It is expected that B5G/6G networks will exploit both terahertz (THz) and millimetre wave (mmWave) frequency bands 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 mmWave and 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 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 of a typical user 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. Moreover, we observe that the superiority of using the DL and UL decoupled cell-association strategy becomes more evident with the dense deployment of THz networks.

翻译：预计B5G/6G网络将同时利用太赫兹（THz）和毫米波（mmWave）频段，并增强用户设备（UE）与小区关联的灵活性。本文提出一种基于随机几何的新型框架，用于分析多层混合毫米波与太赫兹网络中的信干噪比（SINR）和速率覆盖，其中每一层具有特定的基站（BS）密度、发射功率、带宽、基站天线数量及小区关联偏置因子。该框架融合了毫米波与太赫兹信道特性、基站波束成形增益以及遮挡效应的影响。我们研究了下行（DL）与上行（UL）解耦的小区关联策略，并刻画了各层的小区关联概率。基于此，我们解析推导了典型用户在上下行传输中的SINR和速率覆盖概率。通过大量蒙特卡洛仿真验证了解析结果的准确性。数值结果表明，相较于耦合小区关联策略，上下行解耦策略在SINR和速率覆盖方面具有优越性。此外，我们观察到随着太赫兹网络密集部署，采用上下行解耦小区关联策略的优势更加显著。