The integration of sensing capabilities into wireless communication systems has recently emerged as a compelling area of research. By leveraging shared hardware and spectrum for both functions, ISAC systems offer significant cost and resource efficiency. However, their simultaneous operation introduces key challenges, including waveform design, resource allocation, and precoder/combiner optimization in MIMO ISAC systems. Addressing these challenges has sparked numerous research opportunities, as explored in our recent tutorial paper, which examines communication-centric ISAC for next-generation cellular networks [1].
[1] N. González-Prelcic, M. F. Keskin, O. Kaltiokallio, M. Valkama, D. Dardari, X. Shen, Y. Shen, M. Bayraktar, and H. Wymeersch, "The integrated sensing and communication revolution for 6G: Vision, techniques, and applications," Proceedings of the IEEE, 2024.
Localization as a by-product of sparse channel estimation at mmWave bands
Millimeter-wave (mmWave) communication channels exhibit sparsity in both the angular and delay domains. Sparse channel estimation techniques can extract the angle and delay information associated with each propagation path, enabling user localization with a single access point (AP). However, realistic system effects, such as clock offset between the AP and user equipment (UE) and filtering, must be accounted for as demonstrated in [1]–[3]. Moreover, the unique characteristics of indoor environments can be leveraged to enhance localization accuracy, as shown in these studies. Additionally, reconfigurable intelligent surfaces (RISs) have been shown to significantly improve localization performance [1], [3]. Finally, practical hardware impairments, including array calibration errors and mutual coupling, can severely degrade localization accuracy. Therefore, their impact must be carefully considered and mitigated during joint channel estimation and localization [3].
[1] M. Bayraktar, J. Palacios, N. González-Prelcic, and C. J. Zhang, "Multidimensional orthogonal matching pursuit-based RIS-aided joint localization and channel estimation at mmWave," in Proceedings of IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2022, pp. 1-5.
[2] J. Palacios, M. Bayraktar, N. González-Prelcic, and H. Chen, "High accuracy device localization in indoor mmWave networks exploiting channel sparsity and virtual anchor mapping," in Proceedings of IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), April, 2024.
[3] M. Bayraktar, N. González-Prelcic, G. C. Alexandropoulos, and H. Chen, "RIS-Aided joint channel estimation and localization at mmWave under hardware impairments: A dictionary learning-based approach," in IEEE Transactions on Wireless Communications, vol. 23, no. 12, pp. 19696-19712, Dec. 2024.
Monostatic sensing with full-duplex mmWave systems
Downlink (DL) signals transmitted by an AP can reflect off environmental objects and be captured by a colocated receiver, enabling monostatic sensing with full-duplex (FD) transceivers. However, FD operation introduces significant self-interference (SI), necessitating precoder and combiner designs that mitigate SI while supporting ISAC functionalities. To address this, an SI-aware analog full-duplex codebook is proposed in [1], while hybrid precoders/combiners are optimized for joint DL communication and monostatic sensing in [2], [3]. Expanding on these designs, [4] introduces a framework that integrates joint DL/uplink (UL) communication with monostatic sensing. These optimization problems are highly intractable due to the coupling between precoders/combiners and the non-convexity introduced by hybrid architectures. Thus, advanced techniques such as alternating optimization, convex relaxation, iterative methods, and manifold optimization have been employed in [1]–[4].
[1] M. Bayraktar, C. Rusu, N. González-Prelcic, and H. Chen, "Self-interference aware codebook design for full-duplex joint sensing and communication systems at mmWave," in Proceedings of IEEE 9th International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP), 2023, 231-235.
[2] M. Bayraktar and N. González-Prelcic, and H. Chen, "Hybrid precoding and combining for mmWave full duplex joint radar and communication systems under self-interference," in Proceedings of IEEE International Conference on Communications (ICC), 2024.
[3] M. Bayraktar and N. González-Prelcic, H. Chen, and C. J. Zhang, "Near-field full-duplex integrated sensing and communication with dynamic metasurface antennas," to appear in Proceedings of 58th Asilomar Conference on Signals, Systems, and Computers, 2024, pp. 1-5.
[4] M. Bayraktar and N. González-Prelcic, H. Chen, and C. J. Zhang, "Truly full-duplex integrated sensing and single-user communication at mmWave," in Proceedings of IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2024.
Artificial intelligence (AI) and machine learning (ML) have transformed numerous fields over the past decade, with their impact on wireless communications accelerating in recent years, particularly with the development of 6G.
One of the most significant applications of AI in wireless communications is in channel estimation and prediction. Traditional channel estimation methods leverage channel correlations across antennas, time samples, and subcarriers in multicarrier systems; however, these approaches often entail high computational complexity. Additionally, accurate channel statistics are typically required, especially for channel prediction in highly dynamic environments. Recent studies indicate that AI-driven methods can effectively balance computational efficiency and estimation accuracy. Furthermore, neural receivers have the potential to replace multiple signal processing blocks, such as channel estimation and equalization, further enhancing computational efficiency.
In precoder and combiner design for MIMO systems, conventional approaches rely on optimization frameworks that maximize an objective function (e.g., spectral efficiency) or minimize a cost function (e.g., symbol detection error). More complex systems, such as the ones supporting ISAC functionalities, impose additional constraints, often leading to solutions with high computational demands or slow convergence rates. Model-based deep learning is an emerging paradigm that enhances traditional optimization techniques by integrating neural architectures as complementary tools rather than replacing established blocks with black-box AI models. This hybrid approach offers a promising avenue for improving the performance and efficiency of wireless communication systems.