非规则LDPC码的不等错误保护性能研究

提出了一种具有不等错误保护性能的非规则低密度校验(LDPC,low-density parity-check)码信道编码方案, 构造了重量递增校验(weight-increasing parity-check)矩阵,系统编码时,重要信息比特映射到LDPC码的“精华”比特上。AWGN和Rayliegh衰落信道的仿真结果表明,与随机构造的非规则LDPC码相比,WICP-LDPC码具有好的UEP性能。     

On unequal error protection LDPC codes based on plotkin-type constructions

We introduce a new family of unequal error protection (UEP) codes, based on low-density parity-check (LDPC) component codes and Plotkin-type constructions. The codes are decoded iteratively in multiple stages, and the order of decoding determines the level of error protection. The level of UEP among the code bits is also influenced by the choice of the LDPC component codes and by some new reliability features incorporated into the decoding process. The proposed scheme offers a very good tradeoff between code performance on one side and encoding/decoding and storage complexity on the other side. The novel approach to UEP also allows for finding simple approximations for the achievable degrees of UEP, which can be used to govern practical code design implementations.     

Multilevel coded modulation for unequal error protection andmultistage decoding .I. Symmetric constellations

In this paper, theoretical upper bounds and computer simulation results on the error performance of multilevel block coded modulations for unequal error protection (UEP) and multistage decoding are presented. It is shown that nonstandard signal set partitionings and multistage decoding provide excellent UEP capabilities beyond those achievable with conventional coded modulation. The coding scheme is designed in such a way that the most important information bits have a lower error rate than other information bits. The large effective error coefficients, normally associated with standard mapping by set partitioning, are reduced by considering nonstandard partitionings of the underlying signal set. The bits-to-signal mappings induced by these partitionings allow the use of soft-decision decoding of binary block codes. Moreover, parallel operation of some of the staged decoders is possible, to achieve high data rate transmission, so that there is no error propagation between these decoders. Hybrid partitionings are also considered that trade off increased intraset distances in the last partition levels with larger effective error coefficients in the middle partition levels. The error performance of specific examples of multilevel codes over 8-PSK and 64-QAM signal sets are simulated and compared with theoretical upper bounds on the error performance     

非均匀纠错Turbo码在图像无线传输中的应用

本文根据信源泉编码流中信息比特重要性不均匀特点，采用变码率信道编码、分集发送、分集接收、非均匀迭代译码策略，对传统的Turbo码编译码器结构做了改进，给出了实验结果。通过比较发现，改进算法降低了时延，提高了Turbo码译码算法的纠错性能，特别适合于多媒体非实时无线传输业务。     

Two topics on linear unequal error protection codes: Bounds on their length and cyclic code classes

It is possible for a linear block code to provide more protection for selected positions in the input message words than is guaranteed by the minimum distance of the code. Linear codes having this property are called linear unequal error protection (LUEP) codes. Bounds on the length of a LUEP code that ensures a given unequal error protection are derived. A majority decoding method for certain classes of cyclic binary UEP codes is treated. A list of short (i.e., of length less than 16) binary LUEP codes of optimal (i.e., minimal) length and a list of all cyclic binary UEP codes of length less than 40 are included.     

New results on unequal error protection using LDPC codes

In this letter, we propose a new scheme to construct low-density parity-check (LDPC) codes that are suitable for unequal error protection (UEP). We derive UEP density evolution (UDE) formulas for the proposed ensemble over the binary erasure channel (BEC). Using the UDE formulas, high performance UEP codes can be found. Simulation results depict an improvement in the bit error rate of more important bits in comparison with previous results on UEP-LDPC codes.     

On decoding unequal error protection product codes

The decoding of unequal error protection product codes, which are a combination of linear unequal error protection (UEP) codes and product codes, is addressed. A nonconstructive proof of the existence of a good error-erasure-decoding algorithm is presented; however, obtaining the decoding procedure is still an open research problem. A particular subclass of UEP product codes is considered, including a decoding algorithm that is an extension of the Blokh-Zyablov decoding algorithm for product codes. For this particular subclass the decoding problem is solved     

