Optimum sequence multisets for synchronous code-divisionmultiple-access channels

It is shown that the sum capacity of the symbol-synchronous code-division multiple-access channel with equal average-input-energy constraints is maximized precisely by those spreading sequence multisets that meet Welch's lower bound on total squared correlation. It is further shown that the symmetric capacity of the channel determined by these same sequence multisets is equal to the sum capacity     

An Algorithm for Obtaining Welch Bound Equality Sequences for S-CDMA Channels

In this paper we describe the properties of those sequences(matrix) that meet equality in the Welch's lower bound on total squared correlation. These sequences are called also Welch Bound Equality (WBE) sequences. The generalized WBE sequences (matrix) are defined. Same definitions on majorization are introduced in order to characterize the eigenvalues of a hermitian matrix. A new algorithm for generating WBE spreading sequence multisets is proposed. We apply the proposed algorithm when all users have different average-channel-input energy constraint in the case of synchronous CDMA channels. We obtain real optimum signature sequences that maximize the sum capacity of S-CDMA channels.     

Data verification and reconciliation with generalized error-control codes

We consider the problem of data reconciliation, which we model as two separate multisets of data that must be reconciled with minimum communication. Under this model, we show that the problem of reconciliation is equivalent to a variant of the graph coloring problem and provide consequent upper and lower bounds on the communication complexity of reconciliation. Further, we show by means of an explicit construction that the problem of reconciliation is, under certain general conditions, equivalent to the problem of finding error-correcting codes for a general class of errors. Under this equivalence, reconciling with little communication is linked to codes with large size, and vice versa. We show analogous results for the problem of multiset verification, in which we wish to determine whether two multisets are equal using minimum communication. As a result, a wide body of literature in coding theory may be applied to the problems of reconciliation and verification.     

不可预测性与伪随机性是等价的一种应用

伪随机产生器是一种有效的确定性算法,它将随机选择的位种子扩展为较长的伪随机序列,并且这些序列在多项式时间内与真正的随机序列是不可分的。本篇文章中主要是在大整数分解是困难的假设条件下,对Goldreich已构造的一种伪随机产生器,利用不可预测性与伪随机性是等价的方法进行另一种证明。     

On the optimal spreading sequence allocation in flat-fading channels

The sum capacity of optimally allocated spreading sequences with and without power control is studied for synchronous code-division multiple-access channels subject to frequency flat fading. Continuing upon the recently derived characterization of sum capacity for asymmetric received powers with no power control at the transmitter, we present an asymptotic analysis of the sum capacity in the wideband limit of a large number of users and evaluate possible gains compared with the random spread sequences. Next, we discuss group orthogonal optimal sequence allocation and analyze its potential to decrease the complexity of the receiver while achieving the sum capacity of optimally allocated equal-energy sequences. For the power controlled case, we give a general characterization of sum capacity and identify the optimal power-control law and sequence allocation that achieves this capacity. These results are also analyzed in the asymptotic limit of a large number of users.     

多重集的保密计算及应用

安全多方计算是近年来国际密码学界研究的热点问题.多重集作为标准集的推广在实际中有广泛的应用,对于多重集的保密计算问题研究具有重要的意义.本文主要研究两方多重集的交集、并集以及基于阈值和集的保密计算问题.首先针对不同问题设计相应的编码方法,结合Paillier加密方案设计保密计算协议,并应用模拟范例方法严格证明协议的安全性.效率分析和实验验证表明本文所设计的协议是简单高效的.     

混沌理论在水印置乱中的应用

为提高水印的安全性,消除图像水印像素之间的空间相关性,尽可能地分散错误比特,提出了利用Arnold变换以及混沌理论对水印进行置乱预处理方案。从减弱生成的混沌序列前后数值之间的相关性出发,提出了一种随机混沌水印置乱算法,它的混沌初值是由一个随机产生的指针从一个随机生成的数组中选取的,在从混沌序列中选取一个原始位置序列时,并没有进行连续选取,而是根据算法中随机产生的一个扩展系数进行等间隔地抽取,此处类似于模拟信号转化为数字信号时,进行等间隔采样的原理。对原混沌置乱算法进行改进,从而提高了混沌序列的初值灵敏性和置乱效率。     

Opportunistic Space-Division Multiple Access With Beam Selection

In this paper, a novel transmission technique for the multiple-input multiple-output (MIMO) broadcast channel is proposed that allows simultaneous transmission to multiple users with limited feedback from each user. During a training phase, the base station modulates a training sequence on multiple sets of randomly chosen orthogonal beamforming vectors. Each user sends the index of the best beamforming vector and the corresponding signal-to-interference-plus-noise ratio for that set of orthogonal vectors back to the base station. The base station opportunistically determines the users and corresponding orthogonal vectors that maximize the sum capacity. Based on the capacity expressions, the optimal amount of training to maximize the sum capacity is derived as a function of the system parameters. The main advantage of the proposed system is that it provides throughput gains for the MIMO broadcast channel with a small feedback overhead, and provides these gains even with a small number of active users. Numerical simulations show that a 20% gain in sum capacity is achieved (for a small number of users) over conventional opportunistic space division multiple access, and a 100% gain (for a large number of users) over conventional opportunistic beamforming when the number of transmit antennas is four.     

