CN109412736B

CN109412736B - Timing synchronization method for narrowband ad hoc network

Info

Publication number: CN109412736B
Application number: CN201811364292.1A
Authority: CN
Inventors: 王丽; 秦秀娟
Original assignee: Beijing Viga Hangtong Technology Co ltd
Current assignee: Beijing Viga Hangtong Technology Co ltd
Priority date: 2018-11-16
Filing date: 2018-11-16
Publication date: 2020-10-27
Anticipated expiration: 2038-11-16
Also published as: CN109412736A

Abstract

The invention discloses a timing synchronization method of a narrow-band ad hoc network, which completes network time synchronization through the self setting of nodes. Meanwhile, the time hierarchy of the whole network is built gradually along with the realization of the synchronization of the network nodes, and a special hierarchy building stage is not needed, so that the time slot synchronization of the whole network can be realized quickly and efficiently.

Description

Timing synchronization method for narrowband ad hoc network

Technical Field

The disclosure relates to the technical field of communication, in particular to a timing synchronization method for a narrowband ad hoc network.

Background

With the development of wireless communication technology and the increasing demand of people for communication anytime and anywhere, Ad hoc networks are receiving more and more attention due to the characteristics that they do not need fixed facility support, networking is fast, and the like. The MAC layer controls the access of the node to the wireless channel, and the requirement of Ad hoc network for transmitting real-time service and anti-interference communication can be met by adopting time division multiple access at the MAC layer. The time slot synchronization is the primary condition for the network node to perform TDMA access, and the TDMA access system can realize collision-free transmission only on the premise of time slot synchronization. Therefore, the key problem for realizing the TDMA access of the multi-hop Ad hoc network is time slot synchronization.

TDMA access divides time into non-overlapping time segments (frames) and then divides the frames into non-overlapping time slots (channels), which have a one-to-one correspondence with users, and distinguishes user signals from different addresses according to the time slots, thereby completing multiple access.

In an Ad hoc network, a common time synchronization method is to search synchronization signals after a node is powered on, select the time of a node with the highest priority from a plurality of searched synchronization signals as reference time, use the node with the highest priority as a master node, and periodically send the synchronization signals of the master node to realize the time synchronization of the whole network.

The disadvantages of the prior art include:

first, the case of master node destruction is not considered. After networking, the master node may be removed from the network due to movement or damage, and a dynamic selection of the master node is required to ensure the normal operation of the TDMA network and the robustness of time synchronization.

Secondly, when the distance of the movement of the nodes in the network is relatively long and the time signal of the other network can be received, the two networks are fused, and the fusion of the two networks is not considered in the scheme.

Disclosure of Invention

In view of the above, the present disclosure is proposed to provide a narrowband ad hoc network timing synchronization method that overcomes or at least partially solves the above mentioned problems.

According to an aspect of the present disclosure, a narrowband ad hoc network timing synchronization method is provided, which includes:

the method comprises the steps that after a narrowband ad hoc network node is started, signals of other nodes are searched in preset time, and if the node receives time synchronization information from other nodes in the preset time, the node carries out time synchronization according to the received information.

If the narrowband ad hoc network node does not receive information from other nodes within the preset time after being started, the node is the first node of the network, the node is set as a main node, and own time synchronization information is sent in a time control time slot.

When the narrowband ad hoc network node competes for a time control time slot, sending self time synchronization information;

and when other nodes receive the time information higher than the local level, updating and synchronizing the local time information.

The narrowband ad hoc network node at the network edge receives signals of other narrowband ad hoc network nodes, and starts a network fusion process when the network fusion condition is determined to be met; the mesh-melting condition comprises: the direct connection number of the main node of the network where the received signal is located is not less than that of the main node of the network;

the network fusing process comprises the following steps:

setting a network-fusing starting network-fusing mark and a network-fusing timer, and transmitting the network-fusing mark in the network;

before the network-fusing timer is overtime, the timing relation of the network is kept, and signals are received and sent according to the timing relation of the network;

and when detecting that the network fusing timer is overtime, searching the synchronous signal again.

