| With the urgent demand of national health, it is crucial to study low cost, wearable technologies and applications, which can be seamlessly integrated into the daily life, and not limited to time and place for the medical monitoring. WBAN (Wireless Body Area Network) is such an innovative solution. It typically consists of a collection of low-power, miniaturized, and lightweight devices with wireless communication capabilities that operates in, on, or around the body. These devices are able to constitute a network that enables real-time monitoring of human body functions. MAC (Medium Access Control) involves many crucial issues such as energy consumption, scalability, effective communication, as well as the privacy and security of individual medical data. This study focuses on key technologies of WBAN MAC protocol.According to the thought of "theory modeling-protocol design-security protocol" the paper studies several key technologies related to medical monitoring oriented WBAN MAC protocol. Firstly, analytical models are developed for evaluating the performance of the IEEE 802.15.6 CSMA/CA-based MAC protocol under unsaturation condition. Secondly, a hybrid MAC protocol is proposed with short interrupt mechanism, which can improve the energy and time slot utilization efficiency and satisfy the QoS requirements of heterogeneous medical data. Finally, a lightweight key agreement protocol is designed based on the fuzzy commitment mechanism. Furthermore, with the support of WBAN and cloud computing technology, a real-time health monitoring system is built and applied to the practical scenarios, which validates its effectiveness.The main research results and innovation points are as follows:(1) Analytical models are developed for evaluating the performance of the IEEE 802.15.6 CSMA/CA-based medium access control protocol for wireless body area networks (WBAN) under unsaturation condition. A three-dimensional discrete Markov chain is developed to model the backoff procedure of the CSMA/CA mechanism operating in the beacon mode. By solving the Markov chains, the medium access probabilities of all user priorities can be obtained. The embedded Markov chain approach is used to analyze the packet queue in the buffer, and the stationary distribution of the queue length can be computed. Using probability generating functions (PGFs) and Little’s law, the average packet service time and the mean queuing delay can be derived, and thus the average packet delay and system throughput can be obtained. By computing the energy consumption of each node, the energy efficiency of the whole network can be obtained. Simulation results are included to demonstrate the accuracy of the proposed analytical model. It is shown that the proposed model can effectively evaluate the performance of the medium access control protocol for WBAN under unsaturation condition.(2) Targeting at the medical monitoring applications of WBANs, a hybrid MAC protocol (I-MAC) is proposed. By modifying the superframe structure and time slot allocation, I-MAC protocol can improve the energy and time slot utilization efficiency, and meet the real-time and reliability requirements at the same time. A superframe structure with longer length is adopted to avoid unnecessary beacons so as to improve the energy efficiency. Most of the time slots are allocated as GTS to satisfy the transmission of a large amount of periodic medical monitoring data. For random emergency data, short interrupt slots are inserted into the superframe to guarantee the real-time and reliability requirements of these data. Simulation results with different parameter configuration show that I-MAC protocol has higher energy and time slot utilization efficiency than that of 802.15.4, and meets the data delivery delay requirement. When the arrival rate of random medical monitoring data is less than 1 in an interrupt slot, I-MAC protocol has better performance, and it is also effective for low aperiodic stochastic data.(3) Based on physiological signal, the key agreement mechanism of WBAN is deeply studied, and the advantages and disadvantages of two mainstream technologies fuzzy commitment and fuzzy vault are analyzed in detail. By comparison of the numerical results of the energy consumption of the WBAN nodes and the coordinator based on single-hop or multi-hop way, it is concluded that a single hop transmission mechanism consumes less energy for sensor nodes on the body. Thus, based on fuzzy commitment and EGC signal, a lightweight MAC key agreement protocol is proposed. In the initialization phase, the commitment generated by the shared key can avoid the mutual interference between WBANs, and resist the attacks from ultra-wideband radar remote sensing. In key agreement phase, time window mechanism can realize the weak synchronization of the physiological signal, so it avoids the much energy consumption due to precise synchronization. By substituting transmission energy for computation energy, the proposed key protocol can significantly save the energy, because simple bit computation can avoid the restart due to the key agreement failure of the physiological signal. It is analyzed that the proposed protocol can reduce the energy consumption, and improves the anti-attack performance of the key agreement of the WBAN.(4) Finally, based on the hardware and software design and other key technologies, a real-time health monitoring system is constructed with the support of WBAN. The system consists of diversified medical devices, served as sensor node, and the intelligent cloud health detector, served as a coordinator, a lightweight WBAN is deployed, which realizes the accurate perception and monitoring of multiple kinds of physiological parameters of human body. The collected data are processed intelligently, and then are uploaded to health cloud platform of the cloud computing center by the adaptive heterogeneous network, which realizes the intelligent analysis, storage and display of the medical data. By using the mobile APP, a closed-loop medical monitoring system is formed, which enables the real-time detection of personal health condition, mobile query, and remote monitoring and diagnosis. The EGC tests show that the system is effective for remote real-time medical monitoring, and owns good application value.
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