Encryption in fiber-optic transmission is one of remaining issues in modern communication systems. One of the solutions is to use Y-00 quantum-noise randomized stream cipher. In this paper, we propose feedforward carrier phase estimation (CPE) with Y-00 decryption process for digital-coherent detection of phase-shift keying (PSK) Y-00 signal. After decryption of Y-00 signal in a digital domain, carrier phase is estimated by calculating Mth power of signal complex amplitude. Numerical simulations for 10-Gbaud PSK Y-00 signal show that the feedforward CPE with decryption process, which is used by a legitimate receiver who shares keys, successfully tracks phase noise. Consequently, penalty-less demodulation of Y-00 signal is achieved.

This letter proposes an efficient method for combining MU-MIMO Tomlinson Harashima precoding (THP) with user scheduling techniques to realize fairness among users as well as high system capacity. The concept of the proposed approach is to first adopt semiorthogonal user selection (SUS) for throughput maximization and then apply proportional fairness (PF) to the remaining users, which regains fairness lowered by using SUS for throughput maximization. Moreover, considering that THP adopted as a precoder for PF requires the calculation of ordering and precoding for each user combination, the proposed method adopts linear precoding (LP) instead of THP to relax the computational effort during operation of PF. This approach is inspired by the fact that LP achieves almost the same system capacity as THP with ordering when conducting PF. The effectiveness of the proposed method is demonstrated by comparing it to MU-MIMO THP with SUS or PF in terms of system capacity and fairness among users, by means of computer simulations.

We experimentally demonstrated a novel nonlinearity mitigation scheme based on digital signal processing using a three-layer neural network (NN). 40-Gbit/s optical 16QAM signal distorted by SPM was compensated, improving EVM values by about 15%. We also performed numerical simulation of the proposed scheme, and confirmed that the experiment agrees with the results of the simulation. We performed 100 times of learning processes to find weight and bias of each neuron. However, we did not observe any serious local minimum. We also investigated the effect of the number of neurons of the NN on the compensation performance.

In Visible Light Communication (VLC) systems, Run-length limited (RLL) codes are widely used to avoid the long runs of 1’s and 0’s. However, there are a small number of Forward Error Correction (FEC) codes can well incorporate with the traditional RRL codes. In this paper, a serial joint of Polar code and Soft-Input Soft-Output (SISO) RLL decoding scheme is proposed to enhance the transmission efficiency while guaranteeing an equal number of 1’s and 0’s. The simulation results confirm that our proposed algorithm has consistently outperform the existing schemes.

This paper presents a novel dual-channel HF radar system for ionospheric sounding, which is called Wuhan Multifunctional Ionosonde with dual channels (WMI-DC). Based on the Universal Serial Bus (USB), and a high performance FPGA, this newly designed WMI-DC has a complete digital structure, which makes it portable and flexible. And due to the application of m sequence waveform, the WMI-DC can achieve good results with low power. The primary modules and the data processing are illustrated in detail in this paper. The experimental results indicate that the dual-channel system can separate ordinary wave (O-wave) and extraordinary wave (X-wave) from the signals.

We propose a novel XPM compensation scheme using neural-network-based digital signal processing. A 16QAM signal distorted by XPM in optical fiber transmission system was successfully compensated for with the scheme simpler than digital back propagation (DBP). BER and EVM performance was investigated by numerical simulations, and the EVM was improved by more than 40% by the compensation.