## 4 Reliable V2C Communication Using Multiple Paths with Redundancy Mitigation  
We propose a multipath method for V2C communication that employs a dynamic selection of communication paths to address both reliability and redundancy in V2C communication. The proposed method adjusts the number of multiple paths according to the packet loss status in each active path and the desired reliability, as shown in Figure 2. In general, increasing the number of paths for packet duplication transmission improves reliability improvement, whereas decreasing the number of paths reduces redundancy in packet duplication at the receiver side. Initially, a default number of paths is set up on a vehicle. This default number of paths can be employed according to the risk degree and demand reliability of the vehicle. By identifying the packet loss in V2C communication at the cloud server, periodic judgment of reliability matching is carried out at the cloud side. The cloud server processes the judgment of insufficiency or over-redundancy of the current number of paths used. If the current number of paths used is insufficient to reach the target reliability value, the cloud server instructs the vehicle to increase the number of paths in packet delivery. Then, the vehicle attempts to include an additional path in V2C communication the next time around. If the current path number used is overly redundant, the vehicle attempts to delete one of the paths in the multipath connection in the next period. In the following sections, we introduce details of the proposed method, including how to identify the packet losses and how to judge the status of over-redundancy of paths. The algorithm for the proposed method, implemented at the cloud server, is shown in Figure 3. First, the cloud server obtains information on the target reliability and transmission schedule of a vehicle initiating V2X communication. The cloud server then sets up the interval for reliability checks by monitoring end-to-end packet loss on each path in V2C communication. That is, the cloud server periodically assesses and checks the reliability performance of V2C communication on each active path created by the vehicle. Figure 2: Dynamic adjustment of path redundancy. During V2C communication, the reliability of each active path in terms of packet losses is monitored based on the received number of packets and the scheduled delivery of packets. The cloud server calculates the overall reliability of the multipath connection between it and the vehicle based on the total received packets without counting duplicated packets. To enable the broad application of the proposed method, this paper mainly focuses on monitoring and utilizing the status of end-to-end packet loss without needing to identify the factors that cause packet loss. The cloud compares the total effect of the reliability of a multipath connection with the target reliability to judge whether to keep, increase, or decrease the number. of paths In cases where the resulting reliability is less than the target threshold, the cloud server instructs the vehicle to increase the number of paths to improve reliability. In cases where the resulting reliability is greater than or equal to the target reliability but less than the threshold for decreasing the number of paths, the cloud server instructs the vehicle to keep the current number of paths. The cloud sends information for path adjustment to the vehicle via the normal single-path TCP protocol. The threshold for decreasing the number of paths is defined by the sum of the target threshold and an offset value. In cases where the resulting reliability is greater than the threshold for decreasing the number of paths, the cloud server instructs the vehicle to decrease the current number of paths. The algorithm in the proposed method, implemented at the vehicle side, is shown in Figure 4. First, the vehicle determines the target reliability, which can be based on the risk level. The vehicle then informs the cloud server of its target reliability and packet delivery schedule.