CN106452645B - A kind of group of stars method for synchronizing network time based on cross layer design - Google Patents
A kind of group of stars method for synchronizing network time based on cross layer design Download PDFInfo
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- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
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- H04B7/185—Space-based or airborne stations; Stations for satellite systems
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Abstract
A kind of group of stars method for synchronizing network time based on cross layer design uses spread-spectrum signal system in physical layer, by semiduplex H_2O maser mode in affiliated synchronization time slot, calculates the clock deviation between child node and father node, complete the precise synchronization between node.Network Synchronization management, the broadcast synchronization status information into network are used in MAC layer, and carries out the management of synchronous topology, time synchronization father node selection result is supplied to physical layer and is used for inter-node synchronous, to realize the time synchronization between the whole network node.The method of the present invention is suitable for time synchronization demand between the star of an all kinds of group of stars, does not have special requirement for satellite system, versatile, applied widely, on-board processing is simple, has a good application prospect.
Description
Technical field
The invention belongs to satellite communication fields, are related to a kind of satellite network method for synchronizing time, can be realized complex space
Satellite Networking time synchronization under environment, suitable for time synchronization application between the star of an all kinds of group of stars.
Background technique
The network interconnection can promote the service ability of network to the maximum extent between star, the service range of extended network, effectively
Ground makes up single star existing various deficiencies in orbit, thus the Simulation spatial service system that one perfect in shape and function, performance of building are stable.
A formation group of stars compared to previous constellation for, it is desirable that participate in mutual between each satellite platform of formation flight
Position measurement is more accurate, and Formation Configuration is more stable, simultaneously because information exchange to occur between each satellite platform, therefore
It is required that the clock between each satellite platform is strictly unified, the capacity of will of single satellite platform is stronger.Simultaneously as satellite is compiled
The needs of team's integration transmission are needed between satellite node to obtain relative distance information by precision ranging, and are determined based on this
Determine the length that section is protected in transimission power and frame structure.Therefore high-precision Time and Frequency Synchronization result is obtained to adaptation space-time large span
Aerospace Satellite networking be of great significance.
Theoretically, only realize that the frequency of two clocks is consistent with the clock face moment, could be referred to as time synchronization simultaneously.But by
In the adjustable frequency source of frequency, there are certain unstability, therefore difference can not remain one at the time of two clocks in real work
A constant, there is a certain error for the frequency marking of two clocks of permission, as long as constantly the clock face of two clocks of adjustment is poor, so that clock face difference is exhausted
To value be maintained at one can tolerate in the range of, so that it may think that two clocks have reached the time synchronization of certain precision.
In the wireless self-organization network using TDMA system, the synchronizing process of each child node and host node is generally divided into out
Ring synchronization and two steps of closed-loop synchronization.The broadcast synchronization beacon of host node cycle, after each child node detects sync beacon
Just restarting timing immediately, it is synchronous that here it is open loops.Due to the influence of propagation delay, when netting the timing starting of interior each child node
This is different.If each child node only receives the broadcast of host node without sending data to host node, it is clear that open loop
It is enough for synchronizing.For the propagation delay of link, calibrated by the way of closed-loop synchronization：Synchronization node is in fixed time slot
It is interior that ECHO (echo, for surveying the round-trip measurement frame of one kind that time delay uses) grouping is periodically sent to datum node, and lead to
It crosses local clock counter to start counting, datum node will return to the grouping, synchronous section immediately after receiving ECHO grouping
When point receives the ECHO of reply, clock counter stops counting, and can estimate synchronization node and benchmark according to the count value
The chain-circuit time delay of node, such node can refresh link propagation time delay in real time, and amendment open loop is synchronous.In view of not each
Child node and host node are all visible, therefore each child node selects the higher node of clock stratum as synchronization first
Benchmark, each node can send synchronous code in the synchronization time slot where it, to local clock meter after node receives the code
Number device is calibrated, to expand the area coverage of reference clock.
