arXiv subjects

Zhitong Ni

Publications and source records attributed to Zhitong Ni.

7 recordsLinked to original sources

arXiv2026

Semi-Supervised Goal-Oriented Semantic Communication Framework for Foreground Classification

Wireless goal-oriented semantic communication (GSC) has emerged as a promising paradigm by directly optimizing task performance. However, existing GSC frameworks typically operate on entire images and rely on labeled data for classification tasks, which can limit their compression efficiency and increase the risk of overfitting. This paper proposes a novel semi-supervised wireless GSC framework for the unlabeled image foreground classification task. In our proposed framework, a foreground-aware masked autoencoder (MAE) is developed to prioritize semantically important foreground objects, thereby reducing transmission overhead. To enable accurate reconstruction and classification under a limited data size, we further propose a semi-supervised autoencoder (SSAE) that decodes the semantic latent tensor and refines image details by leveraging three complementary information sources, followed by fine-tuning a pre-trained image classification model. The entire pipeline, from foreground masking to classification, is trained in a semi-supervised manner to significantly reduce the need for manual labeling. Simulation results validate that the proposed GSC framework achieves over 90% image classification accuracy while reducing the original image data size by 95%, and demonstrate its strong potential for practical tasks in resource-constrained wireless scenarios.

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arXiv2025

Deep Learning-based OTFS Channel Estimation and Symbol Detection with Plug-and-Play Framework

Orthogonal Time Frequency Space (OTFS) modulation has recently attracted significant interest due to its potential for enabling reliable communication in high-mobility environments. However, the effectiveness of OTFS receivers relies on the inherent characteristic of the Delay-Doppler (DD) domain channel, where the sparsity of the discretized channel varies across different communication scenarios. For instance, the fractional Doppler effect reduces the inherent channel sparsity, which consequently degrades channel estimation accuracy and increases the complexity of symbol detection. Traditional algorithms relying on fixed sparsity priors often require manual design, while purely data-driven deep learning (DL) methods typically struggle to generalize across diverse channel conditions. To address these challenges, we propose a novel unsupervised DL-based plug-and-play (PnP) framework that provides a flexible solution for OTFS receiver design. The proposed framework can be applied to both channel estimation and symbol detection, jointly leveraging the flexibility of optimization-based methods and the powerful generalization capability of data-driven models. Specifically, a lightweight encoder-decoder network (EDN) is incorporated as an implicit channel prior for channel estimation, enabling robust performance across varying levels of channel sparsity. Furthermore, for symbol detection, we realize the PnP framework with a time-domain matrix inversion for model-based equalization, followed by a small multi-layer perceptron (MLP) pre-trained for specific constellations, thereby achieving low complexity and enabling flexible adaptation to various modulation formats. Finally, numerical results demonstrate the effectiveness and robustness of the algorithm.

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arXiv2025

High-Resolution Uplink Sensing in Millimeter-Wave ISAC Systems

Perceptive mobile networks (PMNs), integrating ubiquitous sensing capabilities into mobile networks, represent an important application of integrated sensing and communication (ISAC) in 6G. In this paper, we propose a practical framework for uplink sensing of angle-of-arrival (AoA), Doppler, and delay in millimeter-wave (mmWave) communication systems, which addresses challenges posed by clock asynchrony and hybrid arrays, while being compatible with existing communication protocols. We first introduce a beam scanning method and a corresponding AoA estimation algorithm, which utilizes frequency smoothing to effectively estimate AoAs for both static and dynamic paths. We then propose several methods for constructing a ``clean'' reference signal, which is subsequently used to cancel the effect caused by the clock asynchrony. We further develop a signal ratio-based joint AoA-Doppler-delay estimator and propose an AoA-based 2D-FFT-MUSIC (AB2FM) algorithm that applies 2D-FFT operations on the signal subspace, which accelerates the computation process with low complexity. Our proposed framework can estimate parameters in pairs, removing the complicated parameter association process. Simulation results validate the effectiveness of our proposed framework and demonstrate its robustness in both low and high signal-to-noise ratio (SNR) conditions.

