  This paper analyzes the saturation throughput of a cognitive single hop WLAN
overlaid on a primary IEEE 802.16e TDD WiMAX network. After the contention
among the secondary nodes, the winner node transmits its data packet in the
empty slots of downlink subframes of WiMAX. Regarding the OFDMA structure as
well as time-scheduled resources in WiMAX, the time duration of opportunities
for the secondary network does not follow simple exponential on-off pattern. To
model the dynamic behavior of opportunities for secondary nodes as well as
contentions to exploit the opportunities, we propose an analytical model
comprised of a discrete-time Markov chain and two inter-related open
multi-class queueing networks. The effects of random number of empty slots at
different frames as the result of random amount of download data, random packet
transmission time at WLAN due to random opportunities in different frames, the
dependency of the number of empty slots at consecutive WiMAX frames, and the
details of 802.11 MAC protocol are included in our analytical approach. We
compare the effect of two resource allocations, i.e., horizontal and vertical
striping on the saturation throughput of the cognitive WLAN. Simulation results
confirm the accuracy of our analytical approach in different conditions.