Using networking transmission plan between the star of TDMA system, each inter-satellite is carried out accurately by master-slave synchronisation mode in cluster
Time synchronization, traditional method of synchronization complete open loop synchronization and the closed-loop synchronization between main and subordinate node by the frame interaction of MAC layer.
Fast to ring in star cluster Satellite Networking project, typical interstellar distance is 10~1300km, and transmission rate is 128kbps~1kbps, is passed through
The frame interaction of MAC layer carries out time synchronization between nodes, and synchronization accuracy can become very poor under so low transmission rate, about
10us-1000us, this is much unable to satisfy the demand of TDMA exact time synchronization.
Summary of the invention
Present invention solves the technical problem that being：A kind of star based on cross layer design is overcome the deficiencies of the prior art and provide
Group network method for synchronizing time carries out the synchronous topology management between star cluster node in MAC layer, in physical layer using the signal of spread spectrum
System realizes the synchronization between node by clock deviation between half-duplex time comparison distance measuring method calculate node.In different transmission speed
Under rate, the spread-spectrum code rate of physical layer is remained unchanged, will not because of transmission rate reduction and bring the evil of timing tracking accuracy
Change.The synchronization, it can be achieved that the whole network time is combined by the way that the synchronous topology management of MAC layer is spread ranging with physical layer, to adopt
Synchronization scheme between providing stable, high-precision star with the group of stars network of TDMA system.
The technical solution of the invention is as follows：A kind of group of stars method for synchronizing network time based on cross layer design, including：
(1) start time synchronization function after each satellite node booting；
(2) the in-orbit Network Synchronization status information for listening to other satellite node broadcast of each satellite node, if satellite node exists
The Network Synchronization status information for not listening to other satellite node broadcast in the time of length is set, then is determined role self
For time reference node；If satellite node has collected the Network Synchronization state of surroundings nodes broadcast within the time of setting length
Information then saves the father that the highest node of clock stratum is chosen to be this satellite time synchronization according to the Synchronization Status Message of collection
Point, while determining oneself to be child node；
(3) for time reference node, the synchronization request that new network access node reports is received in MAC layer, and ring in physical layer
The time synchronization process for the child node that should newly network；Synchronization time slot and time slot are distributed to child node, and in the synchronization of each node
The synchronization request of time slot responses child node, completes the synchronization of the whole network time, and synchronizes management to each child node；
(4) for non-temporal datum node, selected father node is issued to physical layer in MAC layer, and send out in physical layer
Play the time synchronization process with father node；After the completion of time synchronization process, child node is to datum node application synchronization time slot and extensively
Sowing time gap, and interacted in synchronization time slot and father node, maintenance synchronous with father node is completed, realizes the same of the whole network time
Step；
(5) after the completion of the time synchronization process of each satellite node, the Synchronization Status Message of broadcasting satellite node itself is carried out
The diffusion of synchronization time, and management and each father node are synchronized to each child node and synchronize maintenance.
The Network Synchronization status information includes node ID, datum node ID, clock stratum, synchronization time slot occupancy shape
State, wherein node ID refers to that the identifier of this star itself, datum node ID refer to the identifier of the whole network time reference place satellite, clock
Rank refers to this star the location of in Time Transmission, and datum node clock stratum is 0 grade, the satellite section with his a jump connection
The clock stratum of point is 1, and so on, remoter with datum node, clock stratum is lower, and synchronization time slot occupied state refers to entirely
Which synchronization time slot is occupied in super frame period, which is unoccupied.
The time synchronization process, including：
The first step：Child node is by t when local clock faceson_sendAfter inserting synchronization frame, synchronization frame, father node are sent to father node
T when sending the clock face in forward position using the child node receivedson_sendWith the time t for receiving synchronization frame forward positionfather_arriveMeter
Calculate local pseudorange tα：
tα=tfather_arrive-tson_send；
Second step：Father node is by t when local clock facefather_sendWith local pseudorange tαIt is filled up to feedback frame and sends back sub- section
Point, t when child node sends the clock face in forward position using the father node receivedfather_sendWith the time for receiving synchronization frame forward position
tson_arriveCalculate local pseudorange tβ：
tβ=tson_arrive-tfather_send；
Third step：Child node is according to the local pseudorange t measuredβAnd receive the local pseudorange t of father nodeαIt is calculated two
Clock deviation Δ t between node：
Δ t=(tα-tβ)/2；
4th step：The time of child node adds Δ t, completes the time synchronization of child node and father node.
