CN116209051A - Self-organizing network time synchronization method based on agile beam pointing - Google Patents
Self-organizing network time synchronization method based on agile beam pointing Download PDFInfo
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Abstract
The invention discloses a self-organizing network time synchronization method based on agile beam pointing, which comprises the following steps: starting a time synchronization function after starting; the non-reference node keeps a monitoring state before receiving the synchronous message, and the phased array wave beam always points to the reference node; after the power-on, the reference nodes respectively point to the non-reference nodes in a polling mode and send time synchronous broadcasting; after confirming the synchronous time slots of the non-reference nodes and the reference nodes, the rest time slots are used for polling other next-stage child nodes which cannot be directly connected with the reference nodes; when a next-level child node is polled, the next-level child node keeps a silent state, after receiving a synchronous polling frame of an upper-level node, the synchronous time slot position of the next-level child node is confirmed, the next-level child node is polled in other asynchronous time slots, and the like, so that the selection and timing of synchronous time slots of all nodes in the network are completed. The method can realize the time synchronization of the multi-node self-organizing network by taking the agile beam phased array as the communication antenna.
Description
Technical Field
The invention belongs to the technical field of networking communication, and particularly relates to a self-organizing network time synchronization method based on agile beam pointing.
Background
Currently, most of the research on application of ad hoc networks to tactical military systems is to use a simple radio frequency physical layer scheme based on omni-directional antennas. In the omni-directional antenna scheme, nodes in a communication distance range can receive wireless signals of any transmitting node, so that neighbor discovery and network topology detection in an ad hoc network are facilitated, and complex antenna pointing control is not needed when time synchronization interaction is carried out.
In a wireless ad hoc network adopting a TDMA system, the synchronization process between each child node and the master node is generally divided into two steps of open loop synchronization and closed loop synchronization.
The master node periodically broadcasts a synchronization beacon, and each child node immediately restarts timing after detecting the synchronization beacon, which is open loop synchronization. The timing of each child node within the network is initially different from one another due to propagation delay. Open loop synchronization is obviously sufficient if each child node only receives the broadcast of the master node and does not send data to the master node.
For the propagation delay of a link, a closed loop synchronization mode is adopted for calibration: the synchronous node periodically transmits an ECHO packet to the reference node in a fixed time slot, and starts counting through a local clock counter, the reference node immediately returns the packet after receiving the ECHO packet, when the synchronous node receives the recovered ECHO, the clock counter stops counting, and the link delay between the synchronous node and the reference node can be estimated according to the count value, so that the node can refresh the link propagation delay in real time and correct open-loop synchronization.
Each node sends an ECHO frame to the reference, starts a local counter from the start of transmission, and automatically returns the frame after the reference is received, except that the transmit and receive addresses are exchanged. When the node receives the returned ECHO frame, it stops counting and sets its value as Count. The link delay between the node and the reference is: delay= (Count = ECHO processing time)/2; wherein the ECHO processing time is related to the processing power of the hardware platform.
Considering that not every sub-node and the main node are visible, every sub-node firstly selects a node with higher clock level as a synchronous reference, every node can send synchronous codes in the synchronous time slot where the node is positioned, and the local clock counter is calibrated after the node receives the codes, so that the coverage area of the reference clock is enlarged.
The clock of the first starting networking node is defined as a 0-level clock, and the clock of a one-hop neighbor node is defined as a 1-level clock; due to the dynamic change of the network topology, each node should refresh the level of its reference clock in real time, and the refresh method is as follows: the clock with the highest clock level is selected as a reference clock, and the own clock level is 1 level lower than the reference clock. That is, if the reference clock level is n, the clock level of the node is n+1. If a plurality of reference clocks exist, the node with the smallest ID number is selected as the synchronous reference.
However, the use of omni-directional antennas presents the following problems: 1) A low data rate; 2) The margin of the link is insufficient in the range of the service flow requirement; 3) Uncontrollable spatial radio frequency signals; 4) Extremely sensitive to interference and thus rendered inoperable; 5) Channel multiplexing sharing is inefficient.
Accordingly, many documents have studied to solve the above-mentioned problems using a high-gain directional antenna. However, when a directional antenna is applied to a dynamic network including mobile nodes, it is required to keep the antenna directions consistent between the transmitting and receiving ends of the link. In order to support fast response and highly dynamic networks, an algorithm or protocol needs to be applied to control communication between a large number of mobile nodes with directional antennas.
Disclosure of Invention
The technical solution of the invention is as follows: the self-organizing network time synchronization method based on the agile wave beam pointing can achieve multi-node self-organizing network time synchronization with the agile wave beam phased array as a communication antenna, and is suitable for various networking communication time synchronization applications.
