Fast algorithm for electromagnetic scattering by buried conductingplates of large size

This letter presents a fast algorithm for electromagnetic scattering by buried conducting plates of large size and arbitrary shape using the conjugate gradient (CG) method combined with the fast Fourier transform (FFT). Due to the use of FFT in handling the cyclic convolutions related to Toeplitz matrices, the Sommerfeld integrals' evaluation for the buried scattering problem, which is usually time consuming, has been reduced to a minimum. The memory required for this algorithm is of the order N-the number of unknowns-and the computational complexity is of order N_iterNlogN (N_iter is the iteration number N_iter≪N for large problems)     

On the Fast Fractional Jacket Transform

Motivated by the center weighted Hadamard matrix, we propose an improved algorithm for the fast fractional jacket transform (FRJT) based on eigendecomposition of the fractional jacket matrix (FRJM). Employing a matrix diagonalization transformation that decomposes a matrix of large size into products of the matrices composed of eigenvectors and eigenvalues, an FRJM of large size can be fast factored into products of several sparse matrices in a recursive fashion. To generate an FRJM of large size, an algorithm for the factorable FRJM can be conveniently designated with a reduced computational complexity in terms of additions and multiplications. Since the proposed FRJM itself concerns interpretation as a suitable rotation in the time-frequency domain, it is applicable for optics and signal processing.     

基于QR分解的LS优化算法研究

本文对基于 QR 分解的 LS 优化算法进行研究，通过构造矩阵的方法，优化 Q 矩阵和 R 矩阵的计算算法，实现了对 LS 算法的优化，减少了算法对时间和空间资源的需求，并对算法进行了时间复杂度和空间复杂度分析，证明了该优化算法的有效性。     

On a Class of Pseudorandom Sequences From Elliptic Curves Over Finite Fields

Following the idea of Xing et al., we investigate a general method for constructing families of pseudorandom sequences with low correlation and large linear complexity from elliptic curves over finite fields in this correspondence. With the help of the tool of exponential sums on elliptic curves, we study their periods, linear complexities, linear complexity profiles, distributions of r-patterns, periodic correlation, partial period distributions, and aperiodic correlation in detail. The results show that they have nice randomness.     

具有低编码复杂度准循环扩展LDPC码的构造方法

PEG(Progressive-Edge-Growth)算法是迄今为止构造性能优异的LDPC中短码的一种有效构造方法,然而直接采用该算法构造的LDPC码的编码复杂度正比于码长的平方,这是其实用化过程中的一个瓶颈。针对这一问题,提出一种具有低编码复杂度和低错误平层的准循环扩展LDPC码的构造方法。该算法在PEG算法基础上,先构造出近似下三角结构的半随机基矩阵,然后再对基矩阵进行扩展,该方法可以在不改变基矩阵的度分布比例情况下,有效消除短环。仿真结果表明,所提出的方法构造的LDPC码比原始的PEG算法构造的随机LDPC码具有更低的错误平层,而且编码复杂度更低,更易于硬件实现。     

Antipodal paraunitary matrices and their application to OFDM systems

Paraunitary (PU) matrices and filterbanks have played an important role in many applications. This paper studies a special class of PU matrices, called antipodal paraunitary (APU) matrices. APU matrices are PU matrices whose coefficient matrices consist of /spl plusmn/1 only. Several new methods will be introduced for the construction of APU matrices. In particular, a new method based on the butterfly structure that has a low cost implementation is proposed. Moreover, one application of APU matrices in precoded orthogonal frequency division multiplexing (OFDM) systems will be considered. By using an APU precoding matrix, the complexity will be very low, and experiments show that the use of APU matrices can greatly enhance the performance.     

Quasi-cyclic LDPC codes for fast encoding

In this correspondence we present a special class of quasi-cyclic low-density parity-check (QC-LDPC) codes, called block-type LDPC (B-LDPC) codes, which have an efficient encoding algorithm due to the simple structure of their parity-check matrices. Since the parity-check matrix of a QC-LDPC code consists of circulant permutation matrices or the zero matrix, the required memory for storing it can be significantly reduced, as compared with randomly constructed LDPC codes. We show that the girth of a QC-LDPC code is upper-bounded by a certain number which is determined by the positions of circulant permutation matrices. The B-LDPC codes are constructed as irregular QC-LDPC codes with parity-check matrices of an almost lower triangular form so that they have an efficient encoding algorithm, good noise threshold, and low error floor. Their encoding complexity is linearly scaled regardless of the size of circulant permutation matrices.     

