## Abstract

Statistical-delay quality of service (QoS) provides bounded link-layer delay over wireless fading channels with a certain delay-bound violation probability. We propose statistical-delay-QoS-aware adaptive modulation (AM) and power allocation for a dual-channel coherent optical wireless communication system over the atmospheric turbulence fading channels. For given statistical-delay constraints and target bit-error-rate requirements, our proposed AM and power allocation maximize the effective spectral efficiency subject to the transmit-power constraints. We develop delay-QoS-aware adaptive transmission schemes by employing independent and joint channel optimizations subject to average transmit-power constraints. We also consider independent, joint, and successive channel optimizations for developing delay-QoS-aware adaptive transmission schemes subject to peak transmit-power constraints. Numerical results demonstrate that our proposed AM and power allocation significantly outperform the conventional adaptive transmission schemes in the strict statistical-delay constraints. Numerical results also depict superiority of the joint channel optimization in the strong turbulence fading and strict statistical-delay constraints.

© 2018 Optical Society of America

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