Spectrum Expansion to Solve the Spectrum Scarcity Problem in Vehicular Network

Many studies show that the 5.9 GHz Dedicated Short Range Communication (DSRC) band with 75 MHz bandwidth is not sufficient to ensure reliable transmission of safety messages for the upcoming intelligent transportation systems. Moreover, the so-called vehicular spectrum scarcity problem is becoming severer in the DSRC band due to the rapid growth of wireless traffic demands in vehicular networks. Meanwhile, many frequency bands allocated to existing RF systems are largely underutilized. Since few new spectrum resources are available for vehicular communications, a potential solution to the spectrum scarcity problem in the DSRC band is to unload portion of the wireless traffic from the DSRC band to the other underutilized bands through spectrum sharing. The most fundamental requirement of the spectrum sharing approach is the protection of legacy users of the underutilized bands. In addition, a novel design of medium access control (MAC) protocols is required because few existing wireless MAC protocols support spectrum sharing functionality.;This dissertation is focused on the resource allocation algorithm development and MAC protocol design to enable spectrum sharing between vehicular networks and other RF systems. Firstly, we study the sharing of the 54 MHz - 698 MHz TV White Space (TVWS) band between vehicular networks and licensed users of the band. The TVWS band has been officially released by FCC for cognitive access, and all existing wireless systems are allowed to access the band on condition that they must conform to FCC regulations on protection of legacy TVWS users. In this work, the channel allocation problem in the cognitive vehicular network is formulated as a nonlinear integer programming problem, to which three efficient approximation algorithms are developed. Secondly, we study the coexistence of vehicular networks and other unlicensed wireless networks in the TVWS band. The motivation of this study is that, multiple heterogeneous wireless networks can operate in the TVWS band simultaneously, which creates a challenging coexistence environment among these networks. In this work, the coexistence issue is formulated as a resource allocation problem in the vehicular networks, to which three efficient approximation algorithms with performance guarantees are developed.;In addition to the TVWS band, we have also studied the vehicular spectrum expansion to the 77 - 81 GHz millimeter wave bands. Firstly, we propose a joint automotive radar-communication system (JARC) where radar imaging and vehicular communications share the 77 - 81 GHz automotive radar band. In this work, we show the trade-off of incorporating vehicular communications in automotive radars. Secondly, a distributed JARC system is developed to enable the spectrum sharing between vehicular communications and radar imaging in the 77 - 81 GHz band. The developed JARC systems consists of three key components: neighbor discovery, link establishment and maintenance, and data delivery. Finally, data delivery performance of the JARC system is evaluated through network simulations.;To sum up, our research demonstrates the feasibility of spectrum expansion technologies to solve the vehicular spectrum scarcity problem. Moreover, we study the most important MAC layer issues and propose both theoretical solutions and implementation details, which facilitates the spectrum expansions.