Search for binary code sequences with low autocorrelation sidelobes by the evolutionary method

The objective of the article is to develop the structure of a system for transmitting information with code division of channels and stochastic usage of systems of binary quasiorthogonal code sequences obtained on the basis of functional transformations of pseudo-random arguments, as well as a description of the principle of its functioning. The aim of the article is to develop a method for transmitting information in satellite communication systems and global navigation satellite systems with code division of channels and stochastic usage of binary quasiorthogonal code sequences obtained on the basis of functional transformations of pseudo-random arguments, providing an increase in structural secrecy. The elements of novelty are obtaining a new structure of an information transmission system with code division of channels and increased structural secrecy, as well as a description of the main stages of the information exchange method based on this system. The method differs from the known ones by stochastic use of binary quasi-orthogonal code sequences obtained on the basis of functional transformations of pseudo-random arguments. The main result of the article is that the presented method of information transmission makes it possible to reduce the impact of deliberate imitating interference and cases of substitution of the signals used by increasing the structural (signal) secrecy of the information transmission system with code division multiplexing and stochastic usage of systems of binary quasi-orthogonal code sequences.

In this paper there are solved two related problems: the development of the method and correspondent algorithm of code binary sequences synthesis with property of minimal level of side lobes of their aperiodic autocorrelation functions. The method is based on discrete representation of autocorrelation function in form of equations system considered on a set of integer numbers, set-theoretical representation of components of the sequence, their integer-number transformations, mutual properties and relations. There are obtained the expressions defining the dependences of absolute value of the sequence elements on a sum of levels of side lobes of aperiodic and periodic correlation functions; there are defined the necessary conditions of existence binary code sequences ; there are developed the mathematical models of binary code sequences components transformations. The efficiency criterion of each proposed algorithm is the relation of amount of all possible variants of binary code sequences of definite size l to amount of defined by proposed algorithms; the expressions for these quantities are obtained. The efficiency of proposed method and algorithms is verified by simulation results and it increases with increase of size l.

For radar and communication systems, the search for code sequences with good correlation properties remains one of important tasks. This work shows the results of the study of aperiodic autocorrelation functions of new code sequences based on persymmetric quasi-orthogonal circulants. The numerical values of the quality parameters such as: the maximum sidelobe level, integrated sidelobe level ratio, and merit factor are given. Applying new code sequences makes it possible to reduce the maximum sidelobe level of the aperiodic autocorrelation function, as well as to reduce the summary energy of the sidelobes, which makes it possible to conclude that their application is promising. The obtained results are aimed at stimulating scientific interest in new bases derived from quasi-orthogonal matrices, as a basis for the revision of signal coding algorithms.

For generating the combination test suite, we have proposed a combination test data global optimization mechanism. Firstly, an encoding process is used to create a one-to-one correspondence between each test case in its complete set and the gene in a binary code sequence. Based on this process, the combination test data generating problem has been translated into a binary genetic code optimization problem. Then, the ethnic group evolution algorithm (EGEA) is used to search the binary code space to find the optimal binary code sequence. In order to refine the genetic structure of each group, a novel ethic group searching approach, searching inside group process is presented. The simulations show this searching process is feasible, which improves the efficiency of optimizing genetic structure and reducing test case set observably.

For an aperiodic invertible sequence of length L, the optimality criterion is chosen to be the minimum noise enhancement factor of the corresponding aperiodic inverse filter. The noise enhancement factor is defined as the ratio of the noise energies at the outputs of the aperiodic inverse and the normalized matched filters of the sequence due to white noise at the filter inputs. Optimal binary sequences of length L/spl les/32 and optimal binary skew symmetric sequences of length 33/spl les/L/spl les/59 were found by exhaustive search. The search for near-optimal sequences is shown to have strong connections to the search for sequences with large products of Golay (1977) merit factor times the minimum of the energy density spectrum. Based on Legendre sequences and on Kronecker product sequences, long near-optimal binary sequences are found that have associated noise enhancement factors close to 1 dB.

Study of digital textual watermarking distortions under Internet attacks in high resolution videos

Steady-state visual evoked potentials (SSVEPs) enable brain-computer interfaces to achieve efficient performance in command detection accuracy and information transfer rate (ITR). However, a limited bandwidth of SSVEPs causes a limited number of possible command in BCIs. Moreover since the amplitude of SSVEP at a particular frequency depends on users, some BCI commands could be executed easily (higher accuracy) and the others hardly (lower accuracy). To solve these problems, the present paper proposes a paradigm of BCI using phase-modulated visual stimuli. The commands of BCI are represented by a combination of binary codes. Two different phases of flickering stimuli correspond to binary codes. A command is determined by the sequence of binary codes which is demodulated from the phases of SSVEP. This protocol can be analogues of binary phase-shift keying (BPSK) in digital communications. Experimental results show that the proposed paradigm achieves even probabilities of command execution, although only a single electrode was used for SSVEP detection.

Under proper feedback strength, an external-cavity feedback semiconductor laser can operate at a chaos state, and its chaotic output can be used as a physical entropy source to generate a physical random number sequence. In this paper, we focus on the influence of feedback strength on the randomness of the obtained binary code sequence. The simulation results show that with the increase of feedback strength, the time delay characteristic peak of the chaotic signal from an external-cavity feedback semiconductor laser first decreases and then increases gradually, meanwhile, the permutation entropy characteristic value of chaotic signal first increases and then decreases gradually, namely, there exists an optimized feedback strength for obtaining the chaotic signal with the weakest time delay signature and high complexity. The randomness of binary code sequences, generated by the chaotic signal from the external-cavity feedback semiconductor laser under different feedback strengths, is tested by NIST Special Publication 800-22, and the influence of feedback strength on the test results is also discussed.

