The Hidden Cost of Caching: Analyzing The Energy Expenditure of Placement in Cache-Aided MISO Networks

Coded caching (CC) has been shown to significantly improve content delivery performance. However, most prior work has largely overlooked the energy cost of the wireless cache placement phase. We study the energy efficiency (EE) of cache-aided multi-antenna networks by jointly considering wireless placement and delivery under a realistic power consumption model, accounting for varying distances between the base station (BS) and users. The cache placement reuse factor (η) is introduced to capture how many delivery sessions benefit from a single cache update. We formulate the overall EE maximization problem and propose optimized multi-antenna transmission strategies for both phases. Simulation results show that CC becomes inefficient when the delivery-to-placement distance ratio or η is small, as placement overhead dominates. Conversely, as the delivery-to-placement distance ratio, η, or cache size increases, CC gains ultimately outweigh the placement cost, even though larger caches initially raise placement energy.