Orthogonal Spectrum Research Articles

Energy-Efficiency Study for Two-tier Heterogeneous Networks (HetNet) Under Coverage Performance Constraints

Recently, heterogeneous networks (HetNet) have been widely studied as an effective approach to provide high network capacity and coverage, which jointly utilizes the technologies of cognitive radio and cooperative communications. However, the dense and random deployment of small-cells (e.g., micro, pico and femtocells) raises important questions about the energy consumption for HetNets. In this paper, we study the optimal energy efficiency of a two-tier heterogeneous network consists of a macro-cell and many small-cells under coverage performance constraints for different spectrum deployments (including orthogonal and co-channel spectrum deployments). Firstly, we derive the closed-form expressions of coverage performance for each tier based on stochastic geometry. Then the relationship between energy efficiency and the density of small-cells for the two-tier network is evaluated, the optimal density of small-cells that maximize energy efficiency under coverage performance constraints for the two-tier network is obtained. The theoretical analysis is validated by simulations.The results show that the energy efficiency of the two-tier networks with orthogonal spectrum deployment is better than that with co-channel spectrum deployment. The results also show that the optimal density of small-cells for maximal energy efficiency is only dependent on the coverage performance of small-cells in orthogonal spectrum deployment scenario. However, in co-channel spectrum deployment scenario, the optimal density of small-cells for maximal energy efficiency is jointly decided by the coverage performance of both macro-cell and small-cell. This work provides an essential understanding for successful deployment of green heterogeneous networks.

Orthogonal code shift keying spread spectrum underwater acoustic communication

Code shift keying (CSK) is generally used to overcome the spreading gain versus data rate limitation in underwater acoustic (UWA) communication as generalized M-ary spread spectrum technology. In addition, the concept of orthogonal CSK is introduced into the UWA communication to achieve higher rate, mitigate crosstalk from the other thoroughfare and utilize the redundant information of CSK adequately. In this paper, we propose a new scheme employing orthogonal double thoroughfare CSK spread spectrum UWA communication with utilizing code phase information combined. First, each symbol integration output form of the proposed method is deduced. Furthermore, the property of orthogonal CSK is analyzed and its bit error rate is investigated as compared with conventional CSK and double thoroughfare CSK via simulation. Finally, the validity of simulation comparison is verified in experiment. 580.6 bps data rate of the proposed communication scheme is realized in 104 bit volume and 4 kHz bandwidth efficiently. It is shown that the proposed method provides significantly improved communication performance through formula, simulation and test.

Spectrum sharing improves the network efficiency for cellular operators

The article describes the potential gain by spectrum sharing between cellular operators in terms of network efficiency. The focus of the study is on a specific resource sharing scenario: spectrum sharing between two operators in cellular downlink transmission. If frequency bands are allocated dynamically and exclusively to one operator - a case called orthogonal spectrum sharing - significant gains in terms of achievable throughput (spectrum sharing gains between 50 percent and 100 percent) and user satisfaction are reported for asymmetric scenarios at link and system level as well as from two hardware demonstrators. Additionally, if frequency bands are allocated simultaneously to two operators - a case called non-orthogonal spectrum sharing - further gains are reported. In order to achieve these, different enablers from hardware technologies and base station capabilities are required. However, we argue that all requirements are fulfilled in 3GPP and newer mobile standards. Therefore, the results and conclusions of this overview article encourage to seriously consider the inter-operator spectrum sharing technologies.

Research on Simulation Model of Nonstationary Stochastic Processes in Natural Disasters

Simulation of nonstationary processes has become an indispensable tool in study and prevention of natural disasters. A new method of simulation of nonstationary random processes is presented based on the orthogonal HHT spectra of sample observations and random phase. It takes advantage of orthogonal EMD, the instantaneous frequency, amplitude of the Hilbert transform and independent random phase angle, thus overcoming difficulties in the estimation of the frequency modulation and interdependence of frequency and amplitude modulation functions faced by most currently available methods. The new method extracts and preserves the true physical features of the process. The examples of earthquake ground motion and subway vibration, as low frequency and high frequency nonstationary process respectively, were simulated in the paper. The time history of sample, Fourier amplitude spectrum of sample, arithmetic average of sample, variance of sample, Wavelet time-frequency distribution of sample amd autocorrelation coefficient of sample compare well with those of the records. Scattering extent of the peaks of the sample processes is also analyzed in the paper. We can conclude that the method has great potential for engineering applications when dealing with nonstationary, nonlinear random peocesses exist in natural disasters, such as earthquake wave, vibration wave , wind wave and ocean wave.