A trapdoor multiple mapping (Corresp.)

A public key cryptosystem is suggested in which a message is enciphered by adding its numerical value to a sum of elements selected randomly from a publicly known knapsack, thus enabling multiple mapping of the message. Data expansion is moderate while reasonable security is maintained. Since the selected knapsack elements are message-independent, the encryption is very fast.     

用于音乐作品版权保护的数字音频水印算法

提出了一种用于音乐作品版权保护的数字音频水印嵌入算法，该算法首先将视觉可辨的二值水印图像降维成一维水印序列并进行随机置乱，再从原始数字音频信号中随机选取采样数据并进行快速傅立叶变换(FFT)，最后结合人类听觉系统(HAS)掩蔽特性选取绝对值较大的FFT系数嵌入水印信息。仿真实验表明：该数字音频水印嵌入算法不仅具有较好的透明性，而且对诸如叠加噪声、有损压缩、低通滤波、重新采样、重新量化等攻击均具有较好的鲁棒性。     

A novel image watermarking scheme against desynchronization attacks by SVR revision

In digital image watermarking, the watermark’s vulnerability to desynchronization attacks has long been a difficult problem. On the basis of support vector regression (SVR) theory and local image characteristics, a novel image watermarking scheme against desynchronization attacks by SVR revision is proposed in this paper. First, some pixels are randomly selected and the sum and variance of their neighboring pixels are calculated; second, the sum and variance are regarded as the training features and the pixel values as the training objective; third, the appropriate kernel function is chosen and trained, a SVR training model will be obtained. Finally, the sum and variance of all pixels’ neighboring pixels are selected as input vectors, the actual output can be obtained by using the well-trained SVR, and the digital watermark can be recovered by judging the output vector. Experimental results show that the proposed scheme is invisible and robust against common signals processing such as median filtering, sharpening, noise adding, and JPEG compression, etc., and robust against desynchronization attacks such as rotation, translation, scaling, row or column removal, shearing, local random bend, etc.     

PAPR Reduction of OFDM Signals Using Partial Transmit Sequences and Reed-Muller Codes

This letter proposes a modified PTS technique using binary Reed-Muller (RM) codes for error correction and PAPR control in BPSK OFDM systems. A RM code is divided into the direct sum of a correcting subcode for encoding information bits and a scrambling subcode for encoding PAPR bits. The transmitted signal of the resulting OFDM sequence is selected with minimum PAPR from a number of candidates which are codewords of a coset of the scrambling subcode. We consider the RM codes in natural and cyclic orderings. Numerical results show that RM codes in cyclic ordering achieve better performance in PAPR reduction than RM codes in natural ordering.     

A method for recovering physiological components from dynamicradionuclide images using the maximum entropy principle: a numericalinvestigation

A method based on the maximum entropy principle is described for recovering physiological components from a sequence of dynamic radionuclide images. The method does not require any assumption about the shapes of the component curves. It is, however, assumed that the components are nonnegative. The method requires normalization of component curves. The sum of squares of each component curve to be estimated is normalized so as to be unity. A first-pass cardiac study and a hepatic study are selected for investigation of applicability of the method. The method is investigated numerically using computer-generated time-activity curves with six components for the cardiac study and seven components for the hepatic study. Within the regions studied, the results have demonstrated that the method may recover the component time-activity curves and the corresponding images of physiological components from a sequence of dynamic radionuclide images. The ability and limitations of the method to recover physiological components are discussed and potential applications are suggested.     

The Subsequence Weight Distribution of Summed Maximum Length Digital Sequences

The statistics of the weight distribution of subsequences of digital sequences called hybrid-sum sequences, formed from the modulo-two sum of several maximum length sequences, are analyzed. The results indicate that a relation exists between the statistics of the weight distribution of the subsequences and the characteristic polynomials of the component maximum length sequences. An analysis procedure is developed for identifying a large group of sequences with good statistical properties for applications requiring the generation of analog pseudorandom noise by filtering digital sequences. Using the analysis approach, the filtering process is approximated by the convolution of the sequence with a sum of unit-step functions. The first five moments of the resulting weighttuples are used to characterize the statistics of the filtered sequence. The analysis reveals that the statistics of the signals generated with the hybrid-sum generator are potentially superior for many applications to the statistics of signals generated with single maximum length sequence generators. Furthermore, fewer calculations are required to evaluate the statistics of a large group of hybrid-sum generators than are required to evaluate the statistics of the same size group of approximately equivalent maximum length sequences. Efficient algorithms that may be used to evaluate the statistics of hybrid-sum sequences are indicated, and example calculations are given.     

