Turbo乘积码的软译码研究

Turbo码作为一种新型的纠错编码类型备受通信界的注目,它的纠错能力接近Shannon极限。阐述了Tur-bo乘积码的软译码原理及其算法。     

Turbo乘积码技术及其性能研究

在分析Turbo乘积码的基本编译码原理的基础上,比较了未编码与编码后系统的差错性能,研究了选取不同分量码、不同迭代次数对TPC译码性能的影响。在不同迭代次数与分量码情况下,进行了仿真实验。仿真实验表明,在相同的差错性能条件下,采用TPC码能带来5~6 dB的编码增益。TPC译码算法简单,没有错误平层,硬件实现复杂度较小,是一种非常实用的信道编码方式。     

Turbo码在基于小波基的OFDM系统中的性能分析

基于离散傅立叶基的正交频分复用(OFDM)技术因其在抗多经衰落方面的优越性能已成为无线传输领域中的研究热点。但是,为了进一步提高频谱利用率,有人提出以小波基来代替傅立叶基。本文给出了Turbo编码的基于小波基的OFDM方案,并给出了其在不同信道下的性能分析。仿真结果表明,在低信噪比时,只需很小的Turbo码译码迭代次数该方案在AWGN和Rayleigh衰落信道下就能获得比较好的性能。     

乘积码基于相关运算的迭代译码

乘积码是一种能以Turbo码的思想实现译码的级联码，具有一般编码无法达到的纠错能力。本文提出一种新的乘积码迭代译码算法，其核心思想是通过输出软信息与接收软信息进行线性迭加的方式来实现反馈，此时只须提供-1和1组成的软输出矩阵就能获得很高的编码增益，仿真表明，将子译码器译码后的结果再进行一次相关运算作为软输出，译码性能可以得到进一步的提高。     

Turbo乘积码在Rayleigh信道下的性能研究

Turbo乘积码（TPC）自从被提出以来表现出了优异的性能。研究了利用扩展汉明码作为其子码的TPC在Rayleigh信道下的性能．给出了不同的子码以及不同的迭代次数下的性能曲线,仿真结果表明了TPC在Rayleigh信道中同样有较强的纠错能力。     

Turbo乘积码构造方法的研究

Turbo乘积码因其具有接近香农限的译码性能和适合高速译码的并行结构,已成为纠错编码领域的研究热点。Turbo乘积码的分量码一般由扩展汉明码构造而成,所以该类码字编码和译码的硬件实现比较简单。当Turbo乘积码采用扩展汉明码作为子码时,随着信噪比的提高,码字的最小码重对误帧率的影响会逐步增大。文中改进了Turbo乘积码编码结构,在只增加较小的编译码复杂度和时延的情况下,提高了码字的最小码重,并减少了最小码重码字在码字空间所占的比例。通过仿真和分析,比较了这种码和TPC码在误帧率性能、码字的最小码重分布以及最小码间距估计上的差异。     

性能接近Turbo卷积码的Turbo三维乘积码

目前一般认为采用迭代译码的Turbo卷积码适合于低码率的情况。而Tur-bo分组码，尤其是Turbo乘积码，则较适合于高码率的应用。文中使用Pyndiah提出的方法研究了Turbo三维乘积码，用试探法对分组失代译码的参数进行了优化实验结果表明，在低码率应用时，例如码率为R=0.536的Turbo三维（32，26，4）^3乘积码的性能已与C.Berrou[1]的Turbo卷积码接近，它也应是低码率纠错应用中一个有竞争力的选择。     

一种改进的Turbo乘积码译码算法

针对Turbo乘积码(TPC)译码复杂度高、运算量大的缺点,分析了一种改进的TPC译码算法。该算法以Chase迭代算法为基础,通过对错误图样重新排序产生新的测试序列,其伴随式可从前次伴随式的基础上修正一位得到,大大简化了计算步骤。在AWGN信道下对新算法进行了Matlab仿真,结果表明,改进的算法在保持译码性能基本不变的前提下,提高了译码速度,降低了译码复杂度。     

Turbo乘积码译码的优化研究

文章研究了Turbo乘积码译码中可靠值序列最小值和次最小值定位问题,分析比较了基于循环伪最大似然算法的TPC译码关键步骤优化的必要性,给出了一种用门电路实现的可靠值序列最小值的优化定位电路,从而提高TPC迭代译码速度。     

