# Cooperative Caching and Resource Allocation in Integrated Satellite-Terrestrial Networks
## 6 Performance Evaluation
### Performance Comparison with Three Different Algorithms  
The experiments are also conducted to evaluate the performance of the proposed CCRA algorithm for the content service compared with two baselines of Greedy and BFS. For Greedy [51], the joint strategy of cooperative caching and resource allocation for the formulated problem can be obtained by searching the neighboring sub-network in a greedy way, where the searching process will be terminated until the first feasible strategy is found. However, for BFS [52], the joint strategy of cooperative caching and resource allocation is searched by BFS based on multi-priority, where all the candidates in one search layer are sorted by content caching, storage resource usage, and service delay in descending order. According to the simulation parameters in Table 2, and \(Q=5\), \(N_{a}=4\), \(M=\{200,210,\cdots,300\}\), the experiment results of each user service are provided for CCRA, Greedy, and BFS in Figure 6, including storage costs, bandwidth costs, and total deployment costs. Figure 6a illustrates the average storage costs of each user service for CCRA, Greedy, and BFS. For Greedy, the cooperative caching services of users are provided by a greedy way, that is, the first available satellite with sufficient storage resources may be used to cache the required content if the required content of one user has not been deployed on the traversed satellites. In that case, the storage costs of each user service can be increased. However, for BFS, the content sharing approach will be given priority for content service to improve the utilization of storage resources when the candidates in one search layer are  
Figure 5: Performance comparison for normalized costs in three different scenarios. (**a**) Normalized storage costs. (**b**) Normalized bandwidth costs. (**c**) Normalized total costs. traversed to obtain the strategy, which can reduce the storage costs as much as possible. Furthermore, for CCRA, the content sharing approach can be given priority for all the satellites in the neighboring sub-network. Therefore, the average storage costs of each user service are the largest for Greedy, followed by BFS, and then CCRA. Note that more users can be provided content services by the content sharing approach as the number of accessed users increases, which will correspondingly reduce the storage costs of each user service, as shown in Figure 6a. On average, the storage costs of each user service for CCRA can reduce by 25.96% for Greedy and 20.61% for BFS. Figure 6b shows the average bandwidth costs of each user service for CCRA, Greedy, and BFS, where it can also be found that the average bandwidth costs of each user service for Greedy and BFS are close and slightly more than that of CCRA. Specifically, the average bandwidth costs of each user service for CCRA, Greedy, and BFS are 7.32 Mbps, 7.57 Mbps, and 7.5 Mbps, respectively. On average, compared with Greedy and BFS, the bandwidth costs of each user service for CCRA can reduce by 3.3% and 2.34%. Furthermore, Figure 6c describes the average total deployment costs of each user service for CCRA, Greedy, and BFS. Considering that Greedy can provide content services for users in a greedy way, it cannot be guaranteed that content services for users are provided by the content sharing approach as much as possible, which can bring the largest total deployment costs of each user service. For BFS, the content sharing approach can be given priority for all the candidates in one search layer but cannot be guaranteed for all the candidates between different search layers. Therefore, the average total deployment costs of each user service are less than that of Greedy. For CCRA, it can be guaranteed that the content sharing approach is given priority for all the satellites in the neighboring sub-network, which is shown in Figure 3. Therefore, the average total deployment costs of each user service for CCRA are less than that of Greedy and BFS.