不等长信源的符号约束MAP联合译码算法

由于不等长编码信源（VLCs）所固有的易于误码扩散的弱点,传统的纠错编码并不能高效地解决其差错控制问题。提出了一种新的针对不等长编码信源的符号约束MAP联合译码算法,利用VLCs双树信源的构造方法,有效地抑制了VLCs的错误扩散;同时,通过将“符号约束”的思想应用于最大后验概率（MAP）译码算法,不仅充分利用了信源先验信息,而且极大地降低了误符号率。实验结果表明,在误符号率为1%时,对于在高斯加性白噪声（AWGN）信道传输情况下的JPEG信源,提出的算法比传统的“比特约束”MAP译码算法有将近0.8 dB的性能增益。     

Joint source-channel coded multidimensional modulation for variable-length codes

Resource-constrained networks such as deep space communications and mobile communications have the phenomena such us large-scale path loss,small-scale fading,and multipath effect,which are very hostile for information transmission.Combining Shannon’s source-channel coding theory with multidimensional modulation,an en/decoding method is proposed in this article called variable-length symbol-level joint sourcechannel and multidimensional modulation.Utilizing symbol-level source a priori information,an optimized symbol-level L-dimensional M-ary phase shift keying(LD-MPSK)constellation mapping function has been derived,which can increase free Euclidean distance between modulated symbols and enhance the decoding performance.It has been shown in the simulation results that the proposed scheme can achieve more than 2 dB signal-to-noise ratio gains compared with the conventional bit-level schemes under the condition of the same error rate.     

Joint source channel VL coding/decoding for deep space communication networks based on a space trellis

This paper presents joint source channel variable length (VL) coding/decoding based on a space trellis.Through constructing a joint decoding plane trellis,better decoding performance can be achieved than by using the bit-level decoding algorithm.However,the plane trellis is complicated,which results in high decoding complexity for decoding VL turbo codes.To solve this problem,we construct a space trellis and design a low-complexity joint decoding algorithm with a variable length symbol-a posteriori probabil...     

H．324中的双速率语音编／解码器算法分析及实现

分析了H．324标准中G．723．1双速率语音编／解码算法的基本原理，通过基于PC机环境的实时语音压缩软件的设计，对该算法的工程化实现与测试进行了探索。     

H.264/AVC中CAVLC编码器的硬件设计与实现

设计了一种H.264标准的CAVLC编码器,对原有软件流程进行部分改进,提出了并行处理各编码子模块的算法结构。重点对非零系数级(level)编码模块进行优化,采用并行处理和流水线相结合的结构,减少了cavlc编码的时钟周期,提供了稳定吞吐量。采用Xilinx公司VirtexⅡ系列的xc2v250 FPGA进行实现验证,最高时钟频率可达158.1 MHz,可满足实时编码H.264高清视频要求。     

基于DSP的甚低速率语音编码算法及其实现

在混合激励线性预测(MELP)算法的基础上,设计一种1 120 b/s MELP甚低速率语音编码算法。该算法通过增加帧长、动态比特分配和多帧联合矢量量化、及参数内插等方法降低语音的编码速率,并已在TMS320VC5416DSP芯片上实时实现。采用美国GL公司的语音质量评估系统VQT,对编解码的实时语音质量进行评估,语音质量感知评价高于3分。实验结果表明,该算法能够满足实际通信要求。     

Extraction of media and plaque boundaries in intravascular ultrasound images by level sets and min/max flow

Abstract: Estimation of the plaque area in intravascular ultrasound images after extraction of the media and plaque–lumen interfaces is an important application of computer‐aided diagnosis in medical imaging. This paper presents a novel system for fully automatic and fast calculation of plaque quantity by capturing the surrounding ring called media. The system utilizes an algorithm that consists of an enhanced technique for noise removal and a method of detecting different iso levels by sinking the image gradually under zero level. Moreover, an important novelty with this technique is the simultaneous extraction of media and lumen–plaque interfaces at satisfactory levels. There are no higher dimensional surfaces and evolution of contours, stopping at high image gradients. Thus, the system runs really fast with curvature velocity only and has no complexity. Experiments also show that this shape‐recovering curvature term not only removes the noisy behaviour of ultrasound images but also strengthens very weak boundaries and even completes the missing walls of the media. In addition, the lumen–plaque interface can be detected simultaneously. For validation, a new and very useful algorithm is developed for labelling of intravascular ultrasound images, taken from video sequences of 15 patients, and a comparison‐based verification is done between manual contours by experts and the contours extracted by our system.     

拥塞／速率控制算法及其在多媒体数据传输中的应用

基于Internet的以UDP为传输协议的实时多媒体数据传输,需要在保证实时性和可靠性基础上,能够与Internet其他服务所使用的TCP协议合理共享有限的带宽,在研究多种拥塞控制算法的基础上,提出了一种简单实用的TCP友好拥塞／速率控制算法,并将该算法应用在一个实用的IP电话软件中,取得了预期的效果。