System BER Research Articles

Time-varying propagation model and dynamic-feedback-phase correction for multiplexed orbital angular momentum beams in atmospheric turbulence.

Freespace optical (FSO) communication in an outdoor setting is complicated by atmospheric turbulence (AT). A time-varying (TV) multiplexed orbital angular momentum (OAM) propagation model to consider AT under transverse-wind conditions is formulated for the first time, and optimized dynamic correction periods for various TV AT situations are found to improve the transmission efficiency. The TV nature of AT has until now been neglected from modeling of OAM propagation models, but it is shown to be important. First, according to the Taylor frozen-turbulence hypothesis, a series of AT phase screens influenced by transverse wind are introduced into the conventional angular-spectrum propagation analysis method to model both the temporal and spatial propagation characteristics of multiplexed OAM beams. Our model shows that while in weak TV AT, the power standard deviation of lower-order modes is usually smaller than that of higher-order modes, the phenomena in strong TV AT are qualitatively different. Moreover, after analyzing the effective time of each OAM phase correction, optimized dynamic correction periods for a dynamic feedback communication link are obtained. An optimized result shows that, under the moderate TV AT, both a system BER within the forward-error-correction limit and a low iterative computation volume with 6% of the real-time correction could be achieved with a correction period of 0.18 s. The research emphasizes the significance of establishing a TV propagation model for exploring the effect of TV AT on multiplexed OAM beams and proposing an optimized phase-correction mechanism to mitigate performance degradation caused by TV AT, ultimately enhancing overall transmission efficiency.

Enhancement of BER of LTE System by Using DCT-Neural Network in Different Channel Models

Enhancement of BER of LTE System by Using DCT-Neural Network in Different Channel Models

Performance analysis of 160 Gbps-60 GHz OFDM-MIMO RoFSO transmission with WDM-PDM dual multiplexing

Abstract An orthogonal frequency division multiplexed-radio over free space optics (OFDM-RoFSO) communication system with dual multiplexing is proposed. Eight input data streams are transmitted simultaneously by using wavelength division multiplexing (WDM) at level 1 and polarization division multiplexing (PDM) at level 2. Input data streams 1–4 and 5–8 are assigned with same set of carrier frequencies i.e. 193.1 THz, 193.3 THz, 193.5 THz and 193.7 THz and separate polarization levels (X and Y polarized) before transmitting through RoFSO link. A total data rate of 160 Gbps (4 × 2 × 20 Gbps) is achieved in this design. With proposed system, channel performance is evaluated under the influence of atmospheric attenuation and turbulence conditions while measuring system BER, Q-factor, SNR and received power etc. The effect of channel crosstalk is analysed for WDM-PDM dual multiplexed design while considering single input single output (SISO) and multiple input multiple output (MIMO) FSO configurations. The overall analysis predicts that a higher transmission rate and improved capacity levels can easily be achieved with dual multiplexed system.

BER for a space uplink laser communication system under an actual optical distortion with a cake-cutting method.

A numerical calculating model is proposed for characterizing the BER performance of the detector working among the 2-D asymmetric distorted spot on the effects of atmospheric turbulence under weak turbulent conditions. Based on the isotropy of the beam wander effect, we introduce a beam wander vector to describe the behavior of the detector drifting among the receiving plane. Furthermore, using the cake-cutting method, the overall PDF of the light intensity is approximated by the average PDF of light intensity intercepted by the detector drifting in all different directions. The results demonstrate that the model obtains the overall PDF of the light intensity received by the detector and analyzes the BER performance of the communication system efficiently. Being an extension of the traditional 1-D calculation, our proposed model has important implications for designing the space uplink optical communication system.

