I’m currently looking into WLAN physical layer simulation models of network simulators to figure out how good they are doing. While studying the ns-3 implementation of the PHY error rate model, I noticed that they are using the number of coded bits to calculate the frame error rate. This seams weird, since all papers on the topic consider the number of data bits.

The bug just got confirmed and the issue should be fixed soon.

It means that for the last eight years or so, ns-3 used the wrong number of bits to calculate the error rate for a WLAN transmission. A 500 byte BPSK-1/2 frame, for example, was treated as a 1000 byte frame.

Fortunately, the impact is not too big. It is the shown by the figure below. The bug causes the error curves to shift to the next higher one (i.e., 100 byte → 200 byte, 200 byte → 400 byte etc.).

Impact of bug.

I also recently published a more comprehensible paper about the Veins PHY implementation.

  • Bastian Bloessl and Aisling O’Driscoll, “A Case for Good Defaults: Pitfalls in VANET Physical Layer Simulations,” Proceedings of IFIP Wireless Days Conference 2019, Manchester, UK, April 2019. [DOI, BibTeX, PDF and Details…]