  Although the performance of the medium access control (MAC) of the IEEE
802.15.4 has been investigated under the assumption of ideal wireless channel,
the understanding of the cross-layer dynamics between MAC and physical layer is
an open problem when the wireless channel exhibits path loss, multi-path
fading, and shadowing. The analysis of MAC and wireless channel interaction is
essential for consistent performance prediction, correct design and
optimization of the protocols. In this paper, a novel approach to analytical
modeling of these interactions is proposed. The analysis considers
simultaneously a composite channel fading, interference generated by multiple
terminals, the effects induced by hidden terminals, and the MAC reduced carrier
sensing capabilities. Depending on the MAC parameters and physical layer
thresholds, it is shown that the MAC performance indicators over fading
channels can be far from those derived under ideal channel assumptions. As
novel results, we show to what extent the presence of fading may be beneficial
for the overall network performance by reducing the multiple access
interference, and how this can be used to drive joint selection of MAC and
physical layer parameters.
