RU2640349C1 - METHOD OF ROUTING IN WIRELESS ZigBee NETWORKS - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: functions of ports, connecting the routers in wireless networks, in the ZigBee networks perform time slots during which communication is performed between the routers of the network. Time slots of the ZigBee superframe structure seem to function as the ports through which the communication between the routers in the ZigBee network is carried out. Before transmitting the beacon, a superframe is formed in the output buffer of each router in the form of a set of memory cells. In each of the cells, to which the slots, corresponding to the routers, are assigned, packets, received from the routers for subsequent transmission, are received. Each router, irrespectively of the others, periodically based on the timer signal broadcasts superframes, limited by beacons. All neighbouring routers, that received the initial beacon, trigger synchronization mechanisms that generate a sequence of time slots and perform a sequential (per each slot) reception of all the packets contained in the corresponding cell. During those slots in which there is no information, transmission does not occur, and only synchronization mechanisms are implemented, during which a small amount of energy is used in comparison with the transmission mode.

EFFECT: increase in the accuracy of routing with two-address packets containing the address of the initial sender and the final recipient.

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Description

The invention relates to wireless communication networks. In particular, to the method of routing in wireless sensor networks ZigBee. These networks provide an alternative to wired connections in distributed control and monitoring systems.

In the networks under consideration, networked sensors form a geographically distributed self-organizing system for collecting, processing and transmitting information. Synchronization for these networks is a complex and important task, since it requires mutual spatio-temporal coordination between nodes. The solution to this problem is possible through the use of a superframe structure in ZigBee networks [1]. The superframe is limited to periodically transmitted beacon frames that allow nodes to synchronize with the network. The active part of the superframe is divided into 16 consecutive time slots and includes three parts: a beacon, a competitive access period (CAP) and a non-competitive access period (CFP). The end of a superframe is an inactive period in which nodes can enter a low-power mode. Collisions of beacons can occur on the network, which, of course, can lead to disruption of network synchronization. These conflicts are resolved in three ways:

- allocation of a time window at the beginning of each superframe reserved for transmitting a beacon frame [2];

- time planning, in which beacon frames of transmitting routers (ZigBee Routers, ZRs) are sent during inactive periods of the duration of superframes receiving ZRs [2];

- time planning, in which the selection of the transmission time of the beacon frames is carried out in an arbitrary time period of the CFP cycle of the beacon signal of the network coordinator (ZigBee Coordinator, ZC) [3].

However, none of the above methods allows, using the super-frame structure, to combine the synchronization and routing functions of the network. Existing routing methods that do not use a super-frame structure lead to a significant increase in energy consumption by nodes, which is quite critical for the networks in question [1].

A fairly large number of routing algorithms have been developed for ZigBee networks, of which DSR (Dynamic source routing) and AODV (Ad hoc On-demand Distance Vector routing) have become most famous [4].

In the DSR protocol, the route to the required node is found by sending from each node a special packet of the route request to all nodes of the environment, i.e. source routing is used without relying on routing tables on each intermediate device. The disadvantage of the DSR protocol is the irrational increase in both the cost of the path to the destination node and the increase in power consumption by the nodes.

A special feature of the AODV protocol is the implicit assumption that any host can participate in the routing process. However, ZigBee networks are heterogeneous networks, as devices have different roles and functions. The disadvantages of this protocol include a significant amount of device memory for storing route tables, as well as significant network traffic, which is necessary for finding routes in branched networks [4].

The closest in technical essence is a routing method in wired networks, based on the construction of a minimum spanning tree (STP (Spanning Tree Protocol)) [5]. However, this method cannot be applied directly to ZigBee networks, as they do not have the ability to block ports, as is the case in wired networks using the STP protocol.

In order to eliminate this drawback, it is proposed that links between ZRs be established during certain time slots.

The essence of the invention lies in the fact that ZC assigns to each of the ZRs certain time slots of the superframe during which this ZR receives information intended for it, and each node transmitting the superframe transmits this ZR only during the slot assigned to this ZR.

The technical result of the invention is the possibility of full-fledged routing with two-address packets containing the address of the initial sender (BUT) and the final recipient (KP), similar to how it is implemented in wired networks of the STP protocol.

In the framework of this invention, a ZigBee cluster tree network is considered, however, the proposed method can be applied to other ZigBee topologies ("star", "mesh"), because he observes the general principles of functioning of the networks in question.

The implementation of the proposed method involves the process of forming a network topology, as a result of which a minimal spanning tree will be built (similar to wire networks operating on the basis of the STP protocol) [5], in which ZC acts as the root and ZRs are the tree vertices. In this case, the entire network is divided into subnets called clusters. Each cluster contains ZRs through which the clusters communicate with each other, and end nodes (ZigBee End Device, ZED) associated only with the ZR of their cluster.

