An anti-noise modem for visible light communication systems using the improved M-ary position phase shift keying

In this paper, we propose an anti-noise modem based on the improved M-ary position phase shift keying (MPPSK) for visible light communication (VLC) systems. The line spectral interferences in the original MPPSK are theoretically analyzed and approximately mitigated by adopting a set of improved waveform samples. Then, within one symbol duration, the peak envelopes of the received signals are captured at each of synchronization bit with a quantity of sampling offsets to improve the proportion of the reliable data tones. In addition, a novel demodulation scheme using an amplitude-position detector based on soft decision is proposed to recover the MPPSK symbols, which can minimize the contamination influence of channel noise on symbol decision. With this scheme, the false alarm error and wrong slot error caused by the multipath fading in VLC channel can be effectively corrected and the bit error rate (BER) performance of the system is significantly improved. Simulation results demonstrate that the proposed scheme reduce the required signal-to-noise ratio (SNR) at least by 2 dB for BER = 10⁻⁴, which show the feasibility and validity of this anti-noise modem.     

A Simulation Analysis of LEDs’ Spatial Distribution for Indoor Visible Light Communication

Visible light communication (VLC) is a promising technology that can jointly be used to accomplish the typical lighting functionalities of the light emitting diodes (LEDs) and data transmission, where light intensity is modulated with the aid of a high rate data that cannot be noticed by the human eye.qu In this paper, a VLC simulation framework to study the effect of LEDs’ distributions on different room dimensions is proposed by considering the performance metrics such as light intensity quality in accordance with the International Organization for Standardization (ISO) recommendation, and data transmission efficiency measured in terms of bit error rate (BER). To achieve that, a VLC communication system is designed that modulates the data, transmits it over the room utilizing the communication channel that is modeled using an accurate ray-tracing algorithm, and receives it. Our work is different from most of the published works, which studied either the data transmission efficiency or lighting quality but not both. In addition, our study investigates the effect of having different rooms dimensions and different number of transmitters on data transmission quality and light illumination. Consequently, this paper can be used as a methodological study to design an efficient VLC system that satisfies the ISO lighting requirement and the VLC application-specific BER requirements. Furthermore, a video transmission use case has been demonstrated, which shows how video quality can be significantly improved when the number of transmitters is increased. However, considering the ISO lighting requirements, one can put a limit on the number of LEDs that can achieve the required application BER and lighting requirements, thus achieving both objectives efficiently.

     

Performance enhancement of visible light communication (VLC) system incorporating WMZCC-OCDMA codes and PDM-QPSK-DSP data encoding

Multi-user optical code division multiplexing (OCDMA) in visible light communication (VLC) is an imminent domain for providing an even distribution of available bandwidth and improved security. Q4R1Zero cross-correlation (ZCC) codes are widely reported, and improved performance is offered by them due to insignificant multiple access interference (MAI). However, practically, MAI exists in ZCC codes due to adjacent weights (W) in the code matrix rows for each user. Therefore, a novel ZCC code with a nonadjacent W is designed in this work to eradicate MAI limitations and is named weight managed ZCC codes (WMZCC). An indoor 100 Gbps/User OCDMA-VLC system is realised using polarisation division multiplexed quadrature phase shift keying (PDM-QPSK) and digital signal processing (DSP). Incorporation of DSP in the coherent receiver compensates the effects of dispersion and nonlinear effects and also performs phase estimation. Further, a state-of-the-art comparison of WMZCC codes with diagonal identity matrix (DIM) and zero cross-correlation resultant weight (ZCCRW) codes has been performed in terms of log symbol error rate (SER), Q factor, error vector magnitude percentage (EVM%) and log bit error rate (BER) log at different VLC lengths, Q4R1Transmitter half angles (THA), incidence half angles (IHA) and optical concentrators (cm²). Constellations are analysed with and without DSP, and according to the author's best knowledge, a 100 Gbps VLC system for five users covering 6 m at −3.42 log BER is demonstrated for the first time. Results revealed that weight management in WMZCC codes makes its performance improve as compared with ZCCRW and DIM codes.     

