论文标题
在缓存存储容量有限的缓存系统中最大化信息的新鲜度
Maximizing Information Freshness in Caching Systems with Limited Cache Storage Capacity
论文作者
论文摘要
我们考虑具有源的缓存更新系统，存储容量有限的缓存和用户。有$ n $文件。来源保留了最新版本的文件，这些版本已通过已知速率进行更新。缓存从源获取新的文件，但它只能存储$ k \ leq n $的最新下载版本的$ k $文件。用户从缓存或源获取文件。如果用户从缓存中获取文件，则根据源的文件状态，接收到的文件可能会过时。如果用户直接从源获取文件，则接收到的文件始终是新鲜的，但是源和用户之间的额外传输时间降低了用户的新鲜度。因此，我们研究将文件存储在高速缓存与直接以额外传输时间为代价的文件之间的权衡。对于这两种情况，我们找到了用户在用户中文件平均新鲜度的分析表达式。然后，我们找到每个文件的最佳缓存状态（即是否将文件存储在缓存处）和在缓存处的相应文件更新速率以最大程度地提高用户的整体新鲜度。我们观察到，当缓存的总更新速率高时，缓存文件会改善用户的新鲜度。但是，当缓存的总更新速率较低时，用户的最佳策略是获得经常更改的文件和直接从源的传输时间相对较小的文件。
We consider a cache updating system with a source, a cache with limited storage capacity and a user. There are $n$ files. The source keeps the freshest versions of the files which are updated with known rates. The cache gets fresh files from the source, but it can only store the latest downloaded versions of $K$ files where $K\leq n$. The user gets the files either from the cache or from the source. If the user gets the files from the cache, the received files might be outdated depending on the file status at the source. If the user gets the files directly from the source, then the received files are always fresh, but the extra transmission times between the source and the user decreases the freshness at the user. Thus, we study the trade-off between storing the files at the cache and directly obtaining the files from the source at the expense of additional transmission times. We find analytical expressions for the average freshness of the files at the user for both of these scenarios. Then, we find the optimal caching status for each file (i.e., whether to store the file at the cache or not) and the corresponding file update rates at the cache to maximize the overall freshness at the user. We observe that when the total update rate of the cache is high, caching files improves the freshness at the user. However, when the total update rate of the cache is low, the optimal policy for the user is to obtain the frequently changing files and the files that have relatively small transmission times directly from the source.
