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In this paper, we extend the Decode-and-Forward cooperative diversity scheme to the context of impulse radio ultrawideband (IR-UWB). We develop coherent and non-coherent schemes that exploit the spatial diversity in a distributed manner among the different terminals of a wireless network. These schemes are specific to IR-UWB and they take advantage of the pulse repetitions used to convey each information symbol. If Nf is the number of pulses per symbol, the coherent scheme is based on joint symbol and pulse coding and it achieves full diversity with any number of relays for Nf > 1. The non-coherent scheme is based on pulse coding and it achieves full diversity with a maximum number of Nf -1 relays.

This paper investigates a hybrid radio frequency (RF)/visible light communication (VLC) ultra-small cell network consisting of multiple optical angle-diversity transmitters, one multi-antenna RF access point (AP), and multiple terminal devices. In the network, the optical transmitters play the primary role and are responsible for delivering information and power over the visible light, while the RF AP acts as a complementary power transfer system. Thus, we propose a novel collaborative RF and lightwave resource allocation scheme for hybrid RF/VLC ultra-small cell networks. The proposed scheme aims to maximize the communication quality-of-service provided by the VLC under a constraint of total RF and light energy harvesting performance, while keeping illumination constant and ensuring health safety. This scheme leads to the formulation of two optimization problems that correspond to the resource allocation at the optical transmitters and the RF AP. Both problems are optimally solved by appropriate algorithms. Moreover, we propose a closed-form suboptimal solution with high accuracy to tackle the optical transmitters' resource allocation problem, as well as an efficient semi-decentralized method. Finally, simulation results illustrate the achievable performance of the investigated system and the effectiveness of the proposed solutions.

Abstract-In this paper, we investigate the cooperative diversity technique as a candidate solution for combating turbulence-induced fading over free-space optical (FSO) links. In particular, we propose a novel cooperation strategy that is suitable for quantum-limited FSO systems with any number of relays and we derive closed-form expressions for the error performance of this strategy. In scenarios where the channel-state-information (CSI) is available at the different nodes, we propose an optimal power allocation strategy that satisfies the Karush-Kuhn-Tucker (KKT) conditions and that further boosts the performance of FSO networks. It turned out that this closed-form optimal solution corresponds to transmitting the entire optical power along the "strongest link" between the source and the destination nodes. A simple procedure is proposed for selecting this link and for distributing the power among its different hops.