LDPC code reconstruction based on algorithm of finding low weight code-words

LDPC code reconstruction without a candidate set is one of the tough problems in channel code reconstruction.First,theoretical analysis was provided for the number of received code-vectors needed for the reconstruction,and a lower bound was derived.Then,according to the lower bound,and based on an algorithm for finding low weight code-words,a new reconstruction method was proposed.It looked for low weight vectors one by one from the dual space of the received code-vector space and used them to reconstruct the sparse parity-check matrices.Number of iterations and the computational complexity of the method were analyzed based on exponential distribution theory.Under noise-free conditions,drawbacks of the existing method,including limited applicable range and large quantity of required data,have been overcame.Under noisy conditions,the proposed method has higher robustness against noise and relatively low complexity,compared to existing methods.For QC-LDPC codes,the reconstruction performance can be further improved using the quasi-cyclic property of their sparse parity-check matrices.     

对合Cauchy-Hadamard型MDS矩阵的构造

MDS矩阵和对合MDS矩阵在分组密码中有广泛应用。该文将考察同时是Hadamard矩阵和Cauchy矩阵的那些MDS矩阵,给出了这类矩阵的结构、构造方法和个数,从而得到了MDS矩阵一种新的构造方法。该文还证明了Cauchy-Hadamard型MDS矩阵都等效于对合的Cauchy-Hadamard型MDS矩阵,并给出了由Cauchy-Hadamard型MDS矩阵构造对合的Cauchy-Hadamard型MDS矩阵的方法。     

基于双向传播算子的互质面阵二维波达方向估计

针对谱峰搜索的二维波达方向估计中现有算法复杂度高,精度受搜索间隔影响较大的问题,给出了一种双向传播算子的互质面阵二维波达方向估计算法,实现了俯仰角和方位角的低复杂、高精度、无模糊联合估计.该方法首先将互质阵列引入到二维波达方向估计中,构造互质平面阵模型,然后采用两次旋转不变传播算子方法计算出不同阵列流型方向上的旋转因子矩阵,根据旋转因子矩阵解算出目标信号的俯仰角和方位角,同时利用互质理论消除了稀疏阵列角度估计的不确定性,证明了互质阵列模型下采用双向传播算子方法进行俯仰角和方位角估计的无模糊性.对算法的复杂度进行理论分析,并给出了平面阵列角度估计的克拉美罗界推导.理论分析与仿真结果表明,算法不需要进行角度匹配和谱峰搜索,在相同条件下的均方根误差性能优于均匀平面阵的多重信号分类算法,并且以较低的复杂度无模糊的达到了高维网格搜索的精度.     

Block‐Mode Lattice Reduction for Low‐Complexity MIMO Detection

We propose a very‐low‐complexity lattice‐reduction (LR) algorithm for multi‐input multi‐output detection in time‐varying channels. The proposed scheme reduces the complexity by performing LR in a block‐wise manner. The proposed scheme takes advantage of the temporal correlation of the channel matrices in a block and its impact on the lattice transformation matrices during the LR process. From this, the proposed scheme can skip a number of redundant LR processes for consecutive channel matrices and performs a single LR in a block. As the Doppler frequency decreases, the complexity reduction efficiency becomes more significant.     

三平行线阵中基于改进传播算子的二维DOA估计方法

提出了一种三平行线阵中基于改进传播算子的二维波达方向估计方法。该方法针对三平行阵列的结构特点,利用三平行线阵中两个相互垂直的双平行线阵,分别构造一个扩展传播矩阵,求得旋转矩阵。然后根据三平行线阵的特性,对分别得到的旋转矩阵进行配对。最后利用配对后的旋转矩阵,联合估计信号的方位角和俯仰角。该方法当俯仰角在70°~ 90°之间时不会出现角度估计失效问题,充分利用了所有阵元信息,提高了角度估计性能,而且具有更低的计算复杂度。仿真验证了提出方法的有效性。      

