How to design proper content placement strategies is one of the major areas of interest in cache-enabled cellular networks. In this paper, we study the probabilistic content placement optimization of base station (BS) caching with cooperative transmission in the downlink of cellular networks. With placement probability vector being the design parameter, non-coherent joint transmission (NC-JT) and coherent joint transmission (C-JT) schemes are investigated according to whether channel state information (CSI) is available. Using stochastic geometry, we derive an integral expression for the successful transmission probability (STP) in NC-JT scheme, and present an upper bound and a tight approximation for the STP of the C-JT scheme. Next, we maximize the STP in NC-JT and the approximation of STP in C-JT by optimizing the placement probability vector, respectively. An algorithm is proposed and applied to both optimization problems. By utilizing some properties of the STP, we obtain globally optimal solutions in certain cases. Moreover, locally optimal solutions in general cases are obtained by using the interior point method. Finally, numerical results show the optimized placement strategy achieves significant gains in STP over several comparative baselines both in NC-JT and C-JT. The optimal STP in C-JT outperforms the one in NC-JT, indicating the benefits of knowing CSI in cooperative transmission.

翻译：如何设计适当的内容配置策略是缓冲型蜂窝网络的主要关注领域之一。在本文件中,我们研究了基站(BS)的概率性内容配置优化与细胞网络下行链中合作传输的连接。由于放置概率矢量是设计参数,因此根据是否有频道国家信息(CSI)来调查如何设计适当的内容配置策略和协调一致的联合传输(C-JT)计划。我们使用随机地貌测量,为NC-JT计划的成功传输概率(STP)提供了一种整体的表达,并为C-JT计划的安全定位提供了一种上限和紧凑的近似值。接下来,我们通过优化放置概率矢量设定,使NC-JT的STP实现最大程度,并优化C-J的近似度。通过利用STP的某些特性,我们在某些案例中获得了全球最佳的合作解决方案。此外,通过使用内部点方法,我们获得了一般情况下的当地最佳解决方案。最后,数字结果显示,NT-JT的优化定位战略在STP中实现了最佳的C-J格式。