极低码率Turbo码及其应用研究

针对极低信噪比条件下的传输,研究了极低码率Turbo码的编译码器结构,仿真分析了其性能。提出了极低码率Turbo码在高带宽容量、复杂信道环境,例如：短波通信、流星余迹通信等系统中的使用方法。比较了极低码率Turbo码与高码率Turbo码加扩频的性能。研究表明,极低码率Turbo码较传统高码率Turbo码有更好的性能,能将自适应调制编码技术向低信噪比环境扩展。     

基于Turbo技术的Modem系统

由于短波信道特性的限制,目前国产短波通信设备中多数没有数据传输装置,远距离短波通信主要是话音及低速手发电报,效率很低且可靠性不高。通过Modem可以将报文数据调制在音频载波上进行传输,并与计算机终端结合实现收发报的自动处理。然而,普通的Modem对信道的信嗓比要求较高,不能胜任这一工作。Turbo码具有超乎寻常的优越性能,文中阐述了用于短波无线语音信道的基于Turbo码技术的Modem系统的设计思想,提供了一种自动报文收发和低速数据传输的解决方案和测试结果。     

武警短波通信纠错编码技术研究

武警短波通信具有设备简单、机动性好、通信距离远等诸多优势,是武警部队通信保障的"保底工程"。而短波信道是变参信道,存在误码率高的问题。文章通过分析三种常用的纠错编码技术:RS码、卷积码、Turbo码,并建立Simulink仿真模型,论证Turbo码纠错性能最佳,能够满足武警部队通信保障需求。     

短波数传中的Turbo均衡技术研究

短波通信由于具有技术成熟、成本低、功耗低及通信范围广等特点,因此被广泛应用。短波通信以电离层作为传输介质,其多径效应会产生码间串扰(Inter-Symbol Interference,ISI)现象,限制了无线传输的速度及质量。为了提高系统可靠性,可采用Turbo均衡技术对接收信号进行处理,该技术利用Turbo编译码思想,结合信道均衡与译码处理,通过迭代以达到消除ISI的目的,因其具有良好的性能,得到了广泛的应用。在介绍数字化短波数传通信系统方案的基础上,对Turbo均衡在短波数传体系的应用进行了重点研究,并完成了整个信号处理流程的设计及仿真,验证了其抑制ISI的功能。     

在卫星移动信道中不同条件下Turbo码的纠错性能研究

研究了采用Turbo码技术的抗衰落性能,首先分析了Turbo码在卫星移动遮蔽Rician衰落信道下的误差纠错性能限,然后通过计算机仿真模拟了三种不同的卫星移动衰落信道下Turbo码的性能,研究了不同衰落信道特性对Turbo码性能的影响情况,同时还讨论了在衰落信道下Turbo码的子码约束长度和交织器长度两个主要参数对性能的影响情况。     

短波衰落信道下Turbo均衡算法研究

短波衰落信道下由于多径和衰落的影响,接收机的解调性能严重恶化,甚至无法正常通信。针对短波信道的特性,阐述了现有的经典Turbo均衡算法与结构,对短波信道的变化情况进行了分析,并提出了Turbo均衡的简化算法,该算法基于最小均方误差准则,利用译码器的输出构造平均信息与方差信息,修正了信道循环矩阵从而使得计算复杂度大大降低。最后对其在衰落信道下的性能进行了仿真,仿真结果表明,提出的Turbo均衡简化算法既降低了复杂度,又不损失性能。     

短波信道下的Turbo码性能研究

基于Watterson短波信道模型,构建了Turbo码在短波信道下的设计和仿真方法。在高信噪比区域中,推导出了不同信道条件下Turbo码的性能界公式;在低信噪比区域中,用Matlab仿真了短波信道下不同的信道条件及Turbo码的主要设计参数对其性能的影响,并给出了Turbo码在短波信道下的设计参数,为实际工程中的应用提供参考。     

大气激光通信系统中Turbo码译码性能仿真

由于大气激光通信信道对光信号的衰减极大,实际通信系统的编码应具有极强纠随机差错和纠突发差错的能力.针对大气激光通信信道的特殊性,结合当前优异的编码技术Turbo码对信道进行编码,通过对大气激光通信信道的分析对Turbo码编译码系统进行修正,建立了基于大气激光通信信道的系统模型,仿真分析了Turbo码实现低误码率的大气激光信息传输的可行性,并分析了采用不同算法和不同交织长度对系统性能的影响,为Turbo码在大气激光通信系统中的应用提供了理论基础.     

