适用于ATM网络的信噪比可分级变码率视频编解码方案

提出一种适用于ＡＴＭ网络的两层信噪比分级变码率视频编解码方案。编码的基本层是一个ＭＰＥＧ－２ＭＰＭＬ定码率编码器，增强层对基本层的量化误差进行细量化和变码率编码。     

减少码率变换再量化误差的优化方案

阐述了码率变换再量化过程中再量化误差的产生及其实质，给出了应用最小均方误差（MSE）准则减少再量化误差的原理，在码率变换再量化器一端，根据首次量化值在量化区间的概率分布中心决定该量化值的区间，有效地消除了量化区间跨区交叠所引入的再量化误差，给出了减少再量化误差方案的实现步骤。实验和模拟结果均表明：该方案有效地减少了再量化误差，获得了较好的图像质量。     

H.263甚低码率视频编码标准的码率控制方法

主要提出ＩＴＵ组织的Ｈ．２６３甚低码率视频压缩编码标准输出码率的控制方案。着重分析了一种通过调整宏观量化器的量化参数来控制Ｈ．２６３编码器输出码率的方法,它能满足在ＰＳＴＮ网上低时延中的码率输出要求。     

一种H.264视频编码码率控制方法

根据视频编码线性率失真函数和对H．264整数变换量化方法分析，提出一种适合于H．264编码算法的码率控制算法。先验证线性率失真函数对H．264编码算法的适用性，再通过将H．264整数变换的量化分解为系数校正和统一量化两个步骤实现了线性率失真函数在H．264码率控制中的应用。实验证明，与JVT—G012码率控制算法相比，码率控制的准确性和信噪比均有所提高。     

34Mbit/s码率的彩色电视信号DPCM分量编码

本文介绍一种彩色电视信号DPCM分量编码方案,它可以用34Mbit/s的码率传送一路广播质量的节目。量化器的设计利用了视觉的掩盖效应。亮度预测器的设计考虑了预测器和量化器间的相互作用,比MMSE预测器节省量化电平。采用定长编码,方案比较简单易行。     

不同量化比特数对超高清图像质量损伤的影响研究

通过挑选比较严格的超高清视频测试序列,采用x264压缩编码软件,计算量化比特数为10和8的各序列在不同码率下的PSNR值,以此来研究不同量化比特数对超高清图像质量损伤的影响。由实验数据得出,同一序列在同一码率下,量化比特数为10相比量化比特数为8的序列的PSNR高0.7 dB左右,也即量化比特数为10的序列相对量化比特数为8的序列码率节省5%~20%左右。     

基于图像特征的视频编码码率控制策略

根据缓存器的状态和信道速率，为待编码帧在图像层上预分配目的编码比特数，并使用小波变换系数来表征图像特性，继而为帧内每一具体宏块选定量化因子，提出了基于图像特征的码率控制策略。仿真结果表明，该码率控制策略能有效地避免缓存器出现上、下溢的情况，并使输出码率趋于稳定。     

一种改进的基于柯西模型的H.264码率控制方法

H.264/AVC编码中的码率控制是通过有效控制输出码流的码率来提高其压缩视频质量的重要技术。本文基于H.264/AVC中的JVT-H017码率控制方案提出了一种改进算法。新算法根据H.264中DCT系数的分布特征,将柯西分布引入到码率控制模块,用更精确的柯西率失真模型取代了原先的二次率失真模型。在此基础上,进一步引入了一种联合PSNR比率和MAD比率进行图像复杂度预测的方法,并依此来调整帧级比特的分配和量化参数,克服了在出现复杂运动或场景切换时,因视频序列相邻帧之间相关性降低而导致的MAD预测失准的情况。实验结果表明,与JVT-H017方案及文献[5]中的算法比较,新的算法不仅具有更精确的码率控制,而且明显改善了输出码率的平稳性及重建图像的PSNR。      

不同码率下自适应压扩量化图象预测编码的性能

本文在笔者提出的一种量化方法基础上研究了自适应压扩量化DPCM(ACQ—DPCM)系统在不同码率下的性能并与相同码率的基本DPCM系统的性能进行了比较。结果表明,由于量化特性与预测误差更好地匹配,ACQ——DPCM的量化信噪比较基本DPCM获得明显改善。其改善程度在1.2—8.8dB。码率愈低,改善程度愈好。在相同码率条件下,对边沿,细节丰富的图象改善较佳,且图象恢复误差峰值普遍降低。     

