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

Sergi Liesegang, Stefano Buzzi

TL;DR

This work tackles uplink coexistence of eMBB+ and mMTC+ in a terminal-centric CF-mMIMO network by introducing time-frequency spreading of mMTC+ within the eMBB+ resource grid. It derives closed-form, lower-bound ergodic-rate expressions under imperfect CSI using the use-and-forget bound and develops a QoS-based power control that maximizes the minimum eMBB+ rate while guaranteeing mMTC+ QoS. Key contributions include explicit SINR and rate bounds for both services, a tractable epigraph-based optimization, and insights into the impact of spreading gain $N$, the number of serving APs, and cross-service interference. The results demonstrate that the proposed scheme achieves good QoS for both 6G cornerstones, with mMTC+ performance only slightly affected by eMBB+ traffic and an optimal spreading factor balancing performance and resource usage.

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.

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

TL;DR

This work tackles uplink coexistence of eMBB+ and mMTC+ in a terminal-centric CF-mMIMO network by introducing time-frequency spreading of mMTC+ within the eMBB+ resource grid. It derives closed-form, lower-bound ergodic-rate expressions under imperfect CSI using the use-and-forget bound and develops a QoS-based power control that maximizes the minimum eMBB+ rate while guaranteeing mMTC+ QoS. Key contributions include explicit SINR and rate bounds for both services, a tractable epigraph-based optimization, and insights into the impact of spreading gain , the number of serving APs, and cross-service interference. The results demonstrate that the proposed scheme achieves good QoS for both 6G cornerstones, with mMTC+ performance only slightly affected by eMBB+ traffic and an optimal spreading factor balancing performance and resource usage.

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.
Paper Structure (11 sections, 21 equations, 3 figures)

This paper contains 11 sections, 21 equations, 3 figures.

Table of Contents

  1. Introduction
  2. System Model
  3. Propagation Channel
  4. Uplink Channel Estimation
  5. Uplink Data Transmission
  6. Spatial Detection
  7. Time-Frequency Despreading
  8. Achievable Data Rate
  9. Power Control Design
  10. Numerical Simulations
  11. Conclusions

Figures (3)

  • Figure 1: Illustrative example of a terminal-centric CF-mMIMO deployment, where $M = 9$ APs with $L = 3$ antennas serve $K_u = 15$ eMBB+ users and $K_d = 10$ mMTC+ devices simultaneously.
  • Figure 2: Rate of eMBB+ users vs. number of mMTC+ devices $K_d$.
  • Figure 4: Rate of eMBB+ users vs. number of serving APs $M_s$.