Design of ward monitoring system based on Zigbee technology

Medical resources are in short supply in my country. Developing a local intelligent monitoring network in hospitals can reduce the workload of medical staff and improve their work efficiency and service quality. The traditional solution is to use wired or simple wireless data transmission and reception. The sensor equipment installed on the monitored person cannot move freely and flexibly and access the network, and the system has no scalability. The use of Zigbee technology provides a new solution for the wireless transmission of sensor signals. Zigbee nodes can cover a range of tens of meters, and routing nodes can be added freely to expand the coverage range, which is very suitable for local hospital inpatient care. Since the data transmission volume of physiological monitoring is not large, Zigbee's 250 kb/s transmission rate can meet the transmission requirements of physiological data. Zigbee sensor nodes can freely access and exit the network, with the characteristics of low power consumption and low cost, so Zigbee wireless sensor networks have good application prospects in local medical monitoring systems.

1 Zigbee-based wireless sensor network system architecture

1.1 Zigbee network topology

Zigbee is a short-range wireless network connection. The main features of this technology are low speed, low power consumption and low cost. It supports a large number of network nodes and multiple network topologies. It works in the ISM bands of 2.4 GHz (global), 868 MHz (Europe) and 915 MHz (USA), and follows the IEEE802.15.4 technical standard. In the Zigbee network, there are three main network topologies, namely star, tree and mesh, as shown in Figure 1.

Figure 1 Zigbee network topology

According to different functions, wireless network nodes include coordinator nodes, router nodes and end devices, which are represented by different shapes in Figure 1. Each Zigbee node is composed of a wireless microcontroller CC2430 with wireless transceiver function, and the Zigbee wireless network software protocol stack is installed inside the wireless microcontroller. In the Zigbee network organization structure, each personal area network must have a unique coordinator node, which is responsible for network timing management, network coordination, storage of network maps, allowing other devices to join the network, network organization, routing information, etc. It is a full-function node, and the wireless transceiver function must be turned on at any time. It plays a very important role in the Zigbee network.

1.2 Ward Monitoring Network Architecture

The ward monitoring system based on Zigbee wireless sensor network is mainly composed of Zigbee wireless sensor nodes with corresponding data collection functions in each ward, several wireless nodes with routing functions in wards, and Zigbee central network coordinator in the hospital. The network coordinator connects the Zigbee wireless network with Ethernet, is the core part of the entire hospital wireless network, and is responsible for the management of wireless sensor network nodes and device nodes. The system structure is shown in Figure 2. In the figure, ZR is an FFD node with routing function, and ZE is a wireless sensor terminal node. Wireless sensor nodes can send data to the wireless gateway through each routing node. Since the monitored person moves freely in the ward or hospital, the routing of the sensor node it carries is dynamically changing. The wireless sensor terminal node and the routing node form an automatically jumping multi-hop network. Since the indoor communication distance of the wireless sensor terminal node is tens of meters, the routing node can be arranged according to the distribution of the ward to cover the activity area to the greatest extent. Therefore, the system has great flexibility and scalability. At the same time, the system can be easily connected to the Internet to form a larger medical monitoring network among hospitals to achieve sharing of medical resources.

Figure 2 Structure of Zigbee-based ward monitoring system

2 Wireless Sensor Network Node Design

4.2 Network Coordinator Node Software Module Design

After the network coordinator is powered on, it first initializes CC2430 and then establishes a wireless network. When an FFD node applies to join, an address is assigned to each FFD node. When data collection is required, the network coordinator issues a data collection instruction, then waits to receive the sampled data, and uploads the data to the host PC through the RS232 port for processing. The network coordinator node software flow is shown in Figure 6.

Figure 6 Network coordinator node software flow chart

5 Experimental Verification

The system comprehensive test basically realizes the design function. The data collected by the blood pressure sensor node is sent to the monitoring PC through the Zigbee wireless sensor network. Professional medical personnel conduct statistical analysis on the data and then propose corresponding medical and nursing plans. The blood pressure measurement data of three patients simulated at one time is shown in Table 1. After the simulation test, the system data collection function is normal, the wireless network information transmission function is normal, and the terminal automatic network access and network jump functions can be realized.

Table 1 Blood pressure measurement data of three terminals in simulation test

This paper introduces a ward monitoring system based on Zigbee wireless sensor network, analyzes and studies the general topology of Zigbee network, uses LC2480 wireless network module of Wireless Dragon Company to realize the design of wireless terminal, studies the interface circuit design of sensor terminal, gives the software design flow chart of routing terminal and network coordinator, and finally conducts a simulated network test. The system has good flexibility and scalability, and can realize remote medical monitoring and information resource sharing between hospitals through the Internet.

The design of wireless sensor network nodes can be composed of a wireless transceiver chip and a microcontroller. With the development of technology, more and more companies have made wireless transceiver chips and microcontrollers into a system on chip. The design uses TI's CC2430. The CC2430 chip is a Zigbee wireless microcontroller using the 8051 core. It includes a high-performance 2.4 GHz DSSS (direct sequence spread spectrum) RF transceiver core and an industrial-grade compact and efficient 8051 controller. The chip integrates the Zigbee RF front end, memory and microcontroller, has 32/64/128 KB programmable Flash and 8 KB RAM, and also includes an analog/digital converter (ADC), several timers, AES-128 security coprocessor, watchdog timer, sleep mode timer with 32 kHz crystal oscillator, power-on reset circuit, power-off detection circuit and 21 programmable I/O pins. The entire network processor module design uses the LC2480 network processing module of Wireless Dragon. The LC2480 network processing module uses the standard Zigbee CC2430 chip and has built-in compatible software developed by Wireless Dragon. The schematic diagram of the LC2480 network processing module is shown in Figure 3.

Figure 3 Schematic diagram of the LC2480 network processing module

3 Sensor terminal node circuit design

The sensor terminal node mainly completes the collection of various physiological data information, such as body temperature, blood pressure and ECG signals. Due to the requirements of the special environment, the design requires small size, low power consumption and strong anti-interference ability. In the design of wireless network nodes, in order to facilitate functional expansion, sufficient sensor interfaces are reserved. If functional expansion is required in actual use, as long as the corresponding data acquisition sensor is connected and the corresponding embedded control software is developed, the wireless sensor network can be directly added to collect and transmit data. Figure 4 shows a design block diagram of a blood pressure sensor interface circuit. According to the characteristics of large impedance, weak signal and instability of blood pressure signal, the blood pressure sensor interface circuit is required to have the characteristics of high gain, high input impedance and high common mode rejection ratio.

Figure 4 Blood pressure sensor interface circuit

The sensor samples the changing pressure signal in the cuff, separates the pulse signal from it, finds the corresponding position of systolic pressure and diastolic pressure, and obtains data. The signal from the sensor is amplified, and the pressure signal is obtained after low-pass filtering and band-pass filtering. It is then amplified and signal conditioned by the main amplifier and sent to the main control system for corresponding processing.

4 Wireless Network Node Software Design

4.1 Routing FFD Node Software Module Design

After the routing FFD module is powered on, it first initializes CC2430 and then tries to join the network. If joining the network is successful, it starts sampling data after receiving the start sampling instruction from the network coordinator, and uses the A/D conversion of CC2430 to convert analog signals into digital signals, and then sends the data packet to the network coordinator. The software flow is shown in Figure 5.

Figure 5 FFD node software flow chart