RCPT码及其在移动通信中的应用

由于无线信道的时变、高误码等特性，要求信道编码方式有较强的抗误码能力，而且能够自适应无线信道状态的变化。码率匹配删余Turbo码（RCPT）能实现这样的编码要求，并且能提供适应不同需要的不等差错保护（UEP）。介绍了RCPT码在移动通信中的应用，讨论了新的自适应编码调制及不等差错保护方案。     

信源信道联合编码技术用于AVS传输的研究

针对误码信道和信源编码的统计特性,提出了一种基于AVS视频序列的联合编码技术,按照重要性对AVS视频层序列码流进行分组重排,信道编码器根据码流信息对其进行比重不等的保护措施,以较低复杂度的运算实现了码率的优化分配.实验表明,与现有的等差错保护相比,在高误码信道中能有效提高AVS码流抗误码性能.     

一种基于联合信源信道自适应的不等错误保护方法

针对误码信道和信源编码的统计特性,提出了一种能有效提高基于DCT变换的视频编码码流的抗误码性能的自适应不等错误保护方法.它基于信道误码的反馈信息,选择DCT的量化参数q和信道编码码率,并进行DCT重排和VLC编码,再对数据流进行不等差错保护.通过实验证明,它在高误码信道中性能优于EEP等.     

无线视频传输中的信源信道联合编码的研究

文章在研究信源信道联合编码方法的基础上,介绍了信源信道联合编码的产生背景、研究意义、应用环境,指出了信源信道联合编码在通信系统中的实际应用。结合编码码流的自身特点,给出了一种以图片组为单位的码流重要性模型,并根据此模型使用不同码率的Turbo码对H.264编码码流进行不等差错保护。     

基于LDPC码率自适应的HARQ系统

在对LDPC码及常用的不等差错保护策略分析的基础上,提出了一种新的码率调整策略,并对该策略的BER和迭代性能进行了分析,证明了其有效性.在该策略的基础上设计了一种基于不等差错保护方法的结合SPIHT和LDPC码的HARQ无线图像传输方案,通过计算机仿真表明该系统的能够起到较好的图像传输保护效果.     

无线衰落信道中H.264视频流的可靠传输

本文提出了一种无线衰落信道中进行H.264视频传输的不等差错保护方案.这种方案通过对视频流的不同重要性的部分进行不同码率的删余卷积信道编码和一种特殊的重传机制来实现不等差错保护机制.仿真结果显示,该方案可以有效改善视频传输的性能,提高视频传输的鲁棒性.     

基于联合信源信道编码的无线图像传输策略设计

针对图像数据在无线信道传输中存在的可靠性与稳定性较差等问题，提出了一种自适应不等差错保护的联合信源信道编码方案。采用基于小波变换的信源编码对原始图像数据进行压缩处理，并对生成的码流进行重要程度划分；基于LDPC码对划分好的码流数据采取不同等级的差错保护措施；最终，反馈信道状况信息给信道编码器并进行码率的自适应调整，从而实现高质量的图像信号传输。仿真实验结果表明，提出的算法具有更高的峰值信噪比(PSNR),相比EEP算法及DE-UEP算法，其PSNR值有0.2～0.4 dB的提升。     

基于抗差错算术编码的不等差错保护图像传输方法

JPEG2000图像的分层特性要求采用不等差错保护方法以实现高效传输,本文提出了一种新型的不等差错保护方法,对不同位平面采用不同码率的抗差错算术码进行编码.与基于信道编码的不等差错保护方法相比,该方法保持了压缩码流的结构,避免了复杂的信道成帧过程.与已有的基于抗差错算术码的等差错保护方法相比,该方法提高了传输图像的质量.     

LDPC和SPIHT联合编码用于图像压缩与保护的方法

提出了结合SPIHT（set partitionine in hierarchical trees）算法和LDPC（Low-Density Parity-Check）码的信源与信道联合编码方案。这一方案充分考虑了SPIHT算法和LDPC码的特性，根据信源编码后数据在重建时的重要程度，进行不同等纠错保护的信道编码方案。通过实验仿真的结果表明，论的方法能够使图像在高码率下达到较好的抗噪性能。     

基于并行级联LDPC码的递增冗余HARQ方案及性能分析

并行级联LDPC码是由多个码率不同的子码,经并行级联后得到的码率可变的LDPC码.本文提出了基于并行级联:LDPC码的递增冗余HARQ方案,给出了这种方案的吞吐量性能封闭解.在AWGN信道和Rayleigh衰落信道下,通过仿真将新方案的性能和随机LDPC码的性能进行了比较.结果显示,并行级联LDPC码的递增冗余HARQ方案性能接近随机LDPC码,但编、译码更简单,参数选择范围更广.     