The child node synchronizes management, including：
The first step：The time slot for waiting child node, detects whether the broadcast frame for receiving child node；If receiving child node
Broadcast frame then continue；Counter adds 1 to enter second step if the broadcast frame for not receiving child node；
Second step：The value for judging counter continues if counter is less than or equal to maximum logout thresholding MAX_exit
The broadcast frame of time slot detection child node to child node；If counter be greater than MAX_exit if by this vertex ticks be move back
Net node；
Third step：The ID number of logout child node is sent to father node in traffic frame.
The father node synchronizes maintenance, including：
The first step：The time slot for waiting father node, detects whether the broadcast frame for receiving father node；If receiving father node
Broadcast frame by counter O reset and continue；Counter adds 1 to enter second step if the broadcast frame for not receiving father node；
Second step：The value for judging counter continues if counter is less than or equal to maximum asynchronous thresholding MAX_asyn
Wait the broadcast frame of the time slot detection child node of child node；This node is labeled as if counter is greater than MAX_asyn
Asynchronous node, and restart networking synchronizing process.
The advantages of the present invention over the prior art are that：
(1) in the method for the present invention, system is synchronized using based on semiduplex spread spectrum time of measuring between node, it can be few as far as possible
Interaction bout under, very high synchronization accuracy is provided, the communication resource rare on star is saved.
(2) the method for the present invention synchronizes Topology Management by MAC layer, convenient for using processor on star by cross layer design
The high management algorithm of complexity is run to optimize Topology Management performance；
(3) the method for the present invention carries out ranging using the modulation system of spread spectrum in physical layer, is provided based on hardware circuit higher
Measurement accuracy, avoid space propagation rate from changing influence to measurement accuracy, be finally completed the whole network time synchronization；
(4) the method for the present invention is that each node distributes exclusive synchronization time slot, is initiated by child node, carries out half pair to father node
It is measured to spread spectrum, in a manner of time division multiple acess, provides independent time synchronization channel for nodes multiple in network, avoid synchronous letter
Number conflict, effectively solve multinode stationary problem.
Detailed description of the invention
Fig. 1 is the flow diagram of the method for the present invention；
Fig. 2 is frame structure schematic diagram of the invention；
Fig. 3 is broadcast frame structural schematic diagram of the present invention；
Fig. 4 is synchronous frame stucture schematic diagram of the present invention；
Fig. 5 is feedback frame structural schematic diagram of the present invention；
Fig. 6 is node initializing of the present invention and infonnation collection process schematic diagram；
Fig. 7 is time reference node selection process schematic of the present invention；
Fig. 8 is node of the present invention synchronization and time slot acquisition process schematic diagram；
Fig. 9 is the time synchronization process schematic diagram of range finder module of the present invention；
Figure 10 is the process flow diagram of time reference node of the present invention；
Figure 11 is the process flow diagram of the non-temporal datum node (networking) of the present invention；
Figure 12 is child node management by synchronization flow chart of the present invention；
Figure 13, which is that father node of the present invention is synchronous, maintains flow chart.
Specific embodiment
As shown in Figure 1, being the process flow of cross-layer group of stars method for synchronizing network time of the present invention, following step is specifically included
Suddenly：
(1) start time synchronization function after each satellite node booting；
(2) the in-orbit Network Synchronization status information for listening to other satellite node broadcast, Network Synchronization status information include：Section
Point ID, datum node ID, clock stratum, synchronization time slot occupied state etc.；
Wherein, node ID refers to that the identifier of this star itself, datum node ID refer to the identification of the whole network time reference place satellite
Number, clock stratum refers to this star the location of in Time Transmission, i.e., datum node clock stratum is 0 grade, with his company of jump
The clock stratum of the satellite node connect is 1, and so on, remoter with datum node, clock stratum is lower, and synchronization time slot occupies
State refers to which synchronization time slot is occupied in entire super frame period, which is unoccupied.
