Optimizing the optical/wireless interface for short-haul access networks

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Fronthaul is the term given to communications between the 5G cellular base station and antenna site (backhaul takes 5G data from the base station to the internet backbone). The enormous client base and aggressive data rates for 5G brings unprecedented fronthaul requirements. Current research finds expedient solutions to burgeoning fronthaul optical transport, such as the spectrally inefficient common public radio interface (CPRI). We will address the lingering questions on how to achieve optimal power and spectral efficiency at the optical/wireless interface. These questions are crucial if we are to meet escalating demand while diminishing the environmental footprint. These networks will be the mainstays of the 70% of the world population using mobile services, and billions of devices that will comprise the internet of things. ******Long reach optical communications drive innovation in optical components and systems. Once technologies mature, dropping price points allow these innovations to be adopted in cost sensitive, short haul networks. Radio-over-fiber is, however, nonexistent in long haul. Taking the latest device breakthroughs and exploiting them for the optical/wireless interface is the objective of this research program. Projects will cover spatial multiplexing, coherent detection and silicon photonics – three of the hottest areas in optical communications – to enable analog (or digital) radio-over-fiber. ******The use of spatial multiplexing holds the promise of increasing fiber capacity by an order of magnitude. Multiple modes or multiple cores in the fiber can carry independent data, much like multiple antennas in wireless. Crosstalk among fiber cores, or modes within cores, limits the increase in fiber capacity. Multiple input, multiple output (MIMO) techniques can overcome crosstalk and are commonly employed in wireless. Current research tests MIMO on optical and MIMO on wireless, assuming that neither will see a performance degradation due to the other. We will examine the impact of optical and wireless channels vis-à-vis MIMO increases in end-to-end reliability and/or capacity.******Optical communications devices evolve at an incredible rate, with the current leap forward focusing on integrated silicon photonics for a panoply of components. The disruptive adoption of coherent optical detection, versus the omnipresent direct detection now in access networks, is one example of where silicon photonics can drive down costs. The sensitivity advantages of coherent detection must be harnessed for radio over fiber, while avoiding the power hungry use of analog to digital converters and extensive digital signal processing (de rigueur in long haul).