Integrating coded caching (CC) into multi-input multi-output (MIMO) setups significantly enhances the achievable degrees of freedom (DoF). We consider a cache-aided MIMO configuration with a CC gain $t$, where a server with $L$ Tx-antennas communicates with $K$ users, each equipped with $G$ Rx-antennas. Similar to existing works, we also extend a core CC approach, designed initially for multi-input single-output (MISO) scenarios, to the MIMO setup. However, in the proposed MIMO strategy, rather than replicating the transmit scheme from the MISO setup, the number of users $\Omega$ served in each transmission is fine-tuned to maximize DoF. As a result, an optimized DoF of ${\max_{\beta, \Omega }}{\Omega \beta}$ is achieved, where ${\beta \le \mathrm{min}\big(G,L \binom{\Omega-1}{t}}\Big/{1 + (\Omega - t-1)\binom{\Omega-1}{t}}\big)$ is the number of parallel streams decoded by each user. For the considered MIMO-CC setup, we also introduce an effective multicast transmit covariance matrix design for the symmetric rate maximization objective solved iteratively via successive convex approximation (SCA). Finally, numerical simulations verify the enhanced DoF and improved performance of the proposed design.

翻译：将编码缓存（CC）集成到多输入多输出（MIMO）设置中，可显著提升可实现自由度（DoF）。我们考虑一种缓存辅助的MIMO配置，其中CC增益为$t$，服务器配备$L$根发射天线，与$K个$用户通信，每个用户配备$G$根接收天线。与现有工作类似，我们将最初为多输入单输出（MISO）场景设计的核心CC方法扩展到MIMO设置中。然而，在所提出的MIMO策略中，并非直接复制MISO设置的传输方案，而是精细调整每次传输中服务的用户数量$\Omega$以最大化DoF。由此实现优化后的DoF为${\max_{\beta, \Omega }}{\Omega \beta}$，其中${\beta \le \mathrm{min}\big(G,L \binom{\Omega-1}{t}}\Big/{1 + (\Omega - t-1)\binom{\Omega-1}{t}}\big)$为每个用户解码的并行流数量。针对所考虑的MIMO-CC设置，我们还提出了一种有效的多播发射协方差矩阵设计，用于对称速率最大化目标，并通过逐次凸逼近（SCA）迭代求解。最后，数值仿真验证了所提出设计的增强DoF与改进性能。