一种自适应线性分散码方案的性能研究

针对线性分散码复杂度较高的问题,提出一种自适应线性分散码(ALDC),并将其应用于协作通信网络.该码可以根据当前信道状态,自适应地选择不同的调制阶数和分散矩阵,以在不同信噪比下获得最优的误码率性能,同时降低译码复杂度.分析了该码在协作系统中的编码与译码,并在误比特率性能上与传统空时分组码和LDC进行了仿真对比.结果表明,ALDC的误码率性能要优于传统的正交空时分组码和LDC,且译码复杂度较低.     

分组相关快衰落信道下自适应Turbo码译码算法研究

分析了分组相关快衰落信道的特性，推导出该信道下Turbo码译码算法；研究了迭代次数对Turbo编码系统的影响，在小信噪比弥散度条件下，提出基于平均信噪比的最佳迭代译码次数自适应选择方案，可以兼顾译码性能和译码速度，得到较低的平均误比特率和较高的平均译码速度。仿真结果说明，本文提出的Turbo码译码算法，降低了对信道估计精度要求的同时，得到精确信道估计时的性能；对于目标误比特率为10^-4时，采用自适应Turbo译码算法，与固定迭代4次相比，平均误比特率降低了40％，提高了系统性能；而与固定迭代8次相比，迭代次数降低了约1／4，提高了译码速度。     

基于LDPC码的BICM系统性能分析

低密度校验码(LDPC)由于其编码增益高、译码速度快、性能接近香农限的优点,目前得到学术界的广泛关注.文中简单介绍了LDPC码及其译码算法,在此基础上结合比特交织编码调制(BICM)系统,并在算法上作出了相应改进.仿真结果表明,在高斯信道、充分交织瑞利信道、相关瑞利衰落信道下,此算法正确有效.     

基于LDPC码的超短波高速数传系统性能研究

为满足超短波高速数传系统的性能要求,对发送序列进行LDPC编码,并选取修正最小和译码算法进行译码。通过自适应均衡技术消除多径干扰,并将接收机分为DFE均衡器和LDPC译码器两部分。基于Matlab仿真平台,构建超短波高速数传系统仿真模型,对典型VHF信道模型下的传输性能进行仿真及分析。仿真结果表明,准循环LDPC码在中高码率下仍能获得较大的编码增益,基于LDPC码的超短波高速数传系统可获得优异的传输性能,具有良好的工程应用前景。     

LDPC码在浅海水声通信中的应用研究

LDPC码具有编码增益高、译码速度快、可并行译码等特点,是当前编码界的一个研究热点。针对复杂多变、强多途和大起伏干扰的浅海水声信道,建立了LDPC码在浅海水声信道中仿真的模型,仿真研究了浅海水声信道下采用和一积译码算法的LDPC码性能。仿真结果表明,LDPC码在3径多途信道下性能优越;当译码迭代3—5次,码长1000bit左右时基本上能满足水声通信对误码率为10^-4的基本要求。     

QC-LDPC码在光纤通信中非对称高斯模型下译码性能分析

QC-LDPC(伪循环-低密度奇偶校验)码在AWGN信道下具有优异的性能,但是在光纤信道下,信道模型不是AWGN模型,而是非对称高斯模型,将QC-LDPC码应用在光纤信道的非对称高斯模型下,若想取得最优的性能,需要修正相应的译码方法。给出了在非对称高斯模型下的修正译码方法,并对算法进行了仿真。仿真结果表明,对译码算法修正后,QC-LDPC码在非对称高斯下能够取得较好的译码性能,在误码率BER为10-6,相对未编码系统,能够获得约7dB净编码增益。同时在非对称高斯模型下译码性能要优于在AWGN模型下译码性能。     

信源反馈条件下Raptor码的一种解码算法

在Raptor码普通译码方法的基础上,结合信源信道联合译码方法,提出一种利用信源解码器反馈信息作为输入的改进译码的算法,并对此算法进行试验仿真以及参数研究。测试结果显示,在信源信道联合编码条件下,使用这种双信息来源的译码的算法,可以使得信道解码的成功率大幅提高,残留误码率大幅降低。最后,将这种算法与JPEG2000信源编码结合测试,图像的PSNR值比普通译码方法最高提高了6dB。在信道条件恶劣的无线传输中具有重要意义。     

紫外光通信系统Turbo码译码性能研究

针对紫外光通信信道的特殊性,采用当前优异的信道编码技术Turbo码进行编码,利用Matlab软件,在瑞利衰落信道务件下,仿真分析不同Turbo码译码算法对译码性能的影响,发现在相同条件下,Log-MAP算法性能好于SOVA算法.这为Turbo码在紫外光通信系统中的应用提供了一定的理论基础.     