短波跳频系统中分组Turbo码在阻塞干扰下的性能分析

该文基于短波跳频(FH)系统的特点,对短波跳频系统中分组 Turbo码的联合上界进行了分析和推导,给出了该编码在阻塞干扰存在的情况时平均误码率上限的数学表达式。并对分组 Turbo码在短波阻塞信道下的性能进行了数值模拟,结果表明:分组 Turbo码用于跳频系统时,在短波慢瑞利衰落的信道下,当信噪比为 20dB,信号阻塞比为 30dB时,可使系统的比特误码率由 10-3降为 10-5。     

基于衰落信道的Turbo码的设计与实现

Turbo码作为一种新颖的信道编码,可以获得接近香农理论极限的性能,IMT-2000已经将Turbo码作为第三代移动通信系统(3G)传输高速业务数据的信道编码标准之一.文中提出了一种在衰落信道下Turbo码的实现模型,并探讨了Turbo编、译码器的设计及其算法,最后用MATLAB语言完成了算法的仿真实现.仿真结果表明,在低信噪比的无线衰落信道中,Turbo码不仅可以获得更大的编码增益,有效地改善系统的性能,而且具有很强的抗衰落、抗干扰能力,在移动通信系统中有着很大的应用潜力.     

Performance of DS-CDMA over measured indoor radio channels usingrandom orthogonal codes

Direct sequence spread spectrum, with its inherent resistance to multipath interference, has become a commercial reality for indoor wireless communications and has been proposed for personal communication networks. To allow multiple users within the limited bandwidths allocated by the FCC, code-division multiple-access (CDMA) is needed. This paper analyzes the performance of CDMA systems using random orthogonal codes over fading multipath indoor radio channels using channel measurements from five different buildings. The effect of RAKE receiver structure is studied, as is the effect of average power control. The average probability of error as a function of signal-to-noise ratio is used as the performance criteria. Results are compared with models for Rayleigh fading channels     

Forward Error Correction Coding for Fading Compensation in Mobile Satellite Channels

Fading in mobile satellite communications severely degrades the performance of data transmission. The channel is modeled with nonfrequency selective Rice and Rayleigh fading. Also, stored channel simulation is used for hardware data transmission. FEC coding with Viterbi decoding of convolutional codes, and Berlekamp-Massey decoding of Reed-Solomon codes, are used to compensate for the fading. In addition to interleaving, channel state and erasure information improve the performance of the decoder. The BER after decoding is calculated for specific codes on several channels and for different transmission schemes. Using very simple channel state and erasure information gives 2-7 dB additional coding gain. These gains have been verified by hardware data transmission on synthetic fading channels and stored mobile satellite channels.     

Robust space-time codes for correlated Rayleigh fading channels

Space-time (ST) coding has emerged as an effective strategy to enhance performance of wireless communications in fading environments. Many different ST coding schemes have been proposed to achieve reliable communications in independent fading channels. However, a design of robust ST codes for correlated fading channels has not been addressed. We propose a simple robust ST coding scheme that achieves robust performance over a wide range of fading conditions. The key to achieve robust performance is to formulate code design criteria that are not dependent on the channel correlation statistics. A provably robust scheme can be formulated by concatenating a full-rank ST block code with an outer encoder. We derive several robust code examples via the concatenated orthogonal ST block code and TCM construction. The simulation results show that some traditional ST codes perform poorly, whereas the proposed codes achieve robust performance over a broad range of fading conditions.     