MPEG-2码率控制中的q域和p域分析

介绍了在MPEG编码中以量化步长q为参数来进行的传统的码率控制，即q域的码率控制算法；然后提出了以传输矩阵中零的百分比p为参数进行率函数的分析；最后基于p-q映射方法提出了p域分析的码率控制算法。     

Combined power and rate adaptation for wireless cellular systems

We extend the throughput optimization technique of Qiu and Chawla (1999) for adaptive modulation, to combine power and rate adaptation in wireless cellular systems. We develop new combined power and rate control algorithms for wireless multimedia systems, in which the transmitted powers and rates of different media users are adapted based on the signal-to-interference power ratio. Using simulations, we show that with appropriately chosen power and rate limits, our proposed combined power and rate control algorithms can achieve a higher throughput when compared to previously proposed algorithms with power control only.     

采用数据扩展技术在OFDM系统中实现不等错误保护传输

本文提出了采用数据扩展技术在正交频分复用（OFDM）系统中实现不等错误保护（UEP）传输的自适应调制算法。利用原始数据符号传输特性相同的特点,分别研究了以提高信道容量为目标,功率一定,最大化传输速率的不等错误保护UEP算法;以及以用户需求为目标,传输速率一定,最小化总功率的不等错误保护UEP算法。这两种算法均可根据待传输数据的要求,保证不同优先级数据的不同传输质量和不同传输速率。仿真结果表明,最大化传输速率UEP算法可以在速率最大化的同时,保证传输质量要求;最小化总功率UEP算法可以在最小化发射功率的前提下,保证传输质量要求。与传统OFDM系统中相应算法的比较结果可以看出,采用数据扩展技术可以大大降低算法复杂度,减少有关调制参数信息的传输,在实现UEP时,在性能和复杂度之间具有较好的折中,具有较高的实际应用价值。      

采用DOE方法优化非晶硅溅射工艺

文中通过使用DOE实验设计方法对磁控溅射设备a-Si靶工艺特性进行能力研究,给出了该设备工艺随功率、压力、温度的设定条件下a-Si介质生长速率与均匀性的变化关系。结果表明,功率和压力是主要决定速率和均匀性的关键因素,基片温度从室温到300℃,a-Si淀积速率基本不变。降低工艺压力对改善均匀性最为明显;工艺温度和功率的降低虽也可以起到改善均匀性的作用,但效果不明显,且三者的变动同时会导致速率的变化,为今后的生产、开发应用提供了参考意见。     

时延约束条件下CDMA系统中基于博弈论的多小区功控算法

本文采用博弈论研究了多小区CDMA功率控制问题。证明了在时延约束条件下联合考虑功率和速率控制的纳什均衡的唯一性,提出了多小区的速率和功率更新算法。仿真表明,本文提出方法可以满足不同用户对速率和时延的不同要求,且系统中各个用户的吞吐量和数据的发送速率有了大幅度的提高。     

Congestion relief on power-controlled CDMA networks

A digital cellular radio code-division multiple-access (CDMA) system can only support a finite number of users before the interference plus noise power density, I₀, received at the cellular base station causes an unacceptable frame-error rate. Once the maximum interference level is reached, new arrivals should be blocked. In a power-controlled CDMA system, the base station can direct mobiles to reduce their power and data rate to reduce interference and allow more users on the system. This approach is employed in TIA IS-95 with respect to the time-varying voice activity on cellular voice channels. We investigate an alternative technique where we adjust the power and data rate of mobile data users to the time-varying interference level to allow more users on a congested system. This scheme was simulated for various proportions of voice and data users and offered traffic levels. Blocking probabilities are reduced in some cases by two orders of magnitude. Message wait time, now a random variable, may exceed the wait time for a constant rate system at high traffic levels. If the cellular carrier has a maximum blocking requirement, an adaptive rate/power system can increase the capacity. For example, a base station that normally supports 26.4 Erlangs offered traffic with 2% blocking can support 33.5 Erlangs with the same blocking probability if adaptive rates and power control are used. Thus, the adaptive rate system can increase the capacity by 27%     

