A new two-code keying scheme for SAC-OCDMA systems enabling bipolar encoding

In this paper, we propose a new two-code keying scheme for enabling bipolar encoding in a high-rate spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) system. The mathematical formulations are derived for the signal-to-noise ratio and bit-error rate (BER) of SAC-OCDMA system based on the suggested scheme using multi-diagonal (MD) code. Performance analyses are assessed considering the effects of phase-induced intensity noise, as well as shot and thermal noises in photodetectors. The numerical results demonstrated that the proposed scheme exhibits an enhanced BER performance compared to the existing unipolar encoding with direct detection technique. Furthermore, the performance improvement afforded by this scheme is verified using simulation experiments.     

Embedded Coded Relay System for Molecular Communications

With the emergence of the COVID-19 pandemic, the World Health Organization (WHO) has urged scientists and industrialists to explore modern information and communication technology (ICT) as a means to reduce or even eliminate it. The World Health Organization recently reported that the virus may infect the organism through any organ in the living body, such as the respiratory, the immunity, the nervous, the digestive, or the cardiovascular system. Targeting the abovementioned goal, we envision an implanted nanosystem embedded in the intra living-body network. The main function of the nanosystem is either to perform diagnosis and mitigation of infectious diseases or to implement a targeted drug delivery system (i.e., delivery of the therapeutic drug to the diseased tissue or targeted cell). The communication among the nanomachines is accomplished via communication-based molecular diffusion. The control/interconnection of the nanosystem is accomplished through the utilization of Internet of bio-nano things (IoBNT). The proposed nanosystem is designed to employ a coded relay nanomachine disciplined by the decode and forward (DF) principle to ensure reliable drug delivery to the targeted cell. Notably, both the sensitivity of the drug dose and the phenomenon of drug molecules loss before delivery to the target cell site in long-distance due to the molecules diffusion process are taken into account. In this paper, a coded relay NM with conventional coding techniques such as RS and Turbo codes is selected to achieve minimum bit error rate (BER) performance and high signal-to-noise ratio (SNR), while the detection process is based on maximum likelihood (ML) probability and minimum error probability (MEP). The performance analysis of the proposed scheme is evaluated in terms of channel capacity and bit error rate by varying system parameters such as relay position, number of released molecules, relay and receiver size. Analysis results are validated through simulation and demonstrate that the proposed scheme can significantly improve delivery performance of the desirable drugs in the molecular communication system.     

Improved BER based on intensity noise alleviation using developed detection technique for incoherent SAC-OCDMA systems

The major drawback of incoherent spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) systems is their inherent intensity noise originating due to the incoherency of the broadband light sources. In this paper, we propose a developed detection technique named the modified-AND subtraction detection for incoherent SAC-OCDMA systems. This detection technique is based upon decreasing the received signal strength during the decoding process by dividing the spectrum of the utilized code sequence. The proposed technique is capable of mitigating the intensity noise effect, as well as suppressing the multiple-access interference impact. Based on modified quadratic congruence (MQC) code, the analytical results reveal that the modified-AND detection offer best bit-error rate (BER) performance and enables MQC code to support higher transmission rate up to 1.25?Gb/s compared to conventional AND detection. Furthermore, we ascertained that the proposed technique enhances the system performance using a simulation experiment.     

Single-user performance of direct-sequence code-division multiple-access using relay diversity and power allocation

In this contribution, the authors investigate the single-user-bound performance of a direct-sequence code-division multiple-access (DS-CDMA) system, where one source mobile terminal (MT) communicates with its base-station (BS) with the assistance of multiple relays. The authors assume that the communications channels experience both propagation pathloss and fast fading, and that the channels from the source MT to the BS and relays as well as that from the relays to the BS may experience different fast fading modelled correspondingly by Nakagami-m distributions. In the study, they assume both the single-user combining using maximal ratio combining and the multiuser combining, which are derived based on the maximum signal-to- interference-plus-noise ratio criterion. The bit-error-rate (BER) performance of the DS-CDMA is investigated associated with considering the locations of the relays as well as the power-allocation among the source MT and relays. From the study and simulation results, it can be shown that the achievable BER performance of the DS-CDMA depends on the locations of the relays and also on the power-allocation among the source MT and relays. When the relays of a source MT are chosen from a different area, the power-allocation should also be adjusted correspondingly in order to achieve the minimum BER. Furthermore, when optimum power- allocation is assumed, the BER performance of the DS-CDMA can be significantly improved, when increasing the number of relays assisting the source MT.     

