Information Theory (cs.IT)
Thu, 24 Aug 2023
1.Eigenvector prediction-based precoding for massive MIMO with mobility
Authors:Ziao Qin, Haifan Yin, Weidong Li
Abstract: Eigenvector decomposition (EVD) is an inevitable operation to obtain the precoders in practical massive multiple-input multiple-output (MIMO) systems. Due to the large antenna size and at finite computation resources at the base station (BS), the overwhelming computation complexity of EVD is one of the key limiting factors of the system performance. To address this problem, we propose an eigenvector prediction (EGVP) method by interpolating the precoding matrix with predicted eigenvectors. The basic idea is to exploit a few historical precoders to interpolate the rest of them without EVD of the channel state information (CSI). We transform the nonlinear EVD into a linear prediction problem and prove that the prediction of the eigenvectors can be achieved with a complex exponential model. Furthermore, a channel prediction method called fast matrix pencil prediction (FMPP) is proposed to cope with the CSI delay when applying the EGVP method in mobility environments. The asymptotic analysis demonstrates how many samples are needed to achieve asymptotically error-free eigenvector predictions and channel predictions. Finally, the simulation results demonstrate the spectral efficiency improvement of our scheme over the benchmarks and the robustness to different mobility scenarios.
2.Separating the Human Touch from AI-Generated Text using Higher Criticism: An Information-Theoretic Approach
Abstract: We propose a method to determine whether a given article was entirely written by a generative language model versus an alternative situation in which the article includes some significant edits by a different author, possibly a human. Our process involves many perplexity tests for the origin of individual sentences or other text atoms, combining these multiple tests using Higher Criticism (HC). As a by-product, the method identifies parts suspected to be edited. The method is motivated by the convergence of the log-perplexity to the cross-entropy rate and by a statistical model for edited text saying that sentences are mostly generated by the language model, except perhaps for a few sentences that might have originated via a different mechanism. We demonstrate the effectiveness of our method using real data and analyze the factors affecting its success. This analysis raises several interesting open challenges whose resolution may improve the method's effectiveness.
3.Constructive Interference based Block-Level Precoding for Scene Expansion: Closed-Form Solutions
Authors:Yiran Wang, Ang Li, Yunsi Wen, Xiaoyan Hu
Abstract: We study closed-form constructive interference based block-level precoding (CI-BLP) for scene expansion in the downlink of multi-user multiple-input single-output (MU-MISO) systems. We extend the analysis on CI-BLP to the case where the number of symbol slots in a block is smaller than the number of user. To this end, we mathematically prove the feasibility of using the pseudo-inverse to express the closed-form expression of the CI-BLP optimal precoding matrix. Building upon this, a quadratic programming (QP) optimization on simplex is obtained without being limited by the relationship between the number of symbol slots in a block and the number of users. We study the low complexity algorithm of large scale QP problem. We first mathematically obtain the rank of the quadratic coefficient matrix in the QP problem. Although the iterative closed-form algorithm for QP problems in CI-based symbol-level precoding (CI-SLP) can be used in certain scenarios, the complexity of the iterative closed algorithm for large-scale QP problems is impractical. In addition, we design a low complexity algorithm based on alternating direction method of multipliers (ADMM), which can efficiently solve large-scale QP problems. We further analyze the convergence and complexity of the proposed algorithm. Numerical results validate our analysis and the optimality of the proposed algorithm, and further show that the proposed algorithm offers a flexible performance-complexity tradeoff by limiting the maximum number of iterations, which motivates the use of CI-BLP in practical wireless systems.