Cooperative virtual MIMO for wireless sleep apnoea monitoring system

Wireless Body Area Network (WBAN), an emerging technology which can continuously monitor the health condition of patients, has been attracting more and more attention recently. The information collected in this system can be shared with remote care providers or hospitals. WBAN is expected to be one of the main technologies for the provision of extremely convenient and efficient assistance to healthcare or medical services. In particular, it is useful for monitoring the physiological parameters of sleep apnoea patients. Conventional physiological data transmission for wireless sleep apnoea monitoring systems has been achieved only in the single input single output (SISO) environment in a WBAN scenario. In such a monitoring system, signal propagation paths may be affected by fading because of reflection, diffraction, energy absorption, shadowing by the body, body movement and the surrounding environment. A novel sleep apnoea monitoring system based on multi-sensor cooperation for the multiple input multiple output (MIMO) technique (also known as virtual MIMO) in WBANs is reported in this thesis. MIMO technology has emerged as a significant research area to combat fading in WBAN systems. MIMO also provides significant capacity increase and diversity gain in the WBAN channel. To monitor physiological parameters, a number of sensor nodes are needed to place in different positions on the body. To implement MIMO in WBAN system it is necessary to place multiple antennas on the tiny sensor nodes. However, due to physical size constraints it is impractical to place multiple antennas on the sensor nodes. To realize the same benefits of MIMO in WBAN systems a novel sensor cooperation technique using various cooperative communication protocols and techniques are introduced in this thesis. In sensor cooperation, the sensors not only send their own physiological information to the base station, but also convey information from adjacent sensor nodes. In order to achieve the goal of the thesis we first implemented the MIMO system in Field Programmable Gate Array (FPGA) to test the feasibility of MIMO using the Alamouti space time block coding technique in a WBAN system. Functional simulation showed the correct implementation of the Alamouti transmitter and receiver in FPGA. The performance of Alamouti space time coding was investigated in the WBAN channel. A prototype of 5.8 GHz rectangular patch antenna has been designed for measuring the correlation coefficient in dynamic WBAN channels. The reason for choosing the 5.8 GHz rectangular patch antenna for WBAN communication is that it is suitable for WBAN systems due to its smaller size compared to other antennas. In addition, the patch antenna is compact at this frequency which is well-suited for WBAN. The correlation coefficient is measured using the receive diversity technique in order to see the diversity gain in the sleep apnoea monitoring system. The measured correlation coefficient showed a low value as expected, which means that significant diversity gain can be achieved in the WBAN system. To implement sensor cooperation in the WBAN system, a number of cooperative relay protocols, for example, amplify and forward (AF), decode and forward (DF), estimate and forward (EF) are proposed. Two other emerging techniques, namely network coding-based cooperative communication and distributed space time coding-based cooperative communication have also been applied to implement sensor cooperation in the sleep apnoea monitoring system. All the cooperative relay protocols have provided significant diversity gain in the wireless sleep apnoea monitoring system of the WBAN channel. Investigation of the cooperative communication techniques revealed that the network coding-based cooperative communication strategy has a better performance in terms of bit error rate (BER) compared with distributed space time coding-based strategy. It is also reliable to handle a large number sensor nodes in the WBAN system. In addition, it enhances throughput and it is capable of working in the highly fading dynamic WBAN environment. Therefore, network coding has been selected for the implementation of virtual MIMO in WBAN for sleep apnoea monitoring. Cooperative virtual MIMO with energy efficient network coding is a promising approach for small sensor nodes in WBAN systems to achieve diversity gain. The main aim of this research is to introduce virtual MIMO in WBANs to transmit physiological data from sensors mounted on a patient to a remote base station. In order to fulfill the main objective of wireless monitoring of physiological parameters of a sleep apnoea patient, the hardware and software development of virtual MIMO using network coding has been achieved in this research. Electrocardiography (ECG) and Electromyogram (EMG)- the two important parameters of the human body are wirelessly transmitted and displayed on a laptop interfaced with the base station. The developed system would be capable of being adapted to time-varying channel conditions due to the patient’s movement and activity. The healthcare budget is decreasing and patients are increasing globally. Hence there is an increasing need to remotely monitor and treat patients. A prototype of a virtual MIMO-based wireless sleep apnoea monitoring system has been developed using zigbee protocols in this research. The results of the research will contribute significantly by enabling the monitoring of patients in their home environment. For example, in Australia, there are many aged care facilities where the system developed here will facilitate the care of elderly patients.