Each ZR, irrespective of the others, periodically sends out broadcast BPDU packets (Bridge Protocol Data Units) with its MAC address, according to the timer signal, and all ZR _i that have a direct connection with it (nodes of its environment in the "tree") receive the specified BPDUs. As a result of broadcasting in each of the ZRs, a table of MAC addresses is formed containing the MAC addresses of the environment nodes included in the "tree" and the corresponding slot numbers, which are distributed by a special algorithm by ZC. When allocating slots, an algorithm is used that minimizes the number of slots, because reuse of slots is allowed, but at different levels (non-interacting) of the network hierarchy.

Consider the principle of operation of the proposed method on the example shown in Fig. 1, where there are the following notation:

1 - beacons;

2 - a slot of a superframe into which received packets are placed (with addresses of NO and KP) for subsequent transmission;

3 - received superframe;

4 - working area ZR ₄ ;

5 - working area ZR ₅ ;

6 - table of MAC addresses ZR ₅ ;

7 - transmitted superframe;

8 - working area ZR ₈ ;

9 - work area ZR ₉ .

The above fragment shows the working areas of four routers that communicate with each other via radio, in particular, ZR (4) interacts with ZR (5), and ZR (5) interacts with ZR (8), ZR (9). For each of the presented ZRs, ZC previously assigned slots (from the superframe format). Assume that in the presented fragment of the network the number of the fixed slot corresponds to the number ZR _i . Each ZR _{i is} configured to work in the respective slots in such a way that for each slot in each of ZR _{i there} is a buffer memory for receiving and transmitting information during this slot.

According to fig. 1 ZR (4) receives a packet in the address part of which there are MAC addresses of BUT and KP. ZR (4) analyzes the received packet (in slot number 4), determines that the addresses of the CP are different from its own, i.e. in this case, ZR (4) is an intermediate node when routing packets on a ZigBee network. ZR (4) analyzes its own table of MAC addresses and determines that to deliver a packet to the address of this control unit, you need to send a packet in slot number 5. ZR (4), which forms its own superframe, places the received packet in cell number 5 (2 ) and after the timer expires, sends the generated superframe to neighboring ZRs (in this case, ZR (5)).

ZR (5), having received the packet in slot number 5, similarly to ZR (4) analyzes the KP's MAC addresses, and then refers to its own table of MAC addresses and, if it did not previously contain such MAC addresses, enters the NO addresses and slot numbers in it, in which ZR (5) will have to send a packet to reach the specified NO addresses (in this case, slot No. 4). At the same time, ZR (5) finds in its table of MAC addresses (6) a line containing the MAC addresses of the control unit and the slot numbers during which it is necessary to poison the information intended for them. In this case, address KP ₈ corresponds to the MAC address ZR (8) and slot number 8, and address KP ₉ corresponds to the MAC address ZR (9) and slot number 9. ZR (5), which forms its own superframe, places information for each ZR to its corresponding slot and after the timer expires it sends the specified superframe (7) to neighboring ZRs (in this case, ZR (8), ZR (9)).

ZR (8) and ZR (9) receive these packets transmitted over their respective slots.

The above processes occur independently in each of the routers of the ZigBee network. From the foregoing, it follows that in the proposed method, the time slots of the super-frame structure seem to perform the functions of ports (similar to the ports in the wired networks of the STP protocols) through which communication between ZRs in the ZigBee network is carried out.

The advantage of the proposed method is that as a result of assigning to each node a specific time slot (from the superframe format) during which it can receive data, it becomes possible to carry out full-fledged routing with two-address packets, by analogy with how it happens in wired networks based on the STP protocol. Each ZRs performs active transmission only in those slots that are assigned to the nodes of the environment. This can significantly reduce the power consumption of ZRs, which is important for the networks under consideration.

Literature

1. Rao V.P., Marandin D. Adaptive Channel Access Mechanism for Zigbee (IEEE 802.15.4) // Proceedings of the 6th international conference on Next Generation Teletraffic and Wired / Wireless Advanced Networking, 2006. - pp. 501-516.

2. Koubaa A., Cunha A., Alves M., Tovar E. TDBS: A time division beacon scheduling mechanism for Zigbee cluster-tree wireless sensor networks // Real-Time Systems Journal, 2008. - Vol. 40. - No. 3. - P. 321-354.

3. Beacon scheduling method in wireless sensor network system: pat. US20060104251 A1; Filed: 11/14/2005; Publ .: 05/18/2006.

4. The effect of heterogeneity on the routing process in ZigBee networks [Electronic resource] - Access mode: http://tm.ifmo.ru/tm2009/src/244bs.pdf

5. Spanning Tree spanning tree algorithm [Electronic resource] - Access mode: http://life-prog.ru/1_10569_algoritm-pokrivayushchego-dereva-Spanning-Tree.html

Claims (1)

A slot routing method in ZigBee wireless networks having superframe time synchronization, characterized in that each router is assigned temporary superframe slots during which it can receive packets destined for it, and each transmitting router sends packets destined for the receiving router only during the slots assigned to the specified host router.

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