CN106879071B - Wireless Mesh network low-delay optimization method based on dynamic time slot allocation - Google Patents
Wireless Mesh network low-delay optimization method based on dynamic time slot allocation Download PDFInfo
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Abstract
The invention provides a wireless Mesh network low-delay optimization method based on dynamic time slot allocation.A node can update own time slot requirement in time according to path information of a data stream by changing the broadcasting sequence of the node in a control frame in Mac algorithm architecture design, and a forwarding node is ensured to obtain a corresponding time slot during time slot allocation; in the time slot competition stage, the path information is added to the related data stream by adjusting the sequence of time slot application in the network, so that the time slot requirement real-time updating of the network node time slot competition stage is completed, and the real-time performance of time slot allocation for the data stream is improved. The network topology information change is timely updated in the broadcast period, so that the node can timely sense and update the network topology change, the overhead of a control protocol is reduced by processing key topology data, and the data transmission efficiency of the whole network is improved.
Description
Technical Field
The invention relates to the technical field of wireless Mesh networks, in particular to a low-delay optimization method of a wireless Mesh network based on dynamic time slot allocation.
Background
The wireless Mesh network generally adopts a Carrier Sense Multiple Access (CSMA) random resource scheduling architecture or a Time Division Multiple Access (TDMA) resource scheduling architecture. Although the network scalability of the CSMA architecture is strong, the problem of hidden terminals cannot be solved, and the collision probability increases with the increase of the number of network nodes, and cannot provide guarantee on end-to-end delay. The TDMA resource scheduling architecture divides channel resources into a plurality of time slots according to time to perform resource scheduling, the protocol design is clear, the problem of hiding terminals can be solved by controlling the interaction of protocols, but the Mac and routing algorithms in the traditional TDMA resource scheduling architecture do not consider the real-time problem of multi-hop data stream and time slot allocation in a Mesh network, and there is room for improvement in time slot allocation efficiency and routing efficiency.
For a wireless Mesh network with a distributed scheduling architecture, a periodic cycle access scheduling mechanism based on time division is adopted, so that the wireless Mesh network has the advantages that a random access scheduling mechanism and a pseudo-random access scheduling mechanism do not have in the aspect of guaranteeing the end-to-end time delay of data. In order to improve the channel resource, i.e. the reuse rate of the time slot, a resource scheduling architecture based on TDMA is generally adopted for the design of a low-latency scheduling architecture of the wireless Mesh network.
The traditional TDMA resource scheduling architecture Mac layer adopts two channel resource allocation methods of fixed time slot allocation and dynamic time slot allocation, the fixed time slot allocation allocates one or more fixed time slots for each node in the Mesh network, and the method is simple and clear in engineering realization, but does not consider the condition that different node time slot requirements are different, so that the problems that the time slot utilization rate is not high and the end-to-end time delay cannot be guaranteed exist. The dynamic time slot allocation does not appoint the number and the position of the fixed time slot for the node, but dynamically allocates the number and the position of the time slot according to the time slot requirement, the service type and the like, a time slot priority design can be used for solving the conflict problem when the time slot position is needed, the design can determine that the time slot can be divided into other time slots with different priorities besides the time slot with the highest priority when a plurality of time slots are needed to be allocated according to the different priorities of each node to the time slot, and aiming at the characteristics of Mesh network data flow, the performance optimization can be carried out on the end-to-end time delay by adopting different time slot priority designs at different time frames.
The traditional dynamic time slot allocation method improves the time slot utilization rate to a certain extent by a method of dynamic allocation after all nodes apply for, but the problem of time slot requirement of a forwarding node in a data stream is not considered during allocation, so that the real-time performance of time slot allocation of the forwarding node in the data stream in the current time frame cannot be ensured, and the end-to-end time delay of data needing multi-hop forwarding cannot be ensured.
The patent application No. 201310108812.3 discloses a channel resource allocation method based on time division multiplexing. By dividing each time slot into a control part and a data part, the control part performs collision-free time slot allocation of a channel by broadcasting and data priority of time slot competition information in a two-hop range, and the time slot allocation method does not consider the time slot requirement of a data stream forwarding node, so that the time slot resources cannot be fully utilized, and the improvement space on the performances such as end-to-end time delay, network throughput and the like is provided.
The patent application No. 201510906203.1 discloses a method for distributed resource allocation in a TDMA-based wireless MESH network. Specifically, the node firstly broadcasts in a two-hop neighbor according to the time slot requirement in a fixed sequence before data transmission, and then dynamically allocates the time slot resources according to the time slot requirement and the load of the node.
The important basis of routing of the routing algorithm of the wireless Mesh network is network topology, for the wireless Mesh network with nodes moving rapidly and high dynamic change of the network topology, topology updating must be accelerated correspondingly, but the acquisition of the complete and detailed network topology is often established on the larger and larger control protocol overhead, the traditional distributed type centerless Mesh network often adopts a mode of flooding broadcasting all the topologies to update the topology, occupies a large amount of precious bandwidth, and the validity of the topology updating cannot be ensured because different establishment time of links in the topology is not taken into consideration, thereby causing adverse effects on the correct execution of the routing algorithm.
The routing algorithm of the wireless Mesh network is divided into heuristic routing and prior routing according to the routing opportunity. The traditional prior routing algorithm only considers network link topology, selects the shortest path according to the hop distance of the path, and does not calculate routing criteria by combining the time slot sequence allocated to the nodes by the Mac layer in the TDMA, and the selected hop shortest path cannot be guaranteed to be the optimal path, so that the data transmission time is greatly increased. The traditional heuristic routing only considers the channel allocation state of the topology during routing, and does not calculate routing criteria aiming at the time slot to be obtained by the dynamic time slot allocation node, so that the optimal routing can not be obtained.