Turbo码自适应编码调制和盲识别

讨论了在平缓衰落信道中Turbo码自适应编码调制和盲识别方法。在发送端,根据反馈的信道状态自适应调整Turbo码编码器的编码方案、调制指数M以及传输功率。接收端则采用调制指数盲识别方法进一步提高信道的利用率。根据要求的误码率和给定的平均功率,采用相应的自适应编码调制和自适应分区方法,可改善系统的平均吞吐量。仿真结果表明,所提出的Turbo码自适应编码调制和盲识别方案可使系统的平均吞吐量有很大的提高。     

低莱斯因子衰落信道下的Turbo码性能研究

基于Turbo码编译码技术,在Rician衰落信道模型下,详细研究了Turbo码Log-MAP译码算法和SOVA译码算法在低Rician因子衰落信道下的性能,并结合调制技术对整个编译码系统进行Matlab仿真。仿真结果表明,在低Rician因子信道下,Log-MAP译码算法的性能优于SOVA译码算法。     

信道自适应UEP技术在H.264视频通信系统中的应用

在进行基于H．264标准的视频通信系统设计时，为提高编码视频流的抗误码性能以及编码器的编码效率，提出了一种信道自适应非平等误码保护(UEP)技术。该技术可根据反馈的信道状态信息自适应地确定H．264编码视频流在网络适配层(NAL)中的工作模式，在丢包信道中结合人眼的视觉特性重新对编码视频信息进行分区并分别采用不同优先级的误码保护。仿真实验表明，在有效提高H．264视频通信系统中解码器输出重构视频图像视觉质量的同时，进一步降低编码器端数据包的打包开销，从而提高编码器的编码效率。     

Channel adaptive CQI reporting schemes for HSDPA systems

HSDPA (high-speed downlink packet access) is an evolved UMTS packet scheme that delivers increased user peak data rates and quality of service. A key technique supporting HSDPA is adaptive modulation and coding (AMC), in which the modulation scheme and the coding rate are changed adaptively according to the downlink channel quality reported by the user equipment (UE). Therefore, the channel quality indication (CQI) reporting scheme is directly related to the accuracy of AMC and the performance of HSDPA. This letter proposes channel adaptive CQI reporting schemes in which UEs report the CQI value intelligently by using information about channel quality. With the proposed schemes, the battery capacity of UE can be conserved and the uplink interference can be lowered by filtering off redundant CQI reports or the transmission error rate can be lowered by fast CQI reports.     

An enhanced channel-quality indication (CQI) reporting scheme for HSDPA systems

A major evolution of UMTS standard is the high speed downlink packet access (HSDPA). One of key techniques supporting HSDPA is the adaptive modulation and coding (AMC) in which the modulation scheme and the coding rate are adaptively changed according to the downlink channel quality reported by the user equipment (UE). Therefore, the channel quality indication (CQI) reporting scheme is directly related to the accuracy of AMC and the performance of HSDPA. This letter proposes an enhanced CQI reporting scheme that can be used when a proportional fair scheduling algorithm (PFA) is used as a packet scheduling algorithm. The proposed scheme uses a dynamic threshold to filter off redundant CQI reports. With the proposed scheme, the battery capacity of UK can be conserved, maintaining the performance of traditional CQI reporting scheme.     