Interference management for LTE‐Advanced Het‐Nets: stochastic scheduling approach in frequency domain

ABSTRACTHeterogeneous networks represent a practical way to face high traffic demands in densely populated areas. Nevertheless, to achieve these advertised data rates, advanced interference management techniques are required. Trying to tackle this problem, this paper presents a stochastic scheduling approach for two‐layer LTE‐Advanced networks. The proposed stochastic frequency‐domain scheduling (SFDS) algorithm seeks the avoidance of cross‐layer and colayer interference, and is based on allocating different portions of the transmission bandwidth probabilistically. The SFDS algorithm is first presented as an interference management solution for an orthogonal frequency‐division multiple access system (i.e. LTE‐Advanced downlink). Later on, the SFDS algorithm is extended to be compatible with single‐carrier frequency‐division multiple access transmissions, and its performance is evaluated when combined with open‐loop power control techniques (i.e. LTE‐Advanced uplink). Extensive system level simulations are carried out to evaluate the performance of SFDS algorithm in a predefined LTE‐Advanced scenario that combines both macrolayer and femtolayer. Results show that the proposed algorithm allows to balance the cross‐layer and colayer interferences, extending the performance trade‐offs that well‐known full‐range spectrum allocation and orthogonal spectrum allocation approaches provide. Copyright © 2012 John Wiley & Sons, Ltd.

Evolutionary algorithms for orthogonal frequency division multiplexing-based dynamic spectrum access systems

This paper proposes two evolutionary algorithms (EAs) to perform dynamic spectrum assignment in distributed OFDM-based cognitive radio access networks. To achieve better radio resource utilization, the central spectrum manager (CSM) jointly considers the type of modulation level which can be used by each radio pair when deciding the number of subcarriers to be assigned. Using the piecewise convex transformations, we reformulate the nonlinear integer programming problem to an integer linear programming so that it is possible to obtain the optimal solution. While the solution to the integer linear programming problem is NP-hard, the proposed EAs provide useful suboptimal solutions especially when the number of radios and subcarriers are large. Our first proposed EA adopts the genetic algorithm. Although the reproduction process generates chromosomes which do not fulfill the constraints, our algorithm integrates the invisible walls technique used in particle swam optimization to retain the diversity while constructing chromosomes for the next generation. The second EA adopts the ant colony optimization approach using a directed multigraph. The vertices are used to represent the subcarriers and each edge corresponds to a possible chosen modulation index of a specific radio. We further obtain the performance of the two EAs through simulations and benchmark them against the optimal solution. Our studies show that ant colony algorithm gives better solutions most of the time, however, its computation time increases much faster compared to generic algorithm when the numbers of users and subcarriers increase.

An orthogonal spectrum sharing scheme for wireless sensor networks

It is not economically viable to allocate a dedicated spectrum band to wireless sensor networks (WSNs). Moreover, sharing a spectrum band with incumbent (primary) system compromises the reliability and performance of both the systems due to interference from one system to another. In this article, we address this limitation by proposing a two-phase orthogonal spectrum sharing protocol for a WSN which exploits multiple sensor nodes to effectively cancel out the interference from a WSN to the primary system, and vice versa. As a consequence, it is possible to achieve spectrum access for the WSN without compromising on the performance of either systems. Performance of WSN as well as the primary system is quantified in terms of average received signal to noise ratio. We then validate the efficiency of the proposed scheme through analytical and simulation results.

A New Spectral Representation of Earthquake Recordings Using an Improved Hilbert-Huang Transform

A new spectral representation method of earthquake recordings using an improved Hilbert-Huang transform (HHT) is proposed in the paper. Firstly, the problem that the intrinsic mode functions (IMFs) decomposed by the empirical mode decomposition (EMD) in HHT is not exactly orthogonal is pointed out and improved through the Gram-Schmidt orthogonalization method which is referred as the orthogonal empirical mode decomposition (OEMD). Combined the OEMD and the Hilbert transform (HT) which is referred as the improved Hilbert-Huang transform (IHHT), the orthogonal intrinsic mode functions (OIMFs) and the orthogonal Hilbert spectrum (OHS) and the orthogonal Hilbert marginal spectrum (OHMS) are obtained. Then, the IHHT has been applied for the analysis of the El Centro earthquake recording. The obtained spectral representation result shows that the OHS gives more detailed and accurate information in a time–frequency–energy presentation than the Hilbert spectrum (HS) and the OHMS gives more faithful low-frequency energy presentation than the Fourier spectrum (FS) and the Hilbert marginal spectrum (HMS).

