141 research outputs found
Efficient Quantized Constant Envelope Precoding for Multiuser Downlink Massive MIMO Systems
Quantized constant envelope (QCE) precoding, a new transmission scheme that
only discrete QCE transmit signals are allowed at each antenna, has gained
growing research interests due to its ability of reducing the hardware cost and
the energy consumption of massive multiple-input multiple-output (MIMO)
systems. However, the discrete nature of QCE transmit signals greatly
complicates the precoding design. In this paper, we consider the QCE precoding
problem for a massive MIMO system with phase shift keying (PSK) modulation and
develop an efficient approach for solving the constructive interference (CI)
based problem formulation. Our approach is based on a custom-designed
(continuous) penalty model that is equivalent to the original discrete problem.
Specifically, the penalty model relaxes the discrete QCE constraint and
penalizes it in the objective with a negative -norm term, which leads
to a non-smooth non-convex optimization problem. To tackle it, we resort to our
recently proposed alternating optimization (AO) algorithm. We show that the AO
algorithm admits closed-form updates at each iteration when applied to our
problem and thus can be efficiently implemented. Simulation results demonstrate
the superiority of the proposed approach over the existing algorithms.Comment: 5 pages, 5 figures, submitted for possible publicatio
Hybrid Evolutionary-based Sparse Channel Estimation for IRS-assisted mmWave MIMO Systems
The intelligent reflecting surface (IRS)-assisted millimeter wave (mmWave) communication system has emerged as a promising technology for coverage extension and capacity enhancement. Prior works on IRS have mostly assumed perfect channel state information (CSI), which facilitates in deriving the upper-bound performance but is difficult to realize in practice due to passive elements of IRS without signal processing capabilities. In this paper, we propose a compressive channel estimation techniques for IRS-assisted mmWave multi-input and multi-output (MIMO) system. To reduce the training overhead, the inherent sparsity of mmWave channels is exploited. By utilizing the properties of Kronecker products, IRS-assisted mmWave channel is converted into a sparse signal recovery problem, which involves two competing cost function terms (measurement error and sparsity term). Existing sparse recovery algorithms solve the combined contradictory objectives function using a regularization parameter, which leads to a suboptimal solution. To address this concern, a hybrid multiobjective evolutionary paradigm is developed to solve the sparse recovery problem, which can overcome the difficulty in the choice of regularization parameter value. Simulation results show that under a wide range of simulation settings, the proposed method achieves competitive error performance compared to existing channel estimation methods
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