In order to solve the technical problems, the invention discloses a self-organizing network time synchronization method based on agile beam pointing, which comprises the following steps:
starting a time synchronization function after each satellite node is started, wherein the network synchronization topology adopts a mode of node identity pre-configuration;
the non-reference node keeps a monitoring state before receiving the synchronous message, and the phased array wave beam always points to the reference node; after the power-on, the reference nodes respectively point to the non-reference nodes in a polling mode and send time synchronous broadcasting;
after confirming the synchronous time slots of the non-reference nodes and the reference nodes, the rest time slots are used for polling other next-stage child nodes which cannot be directly connected with the reference nodes;
when a next-level child node is polled, the next-level child node keeps a silent state, after receiving a synchronous polling frame of an upper-level node, the synchronous time slot position of the next-level child node is confirmed, the next-level child node is polled in other asynchronous time slots, and the like, so that the selection and timing of synchronous time slots of all nodes in the network are completed;
according to the control characteristics of the phased array antenna, 7 time slots are arranged for synchronization information interaction per non-reference node.
In the self-organizing network time synchronization method based on agile beam pointing, the time slot 1 is used for an upper node to send synchronous polling, the time slot 3 is used for a lower node to feed back a synchronous request frame, the time slot 5 is used for an upper node to feed back a synchronous response frame, and the time slots 2 and 4 are used for transmission delay protection, pointing calculation of a phased array antenna and wave control execution delay, so that the conflict of receiving and transmitting states is avoided.
The method for synchronizing the time of the self-organizing network based on the agile beam pointing further comprises the following steps: after each satellite node is started, setting the roles of the satellite nodes as reference nodes and non-reference nodes according to the uploaded synchronous topology parameters; the reference node establishes a system superframe and determines a receiving and transmitting time slot; all non-reference nodes confirm the upper node and the lower node in the synchronous topology, and all lower nodes lead the antenna to always point to the upper node and maintain a receiving state before the time synchronization with the upper node is completed, and wait for receiving the self-owned synchronous frame sent by the upper node; the antenna orientation is calculated by the phased array antenna according to the present star orbit and the target star orbit.
In the self-organizing network time synchronization method based on agile beam pointing, the time step-by-step transmission flow of the node in the unsynchronized state is as follows:
the node antenna points to the upper node all the time and waits for a synchronous frame from the upper node;
after one synchronous interaction with the upper group of nodes is completed, the local time is updated, and the synchronous state is entered.
In the self-organizing network time synchronization method based on agile beam pointing, the time step-by-step transmission flow of the node in the synchronization state is as follows:
judging whether the current multiframe is a synchronous maintenance multiframe of the node to an upper node;
if yes, controlling the phased array antenna to point to an upper node, and waiting for a synchronous frame from the upper node; if not, controlling the phased array antenna to sequentially point to the lower node, and sending a synchronization frame to the lower node so as to trigger a synchronization flow;
the upper node and the lower node complete time synchronization process interaction, and the lower node adjusts the local clock.
In the self-organizing network time synchronization method based on agile beam pointing, the time synchronization process of the upper node and the lower node is divided into three processes of sending a synchronization frame by the upper node, sending a request frame by the lower node and answering the lower node by the upper node, and the specific synchronization process is as follows:
the time synchronization flow of the upper and lower nodes among the nodes is carried out in 7 time slots of the beginning of the multiframe: firstly, an upper node sends a synchronous frame to a lower node to be synchronized, which is used for determining a target lower node which performs time synchronization at this time, the lower node which receives the synchronous frame starts a subsequent synchronous flow, and the lower node which does not receive the synchronous frame does not execute the subsequent synchronous flow;
time t when the subordinate node receiving the synchronous frame clocks the local clock face son_send After filling in the request frame, the request frame is sent to the upper-level clock node, and the upper-level node utilizes the received clock face time t of the front edge sent by the lower-level node son_send Time t from receipt of the request frame leading edge father_arrive Calculating a local pseudo-range t α ：
t α ＝t father_arrive -t son_send
Time t of local clock face by upper node father_send With local pseudo-range t α Filling the response frame and sending the response frame back to the subordinate node; the lower node uses the clock face time t of the front edge sent by the received upper node father_send Time t from receipt of the sync frame preamble son_arrive Calculating a local pseudo-range t β ：
t β ＝t son_arrive -t father_send
The subordinate node is based on the measured local pseudo-range t β Receiving a local pseudo-range t of a superior node α The clock difference delta t between two nodes can be calculated:
Δt＝(t α -t β )/2
and adjusting the clock, wherein the time of the lower node is added with delta t to realize the time synchronization of the lower node and the upper node.
In the self-organizing network time synchronization method based on agile beam pointing, the upper node synchronization time slot antenna pointing and receiving and transmitting state switching flow is as follows:
the time-synchronous upper node sends a synchronous broadcast frame in a synchronous time slot 1, the receiving and transmitting state and the pointing angle of a phased array antenna of the time-synchronous upper node are set in the previous time slot, and the synchronous frame is sent at the starting moment of the synchronous time slot 1;
the synchronous time slot 2-the synchronous time slot 4 are all in a receiving state, a synchronous request frame sent by a subordinate node is received, the receiving and transmitting state and the antenna direction of the synchronous request frame are set in the synchronous time slot 1, and the synchronous time slot 2 is carried out before arriving through the notification of an antenna wave position switching signal;
the synchronous time slot 5 is in a transmitting state, and the upper node sets an antenna pointing and receiving state in the synchronous time slot 4 according to the received synchronous request frame and transmits a synchronous response frame to the lower node; if the synchronous request frame is not received in the preamble receiving time slot, the synchronous response frame is not sent in the time slot;
the synchronous time slot 6 is used for waiting for the subordinate node to receive the synchronous response frame, setting a synchronous state and not transmitting data;
and the synchronous time slot 7 inquires a service data time slot table, determines a subsequent service sending object, and sets corresponding antenna pointing and receiving and transmitting states to complete subsequent service data receiving and transmitting.
