| Summary: | 碩士 === 雲林科技大學 === 電機工程系碩士班 === 97 === IEEE 802.11e is an approved amendment to the IEEE 802.11 standard that defines Quality of service enhancements such as Direct Link Setup (DLS), Block Acknowledgement, and Automatic Power-Save Delivery for wireless applications through modifications to the Media Access Control layer. In this thesis we are concerned with DLS in an IEEE 802.11e network. The communication model under discussion is HCF (hybrid coordination function) controlled channel access operating in contention-free periods. We simulate communication activities with or without DLS at the fixed 54 Mbps and adaptive transmission rates subject to physical signal-to-noise ratios.
We compare throughputs resulting from 11 combinations of voice and data streams sent, either uplink or downlink, within a DLS against those from non-DLS basic service set. Throughputs are measured in the context of different frame size, number of transmitting stations, and distance between communicating parties. Our simulations show that DLS outperforms non-DLS in terms of throughput if the data frame is longer than 275 and 78 bytes, respectively, in fixed and adaptive transmission rate scenarios. This finding implies that DLS may not perform better when delivering shorter voice data frames because direct frame exchanges among stations situated farther apart or some necessary control frames of comparable length should be transmitted at a lower rate. Additionally, we observe that DLS may improve throughput merely by 5% if stations are located close enough to the access point within range of 23,28, and 36 meters. In that case, DLS brings insignificant outperformance. However, when stations are farther away from the access point (within a radius of 60 meters), DLS contributes to significantly higher throughput by an appreciable amount of up to 62%.
Our simulation results delimit and quantify the usefulness of DLS. As a performance study on DLS, this thesis clarifies its use and provides an indication of when the mechanism could be advantageous in which scenarios.
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