Projects
Selected research in wireless communications and signal processing, grouped by topic.
Dense-Array Channel Estimation
Observation design: from ice filling to 2D ice filling
Spatial correlation in dense arrays informs observation design when pilot resources are limited. These studies develop ice filling as a discrete counterpart to water filling. Two-dimensional ice filling and a hybrid-array variant extend this approach to joint transmit-precoder and receive-combiner design. For RIS-aided links, alternating Riemannian optimization jointly designs receive combiners and RIS phase shifts, with adaptive covariance learning from received pilots.
Selected publications
Observation Matrix Design for Densifying MIMO Channel Estimation via 2D Ice Filling IEEE Transactions on Signal Processing, vol. 74, pp. 798–814, 2026.
IEEE citationZ. Zhang and M. Cui, “Observation matrix design for densifying MIMO channel estimation via 2D ice filling,” IEEE Trans. Signal Process., vol. 74, pp. 798–814, 2026, doi: 10.1109/tsp.2026.3657342.
Ice-Filling: Near-Optimal Channel Estimation for Dense Array Systems IEEE Transactions on Wireless Communications, vol. 24, no. 10, pp. 8551–8564, Oct. 2025.
IEEE citationM. Cui, Z. Zhang, L. Dai, and K. Huang, “Ice-filling: Near-optimal channel estimation for dense array systems,” IEEE Trans. Wireless Commun., vol. 24, no. 10, pp. 8551–8564, Oct. 2025, doi: 10.1109/twc.2025.3567797.
Enhancing Channel Estimation in RIS-Aided Systems via Observation Matrix Design IEEE Transactions on Vehicular Technology, vol. 75, no. 10, pp. 25198–25203, Oct. 2026.
IEEE citationZ. Zhang and M. Cui, “Enhancing channel estimation in RIS-aided systems via observation matrix design,” IEEE Trans. Veh. Technol., vol. 75, no. 10, pp. 25198–25203, Oct. 2026, doi: 10.1109/tvt.2026.3697200.
Fluid Antenna Systems
Successive Bayesian reconstruction of spatially continuous channels
Fluid antenna systems require channel estimates at many candidate positions, making exhaustive measurement costly. The successive Bayesian reconstructor (S-BAR) models the spatial channel as a stochastic process. It uses an experiential kernel to guide measurement selection and reconstruct channels at unobserved positions. The method does not rely on angular sparsity or slowly varying channels. Simulations under matched and mismatched channel models assess the value of this prior information.
Selected publications
Successive Bayesian Reconstructor for Channel Estimation in Fluid Antenna Systems IEEE Transactions on Wireless Communications, vol. 24, no. 3, pp. 1992–2006, Mar. 2025.
IEEE citationZ. Zhang, J. Zhu, L. Dai, and R. W. Heath, Jr., “Successive Bayesian reconstructor for channel estimation in fluid antenna systems,” IEEE Trans. Wireless Commun., vol. 24, no. 3, pp. 1992–2006, Mar. 2025, doi: 10.1109/twc.2024.3515135.
Near-Field XL-MIMO
Low-overhead beam training: hierarchical search and Bayesian inference
Near-field beam training must resolve both angle and distance, making exhaustive codebook searches costly. A hierarchical approach constructs multiresolution codebooks with the Gerchberg–Saxton algorithm and adapts them to hybrid arrays without additional time-delay hardware. A subsequent Bayesian regression approach uses correlations among codewords to update a Gaussian process posterior. It infers promising beams from a small set of measurements. Simulations evaluate the tradeoff between training overhead and achievable rate.
Selected publications
Near-Optimal Near-Field Beam Training: From Searching to Inference IEEE Transactions on Wireless Communications, vol. 24, no. 11, pp. 9173–9185, Nov. 2025.
IEEE citationZ. Xu, Z. Zhang, and L. Dai, “Near-optimal near-field beam training: From searching to inference,” IEEE Trans. Wireless Commun., vol. 24, no. 11, pp. 9173–9185, Nov. 2025, doi: 10.1109/twc.2025.3571488.
Hierarchical Beam Training for Extremely Large-Scale MIMO: From Far-Field to Near-Field IEEE Transactions on Communications, vol. 72, no. 4, pp. 2247–2259, Apr. 2024.
