We introduce a new class of fading channels, built as the superposition of two fluctuating specular components with random phases, plus a clustering of scattered waves: the Multi-cluster Fluctuating Two-Ray (MFTR) fading channel. The MFTR model emerges as a natural generalization of both the fluctuating two-ray (FTR) and the $\kappa$-$\mu$ shadowed fading models through a more general yet equally mathematically tractable model. This generalization enables the presence of additional multipath clusters in the purely ray-based FTR model, and the convenience of the new underlying fading channel model is discussed in depth. Then, we derive all the chief probability functions of the MFTR model (e.g., probability density function (PDF), cumulative density function (CDF), and moment generation function) in closed-form, having {a mathematical complexity similar to} other fading models in the state-of-the-art. We also provide two additional analytical formulations for the PDF and the CDF: (i) in terms of a continuous mixture of $\kappa$-$\mu$ shadowed distributions, and (ii) as an infinite discrete mixture of Gamma distributions. Such expressions enable to conduct performance analysis under MFTR fading by directly leveraging readily available results for the $\kappa$-$\mu$ shadowed or Nakagami-$m$ cases, respectively. The performance of wireless communications systems undergoing MFTR fading is exemplified in terms of a classical benchmarking metric like the outage probability, both in exact and asymptotic forms, and the amount of fading.

翻译：我们提出了一类新的衰落信道，该信道由两个具有随机相位的波动镜面分量叠加多个散射波簇构成：多簇波动双射线（MFTR）衰落信道。MFTR模型作为波动双射线（FTR）模型和$\kappa$-$\mu$阴影衰落模型的自然推广，通过一个更为通用且同样数学上易处理的形式实现。这一推广允许在纯射线型FTR模型中引入额外的多径簇，并深入讨论了新底层衰落信道模型的优势。随后，我们以闭式形式推导了MFTR模型的所有主要概率函数（例如概率密度函数、累积分布函数和矩生成函数），其数学复杂度与现有其他衰落模型相当。我们还提供了概率密度函数和累积分布函数的两种额外解析表达式：（i）基于$\kappa$-$\mu$阴影分布的连续混合形式，以及（ii）基于Gamma分布的无限离散混合形式。这些表达式使得可直接利用$\kappa$-$\mu$阴影或Nakagami-$m$情形下的现有结果进行MFTR衰落下的性能分析。通过经典基准指标如中断概率（包括精确和渐近形式）及衰落量，示例了无线通信系统在MFTR衰落下的性能表现。