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Performance Analysis for Hybrid Sub-6GHz-mmWave-THz Networks with Downlink and Uplink Decoupled Cell Association

Yunbai Wang, Chen Chen, Xiaoli Chu

TL;DR

The paper addresses SINR and rate coverage in a general multi-tier hybrid network spanning sub-6 GHz, mmWave, and THz bands, with DL and UL decoupled cell association. It develops a tractable stochastic-geometry framework that models band-specific propagation, LOS/blockage, beamforming gains, and THz molecular absorption, and derives per-tier DL/UL association probabilities as well as SINR and rate coverage expressions, validated by Monte Carlo simulations. Key findings show that DL/UL decoupling offers flexible bias design and improves performance, that increasing THz BS density elevates association to THz but molecular absorption can suppress SINR, and that large antenna arrays at high bands significantly enhance coverage, especially in UL. The results provide practical guidance for bias design, tier densification, and bandwidth allocation in future hybrid sub-6GHz/mmWave-THz networks.

Abstract

It is expected that 5G/6G networks will exploit sub-6 GHz, millimetre wave (mmWave) and terahertz (THz) frequency bands simultaneously and will increase flexibility in user equipment (UE)-cell association. In this paper, we introduce a novel stochastic geometry-based framework for the analysis of the signal-to-interference-plus-noise-ratio (SINR) and rate coverage in a multi-tier hybrid sub-6GHz-mmWave-THz network, where each tier has a particular base station (BS) density, transmit power, bandwidth, number of BS antennas, and cell-association bias factor. The proposed framework incorporates the effects of sub-6 GHz, mmWave and THz channel characteristics, BS beamforming gain, and blockages. We investigate the downlink (DL) and uplink (UL) decoupled cell-association strategy and characterise the per-tier cell-association probability. Based on that, we analytically derive the SINR and rate coverage probabilities for both DL and UL transmissions. The analytical results are validated via extensive Monte Carlo simulations. Numerical results demonstrate the superiority of the DL and UL decoupled cell-association strategy in terms of SINR and rate coverage over its coupled counterpart.

Performance Analysis for Hybrid Sub-6GHz-mmWave-THz Networks with Downlink and Uplink Decoupled Cell Association

TL;DR

The paper addresses SINR and rate coverage in a general multi-tier hybrid network spanning sub-6 GHz, mmWave, and THz bands, with DL and UL decoupled cell association. It develops a tractable stochastic-geometry framework that models band-specific propagation, LOS/blockage, beamforming gains, and THz molecular absorption, and derives per-tier DL/UL association probabilities as well as SINR and rate coverage expressions, validated by Monte Carlo simulations. Key findings show that DL/UL decoupling offers flexible bias design and improves performance, that increasing THz BS density elevates association to THz but molecular absorption can suppress SINR, and that large antenna arrays at high bands significantly enhance coverage, especially in UL. The results provide practical guidance for bias design, tier densification, and bandwidth allocation in future hybrid sub-6GHz/mmWave-THz networks.

Abstract

It is expected that 5G/6G networks will exploit sub-6 GHz, millimetre wave (mmWave) and terahertz (THz) frequency bands simultaneously and will increase flexibility in user equipment (UE)-cell association. In this paper, we introduce a novel stochastic geometry-based framework for the analysis of the signal-to-interference-plus-noise-ratio (SINR) and rate coverage in a multi-tier hybrid sub-6GHz-mmWave-THz network, where each tier has a particular base station (BS) density, transmit power, bandwidth, number of BS antennas, and cell-association bias factor. The proposed framework incorporates the effects of sub-6 GHz, mmWave and THz channel characteristics, BS beamforming gain, and blockages. We investigate the downlink (DL) and uplink (UL) decoupled cell-association strategy and characterise the per-tier cell-association probability. Based on that, we analytically derive the SINR and rate coverage probabilities for both DL and UL transmissions. The analytical results are validated via extensive Monte Carlo simulations. Numerical results demonstrate the superiority of the DL and UL decoupled cell-association strategy in terms of SINR and rate coverage over its coupled counterpart.
Paper Structure (33 sections, 10 theorems, 51 equations, 11 figures, 2 tables)

This paper contains 33 sections, 10 theorems, 51 equations, 11 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Related Works
  3. Contributions
  4. Paper Organisation
  5. System Model
  6. Network Model
  7. Hybrid sub-6GHz-mmWave-THz networks
  8. Blockage
  9. Beamforming Model
  10. Channel Model
  11. Sub-6 GHz
  12. mmWave
  13. THz
  14. Downlink and Uplink Decoupled Cell Association
  15. Sub-6 GHz Cell Association
  16. ...and 18 more sections

Key Result

Lemma 1

Denoting by $D_{k}$ the distance from the typical UE to its nearest LOS BS in the $k^{\mathrm{th}}$ tier, the PDF of $D_{k}$ is given by $f_{D_{k}}(x) = 2\pi\lambda_{k}x \, \mathrm{exp}\!\!\left(\frac{2\pi\lambda_{k}e^{ -(\zeta x + p)}\left(1-e^{\zeta x}+\zeta x\right)}{\zeta^2} -\zeta x -p \right)$

Figures (11)

  • Figure 1: Illustration of DL and UL decoupled cell association in a 3-tier hybrid sub-6GHz-mmWave-THz network. (a) DL. (b) UL.
  • Figure 2: The analytical and simulation results of the association probability versus the ratio of THz to mmWave BS density.
  • Figure 3: The analytical results of the association probability versus the bias factor of the THz tier.
  • Figure 4: The analytical and simulation results of the SINR coverage probability versus the SINR threshold. We present results of a 3-tier hybrid network (s1m1t1) consisting of 1 tier of sub-6 GHz network, 1 tier of mmWave network and 1 tier of THz network, and a 4-tier hybrid network (s1m2t1) consisting of 1 tier of sub-6 GHz network, 2 tiers of mmWave networks and 1 tier of THz network.
  • Figure 5: The analytical and simulation results of the impact of NLOS transmission links on the SINR coverage probability.
  • ...and 6 more figures

Theorems & Definitions (10)

  • Lemma 1
  • Lemma 2
  • Lemma 3
  • Lemma 4
  • Lemma 5
  • Lemma 6
  • Lemma 7
  • Theorem 1
  • Theorem 2
  • Theorem 3