Showing papers on "Hadamard code published in 2017"

Code-Shifted Differential Chaos Shift Keying With Code Index Modulation for High Data Rate Transmission

Abstract: In the general code-shifted differential chaos shift keying (GCS-DCSK) system, multiple bit-streams are simultaneously carried by CS-DCSK signal using Walsh codes. However, its data rate is limited by the available Walsh codes in the Walsh code matrix due to orthogonality constraint of GCS-DCSK signal. In this paper, we propose a new GCS-DCSK scheme with code index modulation (CIM-CS-DCSK), which can achieve higher spectrum efficiency using code index modulation to carry additional bits. In the proposed scheme, the reference chaotic signal is the same as that of GCS-DCSK, and the multiple information bearing signals are simultaneously modulated by the information symbols and the selected Walsh codes with specific indices, which are determined by an integer sequence mapped from information symbols via the natural numbers to $k$ -combinations mapping method. We derive bit error rate of the proposed scheme over the additive white Gaussian noise channel. The numerical results not only verify our analysis but also show the advantage of the proposed scheme over GCS-DCSK. Through analyzing and comparing the numbers of carried bits per transmitted symbol of CIM-CS-DCSK and GCS-DCSK, it is shown that the proposed scheme can obtain higher data rate than GCS-DCSK with the same resource constraints.

Design of a multi-carrier different chaos shift keying communication system in doubly selective fading channels

Abstract: In this paper, a novel chaos modulation scheme, which combines code-shifted differential chaos shift keying (CS-DCSK) with orthogonal frequency division multiplexing (OFDM) is presented, namely OFDM-CS-DCSK. In the proposed scheme, the reference signal and the information bearing signal of CS-DCSK are firstly formed by Walsh code sequences, then different chips of the CS-DCSK signal are mapped onto different subcarriers of OFDM. Utilizing the characteristics of OFDM and CS-DCSK, the proposed scheme has robust performance over time-frequency doubly selective fading channel. In addition, the proposed system has low complexity because channel estimation, channel equalizer and the radio frequency (RF) delay circuits are not required at its receiver. By the computer simulations, bit error rate (BER) performances of the proposed scheme are compared with OFDM-DCSK and CS-DCSK under various channel parameters. Simulation results indicate that the proposed scheme has significant performance advantages over OFDM-DCSK and CS-DCSK in time-frequency doubly selective fading channel.

Full-Optical TOAD based Walsh-Hadamard code generation

Abstract: Transmission of information takes place simultaneously over the same available channel bandwidth in Code Division Multiple Access (CDMA) technique. The spread spectrum (SS) technique is used in CDMA systems for transmission of information by employing spreading codes. A unique spreading code, acts as a signature code, is assigned for each individual user. The signal occupies a bandwidth much larger than the minimum necessary to send the information in SS modulation technique. A synchronized reception with the code at the receiver is applied for dispreading the information before the data recovery. From a long-term, Walsh-Hadamard codes have been employed as spread spectrum codes in CDMA communications due to their ease of generation. Walsh-Hadamard codes are absolutely orthogonal binary user codes which have so many favourite applications in synchronous multicarrier communications. However, the optical application of Walsh-Hadamard codes turns important for optical CDMA to solve the above problem. For this, the designs need the use of nonlinear optics capable of controlling multi-valued signals. To achieve this goal all-optical terahertz optical asymmetric Demultiplexer based design of Walsh-Hadamard codes is explored in this paper.

An M-ary code shifted differential chaos shift keying scheme

Abstract: In this paper, by applying M-ary constellation modulation to code shifted differential chaos shift keying (CS-DCSK), a new M-ary DCSK which is called CS-MDCSK, is proposed. In the proposed scheme, the reference chaos signal is the same with the CS-DCSK, and the two orthogonal components of information bearing signal are obtained by two Walsh codes. Furthermore, the proposed CS-MDCSK is extended to general scheme (GCS-MDCSK), which transmits more than one M-ary constellation information bearing signals with one reference. Since high order constellations are used, the proposed scheme enhances the spectrum efficiency compared to CS-DCSK and GCS-DCSK. By computer simulations, the bit error rate (BER) performance of two proposed systems are compared to that of CS-DCSK and GCS-DCSK, respectively. Simulation results show that the proposed systems outperform the CS-DCSK and GCS-DCSK when 4-ary constellation is applied.