In the self-organizing network time synchronization method based on agile beam pointing, the lower node synchronization time slot antenna pointing and receiving and transmitting state switching flow is as follows:
the lower node is in a full receiving state when in an unsynchronized state, and the antenna direction of the lower node always points to the upper node;
after receiving the synchronous broadcast frame, setting an antenna of the synchronous broadcast frame to be in a transmitting state, and transmitting a synchronous request frame after the antenna finishes the calculation of the pointing angle;
after the synchronization request frame is sent, setting an antenna to a receiving state, and waiting for receiving a synchronization response frame sent by a superior node;
after receiving the synchronous response frame sent by the upper node, calculating the clock difference between the nodes according to the pseudo code synchronous principle, correcting the local time, completing time synchronization and establishing a local super frame time slot;
and inquiring a service data slot table in the synchronous slot 7, determining a subsequent service sending object, setting corresponding antenna pointing and receiving and transmitting states, and completing subsequent service data receiving and transmitting.
The invention has the following advantages:
(1) The invention discloses a self-organizing network time synchronization method based on agile wave beam pointing, nodes adopt a pre-injection time topology mode to determine the upper and lower time transfer relationship between the nodes, engineering realization is simple, and the complex situation that pointing objects cannot be confirmed between the nodes in the early stage of time synchronization is avoided; meanwhile, the global topology optimization is convenient to develop, the node with the most centrality can be selected as a time reference, the time transmission series is reduced, the error accumulation is reduced, and the time synchronization precision is improved.
(2) The invention discloses a self-organizing network time synchronization method based on agile wave beam pointing, wherein non-time reference nodes continuously point to time reference nodes in a receiving state before being out of synchronization, and wait for synchronous polling of the time reference nodes, thereby reducing the complexity of the coordination of the pointing of a receiving end and a transmitting end before the establishment of the synchronous state and avoiding the conflict of the receiving state.
(3) The invention discloses a self-organizing network time synchronization method based on agile wave beam pointing, which enables nodes to efficiently utilize synchronous time slots by designing a time step-by-step transmission method, and transmits a time synchronization state to a lower node in a non-self synchronous time slot, thereby avoiding synchronization signal conflict, effectively solving the problem of multi-node synchronization and finally completing whole network time synchronization.
(4) The invention discloses a self-organizing network time synchronization method based on agile beam pointing, which designs 7 synchronization time slots in order to overcome the postamble of phased array antenna control and consider signal transmission delay and timing errors in time slot arrangement, so that upper and lower nodes can accurately complete three-time synchronization handshake before non-synchronization, and signal receiving and transmitting conflict is avoided.
Drawings
FIG. 1 is a flowchart of a method for time synchronization of an ad hoc network based on agile beam pointing in an embodiment of the present invention;
fig. 2 is a schematic diagram of a superframe structure according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a co-multiframe structure in an embodiment of the present invention;
FIG. 4 is a schematic diagram of a synchronous broadcast frame structure according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a synchronization request frame structure according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of a synchronous acknowledgement frame structure according to an embodiment of the present invention;
FIG. 7 is a flow chart of node initialization and node synchronization topology validation in accordance with an embodiment of the present invention;
FIG. 8 is a time-synchronized progressive delivery flow chart in an embodiment of the invention;
FIG. 9 is a flowchart of a time synchronization interaction between upper and lower nodes according to an embodiment of the present invention;
FIG. 10 is a schematic diagram of a mechanism for controlling a time slot of a higher node according to an embodiment of the present invention;
fig. 11 is a schematic diagram of a lower node timeslot control mechanism according to an embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the embodiments of the present invention disclosed herein will be described in further detail with reference to the accompanying drawings.
One of the core ideas of the invention is: phased array agile beam antennas are used at both ends (such as a transmitting end and a receiving end) of a high-rate data link, and a reasonable solution is provided for the initial time synchronization problem of the networking of the star group ad hoc network by combining a TDMA (Time Division Multiple Access) mechanism. The directional gain across the link provides more link power margin to support space-to-air, space-to-ground, higher data rates and longer range communications. It can greatly reduce the strength of the radio frequency signal in unwanted directions, alleviating the susceptibility of the receiver to interference (although this depends to some extent on the side lobe characteristics of the antenna). Finally, because the directional gain of the antenna determines the space suppression characteristic of the radiation energy, a plurality of pairs of nodes can occupy the same space-time-frequency domain resource without interference.
