IEEE 802.11 WLAN cannot guarantee the QoS of
applications, thus admission control has been proposed as an essen-tial
solution to enhance the QoS. Packet delay and throughput are commonly employed
as assessment criterions to determine whether a new connection can be admitted
into the WLAN. Considering the real network condition, the analytical model is presented
in this paper, which is aimed to evaluate the packet delay and throughput
performance of IEEE 802.11 WLAN in nonsaturated conditions, taking into account
diverse transmission rates and diverse traffic flows (i.e. flows with different
packet sizes and arrival rates) simultaneously. This model is based on Markov
chain and the theoretical predictions are verified by simulation in OPNET 14.5.
We also analyze the influences of transmission rate diversity and traffic flow
diversity on throughput performance. It is observed that, the presence of even
one station with lower transmission rate can cause a considerable degradation
in throughput performance of all the stations when they have the same packet
size and arrival rate. Higher system throughput can be achieved if lower
transmission rate stations transmit packets with smaller size or arrival rate.
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