Energy Based Carrier Sensing in Integrated Medical Environments

Complementary WLAN and WPAN technologies, as well as other wireless technologies will play a fundamental role in the medical environments to support ubiquitous healthcare delivery. This paper investigates energy based carrier sensing and its impact on the coexistence of IEEE WLAN (802.11b) and WPAN (802.15.4) in the 2.4 GHz band. We derived closed-form expressions of energy based clear channel assessment (CCA) and qualified unequal sensing abilities between WLAN and WPAN in additive white Gaussian noise channel and fading channel. The asymmetric CCA is different from the traditional "hidden node" or "exposed node" issues in the homogeneous network. The WPAN is oversensitive to the 802.11b signals and the WLAN is insensitive to the 802.15.4 signals. Choosing an optimal CCA threshold requires some prior knowledge of the underlying signals. In the considered integrated medical environments, energy based CCA can effectively avoid possible packet collisions when they are close within the "heterogeneous exclusive CCA range". However, beyond this range, WPAN can still sense 802.11b signals, but WLAN lose its sense to 802.15.4 signals. This leads to WPAN traffic in a position secondary to the WLAN traffic.