The patent with application number 201310108812.3 discloses a multi-radio frequency multi-channel wireless Mesh network routing method, which considers the load of a forwarding node in a path and the expected transmission time ETT of the path when designing a routing criterion, but only calculates according to the data delivery rate of a link when designing the ETT, and does not consider the time slot distribution dependence property of a wireless Mesh network based on TDMA on the transmission delay, so that the method is not suitable for the design of the wireless Mesh network routing criterion based on time slot distribution.
In the traditional wireless Mesh network, a network layer routing algorithm and a Mac layer are usually designed separately during architecture design so as to reduce the complexity of the architecture design, but the characteristic that a channel scheduling architecture based on dynamic time slot allocation has the dependence on routing is not considered, so that the support degree of the routing algorithm on the Mac layer is often insufficient, and therefore, an optimized space exists in the design of the low-delay wireless Mesh network architecture.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a method for optimizing the media access control MAC of the wireless Mesh network based on the characteristic of dynamic time slot allocation, and further provide a route optimization method based on the optimization of the MAC.
The invention aims to solve the technical problem that a wireless Mesh network low-delay optimization method based on dynamic time slot allocation is characterized in that each node in a wireless Mesh network completes time slot allocation by taking a time frame as a period; the time frame comprises a broadcast 1 time interval, a broadcast 2 time interval and a data frame time interval; the broadcast 1 time interval comprises N broadcast 1 time slots, the broadcast 2 time interval comprises N broadcast 2 time slots, the data frame time interval comprises more than or equal to N data frame time slots, and N is the maximum node number in the wireless Mesh network; each node corresponds to a data frame time slot in the data frame period as a main time slot of the node; each node has different main time slot sequences appointed by the node time slot priority table in different time frames;
each node is correspondingly allocated with a broadcast 1 time slot and a broadcast 2 time slot according to the main time slot sequence of the node in the current time frame in the broadcast 1 time slot and the broadcast 2 time slot; each node broadcasts the time slot requirements and topology changes of the node and the neighbor nodes in each time frame according to the current main time slot sequence to carry out dynamic allocation of the time slots:
1) broadcast 1 period, broadcast slot requirement:
each node generates a 1 st broadcast control frame and broadcasts the 1 st broadcast control frame of the node in a corresponding broadcast 1 time slot, wherein the 1 st broadcast control frame comprises a node ID, the total size of data to be sent and information of each data stream to be sent, the information of each data stream comprises the data size of each data stream, the sending priority of each data stream and the remaining path information of each data stream, and the total size of the data to be sent is the sum of the data sizes of the data streams to be sent in a local broadcast data cache; the local broadcast data cache comprises data stream information to be sent by taking the current node as a source node and data stream information to be forwarded by taking the current node as an intermediate node; when the data stream information to be sent is excessive, so that the length of the 1 st broadcast control frame of the node exceeds the maximum data length of the broadcast 1 time slot sending data, the node puts the data stream information in the maximum data length into the 1 st broadcast control frame according to the sequence of the data stream sending priority from large to small;
the method for calculating the data stream sending priority w comprises the following steps:
w＝α·stream_Length+β·ETT+(1-α-β)·prior
ETT is expected path sending time, prior is the service priority of the data stream, stream _ Length is the data size of the data stream, and alpha, beta are both [0,1] and alpha + beta is less than or equal to 1, which respectively represent the data size of the data stream and the weight coefficient of the expected path sending time;
after receiving the 1 st broadcast control frame sent by other nodes, each node updates a local topology information table according to the received 1 st broadcast control frame, adds the node into a locally maintained one-hop neighbor information table according to a node ID in the 1 st broadcast control frame, and simultaneously checks whether the node is a next forwarding node of the data stream according to the data stream residual path information in the received 1 st broadcast control frame, if so, adds the data size of the data stream, the sending priority of each data stream and the residual path information of each data stream into a local broadcast data cache, and if not, discards the data stream information;
2) broadcast 2 time interval, broadcast neighbor node time slot requirement and topology change:
each node generates a 2 nd broadcast control frame and broadcasts the 2 nd broadcast control frame of the node in a corresponding broadcast 2 time slot, wherein the 2 nd broadcast control frame comprises a node ID, a neighbor node ID, the total size of data to be sent, network topology data and network topology change data; when the network topology data is overlarge, so that the total length of the 2 nd broadcast control frame exceeds the maximum data length sent by the node in the broadcast 2 time slot, the node selects the key topology of the network topology data according to the local topology information table, and selects the key topology to add into the 2 nd broadcast control frame within the maximum data length sent by the broadcast 2 time slot;
after receiving the 2 nd broadcast control frame sent by other nodes, each node updates the node ID in the received 2 nd broadcast control frame to a neighbor list in a local two-hop range, and updates a local topology information table according to the 2 nd broadcast control frame;
3) data frame period, dynamic slot allocation:
obtaining the number of data frame time slots required by the node in the current data frame period according to the total size of data to be sent corresponding to the neighbor nodes in the neighbor list in the local two-hop range:
if the node has no data to send and forward in the current frame, no data time slot is allocated to the node, and the main data frame time slot corresponding to the node is used as an idle time slot; if the node only needs 1 data frame time slot, the main data frame time slot of the node in the current frame period is distributed to the node; if the node needs more than 2 data frame time slots, carrying out idle time slot competition according to the node time slot priority table; if the node is allocated to more than 2 data frame time slots, the node preferentially transmits data which can be forwarded in the current time frame when data transmission is carried out; and the node transmits the data streams in the order of the transmission priority of the data streams from large to small in 1 data frame time slot.