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arXiv2022

Uplink Sensing Using CSI Ratio in Perceptive Mobile Networks

Uplink sensing in perceptive mobile networks (PMNs), which uses uplink communication signals for sensing the environment around a base station, faces challenging issues of clock asynchronism and the requirement of a line-of-sight (LOS) path between transmitters and receivers. The channel state information (CSI) ratio has been applied to resolve these issues, however, current research on the CSI ratio is limited to Doppler estimation in a single dynamic path. This paper proposes an advanced parameter estimation scheme that can extract multiple dynamic parameters, including Doppler frequency, angle-of-arrival (AoA), and delay, in a communication uplink channel and completes the localization of multiple moving targets. Our scheme is based on the multi-element Taylor series of the CSI ratio that converts a nonlinear function of sensing parameters to linear forms and enables the applications of traditional sensing algorithms. Using the truncated Taylor series, we develop novel multiple-signal-classification grid searching algorithms for estimating Doppler frequencies and AoAs and use the least-square method to obtain delays. Both experimental and simulation results are provided, demonstrating that our proposed scheme can achieve good performances for sensing both single and multiple dynamic paths, without requiring the presence of a LOS path.

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arXiv2022

Joint Communications and Sensing Employing Optimized MIMO-OFDM Signals

Joint communication and sensing (JCAS) has the potential to improve the overall energy, cost and frequency efficiency of IoT systems. As a first effort, we propose to optimize the MIMO-OFDM data symbols carried by sub-carriers for better time- and spatial-domain signal orthogonality. This not only boosts the availability of usable signals for JCAS, but also significantly facilitates Internet-of-Things (IoT) devices to perform high-quality sensing. We establish an optimization problem that modifies data symbols on sub-carriers to enhance the above-mentioned signal orthogonality. We also develop an efficient algorithm to solve the problem based on the majorization-minimization framework. Moreover, we discover unique signal structures and features from the newly modeled problem, which substantially reduce the complexity of majorizing the objective function. We also develop new projectors to enforce the feasibility of the obtained solution. Simulations show that, compared with the original communication waveform to achieve the same sensing performance, the optimized waveform can reduce the signal-to-noise ratio (SNR) requirement by 3~4.5 dB, while the SNR loss for the uncoded bit error rate is only 1~1.5 dB.

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arXiv2020

Waveform Optimization with Multiple Performance Metrics for Broadband Joint Communication and Radar Sensing

Joint communication and radar sensing (JCAS) integrates communication and radar/radio sensing into one system, sharing one transmitted signal. In this paper, we investigate JCAS waveform optimization underlying communication signals, where a base station detects radar targets and communicates with mobile users simultaneously. We first develop individual novel waveform optimization problems for communications and sensing, respectively. For communications, we propose a novel lower bound of sum rate by integrating multi-user interference and effective channel gain into one metric that simplifies the optimization of the sum rate. For radar sensing, we consider optimizing one of two metrics, the mutual information or the Cramer-Rao bound. Then, we formulate the JCAS problem by optimizing the communication metric under different constraints of the radar metric, and we obtain both closed-form solutions and iterative solutions to the non-convex JCAS optimization problem. Numerical results are provided and verify the proposed optimization solutions.

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arXiv2020

Uplink Sensing in Perceptive Mobile Networks with Asynchronous Transceivers

Perceptive mobile network (PMN) is a recently proposed next-generation network that integrates radar sensing into communication. One major challenge for realizing sensing in PMNs is how to deal with spatially-separated asynchronous transceivers. The asynchrony between sensing receiver and transmitter will cause both timing offsets (TOs) and carrier frequency offsets (CFOs) and lead to degraded sensing accuracy in both ranging and velocity measurements. In this paper, we propose an uplink sensing scheme for PMNs with asynchronous transceivers, targeting at resolving the sensing ambiguity and improving the sensing accuracy. We first adopt a cross-antenna cross-correlation (CACC) operation to remove the sensing ambiguity associated with both TOs and CFOs. Without sensing ambiguity, both actual propagation delay and actual Doppler frequency of multiple targets can be obtained using CACC outputs. To exploit the redundancy of the CACC outputs and reduce the complexity, we then propose a novel mirrored-MUSIC algorithm, which halves the number of unknown parameters to be estimated, for obtaining actual values of delays and Doppler frequencies. Finally, we propose a high-resolution angles-of-arrival (AoAs) estimation algorithm, which jointly processes all measurements from spatial, temporal, and frequency domains. The proposed AoAs estimation algorithm can achieve significantly higher estimation accuracy than that of using samples from the spatial domain only. We also derive the theoretical mean-square-error of the proposed algorithms. Numerical results are provided and validate the effectiveness of the proposed scheme.

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