Error Characterization of Differential Detection and Non-Differential Detection for MIMO UWOC Systems in Seawater Turbulent Channels

Ocean turbulence is an important factor affecting the development of underwater wireless optical communication (UWOC). To improve the error characteristics of the underwater optical communication system, we propose a differential detection-based multi-receiver-multi-transmitter (MIMO) underwater laser communication transmission method. Additionally, we derive the expressions for calculating the average BER of the MIMO underwater wireless optical communication system with differential detection and non-differential detection in the case that the two transmitted beams are completely uncorrelated. The error characteristics of the MIMO system are simulated and analyzed from the perspective of ocean turbulence intensity and link distance. The simulation results show that the differential detection method has a lower average BER compared to the non-differential detection method in the case of moderate-to-strong ocean turbulence. In addition, the differential detection methods do not have the error floor effect, and non-differential detection methods have the error floor effect. The more the turbulence intensity affects the average BER of the MIMO UWOC system with the increase of the communication link distance, the more obvious is the effect of the turbulence intensity on the average BER of the MIMO UWOC system. Accordingly, the simulation analysis shows that the differential detection method is more suitable for the construction of communication links under long-distance and medium-strong turbulence.

Effect of Wavefront Distortion in Non-Kolmogorov Turbulence on the Performance of Multi-Beam Transmission Coherent Detection

This study aims to address the multi-beam transmission problem of optical wireless coherent communication systems under the influence of non-Kolmogorov turbulence. This paper establishes the mathematical model for mixing efficiency and BER of non-Kolmogorov turbulence wavefront distortion and multi-beam transmission coherent detection systems. The influence of factors such as spectral power-law index, zenith angle, and transmission distance on the communication performance of the system is analyzed, and an experimental system is built using adaptive optics equipment to test the proposed theory. Numerical analyses show that in a non-Kolmogorov turbulence environment, as the spectral power-law index, zenith angle, transmission distance, Fresnel zone, and pointing error attenuation increase, the mixing efficiency of the coherent detection system decreases and the BER increases; under the same conditions, the mixing efficiency and BER of the system are improved after increasing the number of transmission beams at the transmitting end. Experimental research shows that, for the coherent detection system after wavefront correction using adaptive optics, the wavefront PV and RMS variances are 1.68 μm2 and 0.05 μm2 when a single beam of light is transmitted at the transmitting end, and the wavefront PV and RMS variances are 0.23 μm2 and 0.01 μm2 when two beams are transmitted. It is verified that using multi-beam transmission wavefront superposition to suppress wavefront distortion and wavefront jitter can effectively improve the mixing efficiency and BER of the coherent detection system at the receiving end.

ASCO-OFDM based VLC system throughput improvement using PAPR precoding reduction techniques

The huge bandwidth and immunity to electromagnetic interference make visible light communication (VLC) systems the preferred technique for many applications. Unfortunately, the superposition of multiple subcarriers in VLC orthogonal frequency division multiplexing systems leads to a high peak-to-average power ratio (PAPR). So, in this study, we aim to reduce PAPR in VLC systems and improve the system performance by proposing non-distorting PAPR reduction techniques like precoding techniques as it doesn’t affect the system data rate because they do not require any obligatory transmission of side information. Moreover, it has a very good ability to reduce the PAPR without affecting the system BER performance. So, different precoding reduction techniques are proposed like discrete cosine transform (DCT), discrete sine transform (DST), discrete Hatley transform (DHT), and Vandermonde like matrix (VLM), to address the high PAPR and light-emitting diode-restricted linear range problems in VLC systems. The proposed technique using DHT, DCT, DST, and VLM provided a significant advantage in reducing the PAPR by 1.35 dB, 1.46 dB, 2.12 dB, and 2.17 dB, respectively. So the proposed technique is based on using the VLM precoding technique to achieve maximum reachable PAPR reduction value. Also, a comparison of the presented work and related literature reviews for PAPR reduction techniques are held to ensure the validity and effectiveness of the proposed scheme.