(3) if satellite node does not listen to the Network Synchronization state letter of other satellite node broadcast within the sufficiently long time
Breath, then be determined as time reference node for role self；If satellite node saves around having collected within the sufficiently long time
The highest node of clock stratum, then be chosen to be by the Network Synchronization status information of point broadcast according to the Synchronization Status Message of each node
The father node of this star time synchronization determines oneself for child node；
(4) for non-temporal datum node：Selected father node is issued to by the time synchronization Topology Management module of MAC layer
Physical layer；For time reference node：Time synchronization Topology Management module receives the synchronization request that new network access node reports；
(5) for non-temporal datum node：Physical layer initiates the time synchronization process with father node；For time reference section
Point：By the time synchronization process of physical layer response child node；
(6) for non-temporal datum node：To datum node application synchronization time slot and time slot；For time reference section
Point：Synchronization time slot and time slot are distributed to child node；
(7) for non-temporal datum node：And so on, each satellite node according to the above method, respectively in respective synchronization
Time slot is interacted with respective father node, completes maintenance process synchronous with father node, realizes that the high-precision of the whole network time is same
Step.After the completion of the time synchronization process of satellite node, the Synchronization Status Message of broadcasting satellite node itself, for synchronization time
Diffusion, and management is synchronized to each child node.For time reference node：And so on, reference satellite node presses above-mentioned side
Method completes the high-precise synchronization of the whole network time, and to each respectively in the synchronization request of the synchronization time slot response child node of each node
Child node synchronizes management.
Key link therein is described in detail below.
A TDMA system is established, first has to the design of carry out system frame format, all time slot allocations are all in system
It is based on this system frame format, as unit of the time, super frame tim e longest has divided M multi-frame (to guarantee under superframe
Each node has exclusive synchronization time slot, so the value of M should be greater than total satellite node number in satellites formation), each
Multi-frame be made of a synchronization time slot and N number of traffic frame (to make each node there is abundant traffic frame resource to use, N's
Value should be much larger than satellite node number, and e.g., when number of nodes is 8, the value of N can be 256 or 512).
The system frame format that the present invention designs is as shown in Fig. 2, contain M multi-frame in one superframe of system；One multi-frame packet
Containing a synchronization time slot and N number of traffic frame；Synchronization time slot spreads ranging for half-duplex；Broadcast frame is set in traffic frame, is used for
The broadcast of the Synchronization Status Message of each node.
It is related to three kinds of frame structures in the present invention altogether
A) frame structure is broadcasted
Broadcast frame is for information such as sending node clock grade, datum nodes, the selection for child node to father node；Son
Node can send unallocated time slot in broadcast frame requests timeslot number to datum node, and broadcast frame structure is as shown in Figure 3.
Broadcast address：It identifies broadcast frame (5 bit)
Send address：Sending node ID (5 bit)
Clock grade：Send the clock grade (3 bit) of broadcast frame node
Datum node：It indicates synchronization master ID (5 bit)
Multi-frame counts：The multi-frame for sending the node of broadcast counts (5 bit)
CRC：Check bit.
B) synchronous frame stucture
Synchronization frame initiates synchronous process for child node, and structure is as shown in Figure 4.
Destination address：The ID of receiving node fills in the receiving node ID of the synchronization frame；
Send address：The ID of sending node；Fill in the sending node ID of the synchronization frame；
P/F：Synchronization frame and feedback frame distinguishing identifier, the synchronization frame position are 0；
When local clock face：Local synchronization frame forward position issues the moment, reaches synchronization frame epoch for calculating；
CRC：Check bit.
C) frame structure is fed back
Feedback frame is used for the synchronization request of father node response child node, and feedback time information, structure are as shown in Figure 5.