A new code construction algorithm based on Double Weight codes for SAC-OCDMA systems

Abstract: Double Weight (DW) code families are constructed with different algorithms and fixed value of users at basic code matrix. A single code construction algorithm is proposed for DW code families in which, number of users for basic code matrix depends on the code weight and on a constant value. Mapping is used to provide the greater number of users. Affect of basic matrix (used in mapping) on Bit Error Rate (BER) and code length is analyzed. The properties of proposed code construction algorithm are easy code construction, any positive integer value of weight is used for code construction, design of different code set by varying size of basic matrix. Ex-OR function is used in balanced detection technique at receiver. Numerical results are calculated using MATLAB.

An Improved Selective Mapping Technique to Reduce Peak-to-Average Power Ratio in SISO and SIMO OFDM Systems Without Side Information

Abstract: Selective mapping (SLM) is an attractive method to reduce the peak-to-average power ratio (PAPR) without causing any signal distortion in orthogonal frequency division multiplexing (OFDM) systems. The main drawback of this technique is the requirement of sending side information (SI) to the receiver for each data block which results in huge bandwidth and power overheads. Also, it may degrade the bit error rate (BER) performance of the system due to the corruption of SI over the channel. In this paper, we propose a novel technique to reduce PAPR in single input single output and single input multiple output OFDM systems using Hadamard code-based SLM. The proposed method eliminates the need for explicit SI resulting in better bandwidth and power efficiency. The basic idea is to embed the SI of each data block within the data block itself at some specific locations using special multiplying sequences. Furthermore, the proposed scheme yields superior PAPR reduction when compared to that of the conventional SLM for an equivalent system complexity. Simulation studies show that the receiver achieves a better BER performance with the proposed technique as compared to the conventional SLM.

Mobile forward transmission device and method based on Walsh code channel aggregation

Abstract: The invention discloses a mobile forward transmission device and method based on Walsh code channel aggregation, and relates to the field of optical and wireless fusion access networks. The mobile forward transmission device comprises a transmitting terminal, an optical fiber link and a receiving terminal, the transmitting terminal comprises a centralized BBU pool, a DAC and an electro-optic conversion module, the centralized BBU pool comprises a BBU, a channel aggregation model and a training sequence adding module, the receiving terminal comprises a photovoltaic conversion module, an analog-to-digital converter ADC, a frame synchronization module, a channel estimation module, a channel de-aggregation module, a plurality of remote radio frequency heads RRH and an antenna. The mobile forward transmission device disclosed by the invention can greatly reduce the computational complexity and improve the spectral efficiency.

Code multiplexing DCSK (Differential Chaotic Shift Keying) modulator-demodulator based on PFDM (Orthogonal Frequency Division Multiplexing) technology

Abstract: The invention relates to a code multiplexing DCSK (Differential Chaotic Shift Keying) modulator-demodulator based on a PFDM (Orthogonal Frequency Division Multiplexing) technology, and relates to DCSK modulation and demodulation. By utilizing orthogonality of a Walsh code, orthogonality of a reference signal and an information carrying signal on a code domain and overlapping of the reference signal and the information carrying signal on a time domain are implemented, and the problems of different channel responses and poor transmission performance of the reference signal and the information carrying signal, which are caused by channel time selection, are solved; and by utilizing the OFDM technology, each code chip of one frame of signal is propagated on different sub carriers, so that the problem of intersymbol interference caused by channel frequency selection is avoided. Simulation under an Additive White Gaussian Noise (AWGN) channel and a multi-path time-varying channel shows that compared to conventional DCSK, the code multiplexing DCSK system based on the PFDM technology has good transmission performance under the AWGN channel and the multi-path time-varying channel and has resistance to time selection and resistance to frequency selection fading.