Furthermore, a new method for updating the local topology information table and selecting the key topology is also provided.
In addition, each node carries out routing after completing time slot allocation in one time frame, and the routing refers to the main time slot sequence in the node time slot priority table.
The specific steps of routing are as follows:
s1: checking whether the routing algorithm is operated for the first time in the current frame, if so, clearing a route set and a forwarding load table, and executing the step S2, otherwise, executing the step S3;
s2: calculating a network range which can be reached by the node in a time frame according to network topology data acquired in a broadcast 2 time period, adding all nodes in the range into a route set, wherein the route set comprises an ID of the reached node and a shortest ETT path of the reached node, if a target node is not in the route set, turning to a step S3, if the target node is in the route set, successfully finding a route, adding path information for the data flow, storing the data flow into a data cache to be sent, and updating the load of a transfer node in the path in a transfer load table according to the size of the data flow;
s3: traversing each destination node in the route set according to the breadth priority order, and calculating the reachable nodes in the two time frames by combining the main time slot order in the node time slot priority table of the next time frame and the load condition of the nodes; breadth-first order traversal is a common traversal method in the data structures of trees and graphs;
s4: repeating the step S3 until the destination node is added into the route set to complete the route searching or the route searching fails, if the route searching is completed, adding path information to the data stream corresponding to the destination node, and if the route searching fails, placing the data stream corresponding to the destination node into the data stream cache of the route searching failure.
The invention can lead the node to update the time slot requirement of the node in time according to the path information of the data stream by changing the broadcasting sequence of the node in the control frame in the Mac algorithm architecture design, ensure that the forwarding node obtains the corresponding time slot when the time slot is distributed, improve the utilization rate of channel resources and reduce the sending time delay of the data stream.
The invention adds path information to the related data stream by adjusting the sequence of time slot application in the network in the time slot competition stage, completes the real-time updating of the time slot requirement of the network node time slot competition stage, and improves the real-time performance of time slot allocation for the data stream. The network topology information change is timely updated in the broadcast period, so that the node can timely sense and update the network topology change, the overhead of a control protocol is reduced by processing key topology data, and the data transmission efficiency of the whole network is improved. The method can meet the requirements of different network quality of service (QOS) services by calculating the sending priority of the data stream according to the size of the data stream, the path ETT and different attributes of the service priority.
In the routing algorithm, by a greedy algorithm combined with a time slot allocation table, network topology information updated in time at a broadcast stage in a frame period is combined, and path node load is considered, so that a transmission path with shortest time delay can be found for a data stream, the purpose of load balancing is achieved, and the throughput of the whole network is improved. The routing algorithm selects a data stream transmission path according to the dynamic time slot allocation table, a Mac layer control frame is combined with the dynamic time slot allocation algorithm to update time slot requirements for data stream load nodes in time, and the Mac layer and the routing algorithm complete data transmission in a cross-layer cooperation mode.
The invention has the beneficial effects that: the performance of the whole network in the aspects of data throughput, end-to-end time delay and load balance is improved, the channel resource utilization rate of the wireless Mesh network is obviously improved, the end-to-end time delay of the network is reduced, the method is suitable for a wireless Mesh network scene with a TDMA mode for communication resource scheduling, and the wireless Mesh network architecture design with high dynamic and low time delay is met.
Drawings
FIG. 1 is a flow chart of the architectural design of the present invention;
FIG. 2 is a superframe diagram of a periodic round robin scheduling architecture;
FIG. 3 is an exemplary diagram of a Mesh network; FIG. 4 is a topology upgrade flow diagram;
fig. 5 is a flow chart of a routing algorithm.
Detailed Description
The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the scope of the present invention is not limited to the following.
The optimization flow structure of the invention is shown in fig. 1, topology updating needs to be completed on the Mac layer before the routing algorithm is executed, which is an important basis for ensuring routing effectiveness; meanwhile, because the forwarding node in the transmission path of the data stream needs to transmit the time slot, the time frame routing algorithm is the basis of time slot allocation of the next time frame data stream in the Mac layer, which requires that Mac and routing algorithm are designed cooperatively when low-delay design is performed based on the flow.
As shown in fig. 2, the wireless Mesh network periodic cycle scheduling architecture based on dynamic time slot allocation can regard the channel resource of the time slot as different frames according to functions, and a super frame is composed of L time frames, where L is greater than or equal to N, and values are taken according to network requirements and the design of a time slot priority table.
Each time frame is divided into 3 parts, namely a broadcast 1 period, a broadcast 2 period, a data frame period, wherein the broadcast 1 period and the broadcast 2 period may be generally referred to as a control frame period. The broadcast 1 time interval and the broadcast 2 time interval are divided into N time slots, each node is guaranteed to have one time slot for broadcasting control information, the specific time slot length can be designed according to the scale, topological characteristics and service requirements of a network, a data frame is divided into M time slots, M is larger than or equal to N, and each node is guaranteed to have one main time slot belonging to the node. Each node corresponds to a data frame time slot in the data frame period as a main time slot of the node; the master slot order of the nodes specified by the slot priority table is different in different frames for each node.
M can be designed according to the network's requirements for transmission efficiency η, which is given by the following formula.
Wherein, timebroad1For the length of the time slot in broadcast 1 period, timebroad2For the length of the time slot in broadcast 2-segment, timedetaThe slot lengths in the data frame period each contain a guard interval.
