Using measurements from VanLAN, a modest-size

testbed that we have deployed, we analyze the fundamental characteristics

ofWiFi-based connectivity between basestations and vehicles

in urban settings. Our results uncover a more complex picture

than previous work which was conducted in more benign settings.

The interval between a vehicle coming into and going out of range

of a basestation is often marred by intermittent periods of very poor

connectivity. These “gray periods” are hard to reliably predict because

their arrival is not signaled by metrics such as signal strength,

loss rate, speed or distance from the basestation. At the same time,

they also do not consistently occur at the same spot. Our analysis

suggests that gray periods are not caused by the motion of the vehicle

per se but by the variability in the urban radio environment

combined with the vehicle traversing locations that are poorly covered

by the basestation. We also find that knowledge of past connectivity

can be used to identify regions where gray periods are

more likely to occur as well as regions where the vehicle is likely

to experience good connectivity.

PDF file

In  Internet Measurement Conference (IMC)

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