the receiver clock of the unknown moving target node is , bias of receiver clock for unknown moving target node and the transmission channel gain between the transmitter and receiver is The local time of the receiver of the unknown mobile target node. The calculation expression is: in, and The local clock parameters that make up the unknown moving target node; the first The transmitter of each anchor node at a specific local time Sending information to the receiver of an unknown mobile target node at a specific local time. The information was received, and the transmission speed was [missing information]. Let the second frequency domain signal be Second frequency domain signal The specific expression is: When the transmitter sends a signal to the receiver, the observation error of the signal is taken into account. for: in, Independent and identically distributed with zero mean and variance Gaussian distribution, ; In step S4, the signal transmission model The specific expression is: in in, This represents the speed of movement of the unknown moving target node. Indicates the direction of movement of the unknown moving target node. express according to A vector formed by stringing together elements in ascending order. express according to A vector formed by stringing together elements in ascending order. express according to A vector formed by stringing together elements in ascending order. The calculation expression is: in, Represents the beamforming matrix. The following relationship must be satisfied: express The conjugate transpose of . The specific expression is: The specific expression is: in, Indicates the emission angle gain. Indicates the receiver number The signal received by each antenna , Indicates the angle of arrival gain. Indicates the transmitter number The signal transmitted by the antenna, , This indicates the loss caused by transmission distance. This indicates the gain caused by the Doppler frequency shift. The calculation expression is: in, This represents the angle between the line connecting the receiver and the wave source and the direction of velocity. The calculation expression is: in, Indicates the location of the receiver for the unknown moving target node. Indicates the direction of movement of the unknown moving target node. Indicates the location of the anchor node.

2. The mobile communication network clock synchronization method for addressing the Doppler effect according to claim 1, characterized in that, The number of anchor nodes is The number of antennas for the transmitter is [number missing]. Each antenna is oriented according to its direction. The antennas of the receiver are arranged in a specific pattern. Root, each antenna is arranged according to The antenna spacing of the receiver and the transmitter are arranged such that... .

3. The mobile communication network clock synchronization method for addressing the Doppler effect according to claim 2, characterized in that, In step S3, let the first frequency domain signal be... First frequency domain signal The specific expression is: in, Indicates the number of samples. Indicates the first The signal sent by the transmitter , Indicates the first Subcarriers, ; The specific expression for the anchor node position is: ， in, Indicates the first m Anchor node locations; Anchor node local clock parameters include the first Bias of the transmitter clock and the bias of each transmitter clock , No. Local time of each transmitter clock The calculation expression is: Where t is the standard time.

4. The mobile communication network clock synchronization method for addressing the Doppler effect according to claim 1, characterized in that, In step S5, the location of the receiver of the unknown moving target node is set. Antenna direction of the receiver The movement speed of the unknown moving target node The direction of movement of the unknown moving target node Unknown target node local clock parameters 、 and the transmission channel gain between the transmitter and receiver For the parameters to be estimated, calculate using , , , , , The parameters to be jointly estimated for the components and transmission channel gain The specific process for determining the initial estimate and the initial error value is as follows: S51. Obtain the parameters to be jointly estimated The initial value is Transmission channel gain The initial value is ; in, ； S52. Will , , , , , Perform joint estimation to obtain initial estimates of the parameters to be estimated. ; S53. Based on and Solve for the initial error value of the parameter to be estimated. , The specific solution expression is as follows: 。 5. The mobile communication network clock synchronization method for addressing the Doppler effect according to claim 4, characterized in that, In step S6, the specific steps for updating are as follows: S61. Settings for 0-dimensional vector for The cutoff threshold is The deadline is ; S62. Judgment Is it less than , or whether t is greater than or equal to If so, then let , The estimated values ​​are respectively and Output joint estimate Otherwise, let Execute step S63; S63. Using gradient descent to estimate parameters The value is updated to obtain Execute step S64; S64. Calculation The estimated value after the t-th iteration update Using linear regression Update the estimated value, Updated to ; S65. Based on S64 Calculate the error value after the t-th iteration. Return to step S62.

6. The mobile communication network clock synchronization method for addressing the Doppler effect according to claim 5, characterized in that, In step S62, the joint estimate The calculation expression is: 。 7. The mobile communication network clock synchronization method for addressing the Doppler effect according to claim 6, characterized in that, During gradient descent, Each component The update expressions are as follows: in, They represent No. The value after the next iteration. This represents the step size of gradient descent. express gradient, express gradient, express gradient, express gradient, express gradient, express The gradient; right Updated The value is normalized. The normalization calculation expression is: ； right Updated The value is normalized. The normalization calculation expression is: 。 8. The mobile communication network clock synchronization method for addressing the Doppler effect according to claim 7, characterized in that, In step S64, linear regression is used to estimate the parameter. The updated calculation expression is: 。

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