Coexistence of eMBB+ and mMTC+ in Uplink Cell-Free Massive MIMO Networks

2024-04-29

IEEE Wireless Communications and Networking Conference

AI Summary

This paper addresses the coexistence of eMBB+ users and mMTC+ devices in uplink cell-free massive MIMO systems for 6G terminal-centric networks, where tight time-frequency resource coupling poses severe multiple-access challenges under non-ideal channel conditions. Method: We propose a time-frequency spread-spectrum random access mechanism specifically designed for mMTC+, jointly model eMBB+ and mMTC+ traffic, and derive closed-form ergodic rate bounds. The approach integrates a terminal-centric architecture, statistical CSI-based distributed power control, and time-frequency spread-spectrum multiplexing. Contribution/Results: Our framework enables simultaneous QoS guarantees for both service types within shared resource grids; mMTC+ performance suffers only marginal interference from eMBB+. Crucially, we reveal a fundamental trade-off between spreading gain and the number of serving access points—a key insight guiding system design. The work provides theoretical foundations and a practical design paradigm for heterogeneous massive access in 6G.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Multiagent Systems: Mechanism Design
• Machine Learning: Mixture of Experts (MoE)

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• User Modeling, Personalization and Recommendation: Federated recommendation systems and personalization
• Security and Privacy: Large-scale security measurements

Abstract

This paper tackles the problem of designing proper uplink multiple access schemes for coexistence between enhanced mobile broadband+ (eMBB+) users and massive machine-type communications+ (mMTC+) devices in a terminal-centric cell-free massive MIMO system. Specifically, the use of a time-frequency spreading technique for the mMTC+ devices has been proposed. Coupled with the assumption of imperfect channel knowledge, closed-form bounds of the achievable (ergodic) rate for the two data services are derived. Using suitable power control mechanisms, we show it is possible to efficiently multiplex eMBB+ and mMTC+ traffic in the same time-frequency resource grid. Numerical experiments reveal interesting trade-offs in the selection of the spreading gain and the number of serving access points within the system. Results also demonstrate that the performance of the mMTC+ devices is slightly affected by the presence of the eMBB+ users. Overall, our approach can endow good quality of service to both 6G cornerstones at once.

Problem

• Designing uplink multiple access for eMBB+ and mMTC+ coexistence
• Analyzing achievable rate bounds with imperfect channel knowledge
• Multiplexing both services efficiently using power control mechanisms

Innovation

• Time-frequency spreading for mMTC+ devices
• Power control for eMBB+ and mMTC+ multiplexing
• Cell-free massive MIMO with imperfect channel knowledge