On Medium Access for Wireless Ad-hoc and Sensor Networks
The medium access control (MAC) is a sub-layer of the data link layer, the
second layer of the open system interconnection (OSI) model. The MAC sub-layer
is responsible for organizing the access to the shared channel and it is due to
this important responsibility that the performance of networks is substantially
influenced by the MAC protocol. This thesis is based on three contributions,
addressing different issues related to the MAC layer of a variety of wireless
The first contribution in this thesis, paper A, deals with the problem of
designing a MAC protocol for vehicle-to-vehicle (V2V) communication for traffic
safety purposes. Traffic safety applications often require to broadcast
information or warning packets to all the vehicles in a close vicinity with as
little delay as possible. CSMA-based protocols, which is one of the candidates
for the V2V communication MAC, suffer from lack of an efficient and reliable
broadcast method. To address this problem, a new broadcast scheme called Long
Range Busy Tone (LRBT) is proposed.
Two important ranges in the MAC layer, namely the transmission and
interference ranges, are the topics of the second contribution of this thesis.
Weaknesses of the current model for interference range are discussed and an
improved model is obtained by removing some of the simplifying assumptions.
Additionally, the effects of physical layer parameters and a fading channel on
transmission and interference ranges are discussed.
The last part of this thesis is devoted to scheduling co-existing
time-slotted clusters in a Rayleigh fading channel. In this fading channel, no
distance separation guarantees interference free communication. Therefore, the
co-channel interference can be only minimized, if a joint scheduling among all
the clusters is considered. In paper C, this joint scheduling problem, which is
known to be NP-hard, is sub-optimally solved based on Lagrangian relaxation and
the auction algorithm.
EA, Hörsalsvägen 11, floor 4, Chalmers
Opponent: Professor Hannes Hartstein, DSN Research Group, Institute of Telematics, University of Karlsruhe, Germany