Broadband Channel Research Articles

Intercarrier Interference Analysis for High-Speed Trains Based on Broadband Channel Measurements

This letter presents an analysis of intercarrier interference (ICI) in high-speed trains. The ICI is caused by the motion of the receiver together with the carrier frequency offset (CFO). It results in a degradation of the reliability of the OFDM transmission. The analysis is based on a channel sounding measurement campaign for cellular broadband wireless communications with high-speed trains that was carried out in the context of the CORRIDOR project. The considered scenario corresponds to a railway deployed network, where the base station is located directly next to the railway line. We present the ICI power obtained with the measurement campaign and some theoretical results for a simple channel model that captures the main effects observed in the measurements.

Properties and Power Spectral Densities of CP Based OQAM-OFDM Systems

Offset quadrature amplitude modulation OFDM (OQAM-OFDM) systems have low sidelobes but require complex receivers for broadband channels. To deal with this problem, cyclic prefix (CP)-based OQAM-OFDM systems have been proposed in the literature. In this paper, we study OQAM-OFDM and two existing CP based OQAM-OFDM systems and propose a new CP based system with good spectrum performance. We investigate their properties and analyze their power spectral densities (PSDs). We show that the continuous-time transmitted CP-OQAM-OFDM signal after the CP insertion is equivalent to a truncated signal obtained by inserting CP and cyclic suffix (CS) to the discrete-time input data symbols in the OQAM-OFDM system, which simplifies the calculation of the PSD of the transmitted CP-OQAM-OFDM signal and also implies that the PSD of the CP-OQAM-OFDM may be affected by the truncation. We show that the perfect reconstruction (PR) condition for the CP-OQAM-OFDM system is actually the same as that for the OQAM-OFDM system when the length of the prototype filter is not more than the length of the transmitted CP-OQAM-OFDM signal of each block excluding the CP. We also compare three CP-based OQAM-OFDM systems with windowed CP-OFDM systems. Numerical results show that the theoretical and simulated PSDs of the transmitted signals match well, CP-based OQAM-OFDM systems perform better than windowed CP-OFDM systems considering both the PSD and bit error rate (BER) performances, and the newly proposed CP-based OQAM-OFDM system has the best PSD performance in the three CP based OQAM-OFDM systems with an increase of the data rate overhead.

Generalized analysis of MU-MISO time reversal-based systems over correlated multipath channels with estimation error

In this letter, we analyze the performance of multi-user multiple-input single-output time reversal (MU MISO TR)-based systems in a generalized framework. The considered propagation is correlated in both the space and the frequency domains, and channel estimation errors (CEEs) at the transmitter side are also taken into account. We derive a novel average signal-to-interference-plus-noise (SINR) formula in closed-form for TR-based systems. This formula is based on the exact expressions of the expectations of the powers of the desired signal, the inter-symbol interference (ISI) and the inter-user interference (IUI) components. These expressions allow us to reveal, for the first time, properties of time reversal which remained unknown up to now. More precisely, CEE has no influence on the ISI in terms of average power, whereas it degrades the power of the desired message-bearing signal. Moreover, irrespective of the central tap, the other taps of the IUI are independent from the effects of both inter-user correlation and CEE. Our analytical results are validated in both ultra-wideband and conventional broadband channels. Finally, these results are numerically compared to previous works.

On the Existence of Subliminal Channel in Instant Messaging Systems

Subliminal channel is a covert communication channel that can securely exchange secret information. By analyzing the communication protocols and encryption algorithms of two popular instant messaging systems QQ and Skype, this paper devotes the efforts to find whether they satisfy the condition of establishing subliminal channel or not. The broad-band subliminal channel can be established in Skype and QQ messages. Therefore, two subliminal channel schemes are proposed to embed and extract subliminal information. Finally, performances of the proposed subliminal channels are compared with those of the ones based on ElGamal digital signature and Newton channel. Experimental results and theoretical analysis show that they are easy to be implemented with large bandwidth and execute fast.

