Modeling And Analysis Of The Local Delay In MEC-based Vehicular Ad Hoc Networks

With the emergence of new applications in vehicular ad hoc networks(VANETs),vehicular users have an increasing demand for quality of service(Qo S)with low latency and high reliability.Mobile edge computing(MEC)is a distributed computing paradigm for improving the Qo S of a VANET.Delay is one of the major metrics for measuring the Qo S performance of a VANET,and local delay is one of the major components of the delay for a node to transmit a data packet to another node.Thus,reducing local delay is helpful to providing fast computing services for vehicle users and meeting the delay requirement of computing services for vehicle users in an MEC-based VANET.However,local delay depends on various factors,such as different road distributions and node distributions,channel fading characteristics,channel access protocols and inteferences.To reduce the local delay,it is necessary to establish a relationship between the local delay and different factors in order to analyze the impacts of the factors on the local delay.This dissertation studies the modeling and analysis of local delay in MEC-based VANETs for different road scenarios,which is helpful to the deployment of edge nodes in different road scenarios.The main work and contributions of this dissertation include the following four aspects:(1)Modeling and analysis of local delay in an MEC-based VANET for a highway road scenarioThis work studies the modeling and analysis of local delay in an MEC-based VANET and focuses a highway road scenario.In deriving an analytical model,the spatial distribution of highway roads is modeled as an equidistant parallel line process,and the spatial distribution of vehicle nodes on each lane and that of edge nodes along a road side are modeled as independent one-dimensional(1-D)homogeneous Poisson point processes(PPPs),respectively,based on stochastic geometry.The edge node for accommodating the service request of a vehicle node is determined based on a nearest-receiver model,and the edge node for transmitting a computing result to the corresponding service requesting vehicle node is determined based on a nearest-transmitter model.Moreover,a carrier sense multiple access(CSMA)mechanism is considered for channel access,and Rayleigh fading is considered for channel fading.Based on the above assumptions,the successful channel access probability of a vehicle node and that of an edge node are derived,and the successful receiving probability of a receiving node is derived,based on which an uplink local delay model and a downlink local delay model are further derived,respectively.The derived analytical models are validated through simulation results,and the impacts of major parameters on the local delay are investigated.The derived delay model can be used to provide a basis for parameter settings in the deployment of edge nodes in a highway scenario.(2)Modeling and analysis of local delay in an MEC-based VANET for a suburban road scenarioThis work studies the modeling and analysis of local delay in an MEC-based VANET and focuses on a suburban road scenario.In deriving an analytical model,the spatial distribution of suburban roads is modeled as a grid line process based on stochastic geometry,where vertical streets and horizontal streets are perpendicular to each other to form a grid.It is assumed that vehicle nodes on each street are distributed following an independent 1-D homogeneous PPP,and edge nodes are deployed at each intersection with a certain probability.Moreover,it is assumed that a CSMA mechanism is employed by both vehicle nodes and edge nodes for channel access,and the spatial distribution of nodes which access the channel successfully is modeled as a hard core point process(HPP).Independent Nakagami-m fading is considered over all wireless links.Based on the above assumptions,the successful channel access probability of a vehicle node and that of an edge node are derivied and the successful receiving probability of a receiving node is also derived,based on which an uplink local delay model and a downlink local delay model are further derived,respectively.The derived analytical models are validated through simulation results,and the impacts of major parameters on the local delay are investigated.The derived delay model can be used to provide a basis for parameter settings in the deployment of edge nodes in a suburban road scenario.(3)Modeling and analysis of local delay in an MEC-based VANET for an urban road scenarioThis work studies the local delay modeling and analysis in an MEC-based VANET and focuses on an urban road scenario.In deriving an analytical model,a Cartesian rectangular coordinate system is mapped to a cylindrical coordinate system,based on stochastic geometry,and the spatial distribution of urban roads is modeled as a Poisson line process(PLP),which can be regarded as a two-dimensional(2-D)PPP in the cylindrical coordinate system.The spatial distribution of vehicle nodes on each street is modeled as a homogeneous 1-D PPP,and edge nodes are deployed with a certain probability on each road.The spatial distribution of edge nodes deployed on each road is modeled as a homogeneous 1-D PPP.Moreover,a CSMA mechanism is considered for channel access by both vehicle nodes and edge nodes,and the spatial distribution of vehicle nodes successfully accessing the channel and that of edge nodes successfully accessing the channel are approximated as independent homogeneous PPPs,respectively.Based on the above assumptions,the successful channel access probability of a vehicle node and that of an edge node are derived,and the successful receiving probability of a receiving node is also derived,based on which an uplink local delay model and a downlink local delay model are further derived,respectively.The derived analytical models are validated through simulation results,and the impacts of major parameters on the local delay are investigated.The derived delay model can be used to provide a basis for parameter settings in the deployment of edge nodes in an urban road scenario.(4)Modeling and analysis of local delay in an MEC-based Het VNet for an urban scenarioThis work studies the modeling and analysis of the local delay in an MEC-based heterogeneous vehicular network(Het VNet)and focuses on an urban road scenario,where a vehicle node with both an IEEE 802.11 p network interface and a cellular-assisted vehicle-toeverything(C-V2X)network interface needs to request for a computing service from edge nodes.In deriving an analytical model,the spatial distribution of urban streets is modeled as a PLP,the spatial distribution of vehicle nodes with different network interfaces on each street is modeled as a homogeneous 1-D PPP,based on stochastic geometry.Edge nodes which are composed of roadside units(RSUs)and MEC servers are deployed along each street with certain probabilities,and the spatial distribution of edge nodes which are composed of e NBs and MEC servers is modeled as a 2-D PPP.Moreover,a CSMA mechanism is considered for channel access in an IEEE 802.11p-based vehicular network,and an orthogonal frequency division multiple access(OFDMA)mechanism is considered for channel access in a C-V2 X network.Based on the above assumptions,the successful channel access probability of a vehicle node with two network interfaces and that of an edge node are derived,and the successful receiving probability of a receiving node is also derived,based on which an uplink local delay model and a downlink local delay model are further derived,respectively.The derived analytical models are validated through simulation results,and the impacts of major parameters on the local delay are investigated.The derived delay model can be used to provide a basis for parameter settings in the deployment of different types of edge nodes and the policy for the association between vehicle nodes with two network interfaces and different types of edge nodes.