High-precision time synchronization method for TDMA (Time Division Multiple Access) wireless sensor network

Abstract

The invention discloses a TDMA (Time Division Multiple Access) wireless sensor network high-precision time synchronization method, which comprises a central node and a terminal node which need time synchronization, the method comprises the following specific steps: (1) a network synchronization reference generation step, (2) a network communication initiation step, (3) a terminal node scanning and receiving step, (4) a terminal node time slice synchronization establishment step, and (5) a terminal node network synchronization establishment step. According to the high-precision time synchronization method for the TDMA wireless sensor network, physical layer signal characteristics and a TDMA time slot structure are deeply fused, and meanwhile, frequency offset compensation, the anti-interference capability and the multi-node expansibility are guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of communication technologies, and more specifically, to a high-precision time synchronization method for TDMA wireless sensor networks. Background Art

[0002] In a wireless sensor network (WSN), time synchronization is a core basic technology for ensuring network collaborative communication, data fusion, and event serialization. Especially in a communication architecture based on time division multiple access (TDMA), the time synchronization accuracy between nodes directly determines the slot allocation efficiency, channel utilization rate, and overall system performance.

[0003] However, existing mainstream technical solutions face multiple challenges in achieving high-precision synchronization:

[0004] For example, in the traditional FTSP mechanism, the currently widely used flooding time synchronization protocol (FTSP) relies on timestamping at the MAC layer, and the time information of the sending node needs to be encapsulated into the data frame for transmission. The receiving node needs to parse this information and estimate the time deviation in combination with the network delay. However, such methods have the following inherent defects:

[0005] Data transmission overhead: Encapsulating time information occupies the payload, resulting in wasted bandwidth and significantly reducing communication efficiency, especially in high-density networks.

[0006] Software processing delay: The generation, parsing, and deviation calculation of timestamps rely on software processing, and it is difficult to avoid microsecond-level jitters introduced by operating system scheduling, interrupt response, etc.

[0007] Channel access uncertainty: For example, in scenarios using low-power nodes such as CC2530, the clear channel assessment (CCA) and random backoff mechanism before sending lead to unpredictable channel access delays, further deteriorating the synchronization accuracy (typical deviation exceeds 50 μs).

[0008] Therefore, a method that can achieve "zero-overhead" synchronization as much as possible while ensuring frequency offset compensation, anti-interference ability, and multi-node scalability is needed. Summary of the Invention

[0009] The present invention overcomes the deficiencies of the prior art and provides a high-precision time synchronization method for TDMA wireless sensor networks that deeply integrates physical layer signal characteristics with the TDMA slot structure to achieve near "zero-overhead" synchronization while ensuring frequency offset compensation, anti-interference ability, and multi-node scalability.

[0010] The technical solution of the present invention is as follows:

[0011] A high-precision time synchronization method for TDMA wireless sensor networks, including a central node and terminal nodes that need time synchronization. The specific steps are as follows:

[0012] (1) Network synchronization reference generation step: The central node generates network time synchronization parameters, including the slot length, the number of downlink slots, and the number of uplink slots, and generates a periodic slot pulse signal through the slot pulse generation unit to trigger the transmission of the physical layer modulation signal, forming a network time synchronization reference;

[0013] (2) Network communication initiation step: The central node sends a PN frame containing a pseudo-random PN sequence, a synchronization detection word, and a frequency offset estimation sequence in the first slot of the frame period based on the slot pulse signal to initiate network communication;

[0014] (3) Terminal node scanning and receiving step: Unsynchronized terminal nodes continuously detect wireless signals, determine the arrival position of the PN frame through the synchronization detection word, and compensate for the frequency offset through the frequency offset estimation sequence;

[0015] (4) Terminal node time slice synchronization establishment step: The terminal node triggers the local slot pulse generation unit based on the detected PN frame synchronization detection word, obtains the starting point of the time slice by compensating for the transmission duration of the PN sequence, and establishes a periodic slot pulse signal;

[0016] (5) Terminal node network synchronization establishment step: The terminal node determines the slot number within the frame period according to the count of the slot pulse signal, and completes the network time synchronization with the central node.

[0017] Further, the PN frame is sent by the central node in the downlink slot, and the structure of the PN frame includes a pseudo-random PN sequence, a synchronization detection word, and a frequency offset estimation sequence arranged in sequence.

[0018] Further, in the step (4), the local slot pulse generation unit is triggered by hardware, directly compensates for the transmission duration of the pseudo-random PN sequence according to the arrival time of the synchronization detection word, and generates a time slice start pulse signal.

[0019] Further, the slot pulse signal is a periodic signal, its period is the same as the slot length, and the initial count value of the slot number is the first slot number occupied by the PN frame.

[0020] Further, after the terminal node completes network synchronization, it selects to perform data sending or receiving operations in the specified slot according to the slot number.

[0021] Further, the physical layer modulation signal completes waveform data preparation before the arrival of the slot pulse and is automatically sent by the trigger of the slot pulse.

[0022] Further, the frequency offset estimation sequence is used by the terminal node to calculate the frequency offset value and compensate the local clock.

[0023] Further, the frame period includes a downlink time slot and an uplink time slot. The downlink time slot is used for the central node to send PN frames and control information, and the uplink time slot is used for the terminal node to send network maintenance information or service data.

[0024] Further, the synchronization detection word is used to accurately locate the segmentation position of the PN frame for physical layer modulation and demodulation.

[0025] The advantages of the present invention are as follows:

[0026] Through the special PN frame structure design, this solution defines a dedicated physical layer frame (PN frame) containing a pseudo-random sequence (PN), a synchronization detection word, and a frequency offset estimation sequence, replacing the traditional method of encapsulating time information in data frames, and completely eliminating excessive redundant transmission overhead.

[0027] This solution directly processes the characteristics of the modulation signal at the physical layer. Through the physical layer waveform design, the synchronization reference can be directly extracted, avoiding the processing delay of the MAC layer and the network layer. And through the physical layer modulation and demodulation, the synchronization detection word in the PN frame is directly captured, triggering the local time slot pulse generation unit, and combining with the hardware-level time compensation to achieve microsecond-level synchronization accuracy.

[0028] In the frame period and time slot numbering mechanism of this solution, the central node maintains the global frame period, and the terminal node only needs to receive the PN frame to automatically align the time slot number, without complex time deviation calculation, significantly reducing the implementation complexity and energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the frame period of the present invention;

[0030] Figure 2 It is a schematic diagram of the downlink time slot of the central node of the present invention;

[0031] Figure 3 It is a schematic diagram of the network synchronization process of the present invention;

[0032] Figure 4 It is a schematic diagram of the synchronization reference generation of the central node of the present invention;

[0033] Figure 5 It is a schematic diagram of the network synchronization of the terminal node of the present invention;

[0034] Figure 6 It is a schematic diagram of the composition of the PN frame of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments are only specific elaborations of the present invention, and their purpose is to enable those skilled in the art to better understand the technical solutions of the present invention, and should not be regarded as a limitation of the present invention.

[0036] Example 1:

[0037] As Figures 1 to 6 shown, a high-precision time synchronization method for a TDMA wireless sensor network includes a central node and terminal nodes that need time synchronization. The specific steps are as follows:

[0038] (1) Network synchronization benchmark generation step: Based on the application configuration, the central node generates network time synchronization parameters, including the slot length, the number of downlink slots, and the number of uplink slots, etc. The slot pulse generation unit of the central node generates a periodic slot pulse signal according to the slot length information. The pulse edge of each periodic slot pulse signal is used to trigger the transmission of the physical layer modulation signal, and the waveform is sent on the wireless channel. Based on this, the time slice synchronization benchmark of the network managed by the central node is obtained.

[0039] (2) Network communication initiation step: Based on the time benchmark obtained from the time slice synchronization benchmark and the slot parameters configured by the application, the central node sends a PN frame containing a pseudo-random PN sequence, a synchronization detection word, and a frequency offset estimation sequence in the first slot of the frame period based on the slot pulse signal to initiate network communication.

[0040] Among them, the frame period includes downlink slots and uplink slots. The downlink slots are used for the central node to send PN frames and control information, and the uplink slots are used for the terminal nodes to send network maintenance information or service data.

[0041] Specifically, the central node can count each slot and decide on the operation processing in different slots, including wireless signal transmission, reception, etc.

[0042] When transmitting a wireless signal, the central node only needs to prepare the waveform data to be transmitted before each slot pulse arrives, and the physical layer modulation module is automatically triggered to transmit after the slot pulse arrives.

[0043] When receiving a wireless signal, the central node can configure the next slot for reception in advance before the slot count for receiving the signal arrives. At this time, the physical layer demodulation module will automatically receive the wireless signal after the slot pulse arrives.

