Yaron Alpert

Efficient coupled PHY and MAC use of physical Bursts in WiMAX/IEEE 802.16e networks

Abstract We address several issues related to the efficient use of Bursts in WiMAX/IEEE 802.16e systems. We look on the relation between the PHY layer budding blocks (FEC blocks) and the allocation of MAC level frames (PDUs) over these FEC blocks. In particular, we show how to transmit a given amount of MAC level data bits over a given Burst in order to maximize the number of successfully transmitted data bits in the Burst. We also compute, given an amount of data bits to transmit, what is the Burst size that maximizes each of the following three performance criterion: the number of successfully transmitted data bits in the Burst, the maximum ratio between the number of successfully transmitted data bits to the Burst size, and the number of successfully transmitted data bits per PHY slot. For the first problem the paper shows how to optimally divide the Burst into PDUs and shows that sometimes it is more efficient to use less reliable Modulation/Coding schemes. For the second problem the paper shows that using the PHY slots efficiently is the best criterion to consider.

Comparison between TCP scheduling strategies in IEEE 802.11ac based wireless networks

In this paper we investigate two models for traffic transmission of two Transmission Control Protocol (TCP) connections with one connection in Uplink direction and the other in Downlink direction, between an Access Point and a station over an IEEE 802.11ac channel. In one model the traffic of the two connections is mapped to a single Traffic Stream, and in the second model the traffic of the two TCP connections is split into two different Traffic Streams. We assume Error-Free and Error-Prone channels, the Two-Level aggregation method and the Reverse Direction capability of IEEE 802.11ac. The Goodput of the two models is about the same, however, in the first model shorter dedicated transmission periods, denoted Transmission Opportunities (TXOP), are sufficient to achieve the optimal Goodput because TCP Acks are interleaved. Also, using Reverse Direction prevents collisions and improves the Goodput by 1015% over contension based access.

Physical and Medium Access Control criteria for the optimal Medium Access Control protocol data unit size in Automatic Repeat Request-enabled connections in IEEE 802.16e/ WiMAX systems

In this paper, we address an aspect of the mutual influence between the physical PHY layer budding blocks forward error correction FEC blocks and the medium access control 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 protocol data units PDUs, such that a PDU contains an integral number of fixed size data blocks. We compute the optimal size of a PDU according to two criteria, one related to the PHY layer and one related to the MAC layer. In relation to the PHY layer, the criterion maximizes the average number of data bits that are transmitted in a PHY slot. In relation to the MAC layer, the criterion 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 the maximal PDU goodputs in different sizes of the FEC blocks and the data blocks. The main outcome is that the PDU goodput is sensitive in those cases in which data blocks are very large. We also give guidelines on how to choose the best modulation/coding scheme to use in a scenario where the signal-to-noise ratio can change significantly during transmissions, to maximize the PDU goodput. Finally, we compare between the two criteria. Copyright