In environments with high error rates, this selective retransmission mechanism can provide some improvement in the effective throughput of a WLAN using MPDU aggregation over that of one using MSDU aggregation .
Sidelnikov et al presented in  a simple fragmentation-aggregation scheme which combines the MSDU fragmentation and A-MPDU aggregation.
In our case we sent homogenous voice traffic, so maximum expected MSDU can be set equal to nominal MSDU.
Setting lower mean data rate will not gain any voice channel capacity whatsoever, because time required to send one maximum MSDU will be used in TXOP calculations (formula 2).
Additional voice channels can be gained by allowing reasonable packet loss to voice streams, i e granting access to more STAs than is allowed by default allocation algorithm This hardly can be done by tuning the mandatory TSPEC parameters Nominal or maximum MSDU size will not give any positive effect as those parameters are used for TXOP calculation and setting lower values may totally block the TS traffic Lowering mean data rate does not make any sense either--when the system is tuned for one packet delivery per SI, TXOP value will not change even if TSPEC shows less than one packet per SI Tuning [T.
TSPEC parameters for simulated TSs Parameter Value Nominal MSDU size (L) 200 B Maximum MSDU Size (M) 200 B Mean Data Rate ([rho]) 80 kbps Maximum Service Interval ([T.
34 bytes MSDU
1500 bytes Control bit rate 1 Mbps Nominal data rate 2 Mbps and 11 Mbps
4) For the selected traffic flow i, the proposed adaptive packet scheduling scheme will aggregate several MSDUs to form an A-MSDU with the optimized packet length [L.
The reason is as follows: APS can aggregate several MSDUs to form an A-MSDU with the optimized packet length and well regardless of traffic load by providing inter-class and intra-class fairness scheduling for different priority real-time traffic to exercise a discipline to satisfy the diverse QoS requirements, which makes MAPs and STAs adjust their transmissions so that packets are not transmitted excessively.
Moreover, APS will aggregate several MSDUs to form an A-MSDU with the optimized packet length and well regardless of traffic load.