As shown in fig. 1, in this embodiment, the method for time synchronization of an ad hoc network based on agile beam pointing includes:
(1) Starting a time synchronization function after each satellite node is started, wherein the network synchronization topology adopts a mode of node identity pre-configuration;
(2) The non-reference node keeps a monitoring state before receiving the synchronous message, and the phased array wave beam always points to the reference node; after the power-on, the reference nodes respectively point to the non-reference nodes in a polling mode and send time synchronous broadcasting;
(3) After confirming the synchronous time slots of the non-reference nodes and the reference nodes, the rest time slots are used for polling other next-stage child nodes which cannot be directly connected with the reference nodes;
(4) When a next-level child node is polled, the next-level child node keeps a silent state, after receiving a synchronous polling frame of an upper-level node, the synchronous time slot position of the next-level child node is confirmed, the next-level child node is polled in other asynchronous time slots, and the like, so that the selection and timing of synchronous time slots of all nodes in the network are completed;
(5) According to the control characteristics of the phased array antenna, 7 time slots are arranged for synchronization information interaction per non-reference node. The time slot 1 is used for the upper node to send synchronous polling, the time slot 3 is used for the lower node to feed back a synchronous request frame, the time slot 5 is used for the upper node to feed back a synchronous response frame, and the time slots 2 and 4 are used for transmission delay protection, directional calculation of a phased array antenna and wave control execution delay, so that the conflict of receiving and transmitting states is avoided.
In this embodiment, after each satellite node is powered on, its own roles are set as a reference node and a non-reference node according to the synchronization topology parameter that has been uploaded. The reference node establishes a system superframe and determines a receiving and transmitting time slot; all non-reference nodes confirm the upper node and the lower node in the synchronous topology, and all lower nodes lead the antenna to always point to the upper node and maintain a receiving state before the time synchronization with the upper node is completed, and wait for receiving the self-owned synchronous frame sent by the upper node; the antenna orientation is calculated by the phased array antenna according to the present star orbit and the target star orbit.
In this embodiment, the time-step-by-step transfer procedure of the node in the unsynchronized state is as follows: the node antenna points to the upper node all the time and waits for a synchronous frame from the upper node; after one synchronous interaction with the upper group of nodes is completed, the local time is updated, and the synchronous state is entered.
In this embodiment, the time-step-by-step transfer procedure of the node in the synchronous state is as follows: judging whether the current multiframe is a synchronous maintenance multiframe of the node to an upper node; if yes, controlling the phased array antenna to point to an upper node, and waiting for a synchronous frame from the upper node; if not, controlling the phased array antenna to sequentially point to the lower node, and sending a synchronization frame to the lower node so as to trigger a synchronization flow; the upper node and the lower node complete time synchronization process interaction, and the lower node adjusts the local clock.
In this embodiment, the time synchronization process of the upper node and the lower node is divided into three processes of sending a synchronization frame by the upper node, sending a request frame by the lower node, and replying to the lower node by the upper node, and the specific synchronization process is as follows:
the time synchronization flow of the upper and lower nodes among the nodes is carried out in 7 time slots of the beginning of the multiframe: firstly, an upper node sends a synchronization frame to a lower node to be synchronized, the synchronization frame is used for determining a target lower node which performs time synchronization, the lower node which receives the synchronization frame starts a subsequent synchronization process, and the lower node which does not receive the synchronization frame does not execute the subsequent synchronization process.
Time t when the subordinate node receiving the synchronous frame clocks the local clock face son_send After filling in the request frame, the request frame is sent to the upper-level clock node, and the upper-level node utilizes the received clock face time t of the front edge sent by the lower-level node son_send Time t from receipt of the request frame leading edge father_arrive Calculating a local pseudo-range t α ：
t α ＝t father_arrive -t son_send
Time t of local clock face by upper node father_send With local pseudo-range t α Filling the response frame and sending the response frame back to the subordinate node; the lower node uses the clock face time t of the front edge sent by the received upper node father_send Time t from receipt of the sync frame preamble son_arrive Calculating a local pseudo-range t β ：
t β ＝t son_arrive -t father_send
The subordinate node is based on the measured local pseudo-range t β Receiving a local pseudo-range t of a superior node α The clock difference delta t between two nodes can be calculated:
Δt＝(t α -t β )/2
and adjusting the clock, wherein the time of the lower node is added with delta t to realize the time synchronization of the lower node and the upper node.
In this embodiment, the switching flow of the uplink node synchronous slot antenna pointing and receiving state is as follows: the time-synchronous upper node sends a synchronous broadcast frame in a synchronous time slot 1, the receiving and transmitting state and the pointing angle of a phased array antenna of the time-synchronous upper node are set in the previous time slot, and the synchronous frame is sent at the starting moment of the synchronous time slot 1; the synchronous time slot 2-the synchronous time slot 4 are all in a receiving state, a synchronous request frame sent by a subordinate node is received, the receiving and transmitting state and the antenna direction of the synchronous request frame are set in the synchronous time slot 1, and the synchronous time slot 2 is carried out before arriving through the notification of an antenna wave position switching signal; the synchronous time slot 5 is in a transmitting state, and the upper node sets an antenna pointing and receiving state in the synchronous time slot 4 according to the received synchronous request frame and transmits a synchronous response frame to the lower node; if the synchronous request frame is not received in the preamble receiving time slot, the synchronous response frame is not sent in the time slot; the synchronous time slot 6 is used for waiting for the subordinate node to receive the synchronous response frame, setting a synchronous state and not transmitting data; and the synchronous time slot 7 inquires a service data time slot table, determines a subsequent service sending object, and sets corresponding antenna pointing and receiving and transmitting states to complete subsequent service data receiving and transmitting.