The dynamic time slot allocation process comprises the following steps: the time slot nodes are controlled to broadcast the size of the data to be transmitted of the nodes and the size of the data to be transmitted of the neighbors in turn according to a certain sequence, and a time slot allocation algorithm is applied to complete time slot allocation, so that each node can obtain enough time slot resources under the condition of no channel conflict. The time slot allocation algorithm is combined with a node time slot priority table, in order to ensure the uniformity and fairness of a network channel, a certain regular and predictable adjustment is made on the time slot priority table in each time frame, the result is that the main time slot of the node in each time frame changes, the main time slot is the time slot which is fixedly allocated by the node when the time slot is required, and according to the dynamic time slot allocation algorithm, the end-to-end time delay of the wireless Mesh network can be analyzed in the Mac layer as follows.
As shown in fig. 2, when the data flow path is single-hop, the data end-to-end delay is only on the physical layerThe transmission delay of (2) is generally negligible compared to the forwarding delay, and for the convenience of analysis, the transmission delay on the physical layer is set to 0. The forwarding delay is divided into two cases according to whether there is a data time slot in the current time frame after the forwarding node receives the data, i.e. the forwarding delay TrelayAs shown in equation (2):
wherein, Trelay(i, j) represents the forwarding time delay when the node j is the next hop of the node i in the data stream sending path, the unit is the data time Slot, Slot (j) represents the data time Slot number distributed by the forwarding node j, Slot (i) represents the data time Slot serial number distributed by the data node i, and Slot (j) represents the data time Slot serial number distributed by the data node inext(j) The assigned minimum time slot sequence number of the next time frame node j is shown, and M shows the number of time slots divided by a time frame.
From the formula (2), if the forwarding delay of the data stream is to be reduced, the path sequence of the data stream should be designed as much as possible according to the data time slot sequence of the forwarding node, and the time slot information required by the forwarding node must be broadcasted before the Mac layer performs time slot allocation to ensure that the forwarding node can obtain the data time slot, otherwise, the forwarding delay of the forwarding node must be increased by several time frame periods. Therefore, in order to ensure that forwarding nodes in a data stream transmission path can meet the time slot requirement, in a wireless Mesh network designed by a TDMA scheduling architecture adopting dynamic time slot allocation, the Mac algorithm and the routing algorithm must be considered simultaneously, and specific design targets are as follows:
firstly, the architecture design of the Mac layer needs to ensure that the time slot requirements of the data stream forwarding nodes can be updated in time, maintain a topology updating speed matched with the network attributes, and ensure that the time slot order of the forwarding nodes can acquire the time slot requirement information in time under the condition that the data time slot order meets the forwarding requirements in the current time frame, so that the effective time slot allocation aiming at the multi-hop data stream can be completed.
Secondly, the problem of time slot sequence of forwarding nodes in a path is considered in the routing stage of the network layer routing algorithm of the data stream, so that the effective execution of the Mac layer architecture design can be ensured.
Aiming at the analysis, the invention adopts the following steps to complete the design of the wireless Mesh network low-delay MAC and routing architecture based on dynamic time slot allocation. Each node takes a time frame as a period, and Mac and route design is completed based on dynamic time slot allocation in a TMDA channel mode in each time frame.
S1: broadcasting 1 time interval, and carrying out time slot requirement of broadcasting local nodes according to the sequence of main time slots, wherein the time slot requirement comprises the following substeps:
s11: each node broadcasts the time slot requirement of the data stream according to the main time slot sequence in the time frame;
the broadcast Data broad1_ Data includes its own node ID, total size Data _ Length of Data to be transmitted, Data size stream _ Length of Data stream to be transmitted, Data stream transmission priority w and Data stream remaining path information path, if there are multiple Data streams causing the Length of broadcast broad1_ Data to exceed the maximum Data Length that can be transmitted by a broadcast time slot, then according to the service priority of the Data stream, the size stream _ Length of the Data, and the expected path transmission time ETT, the size of the transmission weight w of the Data stream is sorted and the Data stream information with large weight is selected to be added into the broadcast Data, thus not only ensuring that the notification of the remaining forwarding nodes is not affected to update the time slot requirement information, but also reducing certain control protocol overhead, wherein the transmission weight w of the Data stream is calculated according to the following formula:
W＝α·stream_Length+β·ETT+(1-α-β)·prior (3)
wherein, alpha and beta are [0,1], and alpha + beta is less than or equal to 1, which respectively represent the weight coefficients of stream _ Length and ETT, the expected sending time ETT of the path is calculated by a routing layer when selecting a route for data, and the service priority is calculated according to the service type and service requirement provided by the network. The values of alpha and beta can be flexibly set according to the topological characteristics of the Mesh network, the main data type and the service requirement. For example, when α is 1, it means that only the data size is considered, and the expected transmission time ETT and the data priority of the data flow path are not considered; and when β is 1, it means that only the data flow path expected transmission time ETT is considered, regardless of the data size and the data priority; when α ═ β ═ 0, it means that only the priority level that the data type possesses is considered; other cases may be analyzed as such.
The maximum data Length max _ Length that can be transmitted for one slot is calculated as the following formula (4).
max_Length＝timeslot·Bandphy(4)
Wherein, timeslotFor the length of the time slot, BandphyBandwidth provided to the physical layer of the node.
When constructing the broad1_ Data, the node may screen the Data stream information according to the node time slot priority table in the current time frame, if the next forwarding node of the node in the Data stream path has broadcast the broad1_ Data, it indicates that the Data stream is not forwarded by the main time slot of the next forwarding node in the current time frame, and the next forwarding node does not necessarily have other time slots capable of completing forwarding, so that the Data stream is considered not to be eligible for being included in the broad1_ Data for forwarding notification.
The total size Data _ Length of the Data to be transmitted represents the size of the Data to be transmitted of the node in the cache to be transmitted, and is in bytes. The data flow remaining path information path contains a remaining path from the next hop of the node.