基于最大熵的隐马尔可夫模型文本信息抽取

文本信息抽取是处理海量文本的重要手段之一.最大熵模型提供了一种自然语言处理的方法.提出了一种基于最大熵的隐马尔可夫模型文本信息抽取算法.该算法结合最大熵模型在处理规则知识上的优势,以及隐马尔可夫模型在序列处理和统计学习上的技术基础,将每个观察文本单元所有特征的加权之和用来调整隐马尔可夫模型中的转移概率参数,实现文本信息抽取.实验结果表明,新的算法在精确度和召回率指标上比简单隐马尔可夫模型具有更好的性能.     

On identification of certain nonlinear systems (Corresp.)

In the fields of communication and control there sometimes arises the problem of determining the characteristics of a time-invariant system from discrete records of its input and output during a limited interval of time, where the output data are contaminated with random noise. When this system is linear, we can use the convolution sum to obtain a characterization of the output as a linear combination of past inputs. Hill and McMurtry [4] showed that if we choose a Legendre binary noise sequence as input to a linear system, then the least squares approximation to the characterizing coefficients is expressible in a computationally feasible form, even when a large number of coefficients is involved. In this correspondence we characterize a nonlinear system by a generalization of the convolution sum and show that if we choose Golomb's maximal linear recurring binary-noise sequence [2] as input, then the least squares approximation to the characterizing coefficients is expressible in a computationally feasible form. Thus, the maximal linear recurring sequence occupies the same role in investigating certain nonlinear systems that the Legendre sequence occupies in investigating linear systems.     

Multiple-Subcarrier Optical Communication Systems With Subcarrier Signal-Point Sequence

Multiple-Subcarrier Optical Communication Systems With Subcarrier Signal-Point Sequence We propose a multiple-subcarrier (MS) optical communication system with subcarrier signal-point sequence (SSPS). We use the SSPSs having a large minimum value and large Euclidean distances, so that the required dc bias is minimized, and the error-rate performance is improved. Note that in the proposed system, the signal points having the larger minimum value are selected, while the signal points having a lower peak-to-mean-envelope power ratio (PMEPR) are selected in orthogonal frequency-division multiplexing (OFDM) systems. Therefore, the SSPSs good for OFDM with phase shifting by$pi$radian are not necessarily effective for MS optical communication systems. The main contributions of our paper are as follows. We derive transmit sequences having a large minimum value and large Euclidean distances by using 8-PSK and$(8+1)$-APSK. Since a designing optimal sequences would be prohibitively complex, we introduce a reasonable procedure for suboptimal sequence design, obtaining good results. We show that the normalized power requirements and normalized bandwidth requirements of the MS systems with SSPS (MS-SSPS) are smaller than those of the conventional MS systems.     

多点协作下行链路单调协同波束形成算法

研究了单基站功率约束条件下的多点协作多输入单输出干扰下行链路系统的和速率最大化非凸优化问题。为有效求解和速率最大化优化问题,首先采用分层优化方法将和速率最大化优化问题分解成发射功率最小化优化问题和单输入单输出干扰信道的和速率最大化优化问题;其次利用二阶锥规划优化方法求解发射功率最小化优化问题;然后利用凸近似和几何规划方法求解单输入单输出干扰信道的和速率最大化优化问题;最后通过交替求解这两个子优化问题,进而提出了一种新颖的单调协同多点波束成形算法;而且利用单有界序列原理证明了所提算法的收敛性。数值仿真表明所提算法只需约四次迭代即可收敛到稳定点,而且所获得的最优性能非常接近穷举搜索算法的最优性能。      

On the capture probability for a large number of stations

The probability of capture under a model (for a land mobile radio direct sequence spread spectrum system) based on the ratio of the largest received power to the sum of interference powers is examined in the limit of a large number of transmitting stations. It is shown in great generality that the limit depends only on the capture ratio threshold and the roll-off exponent of the distribution of power received from a typical station. This exponent is insensitive to many typical channel effects such as Rician or Rayleigh fading and log-normal shadowing. The model is suitable for large systems with noncoherently combined interference     

Greedy scheduling performance for a zero-forcing dirty-paper coded system

This letter presents two results for multiuser wireless systems employing dirty-paper coding strategies along with greedy scheduling over the broadcast multiple-input multiple-output channel. Specifically, an efficient and suboptimal downlink scheduler is proposed to approximate the maximum sum rate using equal power allocation, and it is shown to approach the maximum sum rate of optimal power allocation for a large number of users under optimal scheduling. The second result demonstrates that the average maximum sum rate can be tightly upper bounded when spatial multiplexing is maximized.