Fading Characteristics Research Articles

Polar coded spatial modulation

A scheme is proposed, called polar coded spatial modulation (PCSM), to provide both detection/decoding of the transmitted symbol and the transmit antenna index in multiple-input-multiple-output (MIMO) antenna systems. Based on the free polar set and the frozen polar set in polar codes, the proposed PCSM scheme maps the transmitted information data in the free polar set and the transmit antenna index bits in the frozen polar set whose positions are known at the receiver. This has the advantage that the bits that identify the transmit antenna are not transmitted to the receiver and do not need to be detected as is the case in conventional spatial modulation (SM). Thus, PCSM presents a spectrally efficient and a power-efficient system. For the simulations, MIMO channels with transmission over independent and identically distributed flat fading characteristics are exploited. Firstly, capacity results for coded SM which is a requirement for the construction of the codes are presented. Consequently, the bit error rate performances of the M-ary quadrature amplitude modulation SM are analysed for various MIMO architectures after which the desirable MIMO architecture is proposed for the PCSM. In addition, the upper and lower bounds on probability of frame error for the transmitted symbol information, under successive cancellation decoding are derived and the PCSM scheme suits the bounds for the suiting architecture.

The Application of RAKE Receiving Technology in the Underwater SS Communication

In recent years, the strategic significance of the oceans is growing as well as its research and development needs. The underwater wireless communication is becoming more and more important. The underwater acoustic communication is one of the few mediums which can conduct the underwater transmission over a long distance, and the multipath effect is the major obstacle of affecting the systems high speed and high reliability. The characteristics of underwater acoustic fading and coherent multi-path channel are studied, and the model of underwater acoustic spreading spectrum (SS) communication system is established. The affect of coding technique on the systems performance are analyzed in detail. The improved RAKE receiving technical solution is put forward, whose simulation analysis and data in different combining ways are given. It is proved that the scheme can better solve the problem of multipath interference in underwater acoustic transmission.

Analysing the orbit influence on multipath fading in global navigation satellite systems

For some critical static applications of Global Navigation Satellite Systems (GNSS), such as monitoring station and reference station in the GNSS control segment, multipath error shows regular fading characteristics related to satellite orbit type. However, for Geostationary Earth Orbit (GEO) satellites, observations under different systems show great diversity, the regularity of the multipath fading characteristic for GEO satellite is not apparent, and the reason is not clear as these observations can be influenced by various factors. To know the reason and the mechanism of these differences is very important for GNSS system building and monitoring, especially for the control segment, one major function of which is monitoring the whole system states and ensuring the system reliability. To explain the differences among these observations, a theoretical analysis about the satellite orbit influence on multipath fading is made in this study. The analysis is based on a proposed factor named orbit multipath fading factor, which can reflect the orbit influence independent from the uncontrolled environment factors. The analysis result shows that for GEO satellites, the multipath fading frequency varies large with time, and is very sensitive to orbit inclination, which can well explain the various fading characteristics actually observed in theory.

An SD Method Utilizing Null Dependency on Transmission Distance Due to Two-Ray Fading

A spatial division (SD) transmission method utilizing the characteristics of two-ray fading due to ground reflection with linear antenna arrays horizontal to the ground is proposed. Formulations of the optimum array arrangements as functions of the transmission distance and achievable channel capacity are clarified. For two- and three-element arrays, channel capacity is respectively doubled and tripled over that of free-space propagation. The proposed method provides increased capacity without the extra signal processing cost incurred when using conventional multiple-input-multiple-output (MIMO) transmission.

A Semiempirical MIMO Channel Model in Obstructed Viaduct Scenarios on High-Speed Railway

A semiempirical multiple-input multiple-output (MIMO) channel model is proposed for high-speed railway (HSR) viaduct scenarios. The proposed MIMO model is based on the combination of realistic single-input single-output (SISO) channel measurement results and a theoretical geometry-based stochastic model (GBSM). Temporal fading characteristics involvingK-factor and Doppler power spectral density (PSD) are derived from the wideband measurement under an obstructed viaduct on Zhengzhou-Xi’an HSR in China. The GBSM composed of a one-ring model and an elliptical model is employed to describe the entire propagation environment. Environment-related parameters in the GBSM are determined by the measured temporal fading properties. And a close agreement is achieved between the model results and measured data. Finally, a deterministic simulation model is established to perform the analysis of the space-time correlation function, the space-Doppler PSD, and the channel capacity for the measured scenario. This model is more realistic and particularly beneficial for the performance evaluation of MIMO systems in HSR environments.

