Multichannel Spectrum Research Articles

Experimental Evaluation of the UV Raman Lidar Sensitivity in Detection of Traces of Chemical Compounds

Experimental results are presented on the remote detection of traces of some chemical compounds on the surface with the help of Raman lidar built on the basis of an excimer KrF laser with a narrow line emission and multi-channel spectrum analyzer based on the diffraction spectrograph and a time gated ICCD camera. The sensitivity of the system is evaluated for the sensing range of 10 m. At the accumulation of the signal over 1000 laser pulses, the detection threshold of the nitrogencontaining chemical compounds of about of units of μg/cm2 has been reached. The effect of the substrate material on the sensitivity of the Ramanlidar method for detecting traces of chemicals on the surface is analyzed.

Sensing‐throughput optimisation for multichannel cooperative spectrum sensing with imperfect reporting channels

The problem of multiband cooperative spectrum sensing with imperfect reporting channels is considered. It is assumed that the secondary users (SUs) make use of an energy detection scheme to sense a number of frequency subbands (assigned to primary users) and report their sensing results to a fusion centre through noisy channels. Exact expressions for the opportunistic throughput, false alarm and missed detection probabilities are derived in terms of the overall sensing-plus-reporting time, sensing subintervals, reporting subintervals and decision thresholds for each SU in each subband. Then, an optimisation problem is formulated that aims to maximise the opportunistic throughput of the cognitive radio network so as to maintain the interference incident on the primary network below a given level. The constraints of the optimisation problem are shown to be non-convex and the conditions under which these constraints become convex are examined. It is also shown that the objective function of the problem is non-convex and two suboptimal techniques are introduced to effectively solve the problem using the algorithms developed for solving convex optimisation problems.

Joint Optimization of Cooperative Spectrum Sensing and Resource Allocation in Multi-channel Cognitive Radio Sensor Networks

Cooperative spectrum sensing (CSS) that utilizes multi-user diversity to mitigate channel instability and noise uncertainty is a promising technique in cognitive radio networks (CRNs). However, the spectrum-sensing parameters which affect the channel-access opportunities of secondary users (SUs) are conventionally regarded as static and treated independently from the resource-allocation strategies. In this paper, joint optimization of CSS, channel access and resource allocation is investigated in an overlay CRN in which each SU carries multi-channel spectrum sensing and transmits the detected energy to a fusion centre in the imperfect reporting channel. An access factor is introduced to describe the channel-access strategies in both cooperative and non-cooperative schemes. Based on the aggregate interference and the transmit power constraints, an optimization problem of multi-channel CSS is formulated to obtain the optimal transmit powers, allocation-access strategies, and sensing threshold of CR system for maximization of the opportunistic throughput. To solve the non-convex problems in both the single and multiple CR systems, the efficient iterative algorithms are developed by exploiting the hidden convexity of the optimization problems. Numerical results show that the performance of our approaches yields a significant enhancement compared with the equal channel-access and equal power-allocation strategy.

Impact of Channel Switching in Energy Constrained Cognitive Radio Networks

In this letter, we investigate the energy efficiency of multichannel spectrum access in cognitive radio networks. We consider two channel access schemes. In one case, a secondary user (SU) is assigned multiple channels and the channels are switched whenever a primary user (PU) returns. In the other, the SU operates on a single channel without switching to other channels. We develop an analytic framework on achievable channel utilization and energy consumption performance of the SU. From the results, we examine the trade-off between SU channel utilization and energy consumption, and identify the PU traffic conditions where one scheme outperforms the other.

Efficient Energy Detection Methods for Spectrum Sensing Under Non-Flat Spectral Characteristics

