Access point, terminal equipment and short-distance communication time synchronization method and system

Abstract

The invention relates to the technical field of communication, and discloses an access point, terminal equipment and a short-distance communication time synchronization method and system.The access point equipment and the terminal equipment each comprise a baseband signal processing unit, a radio frequency unit, an antenna, a global time counter and a clock compensation module. The time synchronization method is executed by a target terminal: receiving a beacon frame broadcasted and sent by an access point; calibration information is embedded in the beacon frame, and the calibration information comprises timestamp information and a transmitting power parameter; calculating actual propagation delay of the access point and the target terminal based on the timestamp information; calculating target propagation delay of the access point and the target terminal based on the transmitting power parameter; calculating a delay error between the actual propagation delay and the target propagation delay; and calibrating the clock skew of the target terminal based on the delay error. The time, frequency and link calibration of the access point and the target terminal can be completed by using the one-way time broadcast, and the calibration precision is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of communication technology, in particular to an access point, a terminal device, and a short-range communication time synchronization method and system. BACKGROUND

[0002] In the field of short-range communication, the crystal oscillator between the access point (AP) and the terminal device (STA) is usually designed independently, which leads to the fact that the clock systems of the two cannot maintain natural synchronization. Over time, this clock difference will gradually accumulate and form a significant absolute time deviation. This timing asynchronization phenomenon is particularly prominent in the uplink transmission of the multi-user multi-input multi-output system (UL-MUMIMO), because each terminal device cannot achieve precise timing alignment, the system must rely on the periodic sending of trigger frames (Trigger Frame) by the access point to coordinate the time synchronization of each terminal, perform frequency offset estimation, and obtain channel state information.

[0003] This synchronization mechanism solves the timing coordination problem of multi-user transmission, but frequent sending of control frames occupies valuable wireless channel resources, significantly reduces the actual transmission efficiency of the system, and becomes an important bottleneck restricting the performance improvement of the system. Especially in high-density user scenarios, the sharp increase in control overhead will further worsen the system throughput, and this design flaw is particularly prominent in current communication systems that pursue efficient spectrum utilization. SUMMARY

[0004] To solve the above technical problems, the present application discloses an access point, a terminal device, and a short-range communication time synchronization method and system, which make the target terminal transmit calibration information to the target terminal through a one-way time broadcast mechanism, calculate and dynamically adjust the local clock of the target terminal based on the propagation delay and frequency error, complete time alignment, power correction, and frequency offset estimation with the access point, and provide reliable timing protection for large-scale terminal concurrent transmission. Specifically, the technical solutions of the present application are as follows: In a first aspect, the present application discloses an access point device, comprising: a first baseband signal processing unit, a first global time counter, a first clock compensation module, and a transmitting antenna; The first baseband signal processing unit is configured to trigger the global time counter when the access point sends frame data to a target terminal; The first global time counter is configured to determine a first sending time; The first clock compensation module is configured to calculate a sending delay, and compensate the first sending time based on the sending delay to obtain a second sending time; the second sending time is the time when the frame data appears at the transmitting antenna.

[0005] In a second aspect, the application discloses a terminal device, comprising: a second baseband signal processing unit, a second global time counter, a second clock compensation module, and a receiving antenna; The receiving antenna is configured to receive frame data transmitted by the access point in the above-mentioned embodiments. The second baseband signal processing unit is configured to perform signal synchronization on the frame data. The second global time counter is configured to record a second receiving time of the terminal after synchronization with the frame data. The second clock compensation module is configured to calculate a receiving delay, and perform delay compensation on the second receiving time based on the receiving delay to obtain a first receiving time; the first receiving time is the time when the frame data appears at the receiving antenna.

