4 research outputs found
Efficient Battery Usage in Wireless-Powered Cell-Free Systems with Self-Energy Recycling
This paper investigates wireless-powered cell-free systems, in which the
users send their uplink data signal while simultaneously harvesting energy from
network nodes and user terminals - including the transmitting user terminal
itself - by performing self-energy recycling. In this rather general setting, a
closed-form lower bound of the amount of harvested energy and the achieved
signal-to-interference-plus-noise ratio expressions are derived. Then, to
improve the energy efficiency, we formulate the problem of minimizing the
users' battery energy usage while satisfying minimum data rate requirements.
Due to the non-convexity of the problem, a novel alternating optimization
algorithm is proposed, and its proof of convergence is provided. Finally,
numerical results show that the proposed method is more efficient than a
state-of-art algorithm in terms of battery energy usage and outage rate.Comment: Accepted as a correspondance at IEEE TV
Mixed Coherent and Non-Coherent Transmission for Multi-CPU Cell-Free Systems
Existing works on cell-free systems consider either coherent or non-coherent
downlink data transmission and a network deployment with a single central
processing unit (CPU). While it is known that coherent transmission outperforms
noncoherent transmission when assuming unlimited fronthaul links, the former
requires a perfect timing synchronization, which is practically not viable over
a large network. Furthermore, relying on a single CPU for geographically large
cell-free networks is not scalable. Thus, to realize the expected gains of
cellfree systems in practice, alternative transmission strategies for realistic
multi-CPU cell-free systems are required. Therefore, this paper proposes a
novel downlink data transmission scheme that combines and generalizes the
existing coherent and non-coherent transmissions. The proposed transmission
scheme, named mixed transmission, works based on the realistic assumption that
only the access points (APs) controlled by a same CPU are synchronized, and
thus transmit in a coherent fashion, while APs from different CPUs require no
synchronism and transmit in a non-coherent manner. We also propose extensions
of existing clustering algorithms for multi-CPU cell-free systems with mixed
transmission. Simulation results show that the combination of the proposed
clustering algorithms with mixed transmission have the potential to perform
close to the ideal coherent transmission.Comment: Submitted for possible publication in IEEE conferenc