  Multi-user spatial multiplexing combined with packet aggregation can
significantly increase the performance of Wireless Local Area Networks (WLANs).
In this letter, we present and evaluate a simple technique to perform packet
aggregation in IEEE 802.11ac MU-MIMO (Multi-user Multiple Input Multiple
Output) WLANs. Results show that in non-saturation conditions both the number
of active stations (STAs) and the queue size have a significant impact on the
system performance. If the number of stations is excessively high, the
heterogeneity of destinations in the packets contained in the queue makes it
difficult to take full advantage of packet aggregation. This effect can be
alleviated by increasing the queue size, which increases the chances to
schedule a large number of packets at each transmission, hence improving the
system throughput at the cost of a higher delay.
