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This paper investigates quantum machine learning to optimize the beamforming in a multiuser multiple-input single-output downlink system. We aim to combine the power of quantum neural networks and the success of classical deep neural networks to enhance the learning performance. Specifically, we propose two hybrid quantum-classical neural networks to maximize the sum rate of a downlink system. The first one proposes a quantum neural network employing parameterized quantum circuits that follows a classical convolutional neural network. The classical neural network can be jointly trained with the quantum neural network or pre-trained leading to a fine-tuning transfer learning method. The second one designs a quantum convolutional neural network to better extract features followed by a classical deep neural network. Our results demonstrate the feasibility of the proposed hybrid neural networks, and reveal that the first method can achieve similar sum rate performance compared to a benchmark classical neural network with significantly less training parameters; while the second method can achieve higher sum rate especially in presence of many users still with less training parameters. The robustness of the proposed methods is verified using both software simulators and hardware emulators considering noisy intermediate-scale quantum devices.

Due to the uncontrolled and complex real-life radio propagation environments, Claude Shannon's information theory of communications describes fundamental limits to state-of-the-art 5G radio access network (RAN) capacity, with respect to fixed radio resource usage. Fortunately, recent research has found that a holographic metasurface-based new physical layer architecture may hold the key to overcome these fundamental limits of current mobile networks under a new paradigm, smart wireless environment (SWE), where the long-standing challenge of mobile communications, fading channel hostility, may be solved, leading to a step-change boost in network performance and user experience. Despite recent research activities in SWE, the best way to implement it as a network operator remains an open challenge. In this industrial review, we adopt a novel yet realistic mobile channel stabilisation perspective for network operators to understand this paradigm shift. More specifically, we provide a technical analysis of the synergy between key next-gen mobile network enablers, e.g., holographic metasurface, wireless sensing, and machine intelligence, as well as of how this synergy leads to a robust future RAN architecture. Against the as yet unclear theoretical boundaries and low technology readiness level (TRL) of SWE enhanced telecommunications, we conclude by identifying critical challenges in future commercial deployments., Comment: This work has been submitted to the IEEE for possible publication

Reconfigurable intelligent surface (RIS) devices have emerged as an effective way to control the propagation channels for enhancing the end-users' performance. However, RIS optimization involves configuring the radio frequency response of a large number of radiating elements, which is challenging in real-world applications due to high computational complexity. In this paper, a model-free cross-entropy (CE) algorithm is proposed to optimize the binary RIS configuration for improving the signal-to-noise ratio (SNR) at the receiver. One key advantage of the proposed method is that it only requires system performance indicators, e.g., the received SNR, without the need for channel models or channel state information. Both simulations and experiments are conducted to evaluate the performance of the proposed CE algorithm. This study provides an experimental demonstration of the channel hardening effect in a multi-antenna RIS-assisted wireless system under rich multipath fading., Comment: accepted by IEEE Wireless Communications Letters