Efficient bit‐plane coding scheme for fine granular scalable video coding

In this paper, we propose a new efficient bit‐plane coding method for fine granular scalable (FGS) video coding. The general structure of the proposed bit‐plane coding method is based on the traditional bit‐plane coding scheme in MPEG‐4 FGS. However, to enhance coding efficiency of bit‐plane encoding, we apply an efficient probability estimation scheme through employing the binary arithmetic coding. For probability estimation, various context models are designed to take advantage of the characteristics of each bit‐plane as well as the correlations of symbols among different bit‐planes. Experimental results show that the proposed FGS coding scheme provides better coding performance, compared to the well‐known FGS coding schemes in MPEG‐4 FGS and JSVM. © 2007 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 16, 113–120, 2006.     

An effective approach for wavelet lifting based on filter optimization and median operator

In JPEG2000, the Cohen–Daubechies–Feauveau (CDF) 9/7‐tap wavelet filter implemented by using the conventional lifting scheme has two problems. The first problem is that the filter coefficients are remaining complex; second, the conventional lifting scheme ignores image edges in the coding process. In this article, we propose an effective wavelet lifting scheme to solve these problems. For this purpose, we design the optimal 9/7‐tap wavelet filters in two steps. In the first step, we select the appropriate filter coefficients; in the second step, we employ a median operator to consider image edges. Experimental results from using the median lifting scheme and combining filter optimization and median lifting show that our proposed methods outperform the well‐known CDF 9/7‐tap wavelet filter of JPEG2000 on edge‐dominant images. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 359–366, 2010     

Two-dimensional multiplexing scheme both with ring radius and topological charge of perfect optical vortex beam

Perfect optical vortex (POV) beam is a special kind of vortex beam, whose radius is independent of its topological charge. In this paper, we propose a two-dimensional multiplexing scheme with a ring radius and topological charge of POV beam. A communication system using the proposed multiplexing scheme with a two-step detection method is presented, and on–off keying modulation is applied to demonstrate the bit error rate (BER) performance under atmospheric turbulence. The numerical results show that the BER performance of the proposed scheme is better than that when only topological charge is multiplexed with the same conditions. The two-dimensional multiplexing scheme has an anti-interference capability since the ring radius is only concerned in magnitude. At the same time, the capacity and the spectral efficiency of the system are improved since both ring radial and topological charge of POV beam are used.     

基于量化步长线性预测和BFOS算法的MPEG-4AAC量化

MPEG-4 AAC的编码性能很大程度上依赖于量化模块的编码效率和收敛速度,但其常用的基于双循环搜索结构的率失真控制器引起编码器性能较差,尤其在低码率时更为突出。提出一种新的量化优化算法。新方案采取单循环结构,用前面数帧的量化信息对当前帧的初始量化步长做线性预测,再用接近最优比特分配的BFOS算法控制量化步长的调节。仿真证明新方案的编码性能明显优于MPEG-4 AAC VM,对比BOFS算法,运算量得到极大降低。     

Effects of diversity schemes and correlated channels on OWC systems performance

The salient features and advantages of free-space optical (FSO) system are very appealing for different applications in a number of communication network sectors. In spite of the advantages and diverse applications of FSO communication, its extensive use is hindered by the atmospheric turbulence-induced fading in real-life scenarios. Spatial diversity technique is one of effective means of mitigating turbulence-induced fading and, consequently, improves the system performance. In this paper, we study the spatial diversity schemes for mitigating turbulence-induced fading in the FSO communication systems using the bit error rate (BER) as a performance metric. The schemes considered are based on orthogonal space–time block codes and repetition codes (RCs). We derive simple approximate closed-form expressions for the error probability of the log-normal FSO links with intensity modulation and direct detection (IM/DD). Furthermore, we also investigate the effects of spatial correlation between the transmit apertures on the system performance. We achieve this using the exponential model for determining the correlations between the apertures. We observe that the proposed BER expressions are able to quantify the effects of spatial diversity schemes and spatial correlations on the system.     

Reducing the peak-to-average power ratio using unitary matrix transformation

A theoretical analysis is presented to show that in orthogonal frequency division multiplexing systems, the peak-to-average power ratio (PAPR) can be reduced by performing a unitary matrix transformation on the input vector of N symbols. The authors also prove that this transformation does not degrade the bit error rate (BER) or power spectral density (PSD) performance. Based on this, the inverse discrete Fourier transform matrix is proposed as the unitary matrix to reduce the PAPR. The simulation results show that the proposed scheme can obtain significant PAPR reduction while maintaining good performance in the BER and the PSD. To further evaluate the performance of the proposed scheme, the authors compare it with some well known PAPR reduction techniques by simulations. It is demonstrated that the proposed scheme can offer better system performance and achieve a better compromise with regard to the PAPR reduction, BER, spectral efficiency and computational complexity.     