In this embodiment, the following switching flow of the synchronous slot antenna pointing and receiving state of the subordinate node is as follows: the lower node is in a full receiving state when in an unsynchronized state, and the antenna direction of the lower node always points to the upper node; after receiving the synchronous broadcast frame, setting an antenna of the synchronous broadcast frame to be in a transmitting state, and transmitting a synchronous request frame after the antenna finishes the calculation of the pointing angle; after the synchronization request frame is sent, setting an antenna to a receiving state, and waiting for receiving a synchronization response frame sent by a superior node; after receiving the synchronous response frame sent by the upper node, calculating the clock difference between the nodes according to the pseudo code synchronous principle, correcting the local time, completing time synchronization and establishing a local super frame time slot; and inquiring a service data slot table in the synchronous slot 7, determining a subsequent service sending object, setting corresponding antenna pointing and receiving and transmitting states, and completing subsequent service data receiving and transmitting.
In summary, the invention discloses a self-organizing network time synchronization method based on agile beam pointing, which controls beam follow-up pointing of each receiving node to a transmitting node according to receiving and transmitting requirements of each node, designs a certain number of synchronization time slots in time slot arrangement, respectively controls beam pointing of master and slave nodes in advance reservation mode in combination with use requirements of phased array antennas, orderly completes interaction of synchronization signaling in each synchronization time slot, and realizes time synchronization among nodes. Meanwhile, in the time slot arrangement of the multiframe, each node respectively completes time synchronization with the master node in a polling mode, and finally, the whole network time synchronization is realized. A stable and high-precision multi-node self-organizing network synchronization scheme is provided for a network communication system adopting a TDMA system.
On the basis of the above-described embodiments, the following is explained with an example.
In this embodiment, a method for synchronizing time of an ad hoc network based on agile beam pointing is provided, including the following steps:
(1) And starting a time synchronization function after the node is started.
(2) And uploading the position parameters of other nodes in the network to the phased array antenna of each node.
(3) Each node determines the own role as a time reference node or a non-time reference node according to the pre-annotating role information.
(4) The non-reference node sets the antenna receiving and transmitting state as a normal receiving state; the reference node establishes a system superframe and determines a transceiving time slot.
(5) And each antenna calculates the pointing angle of the phased array antenna of the satellite to other satellites according to the received orbit parameters of the satellite broadcast and the orbit parameters of other satellites in the network of the ground surface injection.
(6) All non-reference nodes are provided with antennas which always point to the reference nodes; the reference node setting antennas are sequentially directed to the non-reference nodes to be synchronized.
(7) After the reference node selects a non-reference node to be synchronized, firstly, a synchronization frame is sent to the non-reference node to instruct the non-reference node to start ranging and time comparison with the reference node.
(8) The non-reference node sends a request frame to the reference node, and the reference node feeds back a response frame.
(9) And the non-reference node calculates clock difference according to the ranging result, adjusts the to-be-ground clock and establishes a time slot structure consistent with the reference node.
(10) And by analogy, the reference nodes select non-reference nodes to be synchronized in the synchronous time slots of each multiframe respectively according to the method, and the non-reference nodes complete time synchronization signaling interaction with other non-reference nodes through synchronous frame indication to complete time synchronization.
(11) Nodes that are not visible to the reference node one hop continue to silence awaiting synchronized polling by the superordinate node.
(12) After the primary non-reference node determines the self-synchronization time slot, the other synchronization time slots are sequentially pointed to the lower child nodes, and synchronous polling is sent to perform time synchronization, so that the step-by-step transmission of the time synchronization is realized.
(13) And by analogy, according to the pre-injection synchronization topology, all nodes in the network determine the synchronization time slot according to the pre-injection synchronization topology, and complete time synchronization with the upper level, and finally realize time synchronization of the nodes in the whole network.
In this embodiment, a TDMA system needs to be built, and first, a system frame format is designed, all time slot allocations in the system are based on the system frame format, and in units of time, the superframe is longest, and multiple frames are divided under the superframe, where each multiple frame is composed of a synchronization time slot and a data time slot.
In this embodiment, as shown in fig. 2, the designed system frame format is that the superframe is the maximum unit of time slot management, and one superframe of the system is composed of 9 multiframes, the duration of the superframe is 36s, and the duration of the multiframe is 4s; one multiframe comprises 7 synchronous time slots and 25 data time slots, and the multiframe format is shown in fig. 3; the time slot is the minimum time unit of the transceiving control, the time slot length is 125ms, and the time slot consists of four parts of a synchronous sequence SYN, a transmission format indication TFI, data and a guard interval GP. The synchronous time slot is used for bidirectional pseudo code timing; the data time slots are used for communication of traffic data for each node.
In the present embodiment, three frame structures are involved in total:
a) Synchronous broadcast frame structure
The synchronous broadcast frame is used for sending information such as node clock level, reference node and the like, and is used for informing the lower node of starting a synchronous interaction flow by the upper node, and the structure of the synchronous broadcast frame is shown in fig. 4.