一种基于NACK的HSDPA自适应信道质量反馈技术

作为一种B3G技术，HSDPA已经受到广泛的关注，该技术可以提供高速的分组下行数据传输。其关键技术包括AMC，HARQ，FCS等。在HSDPA系统中，其调制方式和编码可以随着下行链路的质量状况自适应改变。因此，信道质量反馈就直接影响AMC的准确度和系统的性能。本文介绍了TD—SCDMA模式下HSDPA中CQI的工作机制和一种基于NACK的自适应信道质量反馈技术。     

一种基于滑动窗的自适应帧率控制策略

主要针对H.264/AVC视频编码技术,提出了一种基于滑动窗的自适应帧率控制策略,用来提供更好的编码效率.不同于常用的时域均匀下采样帧率控制策略,该策略采用滑动窗技术以及帧间MAD实时侦测视频序列的运动情况,并相应地改变跳帧间隔,从而达到自适应的帧率控制.最后将该方法与均匀间隔下采样的帧率控制技术在采用H.264/AVC视频编码技术和CBR信道的情况下进行了比较实验,验证了该策略具有更好的编码效果.     

基于纠错算术码的信源信道自适应联合编解码系统

对信源信道自适应联合编码方法进行了研究,提出了一种新的基于纠错算术码的联合信源信道编解码系统。该系统在编码端利用算术码内嵌禁用符号实现信源信道一体式编码,即利用马尔科夫信源模型和根据信道状态信息自适应地调整禁用符号概率大小从而调整编码码率来实现信道自适应;在解码端,推导出了基于MAP的解码测度数学公式并基于此测度公式提出了一种改进的堆栈序列估计算法。与传统的信道自适应编码算法不同,该自适应编码算法只需调整一个参数:禁用符号,且理论上可获得连续可变的编码码率。实验结果表明,与经典的Grangetto联合编码系统以及分离编码系统相比,所提出的编码系统具有明显改善的性能增益。     

一种基于H.264/AVC 的数据自适应不平等保护策略

根据H.264标准的数据分类功能,提出了一种自适应的数据不平等保护策略.该策略能根据反馈回来的信道状态和解码信息,自适应地调整H.264视频码流各分类区的信道码率.试验结果显示,该策略能有效地提高视频码流的误码鲁棒性.     

Non‐binary type‐II HARQ and its application to an adaptive system

Non‐binary type‐II hybrid ARQ (HARQ), which combines shortened Reed–Solomon (RS) code with ARQ, is proposed. Its throughput is obtained by extending Lin and Yu's analysis of binary type‐II HARQ. The reliability and average delay are also obtained. The analytical results show that non‐binary HARQ outperforms its binary counterpart in throughput, reliability and average delay when proper RS codes are selected. Non‐binary HARQs are applied adaptively in a cellular phone system with uniformly distributed mobile terminals (MTs). MTs switch adaptively between two different hybrid schemes according to the average SNR of the received signals. The adaptive parameters include the size of the modulation constellation, the error‐correction coding and their joint adaptation. Numerical results show that the adaptive scheme always outperforms its non‐adaptive counterparts, and the adaptive modulation scheme is superior to adaptive coding and the joint adaptation scheme when the implementation complexity is a limiting factor. Robustness analysis shows that introducing a mixed modulation scheme in addition to QPSK and 8PSK in the adaptive modulation scheme is unnecessary, and HARQ with adaptive modulation is insensitive to deviations from the optimal threshold, thus facilitating its implementation. Copyright © 2004 John Wiley & Sons, Ltd.     

Adaptive stochastic iterative rate selection for wireless channels

A stochastic algorithm for channel adaptive rate selection (modulation and coding scheme or MCS) is proposed. The algorithm learns the optimal policy by iteratively augmenting a rate selection probability vector. While simple to implement, this technique requires no explicit channel estimation phase. The single bit ACK/NACK signal feedback from the data link layer is used as the input to the stochastic algorithm. As shown in the convergence theorems, the algorithm achieves the optimal rate in "static" channels. A time varying channel is seen as a "quasi-static" channel, and adaptively converged to optimal rates as channel state changes.     

Partial channel information feedback mechanism for FFR-based multi-channel systems

This article puts forward a partial channel state information(CSI) feedback scheme for fractional frequency reuse(FFR)-based orthogonal frequency division multiple access(OFDMA) systems.Efficient CSI feedback strategy plays an important role in opportunistic scheduling because base station(BS) can employ adaptive modulation and coding(AMC) technique to adaptively change transmission rates according to CSI feedback,and therefore the spectrum efficiency can be improved significantly.On the other hand,FFR is a...