Comprehensive partial decoding approach for two-level relay networks

Partial decoding scheme is a scheme in which each relay decodes only part of the transmitted message. Obviously, the achievable rates proposed by the partial decoding scheme subsume the achievable rates proposed by the full decoding scheme. The other motivation of using partial decoding scheme is that there are some special classes of relay networks such as semi-deterministic and orthogonal relay networks such that their capacities are obtained via this scheme. The authors propose a comprehensive partial decoding scheme based on regular encoding/sliding window decoding analysis to propose a new achievable rate for two-level relay networks. In contrast with the previously proposed methods, here the authors consider all possible partial decoding states that can occur between the different parts of the messages of the source and the relays in a two-level relay network. In this way, the common and private parts of the message transmitted by the source are defined to be decoded by the appropriate relays. Moreover, in the proof, the authors take advantage of regular encoding/sliding window decoding scheme that has superiorities to regular encoding/backward decoding and irregular encoding/random partitioning, in having less delay and yielding higher rates, respectively.     

Efficient secure channel coding based on quasi-cyclic low-density parity-check codes

A secure channel coding (joint encryption-channel coding) scheme provides both data security and reliability in one combined process to achieve faster processing and/or more efficient implementation. The issue of using quasi-cyclic low-density parity-check (QC-LDPC) codes in a symmetric-key secure channel coding scheme is addressed. A set of this class of LDPC codes has recently been recommended by the NASA Goddard Space Flight Center for near-earth and deep-space communications. The proposed scheme provides an efficient error performance, an acceptable level of security and a low-complexity practicable implementation. The results indicate that the proposed scheme can efficiently employ large QC-LDPC codes to achieve a relatively smaller secret-key size to be exchanged by the sender and the receiver, and higher information rates in comparison with the previous symmetric-key McEliece-like schemes. Simulation results indicate that there is no trade-off between the error performance and the security level of the proposed scheme unlike that of the previous ones. These characteristics make the proposed scheme suitable for high-speed communications, such as satellite communication systems.     

Performance bounds of space-time block coding in rician and log-normal fading channels

Analytical expressions concerning the capacity and bit error rate (BER) of multiple-input multiple-output systems with space-time block coding (STBC) are derived. Two fading environments are examined, log-normal and Rician channels. A tight closed-form upper bound is presented for the BER of systems operating in log-normal fading environments in addition to an upper bound for the capacity of this type of systems. The latter bound applies to systems that operate under Rician fading as well. The analytical results were validated against ample numerical simulations for three STBC schemes and three phase-shift-keying modulations. The proposed bounds proved to be a tractable way to evaluate the system performance when no closed-form expression for the probability density function or the moment generating function is known     

Performance of a QAM/FSO communication system employing spatial diversity in weak and saturation turbulence channels

In this paper, the bit error rate (BER) performance and outage probability of quadrature amplitude modulation free space optical (QAM/FSO) communications with spatial diversity in turbulent environments are investigated. The equal-gain combining (EGC) and selection combining (SelC) diversity techniques are considered to mitigate turbulence-induced signal fading in the proposed system. The average BER and outage probability expressions are derived for EGC diversity in weak and saturation turbulence channels. The results indicate that using EGC diversity can significantly improve the system performance compared to employing the SelC diversity or single monolithic aperture schemes. Specifically, approximately 4 and 9?dB lower signal-to-noise power ratios are required for the 1?×?4 EGC diversity system than for the 1?×?4 SelC and non-diversity systems at a BER of 10^?10. In addition, the use of diversity techniques also significantly decreases the outage probability. The proposed scheme can be helpful for establishing a spatial diversity FSO system with a low error rate and high transmission rate.     