Destination address: receiving a destination node ID (8 bits);
transmitting address: transmitting node ID (8 bits);
clock level: transmitting a clock level (8 bits) of the broadcast frame node;
reference node: represents a synchronization reference node ID (8 bits);
multiframe counting: a multiframe count (8 bits) of the node transmitting the broadcast;
CRC: and checking the bit.
b) Synchronization request frame structure
The synchronization request frame is used for the child node to initiate a synchronization flow, and the structure of the synchronization request frame is shown in fig. 5.
Destination address: the MAC address of the receiving node fills in the receiving node address of the synchronous frame;
transmitting address: the MAC address of the transmitting node; filling in the address of the sending node of the synchronous frame;
P/F: a synchronization frame and a feedback frame are identified in a distinguishing mode, and the bit of the synchronization frame is 00;
local clock face: the front edge sending time of the local synchronous frame is used for calculating the epoch of the arrival synchronous frame;
CRC: and checking the bit.
c) Synchronous response frame structure
The synchronization response frame is used for the parent node to respond to the synchronization request of the child node and feed back time information, and the structure of the synchronization response frame is shown in fig. 6.
Destination address: the MAC address of the receiving node fills in the receiving node address of the feedback frame;
transmitting address: the MAC address of the transmitting node; filling in the address of the sending node of the feedback frame;
P/F: the synchronous frame and the feedback frame are identified by distinguishing, and the bit of the feedback frame is 11;
local clock face: the local feedback frame front sending time is used for calculating the arrival feedback frame epoch;
local pseudorange values: and when the synchronous frames sent by other nodes reach the epoch, the local pseudo-ranges corresponding to the other nodes are calculated through local spread spectrum capture, and the frames are sent to the corresponding nodes.
Preferably, the node initialization and node synchronization topology confirmation flow is as follows:
the initialization and information collection process of the node is shown in fig. 7, and the node sets its own roles as a time synchronization reference node and a non-reference node according to the uploaded synchronization topology parameters after being started. The reference node establishes a system superframe and determines a transceiving time slot. All non-reference nodes confirm the upper node and the lower node in the synchronous topology, and all lower nodes lead the antenna to always point to the upper node and maintain the receiving state before the time synchronization with the upper node is completed, and wait for receiving the self-owned synchronous frame sent by the upper node. The antenna pointing direction is calculated by the phased array antenna according to the position of the node and the position of the target node. The nodes in the network do not need to be started according to a specific sequence, and the starting time can be freely arranged; after the node is started, the synchronous state is set to be an asynchronous state, and a time synchronization function is started.
Preferably, the time-synchronized progressive delivery procedure is as follows:
not all nodes can be seen with the reference node in one hop, so the time reference should be gradually diffused from the nodes seen from the reference node in one hop to the whole network according to the connection relation of the synchronous topology, and all nodes in the whole network have a unified time reference, namely, the time synchronization of the whole network is completed.
The time progressive transmission flow is shown in fig. 8, and mainly includes:
the node is in an unsynchronized state: the node antenna points to the upper node all the time and waits for a synchronous frame from the upper node; after one synchronous interaction with the upper group of nodes is completed, the local time is updated, and the synchronous state is entered.
The nodes are in a synchronous state: judging whether the current multiframe is a synchronous maintenance multiframe of the node to an upper node; if yes, controlling the phased array antenna to point to an upper node, and waiting for a synchronous frame from the upper node; if not, controlling the phased array antenna to sequentially point to the lower node, and sending a synchronization frame to the lower node so as to trigger a synchronization flow; the upper node and the lower node complete time synchronization process interaction, and the lower node adjusts the local clock.
Preferably, the time synchronization interaction flow of the upper node and the lower node is as follows:
the time synchronization process of the upper node and the lower node is divided into three main processes of sending a synchronization frame by the upper node, sending a request frame by the lower node and answering the lower node by the upper node, and the specific synchronization flow is shown in fig. 9:
the time synchronization process of the upper and lower nodes among the nodes is carried out in 7 time slots at the beginning of the multi-frame, firstly, the upper node sends a synchronization frame to the lower node to be synchronized, the upper node is used for determining the target lower node carrying out time synchronization, the lower node which receives the synchronization frame starts the subsequent synchronization process, and the lower node which does not receive the synchronization frame does not execute the subsequent synchronization process.
Time t when the subordinate node receiving the synchronous frame clocks the local clock face son_send After filling in the request frame, the request frame is sent to the upper-level clock node, and the upper-level node utilizes the received clock face time t of the front edge sent by the lower-level node son_send Time t from receipt of the request frame leading edge father_arrive Calculating a local pseudo-range t α ：
t α ＝t father_arrive -t son_send
Time t of local clock face by upper node father_send With local pseudo-range t α The filled response frame is sent back to the lower node. The lower node uses the clock face time t of the front edge sent by the received upper node father_send Time t from receipt of the sync frame preamble son_arrive Calculating a local pseudo-range t β ：
t β ＝t son_arrive -t father_send
The subordinate node is based on the measured local pseudo-range t β Receiving a local pseudo-range t of a superior node α The clock difference delta t between two nodes can be calculated:
Δt＝(t α -t β )/2
and the clock is adjusted accordingly, and the time synchronization of the lower node and the upper node can be realized by adding delta t to the time of the lower node.