Adaptive Opportunistic Multicast Scheduling Over Next-Generation Wireless Networks

This paper considers the problem of opportunistic multicast scheduling in wireless time-division multiplexing systems with adaptive modulation and channel coding. The problem is first formulated and an effective scheduling scheme is proposed to maximize the multicast throughput while a desired packet error rate is guaranteed. The proposed scheme dynamically selects multicast rates by considering the configuration of the multicast group and instantaneous network states, and thus it can adapt well to network conditions. Extensive simulation results conclusively demonstrate that, compared to the worst-user multicast scheduling, the proposed approach can increase the wireless channel efficiency by large margins, especially when the channel is operating in a lower signal-to-noise ratio region and/or when the multicast group size increases. Besides, the simulations show that the proposed approach can work well in systems with imperfect channel estimation.     

Multistage decision-directed channel estimation scheme for DS-CDMAsystem with M-ary orthogonal signaling

A multistage decision-directed channel estimation scheme is proposed for a coherent direct-sequence code-division multiple-access (DS-CDMA) system with M-ary orthogonal signaling. The receiver with a multistage decision-directed channel estimator makes alternate use of symbol detection and channel estimation in an iterative manner, resulting in a multistage structure where each stage consists of an estimator and a detector. The estimator obtains the estimates of the channel by using the decisions from the detector in the previous stage, and the detector uses these estimates for coherent detection of the transmitted symbols. Modifications to the process of generating the channel estimates and the decision variables are made to mitigate the error propagation in successive stages. It is shown that the performance of the proposed estimation scheme is better than the conventional scheme, especially for channels with high diversity order. The gain is mostly achieved by two stages for channels with low diversity order and by five stages for channels with high diversity order. The proposed scheme can be used to increase the capacity of DS-CDMA systems currently operating in such environments     

Antenna selection and power control in MIMO systems with continuously varying channels

Existing limited feedback methods for Multiple- Input Multiple-Output (MIMO) systems focus largely on block fading conditions whereas, in practice, channels change continuously over time. In this paper, we investigate adaptive transmission over a continuously varying channel (CVC). A combination of Kalman channel tracking, truncated channel inversion (TCI) antenna selection, and power control, is used to achieve bit error rates that are lower than those obtained with existing schemes. Using Kalman filtering for pilot-based channel tracking as well as decision-directed channel tracking, our scheme achieves about 3.6dB gain over the eigen-mode antenna selection scheme and 1.5dB gain over the unitary precoding scheme, when operating at a BER of 10?5.     

Iterative estimation of doubly selective channels with ICI suppression for OFDM using KL-BEM

Channel estimation for orthogonnl frequency division multiplexing(OFDM)systems operating over doubly selective channels is complicated by the existence of intercarrier interference(ICI).This paper extends the idea of estimating time-variant channel impulse response(CIR)via time-averaged CIR.proposed by Hijazi,and proposes a low-complexity channel estimation scheme with ICI suppression based on Karhnnen-Loeve basis expansion model(KL-BEM),which is in a more general form.In the proposed scheme,the KL-BEM coefficients are obtained through their numerical relationship with the time-averaged CIR.The estimation performance is improved by adopting an expectation-maximization(EM)-based iterative structure combined with a low-complexity ICI equalizer and canceller.Theoretical analysis and simulation results show that the proposed scheme achieves superior performance over the original one with lower computational complexity.     