Dispersive dielectrics and time reversal: Free energies, orthogonal spectra, and parity in dissipative media

Free energies of dissipative media are reviewed. Then we use free-energy-optimal excitation and de-excitation fields to generate a dielectric's time-reversal spectrum, with several properties: a) The spectrum generalizes the time-reversal parity from "even" and "odd" of conservative systems to an interval [-1,+1] of "time-reversal eigenvalues" λ in dissipative media. b) It yields eigenmodes that are complete: any state of the medium is optimally excitable or de-excitable by them. c) These excitations are orthogonal with respect to the work function of the medium and, so, d) characterize field excitations for the given medium that, when superimposed, only do work on the medium, not on each other via the medium-field interaction mechanism. Notions of en masse potential and kinetic energy in the dissipative medium arise through even (λ=+1) and odd (λ=-1) parity, but also other energy notions via alternative parity (|λ|<1) under time reversal.

Analytical solution to the coupled evolution of multidimensional NMR data

A substantial time savings in the collection of multidimensional NMR data can be achieved by coupling the evolution of nuclei in the indirect dimensions. In order to save time, the sampling of the indirect dimensions is inherently incomplete. Therefore, many algorithms and samplings schemes have been developed aimed at separating the coevolved frequencies into analyzable data with limited artifacts. This paper extends the use of circulant matrices to describe coupled evolution with convolutions. By understanding the data in terms of convolutions, there is an exact solution to the inversion problem of extracting the orthogonal vectors from the coupled dimensions. Previously, this inversion problem has been solved using peak coordinates extracted from spectra. In contrast, the method described here uses spectra directly. This solution suggests a simple sampling scheme of collecting N orthogonal spectra, and N + 1 projections at specific projection angles, however, the theory developed can be extended generally to arbitrary projection angles. The circulant matrix methodology is demonstrated for simulated and real data. Further, an algorithm for separating overlapped signals in the detected dimension is presented. The algorithm involves the forward calculation of the coupled spectra from the orthogonal spectra, followed by back calculation of the orthogonal spectra from the coupled spectra, thus permitting rigorous cross-validation. This algorithm is shown to be robust in that erroneous solutions give rise to large artifacts.

Ultrawideband noise radar based on antenna arrays with signal recirculation

For radar systems using noise sounding signals with orthogonal spectra, which are radiated with the help of a multielement antenna array, a method for recirculation of noise signals in the feedback loop formed by the transmitting element, the target, and the receiving element is considered. The generalized ambiguity function is used to compare the resolutions and the sidelobe levels along the delay (range) coordinate and the angular coordinate for the cases of a linear equispaced transmitting antenna and an individual receiving antenna in the presence and in the absence of recirculation. Sparse and filled antenna arrays are analyzed for the cases of moderately wideband and ultrawideband total noise signals and different distributions of the center frequencies of partial noise signals over the array elements.

Equivariant homotopy theory for pro–spectra

We extend the theory of equivariant orthogonal spectra from finite groups to profinite groups, and more generally from compact Lie groups to compact Hausdorff groups. The G-homotopy theory is "pieced together" from the G/U-homotopy theories for suitable quotient groups G/U of G; a motivation is the way continuous group cohomology of a profinite group is built out of the cohomology of its finite quotient groups. In the model category of equivariant spectra Postnikov towers are studied from a general perspective. We introduce pro-G-spectra and construct various model structures on them. A key property of the model structures is that pro-spectra are weakly equivalent to their Postnikov towers. We discuss two versions of a model structure with "underlying weak equivalences". One of the versions only makes sense for pro-spectra. In the end we use the theory to study homotopy fixed points of pro-G-spectra.

Model structure on operads in orthogonal spectra

We generalize Berger and Moerdijk’s results on axiomatic homotopy theory for operads to the setting of enriched symmetric monoidal model categories, and show how this theory applies to orthogonal spectra. In particular, we provide a symmetric fibrant replacement functor for the positive stable model structure.

Mean squared error of the empirical best linear unbiased predictor in an orthogonal finite discrete spectrum linear regression model

The mean squared error (MSE) of the empirical best linear unbiased predictor in an orthogonal finite discrete spectrum linear regression model is derived and a comparison with the MSE of the best linear unbiased predictor in this model is made. It is shown that under weak conditions these two mean square errors are asymptotically the same.