When the narrowband ad hoc network node receives a network fusion mark sent by other nodes, a network fusion starting network fusion mark and a network fusion timer are set, and the network fusion mark is spread in the network;

The nodes in the network do not receive the information from the main nodes in the updating period, and elect to generate new main nodes; the election method comprises the following steps:

searching a routing table, obtaining node grades and direct connection number information of each node, and setting the node with the maximum number of the direct connection nodes in a certain time as a main node; the direct connection number information of one node is obtained by receiving time control information from a neighbor node.

The nodes in the network do not receive the information from the main node in the updating period, upgrade the secondary nodes to the main node and start to elect new secondary nodes; the election method comprises the following steps:

searching a routing table, acquiring node grades and direct connection number information of each node, setting the node with the maximum number of the direct connection nodes in a certain time as a main node, and setting the node with the maximum number of the direct connection nodes as a secondary node; the direct connection number information of one node is obtained by receiving time control information from a neighbor node.

Periodically searching a routing table to obtain node levels and direct connection number information of each node, setting the node with the maximum number of direct connection nodes in a certain time as a main node, and setting the node with the maximum number of direct connection nodes as a secondary node; the direct connection number information of one node is obtained by receiving time control information from a neighbor node.

If a narrowband ad hoc network is separated into two sub-networks, the network containing the master node is not affected, and the network without the master node regenerates the master node.

Fusing two narrowband ad hoc networks in the moving process, and selecting a new main node and a new secondary node by comparing the node priority and the direct connection number; the election method comprises the following steps:

According to one or more technical schemes disclosed by the invention, a scheme for timing synchronization of a narrowband ad hoc network is provided, network time synchronization is completed through the setting of nodes, the frame structure designed by the invention is simple, the nodes in the network are synchronized to a specific node, and the safety and reliability of the time synchronization in the network can be ensured. Meanwhile, the time hierarchy of the whole network is built gradually along with the realization of the synchronization of the network nodes, and a special hierarchy building stage is not needed, so that the time slot synchronization of the whole network can be realized quickly and efficiently.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the disclosure. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:

fig. 1 is a schematic flow chart of a timing synchronization method for a narrowband ad hoc network in an embodiment of the present invention;

FIG. 2 is a schematic diagram of node time synchronization according to an embodiment of the present invention;

FIG. 3 is a diagram illustrating a TDMA frame structure according to an embodiment of the present invention;

FIG. 4 is a flowchart illustrating a process of powering off a node according to an embodiment of the present invention;

FIG. 5 is a flowchart illustrating an embodiment of processing a node in an IDLE state;

FIG. 6 is a flow chart illustrating the process of receiving other nodes in a synchronous state according to an embodiment of the present invention;

fig. 7 is a processing flow when no other node is received in the synchronization state according to the embodiment of the present invention.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

The invention provides a design of a timing scheme of a narrow-band ad hoc network, which presets a frame TDMA (time division multiple access) frame structure: the frame structure design is divided into four levels: superframe (super frame), frame (frame), slot (slot), minislot (mslot), superframe consisting of frame, frame consisting of slot, timeslot consisting of minislot 0(mslot0), minislot 1(mslot1) and two transceiving intervals ttg.

The mslot0 channel is used for transmitting data traffic and control signaling (including timing information and routing related information), and for simplicity of design, the mslot0 channel is statically allocated to terminals in a group, mslot0 of each slot is correspondingly allocated to a corresponding terminal, for example, mslot0 of slot0 is allocated to terminal 0, mslot0 of slot1 is allocated to terminal 1, and so on.