Investigation of thermoluminescence characteristics of Li2B4O7:Mn (TLD-800)

Li2B4O7:Mn is a well-known TLD material with an excellent human tissue equivalence. It is used in practice for personnel dose monitoring in variable branches. In the given study, the additive dose (AD), variable heating rate (VHR), peak shape (PS), three points method (TPM), and computerized glow deconvolution (CGCD) methods were used to determine the kinetic parameters of the main glow peak (P3) of Li2B4O7:Mn (TLD-800). In addition, the fading characteristics and the effect of the heating rate on the dose dependence of TL glow curves have been investigated. The results of the analysis have shown that TLD-800 has a general order main glow peak with an activation energy of Ea=0.58eV at 170°C at a linear heating rate of 1°C/s.

Channel level crossing‐based security for communications over fading channels

Several key exchange methods for wireless channels have been proposed in the literature. They are referred to as physical-layer security techniques and are usually based on the channel's fading characteristics and the principle of channel reciprocity. In this study, the authors present key exchange algorithms for wireless fading channels whose operation is based on channel estimation. Specifically, the authors present a complete key exchange scheme that includes channel sampling, thresholding and error reconciliation. Two error reconciliation methods are proposed. The first one is based on neural networks and the second one is based on linear block coding. Simulations of the proposed methods’ performances and levels of security are presented and conclusions are drawn regarding their overall utility.

Characteristics and Explanations of Interference Fading of a $\phi $-OTDR With a Multi-Frequency Source

The characteristics of interference fading in a phase sensitive optical time domain reflectometer (φ-OTDR) system with a three optical frequency source are described in this paper. It is observed in the experiments that the fading appearance is quite stable over 400 different pulse scans for each of frequencies, but different for the three frequencies. A model is proposed to explain the experimental phenomena, in which the fading waveform is expressed by an integral of propagation phase factor, taking non-uniform index distributions along the sensing fiber into account, multiplied by the random Rayleigh scattering coefficient summed within the detector response period. Simulations show that the basic characteristics of experimental observations can be explained by the model.

Airport Surface Propagation Channel in the C-Band: Measurements and Modeling

In this paper, we assess the path loss and the multipath fading characteristics of the airport surface channel based on the measurement data collected at Munich airport at 5.2 GHz. Our goal is to present channel models for the ground, tower and ramp area of the airport surface, which are easy to implement in a channel emulator and suitable for performance evaluation of the future aeronautical airport data link AeroMACS. The channel is in general nonstationary, but within one data frame and correspondingly one simulation run, the WSSUS assumption can be adopted for all scenarios related to an aircraft. However, the assumption loses its validity in the case of service vehicles moving in the NLOS ramp area. The proposed stochastic model for the small scale fading channel uses a sum-of-sinusoids based tapped delay line with a fixed channel parameters which are randomly chosen from the suitable intervals for each new simulation run. Incorporating scatterer movements into the model enables modeling of a nonstationary channel impulse response.

Power Line Carrier Communication Channel Model Applied to Shipboard Electric Network

It is necessary to build a particular communication channel model to investigate shipboard electric network power line carrier technology. And this model must live up to characteristics of ordinary power line as well as shipboard electric network. This paper confirms the lighting network as the PLC application network in the first place, on the basis of lumped parameter transmission model, analyzes shipboard cable AC resistance, describes pulse noises of shipboard loads, and builds the shipboard PLC channel model. Comparing with the PLC multipath model of large land electric network, this channel model also reflects characteristics of high frequency time-varying selective fading and low frequency smooth fading, at the same time, lives up to shipboard electric network characteristics.

