The rising costs of healthcare and the increase in continuous healthcare monitoring of the aging population throughout the world pose challenges for healthcare and medical monitoring. A wireless body area network (WBAN), with medical sensors attached to a human body continuously sending measurements of human physiological parameters to a remote server or physician, has been shown to be adequate for monitoring the patient's health status without constraining his or her normal activities. WBANs must support a combination of low power, quality of service (QoS), high data rate, reliability, and non-interference, to address the gamut of WBAN applications. The IEEE 802.15.6 standard was officially approved in February 2012 for wireless communications in WBANs. The standard provides efficient communication solutions to ubiquitous healthcare and telemedicine systems, interactive gaming, military services, and portable audio/video systems.
The IEEE 802.15.6 standard defines a Medium Access Control (MAC) layer that supports several Physical (PHY) layers, such as Ultra-wideband (UWB), Narrowband (NB), and Human Body Communications (HBC) layers. The focus of this thesis is the short-range wireless communication network that is formed between the sensors and the hub in a WBAN, particularly at the medium access control (MAC) layer. The main focus is on the analytical modeling and performance evaluation of contention-based MAC protocols (supported by NB PHY) for a WBAN. Narrowband wireless communication is arguably top suited to a considerable number of healthcare applications, and is thus the focus of this thesis. The contributions of the dissertation are divided into two main parts.
The first part of the dissertation focuses on the analysis of the IEEE 802.15.6 Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) mechanism. We analytically approach to investigate the behavior of the protocol. We develop a discrete time Markov chain (DTMC) to evaluate the performance measures as throughput, mean frame service and energy consumption of IEEE 802.15.6 CSMA/CA under saturated, non-saturated traffic conditions using a single user priority (homogeneous traffic scenarios). We also study the heterogeneous scenarios (multiple user priorities (UPs)) differentiated by minimum and maximum contention window sizes as shown in the IEEE 802.15.6 standard. We extended the proposed analytical model to consider a portion of the access phases (i.e., EAP1 and RAP1) of the superframe and analyze its impact on the performance of the IEEE 802.15.6 CSMA/CA. While constructing the DTMC, we take into consideration the time spent by a node awaiting the acknowledgement frame, in our DTMC model this state is presented as (i,-1). The analysis is validated against extensive simulation.
In the second part of this dissertation we reconstruct the DTMC model by considering the ACK-timeout state (i,-1) as an additional state in our model that colliding nodes check to learn the fate of their transmission, while other contending nodes performing backoff check that slot as usual. We extended the model for an error-prone WBAN channel. Finally, to reduce the gap between successive contention window sizes we adopted the Fibonacci backoff procedure and compare the results with the binary exponential backoff procedure mentioned in the IEEE 802.15.6 standard.