Example one

In this embodiment, a time synchronization process of a general narrowband ad hoc network node is taken as an example to describe a network synchronization process. As shown in fig. 1, in which,

step 11, searching signals of other nodes in a preset time after the narrowband ad hoc network node is started;

and step 12, if the node receives the time synchronization information from other nodes within the preset time, the node performs time synchronization according to the received information.

And step 13, if the narrowband ad hoc network node does not receive information from other nodes within a preset time after being started, the node is the first node of the network, the node is set as a main node, and own time synchronization information is sent in a time control time slot.

Example two

In this embodiment, a time synchronization process of a general narrowband ad hoc network node is taken as an example to describe a network synchronization process. As shown in fig. 2, there are 7 nodes provided in one block area, wherein,

after the narrowband ad hoc network node is started, searching signals of other nodes in a preset time, setting the node 5 to have the highest grade, firstly setting the node as a main node, and sending own time synchronization information in a time control time slot;

in the step (b), the

nodes

4, 6 and 7 receive the information sent by the node 5 within the preset time to form a network A, and each node elects the node 5 as a main node of the network A and completes network time synchronization; after the

nodes

1, 2 and 3 are started up, if the nodes do not receive information from other nodes within the preset time, the nodes are set as main nodes, and time synchronization information of the nodes is sent in time control time slots to form a network B, C, D;

and (c) the

nodes

1 and 2 and the

nodes

2 and 3 can mutually receive information sent by the other side, meet network fusion conditions, perform network fusion, and combine the network B after convergence for a period of time, wherein each node selects the node 2 as a main node of the network B due to the maximum number of direct connections of the node 2, and completes network time synchronization. At this time, 2 networks as shown in fig. 2 are formed in the area, and each network performs time synchronization individually.

the network fusing process comprises the following steps:

EXAMPLE III

The present embodiment provides a design of a timing scheme for narrowband ad hoc networks, which presets a frame TDMA, i.e. a structure of a time division multiple access frame: the frame structure design is divided into four levels: superframe (super frame), frame (frame), slot (slot), minislot (mslot), superframe consisting of frame, frame consisting of slot, timeslot consisting of minislot 0(mslot0), minislot 1(mslot1) and two transceiving intervals ttg.

The mslot0 channel is used for transmitting data traffic and control signaling (including timing information and routing related information), and for simplicity of design, the mslot0 channel is statically allocated to terminals in a group, mslot0 of each slot is correspondingly allocated to a corresponding terminal, for example, mslot0 of slot0 is allocated to terminal 0, mslot0 of slot1 is allocated to terminal 1, and so on. The method comprises the following steps:

step A: and searching a network after the node is started, and performing time initial synchronization.

Further, the process of step a may be described as follows:

a1: after the nodes are started, signals of other nodes are searched in a specified time, the nodes are only in a receiving state in the time, the length of the searching time depends on the priority of the nodes, and if all the nodes are started at the same time, the node with the highest priority can become a main node.

A2: if the node receives the information from other nodes within the specified time after being started, the node carries out time synchronization according to the received information.

A3: when the node receives the information with the higher than local time level, the node updates the local time information.

A4: after the initial time synchronization is completed, the node sends out the local time information in the time control time slot (mslot0) corresponding to the node.

A5: if the node does not receive information from other nodes within a specified time after the node is started, the node considers itself to be the first node of the network, sets itself as a master node, and sends its time synchronization information in a corresponding time control time slot (mslot 0).

And B: dynamic tracking of network time synchronization.

Because errors are inevitably existed between local clocks of each node of the network, and clock drift is added, after a certain time, if the accumulated errors exceed the tolerance range of the set protection band, time slot errors are generated. Time synchronization tracking is therefore required. In a TDMA time frame structure, each mslot0 is a time synchronization control slot, and time synchronization tracking may be implemented by nodes in the network transmitting time synchronization information in the time synchronization control slots.

Further, the process of step B may be described as follows:

b1: the node updates when it receives time information above the local level.

B2: nodes contend to transmit time synchronization information to a time control slot (mslot 0).

