  We propose a multicast scheduling scheme to exploit content reuse when there
is asynchronicity in user requests. A unicast transmission setup is used for
content delivery, while multicast transmission is employed opportunistically to
reduce wireless resource usage. We then develop a multicast scheduling scheme
for the downlink multiple-input multiple output orthogonal-frequency division
multiplexing system in IEEE 802.11 wireless local area network (WLAN). At each
time slot, the scheduler serves the users by either unicast or multicast
transmission. Out-sequence data received by a user is stored in user's cache
for future use.Multicast precoding and user selection for multicast grouping
are also considered and compliance with the IEEE 802.11 WLAN transmission
protocol. The scheduling scheme is based on the Lyapunov optimization
technique, which aims to maximize system rate. The resulting scheme has low
complexity and requires no prior statistical information on the channels and
queues. Furthermore, in the absence of channel error, the proposed scheme
restricts the worst case of frame dropping deadline, which is useful for
delivering real-time traffic. Simulation results show that our proposed
algorithm outperforms existing techniques by 17 % to 35 % in term of user
capacity.