RSSI quantization and genetic algorithm based localization in wireless sensor networks

This paper studies the problem of mobile target localization in wireless sensor networks and proposes a mobile target localization algorithm based on dynamic ring structure. Firstly, a multiple rings structure is constructed in the network. To obtain the optimal division, a Genetic Algorithm based on elitist preservation strategy is used to set the ring width. Then, a binary coding algorithm is proposed to assign binary code for each ring and determine the target appearing area using binary code sequence. Finally, a comprehensive set of simulations are presented. We conclude that the proposed localization algorithm yields excellent performance.

Employing binary sequences with good autocorrelation properties leads to performance improvement for active sensing systems. Designing such sequences has been studied widely in the literature from optimization point of view. In this paper we consider the problem of designing binary sequences with good aperiodic/periodic auto-correlation functions in terms of Integrated Sidelobe Level (ISL) using machine learning method. Specifically, we propose a novel neural network structure which can learn an algorithm for designing binary sequences with small ISL. We also extend the resulting network, which we refer to as BiSCorN, by designing Low-Correlation Zone (LCZ) binary sequences. Numerical experiments show that our proposed method outperforms state-of-the-art algorithms in terms of ISL, and interestingly Peak Sidelobe Level (PSL).

Protein structures can be encoded into binary sequences (Gabarro-Arpa et al., Comput Chem 2000;24:693-698) these are used to define a Hamming distance in conformational space: the distance between two different molecular conformations is the number of different bits in their sequences. Each bit in the sequence arises from a partition of conformational space in two halves. Thus, the information encoded in the binary sequences is also used to characterize the regions of conformational space visited by the system. We apply this distance and their associated geometric structures to the clustering and analysis of conformations sampled during a 4-ns molecular dynamics simulation of the HIV-1 integrase catalytic core. The cluster analysis of the simulation shows a division of the trajectory into two segments of 2.6 and 1.4 ns length, which are qualitatively different: the data points to the fact that equilibration is only reached at the end of the first segment. The Hamming distance is compared also to the r.m.s. deviation measure. The analysis of the cases studied so far shows that under the same conditions the two measures behave quite differently, and that the Hamming distance appears to be more robust than the r.m.s. deviation.

We consider the problem of designing binary antipodal code sequences (signatures) for overloaded code-division multiplexing (CDM) systems where the number of concurrent users/signals is greater than the code length. Our goal is to provide an overloaded code that can be constructed and decoded quickly and, more importantly, provide satisfactory recovery performance in conjunction with decoder design specifics. We first introduce a fast and practical method for constructing a code set by operating the Kronecker product with two smaller codes. Under such construction, a fast two-stage maximum-likelihood (ML) detection scheme can dramatically reduce the computational complexity of the ML decoder and make CDM systems practically implementable. To improve the performance in terms of bit error rate, we propose hierarchical criteria for code design, which aims at reducing the cross-correlation of code while maintaining a uniquely decodable (errorless) code property. Simulation studies illustrate that the proposed code design can provide satisfactory performance with low-complexity two-stage ML detection.

A functional minimization approach over a discrete and nonconvex set of points inN-space has been adopted to obtaingood binary sequences. In order to achieve this goal, an iterative procedure based upon the well-known enumerative and combinational structures of the problem has been developed. A functional of the form\(\sum\nolimits_{K = 1}^{N - 1} {{{{K \mathord{\left/ {\vphantom {K {[C(K)]}}} \right. \kern-\nulldelimiterspace} {[C(K)]}}} \mathord{\left/ {\vphantom {{{K \mathord{\left/ {\vphantom {K {[C(K)]}}} \right. \kern-\nulldelimiterspace} {[C(K)]}}} {^2 }}} \right. \kern-\nulldelimiterspace} {^2 }}} \) is considered, whereK is the time shift in terms of the number of binary elements andC(K) the corresponding autocorrelation function; however, the method is quite general and could be used for any functional suitable for any given application. By this method, it has been found possible to minimize the functional by orders of magnitude in aboutN/2 steps, with maximum sidelobes around\(\surd N\), whereN is the code length.

A low-complexity joint position and amplitude search algorithm is proposed for deterministic sparse codebooks to be used in code-excited linear predictive coders. The conventional multipulse search is presented as an extension of a general two-stage sequential search, leading to a classification of multistage sequential searches according to the extent that orthogonality constraints are applied throughout the search stages. After its classification, an efficient implementation of the joint search is derived which incorporates backward filtering of the residual target vector and precornputation of autocorrelation elements, bringing about a reduction in complexity of approximately one third in comparison to the focused search within the G.723.1 codec. In particular, considering an extensive speech database, a floatingpoint version of the joint search method reduces down to one third the number of comparisons per subframe relative to the focused search. Moreover, the joint search performs about one thirtieth as many comparisons as the position-exhaustive search. Further, the complexity of a fixed-point implementation of the joint search is below one quarter that of the focused search and stands below those of the G.729A and lS-64l-A coders. Listening tests indicate an equivalence in perceived quality.