Spectral Signatures of Earth’s Climate Variability over 5 Years from IASI

Abstract Interannual variability in spectrally resolved longwave radiances is quantified at a variety of spatial scales using 5 yr of IASI observations. Maximum variability is seen at the smallest scales investigated (10° zonal means) at northern and southern high latitudes across the center of the 15-µm CO2 band. As the spatial scale increases, the overall magnitude of interannual variability is reduced across the spectrum and the spectral shape of the variability changes. In spectral regions sensitive to conditions in the upper troposphere, the effect of increasing spatial scale is relatively small and at the global scale these parts of the spectrum show the greatest year-to-year variability. Conversely, the atmospheric window (8–12 µm), which is sensitive to variations in surface temperature and cloud, shows a marked reduction in interannual variability with increasing spatial scale. Over the 5 yr studied, at global scales the standard deviation in annual mean brightness temperature is less than 0.17 K across the spectrum, dropping to less than 0.05 K across the window. Spectrally integrating the IASI measurements to create pseudobroadband and window channels indicates a variation about the mean that is higher for the broadband channel than for the window channel at the global and quasi-global scales and over the Southern Hemisphere. These findings are in agreement with observations from CERES Terra over the same period and imply that at the largest spatial scales, over the period considered here, fluctuations in mid- to upper-tropospheric temperatures and water vapor, and not cloud or surface temperature, play the dominant role in determining the level of interannual variability in all-sky outgoing longwave radiation.

Broadband DVB-T2 Channels at a Physical Level – Simulation Analysis

Digital video broadcasting (DVB) decreases the proportion of broadcasting channels used for existing programmes. Second-generation DVB standards offer increased bit rates, enabling more programmes per broadcasting channel than in case of the first generation. On the other hand, increased bit rate needed for high definition programmes requires combining of the capacity of few single channels producing a broadband one. Also, statistical multiplexing allows more efficient usage of capacity. Terrestrial broadcasting standard DVB-T2 enables the time frequency slicing (TFS), as a way of connecting channels at the media access control (MAC) level. This paper deals with the two types of a broadband channels at physical layer. Compared to the TFS mode, method proposed here utilizes the allocated bandwidth in a more efficient way. DOI: http://dx.doi.org/10.5755/j01.eee.21.1.5584

A Novel Broadband Line Construction Using 3G Service

Abstract Quite often, it is necessary to upload or download large files in a relatively short time and from or to locations that do not necessarily have adequate infrastructure. If the location is static the needs can be addressed easily. There are high-speed transmission or broadband services offered by a large number of operators through both conventional and fiber optic cables. If the users are moving nomadically or are mobile, then obtaining large-capacity transmission systems is not simple. For some purposes, especially for small and medium-sized companies, they need to have alternative solutions that are economic and technically feasible. Cellular service providers offer 3G Internet services with wide coverage. This study develops an application using 3G services to provide broadband access that is economic and relatively simple. This solution uses multiple 3G connection to transmit information at high speed as if there is broadband channel capacity. Information on a Web Server can be downloaded by the parties concerned. The information retrieval can obtain the necessary capacity using multiple 3G connections. The technique of bundling multiple lower speed channels to obtain high-speed channel is called inverse multiplexing. In this research, the technique is simplified by using a router that has the ability to provide load balancing. This research was carried out by conducting laboratory experiments and field measurements. The experimental results show that the concept of inverse multiplexing through a number of channels with 3G services can run well for downloading files.

Maximizing Throughput of Free Space Communication Systems Using Puncturing Technique

Radio frequency spectrum is too crowded and expensive to install new broadband channels. Free space optical (FSO) communication is a viable technology, which offers enormous bandwidth, license-free spectrum and non-interfering nature. But the FSO link deteriorates significantly due to the atmospheric turbulence and sever weather conditions (fog, cloud and snow). Hybrid FSO/RF communication system with independent coding scheme has been suggested in the literature. But such systems are expensive and have synchronization issue. We propose a hybrid FSO/RF communication system with joint coding scheme. A novel puncturing optimization algorithm is developed, which adaptively tackle fading effects of the individual communication link. The proposed puncturing algorithm gives more than 3 dB power gain over the fixed system.

