Optimization of a QoS Aware Cross-Layer Scheduler by Packet Aggregation

In this paper, the performance of a QoS-aware two-stage cross-layer scheduler utilising a MIMO channel for transmission is considered along with TDMA, OFDMA and SDMA channel access methods which serves a number of users with QoS-constrained data flows. OFDMA and SDMA allow a parallel transmission of packets which can have different transmission durations Clue to Varying physical bit rates and packet lengths. The data flow with the longest packet slows down the other flows because they have to wait until the transmission is complete. This paper proposes packet aggregation where wailing times are reduced by transmitting, more than one packet per user if airtime left. It is shown that this method significantly enhances the QoS parameters throughput and delay. For constant-size packets. shorter delays can be achieved than for variable-size packets. Aggregating non- consecutive packets further enhances file performance, however the packets have to be buffered at the receiver to put them into the correct order.