Cognitive radio is an emerging wireless technology that is capable of efficiently coordinating the use of the currently scarce spectrum resources, and spectrum sensing constitutes its most crucial operation. This paper proposes wideband multichannel spectrum sensing methods utilizing fast Fourier transform or filter-bank-based methods for spectrum analysis. Fine-grained spectrum analysis facilitates optimal energy detection in practical scenarios where the transmitted signal, channel frequency response, and/or receiver frequency response do not follow the commonly assumed boxcar model, which typically assumes, among other things, narrow-band communications with flat spectral characteristics. Such sensing schemes can be tuned to the spectral characteristics of the target primary user signals, allowing simultaneous sensing of multiple target primary signals with low additional complexity. This model is also extended to accounting for the specific scenario of detecting a reappearing primary user during secondary transmission, as well as in spectrum sensing scenarios where the frequency range of a primary user is unknown. Novel analytic expressions are derived for the corresponding probability of false alarm and probability of detection in each case, while the useful concept of the area under the receiver operating characteristics curve is additionally introduced as a single scalar metric for evaluating the overall performance of the proposed spectrum sensing algorithms and scenarios. The derived expressions have a rather simple algebraic representation, which renders them convenient to handle both analytically and numerically. The offered results are also extensively validated through comparisons with respective results from computer simulations and are subsequently employed in evaluating each technique analytically, which provides meaningful insights that are anticipated to be useful in future deployments of cognitive radio systems.

A Mechanistic Study on the Inhibition of Zinc Behavior During Laser Welding of Galvanized Steel

The characteristics of zinc behavior that the zinc layer is vaporized and ionized during laser welding of galvanized steel are closely related to the stability of the molten pool, and the weld keyhole formation, easily leading to weld defects such as pores, splashes, cave, and incomplete fusion. In this paper, an experimental platform was built based on a multichannel spectrum signal acquisition to study spectral characteristics of zinc, plasma temperature, electron density, and bremsstrahlung absorption in laser welding of galvanized steel with the copper addition. The results show that, due to the formation of a copper–zinc solid solution during the laser welding of galvanized steel, the zinc content in the welding joints increased significantly. Meanwhile, by adding an appropriate amount of copper powder, the temperature and oscillation amplitude of the plasma plume during the laser welding of galvanized steel decreased significantly. Further, the inverse bremsstrahlung radiation absorption coefficient decreased, and there was less attenuation of the laser energy when passed through the plasma plume outside the keyhole. Therefore, the method implemented here improved the utilization of laser energy during welding.

Securing coalitional game for distributed cooperative spectrum sensing in multi-channel cognitive radio networks

In this paper, a secure scheme is purposed for coalitional game in multi-channel cognitive radio networks. First, a distributed cooperative attack on multi-channel cooperative spectrum sensing is proposed. In the proposed attack, attackers play two coalitional games to maximize the number of invaded channels in a distributed manner. In the first game, attackers play with their fellow ones to allocate an optimal number of attackers for each channel, while in the second game, they play in the coalitions with other honest cognitive radios so as to conquer as many channels as possible. Then, a hierarchical ID-based key management scheme is proposed, where cognitive radios can only play on a certain number of requested channels and channel access for sensing is limited to the honest cognitive radios selected in the coalitional game. Simulation results show that the proposed attack can considerably decrease the number of potential channels with a low attack cost when security scheme is not considered, in addition to the energy efficiency of the proposed key management scheme. Finally, formal verification of the proposed key management scheme guarantees its immunity and effectiveness.

Design of X-Ray Fluorescence Spectrum Software Based on Linux

According to the research on analysis software of X fluorescent spectrum under the Linux system, a new algorithm of X fluorescence analyzer has been brought up: use the method of energy dispersive X fluorescence analysis, based on the software that can analyze the material composition under the control of ARM - Linux touch screen. This paper fixes on developing software of X fluorescence analyzer; realize the collection and analysis of multi-channel spectrum data, data storage, sample analysis, qualitative and quantitative analysis of the on-site samples, and the research and implementation of corresponding algorithm.

Spectrum sensing and resource allocation for multicarrier cognitive radio systems under interference and power constraints