Unified Analysis for SIR-Based Power and Rate Control in Multipath Fading Channels

In this paper, we present a unified analysis on various signal-to-interference power ratio (SIR)-based power and rate control schemes in independent and nonidentical multipath fading channels. We study wireless direct sequence code division multiple access (DS-CDMA) systems with RAKE reception and derive new expressions for a mobile user's average SIR, average transmission power, and average data rate in terms of the probability distribution of the SIR. The performance of SIR-based combined power/rate control, power control, rate control, truncated power control, and truncated rate control schemes in independent and nonidentical Rayleigh fading channels is presented and compared. By substituting appropriate SIR distributions, this general mathematical framework can be applied to other fading channels such as the Nakagami, Rician, and lognormal channels     

基于符号率动态变频的低功耗DOCSIS上行发射器设计

 为解决DOCSIS上行发射器的高功耗问题,本文在深入剖析信道突发特点和发射器结构的基础上,提出了一种全新的发射器VLSI（超大规模集成电路）设计低功耗体系. 通过引入发射符号率这一性能约束,该体系可使上行数据通路上所有运算电路能根据不同的突发符号率动态调节运算频率,以最小的功耗消耗匹配突发处理的性能要求. 实验结果表明,在不同突发符号率下,所提出体系可使上行发射器的总功耗平均降低67.13%. 本文设计的低功耗上行发射器已应用于符合EuroDOCSIS1.1规范的支持双向有线数字电视点播的Cabl e Modem（CM） SOC（片上系统）平台中,并表现出优良的低功耗特性. 不失一般性,本文所提出的设计体系不仅适用于其他对功耗敏感的通信系统,同时,也将有助于推动超大规模集成电路及SOC设计领域中低功耗这一关键技术的发展.     

Asymmetric power allocation to improve convergence rate of iterative receivers with soft cancellation

The major drawback of iterative receivers is more power consumption and longer latency due to iterations even though iterative receivers can enjoy a good compromise between complexity and performance. Motivated by these issues, we study a simple power allocation strategy in the transmitter side to alleviate the burden in an iterative receiver with interference cancellation by improving convergence rate. We analyze asymmetric power allocation with the extrinsic information transfer (EXIT) chart technique and show that the convergence rate (as well as performance) can be improved.     

Traffic-Aware Link Rate Adaptation for Multi-rate 802.11 Networks

802.11 networks provide multi-rate capability to offer rate adaptability against the time-varying wireless channel. However, how to switch between the available rates has not been standardized. Existing rate adaptation (RA) solutions assume common transmission power and can only passively tune link rate to match the inferred channel condition via different methods. This simple attitude is neither flexible in traffic-aware link rate selection nor effective in energy conservation and spatial reuse since transmission power may be either too low to sustain the link rate or too high that results in unnecessary energy consumption and worse spatial reuse. Different from existing solutions, we think that link rate switch should be driven by traffic load and power control should be considered with rate adaptation together to conserve energy and increase spatial reuse. To this end, we propose a traffic-aware link rate adaptation scheme (TARA) via power control for multi-rate 802.11 networks. Its basic idea consists of a two-step procedure. Firstly, traffic load is sensed in the MAC layer to decide whether link rate should be increased or decreased for the next transmission. Afterwards, power control is carried out in the PHY layer to guarantee that the new link rate can be sustained while minimizing the transmission power. Extensive simulation results show that TARA outperforms typical existing schemes in terms of energy efficiency and throughput.     

组播OFDM系统中基于子载波成对调整的功率分配算法

 研究了在总功率的约束下,组播OFDM系统中最大化组播速率的功率分配问题. 首先引入贪婪算法求解该问题以降低复杂度,但贪婪算法只执行预设的固定次数分配后即停止,其截止条件与功率分配过程中的状态无关,无法有效地提高系统性能;进而提出了两种基于子载波成对调整的功率分配算法,在初始功率分配的基础上选择子载波对交换功率,将功率重新分配给能够使组播速率提高得最多的子载波,并只在无法进一步提高组播速率时才停止调整. 研究和仿真结果表明,所提出的两种调整算法能够有效地提高组播速率,性能接近根据凸函数优化方法求得的最优解,且显著降低了算法的复杂度.