S12: after receiving the broadcast control frame 1 broadcast 1_ Data sent by other nodes, the node needs to complete the update of the two contents. 1) The node is added into a one-hop neighbor information table maintained by the node according to the node ID in the 1 st broadcast control frame broad1_ Data, so that after the broadcast 1, all nodes can acquire the one-hop neighbor node of the node.
2) And meanwhile, checking whether the Data stream is the next forwarding node of the Data stream according to the Data stream surplus path information path in the first broadcast control frame broad1_ Data, if so, adding the Data size stream _ Length, the surplus path and the Data stream sending weight w information of the Data stream into a local broadcast Data cache, otherwise, indicating that the Data stream does not need to be forwarded by the node, and discarding the Data stream information. The node broadcasts the information in the local broadcast Data buffer and the Data stream information as the source node as the 1 st broadcast control frame broadcast 1_ Data in the broadcast 1 time slot belonging to the node.
After receiving the broadcast control frame 1 broadcast 1_ Data sent by other nodes, the node updates the one-hop neighbor of the local topology information table.
If a node has already finished step S11, meaning that its master slot is ranked before the rest of the non-broadcasted node master slots, and it will not assume the Data stream forwarding tasks of the rest of the nodes whose master slot is ranked behind it, then in this step it only needs to complete the part described above under 1), i.e. update the neighbor nodes, as can also be seen from the screening flow analysis of broad1_ Data in step S11.
Considering the topology in fig. 3, assuming that the master timeslot of each node in the current time frame is the node ID, after the node 3 completes sending its own broadcast 1_ Data, in the next broadcast 1 timeslot, it will not appear as a forwarding node in the Data flow path of the broadcast 1_ Data of the remaining nodes 4, 5, 6, 7, 8, because its Data master timeslot 3 is before the Data master timeslot of the nodes 4, 5, 6, 7, 8, at this time, the node 3 only needs to update its own neighbor information according to the broadcast 1_ Data.
That is, when the node has not broadcast its own broadcast 1_ Data, it needs to complete the above-mentioned operations of contents 1) and 2) every time it receives a broadcast 1_ Data, and only needs to complete the operations of contents 1) and 1) after it completes broadcast of broadcast 1_ Data, so that it can reduce the Data processing amount of a large part of nodes.
It can be seen from the above analysis that the later the master time slot sequence of a node is, the higher the probability that the node assumes forwarding tasks is, so that different master time slot sequences used in different time frames in a superframe can play a certain load balancing role.
S2: broadcasting the time slot 2, and broadcasting the time slot requirement and topology change information of the neighbor nodes in the self broadcasting 2 time slot according to the sequence of the main time slot, comprising the following substeps:
s21: the time slot requirement and the topology change of the neighbor node are borne in the 2 nd broadcast control frame broad2_ Data, the time slot requirement is embodied by the total size Data _ Length of Data to be sent, and the topology change is embodied by the network topology Data topology and the network topology change topology _ change. Each node broadcasts the time slot demand information of its own neighbor according to the main time slot sequence in its own time frame, and broadcasts the network topology data topology and the network topology change topology _ change maintained by itself according to its neighbor information. The 2 nd broadcast control frame broad2_ Data comprises its own node ID, neighbor node ID, total Data size to be sent Data _ Length, network topology Data topology and network topology change topology _ change, if the total Length of the broad2_ Data exceeds the maximum Data Length which can be sent by the broadcast time slot, the topology Data is compressed, and the key topology Data is selected to be added into the broadcast Data broad2_ Data.
S22: after receiving the broad2_ Data sent by the neighbor, the node updates the neighbor node information to its own neighbor list in the two-hop range according to the time slot requirement information of the broad2_ Data, and updates its own maintained topology information Table topologic _ Table according to the neighbor information and topology Data.
In the design of topology _ Table, a weight TL (time of living) is attached to each link to represent the degree of recency of the link information acquisition, and the TL value is defined as follows:
in addition, for the wireless Mesh network node in the architecture design, the node maintains one topology information Table topology _ Table to represent the peripheral network topology condition detected by the node, and the data structure of the topology information Table topology _ Table is represented by an adjacency matrix. In order to reduce the bandwidth occupied by the topology updating data, the following two cases are processed:
firstly, when a new node appears in a one-hop neighbor node of a node, topology notification is performed in a manner of broadcasting all topology data, because when a new node appears in a neighbor, it indicates that the new node has not received topology information broadcasted before the node, so that it is impossible to perform superposition update of variables on the previous basis, and therefore, all topology information must be transmitted. Since the slot requirement information of the neighbor already includes a part of topology information, the topology _ Table can remove the part of topology in the slot requirement information of the neighbor, so as to save the channel bandwidth occupied by the topology information. In addition, the topology acquired in the current time frame is identified separately, which indicates that the topology has higher reliability.
Since topologyTable is a data structure of a Graph, the Graph is a set of vertices and edges, i.e., Graph { Vertex, Edge }. In the data structure representation of the graph, the adjacent matrix representation structure is visual and clear, the searching and inserting algorithm is simple, and the square of the number of nodes in the occupied data storage space network is in direct proportion. The adjacency list data structure represents that the occupied data size is in direct proportion to the connectivity of the topological graph along with the number of nodes of the topological graph, so that the occupied storage space is smaller than that of the adjacency matrix data structure, but the searching speed is not higher than that of the adjacency matrix data structure. In summary, the local topology Data maintained at the node is represented by an adjacency matrix Data structure, which can reduce the time complexity in processing some algorithms related to the topology, and the topology Data in broad2_ Data is represented by an adjacency list Data structure, so as to reduce the overhead of the control protocol.
