基于不同等差错保护和动态子载波分配技术的图象传输系统性能研究

充分考虑小波变换后的图象码流、Turbo码以及多载波系统的特性,提出了一种新颖的基于不同等差错保护和动态子载波分配技术的图象传输系统.对图象码流中重要性不同的信息比特,进行不同码率的Turbo码,并在不同信道状态的子载波上传输,对于重要信息采用低码率Turbo编码,并为其选择高信噪比的子载波进行数据传输.这种联合信源信道编码方案以及动态子载波分配技术能够有效的保护图象码流的重要信息,提高了图象码流传输过程中的抗误码性能,改善了静态图象在噪声信道中传输的效果.     

基于减格辅助线性预编码的MIMO图像MDC设计

为了解决实际的无线传输环境中由空间相关性的存在导致的MIMO MDC图像传输系统性能下降的问题,保证图像通信的质量,对基于SPIHT算法所形成的MDC各个码流采用RS码进行不等保护,利用ZF或MMSE减格辅助线性预编码处理,提出一种适宜4×4 MIMO相关信道的MDC传输方案,并在此基础上研究了其在信道确知和信道估计情况下的性能。实验结果表明,基于减格辅助预编码处理的MIMO MDC设计方案比MD-SPIHT方案在性能上有明显提升,因此,更适宜于MIMO空间相关信道。     

基于HQAM的视频传输不等保护方法

针对传统视频传输重建图像质量低的问题,文中提出了一种利用HQAM（分级正交幅度调制）为视频码流中重要性不同部分提供不等保护的无线视频传输方法。由于压缩后视频流中不同部分对传输错误的敏感度不同,因而在视频恢复过程中的重要性也就不同,文中利用HQAM在不增加传输带宽的情况下为高优先级数据（高敏感度）提供较高强度的保护,但是是以牺牲低优先级数据（低敏感度）的误码率为代价的。在仿真环境为加性高斯白噪声信道（ AWGN）下进行了仿真,结果表明,与均等保护相比,在相同信道带宽和Eb/No条件下,该方法有效提高了视频重建质量。     

数据链传输波形抗干扰研究

数据链传输波形抗干扰技术是当前信息化对抗中最重要的技术支撑,掌握数据链传输波形抗干扰技术,有利于在对抗中取得先机。主要参考Link16数据链系统并搭建完整的数据链路模型,对数据链传输波形抗干扰性能进行了研究。首先,对数据链进行了理论论述。然后为了研究该数据链模型传输波形的抗干扰特性,介绍了四种常见的干扰环境。最后,针对干扰环境提出一种基于LDPC码的数据链传输波形抗干扰技术,并对该技术在干扰信道中的干扰性能进行了仿真。仿真实验结果表明,基于LDPC码的数据链传输波形在AWGN和强突发信道环境下,抗干扰性能得到了一定程度的提升,说明该种数据传输链路对数据链传输波形抗干扰十分有效。     

瑞利信道下线性分组码的分集增益研究

比较AWGN信道与瑞利信道的误码性能,研究瑞利信道下分集支数与信息传输可靠性之间的关系。推导线性分组码在瑞利信道下误码率上界的理论表达式,得到分集增益与其最小汉明距离的关系。基于蒙特卡洛法对误码性能进行仿真,并与理论误码率上界进行比较,结果表明线性分组码在瑞利信道下获得的分集增益等于其最小码距。     

RA码交织器的研究与设计

重复累积码(Repeat Accumulate Code,简称RA码)综合了Turbo码和LDPC码的优点,可以进行线性时间的编码及译码,成为了近年来信道编码技术研究的热点。为了改善重复累积码的性能,对其交织器进行优化设计。在几种常见的交织器的基础上提出了奇偶分组交织器的设计方法,并在AWGN信道下基于BP译码算法完成性能分析。仿真结果表明,奇偶分组交织器优于分组交织器,大大降低了信息序列之间的相关性,同时避免了校验矩阵中两类四环的产生,可以提高信息在信道中传输的可靠性。     

FTN系统中两种频域迭代分组判决反馈均衡器仿真分析

超奈奎斯特(FTN)码元速率传输系统可以有效提高数据传输速率,但该系统在接收端引入了无限长的码间串扰(ISI),从而增加了接收复杂度。为此,分析两种能降低FTN系统计算复杂度的频域均衡器,即频域迭代分组判决反馈均衡器(IBDFE)和低复杂度迭代分组判决反馈均衡器(LC-IBDFE)。将IBDFE和LC-IBDFE分别扩展到加性高斯白噪声(AWGN)信道和频率选择性衰落信道中。仿真结果表明,这两种频域均衡器可以应用到衰落信道中,且在多径数目不大的情况下,两者的误码率和AWGN信道条件下十分接近。     

