Design of wireless medical monitoring system based on WPAN technology and JN512 chip

1 Preface

Wireless medical monitoring is the abbreviation of using wireless communication technology to assist medical monitoring. In recent years, with the miniaturization of biomedical sensors, the rapid development and popularization of information processing and wireless data transmission technology, wireless medical monitoring has become a hot topic.

ZigBee is a wireless network communication technology standard that has emerged in recent years. Its outstanding advantages are low cost and low power consumption. It has a large network capacity, small data exchange, and focuses on low-rate signal transmission. It fully meets the transmission requirements of basic physiological signals.

This paper first introduces the wireless medical monitoring technology based on WPAN, then introduces the technical implementation based on JN5121 chip, and experimental verification. Finally, the development prospects and existing issues of wireless medical monitoring network are prospected.

2 Wireless medical monitoring technology based on WPAN

WPAN is a wireless transmission technology developed for establishing wireless connections between devices in a small range. The IEEE Standards Association has developed the IEEE802.15.x standard for this purpose. The transmission technology involved in this article complies with the IEEE802.15.4 (Zigbee) standard specifically developed for low-speed WPAN.

The architecture proposed in this paper is based on WPAN, which is different from wireless telemedicine. This paper focuses on the wireless method from physiological signal acquisition to physiological signal transfer. The wireless medical monitoring method is mainly composed of sensor nodes, wireless data transmission modules and receiving nodes. The receiving node can be connected to the monitoring center, or connected to the monitoring center by Ethernet, wireless wide area network, etc., thus forming a complete medical monitoring network. Under this architecture, medical sensor nodes can be configured according to specific circumstances to form a local or home wireless medical monitoring network. This architecture has great flexibility and scalability. In this architecture, our wireless communication method is based on the Zigbee protocol, and the JN5121 module is used as the wireless transceiver node. Figure 1 describes the system structure diagram of wireless medical monitoring.

Figure 1 System structure diagram of wireless medical monitoring

3 Sensor node design based on JN5121 chip

3.1 JN5121 module introduction

JN5121 is a low-power, low-cost wireless microcontroller compatible with IEEE802.15.4 launched by Jennic. The module has a built-in 32-bit RISC processor, a 2.4GHz band EEE802.15.4 standard wireless transceiver, 64kB ROM and 96kB RAM, providing a variety of solutions for wireless sensor network applications. The highly integrated design simplifies the total system cost. The built-in ROM memory of JN5121 integrates a complete protocol stack for point-to-point communication and mesh network communication; and its built-in RAM memory can support network routing and controller functions without any external expansion of storage space. The built-in hardware MAC address and highly secure AES encryption algorithm accelerator reduce the system's power consumption and processor load. It also supports crystal oscillator sleep and system energy-saving engineering. At the same time, it provides interoperability support for a large number of analog and digital peripherals, which can be easily connected to the user's external application system.

3.2 Sensor Node Design

The wireless physiological sensor consists of two parts: the physiological signal acquisition part and the wireless transmission part. For physiological signal acquisition, we can use various physiological electrodes we need to measure the human body's electrocardiogram, blood saturation concentration, pulse, etc. For the wireless module, we use the S0C chip JN5121 that integrates a microprocessor and an RF chip. The chip can control the processing operation, routing protocol, synchronous positioning, power consumption management and task management of the entire node. Compared with the previous Zigbee radio frequency chip, the use of this chip does not require an external MCU, which effectively saves the chip's peripheral circuits. The use of the chip-on-chip solution can further save some volume and is convenient for the person being monitored to carry. Figure 2 is a physiological wireless sensor solution. [page]

Figure 2 Physiological wireless sensor solution

4 Design of basic programming station

The design of JN5121 chip is based on Zigbee protocol, so first we need to understand the basic knowledge of Zigbee. The physical layer and MAC layer of Zigbee protocol are formulated according to the 802.15.4 standard, while the standards of its network layer and application layer are formulated by Zigbee Alliance. For actual application development based on Zigbee protocol, we only need to call the corresponding API function or develop program code in the application layer. This article briefly introduces several important functions that need to be applied.

In the Jennic Zigbee protocol, there is a basic operating system (BOS). It is a simple time scheduler. It allows two task processes to communicate through a simple information scheduling mechanism. At the same time, BOS controls the execution of Zigbee protocol stack tasks and user tasks. The protocol stack tasks include all processes of the network layer, application sublayer APS (Application Sub-Layer) and Zigbee device objects ZDO (Zigbee Devices). The process scheduling is realized through the event polling application. The whole process is shown in Figure 3.

Figure 3: Scheduling process for implementing a process

5 Experimental verification

We use the JN5121-M00 module sold by Beijing Bokong Company, and the signal is a pulse signal with a sampling frequency of 150Hz. The wireless transmission adopts point-to-point mode. The test shows that there is no significant difference between the results obtained through the Zigbee network and directly using the PC sampling.

6 Conclusion

This paper preliminarily introduces the structure and main functions of JN5121 module, explains the basic programming process of JN5121, and proposes the basic conception of applying JN5121 in wireless medical monitoring technology based on WPAN.

Wireless medical monitoring can reduce the connection between the monitored person and the instrument, obtain better physiological data, and at the same time, allow the monitored person to have more room for activities. The many advantages of wireless medical monitoring are the driving force for the development of wireless medical monitoring technology. With the continuous development of hardware conditions, wireless medical monitoring will surely have a broad space for development.