Home Network Construction Details

Wireless network technology has become an indispensable part of our lives. What should we prepare for components of the home lan? Here we will introduce it to you.

With the development of computer technology, communication technology, and control technology and the improvement of people's material life level, the study of smart home has become a hot topic at home and abroad. at the same time, with the increasing aging society in China, it is also important to improve people's quality of life and reduce medical costs to achieve long-term family monitoring through an easy-to-organize, low-cost, and efficient smart home network. therefore, a home monitoring system based on shared control is proposed. figure 1 is a smart home monitoring system with shared control.

Home Device Information and Human Body information, such as brainwaves and pulse information, are transmitted through wireless networks and routed to dedicated servers on the Internet through a home network. family members or hospitals can use computers anywhere in the world to investigate human activity and equipment recorded on servers. in this way, not only can the current activity be obtained in real time, but the devices in the home can be controlled through instructions, and the historical information and change tendency in any period of time can be investigated, provide suggestions and measures for correct and timely medical care.

Previously, smart home networks were constructed using radio frequency (RF) technology, 802.11, and Bluetooth technology. however, none of these technologies fully meet the requirements for easy organization, low cost, and low power consumption of home networks. the Zigbee protocol is a wireless protocol based on the IEEE802 15.4 standard. It is mainly used in the networking of low-speed and low-power devices. the communication device supports a data transmission rate of 250 kbit/s and supports fast networking of multiple point-to-point connections. in view of the above features of Zigbee wireless network, it can be used to build a home wireless network platform.

L Zigbee network protocol analysis

The Zigbee network protocol stack adopts the Open System Interconnection Model (OSI ). 2. each layer implements some communication functions. and provide services to the senior management. the IEEE 802.15.4 standard only defines the MAC Sub-layer of the PHY layer and data link layer. The PHY layer consists of the RF transceiver and the underlying control module. The MAC Sub-layer provides point-to-point communication service interfaces for high-level access to physical channels. zigbee Alliance defines network layer, application layer, and security layer specifications. NWK is responsible for network layer work. It uses the services provided by IEEE 802.15.4MAC to complete work, and provides data sending and receiving and management services for the upper layer protocol to call APS over NWK, the ZDO application framework and application objects belong to the application support layer (APL ). APS uses the data provided by NWK for transmission.

Multi-path selection is an important function of APS. It provides upper-layer applications to use the network data transmission service Endpoint (like the TCP/IP socket) to match the network address, in this way, aps zdo is the control center of the entire Zigbee network device, which allows multiple applications to use aps zdo cyclically between two communication endpoints. It uses the management services provided by NWK and APS, and matches the Zigbee device profile (ZDP) specification. the Zigbee network supports three types of topology: Star structure, grid structure, and family structure, as shown in figure 3. the gridded and family structures belong to point-to-point star networks, and all nodes communicate with the central coordinator, nodes cannot directly communicate with each other, while nodes in the point-to-point network are within the same radiation range. Any two devices can communicate with each other.

2 considerations for key issues

2.1 network topology Selection

Among the three network topologies supported by the Zigbee protocol, the star topology is the simplest. each monitored device can connect to the access network as a thin device, saving energy and reducing the workload. in the home monitoring system, devices may be distributed in multiple rooms, and monitored objects may also be active in multiple rooms, the wireless communication range of nodes in the star network is small (dozens of meters), and the network coverage is limited, which is not conducive to the expansion of network functions.

Each node in the mesh network can be used as a route node. Therefore, the data flow of the original node can reach the network control point through multiple paths. if a node is disconnected from the network, you can select another path for data transmission. Therefore, the data stream is robust. however, all devices in the network must be full-featured devices, causing high energy consumption. At the same time, route nodes of data streams in the network increase network latency.

The family structure combines the advantages of the star structure and the mesh structure. to save energy, monitoring devices and physiological data collection terminals can be used as end nodes in the network, with fewer Structural Nodes. at the same time, the Coordinator can be used as a network controller to collect data in the network. the network is scalable and can add route nodes and extend the coverage. Therefore, the home wireless network adopts a family-type network topology.

2.2 Design of Network Routing Protocol

The routing protocol is directly related to the performance of the wireless network. the primary issue in the design of routing protocols is that they require low computing complexity and low energy consumption. secondly, because of the mobility of the Monitored object, the network topology structure may change, so it must meet the dynamic routing requirements.

Zigbee supports routing algorithms such as Cluster-tree, AODVjr, and hybrid mode. the AODVjr algorithm is designed to improve the put algorithm to reduce computational workload and save energy. However, the algorithm is complex. The Cluster-tree algorithm is suitable for tree topology structures. figure 4 shows the hierarchy chart of the network tree.

In the figure, Lm indicates the maximum network depth, Cm indicates the maximum number of subnodes, and Rm indicates the maximum number of Route nodes in the subnodes.

The Cskip address space of a node is calculated as follows:

Formula: n is the parent node address; R is the subnode number 1 ~ Cm.

Assume that the address of a node is N and the address of the target node is D. The Cluster-tree Routing Algorithm is as follows:

① If the destination node address of the data to be transmitted is its own address, send the data packet to the upper layer for processing; otherwise, convert it to ②.

② If the target node of the data to be transmitted is its own neighbor node (there is routing information in the route table), send the data directly to the neighbor node; otherwise, convert it to ③.

③ Determine and forward the child node or parent node address.

If D

If D is greater than N, data packets are forwarded to the parent node;

If D> N and D ≤, the packet is forwarded to the child node with the address.

Most nodes in the home wireless network are static, with fewer mobile nodes. The family topology can be used. the Cluster-tree algorithm can be used as the routing protocol to build a home network with stable links and less node interference. in this way, network nodes do not need to save a large amount of routing information, saving memory, low computing complexity, and low energy consumption. in specific design, because the Home monitoring network is a small network with fewer network nodes, you can set fewer network layers to reduce the route computing time.

2.3 Data Sampling Policy

Equipment status and low transmission rate data information have low performance requirements for wireless networks. The Zigbee-based wireless network can meet the bandwidth requirements for data transmission and achieve node energy saving. because physiological signals are transmitted continuously, the effect of physiological data sampling rate on energy consumption and network load needs to be considered.

To send data frames, encapsulate each layer of the network protocol stack. data frames at the application layer must be smaller than 80 B. physiological signals generally belong to low-frequency signals (the effective frequencies of pulse signals are less than 10Hz). When the signal is true, use low sampling frequencies as much as possible to reduce the amount of data transmitted. at the same time, we can cache and package the collected physiological signals and send them together to improve data transmission efficiency and reduce energy consumption on network nodes.