Four-dimensional scheduling for uplink dynamic bandwidth allocation in OFDM-PON

Orthogonal frequency division multiplexing passive optical network (OFDM-PON) has been considered a promising access solution to meet the variable bandwidth demand. In this paper, a novel scheduling for dynamic bandwidth allocation (DBA) at medium access control (MAC) layer is proposed for uplink transmission of OFDM-PON. In order to utilize the bandwidth efficiently, scheduling in four dimensions is adopted in the proposed DBA algorithm. Four dimensions stand for frequency domains, time domains, modulation formats and power allocations. The algorithm is quite flexible. Simulation results and analysis show that the proposed algorithm can efficiently utilize the OFDM bandwidth and make the system highly energy-efficient.     

Dynamic bandwidth allocation of both upstream and downstream in Orthogonal Frequency Division Multiplexing Passive Optical Network

Recently, more and more attention has been paid to the Orthogonal Frequency Division Multiplexing Passive Optical Network (OFDM-PON). And more importance has been attached to the algorithm achieving dynamic bandwidth allocation (DBA) by researchers. In this paper, an algorithm which aims at achieving multi-granularity DBA based on OFDM-PON is proposed. With the change of bandwidth needs, the number of subcarriers and their modulation formats can be adjusted adaptively. To efficiently utilize the bandwidth, the algorithm introduces a scheme from TDM-PON based on cyclic rotation and polling mechanism. An inner ONU queue is also proposed and multiple subcarrier channels are established in both upstream and downstream. Both simulation and analysis show that the bandwidth utilization of OFDM-PON is efficient.     

偏分复用系统信道串扰的理论模型及消除方案

建立了偏分复用(PDM)系统中信道串扰的数学模型,并提出了消除该串扰的方案,即用解复用端一路光信号的射频(RF)功率作为反馈信号以监测光信号在链路中偏振态的变化和在接收端的串扰情况,用粒子群优化(PSO)算法作为逻辑控制单元的算法,控制偏振控制器以消除信道间的串扰。数值仿真了RF功率与信道串扰大小之间的关系,并在2×50Gb/s偏分复用-差分正交移相键控(PDM-DQPSK)传输系统平台上仿真验证了消除串扰方案的效果。结果表明该方案能够大幅降低系统误码率,改善系统性能。     

基于动态混沌映射的三维加密正交频分复用无源光网络

提出了一种基于混沌映射的三维加密正交频分复用无源光网络保密通信系统.该系统通过相关性检测锁定收发端混沌系统参数,实现收发双方混沌系统同步;并利用同步混沌系统生成密钥,实现符号扰动以及二重子载波加密.该加密方案的密钥空间超过10~(86),能够有效对抗穷举攻击.实验实现了13.3 Gb/s基于64进制正交幅度调制的加密正交频分复用信号在25 km标准单模光纤中的传输,并完成了信息的有效解密.     

Analysis of the influence of backscattered optical power over bidirectional PON links

Our aim is to describe the behavior of non-linear scattering effects that arise in standard single mode fiber (SMF), specifically scattering effects that propagate optical power in the reverse direction of the source signal such as Rayleigh Scattering (RS) and Brillouin Scattering (BS). For this purpose, the effects of backscattering phenomena over a bidirectional data transmission in a passive optical network (PON) scheme have been assessed. The impact of these high optical power components over reception at the optical line terminal (OLT) side has been determined when both links use the same wavelength. Bit Error Rate (BER) measurements have been performed with different transmission rates, using several techniques to mitigate the influence of backscattering over the received signal and considering cases with filtered and unfiltered BS.     

光码分多址并行图像传输系统的最佳光正交签名图形构造

图像传输和接入要求系统的吞吐量超过Gb/s,若采用常规光码分多址系统来实现图像传输,对光电器件的要求高、实现难度大,解决方案是采用光码分多址并行图像传输系统.针对并行图像传输的签名序列是一种二维光正交签名图形,是一种全新形式的签名码,构造最大容量的光正交签名图形(最佳光正交签名图形)的方法很少这一问题,提出一种区组设计构造算法.算法的思想是根据差集合和光正交码的关系,将差集合和区组设计的概念推广到二维空间,根据二维差集合和光正交签名图形的关系从而构造出最佳光正交签名图形.详细阐述了构造最佳光正交签名图形的步骤,对算法进行了仿真.仿真结果说明该算法可以有效地构造出最佳光正交签名图形.     