Destination address：The ID of receiving node fills in the receiving node ID of the feedback frame；
Send address：The ID of sending node fills in the sending node ID of the feedback frame；
P/F：Synchronization frame and feedback frame distinguishing identifier, the feedback frame position are 1；
When local clock face：Local feedback frame forward position issues the moment, reaches feedback frame epoch for calculating；
Local pseudorange value：It is calculated when obtaining the synchronization frame arrival epoch that other nodes issue by local spread spectrum acquisition
The corresponding local pseudorange of its node, and binding and layout are sent to corresponding node；
CRC：Check bit.
1) node initializing and infonnation collection process
Initialization and the infonnation collection process of node are as shown in fig. 6, set asynchronous for synchronous regime after node booting
State listens to the synchronized broadcast frame of surroundings nodes sending, can listen to several super frame periods, according to whether receiving broadcast frame judgement
Whether surrounding has synchronizing network.If there is synchronizing network, then the parent information of selection is sent to range finder module, by ranging mould
Block completes the time synchronization process between father node；If surrounding does not have synchronizing network, enter clock reference node selection rank
Section.
After satellite group enters working track, each node can be arranged out freely without being switched in particular order in a group of stars
The machine time；After node booting, asynchronous regime is set by its synchronous regime, and start time synchronization function.
2) time reference node selection process
Time reference node selection process is as shown in fig. 7, mainly include following steps：
The first step：T super frame period of random back (is to listen to the sufficiently long time first, has been deposited with guaranteeing to hear
Network, in addition, the T value of each node be it is determining at random, it is different, it is ensured that always have some node can end first detect
Listen, begin setting up benchmark), and listen to channel whether there is or not broadcast frames.The father node choosing father node if having broadcast frame, and will acquire
ID is sent to range finder module, subsequently completes synchronization time slot acquisition process；Enter second step process if not receiving broadcast frame.
Second step：Broadcast frame is sent on the 1st business time-slot of the 1st multi-frame, the synchronization time slot of range finder module is set
The length of previous synchronization time slot is proposed for the starting of the 1st multi-frame, and is time reference node (each node by this node identification
T super frame period will be listened to, the T of each node is the random value that itself is generated, and is not mutually equal, therefore always have a T most
Small node can be listened to first and be finished, and will be set as benchmark self, and once had on the basis of a node confirmation, other nodes will be same
It walks on this benchmark).What then starting timer (timer length is set as 1 super frame period) listened to that range finder module reports asks
The ID number for seeking network access node distributes time slot and range finder module synchronization time slot if receiving after requesting node ID for the node
(allocation result information will be sent in business time-slot with mode of unicast).
3) node synchronization and time slot acquisition process
Node is synchronous and time slot acquisition is to send the application that networks to father node, by datum node distribution synchronization time slot and
Time slot is completed entirely to enter network process.Detailed process the following steps as shown in figure 8, be made of：
The first step：Receiving this node identification after the broadcast frame of father node is child node, the father node ID that will be synchronized
Range finder module is sent to as parameter and time synchronization timer is set, if range finder module returns to synchronization not in timer time
State then re-starts the first step；Enter second step if range finder module returns to synchronous regime.
Second step：After getting the synchronous regime of range finder module, the time slot allocation result frame for waiting father node to send, record
Datum node distributes to the time slot and synchronization time slot of this node, is sent to range finder module for synchronization time slot as parameter
4) time synchronization process of range finder module
Selected father node is issued to physical layer by the time synchronization Topology Management module of MAC layer, and physical layer initiates half pair
To spread spectrum ranging process it is as shown in Figure 9：
The first step：Master-slave synchronisation process between node carries out in the synchronization frame of 76ms, when child node is by local clock face
tson_sendAfter inserting synchronization frame, superior clock node sends synchronization frame, and host node sends forward position using the child node received
Clock face when tson_sendWith the time t for receiving synchronization frame forward positionfather_arriveCalculate local pseudorange tα：
tα=tfather_arrive-tson_send
Second step：Father node is by t when local clock facefather_sendWith local pseudorange tαIt is filled up to feedback frame and sends back sub- section
Point.T when child node sends the clock face in forward position using the father node receivedfather_sendWith the time for receiving synchronization frame forward position
tson_arriveCalculate local pseudorange tβ：
tβ=tson_arrive-tfather_send
Third step：Child node is according to the local pseudorange t measuredβAnd receive the local pseudorange t of host nodeαIt can be calculated
Clock deviation Δ t between two nodes：
Δ t=(tα-tβ)/2
4th step：And clock is adjusted accordingly, when child node and higher level can be realized plus Δ t in the time of child node
The time synchronization of clock father node.