The investigation of lithium formate hydrate, sodium dithionate and N-methyl taurine as clinical EPR dosimeters

IntroductionEPR-dosimetry using l-α-alanine is an established method for measuring high doses of ionizing radiation. However, since a minimum dose of approximately 4 Gy is required to achieve sufficient low uncertainties (1–2%) for clinical application, alternative dosimeter materials are being inquired. Lithium formate (LiFo) monohydrate has been studied by several groups and has revealed several promising properties in the low dose region (<4 Gy). The fading properties, however, are somewhat unpredictable, and depend on properties not yet fully uncovered. This paper reports the results from a study of lithium formate hydrate and N-methyl taurine as potential low dose EPR dosimeters. Methods and materialsPellet shaped dosimeters of lithium formate monohydrate, lithium formate hydrate, sodium dithionate and N-methyl taurine were produced using a manual Weber press, l-α-alanine was obtained from Harwell dosimeters and irradiated using 60 kV and 6 MV X-ray beams, and Co-60 gamma-rays to a dose of 30 Gy and dose ranges of 0.5–100 Gy and 2–20 Gy respectively. The dosimeters were measured using an Electron Paramagnetic Resonance (EPR)-spectrometer. The detector responses for 6 MV and Co-60 radiation beams, the fading behaviors and signal shape in time were investigated. ResultsLithium formate monohydrate and lithium formate hydrate are apparently associated with near identical EPR-spectra (mainly one broad line), and the same spectrum arises for all radiation energies investigated. The shape of the EPR resonance remains constant with time, but the intensities decreases, and the fading is more prominent for the monohydrate than for the hydrate. The EPR resonance associated with N-methyl taurine is more complex than the resonance associated with LiFo and it changes with time, implying radical transitions and growth. ConclusionsThe study showed that lithium formate hydrate is a strong candidate for EPR dosimetry with slightly better fading characteristics compared to lithium formate monohydrate.

Small-Scale Fading Characteristics in Cellular Networks in Ghana

Fading is the most observed and frustrating problem in transmitting and receiving radio signals. A Study in correlation properties of fading helps to design proper communication systems that are robust to it. In this work, received power signal was obtained by drive-test technique. The analysis was determined using distribution fitting tool in Matlab software 7.5.0 (R2007b). The following fading distributions were used, Rayleigh, Rician, Nakagami-m, Lognormal and Weibull. Weibull fading distribution was found to give the best description of fading experienced in Ghana.On the other hand, Rician distribution, Nakagami-m distribution and lognormal distribution have less agreement with the measured data while Rayleigh fading distribution has much less agreement with measured data. The obtained mean scale parameter and the mean shape parameter in the Weibull distribution for the environment considered were 133.76 and 15.93, respectively. Furthermore, the path loss exponents in the near and far fields were also calculated; and the standard deviation of shadowing fell in the range of 4.368dB to 6.180dB.

Effect of γ-radiation on NaZnSO4Cl:Ce, Dy or Mn ions and retrapping of charges in TL

The thermoluminescence (TL) characteristics and effect of γ-radiation on newly invented NaZnSO4Cl:Ce, Dy or Mn ions and retrapping of charges in TL material prepared by wet chemical method are studied. The sensitivity of the NaZnSO4Cl:Ce, Dy or Mn phosphors is higher than that of CaSO4:Dy with the broadness of the glow peak for various concentrations of Ce, Dy, Mn and different γ-rays doses. The phosphor NaZnSO4Cl:Ce has remarkable high sensitivity as compared to NaZnSO4Cl:Dy or Mn. The phosphors NaZnSO4Cl:Ce, and Mn have a simple TL glow curve structure with a single prominent peak at around the temperature 170 and 190°C, whereas NaZnSO4Cl:Dy has two peaks located at 175 and 298°C indicating single and double trapping sites respectively. TL response, fading and reusability characteristics and the trapping parameters of the phosphor are also studied and it is found that the phosphor is quite suitable for use in dosimetry of ionizing radiations.