[0006] In a third aspect, the application discloses a short-distance communication time synchronization method, which is performed by a target terminal and comprises the following steps: S1: receiving a beacon frame broadcasted by the access point; the beacon frame is embedded with calibration information, and the calibration information comprises timestamp information and a transmission power parameter; S2: calculating an actual propagation delay between the access point and the target terminal based on the timestamp information; S3: calculating a target propagation delay between the access point and the target terminal based on the transmission power parameter; S4: calculating a delay error between the actual propagation delay and the target propagation delay; and calibrating a clock deviation of the target terminal based on the delay error.

[0007] In some embodiments, the timestamp information is the second sending time.

[0008] On this basis, the step S2: calculating an actual propagation delay between the access point and the target terminal based on the timestamp information; specifically comprises: calculating a time difference between the second sending time and the first receiving time, i.e., obtaining the actual propagation delay.

[0009] In some embodiments, the step S3: calculating a target propagation delay between the access point and the target terminal based on the transmission power parameter; specifically comprises: calculating a spatial link attenuation in a signal transmission process based on the transmission power parameter and a receiving power parameter of the target terminal; estimating a spatial distance between the access point and the target terminal through the spatial link attenuation; and calculating the target propagation delay through the spatial distance.

[0010] In some embodiments, the calibration information further comprises preamble length information of the beacon frame.

[0011] On this basis, the short-range communication time synchronization method further comprises: calculating the receiving delay based on the preamble length information, so as to compensate the second receiving time to obtain the first receiving time.

[0012] In other embodiments, the short-range communication time synchronization method further comprises step S5: calculating the carrier frequency offset and the frequency deviation of the local crystal oscillator by analyzing the signal characteristics of the beacon frame; and further calibrating the local clock of the target terminal based on the frequency deviation.

[0013] In a fourth aspect, the application further discloses a short-range communication time synchronization system, comprising an access point device and a plurality of terminal devices; the terminal device is used to execute the steps of the short-range communication time synchronization method in any one of the above embodiments.

[0014] Compared with the prior art, the application has at least one of the following beneficial effects: 1. The global time counter and clock compensation module are added in the chip of the access point device and the terminal device. The clock compensation module can compensate the time stamp information recorded by the global time counter to obtain the second sending time when the frame data actually appears at the transmitting antenna port and the first receiving time when the frame data appears at the receiving antenna port. The accuracy of time synchronization is improved.

[0015] 2. The one-way time broadcast mechanism is adopted in the technical solution of the application. Only the beacon frame carrying the time stamp information and the sending power parameter needs to be periodically sent by the access point, so that the target terminal can complete clock synchronization, frequency calibration and crystal oscillator frequency deviation compensation. Compared with the traditional scheme, the overhead of control signaling is significantly reduced. The system design complexity is simplified, and the overall performance of the short-range communication network is greatly improved.

[0016] 3. The application is especially suitable for uplink multi-user multiple-input multiple-output transmission scenarios. The target terminal can independently adjust the transmission timing by analyzing the time reference information in the access point broadcast frame, so as to realize accurate alignment transmission of multi-user data. The system can improve the throughput while maintaining excellent transmission reliability. The application provides reliable timing guarantee for large-scale terminal concurrent transmission, improves the system efficiency, and avoids waste of air interface resources caused by frequent sending of trigger frames.

[0017] 4、 The application also calculates the carrier frequency offset by analyzing the signal characteristics of the beacon frame, and calculates the frequency deviation of the local crystal oscillator; and further calibrates the local clock of the target terminal based on the frequency deviation. This calibration method based on the carrier frequency offset of the beacon frame can further improve the long-term stability of the clock on the basis of traditional time synchronization, and is particularly suitable for application scenarios with strict requirements on clock accuracy, and forms a complete clock synchronization solution by combining with the timestamp calibration. BRIEF DESCRIPTION OF DRAWINGS

[0018] The above features, technical characteristics, advantages and implementation manners of the application will be further described in the following preferred embodiments in a clear and understandable manner, combined with the accompanying drawings.

[0019] Figure 1 a schematic diagram of a multi-user concurrent transmission scenario; Figure 2 a structural schematic diagram of an access point device and a terminal device of the application; Figure 3 a step flowchart of one embodiment of a short-range communication time synchronization method of the application. DETAILED DESCRIPTION

[0020] In the following description, specific details are set forth in order to provide a thorough understanding of the embodiments of the application. However, persons skilled in the art will understand that the application can be practiced without these specific details. In other instances, well-known structures, devices, circuits, and methods have not been described in detail in order to avoid obscuring the description of the application.

[0021] It should be understood that when used in the specification and the appended claims, the term "comprising" indicates the presence of the described features, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0022] In order to make the drawing simple, only the parts related to the application are shown in each drawing, and they do not represent the actual structure of the product. In addition, in order to make the drawing simple and easy to understand, in some drawings, only one of the components with the same structure or function is shown schematically, or only one of them is labeled. In this document, "one" not only means "only one", but also means "more than one" situation.

[0023] It should be further understood that the term "and / or" used in the specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0024] In addition, in the description of the present application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the specific embodiments of the present application will be described below with reference to the drawings. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained from these drawings without creative labor, and other embodiments can also be obtained.

[0026] Short-Range Communication (SRC) refers to a technology for data transmission between two communication parties within a short distance, usually a few meters to a few tens of meters, such as Bluetooth, Wi-Fi, Zigbee, NFC, etc. Compared with general communication, such as cellular mobile communication, satellite communication, etc.

[0027] In the field of short-range communication, the access point (AP) refers to a wireless communication device as the hub of the network, usually a wireless router or base station, its main role is to manage and coordinate the communication process in the network, including allocating channel resources, scheduling data transmission, maintaining network synchronization and providing connection with the upper layer network. The terminal device (STA) refers to the user equipment accessing the wireless network, such as smart phones, laptops, Internet of Things terminals, etc., which rely on the access point for data transmission and complete the communication process under the control of the access point.

[0028] Short-range communication usually works at a higher frequency band, which enables it to support larger bandwidth and higher data transmission rate, but at the same time brings higher path loss and shorter signal coverage range, and short-range communication is easily affected by co-frequency interference in dense deployment environment, and channel competition problem may be caused when multiple devices coexist. And because the access point and the terminal device use independent crystal oscillator sources, the clock systems of both parties cannot maintain synchronization state. This clock difference will continuously accumulate and expand with the extension of communication time, and then cause significant time deviation problem, reducing the overall communication performance.

[0029] Especially in the multi-user concurrent transmission scenario, as shown in the reference specification Figure 1 , as shown in the reference specification Figure 1Fig. 1 is a schematic diagram of a multi-user concurrent transmission scenario. One access point AP is usually connected with several terminal devices STA, including STA1, STA2, STA3, STA4, etc. The defect of uplink multi-user multiple-input multiple-output is that the terminal devices cannot achieve accurate timing alignment, which makes the access point have to frequently send trigger frames to maintain system synchronization. These trigger frames not only need to complete time synchronization calibration, but also need to bear functions such as frequency offset compensation and channel state estimation. However, the periodic transmission of trigger frames will occupy valuable wireless channel resources, causing the reduction of effective data transmission time, thereby significantly reducing the spectrum utilization efficiency of the entire communication system. This mechanism defect is particularly prominent in the current high-density device access and low-latency demand communication environment, and has become a key bottleneck restricting the performance improvement of the system.

[0030] In view of the above, the present application provides a time synchronization method in short-range communication to solve the time synchronization problem between the access point and the target terminal. The global time counter and the clock compensation module are added in the chip of the access point device and the terminal device. The access point embeds timestamp information and the current transmission power parameter in the frame structure when sending the beacon frame, and these information are transmitted to all target terminals in the form of broadcast. After receiving the beacon frame, the target terminal automatically calculates the signal propagation delay and the frequency error, and then dynamically adjusts the local clock to achieve microsecond-level time alignment with the access point. Referring to the structure diagram of the access point device and the terminal device shown in the accompanying drawings, Figure 2 Figure 2 Fig. 2 is a structure diagram of an access point device and a terminal device according to the present application.

[0031] The access point device comprises a first baseband signal processing unit, a first global time counter, a first clock compensation module, a first radio frequency unit and a transmitting antenna. The first baseband signal processing unit is configured to trigger the global time counter when the access point sends frame data to the target terminal. The first global time counter is configured to determine the first sending time. The first clock compensation module is configured to calculate the sending delay and compensate the first sending time based on the sending delay to obtain the second sending time. The second sending time is the time when the frame data appears at the transmitting antenna.

[0032] In this embodiment, when the access point sends the frame data, the global time counter is triggered by the trigger signal when the baseband signal processing unit starts sending, and the current first sending time is saved by the register.

[0033] The first sending time Tx_T1 is the time when the global time counter is triggered in the access point AP. The second sending time Tx_T2 is the time when the actual frame data really appears at the transmitting antenna port of the access point AP.

[0034] ​Wherein, the frame data is sent from the baseband signal processing unit to the antenna port, and there is a sending delay. The sending delay is Tx_delay, which is a fixed value due to the internal clock and delay of the chip. The specific value of the sending delay can be obtained through chip simulation and measurement.

[0035] Tx_delay = Tx_T2 - Tx_T1; that is, the sending delay = the second sending time - the first sending time. Through the first clock compensation module, the first sending time can be compensated based on the sending delay to obtain the second sending time.

[0036] In some embodiments, the second sending time and the sending power parameter are stored as calibration information in the data segment of the frame data as an independent data element. In order to calibrate the clock of the terminal device after receiving the calibration information.

[0037] The terminal device comprises a second baseband signal processing unit, a second global time counter, a second clock compensation module, a second radio frequency unit, and a receiving antenna. The receiving antenna is used to receive the frame data sent by the access point. The second baseband signal processing unit is used to synchronize the frame data. The second global time counter is used to record the second receiving time of the terminal after synchronizing the frame data. The second clock compensation module is used to calculate the receiving delay and compensate the second receiving time based on the receiving delay to obtain the first receiving time. The first receiving time is the time when the frame data appears at the receiving antenna.

[0038] In the present embodiment, when the terminal device receives the frame data, the terminal device needs to synchronize the signal. When the target terminal receives the frame data to obtain the time element in the frame data, a relatively accurate second receiving time Rx_T2 can be obtained, that is, the time when the terminal device completes the signal synchronization of receiving the frame data. The time accuracy of the second receiving time depends on the synchronization accuracy, and the accuracy is about 0.2us or less. Suppose the time when the frame data appears at the receiving antenna of the target terminal is the first receiving time Rx_T1. There is a receiving delay Rx_delay between the first receiving time and the second receiving time.

[0039] Rx_delay = Rx_T2 - Rx_T1; that is, the receiving delay = the second receiving time - the first receiving time. The receiving delay is determined by the delay of the data processing unit inside the chip, and specifically by the length information of the preamble of the AP framework. The receiving delay can be obtained by the length information of the preamble. In some other embodiments, the length information of the preamble of the received data packet is fixed, that is, the value of the receiving delay is fixed.

[0040] Therefore, the second clock compensation module can perform delay compensation on the second receiving time based on the receiving delay to obtain the first receiving time.

[0041] Based on the above content in the embodiments, one embodiment of the short-distance communication time synchronization method specifically includes the following steps: referring to the description of the accompanying drawings Figure 3 as shown.

[0042] The access point stores the timestamp information and the transmission power parameter as calibration information in the frame structure of the beacon frame as an independent data element. When the access point broadcasts the beacon frame to the target terminal, the calibration information is attached so that the terminal device can calibrate its own clock after receiving the calibration information. One-way time service can be completed between the access point and the target terminal.

