Research and Experiment on ZigBee-based wireless network routing (1)

A wireless sensor network is a special Ad-Hoc network with dense nodes and a large number of distributed areas. Currently, the most promising development prospect is the ZigBee Wireless Network Based on the IEEE 802.15.4 standard. Wireless sensor networks generally do not require high transmission bandwidth, but require low transmission latency and extremely low power consumption, so that users can have a long battery life and many device arrays, the emergence of ZigBee solves this problem. ZigBee has many advantages such as high communication efficiency, low complexity, low power consumption, low speed, low cost, high security, and full digitalization. These advantages perfectly combine ZigBee with wireless sensor networks. At present, the research and development of wireless sensor networks based on ZigBee technology has attracted more and more attention.

ZigBee is a wireless data transmission network platform consisting of up to 65 000 wireless data transmission modules. It is very similar to the existing mobile communication CDMA network or GSM network, each ZigBee network data transmission module is similar to a base station in a mobile network. It can communicate with each other throughout the network. The difference is that the ZigBee network is mainly built for automatic control of data transmission. Each ZigBee network node can directly collect and monitor data with the monitoring object, you can also automatically transfer data transmitted by other network nodes. In addition, each ZigBee network node can be connected to multiple isolated sub-nodes that do not undertake network information transfer tasks in the range of their own signal coverage. ZigBee network nodes support 31 sensors and controlled devices. Each sensor and controlled device have eight different interface methods for collecting and transmitting numbers and analog numbers.

1. Basic Routing Algorithm for WSN

Nodes in ZigBee WSN can be divided into two types: nodes with routing capacity and nodes without routing capacity. For a tree cluster topology, the terminal device is usually a thin RFD device, so there is no routing capacity. the router and the Coordinator are composed of FFD full-featured devices, so there is a routing capacity.

In a tree-cluster-type topology, a routing algorithm combining the tree clustering algorithm and AODVjr algorithm is usually used. The tree clustering algorithm refers to an algorithm for transmitting messages along the tree topology, it is static and does not need to store route tables. This algorithm is applicable to scenarios where nodes are still or less moved. The AODVjr algorithm is an improvement of the Ad Hoc On-Demand Distance Vector routing algorithm. considering factors such as energy saving and ease of use, it simplifies some of the characteristics of the AODVjr algorithm, however, the original functions of the OSS are retained.

The combination of the two algorithms determines the three routing modes of the WSN, namely, disable routing mode, enable routing mode, and force routing mode. To disable the routing mode, you cannot search for paths. Therefore, a network in this mode can only use the tree cluster algorithm to route the routes along the tree topology. The routing mode combines the tree cluster algorithm with the AODVjr algorithm, and determines which routing algorithm is used based on the actual situation. The AODVjr algorithm is fully used in the forced routing mode. If the device has the path search capability, a path search process must be started no matter whether the message transmission path already exists. When the search is complete, data packets are transmitted along the calculated path.

2 routing Mode

There are usually three routing modes: Disable route discovery, enable route discovery, and force route discovery.

SUPPRESS: If a network router exists, the packet route points to the router. Otherwise, data packets are pushed along the tree.

ENABLE: If a network router exists, the data packet route points to the router. If the network router cannot be determined, the router can start a route discovery process. When the discovery is complete, the data packets are transmitted along the calculated route. If the router does not have the routing discovery capability, the data packet will be pushed along the tree.

Forced route discovery (FORCE): If a vro has the routing discovery capability, a route discovery process is started no matter whether the route exists or not. After the discovery is complete, data packets are transmitted along the calculated route. If the router does not have the routing discovery capability, the data packet will be pushed along the tree. This option must be used with caution because it will generate greater network redundancy. It is mainly used to repair damaged routes.

For data forwarding between devices in a tree-like topology, the source address is generally simplified to a route up or a route down ). If LocalAddr <DestAddr <LocalAddr + CSkip (D-1) is a downstream route, otherwise it is an upstream route. Generally, the Network Coordinator or vro contains a list of adjacent devices. This table records the devices in a certain area that are adjacent to each other. If you want to use an adjacent table for routing, you can directly send information as long as the target device is visible in the physical area. For the mesh topology, the route table is used for routing. Generally, the Coordinator or router has its own route table. If the target device has related records in the route table, the information can be sent according to the records in the route table. Otherwise, data must be transmitted along the tree topology.

3 routing process

The routing process involves the following steps:

(1) A device sends a route request command frame to start the route discovery process;

(2) After receiving the command, the corresponding receiving device replies to the response command frame;

(3) evaluate and compare the potential costs of each path (number of jumps and delay time;

(4) Add the best route records to the routing table of each device on this path.