Transmission quality of Group III facsimile on IDR satellite links with circuit multiplication equipment

The focus of this paper is on ways to improve the quality of Group III facsimile on intermediate data rate (IDR) satellite links. First, we present the results of an evaluation of the quality of Group III (G3) facsimile images transmitted on satellite links through circuit multiplication equipment (CME). Based on the results of this study, we propose a model to relate the facsimile image quality requirements to the bit error ratio (BER) on the link. A procedure is introduced to associate the long-term percentage of error-free pages in G3 facsimile transmission with various bit error probability (BEP) masks used for satellite link design. The intent of this procedure is to provide comparable end-to-end transmission quality for international telephone circuits, irrespective of whether the transmission medium is a satellite link or a fibre-optic cable. It is concluded that, unless the performance objectives of satellite systems significantly exceed those derived from CCITT/ITU-T Recommendation G.826, fibre-optic cables will become the preferred choice for international transmission.     

Comparison of Redundancy Reducing Codes for Facsimile Transmission of Documents

A comparison and a valuation of different redundancy reducing coding techniques for the digital transmission of facsimile documents on telephone lines is presented. Especially taken into account are those codes which have been submitted to the International Telegraph and Telephone Consultative Committee (CCITT) for standardization of digital group 3 facsimile machines. The reduction factor and the sensitivity of channel errors of these one- and two- dimensional codes have been investigated by computer simulations using the CCITT test documents and burst error patterns of real telephone lines. For a resolution of 1728 picture elements per line and 3.85 lines per mm one-dimensional run length coding proves to be the most economical solution. Using a higher vertical resolution of 7.7 lines per mm the effects of transmission errors are less visible in the received document and two-dimensional codes become more efficient. To achieve a transmission time of 1 min or less for a size A4 document a transmission bit rate of 4800 bits/s is required. For the higher vertical resolution a transmission time of 1 min cannot be guaranteed for all types of documents with this bit rate even if two-dimensional coding is used.     

Fast codeword search algorithm for image coding based onmean-variance pyramids of codewords

The fast codeword search algorithm based on the mean pyramids of codewords is currently used in image coding applications. A more efficient algorithm is presented for fast codeword searching which is based on the use of mean-variance pyramids of codewords. Experimental results confirm the effectiveness of the proposed method     

Coding and signal space diversity for a class of fading and impulsive noise channels

The transmission over the Gaussian mixture noise channel with perfect channel state information at the receiver side is considered. Lower and upper bounds on the achievable pairwise error probability (PEP) are derived for finite and infinite codeword lengths. It is shown that diversity codes, i.e., unitary transforms, can be applied to achieve a diversity gain. A large class of diversity codes is determined for which-if the codeword length is increased-the PEP between any two codewords approaches either zero or the lower bound on the PEP.     

A new modulation scheme using asymmetric erorr-correcting codesembedded in optical orthogonal codes for optical CDMA

An embedded-modulation scheme is proposed for optical code division multiple access (CDMA). In this scheme, codewords in an asymmetric error-correcting (AEC) code is embedded in a signature sequence in an optical orthogonal code (OOC) used for identification. We classify the codewords of the AEC code according to the number of "1"s in each codeword, and then derive the bit error rate (BER) of the embedded-modulation scheme. Numerical results show that although the performance has the error floor, for achieving the floor value, the embedded-modulation scheme requires less optical energy per bit than the traditional modulation scheme with the correlation and chip-level receivers. The error floor is primarily due to multiaccess interference (MAI), we furthermore apply Reed-Solomon (RS) coding to the embedded-modulation scheme. Consequently, RS coding reduces the floor value to be negligibly small     

An efficient hybrid decoding algorithm for Reed-Solomon codes based on bit reliability

The paper presents a computationally efficient hybrid reliability-based decoding algorithm for Reed-Solomon (RS) codes. This hybrid decoding algorithm consists of two major components, a re-encoding process and a successive erasure-and-error decoding process for both bit and symbol levels. The re-encoding process is to generate a sequence of candidate codewords based on the information provided by the codeword decoded by an algebraic decoder and a set of test error patterns. Two criteria are used for testing in the decoding process to reduce the decoding computational complexity. The first criterion is devised to reduce the number of re-encoding operations by eliminating the unlikely error patterns. The second criterion is to test the optimality of a generated candidate codeword. Numerical results show that the proposed decoding algorithm can achieve either a near-optimum error performance or an asymptotically optimum error performance.     

