Spreading Scheme Research Articles

A scheme to restrain PAPR and frequency selective fading in 64 QAM MB-OFDM UWBoF system

This paper explores the peak-to-average power ratio (PAPR) influence of the base band orthogonal-frequency-division-multiplexing (OFDM) signal and the multiband orthogonal-frequency-division-multiplexing ultra-wideband (MB-OFDM UWB) signal, and compares the performance of discrete fourier transform spread (DFT-spread) scheme with clipping filter (CF) scheme to reducing PAPR in MB-OFDM UWB signal. On this basis, this paper also puts forward a scheme for restraining the influence of high PAPR and frequency selective fading (FSF) in 64 quadrature amplitude modulation (QAM) MB-OFDM UWBoF system, which is based on the combination of DFT-spread and pre-compensation. The results of simulation show that this scheme can improve the receiver sensitivity by 3.30 dB after the transmission of 70 km standard single-mode fiber (SSMF) with the bit error rate (BER) of 1.0 × 10-3, which compared with the situation without DFT-spread and pre-compensation.

LAMMPS lb/fluid fix version 2: Improved hydrodynamic forces implemented into LAMMPS through a lattice-Boltzmann fluid

The first version of this code (Mackay et al., 2013) [10] implemented long-range hydrodynamic interactions into the open-source molecular dynamics package LAMMPS. This was done through the creation of a fix, lb/fluid which was subsequently included as a user-package in the main LAMMPS distribution. Here we substantially update this package by making improvements to its accuracy, adding significant new features, and by simplifying the use of the package. A new two-pass interpolation and spreading scheme is introduced which results in the improved accuracy and numerical stability. New features include new output options, several added computes, and mesh geometry option suitable for micro- and nano-fluidic device simulations. The original package could require fairly careful calibration to obtain accurate thermostating and accurate reproduction of properties related to the hydrodynamic size of objects such as colloids. This process has now been largely automated so that the default settings should suffice for most applications. Program summaryProgram title: fix lb/fluidCPC Library link to program files:https://doi.org/10.17632/2289cnrdtz.1Licensing provisions: GPLv3Programming language: C++Journal reference of previous version: Comput. Phys. Commun. 184 (2013) 2021–2031.Does the new version supersede the previous version?: YesReasons for the new version: The new version improves accuracy, adds new features, and simplifies the use of the package.Summary of revisions: A new two-pass interpolation and spreading scheme is introduced to relate properties on the fluid mesh to off-lattice particle properties. New features include output options, several added computes, and mesh geometry suitable for micro- and nano-fluidic device simulations. Calibration processes have been largely automated so that the default settings should suffice for most applications.Nature of problem: The inclusion of long-range hydrodynamic effects into molecular dynamics simulations requires the presence of an explicit solvent. Prior to the implementation of this fix, the only option for incorporating such a solvent into a LAMMPS [1] simulation is the explicit inclusion of each of the individual solvent molecules. This is obviously quite computationally intensive, and for large system sizes can quickly become impractical.Solution method: As an alternative, we have implemented a coarse-grained model for the fluid, simplifying the problem, while retaining the solvent degrees of freedom. We use a thermal lattice-Boltzmann model for the fluid, which is coupled to the molecular dynamics particles at each fluid time step.

Efficient Technique for PAPR and BER Reduction in Downlink Large Scale MU-MIMO-OFDM System