基于删余等效的高码率卷积码的低复杂度译码方法

根据删余卷积码具有较低的译码复杂度这一特征,提出了一种适用于普通高码率卷积码的低复杂度译码方法。通过多项式生成矩阵表示法,推导了删余卷积码的等效多项式生成矩阵,给出了等效多项式生成矩阵的计算准则。在分析删余卷积码与相同码率普通卷积码的等效关系和区别的基础上,提出了高码率卷积码的删余等效并给出了计算高码率卷积码删余等效后原始码和删余矩阵的方法。以原始码和删余矩阵构成的删余等效结构为译码基础,实现了高码率卷积码的低复杂度译码,其译码复杂度与原始码相当。仿真结果表明,删余等效译码方法相对于正常译码方法,其性能损失很小。     

基于偏最小二乘的低复杂度数字预失真

在宽带场景下,传统的数字预失真(DPD)模型需要更高的阶次和更多的系数来校正功率放大器(PA)强非线性和记忆效应,这就会导致极高的计算复杂度和解算系数时的病态问题.文章围绕复杂DPD模型参数辨识和低复杂度DPD算法实现展开深入研究,提出了一种新的基于偏最小二乘(PLS)的低复杂度DPD方法.所提方法根据PA的前逆输入输...     

大规模服务覆盖网拓扑设计

针对大规模服务覆盖网拓扑设计方法构建效率低的问题,该文提出了以带宽容量为约束条件,基于多商品流的线性规划模型和实现算法,以降低构建算法的时间与空间复杂度。仿真结果表明,该算法在大规模网络情况下,构建效率和资源利用率有显著提高。     

Permutation Decoding and the Stopping Redundancy Hierarchy of Cyclic and Extended Cyclic Codes

We introduce the notion of the stopping redundancy hierarchy of a linear block code as a measure of the tradeoff between performance and complexity of iterative decoding for the binary erasure channel. We derive lower and upper bounds for the stopping redundancy hierarchy via LovÁsz's Local Lemma (LLL) and Bonferroni-type inequalities, and specialize them for codes with cyclic parity-check matrices. Based on the observed properties of parity-check matrices with good stopping redundancy characteristics, we develop a novel decoding technique, termed automorphism group decoding, that combines iterative message passing and permutation decoding. We also present bounds on the smallest number of permutations of an automorphism group decoder needed to correct any set of erasures up to a prescribed size. Simulation results demonstrate that for a large number of algebraic codes, the performance of the new decoding method is close to that of maximum-likelihood (ML) decoding.      

A Fast Decoupled Nominal 2-D Direction-of-Arrival Estimation for Coherently Distributed Source

In this paper, we consider the problem of the nominal 2-D (azimuth and elevation) direction-of-arrival (DOA) estimation for coherently distributed source. This new approach is based on the rotation matrices of three parallel uniform linear arrays as deduced, which has decoupled the nominal 2-D DOA from those of angular spreads. The estimator makes use of the eigenvalue decomposition to beamspace data to estimate the nominal elevation DOA. And then using a new cross-correlation matrix, the nominal azimuth DOA estimates are decoupled from the elevation estimates and can be obtained with no searching. The proposed algorithm has lower computational complexity particularly when the radio of array size to the number of source is large, at the expense of negligible performance loss. Simulation results verify the effectiveness of the proposed method.     

QC－LDPC码的置换矩阵循环移位次数设计

 本文提出了一种循环移位次数的代数设计方法,该方法可用来构造基于置换矩阵的QC-LDPC码的稀疏奇偶校验矩阵H 。这个方法的基本思路是：将构造 q×t置换阵列 H矩阵的问题转化为构造 q×t下标矩阵 S(H)=[aij]的问题,然后根据Fosserier的充分必要条件,设计出能消除小围长（girth）的下标计算表达式 aij=f(q.t.n)。由该方法构造的H 矩阵能消除4环长,围长至少是6。     

双基地MIMO雷达相干目标的角度快速估计算法

针对双基地多输入多输出（MIMO）雷达定位的实时性问题,提出了一种基于Toeplitz矩阵的目标快速定位算法。双基地MIMO雷达接收的信号往往是相干的,因此无法直接应用角度估计算法。首先通过接收的数据得到一组Toeplitz子矩阵,利用这组子矩阵重构得到协方差矩阵,其秩等于目标个数,达到解相干的目的。采用改进多级维纳滤波器（MSWF）的前向递推,不需要通过特征值分解,得到信号子空间,结合ESPRIT算法,估计出目标的发射角度（DOD）和接收角度（DOA）。算法通过构造Toeplitz矩阵解相干,仅改变矩阵结构,降低了计算复杂度,具有较好目标分辨力和解相干能力。