Secondly, when no new node appears in a one-hop neighbor node of the node, the broadcast notification only needs to be performed on the broadcast topology Change information topology _ Change, so that the neighbor node can complete topology update on the basis of receiving the topology information sent by the node before and reduce the size of the broadcast topology data. The Change of the topology is reflected in the addition or the reduction of the edges in the topology map, corresponding to the establishment and the loss of the links in the wireless Mesh network, so that the data of topology _ Change comprises two types of edges, an increased edge and a reduced edge.
In the step S1, the node may acquire the information of the neighboring nodes of one hop around itself and the time slot requirement information updated in time by the neighboring nodes of one hop with respect to the data stream, so that the information is broadcasted in the broadcast 2 period, and when the neighboring nodes receive the information sent by the neighboring nodes around itself, the neighboring nodes can acquire the neighboring information and the time slot requirement in the range of 2 hops, which forms the data base of dynamic time slot allocation.
The step of performing topology update according to the topology Data in broad2_ Data is shown in fig. 4:
(1) adding 1 to all TL which are not 0 in the topology _ Table at the beginning of the broadcast 1 time period, wherein the detection time of all topologies is increased by 1 time frame;
(2) updating two topologies in two ranges according to the neighbor _ Info received in the broadcast 2 period S21, wherein the TL values of the topologies are 1;
(3) when broadcast Data broad2_ Data is received in broadcast 2 period, the topology is updated according to neighbor information and topology information (topology or topology _ Change), the latest topology is adopted during updating, only when the received topology TL value is smaller than the TL value in the topology _ Table of the node or the TL value in the topology _ Table of the node is 0, the latest ascertained link is used as the reference, and when the deleted link is received<m,n>When the topology information of (1) is obtained, TL is addedmnIt is set to 0.
(4) Setting a threshold TL for TL according to actual change characteristics of actual network topologymaxWhen TL exceeds the value of TL in the topologymaxIndicating that the topology already has TLmaxIf the time frame is not updated, the link may be considered to be expired and invalid, and the corresponding TL value is set to 0.
According to the topology updating algorithm and the definition of topology _ Table, it can be seen that the smaller the TL value is, the stronger the real-time performance of the topology is, thus, the definition of the key topology is designed according to the topology _ Table, so that the reasonable selection is conveniently carried out during topology data broadcasting. I.e. the critical topology data is selected in the following steps:
(1) taking the node as a source node, taking a TL value which is not 0 in topology _ Table as a weight of a side, adopting a prim minimum spanning tree algorithm in graph theory to construct a minimum spanning tree, wherein all topologies in the minimum spanning tree are key topology data with highest priority, and according to the definition of the minimum spanning tree, if the topologies are connected graphs, selecting a link represented by an N-1 side, and if the topologies are non-connected graphs, the number of connected sub-graph nodes where the node is located is K, selecting the K-1 side;
(2) topology to be deleted: the topology to be deleted is certain that some nodes discovered by the node through the broadcast 1 are no longer neighbors of the node, and the topology is the topology with the strongest real-time performance, and therefore the topology is also key topology information;
(3) the smaller the TL value in the residual topology is, the more critical the topology is;
(4) the topology within the range of 1 hop in the topology data acquired through the above three steps is deleted, and since the topology information of the 1-hop neighbor is already contained in the "neighbor slot requirement information", it is not repeatedly contained here.
And (3) constructing the key topology information according to the sequence of (1), (2), (3) and (4) until the topology Data in the topology _ Table is completely covered or the size of the broadcast 2_ Data reaches the maximum size capable of being transmitted in the broadcast 2 time slot.
S3: broadcasting the 2 time interval, and performing dynamic time slot allocation according to the timely updated time slot demand information, wherein the dynamic time slot allocation method comprises the following substeps:
s31: calculating the number of time slots which can be divided by the node according to the neighbor time slot requirement information in the two ranges acquired in the step S2;
s32: if the node has no data to send and forward in the current frame, no data time slot is allocated to the node; if the node only needs one data time slot, the main time slot of the node in the current frame period is distributed to the node; if the number of the data time slots which can be distributed by the node exceeds one, selecting the required number of data time slots to be distributed to the node according to the priority of the node on the time slots of the residual distributable nodes;
s33: if the number of time slots allocated to the node is more than 1, data which can be forwarded in the current time frame is preferentially transmitted when data is transmitted.
S4: the routing of the data stream according to the slot allocation priority table, as shown in fig. 5, comprises the following sub-steps:
s41: and checking whether the routing algorithm is operated for the first time in the current frame, if so, clearing the route Set _ Path < > and the forwarding Load table relay _ Load [ ], and executing the step S42, otherwise, executing the step S43.
S42: and (4) running and calculating the reachable network range of the node in a time frame according to the network topology information acquired in the step S2, adding all nodes in the range into a route Set _ Path < > which should include the ID of the reached node and the shortest ETT Path of the reached node, and if the destination node is not in the Set _ Path < >, turning to S43. Otherwise, the path finding is successful, the path information is added to the data flow, the data is stored in a data cache to be sent, and meanwhile, the Load relay _ Load of a forwarding node in the path is increased according to the size of the data. If not, the next step is carried out.
S43: traversing each node in the Set _ Path < > according to the breadth priority order, and calculating the reachable nodes in the two time frames by combining the main time slot order of the time slot allocation priority table of the next time frame and the load condition of the node. In order to avoid the loop in the route, when the next hop node of the Path is calculated, the next hop node must be selected from the complement of Set _ Path < >, the node is brought into Set _ Path < >, and the nodes traversed by Set _ Path < > are marked to avoid repeated traversal. In order to avoid that the load is too concentrated on some forwarding nodes, when the load of a forwarding node exceeds a certain proportion λ of the data length that can be sent in one data time slot, the node is also marked and will not be considered in the subsequent routing process unless the node is in the necessary position of the path to the destination node in the network or all available forwarding nodes have exceeded the load.
