Asymmetric Carrier Sense in Heterogeneous Medical Networks Environment
Bin Zhen, Huan-Bang Li, Shinsuke Hara, Ryuji Kohno · InTech eBooks · 2010
Complementary WLAN and WPAN technologies, as well as other wireless technologies will play a fundamental role to support ubiquitous healthcare delivery.This chapter investigates energy based clear channel assessment (CCA) of IEEE WLAN (802.11b) and WPAN (802.15.4b) system when they coexist in a close space.We derive closed-form expressions of energy based, qualify the asymmetric CCA in both AWGN channel and fading channels, and show the impact of noise uncertainty on CCA operation.In the heterogeneous medical networks environment, WPAN is oversensitive to the 802.11b signals and WLAN is insensitive to the 802.15.4b signals.The asymmetric CCA issue in heterogeneous networks is different from the traditional "hidden node" or "exposed node" issues in homogeneous network.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 802.15.4b signals.This leads to WPAN traffic in a position secondary to the WLAN traffic.A two-band CCA scheme, with an additional CCA detector in auxiliary channel, is proposed to combat the asymmetric CCA issue in the heterogeneous networks.