This article mainly introduces the wireless medical monitoring technology based on WPAN, and then introduces the technology implementation based on JN5121 chip, and test verification. Finally, the development prospect and existing problems of wireless medical monitoring network are prospected.
2 Based on WPAN wireless medical monitoring technology
WPAN is a wireless transmission technology developed to establish a wireless connection between devices in a small area. The IEEE Standards Association has formulated the IEEE802.15.x standard for this purpose. The transmission technology involved in this article complies with IEEE802.15.4 specifically formulated for low-speed WPAN (Zigbee) standard.
The architecture proposed in this paper is based on WPAN, which is different from wireless telemedicine. The focus of this article is on the wireless method from physiological signal acquisition to physiological signal relay. The wireless medical monitoring method is mainly composed of sensor nodes, wireless data transmission modules and receiving nodes. The receiving node can access the monitoring center, or access the monitoring center by Ethernet, wireless WAN, etc., thus forming a complete medical monitoring network. Under this framework, medical sensor nodes can be configured according to specific conditions to form a local or family wireless medical monitoring network. This framework has great flexibility and scalability. In this framework, our wireless communication method is based on the Zigbee protocol and uses the JN5121 module as the wireless transceiver node. Figure 1 describes the system structure of wireless medical monitoring.
Figure 1 System structure diagram of wireless medical monitoring
3 Sensor node design based on JN5121 chip
3.1 Introduction to JN5121 module
JN5121 is a low-power, low-cost wireless microcontroller compatible with IEEE802.15.4 introduced by Jennic. The module has a built-in 32-bit RISC processor, equipped with a 2.4GHz frequency band EEE802.15.4 standard wireless transceiver, 64kB ROM.96kB RAM, providing a variety of solutions for wireless sensor network applications, colleagues highly integrated The design simplifies the total system cost. JN5121's built-in ROM memory integrates a complete protocol stack for point-to-point communication and mesh network communication; while its built-in RAM memory can support network routing and controller functions without requiring any external expansion. The storage space, 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 projects. At the same time provides interoperability support for a large number of analog and digital peripherals can be easily connected to the user's external application system.
3.2 Sensor node design
The wireless physiological sensor is composed of two parts: physiological signal acquisition part and wireless transmission part. Physiological signal acquisition We can use various physiological electrodes we need to measure the body's electrocardiogram, blood saturation concentration, pulse and so on. For the wireless module, we use the S0C chip JN5121 which integrates the microprocessor and the RF chip. The chip can control the processing operation, routing protocol, synchronous positioning, power management and task management of the entire node. Compared with the previous Zigbee radio frequency chip, the use of this chip does not need an external MCU, which effectively saves the peripheral circuit of the chip. Using the on-chip chip solution can save a few points of space, which is easy for the guardian to carry. Figure 2 is a physiological wireless sensor solution.
Figure 2 Physiological wireless sensor solution
4 Design of basic programming station
The design of the JN5121 chip is based on the Zigbee protocol, so first we understand the basic knowledge of Zigbee. The physical layer and MAC layer of the Zigbee protocol are formulated according to the 802.15.4 standard, while the standards of the network layer and the application layer are formulated by the Zigbee alliance. Based on the actual application development of the Zigbee protocol, we only need to call the corresponding API function or develop the program code at the application layer. This article briefly introduces several important functions that need to be applied.
A basic operating system (BOS) in the Jennic Zigbee protocol. It is a simple time scheduler. It allows communication between two task processes through a simple information scheduling mechanism. Colleague 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 object ZDO (Zigbee Debice 0bjects). The scheduling of processes is implemented through polling applications of events. The entire process is shown in Figure 3.
Figure 3 Scheduling process of the realization process
5 Test verification
We use the JN5121-M00 module distributed by Beijing Bokong Co., Ltd. The signal is a pulse signal with a sampling frequency of 150Hz. The wireless transmission adopts the point-to-point method, and the experiment proves that there is no significant difference between the results obtained through the Zigbee network and the direct sampling with PC.
6 Conclusion
This article preliminarily introduced the structure and main functions of the JN5121 module, and explained the basic programming flow of JN5121. The basic concept of application of JN5121 in wireless medical monitoring technology based on WPAN is proposed.
The wireless medical monitoring method can reduce the connection between the guardian and the instrument, and get better physiological data. At the same time, it can allow the guardian to get a larger activity space. Many advantages of the wireless medical monitoring method are the driving force for the development of wireless medical monitoring technology. With the continuous development of hardware conditions, wireless medical monitoring will certainly have a broad development space.
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