Background & Objective: The Orthogonal Frequency Division Multiplexing (OFDM) based large scale multiuser multiple input multiple output (LS-MU-MIMO) system is a preferred choice for signal transmission because it can substantially enhance the spectral and energy efficiency of the next-generation wireless systems. However, there are several practical issues in implementing large multiuser-MIMO-OFDM systems and one of the critical issues is the high Peak-to-Average- Power Ratio (PAPR). Due to the use of a large number of antennas at the Base Station (BS) of an LSMU- MIMO-OFDM system, it requires a large number of Power Amplifiers (PAs) which are needed to be connected to each antenna element. The high PAPR in an OFDM based LS-MU-MIMO system results in the decrease in the efficiency of PAs and enhancement in nonlinear signal distortions. This work is concerned with the reduction in PAPR of LS-MU-MIMO-OFDM systems using the SCFDMA scheme for the downlink transmission. The reduction in PAPR is achieved on the basis of discrete Fourier transform spreading (DFT-S) scheme known as DFT-SC-FDMA. The SC-FDMA scheme can achieve the reduction in PAPR of MIMO-OFDM signal up to the level of single-carrier transmission. Further, the reduction in PAPR is achieved with the sub mapping schemes such as localized FDMA (LFDMA) and distributed FDMA (DFDMA), Interleaved FDMA (IFDMA). Result: In this work, we propose to perform jointly multiuser MMSE precoding, SC-IFDMA and antenna reservation technique to reduce the PAPR and Bit Error Rate (BER) of the large MU-MIMO system. To show the effectiveness of the proposed scheme in the reduction of PAPR with different modulation techniques, subcarriers, and subcarrier mapping schemes, the results are compared with the existing OFDM based large MU-MIMO system. Conclusion: The MATLAB simulation results confirm that our proposed combination of MMSE MUprecoding, SC-IFDMA and antenna reservation technique is able to reduce PAPR and BER to a significant extent for LS-MU-MIMO-OFDM systems.

Multi-user connection performance assessment of NOMA schemes for beyond 5G

Non-orthogonal multiple access (NOMA) is proved to be useful to satisfy the requirements of beyond 5th generation such as massive multi-user connection. Here we compare the performances of two NOMA schemes: low code rate spreading (LCRS) scheme and interleaver division multiple access (IDMA) scheme. It is found that LCRS is superior to IDMA when number of users is small due to coding gain achieved. While IDMA is preferred when number of users is high because repetition applied in IDMA can suppress multi-user interference effectively. And interleaver is important in IDMA for randomizing the interference. Also, this paper evaluates the impact of channel decoder. It is observed that Log-MAP decoder has much better performance than that of Max-LogMAP when number of users is large. Thus, it is recommended to use Log-MAP decoder in NOMA in high user overloading case. We also compared the performance of NOMA by using different type of channel codes. We find that NOMA using specific convolutional code has a better performance than that of using specific LDPC code when number of users is high.

Performance evaluation of chaotic spreading codes in massive MIMO OFDM system

Background/Objectives: Wireless communication systems are growing towards the implementation of 5G communication systems to satisfy the demand of services in future. OFDMA has some shortcoming like one or more subcarriers of OFDM are completely affected due to the characteristic of the transmission channel. Spreading scheme has been introduced to combat the aforementioned issue. Furthermore, communication channels are affected by multipath fading which changes the amplitude of the received signal. This fading severely affects the communication systems. Therefore, it is essential to develop a more robust technique for higher data transmission and larger throughput. The main objective of this study is to design a massive MIMOOFDM system for secure transmission of data. Chaos based sequence is used to spread the data before transmission which will solve intercell interference and improve the security of data. Methods: This study presents a chaos based massive MIMO-OFDM communication system. The proposed chaos based massive MIMO-OFDM system is implemented and its efficacy is evaluated by computing bit error rate. The effectiveness of the proposed system is investigated by varying the parameters including modulation methods such as PSK and QAM, number of users 10, 20 and 30 and spreading factor of 5, 10 and 15. Findings: Results clearly proved that the proposed system provides exceptional performance with 16QAM modulation scheme, 10 users at high spreading factor value of 15. Novelty: The uniqueness of the proposed system is with enhanced performance and usage of novel modulation scheme by varying the spreading factor value, when compared to its peers. Keywords: Communication system; spreading code; chaotic code; massive MIMO-OFDM; bit error rate

Sparse Space-Time-Frequency-Domain Spreading for Large-Scale Non-Orthogonal Multiple Access

A generalised spatial modulation-aided sparse space-time-frequency spreading (GSM/SSTFS) scheme is proposed for supporting large-scale access at a high normalized user-load in next-generation systems by simultaneously exploiting the transmit diversity in the spatial- and frequency-domain. Specifically, in the GSM/SSTFS system employing two transmit antennas (TAs), each user equipment (UE) spreads its signal over two symbol durations, two active TAs, and multiple subcarriers by a unique pre-assigned sparse code, in order to attain spreading in three dimensions (3D). Furthermore, with the aid of GSM, extra information bits are embedded in the TA indices. At the receiver, a joint message passing-aided (JMPA) detector is employed for attaining near-single-user bit error rate (BER) performance, which is also compared to that of conventional multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) systems.