And C: and (5) network convergence. Since the topology of an Ad hoc network may change as nodes move, network convergence may occur when two networks come close.

Further, the process of step C may be described as follows:

c1: the node at the network edge receives signals of other network nodes, firstly judges whether the network fusion condition is met, and starts the network fusion process if the condition is met.

C2: setting a network-fusing starting mark and a network-fusing timer of the edge node, keeping the timing relation of the network before the network-fusing timer is overtime, and receiving and sending signals according to the timing relation of the network.

C3: after other nodes in the network receive the network-fusing marks sent by the nodes, the network-fusing marks and the network-fusing timer of the other nodes are also set, and the network-fusing marks are transmitted before the network-fusing timer is overtime.

C4: and when the node detects that the network-fusing timer is overtime, the node searches the synchronous signal again.

Step D: primary and secondary node selection and switching

The master node time is a reference for the entire network time, and after networking, the master node may be removed from the network due to movement or damage. In order to ensure the normal operation of TDMA and the robustness of time synchronization, a dynamic selection of the primary node and a simultaneous selection of the secondary node are required. The master node is allowed to dynamically transfer and switch during network operation.

Further, there are three main cases in step D:

d1: the master node is disconnected from the network. The secondary node and other nodes in the network assume this to happen if they do not receive information from the primary node within the update period. And rapidly upgrading the secondary node to the primary node, and starting to elect a new secondary node.

D2: the master node periodically transfers. The topology of an Ad hoc network may change as nodes move. In order to keep the hop count of the master node as small as possible with most nodes in the network and improve the accuracy of time synchronization, the master node needs to be transferred periodically. The specific method comprises the following steps: the routing table is periodically searched to obtain the node level and the direct connection number information of each node, the node with the largest number of direct connection nodes in a certain time is set as a main node, the node with the largest number of direct connection nodes is set as a secondary node, and the direct connection number information of one node can be obtained by receiving time control information from a neighbor node.

D3: master node transfer in network splitting and merging. When a network is separated into two sub-networks, the network containing the master node is not affected, and the network without the master node considers that the master node is separated from the network, and the master node is regenerated. If the two networks are fused in the moving process, two main nodes and secondary nodes appear, and a new main node and a new secondary node are selected by comparing the node priority and the direct connection number.

Example four

The embodiment is the design of a timing scheme of a narrowband ad hoc network, and presets a structure of a TDMA frame, namely a time division multiple access frame, wherein the frame structure design is divided into four levels: super frame, slot, micro slot (mslot), super frame is composed of frames, frame is composed of slots, slot is composed of micro slot 0(mslot0), micro slot 1(mslot1) and two transceiving intervals ttg, and fig. 3 is a schematic structural diagram of TDMA frame. The terminals in the team have three states: a power-off state, an IDLE state and a synchronization state, and the processing of the three states is described in detail below with reference to the flowchart.

Fig. 4 is a flowchart of the node in the power-off state, and when the start time is reached, the node state is set to the IDLE state, and the synchronous search time is set. Fig. 5 is a flowchart of the node in IDLE state.

When the narrowband ad hoc network node receives other node information, updating the node state to be a synchronous state, and updating the parameters of the current node according to the transmitting node: and updating the related information of the primary node related parameters, the secondary node related parameters and the timing parameters.

When the nodes are in a synchronous state, the processing flow is divided into the following situations:

(1) when the node is in a sending state and the sending is finished, updating the node state into a receiving state;

(2) updating the node state to be a sending state when the sending time is reached;

(3) the current node receives information of other nodes, and the specific processing flow is shown in fig. 6;

(4) the current node does not receive the information of other nodes, and the specific processing flow is shown in fig. 6;

further, the step (3) is divided into two cases according to whether the transmitting node and the current node are in the same network:

the first condition is as follows: when the transmitting node and the current node are not in the same network, the node firstly judges whether the network-fusing condition is met, namely the direct connection number of the main node of the received network is not less than the direct connection number of the main node of the network, if the condition is met, the network-fusing process is started, the network-fusing mark and the network-fusing timer of the current node are set, and the timing relation of the network is kept before the network-fusing timer is overtime.