基于Cyclic-2伪最大似然算法的Turbo乘积码在高速移动通信系统中的译码方法

采用扩展汉明码作为Turbo乘积码 (TPC)的子码时,与传统的Chase算法相比,Cyclic-2PML(循环 2伪最大似然)算法复杂度低。本文研究了基于该算法的TPC在高速移动通信系统中的译码方法,仿真比较了采用不同子码组合的TPC结合不同的调制方式在高斯信道和多径衰落信道中的性能。结果表明,以(32, 26, 4)扩展汉明码为子码的TPC,不仅具有较高的码率,同时可以获得更好的误比特率性能。     

Performance enhancement of overall LEO/MEO intersatellite optical wireless communication systems

This paper has deeply investigated the performance signature of modulation techniques based low earth orbit (LEO)/medium earth orbit (MEO) intersatellite optical wireless communication systems for possible communication coverage distance of 20 000 km with possible transmission bit rate of 0.5 Tb/s. These modulation techniques that are namely multilevel quadrature amplitude modulation (M‐QAM), multilevel phase shift keying (N‐PSK), multilevel pulse amplitude modulation (H‐PAM), and finally multilevel differential phase shift keying (L‐DPSK) based on different electrical pulse generators for upgrading LEO/MEO intersatellite link operation efficiency. These pulse generators that are namely Gaussian pulse generator (GPG), hyperbolic secant pulse generator (HSPG), and raised cosine pulse generator (RCPG). The variations of maximum Q‐factor, minimum bit error rate (BER), and optical signal‐to‐noise ratio in relation to number of bits/symbol for different modulation techniques can be deeply studied in the presence of vertical cavity surface emitting laser (VCSEL). This study is done with using Optiwave system simulation version 7 for different modulation techniques, and all figures are sketched with using wizard Excel sheet set up. It is observed that maximum Q‐factor and minimum BER are optimized with using GPG and 8‐PAM, as well as 4‐DPSK with both HSPG and RCPG.     

Performance of optical intersatellite links

The performance of optical intersatellite links is described by a model. A significant difference between optical and microwave intersatellite links is the occurrence of so-called burst errors. The statistics of bit error rate for an optical link are derived from simulations taking into account beam mispointing resulting from satellite motions and tracking channel noise. The effect of coding on the bit error rate is also shown. The mutual tracking system between two optical terminals located on different satellites can become unstable if the noise of the tracking loop exceeds a critical value. The results of tracking simulations are presented.     

卫星光通信复合轴跟瞄控制方法研究

提出了用复合轴瞄准控制方法实现卫星光通信跟瞄控制,以提高卫星光通信中跟瞄系统的性能。提出了粗瞄和精瞄系统的模型,并分别设计了控制器。在此基础上,建立了一套跟瞄控制模拟系统。结果表明,所设计制作的跟瞄模拟系统在跟踪的匀角速率运动时的最大跟踪角度偏差仅为14μrad。     

Performance analysis of quantum cryptography protocols in optical earth-satellite and intersatellite links

In this paper we analyze the feasibility of performing Quantum Key Distribution (QKD), in earth-satellite up and downlinks and in intersatellite links, with two quantum cryptography protocols: BB84 and SARG04, and with two implementation options: with and without decoy states. As real measurements in these scenarios are not possible yet, the objective is to obtain results as realistic as possible to support the design of future satellite missions performing QKD. Therefore, we use realistic values for the optical hardware and take into account usual atmospheric conditions. In the same line, we assume specific types of attacks, namely the photon number splitting and the intercept-resend with unambiguous discrimination attacks, which could likely be the main threat to the first satellite-based QKD applications. A lower bound on the key generation rate of SARG04 with two decoy states is presented. The optimum signal- and decoy-states mean photon numbers for each protocol and each distance are also computed. The resulting values for the signal-state are larger than those often employed. We show that it may be possible to establish QKD with LEO (Low Earth Orbit) and, under certain circumstances, with MEO (Medium Earth Orbit) satellites, but not with GEO (Geostationary) ones. Furthermore, we obtain that the optimum signal-state mean photon number for SARG04 with two decoy states is almost independent of the link distance, which greatly facilitates its use in a real scenario.     

