We numerically evaluate Achievable Information Rate (AIR) and Bit Error Rate (BER) performances of Probabilistic Amplitude Shaping (PAS), eight-dimensional modulation with Bit-Interleaved Coded Modulation Iterative Detection (BICM-ID), and conventional two-dimensional 16QAM (Quadrature Amplitude Modulation) for future high-speed optical communication systems. We confirm that end-to-end BER performances of three modulation formats are almost identical at a same transmission rate when the error correction is used once, and the iterative detection makes the performance of eight-dimensional modulation format better. Further, we verify the BER error-free conditions can be estimated by Normalized General Mutual Information (NGMI) for each modulation format.
This letter presents an effective Q factor formula for self-resonant spherical surface antennas. The self-resonant lossless Q factor and radiation efficiency calculated using spherical wave expansion provide an approximated expression for the effective Q factor. The resultant effective Q factor is larger than that of the infinitesimal loop antenna and smaller than that of the infinitesimal dipole antenna. Comparison of the result with the Q factor of spherical helix antennas has shown good agreement. A simple estimation formula can help design a small spherical helix antenna.
This letter investigates the theoretical system capacity of multi-user multiple-input multiple-output (MU-MIMO) orthogonal frequency division multiplexing (OFDM) Tomlinson-Harashima precoding (THP) in the presence of terminal mobility. Considering that MU-MIMO THP has been adopted for OFDM-based mobile broadband systems, analyzing the effects of time-selective fading and the modulo loss peculiar to THP on system capacity is essential. In this study, we theoretically derive both the multi-user interference (MUI) and inter-carrier interference (ICI) resulting from terminal mobility and incorporate these into the modulo loss analysis based on the mod-Λ channel. The theoretical results obtained by the proposed analysis are compared with those of linear precoding, which demonstrates the applicability of THP to OFDM-based mobile broadband systems.