Ad hoc networks capacity scaling problem

A large number of researchers found their interest in addressing the issue of capacity scaling for wireless ad hoc networks. This paper aims to provide a comprehensive overview of the development of capacity scaling laws in wireless networks, highlighting the problem of scaling as one of the basic challenges in their research. The review began with the definition of the notion of bandwidth of random networks, which were taken as a reference model of consideration when determining more advanced strategies for improving throughput capacity. Based on these strategies, other factors that have an impact on capacity scaling laws have been identified and elaborated. Finally, the capacity of hybrid wireless networks, ie networks in which at least two types of nodes functionally exist (ad hoc nodes/infrastructure nodes / auxiliary nodes), was partially investigated.

Fast Auto-Align ment Underwater Wireless Optical Communications Employing Orbital Angular Momentum Modes

Underwater wireless communication plays an increasingly important role in more and more emerging ocean and sea activities. Traditional underwater acoustic communication is limited by low transmission capacity (tens of Kbit/s). Underwater wireless optical communication (UWOC) provides high bandwidth (GHz). Yet the challenge is not only its continuous capacity scaling, but its resistance to environment disturbance, which is an intrinsic weakness of wireless optical communications with high directivity. Here, we propose and demonstrate fast auto-alignment underwater wireless optical communications employing orbital angular momentum (OAM) modes. The OAM multiplexing, an alternative approach of space-division multiplexing, enables capacity scaling. The fast auto-alignment system, having two stages for thorough alignment, facilitates stable and reliable communication link against vibration. Two OAM modes multiplexing transmission link with 4-Gbit/s aggregate capacity is demonstrated in the experiment under four different vibration conditions assisted by the fast auto-alignment system with a response time of 244 Hz. The demonstrations may open up new perspective to robust stable underwater wireless optical communications exploiting spatial modes in practical environment.