Modulation-assisted unequal error protection over the fadingchannel

Unequal error protection (UEP) is essential when different portions of the source data do not contribute evenly to the overall duality of the decoded information. Conventional techniques achieve UEP by independent coding of the bit streams or by adopting conventional unequal error-protection codes. In this paper, we propose a practical alternative to the QPSK-based transmission systems with explicit UEP, such as GSM or IS-54 wireless transmission standards. In this scheme, the task of providing unequal protection is divided between the channel encoder and a nonuniform signal set, which discriminates in favor of the more important bits. The new approach allows for a simpler convolutional encoder and, hence, a less complex decoding procedure. Specifically, a reduction by more than half in the number of encoder states can easily be achieved using our scheme. Countering the degradation of the less important bits, we propose to adopt a high-rate punctured convolutional code to minimize the incurred transmission rate penalty. We also discuss a pilot sequence transmission scheme which realizes a coherent reception. Decentralizing the bit protection culminates in an extra degree of freedom which, in turn, introduces more flexibility into the system design     

具有不等错误保护特性的LDPC 编码调制方案

针对LDPC（low-density parity-check）编码调制系统，提出了一种新的具有不等错误保护特性的调制方案，在一个码字内，利用不同的调制方式对于重要的比特给予较强的保护，对于次要的比特给予较弱的保护，该方案既适用于非规则LDPC码，也适用于规则LDPC码。计算机仿真结果表明，新方案的性能是传统16QAM及4QAM的折衷，当采用1／2码率时，其频带利用率与8PSK相同，但是误码率性能优于8PSK。新方案的性能优于现有文献中基于比特可靠性的调制映射方案，并采用EXIT（extrinsic information transfer）图对新方案的优异性能给出了解释。     

Unequal error protection on turbo-encoder output bits

Traditional turbo codes using BPSK modulation provide equal noise margins for the turbo-encoder output bits. It is shown that imposing unequal error protection (UEP) on the encoder output bits improves the code performance     

Path-compatible pruned convolutional (PCPC) codes

Path pruning, a new coding concept to achieve free distance enlargement for convolutional codes, is proposed. Through path pruning, every convolutional code can be used for unequal error protection (UEP), no matter whether it is originally a UEP code. To avoid undesired path discontinuity and reduce possible path distance loss, a cascaded implementation together with a path-compatible criterion is proposed, under which path-compatible pruned convolutional (PCPC) codes are constructed. Necessary and sufficient conditions are also derived for a subclass of PCPC codes whose decoding can be done by a single decoder for the parent code. Finally, some PCPC codes with good UEP capabilities found by computer search are given     

One-step completely orthogonalisable UEP codes and their softdecision decoding

The concept of one-step complete orthogonality is extended to linear UEP (unequal error protection) codes and then, two soft-decision decoding algorithms for the one-step completely orthogonalisable UEP codes are presented     

Turbo codes-based image transmission for channels with multiple types of distortion

Product codes are generally used for progressive image transmission when random errors and packet loss (or burst errors) co-exist. However, the optimal rate allocation considering both component codes gives rise to high-optimization complexity. In addition, the decoding performance may be degraded quickly when the channel varies beyond the design point. In this paper, we propose a new unequal error protection (UEP) scheme for progressive image transmission by using rate-compatible punctured Turbo codes (RCPT) and cyclic redundancy check (CRC) codes only. By sophisticatedly interleaving each coded frame, the packet loss can be converted into randomly punctured bits in a Turbo code. Therefore, error control in noisy channels with different types of errors is equivalent to dealing with random bit errors only, with reduced turbo code rates. A genetic algorithm-based method is presented to further reduce the optimization complexity. This proposed method not only gives a better performance than product codes in given channel conditions but is also more robust to the channel variation. Finally, to break down the error floor of turbo decoding, we further extend the above RCPT/CRC protection to a product code scheme by adding a Reed-Solomon (RS) code across the frames. The associated rate allocation is discussed and further improvement is demonstrated.     

LDPC码的不等误差保护性能研究

非规则LDPC(low-density parity-check)码具有不等误差保护性能,但是随机编码过程却使这一特性很难实现.现将PEG(Progressive Edge-Growth)算法与信道编码的UEP(Unequal Error Protection)性能相结合,用于构造具有不等误差保护性能的校验矩阵H.AWGN和Rayleigh信道的仿真结果表明,采用PEG算法构造的具有UEP性能的非规则LDPC码能够有效提高系统性能.     

Design of Systematic Unequal Error Protection Raptor Codes Over Binary Erasure Channels

The third generation partnership project (3GPP) and digital video broadcasting-handheld standards recommend systematic Raptor codes as application-layer forward error correction for reliable transmission of multimedia data. In all previous studies on systematic Raptor codes, equal error protection for all data was considered. However, in many applications, multimedia data requires unequal error protection (UEP) that provides different levels of protection to different parts of multimedia data. In this paper, we propose a new design method for Raptor codes that provide both UEP and systematic properties over binary erasure channels. Numerical results show that the proposed UEP design is effective for reliable multi-level protection.     

