Patient-Care Sensing and Monitoring Systems
Wireless sensors that have more advantages relative to wired sensors are playing an important role in improving the quality of life in daily indoor space. The applications include home security systems to improve the safety of our home and vital signs monitoring systems to improve our health. The sensor systems can remotely detect the echo reflected from a person and then estimate the state and/or vital signs such as respiration rate and heart rate, for example. Several types of wireless sensor device have thus far been developed such as video camera, passive infrared (IR), and microwave. The video camera is unacceptable for some applications from a privacy protection point of view, although it can monitor a wide area of the indoor space. Passive IR sensors are generally developed to be dedicated to a relatively small area such as the home entrance and toilet area. Microwave sensors such as Doppler and frequency modulation continuous wave (FM-CW), which are capable of penetrating a variety of nonmetallic materials such as inner walls, provide a wider coverage area when compared with video cameras and IR, but it is susceptible to interference from other wireless radio systems, thereby causing false alarms or false detection. Ultrawideband impulse-radio (UWB-IR) has lately attracted considerable attention in short-range remote sensor applications since it offers high-ranging accuracy, multipath reduction, and environmental friendliness due to the very low energy emission [1–4]. However, it requires very-high-speed analog-to-digital converter (ADC) and high-level processors in order to synchronize and detect the received nanosecond pulse. It may also cause interference to existing or future wireless systems using the same or nearby bands because it occupies a bandwidth wider than 500 MHz. Therefore, the UWB device operated in the lower band of 3.4–4.8 GHz is required to implement the detect-and-avoid (DAA) technique in many countries such as Europe, Korea, and Japan .