Optimal MAC PDU Size in ARQ-enabled Connections in IEEE 802.16e/WiMAX Systems

摘要

In this paper we address an aspect of the mutual influence between the PHY layer budding blocks (FEC blocks) and the MAC level allocations in the Uplink and Downlink of IEEE 802.16e/WiMAX systems, In these systems it is possible to transmit MAC level frames, denoted MAC PDUs, such that a PDU contains an integral number of fixed size Data Blocks. We compute the optimal size of a PDU that maximizes the Goodput of the PDU. The Goodput depends on the success probability of the PDU, which in turn depends on the FEC blocks over which the PDU is allocated. We then compare among the maximum PDU Goodputs in different sizes of the FEC blocks and the Data Blocks. The main outcome is that the PDU Goodput is sensitive only in the case where Data Blocks are very large. We also give guidelines on how to choose the best Modulation/Coding Scheme (MCS) to use in a scenario where the Signal-to-Noise Ratio (SNR) can change significantly during transmissions, in order to maximize the PDU Goodput.