流星余迹通信变速率编码研究

流星余迹通信是一种利用流星电离余迹反射电波实现数据传输的通信方式。衡量流星余迹通信系统性能的指标之一是所采用编码的数据包正确传输概率。通常采用的编码方式为固定速率编码,这种编码数据包传输正确概率较低,系统性能较差。变速率编码根据流星余迹通信信道特点,通过改变数据包中各个码字的码率,提高数据包正确传输概率,改善系统性能。理论分析和仿真结果表明,采用变速率编码系统性能提高。     

Variable-rate coding for meteor-burst communications

The performance of variable-rate Reed-Solomon error-control coding for meteor-burst communications is considered. The code rate is allowed to vary from codeword to codeword within each packet, and the optimum number of codewords per packet and optimum rates for the codewords are determined as a function of the length of the message and the decay rate for the meteor trail. The resulting performance is compared to that obtained from, fixed-rate coding. Of central importance is the derivation of tractable expressions for the probability of correct decoding for bounded-distance decoding on a memoryless channel with a time-varying symbol error probability. A throughout measure is developed that is based on the probability distribution of the initial signal-to-noise ratio     

Image coding using variable-rate side-match finite-state vectorquantization

Future B-ISDN (broadband integrated services digital network) users will be able to send various kinds of information, such as voice, data, and image, over the same network and send information only when necessary. It has been recognized that variable-rate encoding techniques are more suitable than fixed-rate techniques for encoding images in a B-ISDN environment. A new variable-rate side-match finite-state vector quantization with a block classifier (CSMVQ) algorithm is described. In an ordinary fixed-rate SMVQ, the size of the state codebook is fixed. In the CSMVQ algorithm presented, the size of the state codebook is changed according to the characteristics of the current vector which can be predicted by a block classifier. In experiments, the improvement over SMVQ was up to 1.761 dB at a lower bit rate. Moreover, the improvement over VQ can be up to 3 dB at nearly the same bit rate.     

Robust video multicast with joint network coding and video interleaving

In this work, we propose a cross-layer solution to robust video multicast in erasure networks based on random linear network coding (RLNC) in the network layer and video interleaving (VI) in the application layer, and call it the joint RLNC-VI scheme. In the RLNC implementation, we partition one video coding unit (VCU) into several priority levels using scalable properties of H.264/SVC video. Packets from the same priority level of several VCUs form one RLNC generation, and unequal protection is applied to different generations. RLNC provides redundancy for video packets in the network layer and has proved to be useful in a multicast environment. Then, we propose a new packet-level interleaving scheme, called the RLNC-facilitated interleaving scheme, where each received packet corresponds to a new constraint on source packets. As a result, it can facilitate the RLNC decoding at the destination node. Furthermore, we study the problem of optimal interleaving design, which selects the optimal interleaving degree and the optimal redundancy of each generation. The tradeoff between delay and received video quality due to the choice of different VCUs is also examined. It is shown by simulation results that the proposed RLNC-VI scheme outperforms the pure RLNC method for robust video multicast in erasure networks. This can be explained by two reasons. First, the VI scheme distributes the impact of the loss (or erasure) of one VCU into partial data loss over multiple neighboring VCUs. Second, the original video content can be easily recovered with spatial/temporal error concealment (EC) in the joint RLNC-VI scheme.     

Direct sequence CDMA power control, interleaving, and coding

The authors develop and analyze models of power control that consider other aspects of code-division multiple access (CDMA) systems, such as interleaving and coding on the land mobile radio channel. The orientation is that a power control scheme keeps the received powers at the base station almost equal, and the performance degradation incurred if the powers are not exactly equal will be quantified. In doing so, the authors consider the performance implications of control latency and a maximum speech delay constraint. Because of positive correlations between the fading channel amplitudes, the effectiveness of the combination of interleaving and coding in combating the effects of power variations due to slow Rayleigh fading is reduced. It is shown that power control and interleaving/coding are most effective in complementary parameter regions, thus providing a degree of robustness for both fast and slow Rayleigh fading     

Erasure coding for reliable adaptive retransmission in wireless broadcast/multicast systems

In this paper, we present new adaptive automatic repeat request (ARQ) schemes for wireless broadcast/multicast combining erasure coding (EC) and packet retransmission. Traditional approaches rely on retransmitting the lost packets in a point-to-point or point-to-multipoint mode. The main idea behind the presented protocols is to retransmit adaptive combinations of the lost packets using EC, which can help several receivers to recover the lost information with fewer retransmission attempts. We propose two versions of EC-based ARQ protocols, and investigate theoretically the corresponding transmission bandwidths in different contexts. We show through simulation results the efficiency of the proposed protocols with respect to conventional ARQ strategies and new published ARQ works for broadcast/multicast. Finally, a new sliding window NACK feedback policy is presented for the case of a high number of receivers to avoid the feedback implosion problem.     

