Future wireless networks must support heterogeneous services with markedly different requirements, such as enhanced mobile broadband (eMBB), which demand high data rates, and massive machine-type communications (mMTC), which seek long battery lifetimes. Recently, cell-free massive MIMO (CF-mMIMO) has emerged as a promising paradigm for providing uniform service quality and flexible resource allocation in such scenarios.
In this talk, we investigate uplink multiple-access schemes for the coexistence between these two use cases. We consider a non-orthogonal access strategy in which low-rate mMTC transmissions are spread across the time–frequency resources concurrently used by eMBB users, enabling efficient resource reuse while supporting heterogeneous traffic.
Assuming imperfect channel state information, we derive closed-form expressions for the achievable uplink rates of both services, based solely on statistical channel knowledge. For mMTC devices, the analysis explicitly accounts for the finite blocklength (FBL) regime to characterize short-packet transmissions.
To accommodate heterogeneous service requirements, we formulate a power-control problem that maximizes the minimum energy efficiency across mMTC devices while enforcing quality-of-service constraints for eMBB users. The resulting nonconvex fractional optimization is addressed via sequential fractional programming, with formulations that cover both the classical Shannon and FBL regimes.
Numerical results demonstrate that the proposed scheme enables effective multiplexing of eMBB and mMTC traffic while maintaining the desired reliability-efficiency trade-offs. As future work, we plan to investigate learning-based approximations of the proposed optimization framework (e.g., using graph neural networks) to further reduce computational complexity and enable real-time operation.
BIO
Sergi Liesegang (Member, IEEE) received the bachelor’s degree in telecommunication engineering from the Universitat Politècnica de Catalunya (UPC) in 2015, the joint master’s degree in telecommunication engineering from UPC in collaboration with the Technische Universität München (TUM) in 2017, and the Ph.D. degree (cum laude) in signal theory and communications from UPC in 2022. From 2015 to 2018, he was a Research Assistant in the Signal Theory and Communications Department at UPC. From March 2022 to June 2022, he was a Visiting Researcher with the Università degli Studi di Cassino e del Lazio Meridionale (UNICAS). From September 2022 to May 2023, he was a Research Associate with UPC. From June 2023 to July 2025, he was a Post-Doctoral Fellow with the Consorzio Nazionale Interuniversitario per le Telecomunicazioni (CNIT). Since February 2024, he has been the recipient of a Marie Sk?odowska-Curie Actions (MSCA) Individual Grant with UNICAS and is currently on secondment with Nokia Bell Labs Paris-Saclay. His areas of interest include signal processing and wireless communication theory, with special emphasis on beyond-5G and 6G systems.