光放大器对空间量子通信系统性能的改进

为提升自由空间量子通信系统性能,以相敏放大器(PSA)和相位非敏感放大器(PIA)原理为基础,研究了在量子通信系统接收端分别加入PSA、PIA后的高斯调制连续变量量子密钥分发(CVQKD)模型,推导了相应的安全密钥率公式.当信号波长分别为810 nm、1550 nm和3800 nm时,仿真分析了系统受到集体攻击和个体攻...     

星间激光通信发射终端耦合单元的研究

针对星间光通信系统的要求,采用一种新型的半导体激光耦合方案,用前后正交的非球面柱面透镜准直半导体激光束,再经渐变折射率(graduated refractive index,GR IN)自聚焦透镜聚焦,把光束耦合入单模光纤。就此耦合单元,对耦合效率随半导体激光器的位置偏离及角度偏移进行了研究,在光纤尾纤处测得了输出功率随驱动电流的变化关系,单模运行的半导体激光二极管经耦合后的出纤功率可以达到80mW。结果表明,耦合效率随位置偏离及角度偏移的变化灵敏度都不高,这可以满足星间光通信的要求。     

卫星平台振动对星间激光链路的影响和解决方案

分析了振动对卫星光通信的影响以及卫星平台振动产生原因和特点,找出了卫星平台振动规律。针对振动对卫星光通信系统影响问题,定义了补偿因子以描述补偿效果;对于影响较大的低频振动情况,设计并建立了模拟振动补偿系统。实验结果表明,采用前馈补偿技术的模拟振动补偿系统对于10Hz低频振动的补偿效果显著,补偿大约80%的振动。     

基于LDPC码和PPM调制的深空光通信系统性能分析

比较了LDPC码和RS码在PPM调制下的深空光通信系统中的性能,给出了在不同阶数PPM调制下,不同码长LDPC码的性能仿真结果,以及与RS码的比较结果.结果表明,随着PPM调制阶数增加,LDPC码性能会下降.分析了调制阶数影响LDPC码性能的原因.     

Performance evaluation of adaptive routing algorithms in packet‐switched intersatellite link networks

This paper addresses the performance evaluation of adaptive routing algorithms in non‐geostationary packet‐switched satellite communication systems. The dynamic topology of satellite networks and variable traffic load in satellite coverage areas, due to the motion of satellites in their orbit planes, pose stringent requirements to routing algorithms. We have limited the scope of our interest to routing in the intersatellite link (ISL) segment. In order to analyse the applicability of different routing algorithms used in terrestrial networks, and to evaluate the performance of new algorithms designed for satellite networks, we have built a simulation model of a satellite communication system with intersatellite links. In the paper, we present simulation results considering a network‐uniform source/destination distribution model and a uniform source–destination traffic flow, thus showing the inherent routing characteristics of a selected Celestri‐like LEO satellite constellation. The updates of the routing tables are centrally calculated according to the Dijkstra shortest path algorithm. Copyright © 2002 John Wiley & Sons, Ltd.     

Performance enhancement of high-capacity coherent DWDM free-space optical communication link using digital signal processing

In this paper, 1.28 Tbps (32?×?40 Gbps) high-capacity DWDM-FSO link has been investigated for performance enhancement using coherent detection and digital signal processing (DSP). The DP-16QAM-modulated proposed DWDM-FSO link has been analyzed for both adverse weather and turbulent atmospheric conditions. It is observed that when link is subjected to strong turbulence along with adverse weather conditions, the DSP-aided coherent DWDM-FSO receiver achieves target bit error rate (BER) of 10^?4 at signal-to-noise ratio (SNR) of 36.4 dB, while for similar conditions, the SNR requirements for IM/DD-based DWDM-FSO link shoots by 12.8 dB to 49.2 dB. Also, in terms of operational link range, the proposed link even under strong turbulent conditions serves 1.88 km, whereas IM/DD link was restricted to mere 1.12 km for target of BER of 10^?4, thus producing a decent range increment of 760 m. The proposed link has been designed and investigated using OptiSystem? 14.2.