Capacity Approaching Codes for Non-Coherent Orthogonal Modulation

The paper describes a curve-fitting approach for the design of capacity approaching coded modulation for orthogonal signal sets with non-coherent detection. In particular, bit-interleaved coded modulation with iterative decoding is considered. Decoder metrics are developed that do not require knowledge of the signal-to-noise ratio, yet still offer very good performance.     

基于自适应调制的改进型VBLAST检测算法研究

根据检测顺序不同,贝尔实验室垂直分层空时(V-BLAST)检测算法分为正序和逆序检测。本文针对自适应调制的特点首次将两种检测算法结合,提出一种新的混合检测顺序。首先检测调制尺寸已达最大的饱和信道,然后检测信噪比不能满足最低门限的无效信道,最后按检测后信噪比距离门限值最近者优先的原则检测剩余子信道。仿真结果表明,在平均信噪比较高或较低时,混合检测的频谱效率分别趋于正序或逆序检测,当信噪比适中时,新算法的频谱效率优于其它两种算法。     

Adaptive Delta Modulation Systems for Video Encoding

This paper describes several adaptive delta modulators designed to encode video signals. One- and two-dimensional ADM algorithms are discussed and compared. Results are shown for bit rates of 2 bits/pixel, 1 bit/pixel and 0.5 bits/pixel. Pictures showing the difference between the encodeddecoded pictures and the original pictures are presented. Results are also presented to illustrate the effect of channel errors on the reconstructed picture. A two-dimensional ADM using interframe encoding is also presented. This system operates at the rate of 2 bits/pixel and produces excellant quality pictures when there is little motion. We also describe and illustrate the effect of large amounts of motion on the reconstructed picture.     

一种基于PPM的LDPC编译码方案

该文基于LDPC码和PPM调制方式构造了一种适用于UWB无线通信系统的低码率的编译码方案LDPC-PPM。本方案在保证系统性能的前提下,通过改变编码比特到调制符号的映射方式,不但避免了一般编码调制系统中译码和解调之间的迭代运算,而且可以应用快速Hadamard变换(FHT)和基于FHT的后验概率译码(APP-FHT)来进一步降低接收端的译码复杂度。可以证明,该方案等价于BPSK调制下的低码率的LDPC-Hadamard码。仿真结果表明,在信息比特长度是65536,该方案可以在-1.18dB处达到误比特率为 的性能,仅比采用BPSK调制的Turbo-Hadamard码差0.02dB。     

多元速率兼容LDPC码的自适应编码调制系统研究

本文设计了一种基于有限域GF(q)上的多元速率兼容LDPC (RC-LDPC) 码结合高阶调制的自适应编码调制(Adaptive Coded Modulation, ACM) 系统。并提出了多元RC-LDPC码在独立和相关衰落信道下的增量冗余型自适应编码调制方案。本方案中多元LDPC码码率从1/3到5/6灵活变化,以较低的系统复杂度,有效提高了系统的频带利用率。仿真结果表明:随着系统吞吐率提高,多元ACM系统相对于二元ACM系统具有越来越明显的编码增益,最高可达约9 dB。      

Approximately Lower Triangular Ensembles of LDPC Codes With Linear Encoding Complexity

The complexity of brute-force encoding of low-density parity-check (LDPC) codes is proportional to the square value of the block length. Richardson and Urbanke have proposed efficient encoding algorithms for LDPC codes. These algorithms permute the parity-check matrix of the code iteratively, such that it becomes approximately lower triangular. We propose a new approach for efficient encoding of LDPC codes in which we modify the code ensemble to force an approximate lower triangular structure, thus eliminating the need to apply the algorithms of Richardson and Urbanke in this ensemble. We prove that the new ensemble has the same asymptotic threshold as the corresponding standard ensemble. The new ensemble can be used for linear time encoding of an arbitrary code profile. Computer simulations confirm that the performances of the standard and new ensembles are also very similar when using finite length codes     