IEEE citationY. Lu, Z. Zhang, and L. Dai, “Hierarchical beam training for extremely large-scale MIMO: From far-field to near-field,” IEEE Trans. Commun., vol. 72, no. 4, pp. 2247–2259, Apr. 2024, doi: 10.1109/tcomm.2023.3344600.
Holographic and Continuous-Aperture MIMO
Pattern-division multiplexing for continuous-aperture MIMO
In continuous-aperture MIMO, current patterns are functions defined over an aperture. Pattern-division multiplexing (PDM) projects these functions onto finite orthogonal bases, converting the functional optimization into a tractable finite-dimensional problem. Block coordinate descent then optimizes the patterns for multiuser sum rate. Simulations show gains over the evaluated baselines.
Electromagnetic information theory and wavenumber-domain processing
Models of spatially continuous apertures must account for electromagnetic fields and correlations at subwavelength separations. A random-field formulation analyzes mutual information between continuous source and destination regions under white and colored noise. A subsequent overview describes holographic MIMO in the wavenumber domain using a spatial Fourier plane-wave decomposition. It connects this representation to multiplexing, channel estimation, and waveform design, and discusses open questions for wideband systems and network-level operation.
Selected publications
Pattern-Division Multiplexing for Multi-User Continuous-Aperture MIMO IEEE Journal on Selected Areas in Communications, vol. 41, no. 8, pp. 2350–2366, Aug. 2023.
IEEE citationZ. Zhang and L. Dai, “Pattern-division multiplexing for multi-user continuous-aperture MIMO,” IEEE J. Sel. Areas Commun., vol. 41, no. 8, pp. 2350–2366, Aug. 2023, doi: 10.1109/jsac.2023.3288244.
Wavenumber-Domain Signal Processing for Holographic MIMO: Foundations, Methods, and Future Directions IEEE Communications Standards Magazine, vol. 10, no. 2, pp. 127–133, Jun. 2026.
IEEE citationZ. Zhang and L. Dai, “Wavenumber-domain signal processing for holographic MIMO: Foundations, methods, and future directions,” IEEE Commun. Standards Mag., vol. 10, no. 2, pp. 127–133, Jun. 2026, doi: 10.1109/mcomstd.2026.3663934.
Mutual Information for Electromagnetic Information Theory Based on Random Fields IEEE Transactions on Communications, vol. 71, no. 4, pp. 1982–1996, Apr. 2023.
IEEE citationZ. Wan, J. Zhu, Z. Zhang, L. Dai, and C.-B. Chae, “Mutual information for electromagnetic information theory based on random fields,” IEEE Trans. Commun., vol. 71, no. 4, pp. 1982–1996, Apr. 2023, doi: 10.1109/tcomm.2023.3247725.
Reconfigurable Intelligent Surfaces
RIS-aided cell-free networks and multi-hop transmissions
RIS-aided cell-free networks combine distributed base stations with low-cost reflecting surfaces to improve network capacity. A wideband precoding framework jointly optimizes base-station precoders and RIS configurations through fractional programming and alternating optimization. Related studies address energy-efficiency fairness and extend channel models and beamforming design to multihop RIS reflections.
Active RIS: signal modeling, architectures, and wideband beamforming
Multiplicative fading limits the benefit of passive RIS links, particularly when a strong direct link is present. Active RISs address this limitation through signal amplification. This work validates an amplification-and-noise model using a fabricated element and jointly designs transmit and reflection beamforming. Related work examines the energy efficiency of subconnected architectures with shared amplifiers. It also studies grouped-subcarrier designs for wideband channels. An overview discusses RIS fundamentals, common misconceptions, and fading-induced limits.
Compact user-specific RIS for uplink transmission
Large antenna arrays at user devices are constrained by size, cost, and power consumption. This work proposes a compact multilayer user-specific RIS that supports phase control and partial amplitude control of the transmitted signal. Beamforming is designed by alternating optimization to maximize the uplink signal-to-noise ratio.
Selected publications
A Joint Precoding Framework for Wideband Reconfigurable Intelligent Surface-Aided Cell-Free Network IEEE Transactions on Signal Processing, vol. 69, pp. 4085–4101, 2021.
IEEE citationZ. Zhang and L. Dai, “A joint precoding framework for wideband reconfigurable intelligent surface-aided cell-free network,” IEEE Trans. Signal Process., vol. 69, pp. 4085–4101, 2021, doi: 10.1109/tsp.2021.3088755.
