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    Item type:Publication, Access status: without files ,
    Performance analysis of packet aggregation in wlans with simultaneous multi-user access (work in progress)
    (Springer, 2009-05)
    Konsgen, Andreas
    ;
    Islam, Md Shahidul
    ;
    Timm-Giel, Andreas
    ;
    Görg, Carmelita
    A cross-layer wireless LAN system is considered which transmits packets for a number of users simultaneously using OFDMA or SDMA transmission. Due to varying packet lengths and physical bitrates for each user, this results in different transmission times so that users with faster transmissions have to wait until the transmission of the slower users is complete. Packet aggregation can reduce the loss of airtime and enhance the throughput without affecting the delay by filling in the gaps with additional packets which are ready for transmission. In this paper, the throughput is determined analytically and by simulation with and without packet aggregation for some given distribution functions of the packet size and the transmission time. For a more realistic channel model, the throughput enhancement due to packet aggregation is determined by simulations. It is shown that dependent on the distribution of the different flows, a significant throughput enhancement can be achieved.
    Publicationtype: Conference Paper
      54
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    Item type:Publication, Access status: without files ,
    Optimization of a QoS aware cross-layer scheduler by packet aggregation
    (Springer, 2008-09)
    Konsgen, Andreas
    ;
    Islam, Md Shahidul
    ;
    Timm-Giel, Andreas
    ;
    Görg, Carmelita
    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 due 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 waiting times are reduced by transmitting more than one packet per user if airtime is 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 the performance, however the packets have to be buffered at the receiver to put them into the correct order. © 2008 International Federation for Information Processing.
    Publicationtype: Conference Paper
      53