A new approach to exploit channel power imbalance in distributed antenna systems with fiber fronthaul

Cloud Modulation (CM) is a novel transmission method that mitigates the non-linear impairments introduced by the Radio-over-Fiber (RoF) links of a distributed antenna system. In CM, constant-envelope phase-modulated radio symbols are transmitted over the fiber fronthaul to mitigate the non-linear distortion originated by the opto-electrical interfaces, optical fibers, and RF power amplifiers. In contrast to contemporary distributed antenna systems, where the amplitude modulation of the radio signal is already present at the input of the RoF link, the amplitude modulation of received CM symbols is achieved over-the-air by selecting the remote antenna unit that should be active at each time symbol. The propagation characteristics of the wireless channel, whose diffuse nature is typically represented with the CLOUD metaphor, creates the desired amplitude modulation and motivates the name of the proposed transmission method. The guidelines to design CM alphabets for different hybrid fiber-wireless scenarios are presented. Notable performance gains are observed when CM is compared to a joint transmission coordinated multi-point scheme in presence of similar levels of non-linear distortion in the RoF fronthaul.