The application of wireless backhaul communication and power transfer to outdoor small cells (SCs) could significantly decrease their installation cost. In this paper, the concept of indoor optical wireless power transfer (OWPT) to SCs is investigated in the absence of ambient light, i.e. during darkness hours. An experimental study is conducted by the use of up to 4 red laser diodes (LDs), a crystalline silicon (c-Si) solar panel and cell placed at 5.2 m. A value of 69% is measured for the fill factor (FF) of the solar panel. Also, a total power efficiency of 3.2% is measured for an optical wireless (OW) link with an average efficiency of 2 LDs of 26.8%, a solar cell efficiency of 13.3% and only 10.6% of geometrical losses. A comparison of this link with a state-of-the-art inductive power transfer system (IPTS) shows an improvement of the total link efficiency by 2.7 times. Another OW link is implemented with a divergence of full width at 36.8% of the peak intensity of 3 mrad and 5.75 mrad along the small and large axes of the beam, respectively. The experimental levels of harvested power are in the order of mW, whereas approximately 1 W is required for the operation of a SC. Therefore, a 42 laserbased transmitter is designed both analytically and by the use of the simulation tool Zemax. The respective results show the feasibility of delivering 7.2 W of optical power to a solar cell of up to 30 m distance with geometrical losses of only 2%, but a beam enclosure is also required due to eye safety restrictions.Index Terms-Small cells (SCs), optical wireless power transfer (OWPT), energy harvesting (EH), radio frequency (RF), rectennas, diode lasers, quantum well lasers, laser beams, solar energy, energy efficiency.

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Over the past years, TCP has gone through numerous updates to provide performance enhancement under diverse network conditions. However, with respect to losses, little can be achieved with legacy TCP detection and recovery mechanisms. Both fast retransmission and retransmission timeout take at least one extra round trip time to perform, and this might significantly impact performance of latency-sensitive applications, especially in lossy or high delay networks. While forward error correction (FEC) is not a new initiative in this direction, the majority of the approaches consider FEC inside the application. In this paper, we design and implement a framework, where FEC is integrated within TCP. Our main goal with this design choice is to enable latency sensitive applications over TCP in high delay and lossy networks, but remaining application agnostic. We further incorporate this design into multipath TCP (MPTCP), where we focus particularly on heterogeneous settings, considering the fact that TCP recovery mechanisms further escalate head-ofline blocking in multipath. We evaluate the performance of the proposed framework and show that such a framework can bring significant benefits compared to legacy TCP and MPTCP for latency-sensitive real application traffic, such as video streaming and web services.Index Terms-TCP, MPTCP, forward error correction, XOR, multipath, congestion control, wireless networks suboptimal [3], [4], with one of the main limiting factors being TCP's loss recovery time. In such scenarios, it is often an option to replace TCP by UDP, at the expense of compromising benefits such as flow and congestion controls. When MPTCP [5] emerged, enabling simultaneous use of multiple network paths by a single data-stream, it had to take operability and deployment in the Internet into account, hence, making MPTCP look like regular TCP from the network's perspective. Although this integration brings many benefits, it also comes with challenges that hinder MPTCP. Particularly, when the underlying network paths are heterogeneous, MPTCP often underperforms TCP especially for certain latency-sensitive applications [6], [7].Next, we will first put MPTCP in perspective with TCP, also mentioning its performance challenges under certain network environments. We will then discuss our motivation for designing a dynamic XOR-based Forward Error Correction (dFEC) inside TCP, and how this can aid multipath transport for heterogeneous paths. Finally, we will summarise the applications chosen for the evaluations and their requirements.

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