Design of remote medical monitoring system based on ZigBee technology

Abstract: Introducing wireless sensor networks into medical monitoring systems, this paper proposes a remote medical monitoring system architecture and specific implementation method consisting of ZigBee sensors and wireless local area networks. In the system, the short-range communication standard used by nodes and base station devices is the 802.15.4/ZigBee standard, which collects various types of patient information, enables remote medical monitoring of patients at home, and promptly reports the patient's condition to doctors and their families to deal with possible emergencies of patients. While obtaining accurate measurement indicators, it also saves patients from the hard work of running between home and hospital.

Telemedicine is the product of the combination of information technology and medicine. It uses remote communication and computer multimedia technology to provide patients with medical information and medical services. With the rapid development of information technology today, it has become a beautiful landscape in medical communication.

Telemedicine is mainly used in clinical consultation, examination, diagnosis, monitoring, treatment guidance, medical research, communication, medical education and surgical observation. As a part of the telemedicine system, the telemedicine monitoring system transmits the collected physiological parameters and video, audio and image data of the monitored person to the community monitoring center in real time through the communication network, which is used to dynamically track the development of the disease to ensure timely diagnosis and treatment. With the rapid increase of the elderly population in today's society, the role of monitoring in medical resources has become more prominent.

Medical monitoring instruments can be divided into two categories. One is a special instrument used by professional doctors or professional technicians in hospitals to monitor the physiological indicators of patients; the other is a remote medical monitoring system used by patients or their families in the home or outdoors under the guidance of doctors, and the obtained physiological indicators will be transmitted to the relevant doctors in a timely manner. At present, most of the monitoring systems used in hospitals are based on cable connections. They are often large in size and power consumption, not easy to carry, and require use near patients, which restricts the actions of patients and medical staff, increases their burden and risks, and is increasingly unsuitable for today's real-time, continuous, and long-term medical monitoring needs for monitoring important vital characteristics of patients. In order to enable people who often need to measure physiological indicators (such as chronic patients or elderly patients, etc.) to measure certain routine indicators at home in a state of free movement, people are paying more and more attention to telemedicine.

In recent years, with the rapid development and popularization of miniaturization, information processing and wireless data transmission technology of biomedical sensors, the development of wireless medical monitoring systems has become a hot topic. The author has designed a new network monitoring device and system, the purpose of which is to use high-frequency wireless multi-channel data transmission to transmit information between medical sensors and monitoring control instruments, reduce the connection between monitoring equipment and medical sensors, so that the monitored person can have more free space for activities, and obtain more accurate measurement indicators while eliminating the hard work of running between home and hospital. At the same time, a wireless monitoring network is established in the hospital ward, and multiple test items can be completed on the bed, which can greatly facilitate patients' medical treatment and enhance the hospital's modern information management and work efficiency.

1 System Structure

The architecture diagram of the remote medical monitoring system is shown in Figure 1. The system consists of a monitoring base station device and ZigBee sensor nodes to form a micro monitoring network. The central controller is used on the sensor node to control the vital indicator sensors that need to be monitored and collect data. The data is sent to the monitoring base station device through ZigBee wireless communication, and the base station device transmits the data to the connected PC or other network devices. The data can be transmitted to the remote medical monitoring center through the Internet network, and professional medical personnel can conduct statistical observations on the data and provide necessary consulting services to achieve remote medical care. Emergency personnel in the ambulance can also use GPRS to transmit the information of emergency patients in real time, so that the hospital emergency room can prepare in time. Medical sensor nodes can be set according to different needs, so the system has great flexibility and scalability. At the same time, connecting the system to the Internet network can form a larger community medical monitoring network, hospital network, and even the entire city and national medical monitoring network.

Figure 1 Structure diagram of remote medical monitoring system

The system includes wireless personal area network (WPAN), ZigBee network and a series of medical sensor nodes of medical monitoring network. This system has good scalability. For example, medical staff can use WLAN/UMTS gateway and Internet to exchange information with the system during emergency or in other hospitals.

2 Monitoring sensor nodes

2.1 Composition and working principle of monitoring sensors

The main function of medical wireless sensor nodes is to collect human physiological index data, or dynamically monitor the status of certain medical equipment and the treatment process, and transmit the data to the monitoring base station equipment through radio frequency communication.

The block diagram of the medical sensor node is shown in Figure 2, which mainly includes four parts: medical sensor module, ZigBee communication module, processor unit and power supply. The processor unit is shown in Figure 3, which is mainly divided into five parts: CPU, memory, AD conversion, test strip and digital display. According to the needs of low power consumption and processing power, TI's MSP430 series microcontroller is used. The memory part is mainly used to store temporary data collected by the sensor. After the processor transmits the data, the sensor node does not store a large amount of data.

Figure 2 Block diagram of medical sensor node

Figure 3 Processor unit

The working principle of the monitoring sensor is that the control unit first issues an instruction to start monitoring a certain physiological parameter, and then sends the instruction to the physiological information and data acquisition unit through the wireless data communication unit to collect human physiological signals (body temperature, blood pressure, pulse, blood sugar, blood oxygen, etc.), and finally transmits the data to the information processing module in the control and display unit through the wireless data communication unit. On the one hand, the received data is processed and displayed, and on the other hand, the result data is stored in the database for retrieval and playback. The core of the node is the wireless data communication unit and the physiological information and data acquisition unit.