5) process flow of time reference node
Time reference node mainly completes the distribution of time slot and synchronization time slot, and maintains same with the hop node time
Function is walked, process flow is as shown in Figure 10, mainly includes following steps：
The first step：The multi-frame head where this node is judged whether it is, if it is, by range finder module in even number synchronization time slot
The synchronizing process of new network access node is responded, and the ID number of new network access node is reported to CPU.CPU sends in time slot and broadcasts
Frame.Enter second step if multi-frame where non-node.
Second step：The range finder module of time reference node was maintained in the synchronization of the synchronization time slot response child node of child node
Journey.
Third step：The time slot recycling information that each child node reports is received, CPU is that new network access node distributes time slot and records.
4th step：CPU sends new time slot allocation result in traffic frame.
6) process flow of non-temporal datum node (networking)
The request of non-temporal datum node time slot and synchronization time slot and allocation flow are as shown in figure 11, including following several
A step：
The first step：The multi-frame head where this node is judged whether it is, if so, synchronization time slot of the range finder module in odd-numbered frame
Complete the time synchronization between father node；The time synchronization with new network access node is completed in the synchronization time slot of even frame, and will be entered
The ID number of net node is reported to CPU.Broadcast frame is sent in time slot.Enter second step if multi-frame where non-node.
Second step：Range finder module completes the time synchronization maintenance process with child node in synchronization time slot, and CPU receives other sections
The broadcast frame of point.
Third step：The time slot recycling information that child node reports is received, and reports time slot to recycle information to father node.
4th step：CPU issues new time slot allocation result in business time-slot.
7) child node management by synchronization process
The management by synchronization process of child node is as shown in figure 12, includes following process：
The first step：The time slot for waiting child node, detects whether the broadcast frame for receiving child node；If receiving child node
Broadcast frame then continue；Counter adds 1 to enter second step if the broadcast frame for not receiving child node.
Second step：The value for judging counter continues if counter is less than or equal to maximum logout thresholding MAX_exit
The broadcast frame of time slot detection child node to child node；If counter be greater than MAX_exit if by this vertex ticks be move back
Net node.
Third step：The ID number of logout child node is sent to father node in traffic frame
8) father node is synchronous maintains process
The synchronous of father node maintains process as shown in figure 13, mainly includes following steps：
The first step：The time slot for waiting father node, detects whether the broadcast frame for receiving father node；If receiving father node
Broadcast frame by counter O reset and continue；Counter adds 1 to enter second step if the broadcast frame for not receiving father node.
Second step：The value for judging counter continues if counter is less than or equal to maximum asynchronous thresholding MAX_asyn
Wait the broadcast frame of the time slot detection child node of child node；This node is labeled as if counter is greater than MAX_asyn
Asynchronous node, and restart networking synchronizing process.
The content that description in the present invention is not described in detail belongs to the well-known technique of those skilled in the art.