BER versus Data Rate Performance of SCM Transmission over Multimode Fibers at Low-Frequency Passbands with Linear Block Codes

The use of Multimode fibers (MMFs) in the low-frequency region has been studied. It is found that many available low-frequency passbands can be used as channels. However, these passbands are frequency-selective channels, which can negatively affect to the transmitted signal. To lessen this effect, Linear Block Code (LBC) along with a careful selection of passbands is applied. In this work, the performance in terms of BER and data rate for an MMF communication system using a 1-km length MMF at low-frequency passbands with different schemes of LBC is studied. This study uses subcarrier multiplexing (SCM) with a 3-dB modal bandwidth and other low-frequency passbands as channels. The results show that by using (31, 26) LBC and Type-I bit allocation, a data rate of 494 Mbps can be obtained with a BER lower than 10-9. Moreover, a BER lower than 10-14 can be achieved with a data rate of 399 Mbps, which is two-fold higher than the data rate obtained using only the 3-dB modal bandwidth. Additionally, the BER versus data rate for different cases in terms of applying LBC to the system are found and can be practically used as a guideline in selecting a BER and data rate that are suitable for the minimum requirement of a given communication system.

Enhancing Performance of Air–Ground OAM Communication System Utilizing Vector Vortex Beams in the Atmosphere

The modified uplink and downlink atmospheric turbulence channel models were established and employed to assess the system performance of air–ground orbital angular momentum (OAM) communication. The advantage of the vector vortex beam taking the place of the scalar one in the OAM communication system operated in the atmospheric turbulence was verified, that vector vortex beam can guarantee the more homogeneous energy in the circular hollow beam profile and the less phase distortion on signal OAM in the turbulence, which can reduce OAM crosstalk and improve OAM communication performance, especially small topological charge in strong turbulent regime. With the increase in turbulence strength, the vortex beam with a larger topological charge suffered more OAM mode crosstalk, and the average BER of the OAM communication system increased. Bessel–Gaussian (BG) beams with larger beam shape parameters had the strong capability of turbulence disturbance rejection in short-distance atmospheric applications, conversely, Laguerre–Gaussian (LG) beams with suitable parameter selection were preferred for long-distance atmospheric applications. Additionally, compared to the downlink channel, the transmission of OAM mode and the related communication system in the uplink channel are dramatically deteriorated due to atmospheric turbulent effects.

Space Division Multiple Access Based on OIRS in Multi-User FSO System

Optical intelligent reflecting surface (OIRS) is a new type of passive programmable optical devices, and has the potential to expand the application scenarios of traditional optical wireless commnucation. In this paper, an OIRS-based space division multiple access (SDMA) technology is proposed, which realizes accurate SDMA by partitioning the signal input and control of the OIRS, so that a single OIRS can output multiple adjustable optical beams containing different information. By jointly considering the multi-path interference among OIRS regions, OIRS physical model, pointing error, and atmospheric attenuation, we build a mathematical model of the OIRS-based SDMA system. Based on the model, the closed-form expressions for the system BER and outage probability has been derived. It is shown through numerical results that the derivation results are accurate and there is an error floor cased by multi-path interference among OIRS regions. Based on theoretical analysis and simulation results, the effect of each parameter and system design have been discussed.

A Software and Hardware Cooperation Method for Full Nyquist Rate Transmission Symbol Synchronization at E-Band Wireless Communication.

Compared with the conventional pulse-shaping transmission system, the full Nyquist rate transmission system with large bandwidth is sensitive to the sampling phase. It has only one sample available in one symbol period and is easily interfered by the channel, which does not allow the traditional symbol synchronization methods to be used directly. Another challenge is that the resource utilization for sampling data processing needs to be minimized due to the excessive consumption of the high data throughput in hardware resources. To solve these issues, we propose a symbol synchronization method based on the combination of software and hardware, which mainly includes two processes: Obtaining the initial phase by using Chirp signal and MOE criterion before communication; tracking the real-time phase using an on-line gradient table and frequency domain analysis of known data during communication. Both processes are proceeded with a phase adjustable clock. Through hardware verification, the sampling phase can be kept close to the optimal phase, thus ensuring the accuracy of the sampling data, and improving the system BER performance.

