Research On Key Technologies Of MAC Layer In WBAN

The increasing global aging population and incidence of chronic diseases have exacerbated the social problems such as shortage of medical resources and increased medical costs.Healthcare has become a major issue that cannot be ignored.With the development of Information and Communication Technology(ICT),researchers have explored the key technologies in healthcare to solve the problems.In this situation,the Wireless Body Area Network(WBAN)technology has emerged at the right moment.The WBAN is a humancentered,short-range,highly reliable wireless communication network,which consists of a hub and multiple sensor nodes that are interconnected on the surface,inside,or in the proximity of the human body.It collects physiological,behavioral,and other health-related information of the user,and transmits the information to the hub or remote monitoring center to ask for healthy living or treatment advice from the telemedicine system.WBANs can provide continuous and reliable health monitoring for human body with great convenience and comfort but without geographical and medical facilities limitations,changing the paradigm of traditional healthcare systems.At present,WBAN,as the core technology of eHealthcare,can provide innovative solutions for health monitoring,which can effectively alleviate the medical problems caused by the shortage of healthcare resources.However,there are many technical challenges in WBAN for health monitoring.First of all,with the popularization of WBANs,the widespread multi-WBAN coexistence scenario will cause inter-WBAN interference,resulting in incomplete or overdue medical data transmission.The life-threatening data collected by the sensor nodes should be transmitted in high reliability and low delay,otherwise it will threaten people’s lives and lead to catastrophic consequences.Therefore,it is necessary to thoroughly study the interference problems of multi-WBAN coexistence to ensure the reliability and timeliness of information transmission.Secondly,the wearable or implantable sensor devices in WBAN are mainly battery powered with limited capacity.At the same time,sensor nodes have great difficulties in charging or replacing batteries.Energy-efficient communication mechanisms are needed to reduce energy consumption.Furthermore,different sensor nodes in the WBAN generate multiple types of services,such as information,images,or video.Different nodes have various arrival rates and Quality of Service(QoS)requirements.Moreover,there are burst traffic in the network,the transmission of which have higher requirements.The Medium Access Control(MAC)layer plays an important role in achieving energy-saving and real-time data transmissions.Energy-efficient and highly reliable MAC protocols are effective solutions.To address the aforementioned problems,this dissertation studied the key technologies of MAC layer in WBAN and designed a number of schemes to reduce the energy consumption and increase the reliability of data transmission.Specifically,we first analyzed the impacts of dynamic interference in multi-WBAN coexistence on the performance of IEEE 802.15.6 MAC protocol.We also implemented the IEEE 802.15.6 MAC protocol on the hardware platform.Then,in order to reduce the interference of interWBAN and intra-WBAN,a hybrid directional MAC protocol was designed.In addition,a two-round reservation protocol was proposed with considering the data characteristics of WBAN.The main contributions of this dissertation can be summarized as follows:(1)We analyzed the dynamic inter-WBAN interference with the movement of neighbor WBANs in rectilinear motion and curvilinear motion cases.A modified threedimensional Markov chain analysis model was proposed.The interference dynamics were further considered in the performance analysis model,which improved the practicability and credibility of the model.Based on this,we studied and analyzed the impacts of the number of nodes,payload,velocity,and the number of coexisting networks on the throughput and packet access delay of prioritized traffic in the target WBAN.Extensive numerical results proved the validity and accuracy of our proposed performance analysis model.The evaluation results greatly benefitted the network design and management as well as the interference mitigation protocols design.(2)Most of the existing works in WBAN focus on theoretical performance enhancement,whereas works in implementation which is of significance in validation and further research are pretty rare.Therefore,a reliable and efficient WBAN prototype system was designed both in hardware and software based on the IEEE 802.15.6 in this thesis.We constructed the prototype system from modules to system architecture.Moreover,we introduced the function of different modules and the information interaction process in different communication processes.Furthermore,a set of experiments were conducted to verify the prototype system in IEEE 802.15.6.The prototype system was ascertained to meet basic requirements in terms of QoS indexes by extensive experiments,among which we further explored frame error rate that can be a reference for future WBAN studies.(3)We proposed a hybrid Lifetime Extended Directional Approach(LEDA)MAC protocol based on IEEE 802.15.6 to reduce energy consumption and prolong network lifetime.The LEDA MAC protocol took full advantage of directional superiority in energy saving that employs multi-beam directional mode in Carrier Sense Multiple Access/Collision Avoidance(CSMA/CA)and single-beam directional mode in Time Division Multiple Access(TDMA)for alternative in data reservation and transmission according to the traffic varieties.Moreover,the impacts of some inherent problems of directional antennas such as deafness and hidden terminal problem could be decreased owing to that all nodes generate individual beam according to user priorities designated.Furthermore,LEDA MAC employed a dynamic polled allocation period for burst data transmissions to increase the network reliability and adaptability.Extensive analysis and simulation results showed that the proposed LEDA MAC protocol achieves extended network lifetime with improved performance compared with IEEE 802.15.6.(4)We designed a Token-based Two-round Reservation(TTR)MAC protocol based on IEEE 802.15.6 with considering the data features of health monitoring.With analyzing the characteristics of monitoring data,one-round reservation is conducted for periodic data and two-round reservation is generated adaptively for burst data to save energy.Besides,we built a relationship between the appropriate number of allocation slots and heterogeneous data arrival rates,which helps to utilize the time resource more efficiently and save more energy.Furthermore,a token was introduced on the basis of user priority and health severity index to indicate the transmission order of nodes with burst data.The proposed token guaranteed the most emergency data to be transmitted effectively and timely.In addition,a bit sequence scheduled algorithm was proposed for m-periodic monitoring data for network capacity expansion.The simulation results showed that TTR MAC protocol achieved higher energy efficiency and longer lifetime compared with IEEE 802.15.6 and other One-round Reservation MAC protocols for both 1-periodic and m-periodic data.