Adaptive Scheduling in Intelligent Transportation Systems

Abstract: Intelligent Transportation Systems (ITS) can substantially improve roadsafety and trac eciency. This is possible by allowing communicationamong nearby vehicles and among vehicles and xed roadside units. A popularstandard for vehicular communications is IEEE 802.11p. It is basedon a CSMA/CA MAC method that does not guarantee channel access in anite time and so is not suitable for real-time communications. It also needsmethods to control and limit the load, since the transmission of periodicinformation among vehicles can saturate the channel. In this thesis, a newreal-time scheduling algorithm suitable for ITS applications is introduced. Itis based on a TDMA MAC method, where the roadside unit has the tasks toestimate the channel conditions and assign fractions of time slot to users. Alinear programming approach is considered to minimize an index of utility ofthe transmissions. Multi-hop communication scenarios among the vehiclesare considered for both uplink and downlink communications. It is shownhow the optimal duration of the fraction of time slot depends on the channelconditions. A higher channel gain corresponds to a higher transmission timewhereas a lower channel gain corresponds to a lower transmission time. Itis concluded that the approach studied in the thesis can guarantee a highutility provided that the complexity of the optimization is reduced as thenumber of involved vehicles increases.