Case two: when the transmitting node and the current node are in the same network, the specific processing flow is shown in fig. 6, and the following processes are performed:

(1) network fusing treatment, which comprises the following specific treatment processes:

firstly, judging whether the network-fusing mark of the received signal is enabled, and if the condition is satisfied, setting the network-fusing mark and the network-fusing timer of the node.

(2) The method comprises the following steps of direct connection updating processing of a main node, and a specific processing flow is as follows:

firstly, judging whether a condition for updating the direct connection number of the main node is met, if the condition is met, updating the direct connection number of the main node, resetting a timer of the direct connection number of the main node, and updating the relevant parameters of the main node.

Updating conditions of the direct connection number of the main node: and the serial number of the direct connection number of the main node of the transmitting node is greater than the serial number of the direct connection number of the main node of the current node.

(3) And (3) directly connecting secondary nodes for updating, wherein the specific processing flow is as follows:

the update sources of the secondary node are three: and receiving secondary node information in the node information, secondary node information in the local node and the local node. And selecting the secondary node by comparing the direct connection numbers of the three nodes.

(4) One-hop neighbor direct connection updating processing, specifically processing flow:

if the receiving node is in the one-hop neighbor table of the local node, resetting the one-hop neighbor timeout timer of the node; if the receiving node is not in the one-hop neighbor table of the local node, the node is added in the one-hop neighbor table and corresponding parameters are set.

(5) Temporary timing updating processing, and the specific processing flow is as follows:

firstly, judging whether a temporary timing updating condition is met, wherein the judging condition is that the timing grade of the node received by the current time slot is greater than the timing grade of the node received by the local node in the current frame. And when the condition is met, updating the temporary timing grade and the reference time as the time information received by the time slot.

The frame is composed of a plurality of time slots, signals sent by a plurality of nodes can be received in each frame, and the timing scheme selects the signal with the highest timing level received in the frame to correct the timing reference of the node, so the timing information with the highest time level received in the frame needs to be buffered.

Further, when the node information is not received, the specific processing flow is as shown in fig. 7:

(1) network convergence timeout processing, which comprises the following specific processing procedures:

and when the network convergence overtime timer of the local node is overtime, updating the node state to be the IDLE state, and starting to search the network again.

(2) And (3) performing lock losing overtime processing, wherein the specific processing process comprises the following steps:

when the lock losing overtime timer of the local node is overtime, whether the node is in the lowest timing level or not is judged firstly, and if the node is in the lowest timing level, the state of the node is updated to be the IDLE state. If not, the node may simply not receive node information higher than its timing level, so the node timing level is set to the lowest and the out-of-lock timeout timer is reset.

(3) The main node direct connection overtime processing comprises the following specific processing procedures:

and under the condition that the main node direct connection number timer is overtime, setting the node timing grade as the lowest, and setting the main node direct connection number information as invalid.

(4) The timeout processing of the one-hop neighbor comprises the following specific processing flows:

and traversing the one-hop neighbor table of the local node, if the one-hop neighbor table has a node with an overtime timer, deleting the node from the one-hop neighbor table, and updating the number of the one-hop neighbors of the node.

(5) The secondary node direct connection overtime processing comprises the following specific processing procedures:

and when the secondary node overtime timer is overtime or the current node is more suitable to be used as the secondary node, setting the current node as the secondary node and updating the related parameters of the secondary node.

(6) Timing overtime processing, the specific processing procedure is as follows:

and when the timing updating time is reached, if the temporary timing grade and the temporary timing reference time are valid, updating the timing reference time and the timing grade, and resetting the temporary timing grade and the temporary reference time to be invalid.