[0044] Therefore, by making full use of the PN frame to achieve network synchronization, the central node only needs to transmit a PN signal frame in the first slot of each frame period, which also represents the start of network communication, that is, all terminal nodes must successfully receive the PN frame to continue operating to receive and send information in the subsequent slots of the frame period.

[0045] (3) Terminal node scanning and receiving step: Unsynchronized terminal nodes continuously detect wireless signals, determine the arrival position of the PN frame through the synchronization detection word, and compensate for the frequency offset through the frequency offset estimation sequence.

[0046] Specifically, first, a wireless signal arrival is detected. Then, the exact signal arrival position is determined through a synchronization detection word, and the frequency offset is estimated through subsequent frequency offset estimation words.

[0047] (4) Steps for establishing time slice synchronization at the terminal node: The terminal node triggers the local time slot pulse generation unit based on the detected PN frame synchronization detection word, obtains the starting point of the time slice by compensating for the PN sequence time, and establishes a periodic time slot pulse signal. That is, the local time slot pulse generation unit is triggered by hardware and directly compensates for the transmission duration of the pseudo-random PN sequence according to the arrival time of the synchronization detection word to generate a time slice starting pulse signal. The time slot pulse signal is a periodic signal, whose period is the same as the time slot length, and the initial count value of the time slot number is the first time slot number occupied by the PN frame.

[0048] Specifically, when the physical layer demodulation module of the terminal node detects the synchronization detection word in the PN frame, it will trigger the local periodic time slot pulse generation unit to start working. The generated pulse edge is determined by the trigger time and the position of the synchronization word in the PN frame. Specifically, the trigger time compensates for the PN sequence time before the synchronization word to obtain the target pulse edge time, that is, the establishment of time slice synchronization is completed.

[0049] (5) Steps for establishing network synchronization at the terminal node: The terminal node determines the time slot number within the frame period according to the count of the time slot pulse signal to complete the network time synchronization with the central node.

[0050] Specifically, after the time slice synchronization is established at the terminal node, that is, after the periodic time slot pulse is generated, the time slot counting module starts to count the pulse signal, so as to obtain the number of each time slice in the frame period; and the initial count value is 1, that is, the time slot number occupied by the PN frame is 1.

[0051] For the frame period and time slot number mechanism, the central node maintains the global frame period. The terminal node only needs to receive the PN frame to automatically align the time slot number, without complex time deviation calculations. The synchronization process is directly completed automatically by hardware, significantly reducing the implementation complexity and energy consumption. The terminal node only needs to receive the PN frame to automatically align the time slot number, without maintaining a global timestamp or dynamic adjustment algorithm. The central node uniformly maintains the frame period and time slot allocation, realizing the support for plug-and-play type terminal access.

[0052] In summary, this solution combines the characteristics of directly processing modulation signals at the physical layer, directly extracts the synchronization reference through physical layer waveform design, and avoids the processing delays of the MAC layer and network layer. Moreover, it directly captures the synchronization detection word in the PN frame through physical layer modulation and demodulation, triggers the local time slot pulse generation unit, and combines hardware-level time compensation to achieve microsecond-level synchronization accuracy. In the traditional FTSP, time stamping depends on the MAC layer and is affected by channel access delays (such as the CCA mechanism of CC2530 nodes), and the synchronization accuracy is only about 50 μs. However, the synchronization accuracy of this solution can reach <1 μs, which is more than 50 times higher, meeting the requirements of scenarios with strict timing requirements such as industrial control and power systems.

[0053] Embodiment 2:

[0054] As Figure 2 、 6 shown, in combination with Embodiment 1, the PN frame is sent by the central node in the downlink time slot, and the structure of the PN frame includes a pseudo-random PN sequence, a synchronization detection word, and a frequency offset estimation sequence arranged in sequence. Among them, the frequency offset estimation sequence is used by the terminal node to calculate the frequency offset value and compensate the local clock. The synchronization detection word is used for the physical layer modulation and demodulation module to accurately locate the segmentation position of the PN frame.

[0055] Through the special PN frame structure design, a dedicated physical layer frame (PN frame) including a pseudo-random sequence (PN), a synchronization detection word, and a frequency offset estimation sequence is defined, replacing the traditional method of encapsulating time information in the data frame, and completely eliminating excessive redundant transmission overhead. Compared with the traditional FTSP, which needs to encapsulate the transmission time information into the data frame, occupying the payload (the typical occupancy rate is about 5%-10%). This solution completely eliminates the transmission of time information, saves network bandwidth, and especially in a high-density network, the communication efficiency will be increased by 15%-20%.