Cyclic Block-Spreading Direct Discovery for D2D Networks

Device-to-device (D2D) communications has become a pivotal piece to complete the puzzle of future generation of wireless communication systems. The enabling technology for the D2D communications lies in its discovery mechanism. Plenty of works have been proposed to enhance the efficiency of direct D2D discovery without network assistance. Generally, the main idea of these works is to avoid unnecessary collisions during the discovery period. However, owing to the limited resources for D2D discovery, the effectiveness of the collision avoidance based schemes is always restricted. Instead, we aim to make the discovery beacon robust against collisions. To achieve this, the cyclic block spreading (CBS) scheme is proposed to spreading the beacon over multiple subframes without widening the bandwidth and the need of redesigning the beacon. That means that solely minor modification of specification is required. The simulation and analytic results show that using the CBS direct discovery scheme, the performance in terms of outage probability, collision rate and time periods for complete discovery can be significantly improved.

Immersed boundary method with irrotational discrete delta vector for droplet simulations of large density ratio

An accurate estimation of the physical properties of a free-falling raindrop such as its falling speed, shape, and oscillation amplitude are expected to improve the numerical models used for weather forecasting. Developing a numerical tool for Direct Numerical Simulations (DNS) of water droplets by the Immersed Boundary Method (IBM) is one of the efficient ways to obtain empirical formulae for those physical properties. However, it is known that the IBM suffers from two instability problems in capillarity-dominant water droplet simulations. One is the spontaneous generation of unphysical kinetic energy, which is known as parasitic currents, and the other is spurious surface reconstruction. In this work, a new IBM is developed for stable water droplet simulations. A new force spreading scheme, which preserves the irrotational condition, is proposed to remove the spurious currents. Furthermore, B-spline fitting by least squares is adopted to relocate the Lagrangian markers for a smooth surface reconstruction. The conventional scheme and new scheme are implemented in a multigrid finite volume DNS solver and are subjected to standard test cases. It is confirmed that the unphysical parasitic currents are substantially reduced in the new scheme. The new scheme is applied to simulations of an axisymmetric free-falling droplet of low density ratio, a two-dimensional (2D) free-falling water droplet, and a rising bubble to demonstrate its robustness in a wide range of shape deformation and the capability of stable long-time-scale simulations for future application to raindrop simulations.

Design of 100-MeV proton beam spreading scheme with double-ring double scattering method

To obtain a large uniform beam field for proton single event effect (SEE) experiments, the double-ring double scattering method (DDSM) is employed for spreading the 100 MeV proton beam provided by the 100 MeV proton cyclotron at China Institute of Atomic Energy. With the Geant 4 simulations, the fundamentals of the DDSM are further explored, the achieved effect of our DDSM scheme design is presented, and the influences of some possible factors in practice on the produced beam field are discussed. We find that the the outer part of the second scatter plays an important role in enlarging the area of the uniform field and improving its uniformity. We also find that the first scatter and the inner part of the second scatter play a decisive role in determining the proton flux of the uniform area. The scattering between the spread proton beam and the accelerator tube behind the second scatter damages the uniformity and leads the energy of the produced beam field to straggle. Therefore, the tube should be made as short as possible. The size of the initial beam spot on the first scatter affects the produced beam field to some extent. The spot should be focused as much as possible in a circle with a radius of 0.5 cm. At a larger distance, a larger uniform field can be produced due to the spreading of the proton beam along the space. The decrease in the incident proton energy causes the flux and uniformity to decrease, and also leads the energy loss to increase and the energy of the produced proton beam field to straggle. Using our DDSM schematic design, the simulations show that an 8-cm-diameter beam field with a uniformity of ±1.89% can be produced at a distance of 2.4 m, thereby meeting the need for an SEE experiment of a device-level sample, and that a 20-cm-radius beam field with a uniformity of ±5.32% can be created at a distance of 5.0 m, thereby meeting the need for an SEE experiment of a system-level sample of comparable size. By taking into consideration the uniformity and energy straggling, our design is basically applicable to the protons in the 70−100 MeV energy region that the accelerator can provide directly.

