IDMA系统中交织器研究现状

近年来,香港城市大学李坪教授提出的交织分多址(IDMA,Interleaver Division Multiple Access)作为一种新的多址技术已经在各个方面均得到了广泛的研究。交织多址是根据不同的交织器来区分用户的,因此,交织器的设计是IDMA系统中的一个关键技术。许多学者在传统交织器的基础上,提出了多种适用于IDMA系统的交织器设计方案。对国内外关于IDMA系统中交织器的设计方案分类进行阐述与归纳总结,并比较了各种交织器设计方法的优缺点。     

Design of interleavers for turbo codes: iterative interleavergrowth algorithms of polynomial complexity

This paper addresses the problem of designing interleavers for parallel concatenated convolutional codes (PCCCs) tailored to specific constituent codes. We start by establishing the role of the interleaver in the PCCC and the various parameters that influence the performance of the PCCC with a given interleaver. Subsequently, we define a canonical form of the interleaving engine denoted as the finite-state permuter (FSP) and demonstrate the minimal delay property of this canonical form. For any given permutation, we present a procedure for deriving the canonical FSP engine. We address the issue of implementation of the FSP and propose a very simple structure for the FSP. Next, using the structural property of the FSP engine, we develop a systematic iterative technique for construction of interleavers with a complexity that is polynomial in the interleaver size. Subsequently, we develop a cost function that, coupled with the iterative interleaver growth procedure, can be used to design optimized interleavers for PCCCs. We provide examples of application of the interleaver design technique, and compare the designed interleavers with some of the interleavers of comparable size found in the literature     

基于短帧交织的Turbo码编码器研究

本文分析了Turbo码编码器及其输出码字的组成原理,基于使输出码字最小汉明重量最大化和使最小汉明重量输出码字出现的概率最小化的原则,结合结构化交织器和随机交织器的优点,提出了一种伪随机的结构化反块交织器,并进一步提出了采用双伪随机反块交织器的Turbo码编码器方案.该方案有效的增大了Turbo码输出码字的最小汉明距离,同时避免了Turbo码边缘效应且具有伪随机性,因此,可有效的提高系统的纠错性能.仿真实验结果显示,该方案在短帧传输的条件下有着最佳的综合性能.特别是在信噪比高时,采用该方案与采用其它交织器的Turbo码方案相比,在提高系统的可靠性上具有明显的优势.     

Design of cyclic shift interleavers for Turbo Codes

In this paper we consider cyclic shift interleavers for turbo coding. The properties of cyclic shift interleavers are discussed and compared with S-random interleavers. It is shown that the cyclic shift interleavers are equivalent or better than the S-random interleavers in the ability to break low weight input patterns. We estimated the performance of turbo codes with cyclic shift interleavers and compared it with the performance of S-random interleavers for varions interleaver sizes. The simulation results show that a turbo code with a cyclic shift interleaver can achieve a better performance than an S-random interleaver if the parameters of the cyclic shift interleaver are chosen properly. In addition, the cyclic interleavers have the advantages of lower design complexity and memory requirements.     

Improved method for searching interleavers from a certain set using Garello’s method with applications for the LTE standard

In this paper, we propose a method for searching interleavers within a certain class, with the aim of designing turbo codes with good distance spectrum. The method is based on a modified version of Garello’s algorithm and consists in the calculation of frame error rate truncated upper bound. Here, it is applied to quadratic permutation polynomial (QPP) interleavers able to outperform those chosen for the long-term evolution (LTE) standard, for lengths up to 1,504 bits. Three classes of interleavers have been analyzed: (1) the set of QPP interleavers with the largest spread, (2) the set of QPP interleavers with a spread parameter equal to that of LTE interleaver and the highest refined nonlinearity degree, and (3) the complete set of all QPP interleavers for lengths up to 1,008. The distance spectrum optimization is made for all classes. Compared to previous methods for finding QPP-based interleavers, the search complexity is reduced, with improved performances in terms of search time, allowing interleavers of higher length. For lengths up to approximately 450, the best interleavers were found in the first class. For longer lengths, the second class contained the best ones.     