Fading Characteristics of Wireless Channel on High-Speed Railway in Hilly Terrain Scenario

This paper focuses on the fading characteristics of wireless channel on High-Speed Railway (HSR) in hilly terrain scenario. Due to the rapid speed, the fading characteristics of HSR channel are highly correlated with time or Transmit-Receive distance and have their own special property. To investigate the fading characteristics, the measurement is conducted on the Guangzhou-Shenzhen passenger-dedicated line in China with the speed of 295 km/h in the data-collection area at 2.4 GHz. From the measured data, the amplitude of each path is estimated by using the Subspace-Alternating Generalized Expectation-Maximization (SAGE) algorithm along with other parameters of channel impulse responses. Then the fading parameters, including path loss, shadow fading, andK-factor, are analysed. With the numerical results in the measurement and analysis, the fading characteristics have been revealed and modelled. It is supposed that this work has a promotion for HSR communication system design and improvement.

An SDM Method Utilizing Height Pattern Due to Two-Ray Fading Characteristics

A spatial division multiplexing (SDM) transmission method utilizing the characteristics of two-ray fading without relying on narrow beam of the antennas is introduced. This letter formulates the optimized array antenna arrangements and channel capacity as functions of the transmission distance and shows achievable channel capacity for two- and three-element antenna arrays. The letter also describes bandwidth dependency up to 15% bandwidth based on an assumed application to 60-GHz-band gigabit wireless systems. The proposed method provides increased capacity comparable to multiple-input-multiple-output (MIMO) transmission without the extra signal processing cost incurred when using conventional MIMO.

Ultra-wideband Channel Model for Intra-vehicular Wireless Sensor Networks Beneath the Chassis: From Statistical Model to Simulations

Intra-vehicular wireless sensor networks (IVWSNs) are a promising new research area that can provide part cost, assembly, maintenance savings, and fuel efficiency through the elimination of the wires, and enable new sensor technologies to be integrated into vehicles, which would otherwise be impossible using wired means, such as intelligent tires. The most suitable technology that can meet the high reliability requirement of vehicle control systems and the strict energy efficiency requirement of the sensor nodes in such harsh environment containing a large number of metal reflectors at short distance is the ultra-wideband (UWB). However, there are currently no detailed models describing the UWB channel for IVWSNs, making it difficult to design a suitable communication system. We analyze the small-scale and large-scale statistics of the UWB channel beneath the chassis of a vehicle by collecting data at various locations with 81 measurement points per transmitter-receiver pair for different types of vehicles, including the scenarios of turning the engine on and movement on the road. Collecting multiple measurements allows us to both improve the accuracy of the large-scale fading representation and model small-scale fading characteristics. The path-loss exponent around the tires and other locations beneath the chassis are found to be very different, requiring separate models. The power variation around the path loss has lognormal distribution. The clustering phenomenon observed in the averaged power delay profile (PDP) is well characterized by the Saleh-Valenzuela (SV) model. The cluster amplitude and decay rate are formulated as a function of the cluster arrival times using dual-slope linear models. Cluster interarrival times are modeled using Weibull distribution, providing a better fit than the commonly used exponential distribution in the literature, mainly due to the nonrandomness of the local structure of the vehicle. The variations of local PDPs around the small-scale averaged (SSA) PDPs, in decibels, at each delay bin are modeled by Gaussian distribution with variance independent of the value of the delay and distance between the transmitter and the receiver. The analysis of the model parameters for different vehicles and different scenarios demonstrates the robustness of our modeling approach exhibiting small variance in channel parameters for different vehicle types. Finally, the algorithm for generating the channel model is given. The generated PDPs are in good agreement with the experimental profiles, validating our model.

Third-Order Channel Propagation Model-Based Indoor Adaptive Localization Algorithm for Wireless Sensor Networks

In a changing indoor environment, it is very difficult for wireless sensor networks (WSNs) to locate adaptively the target nodes because of the complexity of the propagation path loss. In this letter, the fading characteristics of channel propagation for wireless sensor nodes are tested, the test data are fitted, and the third-order polynomial log-distance path-loss model is proposed. Using the proposed model, an indoor adaptive localization algorithm for WSNs is designed. The algorithm builds a model parameter table according to the received signal strength indication (RSSI) of fixed nodes, and the table is updated with environmental variation. In locating phase, the most suitable parameters are used to estimate the position of target node. Compared to another algorithm, the proposed algorithm improves the average localization accuracy by about 75%.