TPC与MSK的级联码研究

简要阐述了TPC的编码原理和基于Chase算法的迭代译码方法,并通过译码算法仿真得出TPC在AWGN信道下的性能以及TPC与MSK的级联码在AWGN信道下的性能。最后对得到的性能进行了分析,并对其在无线通信方面的应用进行了展望。     

基于MPEG-4的无线视频传输方案的研究

提出一种基于MPEG-4的无线视频传输非等重误码保护方案.根据信道反馈的丢包率信息,自适应选择输出视频流的保护模式.在丢包信道中,对MPEG-4码流中运动信息和纹理信息采取不同的保护力度,使用FEC重点保护运动信息数据提高其对误码的鲁棒性.在无丢包信道中,不对数据进行保护,降低打包开销,减少冗余数据.     

Turbo码的性能分析与仿真

在介绍分析Turbo码的编译码结构、译码算法的基础上,通过计算机仿真手段对AWGN信道中Turbo码在不同参数条件下的译码性能进行了探究和讨论,通过分析各因素对Turbo码性能的影响,为设计Turbo码提供了参数选择的基本原则。     

基于简化高阶调制算法的LDPC编码OFDM系统

低密度校验码（Low Density Parity Check codes）的重新发现是继turbo码之后信道编码领域又一里程碑事件。LDPC码凭借其优异的性能和较低的译码复杂度,被广泛的运用于各种高速通信系统。本文提出了采用简化高阶QAM的LDPC编码OFDM系统（LDPC-COFDM）,在保证高效可靠传输的同时降低了实现复杂度。仿真结果显示这种算法在AWGN和多径衰落信道下均具有良好的性能。     

近似Log-MAP turbo译码器研究

该文研究近似Log-M AP算法在turbo译码器中的应用。文章对基于近似算法的W CDM A turbo译码器在AW GN信道和平坦慢衰落Rayleigh信道上的纠错性能进行了仿真。仿真结果表明,二阶近似Log-M AP turbo译码器与M A P turbo译码器性能等价,优于SO VA turbo译码器0.7-0.9dB。     

第三代移动通信中的Turbo码标准及其应用研究

文章介绍了第三代移动通信系统地面无线接口技术标准中的Turbo码规范,并详细描述了标准中turbo码的关键参量,如交织器的类型、栅格终止方案、删除复用模式等等。此外,该文还采用3GPP和3GPP2所建议的标准,对turbo码在AWGN信道上传送高速数据业务时的纠错性能分别进行了仿真,并对仿真结果进行了比较。     

Multilevel turbo coded-continuous phase frequency shift keying (MLTC-CPFSK)

In this paper, we introduce a Turbo coded modulation scheme, called multilevel turbo coded-continuous phase frequency shift keying (MLTC-CPFSK). The underlying basis of multilevel coding is to partition a signal set into several levels and to encode separately each level through the respective layer of the encoder. In MLTC-CPFSK, to provide phase continuity of the signals, turbo encoder and continuous phase encoder (CPE) are serially concatenated at the last level, while all other levels consist of only a turbo encoder. Therefore, the proposed system contains multiple turbo encoder/decoder blocks in its architecture. The parallel input data sequences are encoded by our multilevel scheme and mapped to CPFSK signals. Then, for the purpose of performance analysis, these modulated signals are passed through AWGN and fading channels. At the receiver side, the input sequence of the first level is estimated by the first turbo decoder block. Subsequently, the other input sequences of other levels are computed using the estimated input bit streams of the respective previous levels. Simulation results are drawn for 4-ary CPFSK two level and 8-ary CPFSK three level turbo codes over AWGN, Rician, and Rayleigh channels for three iterations while frame sizes are chosen as 100 and 1024. It is concluded that satisfactory performance is achieved in MLTC-CPFSK systems for all SNR values in various fading environments.     

Modeling the bit-level stochastic correlation for turbo decoding

After passing a systematic bit through a turbo encoder, the encoding process will introduce some extent of correlation between a systematic bit and its associated parity bits. However, this correlation is neglected in the subsequent turbo decoding process so as to reduce its computational complexity. In this paper, we try to explore the feasibility of modeling the bit-level stochastic correlation for the iterative turbo decoding. By properly adjusting the parameter of the correlation model, we can approximate various degrees of the underlying correlation within the received codewords. Reduction in bit error rate (BER) then may benefit from a more accurate capture of the correlation information at the cost of requiring only a small additional computation complexity. Experimental results indicate that incorporating the correlation model into the turbo decoding process can achieve better BER performance than that of conventional turbo decoders over AWGN channels.     

