Wireless channels and antennas for body-area networks

In this paper a review of recent research in characterizing on-body wireless channels is presented. Path gain random variations caused by body movements in various environments have been investigated at several frequencies, including 2.45 GHz and 5.8 GHz. In a scattering environment, such as an office, the fading of on-body channels was found to undergo a combination of two types of variation, namely, short-term and long-term variations. The short-term variation is due to multipath fading and can be described by either Rician or Nakagami distribution, and the long-term fading usually follows a log-normal, or gamma distribution. The rates of fading expressed in terms of level crossing rate and average fade duration have been also obtained. The effect of these indings on the system design parameters, such as link reliability, fade margin, and required transmitted power, is discussed. Performance of different types of antennas which can be used in WBAN devices has been evaluated as well. It is found that antenna diversity can be successfully applied in order to mitigate the effects of channel fading and interference.