A Node-Based Time Slot Assignment Algorithm for STDMA Wireless Mesh Networks

Most slot assignment algorithms that are proposed for spatial time-division multiple-access (STDMA) mesh networks use a simplified transmission model that does not consider the time-varying fading characteristic of a wireless channel. In addition, these algorithms are usually link based, and scheduling in each slot is fixed and done for links. When the scheduled link is in deep fade or has no traffic, the slot that is given to that link will be wasted. In this paper, we present a node-based slot assignment scheme in which scheduling in each slot is done for nodes and not links. Because a node has multiple links, it can exploit multiuser diversity, i.e., different links have different traffic and fading conditions, to achieve much better performance.

수중 채널 환경에서 측정 데이터를 이용한 빔형성기가 결합된 다이버시티의 상관 계수 분석

수중 통신 시스템에서 통신 센서간의 간격을 증가시켜 다이버시티 기법을 적용하면 통신 시스템의 성능이 증가한다. 하지만 이 경우 통신 시스템의 크기가 증가하기 때문에 이를 실제의 수중 채널 환경에서 사용하는데 문제가 있다. 따라서 본 논문에서는 수중 통신 시스템에 빔형성기가 결합된 다이버시티 기법의 적용가능성을 검증하기 위하여 측정을 수행하였으며, 측정된 데이터를 이용하여 수신 신호의 상관계수를 분석해 봄으로써 빔형성기가 결합된 다이버시티 시스템의 성능을 검증하였다. 이를 위해 본 연구에서는 수중 채널 환경에서 측정한 데이터를 이용하여 센서에 수신된 신호의 페이딩 특성을 추정하고, 각 센서에서 추정된 페이딩 특성을 이용하여 센서간의 간격과 빔형성에 의한 상관계수를 분석하였으며, 그 결과 수중 채널 환경에서 서로 다른 다중경로 방향으로 빔형성을 수행하고 빔형성이 수행된 신호를 이용하여 다이버시티를 수행하면 센서간의 간격을 줄이면서도 최적의 다이버시티 이득을 얻을 수 있음을 알 수 있었다. The diversity techniques can benefit underwater acoustic communications when the distance between sensors is sufficiently apart, and this leads to the increases in the physical size of the communication system: thus it is very hard to practically use such systems in real-environments. Therefore, in this paper, we have collected data from real underwater cannel environments in order to analyze the usability of diversity combined with beamforming techniques. And we have estimated the fading characteristics from the measurement data, and analyzed the correlation coefficients using the estimated fading characteristics. After analyzing the estimated fading characteristics from the measurements data, we found out that by applying diversity techniques on the output signals from beamformers that perform beamforming from different multipath directions, we can reduce the distance between sensors and at the same time benefit from the diversity gain.

Dynamic Propagation Channel Characterization and Modeling for Human Body Communication

This paper presents the first characterization and modeling of dynamic propagation channels for human body communication (HBC). In-situ experiments were performed using customized transceivers in an anechoic chamber. Three HBC propagation channels, i.e., from right leg to left leg, from right hand to left hand and from right hand to left leg, were investigated under thirty-three motion scenarios. Snapshots of data (2,800,000) were acquired from five volunteers. Various path gains caused by different locations and movements were quantified and the statistical distributions were estimated. In general, for a given reference threshold è = −10 dB, the maximum average level crossing rate of the HBC was approximately 1.99 Hz, the maximum average fade time was 59.4 ms, and the percentage of bad channel duration time was less than 4.16%. The HBC exhibited a fade depth of −4 dB at 90% complementary cumulative probability. The statistical parameters were observed to be centered for each propagation channel. Subsequently a Fritchman model was implemented to estimate the burst characteristics of the on-body fading. It was concluded that the HBC is motion-insensitive, which is sufficient for reliable communication link during motions, and therefore it has great potential for body sensor/area networks.