[0043] In this embodiment, the beacon frame is a management frame periodically sent by the access point to the terminal device. It is mainly used to broadcast the existence of the network and the basic parameters so that the client device can discover and connect to the network. The information contained in the beacon frame includes the network name (SSID), the supported rate, the security setting, the timestamp, etc. These help the client understand the network status and decide whether to join. The transmission of the beacon frame is periodic, usually once every 100 milliseconds, to ensure the visibility of the network.

[0044] The target terminal receives the beacon frame broadcasted by the access point, and the beacon frame has embedded calibration information including timestamp information and transmission power parameter. Based on the timestamp information, the actual propagation delay between the access point and the target terminal is calculated. Based on the transmission power parameter, the target propagation delay between the access point and the target terminal is calculated. The delay error between the actual propagation delay and the target propagation delay is calculated, and the clock deviation of the target terminal is calibrated based on the delay error.

[0045] In some embodiments of this embodiment, the step S2 specifically includes calculating the time difference between the second sending time and the first receiving time, i.e. obtaining the actual propagation delay.

[0046] In this embodiment, the calibration information includes timestamp information for indicating the sending time of the beacon frame. Optionally, the timestamp information is the first sending time or the second sending time.

[0047] Preferably, to improve the synchronization accuracy, the timestamp information is the second sending time, i.e. the time when the actual frame data really appears at the transmitting antenna port of the access point AP. The target terminal can obtain the actual propagation delay by subtracting the second sending time from the first receiving time.

[0048] In some other embodiments of the present embodiment, the step S3 specifically comprises: S31, calculating a spatial link attenuation in the signal transmission process based on the transmission power parameter and the reception power parameter of the target terminal; S32, estimating a spatial distance between the access point and the target terminal based on the spatial link attenuation; and S33, calculating the target propagation delay based on the spatial distance.

[0049] In the present embodiment, the process of calculating the spatial link attenuation based on the transmission power parameter and the reception power parameter involves the physical characteristics of wireless signal propagation. Since it is short-range communication, the distance is usually within 100 meters. According to the transmission power of the access point and the reception power of the target terminal, the spatial link attenuation path loss can be calculated. The transmission power parameter refers to the initial power value when the access point AP transmits a signal, and the reception power parameter is the signal strength detected by the target terminal. The spatial link attenuation can be obtained by calculating the difference between the transmission power and the reception power.

[0050] After obtaining the spatial link attenuation, the spatial distance between the access point AP and the target terminal can be estimated using a wireless signal propagation model. The free space path loss model is a commonly used theoretical model. By matching the measured link attenuation with the free space path loss model, the spatial distance between them can be inversely deduced.

[0051] After obtaining the spatial distance, the target propagation delay can be further calculated. The propagation speed of electromagnetic waves in air is close to the speed of light c=3×10^8 m / s, so the propagation delay can be calculated by the formula d / c. The estimation accuracy of the target propagation delay in the present application is about 0.1us=30m / (3e8m / s).

[0052] In some other embodiments of the present embodiment, the step S4 specifically comprises: S41, calculating a delay error between the actual propagation delay and the target propagation delay; and S42, calibrating the clock deviation of the target terminal based on the delay error.

[0053] In the present embodiment, the actual propagation delay is the actual measurement value of the time difference between the time stamps of signal transmission and reception. The target propagation delay is a theoretical value calculated based on the spatial distance. The delay error is the difference between the two. Based on the calculated delay error, the clock of the target terminal can be compensated and calibrated, thereby ensuring that the time synchronization accuracy between the target terminal and the access point AP meets the application requirements.

[0054] On the basis of the above-mentioned embodiments, another embodiment of a short-range communication time synchronization method is disclosed. Compared with the foregoing embodiments, the calibration information in the present embodiment further comprises preamble length information of the beacon frame. Specifically, the method comprises the following steps: The access point stores the timestamp information, the transmission power parameter, and the preamble length information of the AP architecture as calibration information in the frame structure of the beacon frame. When the access point broadcasts the beacon frame to the target terminal, the calibration information is attached so that the terminal device calculates the reception delay.