A new coding scheme of QC-LDPC codes for optical transmission systems

Based on Galois Field (GF(q)) multiplicative group, a new coding scheme for Quasi-Cyclic Low-Density Parity-Check (QC-LDPC) codes is proposed, and the new coding scheme has some advantages such as the simpler construction, the easier implementation encoding, the lower complexity of the encoding and decoding, the more flexible adjustment of the code length as well as the code rate and so forth. Under the condition of considering the characteristics of optical transmission systems, an irregular QC-LDPC (3843,3603) code to be suitable for optical transmission systems is constructed by applying the proposed new coding scheme. The simulation result shows that the net coding gain (NCG) of the irregular QC-LDPC (3843,3603) code is respectively improved 2.14 dB, 1.19 dB, 0.24 dB and 0.14 dB more than those of the classic RS (255,239) code in ITU-T G.975, the LDPC (32640,30592) code in ITU-T G.975.1, the regular SCG-LDPC (3969,3720) code constructed by the Systematically Constructed Gallager (SCG) coding scheme and the regular QC-LDPC (4221,3956) code at the bit error rate (BER) of 10-8. Furthermore, all the five codes have the same code rate of 93.7%. Therefore, the irregular QC-LDPC (3843,3603) code constructed by the proposed new coding scheme has the more excellent error-correction performance and can be better suitable for optical transmission systems.     

A novel construction algorithm of the LDPC code for high-speed long-haul optical transmission systems

According to the transmission characteristics of high-speed long-haul optical transmission system, the main construction method of Low-Density Parity-Check (LDPC) code for optical transmission system is presented and a novel construction algorithm of LDPC code is proposed, the theoretical analysis shows that the parity check matrix of the LDPC code constructed by the proposed construction algorithm has no four-girth phenomenon, this is also theoretically proved out. Both the novel LDPC(3969,3720) code with 6.69% redundancy and the novel LDPC(8281,7920) code with 4.56% redundancy for optical transmission systems are constructed by using the presented construction method and proposed construction algorithm. The simulation results show that the net coding gain (NCG) of the two novel LDPC codes at the eighteenth iteration for the BER of 10^?12 are respectively 1.63 dB and 1.49 dB more than that of the RS(255,239) code in ITU-T G.975. Moreover, the decoding of the LDPC code in the hardware can parallel be implemented, so the decoding speed of the two novel LDPC codes are very rapid, the complexities of implementing the two novel LDPC codes, compared with the concatenated codes in ITU-T G.975.1, are relatively lower, furthermore, the hardware overhead and storage space can relatively be saved and the computation complexity can be reduced in implementing the hardware in the future. As a result, the two novel LDPC codes can better be suitable for high-speed long-haul optical transmission systems.     

Investigation of a high-speed optical FSK scheme for WDM-PON applications with centralized lightwave source

This paper proposes and numerically investigates a novel high-speed wavelength-division-multiplexed passive optical network (WDM-PON) architecture with colorless user terminals based on the use of orthogonal modulation scheme for downstream and upstream transmission. The 40 Gb/s optical frequency shift keyed (FSK) downstream data is generated based on carrier-suppressed modulation. At optical network unit, the downstream signal is directly re-modulated by the 2.5 Gb/s up-stream data and sent back with the same fiber. Error free transmission over 20 km single mode fiber can be observed for both downstream and upstream signals in our simulation. Power budget, tolerance of channel spacing, FSK tone spacing and dispersion are all investigated. Factors that might influence the stability of the system are analyzed and an extended hybrid wired/wireless version of the scheme is also given.     

2x40 Gbit/s Polarization Division Multiplexing With Bit Slot Synchronization

Polarization division multiplexing (PDM) can double the spectral efficiency of an optical transmission system. By means of simulation, the 2x40Gbit/s NRZ PDM system performance under polarization mode dispersion (PMD) and chromatic dispersion has been investigated. To realize the best performance, the bit slots of the two channels should be synchronized.     