Battery-Aware Adaptive Modulation With QoS Constraints

We consider the problem of joint battery management and modulation optimization for maximizing the lifetime of a battery-powered autonomic wireless system while satisfying certain quality-of-service constraints. Our objective is to design the optimal transmission schemes adapting to the battery state, the delay constraints, and channel conditions. A delay-constrained data-transmission scenario is considered, where the battery state information is only available at the beginning of the entire transmission duration. The corresponding problem is formulated as a multiobjective stochastic optimization problem, which is hard to solve. We approximately transform the original problem to a multiobjective deterministic optimization problem by using a lower bound to replace the objective function of the original problem. The optimal, as well as efficient suboptimal solutions are developed. Simulation results are provided to demonstrate that the proposed algorithms can significantly increase the lifetime of the battery-powered autonomic wireless systems.     

V-BLAST OFDM信号调制识别算法

提出了基于高阶累积量的V-BLAST OFDM信号识别算法,用以区分频率选择性衰落信道条件下V-BLAST结构的多载波信号(0FDM)和单载波信号(MFSK、MPSK、MQAM).该算法不需要预先知道信号的载波频率、波特率以及信道的先验信息,直接在中频对信号进行识别处理.仿真结果表明该算法具有良好的识别性能.     

Linear Time Encoding of LDPC Codes

In this paper, we propose a linear complexity encoding method for arbitrary LDPC codes. We start from a simple graph-based encoding method ?label-and-decide.? We prove that the ?label-and-decide? method is applicable to Tanner graphs with a hierarchical structure-pseudo-trees-and that the resulting encoding complexity is linear with the code block length. Next, we define a second type of Tanner graphs-the encoding stopping set. The encoding stopping set is encoded in linear complexity by a revised label-and-decide algorithm-the ?label-decide-recompute.? Finally, we prove that any Tanner graph can be partitioned into encoding stopping sets and pseudo-trees. By encoding each encoding stopping set or pseudo-tree sequentially, we develop a linear complexity encoding method for general low-density parity-check (LDPC) codes where the encoding complexity is proved to be less than 4 ·M ·((k?- 1), where M is the number of independent rows in the parity-check matrix and k? represents the mean row weight of the parity-check matrix.     

LDPC编译码技术研究

LDPC码,即低密度奇偶校验码,本质上是一种线性分组码,其译码性能比Turbo码更接近香农限。文中首先介绍了LDPC码的定义及描述;其次对LDPC码快速编码方法进行分析,对可线性编码的LDPC码构造进行探讨;然后对LDPC的译码技术进行研究;最后对LDPC码的应用前景进行讨论。     

高速并行LDPC编码的FPGA实现

LDPC码具有优异的误码性能,并被很多协议采用,其中CCSDS规范就采用了LDPC码。符合CCSDS规范的LDPC码编码器的设计目的是满足卫星实际应用的需求,降低卫星信道传输的误码率。实现了8位并行LDPC码编码,并优化了矩阵信息的存储设计。在XC2V3000 FPGA实测中,8位并行编码吞吐量达到800 Mbps。     

Joint Adaptive Modulation and Diversity Combining With Downlink Power Control

We consider the problem of finding low-complexity, bandwidth-efficient, and processing-power-efficient transmission schemes for a downlink scenario under the framework of diversity combining. Capitalizing on recent results for joint adaptive modulation and diversity combining (AMDC) schemes, we design and analyze two AMDC schemes that utilize power control to reduce the radiated power and, thus, the potential interference to other systems/users. Based on knowledge of channel fading, the proposed schemes adaptively select the signal constellation, diversity combiner structure, and transmit power level. We show that the novel schemes also provide significant average transmit power gains compared to existing joint adaptive quadratic-amplitude modulation (QAM) and diversity schemes. In particular, over a large signal-to-noise ratio (SNR) range, the transmitted power is reduced by 30%-50%, yielding a substantial decrease in interference to coexisting systems/users, while maintaining high average spectral efficiency, low combining complexity, and compliance with bit-error-rate constraints.     