Interleaver properties and their applications to the trelliscomplexity analysis of turbo codes

In this paper, the basic theory of interleavers is revisited in a semi-tutorial manner, and extended to encompass noncausal interleavers. The parameters that characterize the interleaver behavior (like delay, latency, and period) are clearly defined. The input-output interleaver code is introduced and its complexity studied. Connections among various interleaver parameters are explored. The classes of convolutional and block interleavers are considered, and their practical implementation discussed. The trellis complexity of turbo codes is tied to the complexity of the constituent interleaver. A procedure of complexity reduction by coordinate permutation is also presented, together with some examples of its application     

Interleavers for turbo codes using permutation polynomials over integer rings

A class of deterministic interleavers for turbo codes (TCs) based on permutation polynomials over /spl Zopf//sub N/ is introduced. The main characteristic of this class of interleavers is that they can be algebraically designed to fit a given component code. Moreover, since the interleaver can be generated by a few simple computations, storage of the interleaver tables can be avoided. By using the permutation polynomial-based interleavers, the design of the interleavers reduces to the selection of the coefficients of the polynomials. It is observed that the performance of the TCs using these permutation polynomial-based interleavers is usually dominated by a subset of input weight 2m error events. The minimum distance and its multiplicity (or the first few spectrum lines) of this subset are used as design criterion to select good permutation polynomials. A simple method to enumerate these error events for small m is presented. Searches for good interleavers are performed. The decoding performance of these interleavers is close to S-random interleavers for long frame sizes. For short frame sizes, the new interleavers outperform S-random interleavers.     

Performance of Möbius Interleavers for Turbo Codes

In this paper, we study the minimum free distance and error performance of turbo encoders with Möbius interleavers. In order to be capable of estimating the minimum free distance of these interleavers using binary-fixed point (BFP) algorithm, new deterministic interleavers called “truncated Möbius interleavers” are defined and constructed. It is shown how the shifted cycles of these interleavers can be related to the cycle structure of the primary Möbius transformation and its coefficients. By adjusting some parameters, an upper bound on the number of total tested BFPs for the proposed truncated Möbius interleavers is found. One distinctive property of Möbius interleavers is that their inverse can also be represented and computed with Möbius functions. Simulations are conducted to compare the error performance of the proposed truncated Möbius interleavers with quadratic permutation polynomial (QPP) interleavers whose inverses are also representable by a quadratic equation (Ryu and Takeshita in IEEE Trans Inf Theory 52(3):1254–1260, 2006). It is finally shown that the truncated Möbius interleavers can interleave sequences of information bits faster than QPP interleavers.     

Stream-oriented turbo codes

This work considers the design and performance of a stream-oriented approach to turbo codes which avoids the need for data framing. The stream paradigm applies to both serial and parallel turbo codes using continuous, free-running constituent encoders along with continuous, periodic interleavers. A stream-oriented turbo code based on parallel concatenated convolutional codes (PCCC) is considered and interleaver design criteria are developed for both block and nonblock periodic interleavers. Specifically, several nonblock interleavers, including convolutional interleavers, are considered. Interleaver design rules are verified using simulations where it is shown that nonblock interleavers with small-to-moderate delay and small synchronization ambiguity can outperform block interleavers of comparable delay. For large-delay designs, nonblock interleavers are found which perform within 0.8 dB of the capacity limit with a synchronization ambiguity of N=11     

2-Dimension Interleaver Design for IDMA Systems

A new design method interleavers, 2-dimension interleavers, are proposed for interleave division multiple access （IDMA） systems. With a same interleaving rule named I＇, the row indices and column indices of a traditional block interleaving matrix are scrambled to obtain an interleaver, which is marked as the master interleaver. F is produced by a loworder PN sequence generator. Two ways are provided for generating different interleavers. One is that all interleavers are generated by the circular shifting master interleaver. The other is that different inter leavers are generated by different Ts. Besides, we prove that the minimum distance between two adjacent bits resulted from 2-dimension interleaves is much larger than that of other schemes, such as random interleavers, power interleavers, and shiffting interleaves. The simulation results show that 2-dimension interleavers can achieve much better performance with much less resource consumption than random interleavers in IDMA systems.     

Modified Collision-Free Interleavers for High Speed Turbo Decoding

Inter-window shuffle (IWS) interleavers are a class of collision-free (CF) interleavers that have been applied to parallel turbo decoding. In this paper, we present modified IWS (M-IWS) interleavers that can further increase turbo decoding throughput only at the expense of slight performance degradation. By deriving the number of M-IWS interleavers, we demonstrate that the number is much smaller than that of IWS interleavers, whereas they both have a very simple algebraic representation. Further, it is shown by analysis that under given conditions, storage requirements of M-IWS interleavers can be reduced to only 368 storage bits for variable interleaving lengths. In order to realize parallel outputs of the on-line interleaving addresses, a low-complexity architecture design of M-IWS interleavers for parallel turbo decoding is proposed, which also supports variable interleaving lengths. Therefore, the M-IWS interleavers are very suitable for the turbo decoder in next generation communication systems with the high data rate and low latency requirements.     