Generation and transmission of the double-sideband optical millimeter-wave with signal carried only by optical carrier

In this paper, we have proposed a new scheme to generate double-sideband (DSB) optical millimeter-wave (mm-wave) with signal carried only by optical carrier, and its transmission performance is investigated. The theoretical and numerical results show that the DSB optical mm-wave signal generated by our scheme suffers only from the fading effect, the time shift of the sidebands has little influence on its transmission performance. The signal demodulated from the harmonic photocurrent shows a clear and open eye diagram and has good performance even if the transmission distance is very close to but not just at the fading nodes. The theoretical results are in good agreement with our numerical simulation.     

Photon Generation Scheme of 32-Fold Millimeter-Wave Signal Based on Mach-Zehnder Modulator

This paper proposes a 32-tupling frequency millimeter-wave (MMW) filter-free system based on four Mach-Zehnder Modulators (MZM) connected in parallel and cascaded with a simple radio-fiber (RoF) link structure. The four MZMs are all at the maximum transmission point (MATP), and the radio frequency (RF) driving voltage phase difference between MZMs is π /2. The center carrier is suppressed by using an optical attenuator (OATT) and an optical phase shifter (OPS). Two parallel MZMs can generate ±8th order and ±12th order optical sidebands, and the ±4th order optical sidebands can be suppressed by adjusting the modulation index m of the MZM, using cascaded two dual-parallel MZMS(DPMZM) and the phase difference of the RF signal source is π/4 to generate ±16th order optical sidebands. The theoretical analysis and simulation experiments are performed for the scheme proposed in this paper. The results show that the simulated and theoretical values of the optical sideband suppression ratio (OSSR) for ±16th order optical sideband signals are 60.02 and 59.96 dB, respectively, and the simulated and theoretical values of the RF sideband suppression ratio (RFSSR) for the 32-tupling MMW signal are 56.34 and 53.94 dB, respectively.     

A bandwidth-efficient channel allocation scheme for mitigating FWM in ultra-dense WDM-PON

In this paper, we investigate four-wave mixing (FWM) effects in the ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) system and propose an efficient channel allocation scheme to mitigate the FWM impact. This scheme is formed by grouping signal channels into several blocks with different channel spacing. Through numerical analysis and simulations, our proposed scheme is verified to be able to reduce the FWM effects and have higher bandwidth efficiency than the traditional unequal channel allocation scheme. The simulation results also demonstrate that our proposed scheme can achieve nearly 4 dB increases in optical power budget of the UDWDM-PON systems at the BER of 1e−3, in comparison with the equal spaced channel scheme.     

Investigation of high-speed optical FSK generation scheme based on carrier suppression and phase modulation

We propose and numerically investigate a novel high-speed (40-Gb/s and above) optical frequency shift-keying (FSK) transmitter scheme. By optical carrier-suppressed modulation and differential phase-shift-keying (DPSK) to intensity modulation (IM) conversion, only one light source is needed in the proposed scheme to generate high-speed optical FSK signals. By using a Mach-Zehnder modulator (MZM) as phase modulator and an additional delay interferometer (DI) cascaded after the carrier-suppressed MZM to suppress the remaining carrier, the performance of our scheme can compete with the double-light-source counterparts. The transmission performances of the FSK signal generated with the proposed scheme as well as detuning and bandwidth tolerance of the demodulation filter are also carefully investigated. Simulation results show that the proposed FSK generation scheme is very suitable for the next-generation optical access network and optical label switching network. A potential application of our scheme in high-speed passive optical network is proposed.     

新型四倍频光生毫米波矢量信号调制技术

提出一种基于双并联马赫-曾德尔调制器(MZM)的新型四倍频光生毫米波技术,并用于矢量信号调制。传统的四倍频调制技术,由于数据信号同时调制到+2,-2阶边带上,拍频检测后两个边带上数据信号会产生相位叠加,只适用于不归零码(NRZ)等强度调制格式。提出的矢量信号调制技术将数据信号调制在一个-1阶边带上,另一个+3阶边带不携带数据,在拍频检测后幅度和相位信息被正确保留。同时,四倍频模块降低了传输过程中对电和光器件的带宽需求。理论分析和仿真结果表明,通过此方法产生的携带在60GHz载波上的6.25×108 symbol/s的四相相移键控(QPSK)信号,经过20km单模光纤传输后,误差向量幅度(EVM)损耗可以忽略。     

