Service restoration in multi-modal optical transport networks with reinforcement learning.

Optical transport networks (OTNs), while increasingly popular, can be affected in ways that are challenging to restore efficiently. This study investigates the problem of service restoration under OTNs with an optical channel data unit (ODU)-k switching capability (OTN-OSC) environment. An advantage actor-critic-based service restoration (A2CSR) algorithm is presented with the objective of increasing the service restoration rate. In our experimental setup, A2CSR uses the advanced image recognition model MobileNetV2 and an advantage actor-critic reinforcement learning algorithm. Simulation results show that the proposed A2CSR algorithm can achieve better blocking probability and resource utilisation than the benchmark algorithm (first fit (FF)), and the restoration time is within the acceptable range.

Simultaneous channel estimation and signal detection in wireless ultraviolet communications combating inter-symbol-interference.

One primary challenge in wireless ultraviolet communications (UVCs) is the inter-symbol-interference (ISI), which may block the detection of current informative signal, especially when channel-related characteristics are unknown. In this paper, we propose a UV channel-related Bayesian scheme that can simultaneously estimate the channel characteristics and detect informative signals, which therefore can address the ISI disturbance. By investigating the UV single-scattering photon model, the dynamic behaviors of the channel state information (CSI), which involve the uncertain signal and the unknown channel parameters are formulated. Hence, a sequential Bayesian process is suggested to estimate the UV CSI. Numerical analysis shows that the proposed scheme can obtain a promising estimation performance (i.e., the relative errors are less than 4%), and gain an extra 4dB detection performance compared with imperfect maximum-likelihood sequence detection (MLSD) scheme.

Experimental study of an optimized PSP-OSTBC scheme with m-PPM in ultraviolet scattering channel for optical MIMO system.

An optimized scheme of pulse symmetrical position-orthogonal space-time block codes (PSP-OSTBC) is proposed and applied with m-pulse positions modulation (m-PPM) without the use of a complex decoding algorithm in an optical multi-input multi-output (MIMO) ultraviolet (UV) communication system. The proposed scheme breaks through the limitation of the traditional Alamouti code and is suitable for high-order m-PPM in a UV scattering channel, verified by both simulation experiments and field tests with specific parameters. The performances of 1×1, 2×1, and 2×2 PSP-OSTBC systems with 4-PPM are compared experimentally as the optimal tradeoff between modification and coding in practical application. Meanwhile, the feasibility of the proposed scheme for 8-PPM is examined by a simulation experiment as well. The results suggest that the proposed scheme makes the system insensitive to the influence of path loss with a larger channel capacity, and a higher diversity gain and coding gain with a simple decoding algorithm will be achieved by employing the orthogonality of m-PPM in an optical-MIMO-based ultraviolet scattering channel.

Experimental research on the MRC diversity reception algorithm for UV communication.

Ultraviolet (UV) communication is an emerging communication method with non-line-of-sight, anti-interference, and anti-interception capabilities, along with high flexibility and reliability. Herein, the maximum ratio combining (MRC) diversity reception algorithm for a UV communication system is studied. Simulation and experimental results indicate that single and multiple outputs are useful and achievable, with an obvious diversity gain, and the MRC diversity reception algorithm can reduce the system bit error rate more effectively than the equal-gain combining method. The simulation and experimental results are analyzed, and the differences between them are discussed. These results provide guidelines for UV communication system design and implementation.

Experimental research and comparison of LDPC and RS channel coding in ultraviolet communication systems.

We have implemented a modified Low-Density Parity-Check (LDPC) codec algorithm in ultraviolet (UV) communication system. Simulations are conducted with measured parameters to evaluate the LDPC-based UV system performance. Moreover, LDPC (960, 480) and RS (18, 10) are implemented and experimented via a non-line-of-sight (NLOS) UV test bed. The experimental results are in agreement with the simulation and suggest that based on the given power and 10(-3)bit error rate (BER), in comparison with an uncoded system, average communication distance increases 32% with RS code, while 78% with LDPC code.

Research on multiple-scattering channel with Monte Carlo model in UV atmosphere communication.

A non-line-of-sight (NLOS) ultraviolet (UV) communication channel model is established by using a Monte Carlo simulation method based on photon tracing. This method considers the multiple-scattering effects of UV signal propagation in the atmosphere, and simulates the condition of dual receivers for diversity reception. The channel characteristics of the UV communication are obtained by simulating the photon arrival probabilities. The model is employed to study the characteristics of NLOS UV scattering channels for a variety of scattering conditions, including the separation distance between transmitter and receiver, transmit/receive elevation angle, beam divergence, and field of view. The model has advantages in reliable prediction of UV communication for the dual-receiver condition, as validated by outdoor experiments at fixed elevation angles.

Performance analysis of short-range NLOS UV communication system using Monte Carlo simulation based on measured channel parameters.

The research presented in this paper is a performance study of short-range NLOS ultraviolet (UV) communication system, using a Monte-Carlo-based system-level model, in which the channel parameters, such as the path loss and the background noise are experimentally measured using an outdoor UV communication test-bed. Various transceiver geometry and background noise condition are considered. Furthermore, 4 modulation schemes are compared, which provides an insight into the performance prediction and the system trade-offs among the path loss, the optical power, the distance, the link geometry, the bit rate and the bit error rate. Finally, advices are given on UV system design and performance improvement.

Theoretical and experimental research on diversity reception technology in NLOS UV communication system.

Diversity reception technology is introduced into ultraviolet communication area in this article with theory analysis and practical experiment. The idea of diversity reception was known as a critical effective method in wireless communication area that improves the Gain significantly especially for the multi-scattering channel. A theoretical modeling and simulation method are proposed to depict the principle and feasibility of diversity reception adopted in UV communication. Besides, an experimental test-bed using ultraviolet LED and dual receiver of photomultiplier tube is setup to characterize the effects of diversity receiving in non-line-of-sight (NLOS) ultraviolet communication system. The experiment results are compared with the theoretical ones to verify the accuracy of theoretical modeling and the effect of diversity reception. Equal gain combining (EGC) method was adopted as the diversity mechanism in this paper. The research results of theory and experiment provide insight into the channel characteristics and achievable capabilities of ultraviolet communication system with diversity receiving method.