Ultrasonic Particle Sizing of Disperse Systems with Partly Unknown Properties

AbstractThe determination of particle size distributions from ultrasonic attenuation spectra requires the knowledge of a variety of parameters (material properties and particle concentration) when the analysis is based on analytical models. In this paper, two strategies are tested that allow for the elicitation of size information from attenuation spectra when the relevant model parameters are only partially known. The first strategy uses the data on measured sound speed as additional information, which facilitates the fitting of the unknown model parameters parallel to the calculation of the particle size distribution. The second strategy comprises the formation of an empirical model that is based on the principal components, which are obtained by decomposing a measured attenuation spectrum into a set of orthogonal basic spectra. Both strategies are tested with colloidal emulsions: the first one for the cases of unknown particle concentration and unknown specific heat of the droplets, the second one for monitoring changes in the state of dispersion and in the temperature.

Photocatalytic Degradation-Excitation−Emission Matrix Fluorescence for Increasing the Selectivity of Polycyclic Aromatic Hydrocarbon Analyses

The application of photocatalysis enhancement to calibration of fluorescence excitation-emission matrixes (EEMs) with parallel factor (PARAFAC) analysis is described. In this study, three- and four-way PARAFAC analysis was employed to extract the fluorescent species' spectra from overlapping EEMs. Time-dependent photocatalysis degradation of the polycyclic aromatic hydrocarbons (PAHs) was employed to create an additional dimension for analysis. The consequent four-dimension degradation-EEM data cubes have greater selectivity for each PAH than do three-dimension EEM data cubes alone. On a scale of 0 to 1, with 0 being completely collinear spectra and 1 being orthogonal spectra, including the time-dependent measurements increased the selectivity an average of 21%, from 0.73 to 0.87.

Spectral characteristics of OWSS signal

A recently reported signaling system called orthogonal wavelet spread spectrum (OWSS) is aimed at high speed WLANs. This letter discusses the generation and spectral properties of its basis pulses and the spectral characteristics of the transmit signal. If all virtual channels are active, the theoretical baseband spectrum of the OWSS systems is shown to be perfectly flat. Further, the simulated passband spectrum is found to be relatively flat and 30-40% more compact than that of the familiar 802.11a OFDM, due largely to the avoidance of the prefix, elimination of channel coding and a sharp rolloff.

Performance limits of OWSS: A spectrally efficient WLAN system

Orthogonal wavelet spread spectrum (OWSS) is a new wireless LAN signaling scheme aimed at bit rates of 100 Mbps or higher. Starting with power complementary full-tree wavelet pulses, it spreads them using a suitable set of PN codes. The resulting system pulses preserve the power complementary property and satisfy the generalized Nyquist criterion, while possessing both a wide time and a wide frequency support. Benefits from these properties include successful equalization in spite of deep local fades caused by multipath channels, and high spectral efficiency-30-40% higher than OFDM for comparable net bit rates. This paper presents an overview of OWSS and explores the fundamental limits to its performance. In the overview, it discusses the properties of the OWSS pulses, the transmit signal spectrum, and the structure of the transmitter/receiver. Then, the investigation of fundamental limits to the performance is carried out by formulating the system as a multi-rate signal processing system, using hierarchical matrices, and thereupon minimizing the total mean-square error (TMSE). The TMSE governs the BER performance of the system, and is defined as the sum of the MSE of the unequalized residual error and the MSE due to the channel noise amplified by the forward equalizer. We formulate the problem at the chip level so as to truly discern the fundamental limits to the performance of the equalizer. This approach enables estimation of the optimum equalizer for mitigating the effect of the multipath channel, prior to correlation and detection blocks embedded in the FE-DFE loop, and thereby the system performance. Simulation results demonstrate its effectiveness. For a 108 Mbps system with a 50 ns delayspread channel, a low BER of 10^-^5 and spectral efficiency up to 5.2 bits/s/Hz can be achieved at an Eb/No of 19 dB.

Estimation of variances in orthogonal finite discrete spectrum linear regression models

The Invariant Quadratic Estimators, the Maximum Likelihood Estimator (MLE) and Restricted Maximum Likelihood Estimator (REML) of variances in an orthogonal Finite Discrete Spectrum Linear Regression Model (FDSLRM) are derived and the problems of unbiasedness and consistency of these estimators are investigated.

Monoidal Uniqueness of Stable Homotopy Theory

We show that the monoidal product on the stable homotopy category of spectra is essentially unique. This strengthens work of this author with Schwede on the uniqueness of models of the stable homotopy theory of spectra. Also, the equivalences constructed here give a unified construction of the known equivalences of the various symmetric monoidal categories of spectra (S-modules, W-spaces, orthogonal spectra, simplicial functors) with symmetric spectra. As an application we show that with an added assumption about underlying model structures Margolis' axioms uniquely determine the stable homotopy category of spectra up to monoidal equivalence.