PAPR Analysis of OFDM using Partial Transmit Sequence Method

Orthogonal Frequency Division Multiplexing (OFDM) is one of the most widely used multicarrier transmission and effective technologies in today's communication networks. OFDM has many benefits and drawbacks. High Peak to Average Power Ratio (PAPR) is one of its main drawbacks. The spectral efficiency of the high-power amplifiers decreases with increasing PAPR. Therefore, maintaining a wireless system's efficiency is required to lower the PAPR. A possible method for lowering the high PAPR in OFDM systems is Partial Transmit Sequence (PTS). PTS generates a number of candidate signals, and the best signal with the lowest PAPR is chosen for transmission. The results shows that the PTS technique achieves greater PAPR minimization with less complexity. MATLAB simulation has been used to examine the OFDM system's PSD, spectral efficiency, BER performance, and PAPR analysis.

Research on Performance of Cooperative FSO Communication System Based on Hierarchical Modulation and Physical Layer Network Code

To solve the problem that the channel conditions in asymmetric cooperative FSO communication systems are not fully utilized, and the data reliability deteriorates due to high-order modulation, we proposed a layered modulation, joint physical-layer network coding scheme. In this scheme, we first designate the data priority of the information to be transmitted at the source node. Then, the transmission power of different proportions is allocated to the data based on its priority. Then, the modulated data is sent to each node, and physical-layer network coding is performed on the received data at the relay node. Finally, the relay node sends the encoded information to the destination node, and the destination node recovers the original information using the physical-layer network coding scheme. The simulation results showed that when the average signal-to-noise ratio of the channel was 15 dB, the BER of the cooperative FSO communication system could be reduced to below . In the strong atmospheric turbulence channel, the cooperative FSO communication system can obtain a signal-to-noise ratio gain of about 1.5 dB. Under strong atmospheric turbulence, this scheme could also improve the average channel capacity performance of a cooperative FSO communication system.

End-to-End Learning for Chromatic Dispersion Compensation in Optical Fiber Communication

In this Letter, we investigate the chromatic dispersion compensation problem in optical fiber communication. An end-to-end autoencoder (AE) is proposed to replace the transceiver of the traditional intensity modulation direct detection system. To deal with the obstructed gradient return problem in end-to-end transmission, we introduce a generative adversarial network to simulate the channel transmission process and employ a square-law detector for incoherent detection to reduce the complexity. Simulation results show that the BER of the proposed system can be significantly cut down compared with the conventional electric domain compensation algorithms.

Highly Secure and Reliable 7-Core Fiber Optical OFDM Access System Based on Chaos Encryption Inside Polar Code

A highly secure and reliable optical orthogonal frequency division multiplexing passive optical network (OFDM-PON) based on the chaos encryption inside polar code scheme is proposed. The 3-dimensional Chua's circuit model is adopted to realize chaotic encryption during polar encoding with low complexity. The three chaotic sequences generated by Chua's circuit model are used to encrypt information index bit matrix, frozen bits (during polar encoding) and subcarrier sequence, respectively. The BER and security performance of the optical transmission system are enhanced by our method. A 70 Gb/s polar encoded encrypted 16 quadrature amplitude modulation OFDM signal transmission over a 2 km seven-core fiber is further experimentally demonstrated. The experimental results show that the polar encoded encrypted 16 QAM-OFDM obtains a 2.1 dB gain in receiver sensitivity at a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> under the same bit rate compared to the normal 16 QAM-OFDM without FEC. Moreover, the key space of the proposed scheme is 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">84</sup> , which is large enough to guard against any malicious attacks from illegal ONUs effectively. The combined superiority of BER and security performance enable such OFDM-PON based on chaos encryption inside polar code, to have a high prospect of application in low-cost and reliable optical access system.

O2O: An Underwater VLC Approach in Baltic and North Sea

Recently, underwater visible light communication (UVLC) has become a potential wireless carrier candidate in the acrimonious mingled ocean straits. The combined strait of the North and Baltic ocean is a harsh and strongly turbid aqueous zone that contributes signal fading at a large scale. Due to this, we are proposing a UVLC system within the Baltic–North ocean mingled water under strong turbulence channel conditions. In this study, the Gamma–Gamma distribution is used to model UVLC link under an OOK modulation scheme. Subsequently, the reason for the unavailability of the latest North–Baltic oceanographic data within this bayou, we investigate the BER and outage probability performance of the proposed system within the mingled strait for the whole year during 1996s. Throughout, this work, the performance is obtained individually in both of the oceans and then compared with the heterogeneous state. It is noteworthy that the analytical work has been considered of the following distinct physio-chemical properties and the data provided for each ocean. Additionally, the simulation results are verified the analytical work of the proposed system model.

