  The strength of carrier-sense multiple access with collision avoidance
(CSMA/CA) can be combined with that of time-division multiple access (TDMA) to
enhance the channel access performance in wireless networks such as the IEEE
802.15.4-based wireless personal area networks (WPANs). In particular, the
performance of legacy CSMA/CA-based medium access control (MAC) scheme in
congested networks can be enhanced through a hybrid CSMA/CA-TDMA scheme while
preserving the scalability property. In this paper, we present distributed and
centralized channel access models which follow the transmission strategies
based on Markov decision process (MDP) to access both contention period and
contention-free period in an intelligent way. The models consider the buffer
status as an indication of congestion provided that the offered traffic does
not exceed the channel capacity. We extend the models to consider the hidden
node collision problem encountered due to the signal attenuation caused by
channel fading. The simulation results show that the MDP-based distributed
channel access scheme outperforms the legacy slotted CSMA/CA scheme. This
scheme also works efficiently in a network consisting of heterogeneous nodes.
The centralized model outperforms the distributed model but requires the global
information of the network.