Channel capacity of the distributed MIMO relay in visible light communication systems

Visible light communication (VLC) is a novel paradigm that uses light-emitting diode (LED) light as an information carrier and has several advantages over radio-frequency communication in terms of the bandwidth, security and multi-path fading. When the VLC system is considered in an indoor environment, LED lamps, which are placed at the ceiling to provide ambient light, can offer rich spatial resources for VLC as distributed intermediate relaying terminals. This paper introduces a novel distributed multiple-input multiple-output (D-MIMO)-relaying VLC scheme and analyzes its communication performance. Using the sum rate of the broadcasting and multiple access relay channels, a tight upper bound on the channel capacity was derived. The numerical results showed that the D-MIMO-relaying VLC scheme outperformed the direct-path-based scheme in terms of the channel capacity. For a given indoor environment, the capacity of D-MIMO-relaying VLC can be improved further by selecting the appropriate relay parameters, such as the number of LED–PD pairs in a relay, distance between relays and height of relays.     

On the Decision-Feedback Equalizer in Optically Amplified Direct-Detection Systems

This paper investigates the combined feed-forward and decision-feedback equalizer (DFE) in a lightwave system with optical amplifiers and a direct-detection receiver. Based on a nonlinear channel model, the paper provides a modification of the classical minimum mean square error theory of the DFE. Furthermore, an analytical method that is capable of accurate bit error rate (BER) evaluation is used to optimize the DFE for minimum BER. The paper evaluates the DFE performance for both optical ON-OFF keying and duobinary modulation formats in the presence of chromatic dispersion as well as the DFE performance for the mitigation of higher order polarization mode dispersion in first-order compensated systems. The paper shows that the DFE can compensate for the BER degradation due to narrow-band receiver-side optical filtering and can significantly improve the spectral efficiency of dense wavelength-division multiplexed systems.     

基于非正交多址的室内可见光通信系统性能优化方法

室内可见光通信(Visible Light Communication, VLC)系统常用的非对称限幅光OFDM(Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing, ACO-OFDM)与直流偏置光OFDM(DC-biased Optical OFDM, DCO-OFDM)采用加循环前缀、信道均衡和载波复用等方法解决信道干扰及多用户复用问题,但均以牺牲有效性为代价。非正交多址(Non-orthogonal Multiple Access, NOMA)通过功率域复用提高频谱利用率,利用串行干扰消除(Successive Interference Cancelling, SIC)进行多用户信号处理,有效兼顾可靠性与有效性。将NOMA应用于室内可见光系统,建立基于NOMA-DCO-OFDM的可见光信号传输及信道增益模型。通过功率域多用户信道差异计算信道增益,进行功率分配实现功率域复用,提高系统容量和通信速率;利用SIC按功率分配算法对用户逐一解调,减弱信道干扰,提高可靠性。通过理论分析和仿真实验验证表明:该系统的通信速率达到6.8×107 bit·s?1,且合速率受用户数量的影响不显著。2用户下,误码率(Bit Error Rate, BER)为10?4时用户1有5.2 dB左右的性能提升,用户2有2.3 dB左右的性能提升,通信可靠性也明显提高。     

天气影响下Ka频段移动卫星通信系统的性能

本文建立了ka频段移动卫星通信系统模型,并利用计算机进行仿真给出了不同天气时信号的误码率,为实际的系统设计提供了理论基础。在本文中信道模型建立为雨衰和多径阴影衰落信道。在该模型中,雨衰信道服从高斯分布,阴影衰落信道服从Nakagami-Rayleigh分布。与现在广泛应用的Loo模型相比,此阴影模型能够更好地利用计算机进行仿真,并能提供较清晰的数学表达式,对陆地移动卫星系统进行定性定量的性能预测。     

多径衰落信道中导引符号辅助的二维扩频相干解调的性能分析

在多径衰落信道中,本文分析了导引辅助的二维扩频相干解调的误码率性能.提出了信道的时频二维相关区域的概念,给出了信道时频二维信道相关特性的计算方法.结果表明,分析与仿真的误码率相近;当二维扩频的扩频增益对应的时频二维区域大于信道的时频二维相关区域时,再增大扩频增益会导致误码率性能变差.     