2.2 Wireless data communication unit

In hospitals, the medical monitoring equipment used has very high requirements for electromagnetic radiation. For the equipment, the electromagnetic waves radiated should not interfere with the normal operation of other equipment, and at the same time, it should have a certain anti-interference ability and not be interfered by the electromagnetic waves radiated by other equipment. Therefore, the design of medical equipment used in hospitals or homes using wireless communication must take this into full consideration.

In this system, the radio frequency communication used is the globally open and free 2.4 GHz ISM band, and the communication standard adopted is the 802.15.4/ZigBee standard. It is a low-complexity, low-power and low-cost wireless communication technology that can transmit medical data at a transmission rate of 20 to 250 kb/s within a range of 10 to 75 m. It coordinates and communicates among thousands of tiny sensors based on the 802.15.4 standard. These sensors only require a small amount of energy and transmit data from one sensor to another through radio waves in a relay manner, so the communication efficiency is very high. It can use ordinary dry batteries as a power source, and under normal circumstances, it can support 6 to 24 months, greatly reducing the trouble of frequent battery replacement.

To reduce costs, the ZigBee standard defines two types of devices: full function device (FFD) and reduced function device (RFD).

FFD can work in three different modes: ① Personal area network (PAN) coordinator; ② Coordinator; ③ Device. As a slave device, RFD does not need to transmit a large amount of data and only occupies a small amount of resources. A simplest WPAN can be formed by adding an FFD to an RFD, in which the FFD acts as a PAN coordinator to perform communication functions. Therefore, there must be at least one FFD as a PAN coordinator in any star network. In this system, ZigBee devices usually exist in two network structures: star and mesh. The network topology is shown in Figure 4.

Figure 4 ZigBee network topology diagram

The star network structure is a communication structure in which FFD acts as a PAN coordinator to complete the communication with the devices. In this network, the function of the PAN coordinator is to initialize the network, terminate and route information. Star networks are widely used in small areas such as automated homes, personal medical monitoring systems and hospital wards.

2.3 Physiological information and data acquisition unit

In the system, the medical sensor module mainly realizes the following functions: measurement of body temperature, blood pressure, blood oxygen and blood sugar, etc. Among them, the body temperature measurement integrates the YSI body temperature probe produced by Beijing Maichuang Company, the blood pressure measurement integrates the KNM non-invasive blood pressure measurement module of Maichuang Company, and the blood oxygen measurement integrates the SWS01 blood oxygen measurement module of Maichuang Company.

The wireless node has reserved abundant interfaces for the expansion of sensors. If other types of physiological indicator data are needed, such as body temperature, electrocardiogram and other data, you only need to connect the corresponding sensor to the reserved interface to form a new wireless sensor node, develop the corresponding embedded control and processing software, and then you can directly add the node to the wireless sensor network.

3 GPRS/UM TSWLAN Gateway

Compared with WLAN, which has high transmission rate and low coverage, GPRS/UMTS has the characteristics of low transmission rate and high coverage. This system uses GPRS/UMTSWLAN gateway to achieve seamless connection between UMTS and WLAN. This allows devices equipped with UMTS and WLAN interfaces to switch freely between the two networks.

Generally speaking, there are two ways to integrate WLAN and UMTS: tight coupling and loose coupling. In a tight coupling system, the WLAN gateway is directly connected to the UMTS network. In a loose coupling system, the WLAN gateway is not directly connected to the UMTS network, but through the Internet or IP backbone network as an intermediary. In this system, a loose coupling system is used to achieve communication between handheld mobile devices and the UMTS network. The loose coupling architecture of WLAN and UMTS is shown in Figure 5.

Figure 5 Loosely coupled architecture of WLAN and UMTS

4 Experimental Verification

The system has achieved preliminary results in the comprehensive test process. The data collected by the vital signs sensor on the sensor node is sent to the monitoring base station device through ZigBee wireless communication and displayed on the LCD of the base station device. The total data transmission volume for each patient is between 22 and 76 kb/s (depending on the number of electrocardiogram electrodes). The frequency range and data volume of commonly used measurement signals are shown in Table 1. The base station device transmits the data to the connected PC or other network device, and transmits the data to the remote medical monitoring center through the In2ternet network. Professional medical personnel conduct statistical analysis on the data and provide necessary consulting services to realize telemedicine. For example, in an ambulance, emergency personnel can also realize real-time transmission of emergency patient conditions through GPRS, so as to facilitate timely preparation of the hospital emergency room.

Table 1 Frequency range and data volume of commonly used measurement signals

5 Conclusion

The new network monitoring device and system designed can reduce the connection between monitoring equipment and medical sensors, and obtain more accurate measurement indicators while eliminating the trouble of patients running between home and hospital. At the same time, a wireless monitoring network is established in the hospital ward, and many test items can be completed on the bed, which greatly facilitates patients to see a doctor. In addition, this system is also highly flexible and scalable. Through the Internet, patients who are far away from hospitals and other medical institutions can also get the necessary medical monitoring and remote doctor's consultation and guidance at any time. The author will further develop the software and hardware of the system to improve its stability and practicality. At the same time, the upper management software will be customized and developed according to special needs, and the medical monitoring management platform software will be improved.