Variable-rate hybrid ARQ for meteor-burst communications

The authors introduce a form of automatic repeat request (ARQ), referred to as variable-rate type-I hybrid ARQ, in which the code rate varies in response to the fluctuations in the power received from a meteor trail. For one implementation, the source or the destination periodically obtains estimates of the signal power at the destination, and the source uses these estimates to select the rate of the code. For an alternative approach, the code rate is determined completely by the decoding successes and failures during previous transmissions. The performance measure is the throughput per trail, which is defined as the expected number of information bits received correctly for a given meteor trail. Numerical results for Reed-Solomon codes are included to illustrate the relative performance of the various schemes. It is shown that the throughput is larger for both implementations of variable-rate type-I hybrid ARQ than for fixed-rate type-I hybrid ARQ and ARQ without forward error correction     

On the optimum average distortion attainable by fixed-rate coding of a nonergodic source

A simple proof is given for the Gray-Davisson result on the ergodic decomposition of the optimum average distortion attainable by fixed-rate coding of a nonergodic source, for the special ease of a bounded distortion measure. A second proof is given for a more general class of distortion measures using a result of Ziv.     

Incremental-redundancy transmission for meteor-burst communications

The performance of type-II hybrid automatic repeat request (ARQ) is compared to that of fixed-rate type-I hybrid ARQ for meteor-burst communications. Maximum throughput is obtained for meteor-burst communications by using a transmission scheme for which the information rate of the code, varies in response to the fluctuations in the power received from a meteor trail. For type-II hybrid ARQ, a variation in the code rate is inherent in the coding scheme. On the first transmission that is made for a data block, a code of relatively high rate is used, but if an additional transmission is required, only redundant symbols are sent, and this reduces the overall rate of the code. The performance measure is the throughput per trail, which is defined as the expected number of successfully received information bits for a given meteor trail. The authors also develop an approximation for the average value of the throughput, averaged over the parameters of the meteor trail. Numerical results for Reed-Solomon codes are included to illustrate the relative performance of the various schemes. It is shown that the throughput is larger for type-II hybrid ARQ than for either fixed-rate type-I hybrid ARQ or ARQ without forward-error-correction     

Video coding and delivery challenges for next generation IPTV

Current generation, large-scale, Internet protocol television (IPTV) systems borrow heavily from the broadcast industry, which makes a number of delivery assumptions that do not apply to IP networks. Consequently we can perceive major improvements if we better match the delivery of IPTV services with the underlying network transport. We can expect next generation IPTV systems to adapt video streams dynamically to maximise throughput, allow constant quality delivery, and degrade gracefully in congested networks. This paper outlines the challenges in optimising IPTV delivery and the contribution that BT’s research has made to overcoming some of these.     

Message waiting time performance for meteor-burst communicationsystems

The performance is investigated of the meteor-burst channel in terms of the waiting time required to reliably transmit a message of length N bits. Two modulation techniques are considered. The first is the traditional fixed-rate modulation scheme where the modem operates at a constant bit rate whenever the channel is available for message traffic. The second is an adaptive modulation method where the channel symbol rate varies continuously to match the time-varying signal-to-noise ratio at the receiver. Upper and lower bounds on waiting time for the general case are derived using probabilistic arguments. Novel closed-form expressions for waiting time and optimal bit rate are derived for the fixed-rate modem. Bounds on mean waiting time are derived for the adaptive-symbol-rate modem. It is shown that for fixed-rate modems operating at the optimal bit rate and for adaptive modems operating at a minimum bit rate equal to this rate, the improvement in mean waiting time can never exceed a factor of two     

A limit on optimum performance degradation in fixed-rate coding of the discrete Fourier transform (Corresp.)

The discrete Fourier transform (DFT) often is used instead of the optimum Karhunen-Lograve{e}ve transform (KLT) in encoding a stationary normal time series, because the recursive FFT is computationally efficient and yields "nearly" uncorrelated components. Substituting the DFT for the KLT and then treating its components as if they were uncorrelated reduces the ultimate performance attainable in fixed-rate source coding. We address the problem of this performance degradation by deriving a simple and easily applied upper bound on the increase in the distortion-rate function (DRF) for the mean-squared error criterion incurred by substitution of the DFT for the KLT.     

Improved side information generation algorithm for Wyner-Ziv video coding简

Side information has a significant influence on the rate-distortion（RD） performance of distributed video coding（DVC）. In the conventional motion compensated frame interpolation scheme, all blocks adopt the same side-information generation method regardless of the motion intensity inequality at different regions. In this paper, an improved method is proposed. The image blocks are classified into two modes, fast motion and slow motion, by simply computing the discrete cosine transformation（DCT） coefficients at the encoder. On the decoder, it chooses the direct interpolation and refined motion compensated interpolation correspondingly to generate side information. Experimental results show that the proposed method, without increasing the encoder complexity, can increase the average peak signal-to-noise ratio（PSNR） by up to 1~ 2 dB compared with the existing algorithm. Meanwhile, the proposed algorithm significantly improves the subjective quality of the side information.     