纠正随机错误与长突发删除的多进制乘积码研究

考虑多进制LDPC码的符号特性,以及对其残留错误和删除的分析,本文采用多进制LDPC码作为内码,相同Galois域下的高码率RS码作为外码来构造多进制乘积码;并提出了一种低复杂度的迭代译码方案,减少信息传输的各类错误。在译码时,只对前一次迭代中译码失败的码字执行译码,并对译码正确码字所对应的比特初始概率信息进行修正,增强下一次迭代多进制LDPC译码符号先验信息的准确性,减少内码译码后的判决错误,从而充分利用外码的纠错能力。仿真结果显示,多进制乘积码相较于二进制LDPC乘积码有较大的编码增益,并通过迭代进一步改善了性能,高效纠正了信道中的随机错误和突发删除。对于包含2%突发删除的高斯信道,在误比特率为10^-6时,迭代一次有0.4 dB左右的增益。     

基于特征值苑配的变比特率相关矢量量化图像编码算法

该文提出了一种用于图像编码的新颖的变比特率相关矢量量化器。在编码之前,首先计算各码字的四个特征值,然后根据各特征值的升序排列得到相应的四个排序码书。在对当前输入矢量(当前处理图像块)进行编码的过程中,充分考虑当前处理图像块与其相邻图像块之间的相关性以及各码字特征值与该输入矢量特征值之间的匹配性。测试结果表明,该算法与传统矢量量化(VQ)器相比,虽然在编码质量上有少许下降,但降低了比特率并加快了编码速度。     

Hybrid ARQ scheme using interleaved Reed-Solomon codes in apower-controlled DS-CDMA cellular system

A new hybrid automatic repeat request (ARQ) scheme is proposed for data transmission in a power-controlled direct sequence (DS) code division multiple access (CDMA) system cellular system. The data frame is composed of interleaved Reed-Solomon codes. The depth of interleaving is determined by a power-control interval. After decoding each codeword with algebraic decoding, the post-decoding processor decides whether to accept the codeword or to discard it by using channel state information from the power-control processor. The proposed hybrid ARQ scheme significantly reduces the probability of undetected error among accepted codewords without significantly reducing the throughput     

Deorthogonalization of ODS-CDMA QPSK by AM/PM Nonlinearity

When using a conventional demodulator, a sufficient condition to maintain ODS-CDMA codeword orthogonality is constant relative channel amplitude over the codeword duration. When transmitted over a memoryless, AM/PM nonlinearity channel, the chip-to-chip fluctuating amplitude of a composite ODS-CDMA QPSK waveform produces a chip-to-chip fluctuating phase that deorthogonalizes the ODS-CDMA codewords, resulting in an additional multiple access self-interference similar to that found in asynchronous DS-CDMA. For ODS-CDMA QPSK in an AM/PM nonlinearity channel, we utilize the Central Limit Theorem, derive, and evaluate: (i) an expression for the signal-to-distortion ratio at the demodulator output, (ii) an expression for the uncoded bit error probability, and (iii) an upper bound on the convolutionally-coded bit error probability. We find that the degradation to BER depends on both the AM/PM nonlinearity slope and the ODS-CDMA channel loading.     

Design of SCMA codebook based on chaotic signal and system performance analysis

Sparse code multiple access (SCMA) technology is one of the multiple access technology schemes for the new generation of 5G.In order to solve the transmission requirement of massive users,the logistic chaos sequence was proposed instead of the random sequence in the original system to select the codeword.The constellation method based on trellis coded modulation (TCM) subset segmentation with the mapping matrix was used to generate codebook in the encoder,and decoded through message passing algorithm (MPA) detection method.The simulation results show that the bit error rate (BER) is low when the system uses the pseudo-random sequence of chaos to select the codeword,and the system also performs well under the condition of high overload rate.     

一种基于码本轮转的有限反馈量化方法

大规模多输入多输出（Multiple-Input Multiple-Output,MIMO）系统中随着天线数目的增加,其反馈比特数将随之大幅度增加。为此,提出了一种基于码本轮转的有限反馈量化方法。该方法中,用户在前一时刻得到最佳码字之后,在码本中选取轮转区域构成虚拟码本,判断当前时刻的信道向量,满足轮转条件的用户将虚拟码本轮转到码本起始位置,在虚拟码本中进行量化;不满足轮转条件的用户在原始码本中进行量化,选出当前时刻的最优码字。反馈比特数分析与仿真结果表明,所提方法可轮转的虚拟码本减少了量化码字的数量,从而减少了反馈比特数,是系统性能与反馈比特数的一种折中。     

Extending the BACIC algorithm for robust transmission over a noisy channel

This study introduces error control to the block arithmetic coding for image compression (BACIC): a new method for lossless bilevel image compression. BACIC can successfully transmit bilevel images when channel bit error rates are as high as 10/sup -3/ while providing compression ratios twice that of G3, the only facsimile standard which incorporates error control into its algorithm.     

Restoration of lossy compressed noisy images

Noise degrades the performance of any image compression algorithm. However, at very low bit rates, image coders effectively filter noise that may he present in the image, thus, enabling the coder to operate closer to the noise free case. Unfortunately, at these low bit rates the quality of the compressed image is reduced and very distinctive coding artifacts occur. This paper proposes a combined restoration of the compressed image from both the artifacts introduced by the coder along with the additive noise. The proposed approach is applied to images corrupted by data-dependent Poisson noise and to images corrupted by film-grain noise when compressed using a block transform-coder such as JPEG. This approach has proved to be effective in terms of visual quality and peak signal-to-noise ratio (PSNR) when tested on simulated and real images.     

