Wireless Sensor Network is an emerging technology that integrates sensor technology, embedded computing technology, modern network and wireless communication technology, distributed information processing technology, and other fields. This technology has a wide range of application scenarios.

With the development of technology, WSN (Wireless Sensor Network) will have a profound impact on many aspects of medical practice. This article mainly elaborates on the architecture of wireless sensor network medical monitoring system and the general principles of monitoring node design.

Architecture of Wireless Sensor Networks

A large number of sensor nodes are arranged within the monitoring area, and self-organizing networks are used between nodes, as well as wireless communication technology for data forwarding. Each node has dual functions of data collection and data fusion forwarding. The node conducts preliminary data processing and information fusion on the information it has collected and the information forwarded to it by other nodes, and then transmits it to the base station in the form of relay transmission by adjacent nodes, and then transmits it to the end user through the base station in the form of Internet, satellite, etc.

Nodes are the basic functional units of wireless sensor networks, and their designs vary depending on their specific applications. The basic components of a sensor node include a sensing unit, a processing unit, a communication unit, and a power supply. In addition, functional units can be added according to specific application requirements, such as positioning systems, mobile systems, and self powered power supply systems.

The application of wireless sensor networks in healthcare

Wireless sensor networks, utilizing their own advantages such as low cost, simplicity, speed, and real-time non-invasive collection of various physiological parameters of patients, have great potential for development in medical research, hospital general/ICU wards, or home daily monitoring, and are currently a hot research topic.

Placing miniature sensor nodes on patients to detect human body parameters can remotely monitor physiological parameters such as heart rate, blood pressure, electrocardiogram, heart sound, etc., and summarize and transmit the information to the monitoring center for timely processing and feedback; The long-term collection of physiological data of the observed human body using WSN is very helpful for understanding human health status and researching human diseases. In addition, it has also been applied in many aspects such as drug management, development of new drugs, and blood management. In summary, wireless sensor networks provide a more convenient and cost-effective means of implementation for future remote medical monitoring systems.

Medical architecture based on wireless sensor networks

The medical monitoring system based on wireless sensor networks mainly consists of medical sensor nodes, medical monitoring base stations (medical SINK nodes), and community/hospital monitoring centers.

Medical sensor nodes and monitoring base stations form a personal/home or ward wireless sensor network, and multiple such networks can form a community or entire hospital monitoring network, or even a larger remote medical monitoring system. Firstly, medical sensor nodes collect physiological parameters of the human body, and after simple processing of the collected parameters, transmit the data directly or indirectly to the base station through wireless communication in a hop by hop manner. The monitoring base station further processes the data and forwards it to the monitoring center for analysis and timely feedback to the patient. The monitoring center can also use various methods (such as the Internet, mobile communication networks, etc.) for remote data transmission and share information with other monitoring centers.

Design of Medical Sensor Nodes

The basic structure of medical sensor nodes includes processing modules, sensor modules, wireless transceiver modules, and power supply modules.

The sensor module is used for sensing, collecting, and converting external sensor signals. It is the module where the entire node truly comes into contact with external signals. However, medical sensors measure living organisms. Especially the human body, which can be said to be a complex system in the world, has a high degree of correlation between various physiological variables and is not easy to approach. So medical sensors need to extract predicted physiological quantities from numerous phenomena, obtain reliable and meaningful measurement data, while ensuring the safety of the measured object.

Due to the fact that most human body parameters are weak signals, usually only at the level of a few mV or even lower, and there are various types of noise (measurement environment noise, instrument human friction noise, and instrument itself noise, etc.), power frequency interference (caused by the presence of a 50 Hz electromagnetic field around the measurement environment), and various noise and other adverse factors. Therefore, in the specific design of medical sensor nodes, an analog circuit processing module is added, which generally includes the following parts: amplification circuit, filtering circuit, notch circuit, and analog-to-digital (A/D) conversion circuit. In node design, the amplification circuit generally adopts multi-stage amplification (three or four stages), and the final amplification circuit generally has a level boosting function in addition to the amplification function; Filtering circuit: It should meet the requirements of concise and reasonable cut-off frequency, flexible and convenient adjustment of high-low pass cut-off frequency, and reasonably filter out high-frequency and low-frequency interference in the signal; Notch circuit: Currently, symmetrical double-T resistive capacitive active notch filters, integrated switch capacitor devices, and asymmetric resistive capacitive network notch filters are widely used. In short, the analog circuit processing module mainly amplifies, filters, and traps the collected signals, removes noise and interference from the signals, and extracts useful signals.

The processor module is the core of the sensor node, responsible for device control, task allocation and scheduling, data integration and transmission of the entire node. Currently, the most commonly used processor modules are Atmel's AVR series microcontrollers, TI's MSP430 ultra-low power processors, Motorola and Renesas processors, and ARM microcontrollers as 32-bit embedded processors. In node design, it is necessary to program the processor module to control the acquisition and A/D conversion of the sensing module, as well as to control the transmission and reception of the wireless communication module.

The wireless transceiver module is used for data communication between nodes. The wireless transceiver modules that are widely used in the wireless field are CCl000, CC2420, and CC2430 from Chipcon. The commonly used wireless communication technologies include IEEE 802.1lb, IEEE 802.15.4 (ZigBee), Bluetooth, UWB, RFID, IrDA (infrared), etc. Most monitoring systems use IEEE 802.15.4 (ZigBee) and Bluetooth to achieve data communication between nodes and base stations.

The power module provides energy to the node and is the fundamental module of the entire wireless sensor node. However, due to the limitation of node volume, the energy of sensor nodes is very limited. Therefore, in the entire node design, low power consumption and high precision are the main requirements, and a series of effective measures are taken to save energy. In addition, medical sensor nodes cannot frequently replace batteries, which affects people's normal lives. Therefore, the designed medical nodes should have a longer lifecycle.

Challenges of Medical Wireless Sensor Network Monitoring System

Although wireless sensor networks have their advantages in building medical monitoring systems, there are still the following challenges when applied to practical healthcare:

Dynamic networking and node mobility management in large-scale networks: When the monitoring system expands to communities, cities, and even the whole country, its network scale is huge, and both monitoring nodes and base stations have a certain degree of mobility. Therefore, it is necessary to design a suitable network topology management structure and node mobility management method.

Data integrity and compression: Nodes sometimes need to monitor human body parameters for up to 24 hours. The amount of data collected by nodes is large, but their storage capacity is small. Compression algorithms are often used to reduce the amount of data storage and transmission. However, traditional data compression algorithms have too much overhead and are not suitable for sensor nodes. In addition, compression algorithms should not damage the original data, otherwise it may cause misdiagnosis of patients.

Data security: Wireless sensor network nodes are self-organizing and vulnerable to attacks. In addition, patient information needs to be kept confidential. However, the computing power of sensor nodes is quite limited, and traditional security and encryption techniques are not applicable. Therefore, it is necessary to design an encryption and decryption algorithm suitable for sensor nodes.