Exploiting high rate differential algebraic space‐time block code in downlink multiuser MIMO systems

This paper considers a multiuser multiple-input multiple-output (MIMO) space-time block coded system that operates at a high data rate with full diversity. In particular, they propose to use a full rate downlink algebraic transmission scheme combined with a differential space-time scheme for multiuser MIMO systems. To achieve this, perfect algebraic space-time codes and Cayley differential transforms are employed. Since channel state information (CSI) is not needed at the differential receiver, differential schemes are ideal for multiuser systems to shift the complexity from the receivers to the transmitter, thus simplifying user equipment. Furthermore, orthogonal spreading matrices are employed at the transmitter to separate the data streams of different users and enable simple single user decoding. In the orthogonal spreading scheme, the transmitter does not require any knowledge of the CSI to separate the data streams of multiple users; this results in a system which does not need CSI at either end. With this system, to limit the number of possible codewords, a sphere decoder is used to decode the signals at the receiving end. The proposed scheme yields low complexity transceivers while providing full rate full diversity with good performance. Simulation results demonstrate the effectiveness of the proposed scheme.

Resource Usage Prediction Models for Optimal Multimedia Content Provision

This paper proposes a network architecture that utilizes novel resource prediction models for optimal selection of multimedia content provision methods. The proposed research approach is based on a prototype system, which exploits a resource prediction engine (RPE), utilizing time series and epidemic spread models, for optimal and balanced distribution of the streaming data among content delivery networks, cloud-based providers and home media gateways. The proposed epidemic diseases models adopt the characteristics of the multimedia content delivery over the network architecture. In this context, this paper aims to present the advantages of using such models, by presenting and analyzing an epidemic spread scheme for video-on-demand (VoD) delivery, to predict future epidemic spread behavior. In addition, this paper presents two algorithms, adopted in the prototype network architecture, for optimal selection of multimedia content delivery methods, as well as balanced delivery load, by exploiting the RPE. Both algorithms and models are evaluated to establish their efficiency, toward effectively predicting future network traffic demands. The simulation results verify the validity of the proposed approach, identifying fields for future research and experimentation.

Transmission of nanoscale information-based neural communication-aware ligand–receptor interactions

In this paper, we develop an analytical framework for modeling the transmission of nanoscale information in nanonetwork-based molecular communication and aware of ligand–receptor interactions. In this framework, we consider the interconnection among nanomachines, which carry nanoscale information, is accomplished by collision and adhesion process while the information is transported by adopting neural communication-aware ligand–receptor interactions. The ligand–receptor interactions will be investigated by deploying biophysical parameters such as binding affinity, the density of receptors and the contact area; then, we make use of these parameters to design nanonetwork. Furthermore, we present a propagation scheme for modeling the transmission of information in the proposed nanonetwork with the help of epidemic disease spreading scheme. The key performance analysis of the proposed nanonetwork in terms of packet delay, throughput and tolerant traffic rate is provided. The results reveal that it is necessary to take into account the ligand–receptor interactions for more realistic realization of the nanoscale information transmission.

Chaotic direct-sequence spread-spectrum with variable symbol period: A technique for enhancing physical layer security

In chaotic direct-sequence spread-spectrum (DSSS) technique, chaotic sequences with typical properties such as aperiodic variation, wideband spectrum, good correlation, and initial condition sensitivity have been used as spreading codes in order to improve the security at physical layer. However, a number of recent studies have proved that an intruder can recover chaotic sequences by blind estimation methods and use the sequences to detect symbol period, which will result in the original data being exposed. To overcome this security weakness, this paper proposes a novel chaotic DSSS technique, where the symbol period is varied according to behavior of the chaotic spreading sequence in the communication process. The data with variable symbol period is multiplied with the chaotic sequence to perform the spread-spectrum process. Discrete-time models for the spreading scheme with variable symbol period and the despreading scheme with sequence synchronization are presented and analyzed. Multiple-access performance of the proposed technique in the presence of the additional white Gaussian noise (AWGN) is calculated by means of both theoretical derivation and numerical computation. Computer simulations are carried out and simulated performances are shown to verify the estimated ones. Obtained results point out that our proposed technique can protect the DSSS systems against the detection of symbol period from the intruder, even if he has full information on the used chaotic sequence.