A low-complexity method for fixed-rate entropy-constrained vector quantization

This paper describes a new approach to fixed-rate entropy-constrained vector quantization (FEVQ) for stationary memoryless sources where the structure of codewords are derived from a variable-length scalar quantizer. We formulate the quantization search operation as a zero-one integer-optimization problem, and show that the resulting integer program can be closely approximated by solving a simple linear program. The result is a Lagrange formulation which adjoins the constraint on the entropy (codeword length) to the distortion. Unlike the previously known methods with a fixed Lagrange multiplier, we use an iterative algorithm to optimize the underlying objective function, while updating the Lagrange multiplier until the constraint on the overall rate is satisfied. The key feature of the new method is the substantial reduction in the number of iterations in comparison with previous related methods. In order to achieve some packing gain, we combine the process of trellis-coded quantization with that of FEVQ. This results in an iterative application of the Viterbi algorithm on the underlying trellis for selecting the Lagrange multiplier. Numerical results are presented which demonstrate substantial improvement in comparison with the alternative methods reported in the literature.     

Disparity field and depth map coding for multiview 3D image generation

In the present paper techniques are examined for the coding of the depth map and disparity fields for stereo or multiview image communication applications. It is assumed that both the left and right channels of the multiview image sequence are coded using block- or object-based methods. A dynamic programming algorithm is used to estimate a disparity field between each stereo image pair. Depth is then estimated and occlusions are optionally detected, based on the estimated disparity fields. Spatial interpolation techniques are examined based on the disparity/depth information and the detection of occluded regions using either stereoscopic or trinocular camera configurations. It is seen that the presence of a third camera at the transmitter site improves the estimation of disparities, the detection of occlusions and the accuracy of the resulting spatial interpolation at the receiver. Various disparity field and depth map coding techniques are then proposed and evaluated, with emphasis given to the quality of the resulting intermediate images at the receiver site. Block-based and wireframe modeling techniques are examined for the coding of isolated depth or disparity map information. Further, 2D and 3D motion compensation techniques are evaluated for the coding of sequences of depth or disparity maps. The motion fields needed may be available as a byproduct of block-based or object-based coding of the intensity images. Experimental results are given for the evaluation of the performance of the proposed coding and spatial interpolation methods.     

Unequal Erasure Protection Technique for Scalable Multistreams

This paper presents a novel unequal erasure protection (UEP) strategy for the transmission of scalable data, formed by interleaving independently decodable and scalable streams, over packet erasure networks. The technique, termed multistream UEP (M-UEP), differs from the traditional UEP strategy by: 1) placing separate streams in separate packets to establish independence and 2) using permuted systematic Reed–Solomon codes to enhance the distribution of message symbols amongst the packets. M-UEP improves upon UEP by ensuring that all received source symbols are decoded. The R-D optimal redundancy allocation problem for M-UEP is formulated and its globally optimal solution is shown to have a time complexity of $O(2^{N}N(L+1)^{N+1})$ , where $N$ is the number of packets and $L$ is the packet length. To address the high complexity of the globally optimal solution, an efficient suboptimal algorithm is proposed which runs in $O(N^{2}L^{2})$ time. The proposed M-UEP algorithm is applied on SPIHT coded images in conjunction with an appropriate grouping of wavelet coefficients into streams. The experimental results reveal that M-UEP consistently outperforms the traditional UEP reaching peak improvements of 0.6 dB. Moreover, our tests show that M-UEP is more robust than UEP in adverse channel conditions.      

音视频编码标准选择上的“是与非”

虽然MPEG-2与H．264标准有着千丝万缕的纠葛，但二者都不客气地觊觎着下一代的主流音视频编码标准。加入这一战团的还有来自巨无霸微软的自成体系的VC-1标准以及在中国国内蓄势待发的AVS标准，因此无论是流媒体，高清数字电视、3G应用还是视盘编码领域，都将成为行业寡头们拼杀争夺的重要城池。但既然能形成寡头竞争，那么这些技术必定各有所长，实力相当，否则也无法形成势均力敌的局面。     

A unified algorithmic framework for variable-rate TDM switchingassignments

A unified algorithmic framework for time-optimal transmission scheduling is obtained for satellite-switched time-division multiple access systems with M uplink and N downlink beams. System capability may vary from the basic configuration of one carrier per beam to complex configurations of variable number of carriers for each beam and variable transmission rate for each beam. The computational complexity for time-optimal transmission scheduling remains strongly polynomial at O(M ²N²) and the number of switching configurations is at most MN+1 for all system configurations considered     

Product and interleaving of anticodes

Two techniques are presented for constructing new anticodes from known anticodes, namely the product and interleaving of anticodes. The product of anticodes (m/sub 1/, k/sub 1/, delta /sub 1/) and (m/sub 2/, k/sub 2/, delta /sub 2/) produces an (m/sub 1/m/sub 2/, k/sub 1/k/sub 2/, delta ) anticode, where delta /sub 1/ delta /sub 2/>