A low complexity enhanced-NOMA scheme to reduce inter-user interference, BER and PAPR in 5G wireless systems

Non-orthogonal multiple access (NOMA) has been recognized as an attractive technique to address the increasing traffic demands for heterogeneous wireless networks. The conventional fast Fourier transform NOMA (FFT-NOMA) system causes inter-user-interference (IUI), and high peak to average power ratio (PAPR) because of the superposition of multiple users on the same frequency subchannel. To reduce the PAPR, IUI, and bit error rate (BER) in a FFT-NOMA system, the enhanced-NOMA (E-NOMA) scheme is proposed that consists of a new low-complexity modified version of the conventional selected mapping (CSLM) cascaded with the Walsh–Hadamard transform (WHT). Simulation results demonstrate that the proposed E-NOMA scheme outperforms the FFT-NOMA with reference to PAPR and BER about 4.3 dB and 9.5 dB, respectively. Furthermore, at least 56% computational complexity reduction is achieved compared to an SLM-based NOMA method.

Efficient PAPR reduction scheme for OFDM-NOMA systems based on DSI & precoding methods

Orthogonal Frequency Division Multiplexing (OFDM)-based Non-Orthogonal Multiple Access (NOMA) systems are one of the promising technologies to be implemented in novel broadcasting and communication systems. One of the main challenges in OFDM-based systems is the high peak to average power ratio (PAPR), which degrades the system efficiency. Partial transmit sequence (PTS) and precoding approaches are among the best PAPR reduction schemes. The PAPR reduction in precoding methods is not as good as PTS-based ones. On the other hand, PTS-based methods are computationally complex and mostly degrade the system BER. In this paper, an efficient PAPR reduction scheme, based on the precoding and dummy sequence insertion (DSI) techniques, is proposed to overcome the previous limitations. Furthermore, a novel dummy sequence generation procedure is devised for the proposed method. We demonstrate that the developed scheme has a remarkably better PAPR reduction and BER performance than the precoding and PTS-based approaches. Moreover, it is computationally much less complex compared to the PTS methods.

Novel multi-user MC-CSK modulation technique in visible light communication

A novel multi-user modulation technique is proposed by using Manchester Coded Code Shift Keying (MC-CSK) system along with Double Padded-Modified Prime Code Sequence (DP-MPCS) in the visible light communication (VLC). In the VLC link, MC-CSK employed to enhance the bit rates and reduce BER includes effective fluctuation. In this work, the direct current in modulated signal, which includes a series of 0’s or 1’s are decreased by using Manchester coding. The proposed MC-CSK technique, however, uses M signaling waveforms which are mostly derived from a single pseudo random noise circular shift code. The proposed MC-CSK, system performance is compared with conventional modulation technique. Eventually, the results indicate that the MC-CSK coding focus on DP-MPCS outperforms the system BER performance, mitigate the interference, and, improve the system throughput over the conventional modulation techniques.

Performance Evaluation of a Tactical Data-Link System Based on MSK and 16QAM

Tactical data links are becoming more widely used in the military, as they can greatly improve the efficiency of various combat units. Such tactical data links must be able to transmit large volumes of data at high speed in complex communication environments while ensuring reliability. This paper studies the influence of 16-ary Quadrature Amplitude Modulation (16QAM) and Minimum Frequency-shift Keying(MSK) modulation on the transmission performance of data chain system. The simulation results show that 16QAM modulation can meet the requirements of tactical data link system for BER and data transmission rate, and the technical complexity is in the middle; the system BER of MSK modulation is lower, and a large number of data transmission can be realized at high speed. When the SNR reaches 50dB, the BER of MSK modulation can be reduced to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> order of magnitude, which is better than Quadrature Phase Shift Keying (QPSK) modulation, that is, the data chain system based on MSK modulation can meet the transmission requirements of data chain when the signal-to-noise ratio is large.