多进制LDPC码编译码研究

低密度奇偶校验(LDPC)码是当前广泛应用的信道编码方式.多进制LDPC码在各类噪声的干扰下,纠错性能仍然极好,是如今信道编码学者重点研究方向.主要研究多进制LDPC码的编码和译码方法,通过软件仿真,分别对比不同编码和译码方法的纠错性能,并分析造成纠错性能差异的原因.主要对一种由二进制LDPC码中元素替换得到的四进制LDPC码,通过软件进行仿真分析,并最终得到5/6码率,采用16符号正交幅度调制(16QAM)方式的四进制LDPC码的编码结构.     

多进制（Q-ary）LDPC码的编译码原理

多进制(Q-ary)LDPC码是将二进制LDPC码一般化到有限域GF(q),其校验矩阵元素不再是(0,1),而是集合(0,1,…,q-1),其译码仍然采用高效的信度传递迭代译码算法.本文主要阐述了多进制LDPC码的编译码原理,并介绍了一种可简化译码的傅立叶变换译码算法.通过将多进制LDPC码的性能与二进制LDPC码和RS码的性能进行比较,可以看出多进制LDPC码在磁存储系统、下一代ADSL系统以及深空通信方面将是取代RS码的强有力的候选,有极其重要的应用价值.     

LDPC码的有效编码算法研究

LDPC码编码结构中短环的存在,导致译码时的重复迭代,降低了译码性能。介绍了一种编码算法,该算法先通过Richardson和Urbanke提出的Efficient编码算法对LDPC码的校验矩阵优化,然后再主要研究其二分图中长度为4的短环,提出了一种校验矩阵H的消4-环算法。最终实现了降低编码的复杂度的同时,译码效率也得到提高。     

LDPC码快速编码器的DSP设计与实现

对CCSDS131.1-0-2(Experimental Specification)中提出的一类准循环LDPC删余码进行研究,分析了该类码的特点,并仿真了其性能;结合其特点,对编码中的"贪婪算法"进行一定的改进,设计了快速编码算法.通过对TMS320C6416DSP平台的功能与运算技巧的结合,对编码算法代码进行合理优...     

DVB-S2标准LDPC码编码算法研究

随着VLSI的高速发展,低密度奇偶校验码(LDPC)作为一种高效且易于实现的差错控制方法被DVB组织接纳为下一代数字视频广播标准(DVB S2)的信道编码方案。研究了用于DVB S2标准LDPC码的非规则重复累加(IRA)编码算法,重点探讨了该码的生成矩阵特点以及编码的一般步骤,用C语言编写了实现该算法的软件,并进行了性能仿真。仿真结果表明该LDPC码在AWGN信道中极低信噪比情况下仍具有较好的纠错性能。     

一种高效的LDPC编码器的DSP设计与实现

目前,大多数LDPC编码器采用的是FPGA实现,文中根据Richarson和Unbanke提出的有效编码算法,具体分析了基于该算法的编码器在DSPs上的设计思路,并联合考虑校验矩阵的存储与运算,给出一种高效的存储方式和矩阵向量乘法的计算方法.此外,结合DSPs的软件流水功能,对程序进行了优化,使实现编码所需的指令周期大幅减少,从而提高编码速率..     

宽带无线TDMA系统的自适应调制技术

无线多媒体业务的快速增长促进了宽带无线ＴＤＭＡ通信系统的研究和开发,宽带无线ＴＤＭＡ通信系统方面出现了一些新的技术和系统设计概念。讨论宽带无线ＴＤＭＡ系统中采用的自适应调制技术。     

Impact of Spatial Channel Reuse and Adaptive Modulation on Wireless Mesh Network Capacity

The capacity analysis based on the concept of collision domains may be applied to wireless networks with mesh topology, e.g. wireless backhaul networks for rural areas, sensor networks, etc. The strength of the method is the fact that it may be easily fitted to any MAC protocol, routing algorithm, channel allocation method, and, therefore, is a valuable tool for verification and performance analysis of such algorithms. However, simplifications assumed by some authors may lead to erroneous results, e.g. significantly underestimated capacity of the WMN. Therefore, phenomena specific to wireless networks, such as spatial channel reuse, and features specific to wireless standards, such as link adaptivity, should be included in the analysis, as presented in this paper.