无线信道中的联合信源信道编码

该文提出了一种噪声信道下传输渐进图像的联合信源信道编码方法。该方法根据信道条件的好坏动态的调整信源编码速率和信道编码速率，因此极大地提高了系统的性能和编码效率。同时该方法还具有结构简单，易于实现等优点。试验证明本方法与以前文献中提出的EEP方法以及UEP方法相比，在信噪比低时即信道条件恶劣的情况下，能够明显提高恢复图像的质量。     

时间-频率双选择性衰落信道的最小二乘估计方法

高速移动下的无线宽带通信要经历时间和频率双选择性衰落,信道估计质量的好坏对整个系统的性能有重要的影响。该文利用复指数基扩展模型,提出一种基于最小二乘的时频双选信道估计方法,接收机不需要信道的统计信息,也不需要预先估计噪声方差,接收机复杂度较低;在该信道估计算法的基础上,基于信道估计均方误差最小准则,分析并推导出优化的训练序列所要满足的条件。仿真结果表明,在由Jakes模型产生的时频双选衰落信道下,在一定的信噪比范围内,该文方法的信道均方误差性能优于现有的方法。     

Channel Selection for Spectrum Sharing in Wireless Networks

In this paper, we study a spectrum sharing network (SSN) where a spectrum sharing device (SSD) coexists with multiple wireless communication systems (WCSs) in the same channel. The SSD can operate with either a duty cycle (DC) channel access mechanism or a listen‐before‐talk (LBT) channel access mechanism, whereas WCSs operate with an LBT mechanism. An opportunistic channel selection scheme for the SSD in the SSN is first proposed to minimize the outage probability. The optimal data transmission time for the DC‐based SSD is derived to further improve the outage probability. We also derive the exact and closed‐form outage probability of the proposed channel selection in the SSN by assuming that the number of WCSs operating in each channel is uniformly distributed. The simulation results show that the proposed channel selection scheme outperforms other channel selection schemes. It was also observed that a DC‐based SSD with an optimal data transmission time provides a better outage performance than an LBT‐based SSD. As the number of available channels increases, the channel selection scheme plays an important role in minimizing the outage probability of the SSNs.     

A 20 Gb/s triple-mode (PAM-2, PAM-4, and duobinary) transmitter

Increasing data rates over electrical channels with significant frequency-dependent loss is difficult due to excessive inter-symbol interference (ISI). In order to achieve sufficient link margins at high rates, I/O system designers implement equalization in the transmitters and are motivated to consider more spectrally-efficient modulation formats relative to the common PAM-2 scheme, such as PAM-4 and duobinary. This paper reviews when to consider PAM-4 and duobinary formats, as the modulation scheme which yields the highest system margins at a given data rate is a function of the channel loss profile, and presents a 20 Gb/s triple-mode transmitter capable of efficiently implementing these three modulation schemes and three-tap feed-forward equalization. A statistical link modeling tool, which models ISI, crosstalk, random noise, and timing jitter, is developed to compare the three common modulation formats operating on electrical backplane channel models. In order to improve duobinary modulation efficiency, a low-power quarter-rate duobinary precoder circuit is proposed which provides significant timing margin improvement relative to full-rate precoders. Simulation results of the proposed transmitter in a 90 nm CMOS technology compare operation with the different modulation schemes over three backplane channels with different loss profiles.     

Progressive transmission of images over fading channels using rate-compatible LDPC codes.

In this paper, we propose a combined source/channel coding scheme for transmission of images over fading channels. The proposed scheme employs rate-compatible low-density parity-check codes along with embedded image coders such as JPEG2000 and set partitioning in hierarchical trees (SPIHT). The assignment of channel coding rates to source packets is performed by a fast trellis-based algorithm. We examine the performance of the proposed scheme over correlated and uncorrelated Rayleigh flat-fading channels with and without side information. Simulation results for the expected peak signal-to-noise ratio of reconstructed images, which are within 1 dB of the capacity upper bound over a wide range of channel signal-to-noise ratios, show considerable improvement compared to existing results under similar conditions. We also study the sensitivity of the proposed scheme in the presence of channel estimation error at the transmitter and demonstrate that under most conditions our scheme is more robust compared to existing schemes.     

Inter-Frame, Fine Frequency/Phase Synchronization forSimple Space-Time-Coded OFDM Receivers

This paper proposes an enhanced receiver (Rx) configuration for multiple-input, multiple-output (MIMO) OFDM systems, operating under the composite effect of phase noise (PHN), residual frequency offset (RFO) and the transmission channel, herein modeled as quasi-static but unknown. The proposed Rx identifies the different impairments by exploiting their different time constants and compensates for each one accordingly. It includes a novel inter-frame fine frequency synchronization (FFS) scheme, which is closely coupled to an intra-frame adaptive phase synchronizer/channel estimator. The proposed scheme is evaluated for a 2 times 2, Alamouti space-time code (STC), and is shown to provide significant performance gain. The theory can be employed with any other STC scheme.