Adaptive WHTS-Assisted SDMA-OFDM Scheme for Fair Resource Allocation in Multi-User Visible Light Communications

This paper proposes applying Walsh-Hadamard transform spreading (WHTS) in conjunction with space-division multiple access (SDMA) in an orthogonal frequency-division multiplexing (OFDM) system to provide enhanced multi-user downlink capability in visible light communication (VLC) scenarios. VLC environments are characterized by strong interference from the emissions of adjacent lamps. Thus, SDMA-OFDM schemes can be applied to enable multi-user capability while ensuring a highly efficient use of the limited available bandwidth. However, these SDMA-OFDM systems can only provide multiple access for a small number of users whenever there is enough channel diversity to separate the users' information. This is the case, for example, when each single user is associated with a specific emitting lamp and angle-diversity receiving techniques are applied. However, to accommodate a greater number of users requires a user's distribution in the frequency domain. In this sense, the proposed Walsh-Hadamard transform spreading scheme provides a fair assignment of the available subcarriers among the different users leading to an identical throughput and bit error rate (BER) for users allocated to the same emitting lamp. This BER is also controllable by means of an adaptive throughput mechanism. The numerical results show that the proposed adaptive WHTS-assisted SDMA-OFDM system in a full-user scenario presents a similar performance to that of an adaptive SDMA-OFDM system irrespective of the number of users per lamp, while providing enhanced multi-user capability. Finally, an adaptive algorithm for resource allocation is evaluated, demonstrating a high degree of satisfaction (regarding demanded data rates) when large numbers of users are simultaneously served.

A Randomized Space-Time Spreading Scheme for Massive MIMO Channels

We consider a wireless transmission scheme based on randomized space-time spreading (STS) systems over massive multiple-input multiple-output (MIMO) channels. In the systems, the signals are spread by spreading matrices over time and antenna domains at the transmitter. We propose that the spreading matrices are generated from binary pseudo-noise (PN) and mutual quasi-orthogonal sequences, by partitioning each of the sequences into subsequences treated as real and imagination parts of rows or columns of a spreading matrix. We give a likelihood ascent search (LAS) detector for the STS systems and analyze its computational complexity. The number of multiplication and division operations for the LAS detector does not depend on its iterative process and the number of chips in the bit period. We use Monte Carlo method to solve the bit error rates (BERs) of the STS systems and to count numbers of evaluating bits in the LAS detectors. We choose the system parameters, such as the number of chips in the bit period and the transmission bit rates, according to BER performance and/or the numbers of evaluating bits attained from Monte-Carlo method. With the spreading matrices, the detection, and the suitable parameters, the STS systems achieve BERs near to their single-bit performance, which is the BER of a STS system with a single bit spread by orthonormal sequences at each transmitting antenna. We also compare our systems with V-BLAST-like spatial multiplexing systems with BPSK signals to show the improvement of the BER performance.

A study of three-dimensional optical code-division multiple-access for optical fiber sensor networks

This study proposes a novel optical fiber sensor (OFS) network using three-dimensional (3-D) wavelength/time/spatial optical code-division multiple-access (OCDMA) scheme. The proposed 3-D modified quadratic congruence/M-matrix (MQC/M-matrix) coding scheme overcome the restriction of single pulse per row inherent in traditional three-dimensional codes and maintain a high signal-to-noise ratio even when source power is low. The 3-D system is implemented using optical switches (OSW), fiber-Bragg gratings (FBGs), optical splitter and optical combiner. The noises of phase-induced intensity noise (PIIN) and multiple access interference (MAI) in the decoding mechanism can be suppressed by using a spectral spreading scheme and balance-detection in the receivers. By constructing 3-D codes using bipolar pseudorandom (PN) codes rather than unipolar codes provides a significant increase in the maximum permissible number of active sensor nodes.

