Research On Clustering-based Power Control In Cooperative Vehicular Communication System

Relay cooperative communication technology has been utilized for enhancing the reliability and connectivity of communication links,expanding communication coverage,and achieving spatial diversity.The application of relay cooperative communication technology in vehicular communication system can improve traffic efficiency and traffic safety factor.However,due to the high mobility of vehicles,the topology of the vehicular communication network changes rapidly.The clustering algorithm is used to divide the whole network into multiple vehicle group subnets,which helps the system to respond to the rapidly changing topology and improve the stability and reliability of communication.The resource allocation strategy determines the performance improvement of the cooperative vehicular communication system.As an important part of resource allocation,power control can reduce the energy consumption of vehicular equipment and mutual interference between vehicular nodes.Based on the above considerations,the main contributions of this dissertation are as follows:First,the fundamental theories of cooperative vehicular communication system are outlined,including network architecture of vehicular communication system,vehicle clustering algorithm,non-orthogonal multiple access(NOMA)technology and cooperative communication technology.Second,focusing on the cross roads congestion scenarios of cities,an optimized k-means clustering algorithm and a power control scheme for clustering head vehicles(CHVs)are proposed.The proposed clustering algorithm can quickly select CHVs based on the vehicle density parameter.And the cooperative communication among CHVs can be utilized for alleviating traffic congestion and stabilizing the network topology.Moreover,the incremental hybrid decode-amplify-forward cooperative strategy is adopted to minimize the transmission power of CHVs under the constraint of system outage probability,which achieves the goal of green vehicle-to-vehicle communications.Numerical simulations show that the CHVs selected by the optimized clustering algorithm are always at a high vehicle density position and are close to the center of cluster.And the proposed cooperative forwarding strategy and power control scheme can significantly reduce the total power consumption of CHVs.Third,in order to make the clustering algorithm more suitable for actual urban road traffic,we focus on the car-following scenario and propose a clustering algorithm for dynamically classifying the vehicles.The clustering algorithm uses the car-following distance and the speed difference of adjacent vehicles to adjust the size of the cluster.Furthermore,in order to improve the throughput of the cooperative vehicular communication system and ensure the fairness among CHVs,based on the cooperative NOMA technology,a power control scheme for the downlink between the base station(BS)and the CHV is proposed.By adjusting the power allocation coefficients,the scheme maximizes the minimum achievable rate of CHVs at the total transmission power given by BS.Numerical simulations show that the CHVs selected by the proposed clustering algorithm can achieve an optimal trade-off between the vehicles' relative speed and transmission power.Moreover,at the same total transmission power of BS,the proposed NOMA-based power control scheme can significantly improve the minimum achievable rate of CHV compared to the conventional NOMA and the fixed NOMA algorithms.