Space-time codes for high data rate wireless communication:performance criterion and code construction

We consider the design of channel codes for improving the data rate and/or the reliability of communications over fading channels using multiple transmit antennas. Data is encoded by a channel code and the encoded data is split into n streams that are simultaneously transmitted using n transmit antennas. The received signal at each receive antenna is a linear superposition of the n transmitted signals perturbed by noise. We derive performance criteria for designing such codes under the assumption that the fading is slow and frequency nonselective. Performance is shown to be determined by matrices constructed from pairs of distinct code sequences. The minimum rank among these matrices quantifies the diversity gain, while the minimum determinant of these matrices quantifies the coding gain. The results are then extended to fast fading channels. The design criteria are used to design trellis codes for high data rate wireless communication. The encoding/decoding complexity of these codes is comparable to trellis codes employed in practice over Gaussian channels. The codes constructed here provide the best tradeoff between data rate, diversity advantage, and trellis complexity. Simulation results are provided for 4 and 8 PSK signal sets with data rates of 2 and 3 bits/symbol, demonstrating excellent performance that is within 2-3 dB of the outage capacity for these channels using only 64 state encoders     

Receiver design in multicarrier direct-sequence CDMA communications

Multicarrier direct-sequence code-division multiple access (MC-DS-CDMA) has emerged recently as a promising candidate for the next generation broad-band mobile networks. We consider the design of multiuser receivers for MC-DS-CDMA communications over fading channels. We present a class of spreading codes that enables the simple despreading-combining receiver to achieve the performance of the optimum multiuser linear receiver. These codes are shown to be optimum for independent fading channels under a code design criterion derived. Also derived are analytic solutions of optimum spreading codes for any given channel fading statistics. Simulation results are provided to demonstrate the significant gains in performance and simplicity due to the proposed techniques     

Performance bounds of continuous and blockwise decoded turbo codesin Rician fading channel

As a powerful coding technique, turbo codes offer great promise for improving the reliability of communication over wireless channels where fading is the main impairment. The performance of turbo codes on the Rice fading channel is explored, considering both the fully-interleaved channels and correlated Rice slow-fading channels     

Adaptive Receiver for Digital Communication Over HF Channels

The fading characteristics of the HF channel make communication over this channel difficult, even at moderate data rates. In this correspondence, a practical communication system is presented which has a near-optimal receiver for data detection and adaptive optimization of the receiver to channel parameters. The channel tracking is performed during the training sequence as well as during the detected data sequence. The receiver is fast converging, therefore suitable for frequency hopping. The correspondence presents the performance obtained on fading HF channels and the computational complexity via comparisons to previously published results. The performance is shown to be superior at comparable computational complexity.     

莱斯信道中Polar码的构造及性能分析

Polar码是由Arikan提出的一种新的编码方式。它是基于信道极化理论,被证明在二进制离散无记忆信道下能够获得信道对称容量。本文给出了polar码在莱斯信道下的构造及性能分析,针对莱斯信道已知信道边信息（CSI）和未知信道边信息（NCSI）两种情况分别进行polar码的构造。仿真结果表明:相比于LDPC码,polar码的性能更加优良。此外,莱斯因子K越大,polar码的误比特率就越小。polar码在信道边信息已知的情况下性能比信道边信息未知时的好。因此Polar码在莱斯衰落信道中具有很好的性能,非常适合未来移动通信技术。      

A new low SNR,correlated fading-suited space-time block code based on zero-padding and unitary transforms

In recent years, extensive studies have been done to design space-time codes appropriate for communications over fading channels in multiple input-multiple output (MIMO) systems. Most of these designs have been based upon the assumption that the channel fading coefficients are uncorrelated hence independent jointly Gaussian random variables. Naturally the best strategy in such situations that the elements of the channel matrix are independent is to employ diversity techniques to combat the adverse effects of these fading media and thus the most famous space-time codes, i.e. orthogonal and trellis codes have been designed with an eye to realizing the maximum attainable diversity order in a MIMO system. In this paper, we will remove this practically difficult to meet condition and shall introduce a new linear space-time block code based on zero-padding and unitary transforms that due to having some inherent redundancy as well as diversity is better-suited to correlated fading channels. We will discuss the properties of the proposed code, derive its maximum likelihood (ML) decoder and provide simulation results which show its superiority over the highly used orthogonal space-time block codes in a wide range of signal to noise ratios in correlated fading channels.     

Turbo码在无线图像传输系统中的应用

通过Matlab仿真,信源编码采用矢量量化法,对静止图像通过无线瑞利(Rayleigh)衰落信道传输时,不采用信道编码和采用Turbo码作为信道编码两种情况进行了研究。依据失真度的主观评价,对两种情况下重构的图像进行了比较和分析。结果表明,Turbo码具有很强的抗衰落和抗多径效应能力,它不仅有效地提高了无线图像传输的可靠性,而且大大节省了系统发射功率。