Network Coding Based Information Spreading in Dynamic Networks With Correlated Data

In this paper, we design and analyze information spreading algorithms for dynamic networks with correlated data. In these networks, either the data to be distributed, the data already available at the nodes, or both are correlated. Moreover, nodes' availability and connectivity is dynamic - a scenario typical for wireless networks. Our contribution is twofold. First, although coding schemes for correlated data have been studied extensively, the focus has been on characterizing the rate region in static networks. In an information spreading scheme, however, nodes may communicate by continuously exchanging packets according to some underlying communication model. The main figure of merit is the stopping time - the time required until nodes can successfully decode. While information spreading schemes, such as gossip, are practical, distributed, and scalable, they have only been studied for uncorrelated data. We close this gap by providing techniques to analyze network-coded information spreading in dynamic networks with correlated data. Second, we give a clean framework for oblivious dynamic network models that in particular applies to a multitude of wireless network and communication scenarios. We specify a general setting for the data model and give tight bounds on the stopping times of network-coded protocols in this wide range of settings. En route, we analyze the capacities seen by nodes under a network-coded information spreading protocol, a previously unexplored question. We conclude with extensive simulations, clearly validating the key trends and phenomena predicted in the analysis.

Finite Field Spreading for Multiple-Access Channel

As a generalization of the binary spreading scheme in conventional direct-sequence code-division multiple-access (DS-CDMA) and interleave-division multiple-access (IDMA), a finite field spreading scheme is proposed for a synchronous multiple-access channel (MAC) with Gaussian noise and equal-power users. For each user, each information symbol over a finite field is spread into a length-L field vector by L-field multiplications. At the receiver, an iterative multi-user decoding algorithm on a factor graph is developed to recover each user's information symbol. To estimate the bit error rate performance of an uncoded finite field spreading system, an extrinsic information transfer analysis of the finite field despreading is given. This analysis shows that in addition to overcoming multi-user interference, the finite field spreading scheme can also provide an additional coding gain to overcome Gaussian noise compared with the conventional spreading scheme. This coding gain increases with the field order. The finite field spreading serially concatenated with a nonbinary low-density parity-check (LDPC) code, with field order 64, approaches the MAC capacity within 0.26 dB at a sum rate of 0.25.

A study of design approach of spreading schemes for viral marketing based on human dynamics

Before launching a real viral marketing campaign, it is needed to design a spreading scheme by simulations. Based on a categorization of spreading patterns in real world and models, we point out that the existing research (especially Yang et al. (2010) Ref. [16]) implicitly assume that if a user decides to post a received message (is activated), he/she will take the reposting action promptly (Prompt Action After Activation, or PAAA). After a careful analysis on a real dataset however, it is found that the observed time differences between action and activation exhibit a heavy-tailed distribution. A simulation model for heavy-tailed pattern is then proposed and performed. Similarities and differences of spreading processes between the heavy-tailed and PAAA patterns are analyzed. Consequently, a more practical design approach of spreading scheme for viral marketing on QQ platform is proposed. The design approach can be extended and applied to the contexts of non-heavy-tailed pattern, and viral marketing on other instant messaging platforms.

Optimum Spread Code Applied in Indoor Visible Light Data Transmission for Optical Multipath Dispersion Reduction

In an indoor visible light communication (VLC) system, diffuse channels are very easily caused by numerous reflections of the optical signals from the obstacle surface, resulting in optical multipath dispersion which can further reduce the bit error rate (BER) performance of wireless communication system. In this paper, we investigated non-directed LOS links and optimized the design of this short-range communication model using white light-emitting diodes illumination. In our VLC system, we proposed spreading scheme to combat the severe effects of multipath dispersion. We compared the BER performances of four spread codes on the diffuse channel: pseudo random code, Walsh code, m-sequence code, and gold code. Through the analysis and comparison of simulation results, we obtained the optimum spread code, namely Walsh code, which can alleviate the serious effects of multipath dispersion.