Active RIS vs. Passive RIS: Which Will Prevail in 6G? IEEE Transactions on Communications, vol. 71, no. 3, pp. 1707–1725, Mar. 2023.
IEEE citationZ. Zhang et al., “Active RIS vs. passive RIS: Which will prevail in 6G?,” IEEE Trans. Commun., vol. 71, no. 3, pp. 1707–1725, Mar. 2023, doi: 10.1109/tcomm.2022.3231893.
Compact User-Specific Reconfigurable Intelligent Surfaces for Uplink Transmission IEEE Transactions on Communications, vol. 70, no. 1, pp. 680–692, Jan. 2022.
IEEE citationK. Liu, Z. Zhang, L. Dai, and L. Hanzo, “Compact user-specific reconfigurable intelligent surfaces for uplink transmission,” IEEE Trans. Commun., vol. 70, no. 1, pp. 680–692, Jan. 2022, doi: 10.1109/tcomm.2021.3124953.
Localization, Sensing, and Radio Maps
Signal-multiplexing ranging and asynchronous vehicle localization
Accurate network ranging must account for clock drift without excessive exchanges between node pairs. Signal-multiplexing network ranging reuses transmissions and timestamp relationships to mitigate clock errors while limiting signaling overhead. Extensions use reflected non-line-of-sight signals for joint localization and sensing. They also introduce a network-measuring protocol for relative localization among asynchronous moving vehicles. The studies evaluate ranging accuracy, positioning robustness, and measurement timeliness.
Urban 3D radio-map reconstruction from sparse UAV measurements
Three-dimensional urban radio maps support UAV communications, but obtaining dense measurements is costly. This work collects an urban UAV dataset to develop and evaluate a Gaussian process regression framework for radio-map reconstruction from sparse observations. Offline clustering and posterior-guided online point selection identify informative measurements.
Selected publications
Signal-Multiplexing Ranging for Network Localization IEEE Transactions on Wireless Communications, vol. 21, no. 3, pp. 1694–1709, Mar. 2022.
IEEE citationZ. Zhang, H. Zhao, J. Wang, and Y. Shen, “Signal-multiplexing ranging for network localization,” IEEE Trans. Wireless Commun., vol. 21, no. 3, pp. 1694–1709, Mar. 2022, doi: 10.1109/twc.2021.3106172.
Enhancing Timeliness in Asynchronous Vehicle Localization: A Signal-Multiplexing Network Measuring Approach IEEE Transactions on Intelligent Transportation Systems, vol. 25, no. 10, pp. 13729–13743, Oct. 2024.
IEEE citationH. Zhao, Z. Zhang, L. Xu, Y. Wang, and Y. Shen, “Enhancing timeliness in asynchronous vehicle localization: A signal-multiplexing network measuring approach,” IEEE Trans. Intell. Transp. Syst., vol. 25, no. 10, pp. 13729–13743, Oct. 2024, doi: 10.1109/tits.2024.3404784.
High-Efficiency Urban 3D Radio Map Estimation Based on Sparse Measurements IEEE Transactions on Vehicular Technology, vol. 74, no. 10, pp. 16488–16493, Oct. 2025.
IEEE citationX. Chen, X. Zhong, Z. Zhang, L. Dai, and S. Zhou, “High-efficiency urban 3D radio map estimation based on sparse measurements,” IEEE Trans. Veh. Technol., vol. 74, no. 10, pp. 16488–16493, Oct. 2025, doi: 10.1109/tvt.2025.3573595.
Rydberg Atomic Receivers
Atomic reception for wireless communication and sensing
Rydberg atomic receivers detect radio signals through atomic transitions. This collaborative article reviews their operating principles and recent developments. It presents experiments on OFDM reception and image transmission using quantized deep joint source-channel coding. The discussion covers practical limitations and potential applications in multiband communication, sensing, and energy-efficient wireless systems.
Selected publications
Rydberg Atomic Receivers for Net-Zero 6G Wireless Communication and Sensing: Progress, Experiments, and Sustainable Prospects IEEE Communications Magazine, vol. 64, no. 8, pp. 52–59, Aug. 2026.
IEEE citationY. Tao et al., “Rydberg atomic receivers for net-zero 6G wireless communication and sensing: Progress, experiments, and sustainable prospects,” IEEE Commun. Mag., vol. 64, no. 8, pp. 52–59, Aug. 2026, doi: 10.1109/mcom.001.2500610.