Nonbinary LDPC code for noncoherent underwater acoustic communication under non-Gaussian noise

Abstract: Concatenated code based on nonbinary LDPC code and Hadamard code is used for noncoherent underwater acoustic communication system. 32-ary (620, 320) regular LDPC code and irregular LDPC code is constructed by quasi-cyclic extension method and Progressive edge-growth (PEG) algorithm, respectively. Under non-Gaussian noise model, Gaussian mixture model (GMM) is used to fit the noise, and the parameters in GMM is estimated by Expectation Maximization (EM) algorithm, the probability density of noise is further estimated. In Rayleigh fading channel, posterior probabilities of Hadamard code-words are calculated based on GMM, and nonbinary LDPC code is further decoded by Belief Propagation (BP) algorithm based on Tanner graph. It is verified by simulation that concatenated irregular LDPC code and Hadamard code has a 0.4 dB benefit than concatenated regular LDPC code and Hadamard code under white Gaussian noise; under Gaussian mixture noise, the EM algorithm based on GMM can exactly estimate the probability density of noise and improve the error correcting performance of concatenated code, the performance gap is 0.1 dB compared to results in known probability density condition. Noise samples were acquired by experiments carried out in deep sea and shallow lake. Under actual noise, the advantages of concatenated code based on GMM in practical application is verified.

Fusion code index-modulated multi-ary differential chaos shift keying modem

Abstract: The invention provides a fusion code index-modulated multi-ary differential chaos shift keying modem and relates to the field of wireless communication, wherein a receiver is free of any delay unit. Meanwhile, the fusion code index-modulated multi-ary differential chaos shift keying modem improves the system transmission data rate. The subscript value of a Walsh code is adopted as a carrier for the transmission of information bits, so that the number of bits transmitted by the system is improved. The transmission data rate and the energy efficiency of the system are improved effectively. In the orthogonal code multiplexing manner, delay units are effectively eliminated, and the complexity of system implementation is lowered. The simulations of AWGN channels and multi-path rayleigh fading channels show that, compared with the conventional DCSK, the fusion code index-modulated multi-ary DCSK system has certain performance advantages.

Code multiplexing differential chaotic modulator-demodulator for integrated code subscript modulation

Abstract: The invention discloses a code multiplexing differential chaotic modulator-demodulator for integrated code subscript modulation and relates to modulation and demodulation in a communication system The code multiplexing differential chaos modulator-demodulator comprises a modulator and a demodulator The modulator comprises a binary/decimal converter, a serial/parallel converter, a natural number/combinatorial number mapper, a Walsh code selection controller, a chaotic signal generator, Q+1 Walsh code generators, a multiplier, a time delay unit, a shift switch and an adder The combinatorial comprises a receiver, a multiplier, a square wave generator, an accumulator, an absolute value resolver, a comparison and selection controller, the shift switch, a decision device, the natural number/combinatorial number mapper and the binary/decimal converter Transmitted information bits are mapped on selection of a Walsh code, a transmission data rate is improved, the bandwidth is increased, the energy efficiency is improved, and the bit error rate performance under an AWGN channel and a multi-path Rayleigh fading channel is equal to or better than that under conventional DCSK (Differential Chaotic Shift Keying) The modulator-demodulator is competitive in a short-distance communication application

Supervised hashing with extreme learning machine

Abstract: Supervised hashing methods, which aim to generate semantic similarity-preserving binary codes, have been proposed to improve the performance of large-scale image retrieval. However, learning binary codes remains an NP-hard problem due to the binary constraints and complex computation. Existing hashing methods have never explored the potentiality of the label information, leading to a limited performance. To address these problems, we propose a simple supervised hashing method based on extreme learning machine (ELM). And we generate the supervised information in ELM by target code learning instead of using the traditional label code to fit the retrieval problem. With this modified label code, our method can produce high-quality binary codes and obtain high retrieval precision. Comprehensive experiments have shown our superiority to other state-of-the-art methods.

Circulant Hadamard matrices as HFP-codes of type $C_{4n}\times C_2$

Abstract: We prove that a circulant Hadamard code of length $4n$ can always be seen as an HFP-code (Hadamard full propelinear code) of type $C_{4n}\times C_2$, where $C_2=\langle u\rangle$ or the same, as a cocyclic Hadamard code. We compute the rank and dimension of the kernel of these kind of codes.