[0056] Embodiment 3:

[0057] In combination with Embodiment 1, it may further include step (6), which is specifically as follows:

[0058] (6) Terminal node data sending step: After the terminal node completes network synchronization, it selects to perform data sending or receiving operations in the specified time slot according to the time slot number.

[0059] That is, through the time slot number maintained by the terminal node itself, it can perform selective operations in each time slot of the entire frame period, including receiving network control information from the central node, sending network maintenance information, sending service data, etc. The specific methods and processes are the same as those of the central node.

[0060] In summary, the present solution utilizes a specially defined communication network information frame structure without any data transmission overhead. Moreover, the time synchronization between nodes is simplified to TDMA time slot synchronization, which can be directly implemented by hardware. It is easier to achieve high-precision synchronization without requiring additional processing of time information by receiving nodes.

[0061] It should be noted that other technical features of the present invention are all existing technologies, so they will not be elaborated here.

[0062] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as within the protection scope of the present invention.

Claims

1. A high-precision time synchronization method for TDMA wireless sensor networks, characterized in that It includes a central node and terminal nodes that require time synchronization. The specific steps are as follows: (1) Network synchronization reference generation step: The central node generates network time synchronization parameters, including the slot length, the number of downlink slots, and the number of uplink slots, and generates a periodic slot pulse signal through a slot pulse generation unit to trigger the transmission of a physical layer modulation signal, forming a network time synchronization reference; (2) Network communication initiation step: Based on the slot pulse signal, the central node sends a PN frame containing a pseudo-random PN sequence, a synchronization detection word, and a frequency offset estimation sequence in the first slot of the frame period to initiate network communication; (3) Terminal node scanning and receiving step: Unsynchronized terminal nodes continuously detect wireless signals, determine the arrival position of the PN frame through the synchronization detection word, and compensate for the frequency offset through the frequency offset estimation sequence; (4) Terminal node time slice synchronization establishment step: The terminal node triggers the local slot pulse generation unit based on the detected PN frame synchronization detection word, obtains the starting point of the time slice by compensating the PN sequence time, and establishes a periodic slot pulse signal; (5) Terminal node network synchronization establishment step: The terminal node determines the slot number within the frame period according to the count of the slot pulse signal, and completes the network time synchronization with the central node.

2. The high-precision time synchronization method for a TDMA wireless sensor network according to claim 1, characterized in that The PN frame is sent by the central node in the downlink slot, and the structure of the PN frame includes a pseudo-random PN sequence, a synchronization detection word, and a frequency offset estimation sequence arranged in sequence.

3. A high-precision time synchronization method for a TDMA wireless sensor network according to claim 1, characterized in that, In the step (4), the local slot pulse generation unit is triggered by hardware, and directly compensates for the transmission duration of the pseudo-random PN sequence according to the arrival time of the synchronization detection word to generate a time slice starting pulse signal.

4. A high-precision time synchronization method for a TDMA wireless sensor network according to claim 1, characterized in that The slot pulse signal is a periodic signal, and its period is consistent with the slot length, and the initial count value of the slot number is the first slot number occupied by the PN frame.

5. A high-precision time synchronization method for a TDMA wireless sensor network according to claim 1, characterized in that After the terminal node completes network synchronization, it selects to perform data sending or receiving operations in the specified slot according to the slot number.

6. A high-precision time synchronization method for a TDMA wireless sensor network according to claim 1, characterized in that, The physical layer modulation signal completes waveform data preparation before the slot pulse arrives and is automatically sent by the slot pulse trigger.

7. A high-precision time synchronization method for a TDMA wireless sensor network according to claim 1, characterized in that The frequency offset estimation sequence is used by the terminal node to calculate the frequency offset value and compensate the local clock.

8. A high-precision time synchronization method for a TDMA wireless sensor network according to claim 1, characterized in that, The frame period includes downlink slots and uplink slots, where the downlink slots are used for the central node to send PN frames and control information, and the uplink slots are used for the terminal node to send network maintenance information or service data.

9. A high-precision time synchronization method for a TDMA wireless sensor network according to claim 1, characterized in that, The synchronization detection word is used for accurately positioning the segmentation position of the PN frame in physical layer modulation and demodulation.

Images