Multicarrier waveforms have been commonly recognized as strong candidates for cognitive radio. In this paper, we study the dynamics of spectrum sensing and spectrum allocation functions in cognitive radio context using very practical signal models for the primary users (PUs), including the effects of power amplifier nonlinearities. We start by sensing the spectrum with energy detection-based wideband multichannel spectrum sensing algorithm and continue by investigating optimal resource allocation methods. Along the way, we examine the effects of spectral regrowth due to the inevitable power amplifier nonlinearities of the PU transmitters. The signal model includes frequency selective block-fading channel models for both secondary and primary transmissions. Filter bank-based wideband spectrum sensing techniques are applied for detecting spectral holes and filter bank-based multicarrier (FBMC) modulation is selected for transmission as an alternative multicarrier waveform to avoid the disadvantage of limited spectral containment of orthogonal frequency-division multiplexing (OFDM)-based multicarrier systems. The optimization technique used for the resource allocation approach considered in this study utilizes the information obtained through spectrum sensing and knowledge of spectrum leakage effects of the underlying waveforms, including a practical power amplifier model for the PU transmitter. This study utilizes a computationally efficient algorithm to maximize the SU link capacity with power and interference constraints. It is seen that the SU transmission capacity depends critically on the spectral containment of the PU waveform, and these effects are quantified in a case study using an 802.11-g WLAN scenario.

Frequency-pattern functional tomography of magnetoencephalography data allows new approach to the study of human brain organization.

A method based on a set of new theorems for the analysis of multichannel time series is described, based on precise Fourier transform and coherence analysis of the restored signals from a detailed set of frequency components. Magnetic field recordings of spontaneous and evoked activity by means of magnetic encephalography demonstrated that multichannel precise Fourier spectrum contains a very large set of harmonics with high coherence. The inverse problem can be solved with great precision based on coherent harmonics, so the technique is a promising platform of general analysis in brain imaging. The analysis method makes it possible to reconstruct sites and timing of electrical activity generated by both spontaneous and evoked brain function at different depths in the brain in the millisecond time range.

Risk-Aware Cooperative Spectrum Access for Multi-Channel Cognitive Radio Networks

In this paper, risk-aware cooperative spectrum access schemes for cognitive radio networks (CRNs) with multiple channels are proposed, whereby multiple primary users (PUs) operating over different channels choose trustworthy secondary users (SUs) as relays to improve throughput, and in return SUs gain transmission opportunities. To study the multi-channel cooperative spectrum access, cooperation over single channel is investigated first, which involves a PU selecting the suitable SU and granting a period of access time to the selected SU as a reward, considering trustworthiness of SUs. The above procedure is modeled as a Stackelberg game, through which access time allocation and power allocation are obtained. Based on the above results, cooperation over multiple channels is studied from the perspectives of the primary network and secondary network, respectively. Two schemes are proposed accordingly: the primary network-centric matching (PCM) scheme and the secondary network-centric cluster-based (SCC) scheme. In PCM scheme, cooperating SU for each channel is determined to maximize the total utility of the primary network, which is formulated as a maximum weight matching problem. In SCC scheme, SUs first form a cluster to share the channel state information (CSI), and the best SUs are selected for cooperation with PUs over different channels to obtain the maximum aggregate access time for the secondary network. Then, SUs share the obtained resource using congestion game and quadrature signalling. Numerical results demonstrate that, with the proposed schemes, PUs can achieve higher throughput, while SUs can obtain longer average access time, compared with the random channel access approach.

Developing an Advanced Prototype of the Acousto-Optical Radio-Wave Spectrometer for Studying Star Formation in the Milky Way

The designed practically prototype of an advanced acousto-optical radio-wave spectrometer is presented in a view of its application to investigating the Milky Way star formation problems. The potential areas for observations of the cold interstellar medium, wherein such a spectrometer can be exploited successfully at different approximations, are: 1) comparison of the Milky Way case with extragalactic ones at scale of the complete galactic disk; 2) global studies of the Galactic spiral arms; and 3) characterization of specific regions like molecular clouds or star clusters. These aspects allow us to suggest that similar instrument will be really useful. The developed prototype of spectrometer is able to realize multi-channel wideband parallel spectrum analysis of very-high-frequency radio-wave signals with an improved resolution power exceeding 103. It includes the 1D-acousto-optic wide-aperture cell as the input device for real-time scale data processing. Here, the current state of developing this acousto-optical spectrometer in frames of the astrophysical instrumentation is briefly discussed, and the data obtained experimentally with a tellurium dioxide crystalline acousto-optical cell are presented. Then, we describe a new technique for more precise spectrum analysis within an algorithm of the collinear wave heterodyning. It implies a two-stage integrated processing, namely, the wave heterodyning of a signal in an acoustically square-law nonlinear medium and then the optical processing in the same solid-state cell. Technical advantage of this approach lies in providing a direct multi-channel parallel processing of ultra-high-frequency radio-wave signals with the resolution power exceeding 104. This algorithm can be realized on a basis of exploiting a large-aperture effective acousto-optical cell, which operates in the Bragg regime and performs the ultra-high-frequency co-directional collinear acoustic wave heterodyning. The general concept and basic conclusions here are confirmed by proof-of-principle experiments with the specially designed cell of a new type based on a lead molybdate crystal.