Effect of channel impulse response on matched filter performance in the 2013 Target and Reverberation Experiment

Active sonar performance is determined by the characteristics of the target, the sonar system and the effect of the environment on the received waveform. The two main influences of the environment are propagation effects and the contamination of the target echo with a background. The ambient noise and reverberation are mitigated by means of signal processing, mostly through beamforming and matched-filtering. The improvement can be quantified by the signal to noise ratios before and after processing. Propagation effects can have a large influence on the gains obtained by the processing. To study the effect of the channel on the matched filter performance, broadband channel impulse responses were modeled and compared to measurements acquired during the Office of Naval Research-funded 2013 Target and Reverberation Experiment (TREX). In shallow water, a large time spread is often observed, reducing the effectiveness of the matched filter. TREX data show, however, a limited time spread. Model predictions indicate that this could be caused by a rough sea-surface, which while increasing propagation loss, at the same time increases matched filter gain.

Bio-Inspired Electromagnetic Orientation for UAVs in a GPS-Denied Environment Using MIMO Channel Sounding

When external positioning systems are not available, other navigation methods must be used to guide unmanned air vehicles. We propose a bioinspired technique related to MIMO channel sounding for discriminating aircraft position and bearing. By analogy with the acoustic orientation used by certain bird species to return to a specific location in a dark cave, we refer to the proposed method as electromagnetic orientation (EO). A scattering model is used to generate simulated MIMO channel matrices for randomly generated propagation environments. Several variants of a basic propagation channel sounding-based method for EO discrimination are considered, including orientation with a single-frequency propagation channel matrix, channel covariance matrix, and broadband channel sounding data. At X band, the difference between a measured channel matrix and a stored, a reference channel matrix can be used to discriminate position to centimeter scale accuracy. Using the higher order correlation statistics of the channel matrix, the range scale can be increased to on the order of a meter. The method was used experimentally to localize the position of a UAV with channel probing data collected with a frequency modulated, continuous wave (FMCW) radar.

Retrieval of sulfur dioxide from a ground-based thermal infrared imaging camera

Abstract. Recent advances in uncooled detector technology now offer the possibility of using relatively inexpensive thermal (7 to 14 μm) imaging devices as tools for studying and quantifying the behaviour of hazardous gases and particulates in atmospheric plumes. An experimental fast-sampling (60 Hz) ground-based uncooled thermal imager (Cyclops), operating with four spectral channels at central wavelengths of 8.6, 10, 11 and 12 μm and one broadband channel (7–14 μm) has been tested at several volcanoes and at an industrial site, where SO2 was a major constituent of the plumes. This paper presents new algorithms, which include atmospheric corrections to the data and better calibrations to show that SO2 slant column density can be reliably detected and quantified. Our results indicate that it is relatively easy to identify and discriminate SO2 in plumes, but more challenging to quantify the column densities. A full description of the retrieval algorithms, illustrative results and a detailed error analysis are provided. The noise-equivalent temperature difference (NEΔT) of the spectral channels, a fundamental measure of the quality of the measurements, lies between 0.4 and 0.8 K, resulting in slant column density errors of 20%. Frame averaging and improved NEΔT's can reduce this error to less than 10%, making a stand-off, day or night operation of an instrument of this type very practical for both monitoring industrial SO2 emissions and for SO2 column densities and emission measurements at active volcanoes. The imaging camera system may also be used to study thermal radiation from meteorological clouds and the atmosphere.

Research on Broadband Channel Characteristics and Hardware Testbed for Power Line Communication System

With the decision to construct the smart grids around China, the power line communications (PLC) on the low-voltage (LV) distribution networks have become one of the potential technologies to commute the information between the end users and the power provider. Comprehensive and well-founded knowledge of the LV power line channel is the foundation to establish realistic modeling of the channel characteristics. The growing power line communication (PLC) technology is providing new potential for emerging applications such as G3 and Prime. In this paper, we have proposed a OFDM based channel sounding test bed to measure PLC channel within frequency band 100 kHz-2 MHz. A souding signal for the PLC channel is designed and a time-domain measurement method for the time-varying PLC propagation is presented. The experimental results of PLC channel characteristics under different scenarios are and analyzed.