Two-dimensional soft-input source decoding for robust transmission of compressed images

The transmission of compressed images over highly corrupted channels is addressed. The implicit residual redundancy inherent in the quantised subband images and the bit-reliability information at the channel output are utilised for error protection. As a novelty a known estimation technique is extended to the two-dimensional case, where both horizontal and vertical correlations are exploited. Especially for very noisy channels the quality of the reconstructed image is greatly increased compared to one-dimensional approaches.     

One-Way Multiaddress Satellite Data Communication System

An experimental one-way multiaddress data communication system accommodating many small receive-only terminals is described. In this system, a digital facsimile is used as the output equipment. A simple one-way transmission protocol adopting the flag synchronization method has been developed so that facsimile equipment of different speeds can be used. The receive-only terminal comprises an antenna, an RF receiver, a demodulator, and a channel selector. The antenna is an offset parabolic type with an effective diameter of 60 cm and uses a printed spiral type primary radiator. Dimensions of the terminal are 70 cm wide, 88 cm deep, and 126 cm high. The satellite channel bit rate is 64 kbits/s in order to transmit multiple facsimile data simultaneously. Experiments using the Japanese "CS" satellite have been carried out to verify the system feasibility. The normal bit error rate was less than 10^-6and line errors occurred less than once in three facsimile transmissions.     

Decoding real block codes: activity detection Wiener estimation

New decoding procedures for real-number block codes which are constructed by imposing constraints in the discrete Fourier transform (DFT) domain are examined. The codewords are corrupted by small levels of roundoff noise and possibly occasionally by a few large excursions of random disturbances. The error-correcting procedure is separated into two parts, large activity detection followed by error value estimation, particularly the larger errors. The first part determines if large excursions are present, roughly identifying their locations, while the second part is a Wiener minimum mean-squared error estimation technique providing a stochastic correction to the corrupted components. The activity-detecting part determines locations for large increases in the Wiener estimator's gain. A computationally intensive Bayes hypothesis testing approach is shown to be very effective at locating large activity positions, but a more efficient modified Berlekamp-Massey (1969) algorithm is developed which leads to excellent mean-squared error performance. Extensive simulations demonstrate individual codeword corrective actions and compare the average mean-squared error performance between coded and unprotected data. The error level improvement ranges from three to four orders of magnitude     

An integrated temporal error concealment for H.264/AVC based on spatial evaluation criteria

Owing to error-prone transmission networks, the compressed video bit stream is prone to packet loss in the transmission channel. This loss causes serious distortion and the distortion will propagate to successive frames, especially in highly compressed video coding standard. Therefore, it is very important to efficiently enhance the restored result. In this paper, an integrated temporal error concealment technique for H.264/AVC is proposed. The technique could effectively restore the corrupted data by adaptively integrating error concealment approaches with the adaptive weight-based switching algorithm. The integrated mechanism is based on spatial evaluation criteria, judged by boundary distortion estimation and texture intensity. Experimental results show that the technique could effectively enhance the performance of error concealment.     

基于均匀网格编码量化的超光谱图像自适应压缩

提出一种基于小波系数分类的超光谱图像压缩方法．算法首先将各波段小波分解并将所得子带划分成子块,而后根据子块活动性将其分类．在分类基础上,使用预测差分技术去除谱间冗余,此过程中分别求取各子类的预测系数以反映子带的局部相关性,而后利用均匀网格编码量化方法来量化残差系数序列,最后使用自适应算术编码对量化码字进行熵编码,为使编码器能在所有系数序列中最优地分配比特,本文提出一个基于序列统计特性和网格编码量化器率-失真特性的比特分配算法,实验证明该方法能高效地压缩超光谱图像,表现出优异的压缩性能。     

Enhancement of one-dimensional variable-length DPCM imagescorrupted by transmission errors

Methods are presented for enhancing one-dimensional variable-length differential pulse-code modulation (VLDPCM) images corrupted by transmission errors, are presented. The proposed methods take advantage of the VLDPCM code's high sensitivity to errors. Two methods are described. The first involves no increase of transmitted bit rate and consists of processing the corrupted image. The second method involves the transmission of additional information to enable an almost exact reconstruction of the original image. The amount of added redundancy can be reduced at the cost of performing more computations. In a simulation, the authors used less than 7% redundancy. Both methods achieve significant improvements which are demonstrated by the simulation results. The simulation results include original, corrupted, and enhanced images as well as the signal-to-noise ratio (SNR) versus bit-error rate (BER) curve. For BER 10^-3, the SNR (signal-to-noise ratio) gains for the first and second methods are greater than 17 and 44 dB, respectively