空时编码在瑞利衰落信道下的性能分析

以正交空时分组码为例讨论了空时编码技术的性能特征。给出了各种STC-OFDM系统的BER性能。理论分析和仿真结果表明,STBC-OFDM系统在频率选择性的瑞利衰落信道下,性能优于其它STC-OFDM系统。     

基于重叠与正交信号的超宽带系统性能研究

文章首先介绍了跳时超宽带(TH-UWB)信号,推导了在加性高斯白噪声(AWGN)信道条件和多径条件(MP)下,基于重叠和正交脉冲信号的系统误码率公式,并给出了仿真结果.仿真结果表明,在AWGN信道条件下,基于重叠脉冲信号的跳时二进制脉位调制(TH-BPPM)系统的性能优于基于正交脉冲信号的系统.多径条件下的正交TH-BPPM系统的性能优于AWGN信道条件下的系统性能.     

Transmission performance of all-optical domain orthogonal frequency division multiplexing signals due to fiber nonlinearities for long-reach PON applications

This study examined the performance of 110 Gb/s all-optical domain orthogonal frequency division multiplexing (AO-OFDM) signal transmission systems using optical multi-carrier generation and optical 2-subcarrier modulation under the effects of chromatic dispersion and fiber nonlinearity. The numerical simulation results showed that the performance degradation of AO-OFDM signals lies in the inter-carrier interference between the subcarrier signals generated from the fiber nonlinearities. The numerical simulation showed that the calculated BER of the AO-OFDM channels has some power penalties at 10^?9 BER for the fiber chromatic dispersion effect. The calculated receiver sensitivity at 10^?9 BER showed additional degradation at the central subcarrier channel by applying a fiber launching power of 12 dBm after transmission over a 100 km standard single-mode fiber (SMF) link. The simulation results are expected to be useful for multi-service systems employing AO-OFDM technology in the future long-reach passive optical network (PON) applications.     

多径瑞利衰落信道条件下射频干扰抵消误差对CCFD系统中OFDM性能的影响

针对同时同频全双工无线通信系统,考虑远端到近端的无线信道为多径瑞利衰落信道,近端发射天线到接收天线的自干扰信道为加性白高斯噪声信道,分析了同时同频全双工传输场景中,自干扰射频抵消幅度及载波相位误差对OFDM误码率的影响。结果表明,在相同信干比和信噪比条件下,幅度和载波相位估计误差的绝对值越小,误码率越低;针对载波频率2.3 GHz, OFDM子载波个数4096,子载波间隔15 kHz的同时同频全双工传输方式,在信干比为-70 dB,误码率为10-2时,若期望信噪比损失小于0.8 dB,则需要射频干扰抵消的载波相位估计误差的绝对值小于610-6,幅度估计相对误差的绝对值小于310-5;若期望获得40 dB的射频自干扰抑制效果,则射频干扰抵消的载波相位估计误差的绝对值小于0.5,幅度估计相对误差绝对值小于1%。     

OFDM-CPM通信系统的设计与分析

分析了正交频分复用-连续相位调制通信系统的特点,设计了一种易于工程实现的调制解调方案。在多径加高斯白噪声环境下,对比了OFDM-CPM系统与OFDM-QPSK系统的误码率特性,研究了调制指数对OFDM-CPM系统误码率的影响,以及卷积码对OFDM-CPM系统误码率的改善。     

PAPR reduction for OFDM‐based visible light communication systems using proposed hybrid technique

Orthogonal Frequency Division Multiplexing (OFDM) is utilized with visible light communication (VLC) systems to decrease the impacts of inter‐symbol interference and to achieve communication with high speed of data transmission and huge bandwidth. In any case, the main problem in OFDM‐based VLC systems is high peak‐to‐average power ratios (PAPRs). This paper proposes a hybrid PAPR reduction technique based on signal transformation combined with clipping. The Hadamard transform is used in the proposed technique to reduce the PAPR without affecting the bit error rate (BER) of the VLC systems. The optimum clipping threshold at which the PAPR is reduced simultaneously with the improvement the BER of the VLC systems is also determined. The performance of the proposed system is assessed in terms of complementary cumulative distribution function and the BER. The obtained results demonstrate that the proposed procedure can simultaneously decrease the PAPR and achieve good BER performance compared to the OFDM‐based VLC system.     