基于组合交织器的高码率RA码的设计

针对一般交织器结构的重复累积(RA)码的奇偶校验矩阵中出现的短环问题,提出将一种组合技术应用于RA码的交织器结构,设计一种新型的组合交织器,使得产生的RA码具有高码率且无4环。仿真结果显示,在码长较长和高码率的情况下,组合交织的RA码译码性能优于传统交织器。     

分布式视频编码中符号Turbo码交织器的设计

分析了交织器在Turbo码中的作用,指出了现有的几种交织器的缺点.设计了两种新型的基于块交织的S随机交织器和基于伪随机交织的S随机交织器.仿真结果表明,与现有的几种交织器相比,这两种交织器在Turbo码译码迭代次数及延时方面性能更好,更适合于分布式视频编码系统.     

Optimization of degree-profile matching interleavers for LDPC-coded modulation

In this paper we introduce the concept of degree-profile matching interleavers (DPM-interleavers) and propose an LDPC-coded modulation scheme with a DPM-interleaver for 2^m-PAM. One advantage of our scheme over conventional LDPC-coded modulation schemes is to support various modulation orders in a single coder/decoder by properly choosing DPM-interleavers according to each modulation order. Given the degree distribution for a good binary LDPC code, we present the optimized degree-profiles for DPM-interleavers by density evolution in the cases of 4-PAM and 8-PAM, respectively. Simulation results show that our proposed scheme provides compatible performance with those of conventional LDPC-coded modulation schemes     

Permutation Polynomial Interleavers: An Algebraic-Geometric Perspective

An interleaver is a critical component for the channel coding performance of turbo codes. Algebraic constructions are important because they admit analytical designs and simple, practical hardware implementation. The spread factor of an interleaver is a common measure for turbo coding applications. Maximum-spread interleavers are interleavers whose spread factors achieve the upper bound. An infinite sequence of quadratic PPs over integer rings that generate maximum-spread interleavers is presented. New properties of PP interleavers are investigated from an algebraic-geometric perspective resulting in a new non- linearity metric for interleavers. A new interleaver metric that is a function of both the nonlinearity metric and the spread factor is proposed. It is numerically demonstrated that the spread factor has a diminishing importance with the block length. A table of good interleavers for a variety of interleaver lengths according to the new metric is listed. Extensive computer simulation results with impressive frame error rates confirm the efficacy of the new metric. Further, when tail-biting constituent codes are used, the resulting turbo codes are quasi-cyclic.     

一种新型交织器的设计

在简单介绍两种常用交织器的基础上,给出了随机分组交织器的设计,并进行了计算机仿真。结果表明,此交织器设计简单,占用内存少,性能明显优于分组交织器,而仅次于随机交织器。     

Variable-size interleaver design for parallel turbo decoder architectures

In this paper, we propose two techniques to design good S-random interleavers, to be used in parallel and serially concatenated codes with interleavers. The interleavers designed according to these algorithms can be shortened, in order to support different block lengths in such a way that all the permutations obtained by pruning, when employed in a parallel turbo decoder, are collision-free. The first technique, suitable for short and medium interleavers, guarantees the same performance of nonparallel interleavers in terms of spreading properties, simulated frame-error probabilities, and obtainable minimum distance of the actual codes. The second algorithm, to be used for large block lengths, permits achieving high degrees of parallelism at the price of a slight degradation of the spread properties, and also to change the degree of parallelism on-the-fly. The operations of a parallel turbo decoder employing these interleavers are described, and an example of the advantages of the proposed techniques is provided in a realistic system framework.     

信道交错器的实现方案及其优缺点

系统地介绍信道交错器(Interleaver)技术的发展状况,包括最基本的Interleaver类型和最新发展起来的一些技术,同时对比了各种Interleaver技术的优缺点,指出Interleaver技术还存在的问题,并描述Interleaver技术的应用前景。     

Construction of turbo code interleaves from 3-regular Hamiltonian graphs

In this letter, we present a new construction of interleavers for turbo codes from 3-regular Hamiltonian graphs. The interleavers can be generated using a few parameters, which can be selected in such a way that the girth of the interleaver graph (IG) becomes large, inducing a high summary distance. The size of the search space for these parameters is derived. The proposed interleavers themselves work as their de-interleavers.