# UAV-Assisted Caching Strategy Based on Content Cache Pricing in Vehicular Networks
## 3 System Model
### Caching Model and Content Delivery Strategy
For the case where the UAV and one RSU caches \(f_{i}\) and the other RSU does not, the UAV stays on the road section where the RSU that caches \(f_{i}\) is located. Take the case where \(R_{l}\) caches \(f_{i}\), \(R_{r}\) is not cached, and the UAV stays on the \(R_{l}\) side, as shown in Figure 3b. When a vehicle drives in from the \(R_{r}\) side of the roadway, if the vehicle user sends a request when it is not in the coverage range of the UAV, e.g., \(V_{5}\), the user will first obtain \(f_{i}\) from \(R_{l}\) and continue to obtain \(f_{i}\) from the UAV if the content is still not fully obtained when it drives into the coverage range of the UAV. If the vehicle user sends a request within the coverage area of the UAV, e.g., \(V_{6}\), it will first obtain \(f_{i}\) from the UAV, then continue to obtain \(f_{i}\) from \(R_{r}\) if the content is still not fully available when driving out of the UAV's coverage area. If the content is still not fully available when driving out of the section where \(R_{r}\) is located, it will enter a wait state until it has driven the entire section and then obtain the content from the CP. If the vehicle user requests \(f_{i}\) after driving through the UAV coverage, e.g., \(V_{7}\), it first obtains content from \(R_{l}\) and, if it still does not fully obtain \(f_{i}\) when it leaves the section where \(R_{l}\) is, it enters a wait state until it leaves the \(R_{r}\) section and obtains \(f_{i}\) from the CP. When the vehicle enters from the \(R_{r}\) side of the road, e.g., \(V_{8}\), it sends a request and then enters a wait state until it enters the \(R_{l}\) section and starts to obtain \(f_{i}\) from \(R_{l}\); if it still has not fully obtained the content when it enters the UAV coverage, it continues to obtain it from the UAV. For the case where the UAV and one RSU caches \(f_{i}\) and the other does not, the UAV stays on the road section where the RSU that does not cache the content is located. Take the example of \(R_{l}\) caching \(f_{i}\), \(R_{r}\) not caching, and the UAV staying on the \(R_{r}\) side, as shown in Figure 3c. When a vehicle drives in from the \(R_{r}\) side of the roadway, as in \(V_{9}\), it first acquires content from \(R_{l}\) and, if it does not fully acquire content when driving out of the \(R_{l}\) roadway, it continues to acquire \(f_{i}\) from the UAV. When the vehicle is approaching from the \(R_{r}\)-side section, if the vehicle user sends a request when it is not in the coverage area of the UAV, e.g., \(V_{10}\), it enters a wait state until it is in the coverage area and obtains \(f_{i}\) from the UAV. If the vehicle user sends a request, e.g., \(V_{11}\), while in the coverage area of the UAV, it first obtains \(f_{i}\) from the UAV and, if the content is still not fully obtained when driving out of the coverage area of the UAV, it enters the wait state until it drives into the \(R_{r}\) side section and obtains \(f_{i}\) from the \(R_{r}\). If the vehicle user sends a request, e.g., \(V_{12}\), after driving through the coverage area of the UAV, it enters the wait state until it drives into the \(R_{r}\) side section and obtains \(f_{i}\) from the \(R_{r}\).