On certain features of spectrum recording and photometric measurements of spectral lines using a MFS-MAES-based digital spectrograph

Features of recording spectra and performing photometric measurements of spectral lines using a digital spectrograph, which is based on an MFS-8 setup with a MAES multichannel emission spectrum analyzer (photodiode array assembly), are studied. Possibilities of optimizing the analytical signal and time parameters of the spectrum exposure for extending the linear range of the calibration curve and increasing the concentration sensitivities both in areas of low and high contents of determined elements by the atomicemission spectral analysis are shown.

Traffic-Aware Channel Sensing Order in Dynamic Spectrum Access Networks

In this paper we present new results on the problem of finding the best channel sensing order for multi-channel Dynamic Spectrum Access (DSA) networks. We start with the general assumption that all Secondary Users (SUs) cooperatively sense each Primary User (PU) channel at one time. Then, the SU sensing results are reported to a DSA base station that schedules SU transmissions in order to maximize DSA network throughput. We then assume that PU traffic parameters are not perfectly known to DSA network and change over time, and propose a novel PU channel sensing order scheme based on the quality of PU traffic estimation. We adopt a maximum likelihood estimator to estimate the traffic statistics of PU channels and derive the Cramer-Rao (CR) bounds for the PU traffic estimation performance. Based on the CR bound and its Gaussian approximation, we analyze the impact of the estimation error on the DSA network throughput by computing a new metric called sensing order confidence, i.e., the probability that the best selected sensing order is not affected by PU traffic estimation errors. Finally, we formulate a convex optimization problem to determine the minimum number of PU channel state samples required for estimating PU traffic parameters after determining a certain constraint on the sensing order confidence metric to achieve the best sensing order.

Optimisation of multi‐channel cooperative sensing in cognitive radio networks

Cooperative spectrum sensing (CSS) is a promising technique in cognitive radio networks (CRNs) that utilises multi- user diversity to mitigate channel instability and noise uncertainty. In this study, the relationship between 'cooperation mechanisms' and 'spatial-spectral diversity' over multiple channels jointly sensing is investigated in the presence of an imperfect reporting channel. The multiple channels are sensed at the receiver built on the filter bank-based multi-carrier system. The multi-channel CSS strategies are modelled by the introduced 'cooperative ratio' to balance the requirements on 'sensing accuracy', 'efficiency' and 'overhead', which is quantitatively characterised by the energy consumption. The target of CSS is to maximise the aggregate opportunistic throughput of secondary users (SUs) by jointly considering constraints on sensing overhead and the aggregate interference to primary users (PUs). The optimisation is divided into two sequential sub- optimisation processes, 'multi-user diversity optimisation' and 'multi-channel diversity optimisation'. An approach is developed from generic algorithms to solve the two sub-problems. Numerical results show that the optimal CSS scheme is effective in improving channel utilisation for SUs with low interference to PUs. This study establishes a valuable cooperative model for the design of multi-channel spectrum sensing algorithms in CRNs.

True-MCSA: A Framework for Truthful Double Multi-Channel Spectrum Auctions

Spectrum auctions motivate existing spectrum owners (as sellers) to lease their selected idle channels to new spectrum users (as buyers) who need the spectrum desperately. The most significant requirement is how to make the auctions economic-robust (truthful in particular) while enabling spectrum reuse. Furthermore, in practice, both sellers and buyers would require to trade multiple channels at one time, while guaranteeing their individual profitability. Unfortunately, existing designs can not meet all these requirements simultaneously. We address these requirements by proposing True-MCSA, a framework for truthful double multi-channel spectrum auctions. True-MCSA introduces novel virtual buyer group (VBG) splitting and bidding algorithms, and applies a proper winner determination and pricing mechanism to achieve truthfulness and other economic properties, meanwhile successfully dealing with multi-channel requests from both buyers and sellers and improving spectrum utilization. Our experiments show that the auction efficiency is impacted by the economic factors with efficiency degradations within 30%, under different settings. Furthermore, the experimental results indicate that we can improve the auction efficiency by choosing a proper bidding algorithm and using a positive base bid. True-MCSA makes an important contribution on enabling spectrum reuse to improve auction efficiency in multi-channel cases.

