Cooperative and multi-channel energy-based sensing in the vehicular environment
Creators: name: Borota, Dušan
Publisher: name: No Publisher Supplied
Year: 2012

description: Vehicular networking has significant potential to enable diverse range of applications,  including safety and convenience. As the number of vehicles and applications using  wireless spectrum grow, one can expect to see a shortage of either spatially or temporally available spectrum. In this thesis, we advocate that dynamic spectrum access  for vehicles be the first step towards solving the spectrum shortage. For this, vehicles  must be able to sense the availability of spectrum before attempting to transmit. The  existence of other transmitters should be detected in order not to cause or experience  interference. However, spectrum sensing in vehicular environments is a challenging  task due to mobility, shadowing and other factors that govern vehicular environments.  Therefore, spectrum sensing by a single vehicle may not be able to provide accurate  information about the spectrum vacancies. Cooperative spectrum sensing, on the other  hand, uses spatial diversity and can be employed to overcome the limitations associated  with a single sensor/vehicle. Moreover, spectrum sensing in vehicular environments is challenged by mobility of sensors and reflectors causing significant variations in received  signal power. Signal power variations over time were not included in sensing system  models dealing with wide spectrum sensing.  In the first part of this thesis we investigate cooperative spectrum sensing performance in a vehicular environment for sensing signals transmitted from i) a roadside  infrastructure and ii) radios located on other vehicles, by using energy-based detection of a transmitted pilot tone as an example. Our goal is to characterize the limits  on detection speed and reliability of simple hard and soft cooperative energy-based  schemes for this environment. We show how cooperation reduces sensing time by a  factor of five in an AWGN channel. The cooperative sensing time reduction is far  more significant in a vehicular environment with fading and shadowing. Finally, we illustrate how infrastructure-to-vehicle scenario favors soft equal gain combining while  vehicle-to-vehicle scenario favors hard fusion OR rule. In the second part of this thesis we propose a sensing system model for wide band  spectrum sensing that encompasses signal power variations over time. Then we propose  to use Maximum Likelihood (ML) channel occupancy detection to determine spectrum  sub-band activity vector. We are using adjacent lane traffic channel model with set of  parameters validated in Winlab experiments, and focus on determining sensing time  needed to achieve certain sensing performance. We focus on NTSC TV spectrum and  show how using energy-based ML channel occupancy detector of three adjacent NTSC  channels, with transmit power of 1kW, at 10km distance from transmitter, with power  variance higher than 3dB, sensing time of 1msec is sufficient to obtain PMISS = 0.01  for range of speeds from 20 to 140km/h. Moreover, since we use ML which minimizes  overall probability of error when all activity vectors are equally probable, this work  provides not only a sensing approach but an assessment of how well any other technique  may perform in a mobile environment.