Measurement-based Modeling of IEEE 802.11a PHY - Capture E ect, Preamble Detection and Carrier Sense ,✩✩
Jeongkeun Lee, Jiho Ryu, Sung-Ju Lee, Taekyoung Kwon · 2009
In wireless networks, modeling of the physical layer behavior is an important yet di cult task. Modeling and estimating wireless interference is receiving great research attention, and is crucial in a wireless network performance study. The physical layer capture, preamble detection, and carrier sense threshold are three key components that play important roles in successful frame reception in the presence of interference. Using our IEEE 802.11a wireless network testbed, we carry out a measurement study that reveals the detailed operation of each component and in particular we show the terms and conditions (interference timing, signal power di erence, bitrate) under which a frame survives interference according to the preamble detection and capture logics. Based on the measurement study, we show that the operations of the three components in real IEEE 802.11a systems di er from those of popular research simulators and present our modifications of the IEEE 802.11a PHY models to NS-2 and QualNet network simulators. The modifications can be summarized as follows. (i) The current simulators’ frame reception is based only on the received signal strength. However, the real 802.11 systems can start the frame reception only when the Signal-to-Interference Ratio (SIR) is high enough to detect the preamble. (ii) Di erent chipset vendors implement the frame reception and capture algorithms di erently, resulting in di erent operations for the same event. We provide di erent simulation models for several popular chipset vendors and show the performance di erences between the models. (iii) Based on the 802.11a standard setting and our testbed observation, we revise the simulator to set the carrier sense threshold higher than the receiver sensitivity while the current simulators set the threshold equal to the receiver sensitivity. We implement our modifications to the QualNet simulator and evaluate the impact of PHY model implementations on the wireless network performance which result in up to six times of net throughput increase.