Physical layer security in power line communication networks: an emerging scenario, other than wireless

The authors consider the secure transmission of information over power line communication (PLC) networks. The focus is on the secrecy guaranteed at the physical layer, named physical layer security (PLS). Although PLS has been deeply investigated for the wireless case, it is not the same for the PLC environment. Thus, starting from the knowledge in the wireless context, the authors extend the results to typical PLC scenarios. In particular, the PLC channel statistics is evaluated and a performance comparison among PLC and wireless channels is performed, in terms of secrecy rate distribution. For the PLC case, the secrecy rate distribution, under a total power constraint, is evaluated for both optimal and uniform power distributions in broadband channels. To provide experimental evidence, the authors consider channel measures obtained in an in-home measurement campaign. The underlying network presents a tree topology, which introduces frequency and spatial correlation among channels, and suffers from the keyhole effect, generated by branches that depart from the same node. As shown by the numerical results, these effects can reduce the secrecy rate. Finally, the authors evaluate the secrecy rate region for the multi-user broadcast channel considering both simulated channel realisations and experimental channel measures.

Feasibility Demonstration of a Mode-Division Multiplexed MIMO-Enabled Radio-Over-Fiber Distributed Antenna System

In this paper the feasibility of mode-division multiplexing (MDM) for implementing multiple-input multiple-output (MIMO)radio-over-fiber (RoF)distributed antenna systems (DAS) is experimentally demonstrated, where the MIMO algorithm is able to reconstruct the data signals by overcoming distortion and cross-talk in both the free-space RF and optical fiber channels. This is achieved through RF characterization of an MDM RoF link, which is experimentally demonstrated to be capable of supporting at least $4 \times 4$ MIMO with 6 GHz channels over long lengths of MMF (2 km compared to $\sim$ 300 m typically found in MMF-based RoF DASs) and under tight fiber bending conditions (bend radius as low as 7.6 mm), which are commonly encountered in in-building fiber installations. First, experimental RF measurements are performed over a 2 km section of OM2 fiber, mode-multiplexed using a spatial light modulator (SLM) based MUX/DEMUX system, and it is shown to offer an RF condition number of <14 dB for up to $4 \times 4$ MIMO with 6 GHz channels, sufficient to enable good performance for most modern wireless protocols. Next, the effect of fiber curvature on RF performance is experimentally analysed using a 10 m section of OM3 fiber. It is seen that with a bend radius as low as 7.2 mm, a condition number of ${\sim}10$ dB can be achieved for up to a $6 \times 6$ MIMO system with 6 GHz channels. Although an SLM-based MUX/DEMUX is used here, condition number is not dependent on the exact mode-launching system used provided that orthogonal combinations of modes are excited, which is true of most MDM systems. It is therefore concluded that the RF characterization presented here demonstrates by proof-of-principle the feasibility of graded-index) MMF to support at least $4 \times 4$ MIMO with broadband channels via MDM over lengths up to 2 km and with fiber bend radii as low as 7.2 mm.

High Isolation and Compact Microstrip Diplexer for Broadband and WLAN Application

A high isolation and compact microstrip diplexer for broadband and wireless local area network (WLAN) application is proposed in this paper. It is achieved by using the combination of a broadband bandpass filter (BPF) composed of one open stub and two short stubs of different size loaded in 50Ω feed lines. The tapped stub can not only generate two zeros to deepen the stopband, but also connect other BPF without deterioration of in-band performance. Hence, the compact diplexer combines two BPFs without extra junction matching network. The mutual loading effect approximately equivalent to a coupled resonator can create one zero at the passband edge to improve the isolation. The proposed microstrip diplexer is designed and fabricated, and it has a 1dB fractional bandwidths (FBW) of 60% at 3.5GHz for broadband channel and 3% at 5.8GHz for WLAN channel . The simulated and measured results are presented and good agreement is obtained.

All-Raman-Amplified, 73 nm Seamless Band Transmission of 9 Tb/s Over 6000 km of Fiber

We report wavelength-division-multiplexed transmission of ninety 128-Gb/s polarization-multiplexed quadrature-phase-shift-keyed channels in a seamless 73 nm band over 60 × 100 km of ultra-large-area fiber. Co- and counter-pumped all-Raman amplification in the fiber spans, single-stage discrete Raman amplifiers, and broadband wavelength selective switch and channel equalizer were utilized to achieve optical signal-to-noise-ratio margin of more than 3 dB after 6000 km transmission of the 9 Tb/s capacity.

Compressive sensing based Bayesian sparse channel estimation for OFDM communication systems: high performance and low complexity.

