PERFORMANCE MEASUREMENTS FOR WiMAX NETWORKS

It has been noted that, at the time of writing, there is not much published work available regarding real-life performance evaluation of WiMAX networks. However, some of the currently available literature will be briefly described in this section.

WiMAX test-bed based results for measurements in the field have been reported. The Alvarion test bed, BreezeMax http://www.alvarion.com/, operating in the 3.5 GHz licence band and fully IEEE 802.16-2004 compliant, has been employed for measurements. Experimental data has been collected for four nodes operating in PMP mode in a rural residential environment. A sectorial antenna with a gain of 14 dbi, covering all three SS (FDD half duplex), has been deployed. All nodes run using a Linux distribution and are attached to WiMAX equipment through the Ethernet. Data flow and CBR VoIP are generated by the freely available tool known as D-ITG, http://www.grid.unina.it/software/ITG/;

It has been observed that the performance of a G.711 codec is far too low to be acceptable and SS cannot support more than two high quality calls. The G.723.1 codec outperforms G.729.2. It has been pointed out that UL measurements contradict simulation results and its earlier version, where larger delays in UL are ascribed to bandwidth request mechanisms and PHY overhead. Due to activation of piggybacking for bandwidth reservation. It has also been pointed out that the R-factor, E-model, needs to be considered for scheduler design, though, nothing has been mentioned about the type of scheduler that was being used at SSs and BS during the test-bed measurements.

Recently, a performance study of UL Scheduling algorithms for PMP WiMAX has been carried out. It has studied major scheduling algorithms using the NS-2 simulator. Also, it provides pseudocode for various schedulers in a simple and accessible manner. The existing scheduling mechanisms have been divided into three categories: homogenous, heterogenous, and opportunistic types. It has been reported that EDF and (EDF+WFQ+FIFO) result in the lowest average delay for rtPS and ertPS; WRR, WFQ, and (EDF+WFQ) provide a fair distribution of bandwidth; the (EDF+WFQ) hybrid setup is fairer than (EDF+WFQ+FIFO). In addition, it has been concluded that most of the legacy schedulers are not very suitable for WiMAX applications. However, WFQ, cross-layer, and queueing theoretic-based schedulers are seen to be promising candidates for applications in a WiMAX network.