The connectivity, the node location, and the service attribute of the network of the value of λ are related, and should be determined according to specific situations, for example, in the mesh network topology of fig. 3, if the node 5 is a cut point in the route from the node 1 to the node 3, it is a forwarding node of the path, so λ is not considered, and for other forwarding nodes, such as the node 4 and the node 7, λ may be considered to achieve the effect of load balancing.
S44: repeating the S43 process until a destination node is added into the Set _ Path < > and adding Path information for the data stream, completing the routing of the data stream, if all nodes in the connected subgraph where the node is located in the topology are added into the Set _ Path < > and no destination node exists, indicating that the routing fails, putting the data stream into a routing failure data stream cache, adding 1 to the routing times, and no routing is performed for the data in the current frame. The path-finding strategy adopted by the invention is a greedy algorithm, and ensures that the result of each search is always the path with the minimum ETT.
S45: when a data stream to a new destination node is generated in the current time frame, firstly inquiring whether the destination node is already in Set _ Path < > or not, if not, jumping to the step S43, and continuously traversing unmarked nodes according to the breadth priority order; if yes, detecting whether the path can load the transmission of the data stream according to the existing load of the path, if yes, directly adding the path information of the path into the data stream, updating the load of the forwarding node, and adding the data stream into a data cache to be sent; if the data stream can not be searched again from the previous node of the path failure node, if the available forwarding nodes exceed the load, the next time frame main time slot sequence of the available forwarding nodes is used as the basis of the routing algorithm.
Considering the mesh network topology in fig. 3, if the node 8 sends data to the node 5, there is a transmission Path of 8-7-4-5 in the current route Set _ Path < > but the load of the node 4 has exceeded, the node 7 before the node 4 in the Path continues to traverse and find the route of the node 5, and if the load of the node 7 also exceeds, the next time frame main time slot of the nodes 5 and 7 is selected as the basis for calculation when the ETT is calculated.
S46: checking whether the data stream cache is empty, if not, re-routing the data stream generated before the current time frame, if the re-routing is successful, taking out the data stream and adding the data stream into the data cache to be sent, if so, adding 1 to the routing frequency of the data stream, and if the routing frequency exceeds a value time _ Failuer, indicating that the data stream fails to routeThe data is discarded. Setting of time _ Failuer general sum threshold TLmaxAnd correspondingly, the attribute related to the network topology change.
And S5, after a new time frame is started, entering the step S1 according to the sequence of the master time slots of the nodes in the time frame to start a new Mac and routing algorithm execution period.
Claims (6)
1. The wireless Mesh network low-delay optimization method based on dynamic time slot allocation is characterized in that each node in the wireless Mesh network performs time slot allocation by taking a time frame as a period; the time frame comprises a broadcast 1 time interval, a broadcast 2 time interval and a data frame time interval; the broadcast 1 time interval comprises N broadcast 1 time slots, the broadcast 2 time interval comprises N broadcast 2 time slots, the data frame time interval comprises more than or equal to N data frame time slots, and N is the maximum node number in the wireless Mesh network; each node corresponds to a data frame time slot in the data frame period as a main time slot of the node; each node has different main time slot sequences appointed by the node time slot priority table in different time frames;
each node is correspondingly allocated with a broadcast 1 time slot and a broadcast 2 time slot according to the main time slot sequence of the node in the current time frame in the broadcast 1 time slot and the broadcast 2 time slot; each node broadcasts the time slot requirements and topology changes of the node and the neighbor nodes in each time frame according to the current main time slot sequence to carry out dynamic allocation and topology maintenance of the time slots:
1) broadcast 1 period, broadcast slot requirement:
each node generates a 1 st broadcast control frame and broadcasts the 1 st broadcast control frame of the node in a corresponding broadcast 1 time slot, wherein the 1 st broadcast control frame comprises a node ID, the total size of data to be sent and information of each data stream to be sent, the information of each data stream comprises the data size of each data stream, the sending priority of each data stream and the remaining path information of each data stream, and the total size of the data to be sent is the sum of the data sizes of the data streams to be sent in a local broadcast data cache; the local broadcast data cache comprises data stream information to be sent by taking the current node as a source node and data stream information to be forwarded by taking the current node as an intermediate node; when the data stream information to be sent is excessive, so that the length of the 1 st broadcast control frame of the node exceeds the maximum data length of the broadcast 1 time slot sending data, the node puts the data stream information in the maximum data length into the 1 st broadcast control frame according to the sequence of the data stream sending priority from large to small;
the method for calculating the data stream sending priority w comprises the following steps:
w＝α·stream_Length+β·ETT+(1-α-β)·prior
ETT is expected path sending time, prior is the service priority of the data stream, stream _ Length is the data size of the data stream, and alpha, beta are both [0,1] and alpha + beta is less than or equal to 1, which respectively represent the data size of the data stream and the weight coefficient of the expected path sending time;
after receiving the 1 st broadcast control frame sent by other nodes, each node updates a local topology information table according to the received 1 st broadcast control frame, adds the node into a locally maintained one-hop neighbor information table according to a node ID in the 1 st broadcast control frame, and simultaneously checks whether the node is a next forwarding node of the data stream according to the data stream residual path information in the received 1 st broadcast control frame, if so, adds the data size of the data stream, the sending priority of each data stream and the residual path information of each data stream into a local broadcast data cache, and if not, discards the data stream information;
2) broadcast 2 time interval, broadcast neighbor node time slot requirement and topology change:
each node generates a 2 nd broadcast control frame and broadcasts the 2 nd broadcast control frame of the node in a corresponding broadcast 2 time slot, wherein the 2 nd broadcast control frame comprises a node ID, a neighbor node ID, the total size of data to be sent, network topology data and network topology change data; when the network topology data is overlarge, so that the total length of the 2 nd broadcast control frame exceeds the maximum data length sent by the node in the broadcast 2 time slot, the node selects the key topology of the network topology data according to the local topology information table, and selects the key topology to add into the 2 nd broadcast control frame within the maximum data length sent by the broadcast 2 time slot;
after receiving the 2 nd broadcast control frame sent by other nodes, each node updates the node ID in the received 2 nd broadcast control frame to a neighbor list in a local two-hop range, and updates a local topology information table according to the 2 nd broadcast control frame;
3) data frame period, dynamic slot allocation:
obtaining the number of data frame time slots required by the node in the current data frame period according to the total size of data to be sent corresponding to the neighbor nodes in the neighbor list in the local two-hop range:
if the node has no data to send and forward in the current frame, no data time slot is allocated to the node, and the main data frame time slot corresponding to the node is used as an idle time slot; if the node only needs 1 data frame time slot, the main data frame time slot of the node in the current frame period is distributed to the node; if the node needs more than 2 data frame time slots, carrying out idle time slot competition according to the node time slot priority table; if the node is allocated to more than 2 data frame time slots, the node preferentially transmits a data stream which can be forwarded in the current time frame when data is transmitted; and the node transmits the data streams in the order of the transmission priority of the data streams from large to small in 1 data frame time slot.