Claims (5)
1. a kind of group of stars method for synchronizing network time based on cross layer design, it is characterised in that including：
(1) start time synchronization function after each satellite node booting；
(2) the in-orbit Network Synchronization status information for listening to other satellite node broadcast of each satellite node, if satellite node is being set
The Network Synchronization status information for not listening to other satellite node broadcast in the time of length, then when being determined as role self
Between datum node；If satellite node has collected the Network Synchronization state letter of surroundings nodes broadcast within the time of setting length
The highest node of clock stratum, then is chosen to be the father node of this satellite time synchronization by breath according to the Synchronization Status Message of collection,
Determine oneself to be child node simultaneously；
(3) for time reference node, the synchronization request that new network access node reports is received in MAC layer, and new in physical layer response
The time synchronization process of networking child node；Synchronization time slot and time slot are distributed to child node, and in the synchronization time slot of each node
The synchronization request of child node is responded, the synchronization of the whole network time is completed, and management is synchronized to each child node；
(4) for non-temporal datum node, selected father node is issued to physical layer in MAC layer, and physical layer initiate with
The time synchronization process of father node；After the completion of time synchronization process, child node is to datum node application synchronization time slot and when broadcasting
Gap, and interacted in synchronization time slot and father node, maintenance synchronous with father node is completed, realizes the synchronization of the whole network time；
(5) after the completion of the time synchronization process of each satellite node, the Synchronization Status Message of broadcasting satellite node itself is synchronized
The diffusion of time, and management and each father node are synchronized to each child node and synchronize maintenance.
2. a kind of group of stars method for synchronizing network time based on cross layer design according to claim 1, it is characterised in that：Institute
The Network Synchronization status information stated includes node ID, datum node ID, clock stratum, synchronization time slot occupied state, interior joint
ID refers to that the identifier of this star itself, datum node ID refer to that the identifier of the whole network time reference place satellite, clock stratum refer to this
For star the location of in Time Transmission, datum node clock stratum is 0 grade, the clock grade with the satellite node of his a jump connection
Not Wei 1, and so on, remoter with datum node, clock stratum is lower, and synchronization time slot occupied state refers in entire super frame period
Which synchronization time slot is occupied, which is unoccupied.
3. a kind of group of stars method for synchronizing network time based on cross layer design according to claim 1 or 2, feature exist
In：The time synchronization process, including：
The first step：Child node is by t when local clock faceson_sendAfter inserting synchronization frame, synchronization frame is sent to father node, father node utilizes
T when the local clock face that the child node received is sentson_sendWith the time t for receiving synchronization frame forward positionfather_arriveCalculate this
Ground pseudorange tα：
tα=tfather_arrive-tson_send；
Second step：Father node is by t when local clock facefather_sendWith local pseudorange tαIt is filled up to feedback frame and sends back child node, son
T when the local clock face that node is sent using the father node receivedfather_sendWith the time for receiving synchronization frame forward position
tson_arriveCalculate local pseudorange tβ：
tβ=tson_arrive-tfather_send；
Third step：Child node is according to the local pseudorange t measuredβAnd receive the local pseudorange t of father nodeαTwo nodes are calculated
Between clock deviation Δ t：
Δ t=(tα-tβ)/2；
4th step：The time of child node adds Δ t, completes the time synchronization of child node and father node.
4. a kind of group of stars method for synchronizing network time based on cross layer design according to claim 1 or 2, feature exist
In：The child node synchronizes management, including：
The first step：The time slot for waiting child node, detects whether the broadcast frame for receiving child node；If receiving the wide of child node
Frame is broadcast then to continue；Counter adds 1 to enter second step if the broadcast frame for not receiving child node；
Second step：The value for judging counter continues waiting for son if counter is less than or equal to maximum logout thresholding MAX_exit
The broadcast frame of the time slot detection child node of node；If counter be greater than MAX_exit if by this vertex ticks be logout section
Point；
Third step：The ID number of logout child node is sent to father node in traffic frame.
5. a kind of group of stars method for synchronizing network time based on cross layer design according to claim 1 or 2, feature exist
In：The father node synchronizes maintenance, including：
The first step：The time slot for waiting father node, detects whether the broadcast frame for receiving father node；If receiving the wide of father node
Frame is broadcast by counter O reset and is continued；Counter adds 1 to enter second step if the broadcast frame for not receiving father node；
Second step：The value for judging counter continues waiting for if counter is less than or equal to maximum asynchronous thresholding MAX_asyn
The broadcast frame of the time slot detection child node of child node；By this node labeled as non-same if counter is greater than MAX_asyn
Node is walked, and restarts networking synchronizing process.
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