[0055] The target terminal calculates the reception delay based on the preamble length information, and compensates the second reception time to obtain the first reception time.

[0056] Specifically, the preamble is a fixed mode signal at the beginning of the data frame, mainly undertakes key functions such as automatic gain control (AGC) adjustment, frequency synchronization, symbol timing synchronization, and the terminal device needs to rely on the preamble to complete these preparations to accurately parse the subsequent valid data.

[0057] Because the preamble length may be different under different communication standards or configurations, if the length information is not clear, the terminal device will be difficult to accurately determine the start time of the actual data part, thereby causing time measurement error. By obtaining the preamble length information, the terminal can accurately calculate the duration of the preamble, thereby inversely deducing the accurate time point of the start of the data reception from the end time of the preamble.

[0058] In a specific implementation, after detecting the frame start boundary, the terminal device starts timing counting according to the known preamble length information, and when the preamble duration reaches the set value, the first data reception time is determined.

[0059] Another embodiment of the short-range communication time synchronization method provided in the present application is based on any one of the above embodiments, and further includes: The method further includes the step S5 of calculating the carrier frequency offset and deducing the frequency deviation of the local crystal oscillator by analyzing the signal characteristics of the beacon frame, and further calibrating the local clock of the target terminal based on the frequency deviation.

[0060] In the embodiment, the carrier frequency offset information can be extracted by analyzing the signal characteristics of the received beacon frame, and the frequency deviation of the local crystal oscillator of the terminal is further deduced. Specifically, when the terminal device receives the packet, the known fixed training sequence or preamble part in the beacon frame is captured, the reference signals with specific spectral characteristics are used, and the deviation between the actual received signal and the theoretical value of the standard frequency is calculated by using the frequency domain correlation or phase difference method. The deviation is the carrier frequency offset.

[0061] Since the carrier frequency offset is mainly caused by the frequency inconsistency of the crystal oscillator at the receiving and transmitting ends, the carrier frequency offset value measured can be converted into the actual frequency deviation value of the local reference crystal oscillator by pre-calibrating the frequency conversion relationship of the radio frequency front-end mixer. After obtaining the frequency deviation, the terminal device dynamically adjusts the local clock frequency. For positive deviation, the clock counting frequency is appropriately reduced, and for negative deviation, the frequency is increased. The frequency difference is gradually eliminated through closed-loop control, and the calibration accuracy is further improved.

[0062] On the basis of the above embodiment, the access point AP and the terminal device STA will receive the beacon frame at regular intervals to complete the information interaction between the access point AP and the terminal device STA. The interaction interval between the two will not exceed 0.3s. Assuming that the period of the beacon frame is 0.3s. Then, after each correction is completed, the time deviation of the access point AP and the terminal device STA is 0.4us. The frequency offset of the crystal oscillator can be obtained through the frequency deviation estimation. Assuming that the residual offset of the crystal oscillator after frequency deviation correction is 1ppm, therefore, the maximum time drift is 0.3s 1e-6=0.3us. Therefore, the maximum time deviation of the access point AP and the terminal device STA is 0.2 (synchronization accuracy) + 0.1 (air interface delay accuracy) + 0.3 (clock drift) = 0.6us during the entire time period. It can be seen that the time calibration accuracy of the technical solution of the present application can reach 0.6us. The calibration accuracy of 0.6us used in the uplink multi-user multiple-input multiple-output transmission scenario can fully meet the requirements.

[0063] Based on the same concept, the present application also discloses a short-range communication time synchronization system. The system includes an access point device and a plurality of terminal devices. The system is used to implement the steps described in any one of the method embodiments. The short-range communication time synchronization method and the short-range communication time synchronization system of the present application have the same technical concept, and the technical details of the embodiments of the two can be mutually applicable. In order to reduce repetition, this time will not be repeated.

