We propose a radio-over-fiber (RoF) system with 1-bit outphasing modulation. The proposed RoF system does not require a power-hungry digital-to-analog converter in access points and relaxes the operation speed of optical transceivers to reduce device cost. We introduce two configurations to enable 1-bit outphasing modulation in our system; mixed-signal and all-digital configurations. In the mixed-signal configuration, the effects of harmonics and phase/amplitude mismatch on the adjacent channel leakage ratio (ACLR) were analyzed through simulation, and wideband transmission with a signal bandwidth of 400 MHz was experimentally verified, complying with the 3rd Generation Partnership Project (3GPP) standard for millimeter-wave band. Moreover, wide-band transmission with a signal bandwidth of 1 GHz was also experimentally verified for beyond-5G and 6G. The all-digital configuration can be implemented in a standard digital design flow. This configuration was also verified to comply with the 3GPP standard by properly selecting the intermediate and sampling frequencies to mitigate the effects of folded harmonics and quantization noise. Finally, the proposed RoF system with both configurations has been shown to have a higher bandwidth efficiency compared with other systems complying with the 3GPP standard for the ACLR. Therefore, the proposed RoF system provides a cost-effective in-building wireless solution for 5G and 6G mobile network systems.

Power amplifiers (PAs) are key components of mobile base stations. In the last decade, the power efficiency of PAs for 3G/4G mobile base stations has risen to over 50% as a result of employing efficiency enhancement techniques, such as Doherty, envelope tracking, and outphasing, in combination with GaN devices and digital predistortion. This trend has significantly contributed to reducing the power consumption of mobile base stations. Furthermore, digital transmitters using switch-mode PAs have the potential of breaking through the 70% efficiency level. Achieving this goal will require advances not only in circuitry but also in device technology. For active antenna systems of 5G mobile systems, ease of integration, as well as high efficiency, becomes important for PAs, and thus, Si-based devices will play a major role.