A multi-channel full-duplex 60-GHz-band radio-over-fiber system

We propose and simulate a novel full-duplex radio-over-fiber system using a single light source at central station (CS). The scheme is employed to generate 60-GHz optical millimeter wave at CS for down-link transmission while the same optical carrier is reused at base station for up-link connection. There is no additional laser source for the upstream data generation in the base station. The bidirectional full-duplex 2.5 Gb/s data are successfully transmitted over 40 km standard single-mode fiber (SMF). The power penalty for the down-link data after transmission over 40 km SMF is less than 0.6 dB, while for the up-link data, the power penalty after transmission over 40 km SMF is neglected. This system shows good performance over long-distance delivery and has important applicable value in high radio frequency (RF) sector and multi-channel full-duplex system.     

A full-duplex radio-over-fiber link with 12-tupling mm-wave generation and wavelength reuse for upstream signal

A full-duplex radio-over-fiber (RoF) link with a novel scheme to generate 60 GHz mm-waves from a 5 GHz RF signal source is investigated. In the RoF downlink, the required frequency of the RF oscillator is reduced greatly. Since the optical carrier is not modulated by downstream data, part of it is reused to carry upstream data and the upstream data is transmitted to the central station using optical single-sideband modulation. In this way, a single wavelength is used for both downstream and upstream transmissions. Based on this scheme, a full-duplex RoF link is built and its transmission performance is analyzed. Theoretical analysis and numerical simulation show that the downstream signal cannot only eliminate code form distortion caused by time shift of the code edges, but also reduce the influence of the fading effect as the 60 GHz DSB optical mm-wave signal is transmitted along the fiber, and the upstream signal is immune to both fading effect and time shift of the code edges.     

采用OFDM信号作为标记的光分组交换方案

以光正交频分复用信号作为光标记,利用两个不同波长的光载波分别经过强度调制,产生了10 Gb/sOOK光载荷和2.5 Gb/sOFDM光标记。测得了光分组信号经光纤传输前后接收载荷的眼图和标记的星座图以及误码率曲线,结果表明:经过40 km光纤传输后,载荷与标记的功率代价分别为1dB和0.5dB。     

Flexible polarization demultiplexing method based on an adaptive process noise covariance Kalman filter

A flexible polarization demultiplexing method based on an adaptive Kalman filter(AKF) is proposed in which the process noise covariance has been estimated adaptively. The proposed method may significantly improve the adaptive capability of an extended Kalman filter(EKF) by adaptively estimating the unknown process noise covariance. Compared to the conventional EKF, the proposed method can avoid the tedious and time consuming parameter-by-parameter tuning operations. The effectiveness of this method is confirmed experimentally in 128 Gb/s 16 QAM polarization-division-multiplexing(PDM) coherent optical transmission systems. The results illustrate that our proposed AKF has a better tracking accuracy and a faster convergence(about 4 times quicker)compared to a conventional algorithm with optimal process noise covariance.     

一种组件透射式成像光谱仪设计

针对反射式成像光谱系统普遍存在多次反射(和衍射)产生杂散光和装调难度大等问题,设计了一种高性能透射式系统,全部使用通用光学组件,简化了系统结构,降低了成本和装调难度,较传统成像光谱仪有更广的适用范围。该设计中全部部件都非定制,可以根据应用场合更换,具有较好的灵活性,采用透射的方式,减少了杂散光的影响。利用ZEMAX软件仿真、优化了搭配两组不同物镜的系统光路,对畸变、MTF、色差等性能进行测试。对比25和50 mm物镜的系统性能,发现望远镜头的更换对整个系统成像质量的影响不大。参照设计参数成功搭建出一台成像光谱仪,其中望远物镜采用准对称双高斯结构,有利于控制场曲和畸变;采用透射式平面衍射光栅作为分光器件,制作工艺成熟,无需定制,装调简单。光谱分辨率和畸变测试结果显示该系统拥有良好的畸变控制能力,光谱分辨率达到2 nm,满足设计要求,利用标定后的系统测得的氘灯光谱取得了较为理想的结果。