# Ultra-Wideband Analog Radio-over-Fiber Communication System Employing Pulse-Position Modulation
## 1 Introduction  
With the advent of current 5G Advanced and future 6G networks [1], fronthaul solutions, such as radio-over-fiber (RoF), have gained prominence as a means of enhancing communication systems [2]. RoF employs optical fibers to create the fronthaul links for radio frequency (RF) signal transmission, offering a sizable usable bandwidth and low attenuation. Employment of RoF alleviates bandwidth constraints while enabling the distribution of antenna units (AUs) over longer distances without frequent amplification [3]. Additionally, RoF technology can support centralized processing and signal generation [4], reducing the complexity and power consumption of the entire network. A promising RoF technology for 5G Advanced and 6G networks is ARoF [4]. In ARoF, an analog waveform modulates the optical transmitter, generating an analog optical signal transmitted through the fronthaul link. This approach minimizes the need for power-hungry, high-speed analog-to-digital converters (ADCs) and digital-to-analog converters(DACs) compared to traditional digital interfaces [4], enabling the use of low-complexity and energy-efficient AUs. For these reasons, ARoF technology offers a spectrally efficient, power-efficient, and low-complexity solution. As next-generation networks plan to utilize even higher frequency bands, this becomes particularly important [2]. Consequently, ARoF technology has been explored in recent research for millimeter-wave [5; 6] and terahertz links [7; 8]. Additionally, ARoF is being considered for future distributed multiple-input multiple-output (D-MIMO) systems in 6G networks [4; 9], which rely heavily on a distributed AU architecture to enhance wireless coverage. Applications of ARoF technology include wireless communications, distributed sensor networks, radars, space communication systems, and many other applications [10]. In Figure 1, a visualization of the physical and wireless RF connections between the central office, base station, and user equipment is provided, depicting a communication system for remote sensing and space applications involving low Earth orbit, geostationary Earth orbit, and deep space satellites. ARoF is an increasingly popular solution for 5G Advanced and upcoming 6G telecommunication standards, leveraging millimeter-wave signals to support high-capacity broadband applications [11; 12; 13]. In [14], a hybrid architecture for 5G mobile networks based on the ARoF technological concept is described. The authors propose a long-range wireless communication solution with 1 km optical fiber and 20 m free-space optical communication (FSO) fronthaul, using quadrature amplitude modulation (QAM) signal with 700 MHz carrier, achieving 60 Mb/s data transmission rate. The paper [15] demonstrates the seamless integration of ARoF with FSO and mm-wave wireless communication systems and shows satisfactory performance with QAM signals at simulated data transmission speeds exceeding 10 Gb/s. ARoF technology can increase the performance of phased antenna arrays by using the modulation instability phenomenon [16]. The authors have demonstrated modulation instability gain of 38.1 dB by using 45 km long optical fiber. Another possibility is to use a single light source at the central office to achieve full duplex communication [17]. The presented system has achieved 2.5 Gb/s data transmission over 40 km long SMF. Ultra-wideband (UWB) technology has emerged as a promising innovation for RF that allows for the use of ultra-short pulses for transmitting information, as well as applications in integrated sensing and communications (ISAC), radar technology, and distributed sensor networks [18]. Research on UWB modulation schemes [19; 20] for use in ARoF communication systems has been conducted in the past. For example, paper [21] presents an UWB over fiber  
Figure 1: Usage scenarios for the proposed UWB ARoF technology. communications system based on asymmetric Mach-Zehnder interferometer for optical modulation.