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- This example measures the IEEE 802.11 wireless network throughput from a
- number of hosts to the access point (AP). The theoretical maximum
- throughput can be calculated using the attached Excel sheet. The host and
- the access point transmitter powers are configured so that every host hears
- all the others.
- 1. Single-host throughput
- Throughput is measured by the "sink" submodule of the AP. It is recorded
- into the output scalar file, but can also be inspected during runtime.
- The Excel sheet includes throughput measured by the simulation, and compares
- it to the theoretical maximum which is roughly 5.12 Mbps (at 11 Mbps bitrate
- and 1000-byte packets). The theoretical value and the simulation output
- are very close, the difference being less than 1 kbps.
- 2. Multi-host throughput
- In this case, the average backoff interval on the channel is smaller which
- would increase throughput, but are also collisions. This makes the
- calculation of the theoretical maximum rather complicated. To simplify
- things, the Excel sheet does not consider collisions when calculating the
- maximum throughput. For 3 hosts the minimum backoff period is (n - 1) ^ 2 /
- (4 * n) where n is the contention window size, that is, n=32. This shows an
- average contention window of roughly 7.5, and an increased total channel
- throughput.
- The difference between the theoretical throughput maximum and the measured
- throughput is caused by collisions. Adding the number of frame collisions
- to the number of correctly received frames makes the difference less than
- 50 kbps. The difference is probably caused by inter-frame spacing: the
- simulation waits EIFS after detecting a collision, but the spreadsheet
- calculates with DIFS.
- The experiments are were inspired by the following paper:
- S. Choi, K. Park and C. Kim, "On the Performance Characteristics of WLANs:
- Revisited", Proceedings of the ACM SIGMETRICS 2005, pp. 97-108, 2005.
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