Wireless Sensor Network (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 of technology. 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 the architecture of wireless sensor network medical monitoring system and the general principles of monitoring node design.
Wireless sensor network architecture
A large number of sensor nodes are arranged in the monitoring area. The nodes use self-organization for networking and wireless communication technology for data forwarding. Each node has the dual functions of data collection and data fusion forwarding. The node performs preliminary data processing and information fusion on the information collected by itself and the information forwarded to it by other nodes, and then transmits it to the base station through the relay transmission of the neighboring node, and then transmits it to the end user through the base station through the Internet, satellite, etc.
The node is the basic functional unit of the wireless sensor network. The specific application is different, and the design of the node is also different. The basic components of the sensor node are: sensing unit, processing unit, communication unit and power supply. In addition, functional units can be added according to specific application requirements, such as positioning systems, mobile systems, and power supply self-powered systems.
Application of wireless sensor network in medical treatment
The wireless sensor network uses its own advantages (such as low cost, simple, fast, and non-invasive collection of various physiological parameters of patients in real time, etc.), making it useful in medical research, hospital general / ICU wards, or family daily monitoring. The great development potential is a hot spot in the current research field.
A micro sensor node for detecting human parameters is placed on the patient, which can monitor the patient's heart rate, blood pressure, electrocardiogram, heart sound and other physiological parameters in real time, and transmit the information to the monitoring center for timely processing and feedback; use WSN's long-term collection of human physiological data of the observed subjects is very helpful for understanding human health and studying human diseases. In addition, it also has its unique applications in many aspects such as drug management, research and development of new drugs, and blood management. In short, the wireless sensor network provides a more convenient and low-cost implementation method for the future remote medical monitoring system.
Medical architecture based on wireless sensor network
The medical monitoring system based on wireless sensor network is mainly composed 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 / family or ward wireless sensor network. Multiple such networks can form a community or the entire hospital monitoring network, or even a larger range of remote medical monitoring systems. First, the medical sensor node collects human physiological parameters, and after simple processing of the collected parameters, the data is transmitted to the base station directly or indirectly hop by hop through wireless communication. The guardianship base station further processes the data and forwards it to the guardianship center. The guardianship center performs analysis and processing, and promptly feeds back information to the patient. The monitoring center can also use a variety of methods (Internet, mobile communication network, etc.) for remote data transmission to share information with other monitoring centers.
Design of medical sensor nodes
The basic structure of a medical sensor node includes a processing module, a sensor module, a wireless transceiver module, and a power supply module.
The sensor module is used to sense, collect and convert external sensor signals. It is the module that the whole node is really in contact with external semaphores. However, medical sensors are based on living objects. In particular, the human body is arguably the most complex system in the world. There is a high degree of correlation between various physiological variables and it is not easy to access. Therefore, the medical sensor must take out the predicted physiological quantity from many phenomena, and obtain reliable and meaningful measurement data, and at the same time, it must ensure the safety of the measured object.
Since human body parameters are mostly weak signals, generally only a few mV level or lower, and there are many kinds of noise (measurement environmental noise, instrument and human friction noise and instrument itself noise, etc.), power frequency interference (from the measurement environment around 50 Caused by the electromagnetic field of Hz) and various noises and other unfavorable factors. Therefore, in the design of a specific medical sensor node, an analog circuit processing module is added. The module generally includes the following parts: an amplifier circuit, a filter circuit, a trap circuit, and an analog-to-digital (A / D) conversion circuit. In the node design, the amplifier circuit generally adopts multi-stage amplification (three-level or four-level). In addition to the amplification function, the final-stage amplification circuit generally also has a level-up function; filter circuit: it should meet the circuit's concise, reasonable cut-off frequency, and flexible Convenient adjustment of high and low pass cut-off frequency and other requirements, reasonable filtering of high-frequency and low-frequency interference in the signal; notch circuit: currently widely used symmetrical double T resistance-capacitive active wave trap or integrated switch capacitor device and asymmetric Resistance-capacitance network trap etc. In short, the analog circuit processing module mainly amplifies, filters, and traps the collected signals to remove noise and interference from the signals and extract useful signals.
The processor module is the core of the sensor node and is responsible for device control, task allocation and scheduling, data integration and transmission of the entire node. At present, the most 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 the node design, it is necessary to program the processor module to realize the acquisition control of the sensor module, the realization of A / D conversion, and to control the transceiver 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 ChipCon's CCl000, CC2420, and CC2430. Commonly used wireless communication technologies are: 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 implement data communication between nodes and between nodes and base stations.
The power module provides energy to the node and is the basic module of the entire wireless sensor node. However, due to the limited volume of the node, the energy of the sensor node is very limited. Therefore, in the whole 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 life. Therefore, the designed medical node should have a long life cycle.
Challenges in medical wireless sensor network monitoring system
Although wireless sensor networks have their unique advantages in the formation of medical monitoring systems, the following challenges still exist in the application of actual medical treatment:
Dynamic networking and node mobility management in large-scale networks: When the monitoring system is extended to communities, cities, and even the whole country, its network scale is huge, and both monitoring nodes and base stations have certain mobility. Therefore, an appropriate network topology management structure and node mobility management method must be designed.
Data integrity and data compression: Nodes sometimes need to monitor human parameters for up to 24 hours. The amount of data collected by nodes is large, and the storage capacity of nodes is small. Compression algorithms are often used to reduce the amount of data storage and transmission. However, the traditional data compression algorithm is too expensive and not suitable for sensor nodes. In addition, the compression algorithm cannot damage the original data, otherwise it will cause erroneous diagnosis of the patient.
Data security: The wireless sensor network nodes are self-organized to form a network and are vulnerable to attacks. In addition, the patient's information needs to be kept confidential. However, the computing power of sensor nodes is quite limited, and traditional security and encryption technologies are not applicable. Therefore, an encryption and decryption algorithm suitable for sensor nodes must be designed.
Summary and outlook
With the development of technology, wireless medical sensor nodes are gradually developing toward multi-parameters, intelligence, miniaturization, and low power consumption. Wireless sensor networks will also be gradually applied to the medical field. The development and establishment of an intelligent ward and community monitoring system is the trend of medical development at home and abroad.
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