Performance improvement in detection and estimation of MC-CDMA systems over MIMO channels

Multiple-input Multiple-output (MIMO) multi-carrier code division multiple access (MC-CDMA) is a strong candidate for the downlink of future mobile communications to obtain high data rates. Nevertheless, during any transmission over fading channel, performance of MC-CDMA systems are highly degraded due to the presence of multiple access interference (MAI). Multi-user detection (MUD) and channel estimation play a major role in overcoming MAI and characterising the channel, respectively. In this paper, space time serial interference cancellation (STSIC) detection using random and Gold codes and turbo aided iterative channel estimation (ICE) techniques are extended for MC-CDMA system MIMO channels to overcome MAI. Simulation results show STSIC outperforms optimal MUD and linear MUD techniques in mitigating MAI and turbo aided ICE surpasses ICE in characterising the channel with reduced error rates.     

Some “goodness” properties of LDA lattices

We study some structural properties of Construction-A lattices obtained from low density parity check codes over prime fields. Such lattices are called low density Construction-A (LDA) lattices, and permit low-complexity belief propagation decoding for transmission over Gaussian channels. It has been shown that LDA lattices achieve the capacity of the power constrained additive white Gaussian noise (AWGN) channel with closest lattice-point decoding, and simulations suggested that they perform well under belief propagation decoding. We continue this line of work and prove that these lattices are good for packing and mean squared error quantization and that their duals are good for packing. With this, we can conclude that codes constructed using nested LDA lattices can achieve the capacity of the power constrained AWGN channel, the capacity of the dirty paper channel, the rates guaranteed by the computeand-forward protocol, and the best known rates for bidirectional relaying with perfect secrecy.     

Robust progressive image transmission over OFDM systems using space-time block code

A joint source-channel coding (JSCC) scheme for robust progressive image transmission over broadband wireless channels using orthogonal frequency division multiplexing (OFDM) systems with spatial diversity is proposed for the application environments where no feedback channel is available such as broadcasting services. Most of current research about JSCC focuses on either binary symmetric channels (BSC) or additive white Gaussian noise (AWGN) channels. To deal with fading channels in most previous methods, the fading channel is modeled as two state Gilbert-Elliott channel model and the JSCC is normally aimed at the BER of bad channel status, which is not optimal when the channel is at good status. By using diversity techniques and OFDM, the frequency selective fading effects in broadband wireless channels can be significantly decreased and we show that subchannels in OFDM systems approach Gaussian noisy channels when the diversity gain gets large; as a result, the system performance can be improved in terms of throughput and channel coding efficiency. After analyzing the channel property of OFDM systems with spatial diversity, a practical JSCC scheme for OFDM systems is proposed. Simulation results are presented for transmit diversity with different numbers of antennas and different multipath delay and Doppler spread. It is observed from simulations that the performance can be improved more than 4 dB in terms of peak signal-to-noise ratio (PSNR) of the received image Lena and the performance is not very sensitive to different multipath spread and Doppler frequency.     

基于Turbo乘积码的SISO-OFDM系统在IMT-2000信道下的性能

综合Turbo码和乘积码的特点，介绍了宽带移动通信中的一种先进信道编码方式-Turbo乘积码的编码与译码，提出了一种新的基于Turbo乘积码的SISO（Single-Input Single-Output，单入单出）-OFDM（Orthogonal Frequency-Division Multi-plexing，正交频分复用）方案，并对某移动用户的上行链路通过IMT-2000信道后的性能进行了仿真．仿真和分析表明该系统在信噪比大于15dB时，其误码率可达到10^-6，为进一步进行MIMO（Multiple-Input Multiple-Output，多入多出）-OFDM系统的研究奠定了基础．     

具有UEP特性的LT编码方案

图像和视频文件在传输中对数据可靠性要求较高.为此,提出一种具有不等差错保护(UEP)特性的LT编码方案.研究无线信道中具有不等差错保护特性的LT码,通过增加适量重要信息比特,提高其在编码过程中被选中的概率,以实现对其保护.实验结果表明,在加性白高斯噪声和快瑞利衰落信道中,该编码方案能呈现较好的UEP特性.