2. The method for optimizing the low latency of the wireless Mesh network based on the dynamic time slot allocation according to claim 1, wherein the local topology information Table topologic _ Table maintained by each node is:
each element TL in the local topology information tableijRepresents the link condition j between the nodes i and j as 1, 2, …, N, i as 1, 2, …, N; when TLijIf the value is 0, the link does not exist or is not detected between the nodes i and j; when TLijIf not 0, it indicates that there is a link between the nodes i and j, i.e. there is an edge in the topology map, the specific value is the link probing time between the nodes i and j, the unit is a time frame, which is used to indicate the degree of recency acquired by the link, and the smaller the value is, the smaller the link signal isThe newer the information.
3. The method as claimed in claim 2, wherein the step 2) selects the key topology data in the following order until the topology data in the local topology information table is completely covered or the 2 nd broadcast control frame size reaches the maximum data length of one broadcast 2 slot transmission:
(1) taking the node as a source node, constructing a minimum spanning tree according to a topological graph formed by a local topological information table, wherein all links in the minimum spanning tree are key topological data with the highest priority;
(2) according to the 1 st broadcast control frame, the link which is no longer the neighbor node in the one-hop range of the own node is obtained;
(3) according to TLijSelecting links which are not selected in the local topology information table from small to large;
(4) and deleting the links within the range of 1 hop in the currently acquired topology data.
4. The method for optimizing the low delay of the wireless Mesh network based on the dynamic time slot allocation as claimed in claim 2, wherein the information update of the local topology information table comprises the following steps:
broadcasting 1 time period, and adding 1 to all element values which are not 0 in the local topology information table;
broadcasting 2 time period, setting TL of element in local topology information table corresponding to link in neighbor list in local two-hop rangeijA value of 1; TL of link in network topology data in received 2 nd broadcast control frameijUsing the TL of the link in the network topology data in the 2 nd broadcast control frame only when the value is smaller than the corresponding element value of the local topology information table or when the corresponding element value of the local topology information table is 0ijUpdating the value of the corresponding element; when a link needing to be deleted is received, the value of a corresponding element of a local topology information table of a setter is 0; and when the element value of an element in the local topology information table is larger than the set expiration threshold, setting the corresponding element value to 0.
5. The dynamic timeslot allocation-based wireless Mesh network low latency optimization method of claim 1, wherein each node in the wireless Mesh network performs routing after completing timeslot allocation in a time frame, and the routing refers to a main timeslot sequence in the node timeslot priority table.
6. The method for optimizing the low delay of the wireless Mesh network based on the dynamic time slot allocation as claimed in claim 5, wherein the routing specifically comprises the steps of:
s1: checking whether the routing algorithm is operated for the first time in the current frame, if so, clearing a route set and a forwarding load table, and executing the step S2, otherwise, executing the step S3;
s2: calculating a network range which can be reached by the node in a time frame according to network topology data acquired in a broadcast 2 time period, adding all nodes in the range into a route set, wherein the route set comprises an ID of the reached node and a shortest ETT path of the reached node, if a target node is not in the route set, turning to a step S3, if the target node is in the route set, successfully finding a route, adding path information for the data flow, storing the data flow into a data cache to be sent, and updating the load of a transfer node in the path in a transfer load table according to the size of the data flow;
s3: traversing each destination node in the route set according to the breadth priority order, and calculating the reachable nodes in the two time frames by combining the main time slot order in the node time slot priority table of the next time frame and the load condition of the nodes;
s4: repeating the step S3 until the destination node is added into the route set to complete the route searching or the route searching fails, if the route searching is completed, adding path information to the data stream corresponding to the destination node, and if the route searching fails, placing the data stream corresponding to the destination node into the data stream cache of the route searching failure.
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| CN109104767B (en) * | 2018-07-30 | 2023-04-18 | 武汉中元通信股份有限公司 | Dynamic time slot allocation optimization method |
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| CN111642022B (en) * | 2020-06-01 | 2022-07-15 | 重庆邮电大学 | Industrial wireless network deterministic scheduling method supporting data packet aggregation |
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