In orthogonal frequency division modulation (OFDM) communication systems, channel state information (CSI) is required at receiver due to the fact that frequency-selective fading channel leads to disgusting intersymbol interference (ISI) over data transmission. Broadband channel model is often described by very few dominant channel taps and they can be probed by compressive sensing based sparse channel estimation (SCE) methods, for example, orthogonal matching pursuit algorithm, which can take the advantage of sparse structure effectively in the channel as for prior information. However, these developed methods are vulnerable to both noise interference and column coherence of training signal matrix. In other words, the primary objective of these conventional methods is to catch the dominant channel taps without a report of posterior channel uncertainty. To improve the estimation performance, we proposed a compressive sensing based Bayesian sparse channel estimation (BSCE) method which cannot only exploit the channel sparsity but also mitigate the unexpected channel uncertainty without scarifying any computational complexity. The proposed method can reveal potential ambiguity among multiple channel estimators that are ambiguous due to observation noise or correlation interference among columns in the training matrix. Computer simulations show that proposed method can improve the estimation performance when comparing with conventional SCE methods.

Effects of habitat light conditions on the excitation quenching pathways in desiccating Haberlea rhodopensis leaves: An Intelligent FluoroSensor study

Resurrection plants can survive dehydration to air-dry state, thus they are excellent models of understanding drought and dehydration tolerance mechanisms. Haberlea rhodopensis, a chlorophyll-retaining resurrection plant, can survive desiccation to relative water content below 10%. Leaves, detached from plants of sun and shade habitats, were moderately (∼50%) dehydrated in darkness. During desiccation, chlorophyll a fluorescence was detected by the recently innovated wireless Intelligent FluoroSensor (IFS) chlorophyll fluorometer, working with three different detectors: a pulse-amplitude-modulated (PAM) broadband channel and two channels to measure non-modulated red and far-red fluorescence. No change in area-based chlorophyll content of leaves was observed. The maximal quantum efficiency of photosystem II decreased gradually in both shade and sun leaves. Shade leaves could not increase antennae-based quenching, thus inactivated photosystem II took part in quenching of excess irradiation. Sun leaves seemed to be pre-adapted to quench excess light as they established an intensive increase in antennae-based non-photochemical quenching parallel to desiccation. The higher far-red to red antennae-based quenching may sign light-harvesting complex reorganization. Thus, compared to PAM, IFS chlorophyll fluorometer has additional benefits including (i) parallel estimation of changes in the Chl content and (ii) prediction of underlying processes of excitation energy quenching.

ON THE JITTER RADIATION

In a small scale turbulent medium, when the nonrelativistic Larmor radius $R_{\rm L}=mc^2/eB$ exceeds the correlation length $\lambda$ of the magnetic field, the magnetic bremsstrahlung of charged relativistic particles unavoidably proceeds in the so-called jitter radiation regime. The cooling timescale of parent particles is identical to the synchrotron cooling time, thus this radiation regime can be produced with very high efficiency in different astrophysical sources characterized by high turbulence. The jitter radiation has distinct spectral features shifted, compared to synchrotron radiation, towards high energies. This makes the jitter mechanism an attractive broad-band gamma-ray production channel which in highly magnetized and turbulent environments can compete or even dominate over other high energy radiation mechanisms. In this paper we present a novel study on spectral properties of the jitter radiation performed within the framework of perturbation theory. The derived general expression for the spectral power of radiation is presented in a compact and convenient for numerical calculations form.

A Study of Performance Enhancement Schemes for Multicarrier Transmission

OFDM allow the transmission of high data rates over broadband channel due to the spectral bandwidth efficiency, robustness to the multipath delay etc. However OFDM signal are very sensitive to nonlinear effects due to the high peak-toaverage power radio (PAPR), which is one of the major drawback of OFDM system. The high PAPR results, high inband distortion and out-of- band radiation ,inter-carrier interference(ICI) and degradation of bit error rate (BER) performance, all these losses occur due to the non-linearity of HPA(high power amplifier). The complexity of analog-todigital converter (ADC) and digital-to- analog converter (DAC) also get increased if the PAPR of OFDM signal is high. Thus in OFDM system one of the important research areas is reduction of PAPR . This paper reviews the conventional PAPR reduction schemes for achieving the low computational complexity in wireless communication systems.