[0064] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the division of the above program modules is taken as an example, and in actual application, the above functions can be completed by different program modules according to needs, that is, the internal structure of the device is divided into different program units or modules to complete all or part of the functions described above. Each program module in the embodiment can be integrated in one processing unit, or each unit can be physically present separately, or two or more units can be integrated in one processing unit. The above integrated units can be realized in the form of hardware or software program units. In addition, the specific names of each program module are only for easy distinction, and do not limit the protection scope of the present application.

[0065] While the preferred embodiments of the application have been described, additional variations and modifications can be made to these embodiments by those skilled in the art once they learn of the basic inventive concepts. Therefore, the appended claims are intended to cover all such additional variations and modifications as fall within the scope of the application.

Claims

1. An access point device, characterized in that, include: The system comprises a first baseband signal processing unit, a first global time counter, a first clock compensation module, and a transmitting antenna; The first baseband signal processing unit is used to trigger the global time counter when the access point sends frame data to the target terminal; The first global time counter is used to determine the first transmission time; The first clock compensation module is used to calculate the transmission delay and perform delay compensation on the first transmission time based on the transmission delay to obtain a second transmission time; the second transmission time is the moment when the frame data appears on the transmitting antenna.

2. A terminal device, characterized in that, include: The system comprises a second baseband signal processing unit, a second global time counter, a second clock compensation module, and a receiving antenna. The receiving antenna is used to receive frame data sent by the access point as described in claim 1; The second baseband signal processing unit is used to perform signal synchronization on the frame data; The second global time counter is used to record the second reception time when the current terminal completes the synchronization of the frame data; The second clock compensation module is used to calculate the reception delay and perform delay compensation on the second reception time based on the reception delay to obtain the first reception time; The first reception time is the moment when the frame data appears at the receiving antenna.

3. A short-range communication time synchronization method, characterized in that, Performed by the terminal device according to claim 2, the steps include: S1: Receive a beacon frame broadcast by the access point; the beacon frame contains calibration information, including timestamp information and transmit power parameters; S2: Based on the timestamp information, the actual propagation delay between the access point and the target terminal is calculated; S3: Based on the transmission power parameters, the target propagation delay between the access point and the target terminal is calculated; S4: Calculate the delay error between the actual propagation delay and the target propagation delay; The clock deviation of the target terminal is calibrated based on the delay error.

4. The short-range communication time synchronization method as described in claim 3, characterized in that, The timestamp information is the second sending time.

5. The short-range communication time synchronization method as described in claim 4, characterized in that, Step S2: Based on timestamp information, calculate the actual propagation delay between the access point and the target terminal; specifically including: The actual propagation delay is obtained by calculating the time difference between the second transmission time and the first reception time.

6. The short-range communication time synchronization method as described in claim 3, characterized in that, Step S3: Based on the transmit power parameters, calculate the target propagation delay between the access point and the target terminal; specifically including: Based on the transmit power parameters and the receive power parameters of the target terminal, the spatial link attenuation during signal transmission is calculated; The spatial distance between the access point and the target terminal is estimated by the spatial link attenuation; the target propagation delay is calculated by the spatial distance.

7. The short-range communication time synchronization method as described in claim 3, characterized in that, The calibration information also includes the preamble length information of the beacon frame.

8. The short-range communication time synchronization method as described in claim 7, characterized in that, Also includes: The receiving delay is calculated based on the preamble length information; This is to facilitate delay compensation for the second reception time, thereby obtaining the first reception time.

9. A short-range communication time synchronization method as described in claim 3, characterized in that, The method also includes step S5: calculating the carrier frequency offset and estimating the frequency deviation of the local crystal oscillator by analyzing the signal characteristics of the beacon frame; and further calibrating the local clock of the target terminal based on the frequency deviation.

10. A short-range communication time synchronization system, characterized in that: It includes an access point device and several terminal devices; the terminal devices are used to perform the steps of a short-range communication time synchronization method according to any one of claims 3-9.

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