Subband decomposition strategies for object‐based image coding

In order to attain perfect reconstruction, subband decomposition of arbitrarily shaped objects requires special strategies to deal with the decimation problem. One of the two strategies described in this paper (scheme 1) inserts pixels with amplitudes equal to the mean values of the neighboring ones belonging to the object. The requirement of transmitting (coding) these pixels reduces the coding gain and is avoided by the second strategy (scheme 2) examined in this paper. This strategy determines specific values of the pixels added to the object in such a way that they result in predefined amplitudes after decimation. For this reason, this method outperforms scheme 1. PSNR versus bit rate are presented for two objects. © 2003 Wiley Periodicals, Inc. Int J Imaging Syst Technol 13, 179–187, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.10054     

多径信道下基于频域均衡的超奈奎斯特传输

针对在多径信道下进行超奈奎斯特(FTN)传输时,同时存在由FTN与多径信道引入的双重符号间干扰(ISI)的问题,提出了应用频域均衡与低密度奇偶校验(LDPC)编码相结合的接收机结构来提高系统传输性能。该接收机构在接收端利用频域均衡器对由FTN与多径信道引入的符号间干扰进行频域均衡,均衡后的信号再通过LDPC信道译码器,利用最大后验概率准则(MAP)进行判决,最终恢复出原始信息。仿真实验显示,基于频域均衡的FTN传输系统可改善系统传输的误码性能。     

Reversible Data Hiding Based on Run-Level Coding in H.264/AVC Video Streams

This paper presents a reversible data hiding (RDH) method, which is designed by combining histogram modification (HM) with run-level coding in H.264/advanced video coding (AVC). In this scheme, the run-level is changed for embedding data into H.264/AVC video sequences. In order to guarantee the reversibility of the proposed scheme, the last nonzero quantized discrete cosine transform (DCT) coefficients in embeddable 4×4 blocks are shifted by the technology of histogram modification. The proposed scheme is realized after quantization and before entropy coding of H.264/AVC compression standard. Therefore, the embedded information can be correctly extracted at the decoding side. Peak-signal-noise-to-ratio (PSNR) and Structure similarity index (SSIM), embedding payload and bit-rate variation are exploited to measure the performance of the proposed scheme. Experimental results have shown that the proposed scheme leads to less SSIM variation and bit-rate increase.     

Comparison of direct-sequence impulse radio and direct-sequence ultra-wide bandwidth in multi-user interference

A new ultra-wide bandwidth communication system using both a time-hopping (TH) sequence and a direct spreading sequence, called direct-sequence impulse radio (DS-IR), has recently been proposed. An exact analysis to evaluate the bit error rate (BER) performance of this new scheme in multi-user interference (MUI) is provided. On the basis of this new analysis, ultra-wideband communication systems employing TH, direct-sequence and the newly proposed DS-IR schemes operating in MUI are accurately compared in terms of the BER. Our results indicate that DS-IR outperforms the TH binary phase-shift keying (BPSK) system. However, its performance is poorer than the performance of the conventional full-duty direct sequence BPSK system. Compared with the low-duty direct sequence BPSK system, DS-IR achieves a better error rate performance for medium and large signal-to-noise power-ratio values.     

Peak-to-average power ratio reduction in space-time block coded multi-input multi-output orthogonal frequency division multiplexing systems using a small overhead selective mapping scheme

The selective mapping (SLM) scheme is one of the most popular peak-to-average power ratio (PAPR) reduction techniques proposed for multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. One of the major disadvantages of this scheme is the need for the transmission of side information (SI) bits to enable the receiver to recover the transmitted data. The authors present a small overhead SLM (s-SLM) scheme for space-time block coded (STBC) MIMO-OFDM systems. This proposed scheme improves the system bandwidth efficiency and achieves a significantly lower bit error rate (BER) than the individual SLM (i-SLM) and direct SLM (d-SLM) schemes. In addition, approximate expressions for the complementary cumulative distribution function (CCDF) of the PAPR and the average BER of the proposed s-SLM scheme are derived. The simulation results show that the proposed s-SLM scheme improves the detection probability of the SI bits and hence gives a better performance than the i-SLM and the d-SLM schemes.     

基于ARM7微处理器距离保护的研究

为了适应现代超高压电网稳定运行的要求，微机距离保护装置在硬件和软件上都提出了越来越高的要求。本文在总结了输电线路微机距离保护研究现状的基础上，分析了国内现有微机保护硬件的现状，对比了8位、16位单片机（SCM）以及32位DSP的保护方案，并总结了其优缺点，提出了一种基于ARM微处理器的保护方案。本文将实时操作系统μC／OS—II与模块化硬件设计相结合，共同构成一个可以重复利用的软硬件数字系统平台，除了可以最大限度地提高开发的效率、减少资源的浪费外，还可以通过长期对于该平台的研究，逐步优化平台软硬件资源，提高其性能，并满足日益复杂的应用需求。本文尝试了用任务方式实现保护的并行处理，大大提高软件的可读性和可靠性，也为将来任务扩展提供条件。