Walsh-hadamard code design using optical nonlinear material

Abstract: In this paper, the Walsh-Hadamard code design using optical nonlinear material is presented. Walsh-Hadamard codes are absolutely orthogonal binary user codes which have so many favourite applications in synchronous multicarrier communications. However, the optical application of Walsh-Hadamard codes has been important role for optical CDMA. Realization comes has nonlinear optics has been increased interest for all-optical signal processing in high speed photonic networks due to its inherent attributes of polarization. To this aim, the designs need the use of optical nonlinear material capable of controlling multi-valued signals. To achieve this goal the polarization properties of light for Walsh-Hadamard codes design is explored in this paper and the superiority of the proposed scheme is verified by simulation results.

Application of Enhanced Hadamard Error Correcting Code in Video-Watermarking and his comparison to Reed-Solomon Code

Abstract: Error Correcting Codes are playing a very important role in Video Watermarking technology. Because of very high compression rate (about 1:200) normally the watermarks can barely survive such massive attacks, despite very sophisticated embedding strategies. It can only work with a sufficient error correcting code method. In this paper, the authors compare the new developed Enhanced Hadamard Error Correcting Code (EHC) with well known Reed-Solomon Code regarding its ability to preserve watermarks in the embedded video. The main idea of this new developed multidimensional Enhanced Hadamard Error Correcting Code is to map the 2D basis images into a collection of one-dimensional rows and to apply a 1D Hadamard decoding procedure on them. After this, the image is reassembled, and the 2D decoding procedure can be applied more efficiently. With this approach, it is possible to overcome the theoretical limit of error correcting capability of ( d -1)/2 bits, where d is a Hamming distance. Even better results could be achieved by expanding the 2D EHC to 3D. To prove the efficiency and practicability of this new Enhanced Hadamard Code, the method was applied to a video Watermarking Coding Scheme. The Video Watermarking Embedding procedure decomposes the initial video trough multi-Level Interframe Wavelet Transform. The low pass filtered part of the video stream is used for embedding the watermarks, which are protected respectively by Enhanced Hadamard or Reed-Solomon Correcting Code. The experimental results show that EHC performs much better than RS Code and seems to be very robust against strong MPEG compression.

Multidimensional Enhanced Hadamard Error Correcting Code in Comparison with Reed-Solomon Code in Video-Watermarking Applications

Abstract: Watermarking technology.play a central role in the digital right management for multimedia data. Especially a video watermarking is a real challenge, because of very high compression ratio (about 1:200). Normally the watermarks can barely survive such massive attacks, despite very sophisticated embedding strategies. It can only work with a sufficient error correcting code method. In this paper, the authors introduce a new developed Enhanced Multidimensional Hadamard Error Correcting Code (EMHC), which is based on well known Hadamard Code, and compare his performance with Reed-Solomon Code regarding its ability to preserve watermarks in the embedded video. The main idea of this new developed multidimensional Enhanced Hadamard Error Correcting Code is to map the 2D basis images into a collection of one-dimensional rows and to apply a 1D Hadamard decoding procedure on them. After this, the image is reassembled, and the 2D decoding procedure can be applied more efficiently. With this approach, it is possible to overcome the theoretical limit of error correcting capability of (d-1)/2 bits, where d is a minimum Hamming distance. Even better results could be achieved by expanding the 2D to 3D EMHC. A full description is given of encoding and decoding procedure of such Hadamard Cubes and their implementation into video watermarking procedure.To prove the efficiency and practicability of this new Enhanced Hadamard Code, the method was applied to a video Watermarking Coding Scheme. The Video Watermarking Embedding procedure decomposes the initial video through Multi-Level Interframe Wavelet Transform. The low pass filtered part of the video stream is used for embedding the watermarks, which are protected respectively by Enhanced Hadamard or Reed-Solomon Correcting Code. The experimental results show that EHC performs much better than RS Code and seems to be very robust against strong MPEG compression.

Hybrid C&C-DMA Scheme for Multi-User Access in Large-Scale VLC Network

Abstract: We propose a multi-user access scheme based on Color-code division multiple access (C&C-DMA) in VLC network. The experiment shows BERs of four users under one color channel are below 3.8 × 10∼3 when total data rate is 32Mbps by adopting conversed Walsh code and RGB LED.