A Low-Complexity Cache-Aided Multi-antenna Content Delivery Scheme
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We study downlink beamforming in a single-cell network with a multi-antenna base station (BS) serving cache-enabled users. Proactive caching and coded delivery provides global caching gains by dividing the files into subfiles and creating multicasting opportunities across users. For a given common rate of the files in the system, we first formulate the minimum transmit power at the BS with beamforming transmission, which corresponds to a multiple multicast problem, as a non-convex optimization problem. While a stationary solution to this problem can be found through successive convex approximation (SCA), the complexity of the problem grows exponentially with the number of subfiles that must be delivered to each user, which itself grows exponentially with the number of users in the system. Therefore, we introduce a low-complexity alternative through time-sharing that limits the number of subfiles that can be received by a user in each time slot. It is shown through numerical simulations that, the reduced-complexity beamforming scheme has minimal performance gap compared to transmitting all the subfiles jointly, and outperforms the state-of-the-art at all SNR and rate values with sufficient spatial degrees of freedom, and in the high SNR/high rate regime when the number of spatial degrees of freedom is limited.
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