Interleaving effects on BER fairness and PAPR in OFDMA System

Considering an Orthogonal Frequency Division Multiple Access (OFDMA) system, in this study we analyze the role of interleavers from their capability in ensuring uniformity of Bit Error Rate (BER) performance amongst the active users. In addition, we also investigate their Peak to Average Power Ratio (PAPR) properties. From the uniformity or fairness in BER perspective, we first consider a generic system and show that for a slowly changing multipath channel, individual user’s BER performance can vary from each other to a great extent, implying that the propagation channel effect is unfairly distributed on the users. Applying different types of frequency interleaving mechanisms, we demonstrate that the choice of interleaving can ensure better BER fairness on an individual user basis. In particular, by introducing the application of cyclically shifted random interleaver, we demonstrate its effectiveness in achieving BER fairness dispersion in individual users BER reduced by 89% compared to no interleaving at 15 dB Signal to Noise Ratio. We then explore the comparative performance of different interleavers considering variable number of total subcarriers, variable number of users and variable number of subcarriers per users. Finally, going back to the generic OFDMA, we investigate the PAPR distribution of different interleavers at various active user densities. Based on the results we conclude that when the total number of subcarriers per user is relatively low, i.e., a system which is heavily loaded with active users, cyclically shifted random interleavers can effectively ensure uniform performance amongst active users with reduced system complexity and manageable PAPR. In all other cases, interleaving with fixed amount of subcarrier spacing is the best solution.     

Four-wave mixing reduction technique based on smart filter approach

This paper proposed a new technique to suppress the four-wave mixing (FWM) effect by using a smart filter technique. The behaviour of FWM and the performance of wavelength division multiplexing systems with 4 and 16 channels were simulated in the presence of the proposed technique. The simulation was also performed under different parameters such as input power, number of channels and channel spacing. The FWM power drastically decreases by 12 and 19 dB for the 4 and 16 channels, respectively, when the smart filter is used as compared with the conventional system. In terms of system performance, the suggested approach for 4 and 16 channels at the first channel offers low bit error rate (BER) values of 3.23 × 10^?23 and 1.7 × 10^?21, respectively. The smart filter with the channel spacing variation for the 4-channel system subsequently improved the BER value at the fourth channel. Results confirm that the smart filter approach is an active solution that can suppress the FWM effect in optical transmission systems.     

三阶色散效应对光码分多址系统误码率的影响

光码分多址(OCDMA)系统的误码率是评价系统性能的重要指标,由于色散和非线性效应会导致超短光脉冲在光纤传输过程中脉宽的展宽,进而影响OCDMA系统的误码率。在基于理想情况的OCDMA系统误码率定义的基础上,研究了三阶色散和三阶非线性效应对系统误码率的影响,进一步分析了有硬限幅器和二维OCDMA系统的误码率。结果表明,三阶色散和三阶非线性效应都会导致OCDMA系统误码率的增大,但三阶非线性效应对系统性能影响没有三阶色散效应明显;在系统参数相同基础上,接收端引入光硬限幅器和系统采用二维编码均可优化系统性能。     

多径下Turbo码IDMA网络编码中继合作系统性能分析

基于交织多址网络编码中继合作系统,分析了其采用Turbo编码后在多径信道环境下的系统性能。研究了该系统中利用不同交织器来实现多用户的多址接入方式以及网络编码的中继合作机制。将多径信道以及Turbo编码融入该系统中,搭建计算机仿真环境,通过仿真数据分析系统性能。仿真结果表明,在多径信道环境下,采用Turbo编码的交织多址网络编码中继合作系统的系统误码率有明显改善。     

Optical power budget enhancement in next-generation DDO-OFDM-based optical access networks using square root module

A passive optical network based on orthogonal frequency division multiplexing (OFDM-PON) gives improved performance for high speed optical access network due to its greater resistance to fiber dispersion and higher bandwidth efficiency. In optical fiber communication, chromatic dispersion (CD) is a linear distortion in fiber, but it is converted into nonlinear distortion due to square-law characteristic of photo diode detector at the receiver side resulting in degradation of performance. To compensate for this nonlinear distortion, we proposed to use a linearized receiver circuit with square root module (SRM) device which can improve the performance of system in terms of CD tolerance. In this paper, we have analytically analyzed the performance of OFDM-PON system with and without SRM device for direct-detection optical OFDM-PON (DDO-OFDM-PON) system. At BER of \(10^{-3}\), which is the limit of forward error correction, there is 11.1 and 13.5 dB improvement in optical budget with SRM for downstream and upstream direction, respectively, as compared to conventional DDO-OFDM-PON system.