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Cell-Free Terahertz Massive MIMO: A Novel Paradigm Beyond Ultra-Massive MIMO

Wei Jiang, Hans D. Schotten

TL;DR

The paper addresses the limited transmission range of THz communications and sensing due to high propagation and absorption losses. It proposes CFmMIMO-THz, distributing antennas across many APs and always selecting the closest AP to shorten the link, as an alternative to conventional UMMIMO beamforming. Using simulations at 300 GHz with 10 GHz bandwidth, 5 dBm transmit power, and 20 dBi antennas, CFmMIMO-THz achieves higher spectral and energy efficiency than UMMIMO, with data rates improving from around 163.3 Gbps to 234.6 Gbps at short range and from 42.1 Gbps to 114.8 Gbps at longer ranges. The results advocate CFmMIMO as a practical THz deployment paradigm for 6G ISAC and related THz applications.

Abstract

Terahertz (THz) frequencies have recently garnered considerable attention due to their potential to offer abundant spectral resources for communication, as well as distinct advantages in sensing, positioning, and imaging. Nevertheless, practical implementation encounters challenges stemming from the limited distances of signal transmission, primarily due to notable propagation, absorption, and blockage losses. To address this issue, the current strategy involves employing ultra-massive multi-input multi-output (UMMIMO) to generate high beamforming gains, thereby extending the transmission range. This paper introduces an alternative solution through the utilization of cell-free massive MIMO (CFmMIMO) architecture, wherein the closest access point is actively chosen to reduce the distance, rather than relying solely on a substantial number of antennas. We compare these two techniques through simulations and the numerical results justify that CFmMIMO is superior to UMMIMO in both spectral and energy efficiency at THz frequencies.

Cell-Free Terahertz Massive MIMO: A Novel Paradigm Beyond Ultra-Massive MIMO

TL;DR

The paper addresses the limited transmission range of THz communications and sensing due to high propagation and absorption losses. It proposes CFmMIMO-THz, distributing antennas across many APs and always selecting the closest AP to shorten the link, as an alternative to conventional UMMIMO beamforming. Using simulations at 300 GHz with 10 GHz bandwidth, 5 dBm transmit power, and 20 dBi antennas, CFmMIMO-THz achieves higher spectral and energy efficiency than UMMIMO, with data rates improving from around 163.3 Gbps to 234.6 Gbps at short range and from 42.1 Gbps to 114.8 Gbps at longer ranges. The results advocate CFmMIMO as a practical THz deployment paradigm for 6G ISAC and related THz applications.

Abstract

Terahertz (THz) frequencies have recently garnered considerable attention due to their potential to offer abundant spectral resources for communication, as well as distinct advantages in sensing, positioning, and imaging. Nevertheless, practical implementation encounters challenges stemming from the limited distances of signal transmission, primarily due to notable propagation, absorption, and blockage losses. To address this issue, the current strategy involves employing ultra-massive multi-input multi-output (UMMIMO) to generate high beamforming gains, thereby extending the transmission range. This paper introduces an alternative solution through the utilization of cell-free massive MIMO (CFmMIMO) architecture, wherein the closest access point is actively chosen to reduce the distance, rather than relying solely on a substantial number of antennas. We compare these two techniques through simulations and the numerical results justify that CFmMIMO is superior to UMMIMO in both spectral and energy efficiency at THz frequencies.
Paper Structure (10 sections, 5 figures, 2 tables)

This paper contains 10 sections, 5 figures, 2 tables.

Table of Contents

  1. Introduction
  2. The Major Challenges
  3. High Spreading Loss
  4. Atmospheric Absorption
  5. Weather Effects
  6. Line-of-Sight Blockage
  7. Ultra-Massive MIMO
  8. Cell-Free Terahertz Massive MIMO (CFmMIMO-THz)
  9. Simulations
  10. Conclusions

Figures (5)

  • Figure 1: Six usage scenarios for IMT-2030 and four overarching aspects.
  • Figure 2: Illustration of atmospheric absorption Ref_jiang2023terahertz.
  • Figure 3: Structure of array-of-subarrays-based UMMIMO for THz signals.
  • Figure 4: The comparison of ultra-massive MIMO, on the left side, and cell-free Terahertz massive MIMO on the right side. The base station is equipped with a UMMIMO antenna array, suffering from long transmission distance. In contrast, the proposed CFmMIMO-THz system can substantially reduce the communication distance by selecting the closest AP for the user.
  • Figure 5: Performance comparison between UMMIMO and CFmMIMO-THz in terms of data rates as a function of communication distances.