In this work, we investigate the performance of a millimeter waves (mmWaves) cellular system with free space optical (FSO) backhauling. MmWave channels are subject to Nakagami-m fading while the optical links experience the Double Generalized Gamma including atmospheric turbulence, path loss and the misalignment between the transmitter and the receiver aperture (also known as the pointing errors). The FSO model also takes into account the receiver detection technique which could be either heterodyne or intensity modulation and direct detection (IM/DD). Each user equipment (UE) has to be associated to one serving base station (BS) based on the received signal strength (RSS) or Channel State Information (CSI). We assume partial relay selection (PRS) with CSI based on mmWaves channels to select the BS associated with the highest received CSI. Each serving BS decodes the received signal for denoising, converts it into modulated FSO signal, and then forwards it to the data center. Thereby, each BS can be viewed as a decode-and-forward (DF) relay. In practice, the relay hardware suffers from nonlinear high power amplification (HPA) impairments which, substantially degrade the system performance. In this work, we will discuss the impacts of three common HPA impairments named respectively, soft envelope limiter (SEL), traveling wave tube amplifier (TWTA), and solid state power amplifier (SSPA). Novel closed-forms and tight upper bounds of the outage probability, the probability of error, and the achievable rate are derived. Capitalizing on these performance, we derive the high SNR asymptotes to get engineering insights into the system gain such as the diversity order.

中文翻译：

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在反馈延迟和硬件限制下使用 FSO 回程进行毫米波蜂窝分析的可行方法

在这项工作中，我们研究了具有自由空间光学 (FSO) 回程的毫米波 (mmWaves) 蜂窝系统的性能。毫米波信道会受到 Nakagami-m 衰落的影响，而光链路会经历双重广义 Gamma，包括大气湍流、路径损耗以及发射器和接收器孔径之间的未对准（也称为指向误差）。FSO 模型还考虑了接收器检测技术，该技术可以是外差或强度调制和直接检测 (IM/DD)。每个用户设备 (UE) 必须基于接收信号强度 (RSS) 或信道状态信息 (CSI) 与一个服务基站 (BS) 相关联。我们假设部分中继选择 (PRS) 与基于毫米波信道的 CSI 来选择与最高接收 CSI 相关联的 BS。每个服务 BS 对接收到的信号进行解码以进行去噪，将其转换为调制的 FSO 信号，然后将其转发到数据中心。因此，每个 BS 可以被视为一个解码转发 (DF) 中继。在实践中，继电器硬件会遭受非线性高功率放大 (HPA) 损伤，这会大大降低系统性能。在这项工作中，我们将讨论分别命名为软包络限幅器 (SEL)、行波管放大器 (TWTA) 和固态功率放大器 (SSPA) 的三种常见 HPA 损伤的影响。推导出新的封闭形式和中断概率、错误概率和可实现率的紧上界。利用这些性能，我们推导出高 SNR 渐近线，以深入了解系统增益，例如分集阶数。