立体视频图像编码的研究进展

从编码方案、关键技术和评价准则3个方面综述了立体视频图像编码研究的发展.阐明了各种编码方案的特点及适用范围.详细分析了立体视频图像编码中视差估计、运动估计、遮挡检测、残差图像编码和码率控制5大关键技术,总结了各项技术的发展现状.最后指出了立体视频图像编码研究中存在的问题,并对未来的研究方向进行了展望.     

ATM视频传输中信元丢失的分析与对策

ＡＴＭ的出现使得我们能够实时地,高效地传输视频信号,但同时在传输过程中ＡＴＭ的信元丢失将是导致解压缩后的图像质量严重下降。文章首先基于ＭＰＥＧ－２标准,给出了一个基本的视频通信系统框架及各部分的码流格式,然后分析了系统中信元丢失的原因,特点和影响。文中给出了现有的各种减少信元丢失的方法及其如何隐藏信元丢失对图像质量造成的影响,分析其优质和适用场合,并讨论了以后的研究方向。     

MC V-BLAST系统的MIMO信道盲估计

本文研究多载波垂直分层空时(MC V-BLAST)系统的下行频率选择性衰落多输入多输出(MIMO)无线信道估计问题.本文首先为MC V-BLAST系统提出了一种新颖的移不变性编码方法.利用上述移不变性性质,本文进一步提出了相应的下行频率选择性衰落MIMO无线信道的盲估计方法.仿真结果表明了本文移不变性编码方法的有效性和信道盲估计方法的性能.     

宽带网络SOQPSK突发波形

空基网络通信应用中,采用恒包络波形体制可以降低设备特别是功放的复杂度,因此高效的成形偏移四相相移键控(SOQPSK)信号非常适合于空基网络。但是机载通信中多普勒频移较大,在低信噪比和短突发条件下,SOQPSK相干接收机必须有精确的载波频率和相位同步才能获得较好的性能。针对低信噪比和短突发场景,提出了基于Turbo乘积码（TPC）编码的扩频SOQPSK宽带网络波形,并设计了导频与数据帧结构,利用译码器输出的软信息来改善载波同步的性能,通过迭代操作和联合解调、解扩,增强了系统的同步性能。仿真结果表明,在误码率为10-6时所需Eb/N0为3.65 dB,达到了波形设计指标要求。     

Cooperative secret key generation for multi-hop relaying systems in Internet of things

The achievable key rate of secret key generation method in multi-hop relaying systems was relative low in Internet of things.A cooperative secret key generation algorithm based on network coding was proposed to improve the achievable key rate.Firstly,all the nodes send training sequences in turn to estimate the channels.After that the relays employ secure network coding technique to assist the two legitimate users to obtain the correlative observations of the same wireless channel,with nothing leakage about the channel information to the eavesdropper.Finally,the two legitimate users agreed on a common secret key directly over the public channel.Theoretical and simulation results validate the performance of the proposed secret key generation algorithm,and obtain that increasing the wireless transmission paths,selecting the transmission path with less hops and larger variance channels can further improve the achievable secret key rate.     

SER‐Based Relay Selection for Two‐Way Relaying with Physical Layer Network Coding

To enhance the symbol error rate (SER) performance of the two‐way relay channels with physical layer network coding, this letter proposes a relay selection scheme, in which the relay with the maximal minimum distance between different points in its constellation among all relays is selected to assist two‐way transmissions. We give the closed‐form expression of minimum distance for binary phase‐shift keying and quadrature phase‐shift keying. Additionally, we design a low‐complexity method for higher‐order modulations based on look‐up tables. Simulation results show that the proposed scheme improves the SER performance for two‐way relay networks.     

一种基于显著不相关检验的快速分形图像编码方法

针对分形编码计算量过大的缺点,本文提出一种基于显著不相关检验的分形编码方法。对于文中的测试图像（Lenn256×256×8ppb和Boat256×256×8ppb）,其编码速度比基于子块分类的分形编码方法快2～15倍,而解码图像质量（PSNR）没有明显下降,压缩比还有一定的提高。     

一种基于Arnold置乱和DCT编码的无载体信息隐藏方法北大核心CSCD

近年来十分火热的搜索映射式无载体信息隐藏虽具有一定的鲁棒性,但其隐藏容量较低、传输负载大且算法复杂度高。针对以上问题,该文章提出一种基于Arnold置乱和离散余弦变换(discrete cosine transform,DCT)编码的无载体信息隐藏方法。该算法先对图片进行Arnold置乱,再对DCT后的低频系数进行编码,接着更换置乱参数来构建索引表。选择索引表中与秘密信息相同的编码值所对应的参数构建候选队列,最后筛选出鲁棒性强的参数作为密钥发送给接收方。实验结果表明,该方法与现有方法相比大大提高了嵌入容量,拥有更强的抗JPEG压缩性能。并且减少了传输负载,算法简捷,具有较强的应用价值。     

Adaptive depth truncation filter for MVC based compressed depth image

In multiview video plus depth (MVD) format, virtual views are generated from decoded texture videos with corresponding decoded depth images through depth image based rendering (DIBR). 3DV-ATM is a reference model for the H.264/AVC based multiview video coding (MVC) and aims at achieving high coding efficiency for 3D video in MVD format. Depth images are first downsampled then coded by 3DV-ATM. However, sharp object boundary characteristic of depth images does not well match with the transform coding based nature of H.264/AVC in 3DV-ATM. Depth boundaries are often blurred with ringing artifacts in the decoded depth images that result in noticeable artifacts in synthesized virtual views. This paper presents a low complexity adaptive depth truncation filter to recover the sharp object boundaries of the depth images using adaptive block repositioning and expansion for increasing the depth values refinement accuracy. This new approach is very efficient and can avoid false depth boundary refinement when block boundaries lie around the depth edge regions and ensure sufficient information within the processing block for depth layers classification. Experimental results demonstrate that the sharp depth edges can be recovered using the proposed filter and boundary artifacts in the synthesized views can be removed. The proposed method can provide improvement up to 3.25 dB in the depth map enhancement and bitrate reduction of 3.06% in the synthesized views.     

Performance analysis of modulation diversity with OSTBC transmission over Nakagami-m fading channels

In this paper performance of modulation diversity with multiple-input multiple-output transmission is studied over flat Nakagami-m fading channels with arbitrary fading parameter m. In the system, orthogonal space-time block coding and maximal ratio combining like combiner are used for transmission and reception, respectively. Exact pairwise error probability expression is derived to observe performance of the system. Moreover, in order to obtain the diversity order of the system, asymptotic pairwise error probability expression is also derived. Optimum rotation angles are analytically obtained for binary and quadrature phase shift keying modulations. Theoretical results are validated by Monte Carlo simulations.