基于H.264的码率控制的改进方法研究

码率控制是H.264中的一个重要的组成部分,其目标是在特定的条件下调整编码后的码流来满足的实际需求.最佳的码率控制由合适的比特分配和精准的比特率控制所共同决定.首先阐述了H.264中的码率控制方法及其要解决的问题,然后对JVT关于H.264中码率控制的几个重要提案进行了深入分析,在此基础上结合现阶段的一些研究成果讨论了H.264码率控制改进方法.

AN EFFICIENT BIT RATE ALLOCATION ALGORITHM FOR MOTION JPEG2000 TRANSPORT IN TILE ENCODING

An efficient bit rate allocation algorithm for video sequence transmission in motion JPEG2000 is presented. In many cases,the moving portions of video are often the interested regions. Based on tile encoding of JPEG2000,the important regions are discerned by two parameters. One is the complexity of a tile;the other is the motion activity of a tile. Thus an adaptive rate-allocation is re-alized in a lower complexity and the perceptive quality of a frame is improved. Experimental results show the effectiveness of this algorithm.

Performance of an Improved One-Way Error Reconciliation Protocol Based on Key Redistribution

In data post-processing for quantum key distribution, it is essential to have a highly efficient error reconciliation protocol. Based on the key redistribution scheme, we analyze a one-way error reconciliation protocol by data simulation. The relationship between the error correction capability and the key generation efficiency of three kinds of Hamming code are demonstrated. The simulation results indicate that when the initial error rates are （0,1.5%], （1.5,4%], and （4,11%], using the Hamming （31,26）, （15,11）, and （7,4） codes to correct the error, respectively, the key generation rate will be maximized. Based on this, we propose a modified one-way error reconciliation protocol which employs a mixed Hamming code concatenation scheme. The error correction capability and key generation rate are verified through data simulation. Using the parameters of the posterior distribution based on the tested data, a simple method for estimating the bit error rate （BER） with a given confidence interval is estimated. The simulation results show that when the initial bit error rate is 10.00%, after 7 rounds of error correction, the error bits are eliminated completely, and the key generation rate is 10.36%; the BER expectation is 2.96×10^-10, and when the confidence is 95% the corresponding BER upper limit is 2.17×10^-9. By comparison, for the single （7,4） Hamming code error reconciliation scheme at a confidence of 95%,the key generation rate is only 6.09%, while the BER expectation is 5.92x 10＂9, with a BER upper limit of 4.34×10^-8. Hence, our improved protocol is much better than the original one.

Dynamic Energy Saving Subcarrier, Bit and Power Allocation in OFDMA Relay Networks

To reduce energy consumption while maintaining users＇ Quality of Service （QoS） in Orthogonal Frequency Division Mul- tiplex Access （OFDMA） relay-enhanced net- works, an adaptive energy saving subcarrier, bit and power allocation scheme is presented. The optimal subcarrier, bit and power alloca- tion problems based on discrete adaptive modula- tion and coding scheme have been previously formulated for relay-enhanced networks, and have been reformulated into and solved by integer programming in optimization theory. If the system still has a surplus of subcarriers after resource allocation, we carry out Band- width Exchange （BE） to enable more subcar- riers to participate in transmission to save en- ergy. In addition, as the relay selection scheme is closely linked with heuristic energy saving resource allocation, a relay selection scheme is proposed. Simulation results indicate that the proposed algorithm consumes less energy when transmitting the same number of bits than greedy energy saving schemes, although its spectrum efficiency is worse.

Region-of-interest based rate control for UAV video coding

To meet the requirement of high-quality transmission of videos captured by unmanned aerial vehicles （UAV） with low bandwidth, a novel rate control （RC） scheme based on region-of-interest （ROI） is proposed. First, the ROI information is sent to the encoder with the latest high efficient video coding （HEVC） standard to generate an ROI map. Then, by using the ROI map, bit allocation methods are developed at frame level and large coding unit （LCU） level, to avoid inaccurate bit allocation produced by camera movement. At last, by using a better robustness R-2 model, the quantization parameter （QP） for each LCU is calculated. The experimental results show that the proposed RC method can get a lower bitrate error and a higher quality for reconstructed video by choosing appropriate pixel weight on the HEVC platform.

Performance analysis of quantum key distribution based on air-water channel

Considering the air-water interface and ocean water’s optical attenuation,the performance of quantum key distribution(QKD)based on air-water channel is studied.The effects of photons’various incident angles to air-water interface on quantum bit error rate(QBER)and the maximum secure transmission distance are analyzed.Taking the optical attenuation of ocean water into account,the performance bounds of QKD in different types of ocean water are discussed.The simulation results show that the maximum secure transmission distance of QKD gradually reduces as the incident angle from air to ocean water increases.In the clearest ocean water with the lowest attenuation,the maximum secure transmission distance of photons far exceeds the the working depth of underwater vehicles.In intermediate and murky ocean waters with higher attenuation,the secure transmission distance shortens,but the underwater vehicle can deploy other accessorial methods for QKD with perfect security.So the implementation of OKD between the satellite and the underwater vehicle is feasible.