On block-coded modulation using unequal error protection codes overRayleigh-fading channels

This paper considers block-coded 8-phase-shift-keying (PSK) modulations for the unequal error protection (UEP) of information transmitted over Rayleigh-fading channels. Both conventional linear block codes and linear UEP (LUEP) codes are combined with a naturally labeled 8-PSK signal set, using the multilevel construction of Imai and Hirakawa (1977). Computer simulation results are presented showing that, over Rayleigh-fading channels, it is possible to improve the coding gain for the most significant bits with the use of binary LUEP codes as constituent codes, in comparison with using conventional binary linear codes alone     

非规则准循环OOC-LDPC码在图像传输中的应用

介绍了非规则准循环OOC-LDPC码的构造,并将其应用到图像传输中,根据SPIHT压缩图像编码后的码流具有渐进性的特点,进行不等差错保护。在AWGN信道下仿真结果表明,非规则准循环OOC-LDPC码具有很好的纠错能力和不等差错保护特性。     

Source-optimized irregular repeat accumulate codes with inherent unequal error protection capabilities and their application to scalable image transmission.

The common practice for achieving unequal error protection (UEP) in scalable multimedia communication systems is to design rate-compatible punctured channel codes before computing the UEP rate assignments. This paper proposes a new approach to designing powerful irregular repeat accumulate (IRA) codes that are optimized for the multimedia source and to exploiting the inherent irregularity in IRA codes for UEP. Using the end-to-end distortion due to the first error bit in channel decoding as the cost function, which is readily given by the operational distortion-rate function of embedded source codes, we incorporate this cost function into the channel code design process via density evolution and obtain IRA codes that minimize the average cost function instead of the usual probability of error. Because the resulting IRA codes have inherent UEP capabilities due to irregularity, the new IRA code design effectively integrates channel code optimization and UEP rate assignments, resulting in source-optimized channel coding or joint source-channel coding. We simulate our source-optimized IRA codes for transporting SPIHT-coded images over a binary symmetric channel with crossover probability p. When p = 0.03 and the channel code length is long (e.g., with one codeword for the whole 512 x 512 image), we are able to operate at only 9.38% away from the channel capacity with code length 132380 bits, achieving the best published results in terms of average peak signal-to-noise ratio (PSNR). Compared to conventional IRA code design (that minimizes the probability of error) with the same code rate, the performance gain in average PSNR from using our proposed source-optimized IRA code design is 0.8759 dB when p = 0.1 and the code length is 12800 bits. As predicted by Shannon's separation principle, we observe that this performance gain diminishes as the code length increases.     

一种抗误码能力强的无线信道图像传输方案

本文提出一种新的综合源编码和信道编码的无线信道图像传输方案，对子波变换后各个子带采用基于统计特性的变系数定长（VCFL）编码，数据经过Reed-Solomon编码后选择不同码率的码率兼容删除卷积码（RCPC）编码以提供不同程度的差错保护（UEP），最后数据经交织后传输。在给定传输的总比特数的情况下，通过优化算法使总体失真最小。模拟结果表明新方案在无线衰落信道上表现出良好的性能。     

Complementary punctured-pair convolutional codes for digital audio broadcasting

Hybrid in-band on-channel (IBOC) broadcasting systems for digital audio radio have the capability of simultaneously transmitting analog FM and digital audio of CD-like quality. Due to fading and interference in the already-crowded FM band, the signal design for the hybrid IBOC system is very challenging. It has been proposed to use a method of double sideband transmission where the digital information is transmitted by means of orthogonal frequency-division multiplexing (OFDM) on both sides of the analog host FM and where the digital information can be recovered when one sideband is partially or even totally lost. This leads to an interesting channel coding problem, where we search for optimal pairs of high-rate codes that form good combined low-rate codes, which are better than classic code combining techniques. Furthermore, we also search for rate-compatible punctured convolutional codes which can be used for two-level unequal error protection (UEP) of digital audio. Since some of the tones in the multitone modem (OFDM) are more exposed to interference than others, optimal assignments of convolutional code bits to tones depending on their spectral position are also found. A large number of new codes with memory 6 and 8 are presented both for equal error protection and UEP.