Preferably, the switching flow of the synchronous time slot antenna pointing and receiving state of the upper node is as follows:
the control of the phased array antenna has certain postwading property, after the pointing object is determined, a control code (the pointing object and the receiving and transmitting state) is required to be sent to the phased array antenna wave control calculation unit for calculating the pointing angle, and after the calculation is finished, the phased array antenna is controlled by switching pulses to finish the execution of the pointing angle and the setting of the receiving and transmitting state. Thus, on a synchronous slot arrangement, 7 slots are employed for accomplishing the synchronous flow interactions. The process flow is shown in fig. 10, and mainly comprises: the time-synchronous upper node sends a synchronous broadcast frame in a synchronous time slot 1, the receiving and transmitting state and the pointing angle of a phased array antenna of the time-synchronous upper node are set in the previous time slot, and the synchronous frame is sent at the starting moment of the synchronous time slot 1; the synchronous time slot 2-the synchronous time slot 4 are all in a receiving state, a synchronous request frame sent by a subordinate node is received, the receiving and transmitting state and the antenna direction of the synchronous request frame are set in the synchronous time slot 1, and the synchronous time slot 2 is carried out before arriving through the notification of an antenna wave position switching signal; the synchronous time slot 5 is in a transmitting state, and the upper node sets an antenna pointing and receiving state in the synchronous time slot 4 according to the received synchronous request frame and transmits a synchronous response frame to the lower node. If the synchronous request frame is not received in the preamble receiving time slot, the synchronous response frame is not sent in the time slot; the synchronous time slot 6 is used for waiting for the subordinate node to receive the synchronous response frame, setting a synchronous state and not transmitting data; and the synchronous time slot 7 inquires a service data time slot table, determines a subsequent service sending object, and sets corresponding antenna pointing and receiving and transmitting states to complete subsequent service data receiving and transmitting.
Preferably, the switching flow of the synchronous time slot antenna pointing and receiving state of the lower node is as follows:
similar to the upper node time slot control mechanism, the lower node synchronous time slot antenna pointing and receiving state switching flow is shown in fig. 11, and includes the following steps: the lower node is in a full receiving state when in an unsynchronized state, and the antenna direction of the lower node always points to the upper node; after receiving the synchronous broadcast frame, setting an antenna of the synchronous broadcast frame to be in a transmitting state, and transmitting a synchronous request frame after the antenna finishes the calculation of the pointing angle; after the synchronization request frame is sent, setting an antenna to a receiving state, and waiting for receiving a synchronization response frame sent by a superior node; after receiving the synchronous response frame sent by the upper node, calculating the clock difference between the nodes according to the pseudo code synchronous principle, correcting the local time, completing time synchronization and establishing a local super frame time slot; and inquiring a service data slot table in the synchronous slot 7, determining a subsequent service sending object, setting corresponding antenna pointing and receiving and transmitting states, and completing subsequent service data receiving and transmitting.
Although the present invention has been described in terms of the preferred embodiments, it is not intended to be limited to the embodiments, and any person skilled in the art can make any possible variations and modifications to the technical solution of the present invention by using the methods and technical matters disclosed above without departing from the spirit and scope of the present invention, so any simple modifications, equivalent variations and modifications to the embodiments described above according to the technical matters of the present invention are within the scope of the technical matters of the present invention.
What is not described in detail in the present specification belongs to the known technology of those skilled in the art.
Claims (8)
1. The self-organizing network time synchronization method based on agile beam pointing is characterized by comprising the following steps:
starting a time synchronization function after each satellite node is started, wherein the network synchronization topology adopts a mode of node identity pre-configuration;
the non-reference node keeps a monitoring state before receiving the synchronous message, and the phased array wave beam always points to the reference node; after the power-on, the reference nodes respectively point to the non-reference nodes in a polling mode and send time synchronous broadcasting;
after confirming the synchronous time slots of the non-reference nodes and the reference nodes, the rest time slots are used for polling other next-stage child nodes which cannot be directly connected with the reference nodes;
when a next-level child node is polled, the next-level child node keeps a silent state, after receiving a synchronous polling frame of an upper-level node, the synchronous time slot position of the next-level child node is confirmed, the next-level child node is polled in other asynchronous time slots, and the like, so that the selection and timing of synchronous time slots of all nodes in the network are completed;
according to the control characteristics of the phased array antenna, 7 time slots are arranged for synchronization information interaction per non-reference node.
2. The method for time synchronization of ad hoc network based on agile beam pointing according to claim 1, wherein slot 1 is used for transmitting synchronous poll from an upper node, slot 3 is used for feeding back a synchronization request frame from a lower node, slot 5 is used for feeding back a synchronization response frame from an upper node, slot 2 and slot 4 are used for transmission delay protection and pointing computation and wave control execution delay of phased array antennas, so as to avoid transmit-receive status collision.
3. The agile beam pointing based ad hoc network time synchronization method of claim 2, further comprising: after each satellite node is started, setting the roles of the satellite nodes as reference nodes and non-reference nodes according to the uploaded synchronous topology parameters; the reference node establishes a system superframe and determines a receiving and transmitting time slot; all non-reference nodes confirm the upper node and the lower node in the synchronous topology, and all lower nodes lead the antenna to always point to the upper node and maintain a receiving state before the time synchronization with the upper node is completed, and wait for receiving the self-owned synchronous frame sent by the upper node; the antenna orientation is calculated by the phased array antenna according to the present star orbit and the target star orbit.
4. The ad hoc network time synchronization method based on agile beam pointing according to claim 3, wherein the time progressive transfer flow of the node in the unsynchronized state is as follows:
the node antenna points to the upper node all the time and waits for a synchronous frame from the upper node;
after one synchronous interaction with the upper group of nodes is completed, the local time is updated, and the synchronous state is entered.
5. The ad hoc network time synchronization method based on agile beam pointing according to claim 3, wherein the time progressive transfer flow of the node in the synchronization state is as follows:
judging whether the current multiframe is a synchronous maintenance multiframe of the node to an upper node;
if yes, controlling the phased array antenna to point to an upper node, and waiting for a synchronous frame from the upper node; if not, controlling the phased array antenna to sequentially point to the lower node, and sending a synchronization frame to the lower node so as to trigger a synchronization flow;
the upper node and the lower node complete time synchronization process interaction, and the lower node adjusts the local clock.
6. The method for time synchronization of ad hoc network based on agile beam pointing according to claim 3, wherein the time synchronization process of the upper node and the lower node is divided into three processes of an upper node sending synchronization frame, a lower node sending request frame and an upper node answering lower node, and the specific synchronization process is as follows:
the time synchronization flow of the upper and lower nodes among the nodes is carried out in 7 time slots of the beginning of the multiframe: firstly, an upper node sends a synchronous frame to a lower node to be synchronized, which is used for determining a target lower node which performs time synchronization at this time, the lower node which receives the synchronous frame starts a subsequent synchronous flow, and the lower node which does not receive the synchronous frame does not execute the subsequent synchronous flow;
time t when the subordinate node receiving the synchronous frame clocks the local clock face son_send After filling in the request frame, the request frame is sent to the upper-level clock node, and the upper-level node utilizes the received clock face time t of the front edge sent by the lower-level node son_send Time t from receipt of the request frame leading edge father_arrive Calculating a local pseudo-range t α ：
t α ＝t father_arrive -t son_send
Time t of local clock face by upper node father_send With local pseudo-range t α Filling the response frame and sending the response frame back to the subordinate node; the lower node uses the clock face time t of the front edge sent by the received upper node father_send Time t from receipt of the sync frame preamble son_arrive Calculating a local pseudo-range t β ：
t β ＝t son_arrive -t father_send
The subordinate node is based on the measured local pseudo-range t β Receiving a local pseudo-range t of a superior node α The clock difference delta t between two nodes can be calculated:
Δt＝(t α -t β )/2
and adjusting the clock, wherein the time of the lower node is added with delta t to realize the time synchronization of the lower node and the upper node.
7. The ad hoc network time synchronization method based on agile beam pointing according to claim 3, wherein the upper node synchronization time slot antenna pointing and transceiving state switching flow is as follows:
the time-synchronous upper node sends a synchronous broadcast frame in a synchronous time slot 1, the receiving and transmitting state and the pointing angle of a phased array antenna of the time-synchronous upper node are set in the previous time slot, and the synchronous frame is sent at the starting moment of the synchronous time slot 1;
the synchronous time slot 2-the synchronous time slot 4 are all in a receiving state, a synchronous request frame sent by a subordinate node is received, the receiving and transmitting state and the antenna direction of the synchronous request frame are set in the synchronous time slot 1, and the synchronous time slot 2 is carried out before arriving through the notification of an antenna wave position switching signal;
the synchronous time slot 5 is in a transmitting state, and the upper node sets an antenna pointing and receiving state in the synchronous time slot 4 according to the received synchronous request frame and transmits a synchronous response frame to the lower node; if the synchronous request frame is not received in the preamble receiving time slot, the synchronous response frame is not sent in the time slot;
the synchronous time slot 6 is used for waiting for the subordinate node to receive the synchronous response frame, setting a synchronous state and not transmitting data;
and the synchronous time slot 7 inquires a service data time slot table, determines a subsequent service sending object, and sets corresponding antenna pointing and receiving and transmitting states to complete subsequent service data receiving and transmitting.
8. The ad hoc network time synchronization method based on agile beam pointing according to claim 3, wherein the following switching flow of the synchronization time slot antenna pointing and transmitting/receiving state of the subordinate node is as follows:
the lower node is in a full receiving state when in an unsynchronized state, and the antenna direction of the lower node always points to the upper node;
after receiving the synchronous broadcast frame, setting an antenna of the synchronous broadcast frame to be in a transmitting state, and transmitting a synchronous request frame after the antenna finishes the calculation of the pointing angle;
after the synchronization request frame is sent, setting an antenna to a receiving state, and waiting for receiving a synchronization response frame sent by a superior node;
after receiving the synchronous response frame sent by the upper node, calculating the clock difference between the nodes according to the pseudo code synchronous principle, correcting the local time, completing time synchronization and establishing a local super frame time slot;
and inquiring a service data slot table in the synchronous slot 7, determining a subsequent service sending object, setting corresponding antenna pointing and receiving and transmitting states, and completing subsequent service data receiving and transmitting.
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