Real-World Empirical Studies on Multi-Channel Reliability and Spectrum Usage for Home-Area Sensor Networks

Home area networks (HANs) consisting of wireless sensors have emerged as the enabling technology for important applications such as smart energy. These applications impose unique network management constraints, requiring low data rates but high network reliability in the face of unpredictable wireless environments. This paper presents two in-depth empirical studies on wireless channels in real homes, providing key design guidelines for meeting the network management constraints of HAN applications. The spectrum study analyzes spectrum usage in the 2.4 GHz band where HANs based on the IEEE 802.15.4 standard must coexist with existing wireless devices. We characterize the ambient wireless environment in six apartments through passive spectrum analysis across the entire 2.4 GHz band over seven days in each apartment. We find that the wireless conditions in these residential environments are much more complex and varied than in a typical office environment. Moreover, while 802.11 signals play a significant role in spectrum usage, there also exists non-negligible noise from non-802.11 devices. The multi-channel link study measures the reliability of different 802.15.4 channels through active probing with motes in ten apartments. We find that there is not always a persistently reliable channel over 24 hours, and that link reliability does not exhibit cyclic behavior at daily or weekly timescales. Nevertheless, reliability can be maintained through infrequent channel hopping, suggesting dynamic channel hopping as a key tool for meeting the network management requirements of HAN applications. Our empirical studies provide important guidelines and insights in designing HANs for residential environments.

Spectral Analysis of Acoustic Emission Signals Using NI Systems

This paper describes a software and hardware analytical complex of spectral characteristics. The analysis complex includes the research of the signals with the ability to create a database for identification. Analysis of the spectral characteristics by using special instruments - spectrum analyzer. Presents the results of the evaluation of scientific and practical significance of the software developed. Spectral data multichannel analyzer spectrum was obtained with DAQ-device National Instruments.

Threshold optimization of cooperative spectrum sensing in cognitive radio networks

We consider the threshold optimization problem of cooperative spectrum sensing for cognitive radio (CR) and investigate the threshold optimization algorithm for both single‐channel and multichannel cooperative spectrum sensing. In order to obtain the optimal threshold for single‐channel cooperative spectrum sensing, we deploy the fusion rules AND Logic, OR Logic, and K‐OUT‐N Logic. Moreover, an iterative optimization algorithm is proposed to obtain optimal CRs in cooperative spectrum sensing and their optimal thresholds. In multichannel cooperative spectrum sensing, two threshold optimization methods—namely nonrestrained multichannel threshold optimization (NRMTO) and restrained multichannel threshold optimization (RMTO)—have been proposed in order to decrease the total error detection probability of all the subchannels. The simulation results show that in single‐channel cooperative spectrum sensing the proposed algorithm outperforms traditional cooperative spectrum sensing with the uniform threshold if the SNR is different, while decreasing the detection performance slightly if the SNR is identical. The results also indicate that the NRMTO can achieve the minimal total error detection probability of multichannel cooperative spectrum sensing, while the RMTO can guarantee the detection performance of each subchannel but with a higher total error detection probability.

Automated multichannel broadband spectrum analysis of fibre-optic grating sensors

In this paper, we report methods for spectrum analysis and data processing algorithms. An automated multi–channel spectrum measurement system is introduced with controlled fibre–optic signal switching and spectrum analysis with linear CCD photodiode array, diffraction grating and precise stepper motor. The designed system demands advanced measurement and data processing techniques. This paper reports the implemented methods for automated multi–channel measurements, accuracy improvement, noise cancellation techniques and fibre–optic grating sensor measurements.