The timing update time may typically be chosen at the end of frame or the start of frame time.

(7) The master node update timeout processing, according to the foregoing description, needs to periodically transfer the master node in order to keep the hop count of the master node as small as possible with most nodes in the network and improve the accuracy of time synchronization. The specific treatment process comprises the following steps:

when the update time of the main node is reached, comparing the direct connection number of the main node and the secondary node, if the secondary node is more suitable to be used as the main node and the secondary node is a local node, setting the secondary node as the main node, and setting the timing grade as the highest grade; if the secondary node is more suitable as the primary node and the secondary node is not the local node, the secondary node is set as the primary node and the timing level is set to be the lowest. And the local node is taken as a secondary node, and the related parameters of the primary node and the secondary node are updated.

In summary, the embodiments of the present invention provide a narrowband ad hoc network timing scheme, where a frame structure designed by the present invention is simple, and a node in a network sends time synchronization information in a corresponding time control slot (mslot0), so that the node in the network is synchronized with a specific node, and the security and reliability of time synchronization in the network can be ensured. The time hierarchy of the whole network is built gradually along with the realization of the synchronization of the network nodes, and a special hierarchy building stage is not needed, so that the time slot synchronization of the whole network can be realized quickly and efficiently.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the disclosure may be practiced without these specific details. In some instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the disclosure, various features of the disclosure are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. However, the disclosed method should not be interpreted as reflecting an intention that: that is, the claimed disclosure requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this disclosure.

Those skilled in the art will appreciate that the modules in the device in an embodiment may be adaptively changed and disposed in one or more devices different from the embodiment. The modules or units or components of the embodiments may be combined into one module or unit or component, and furthermore they may be divided into a plurality of sub-modules or sub-units or sub-components. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the processes or elements of any method or apparatus so disclosed, may be combined in any combination, except combinations where at least some of such features and/or processes or elements are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.

Moreover, those skilled in the art will appreciate that while some embodiments described herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the disclosure and form different embodiments. For example, any of the embodiments claimed in the claims can be used in any combination.

Various component embodiments of the disclosure may be implemented in hardware, or in software modules running on one or more processors, or in a combination thereof. The present disclosure may also be embodied as apparatus or device programs (e.g., computer programs and computer program products) for performing a portion or all of the methods described herein. Such programs implementing the present disclosure may be stored on a computer-readable medium or may be in the form of one or more signals. Such a signal may be downloaded from an internet website or provided on a carrier signal or in any other form.

It should be noted that the above-mentioned embodiments illustrate rather than limit the disclosure, and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. The word "comprising" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The disclosure may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the unit claims enumerating several means, several of these means may be embodied by one and the same item of hardware.

The foregoing is directed to embodiments of the present disclosure, and it is noted that numerous improvements, modifications, and variations may be made by those skilled in the art without departing from the spirit of the disclosure, and that such improvements, modifications, and variations are considered to be within the scope of the present disclosure.

Claims

1. A timing synchronization method for a narrowband ad hoc network is characterized by comprising the following steps:

searching signals of other nodes in a preset time after the narrowband ad hoc network node is started, and if the node receives time synchronization information from other nodes in the preset time, the node performs time synchronization according to the received time synchronization information;

the network fusing process comprises the following steps:

2. The method of claim 1, wherein the method further comprises:

if the narrowband ad hoc network node does not receive information from other nodes within the preset time after being started, the node is the first node of the network, is set as a main node, and sends own time synchronization information in a time control time slot.

3. The method of claim 1, wherein the method further comprises:

4. The method of claim 1, wherein the method further comprises:

5. The method of claim 1, wherein the method further comprises:

6. The method of claim 1, wherein the method further comprises:

7. The method of claim 1, wherein the method further comprises:

8. The method of claim 1, wherein the method further comprises:

9. The method of claim 1, wherein the method further comprises: