Probabilistic Placement Optimization for Non-coherent and Coherent Joint Transmission in Cache-Enabled Cellular Networks

TL;DR

This paper develops probabilistic content placement strategies for cache-enabled cellular networks, optimizing joint transmission schemes with and without channel state information to improve successful transmission probability.

Contribution

It introduces a unified optimization framework for probabilistic content placement in cooperative cellular transmission, deriving analytical expressions and proposing algorithms for optimal solutions.

Findings

Optimized placement strategies significantly improve transmission success probability.

C-JT with CSI outperforms NC-JT without CSI in transmission success.

Proposed algorithms achieve near-optimal solutions with practical computational complexity.

Abstract

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.