Measuring the impact of slow user motion on packet loss and delay over IEEE 802.11b wireless links

Abstract

IEEE 802.11b compliant WLAN technology is increasingly used for cordless telephone services. Often, a WLAN phone is moved during a call. In the present paper we explore to what extent slow user motion influences the wireless link quality. We conducted extensive measurements with speech over commercial WLAN equipment using an experimental environment enforcing controlled motion. Our experiments show that -in contrast to the common assumption -an increase of motion speed can result in a better link quality: The packet loss rate and variance, measured after link-layer retransmissions, decreases. In addition, our measurements demonstrate that the modulation type, the maximal number of retransmissions, the experimental setting, and even the quality of power supply are the dominant influences on link quality.

Frame Delay, Loss Rate and Throughput Analysis for Video Applications over time correlated 802.11a/g channels

“…3 the log of the Probability Distribution Function (PDF) for the total frame delay is shown for time-correlated transmissions for all three Doppler frequencies. It can be seen that the total MAC-to-MAC delay increases significantly as the maximum Doppler shift decreases, and this agrees well with results reported in [6] [7]. A peak delay of around 12ms was observed for a maximum 80Hz Doppler shift, while delays reached 85ms for a maximum 4Hz Doppler shift.…”

“…This type of model is most suited to the simulation of slow fading channels [5]. The impact of Doppler spread on the packet loss and delay statistics for an 802.11 WLAN was investigated in [6] via experimental measurement. In [7], the packet loss rate and delay was analysed using a Jakes time-correlated Rayleigh fading simulator for various Doppler frequencies.…”

Measuring Round Trip Times to Determine the Distance Between WLAN Nodes

“…This features measuring conditions that are independent of variable interrupt latencies. In [10] we showed that measuring the time of a packet's arrival in the operating system's kernel (e.g. during an interrupt) entails quite imprecise results due to falsification by the variable interrupt latency.…”

“…The first measurement campaign was conducted to study the impact of slow-user motion on packet loss and delay as described in [10]. At the same time, we also measured the impact of distance on the round trip times.…”

“…Experimental Setup: The measurement was conducted twice: First in a gymnasium [10] and later in the in the countryside where one could expect the channel to be free of disturbing noise coming from other radiating devices. The data communication took place between the local and the remote node.…”