Deep Fading Research Articles

Fade and Interfade Duration Characteristics in a Slant-Path <italic>Ka</italic>-Band Link

Satellite-to-earth links are subject to several propagation effects in the troposphere, being rain attenuation the impairment that can cause the deepest fades. In this paper, the duration of both fades and the intervals between consecutive fades (interfade intervals) are characterized on the basis of the results of a long-term slant-path Ka -band propagation experiment carried out in Madrid, Spain. The experimental and statistical results included in this paper correspond to seven complete years of measurements, a period large enough to characterize not only the average-year statistics of fade dynamics but also their variability, which is assessed on the basis of annual statistics of durations. The obtained average-year statistics of fade durations are in many cases close to the predictions made by the International Telecommunication Union-Radiocommunications and Communications Research Center Canada models, although the predictions could be improved with a better selection of the parameters of the distributions used in the models. Interfade duration statistics are also presented and related to recent modeling efforts. The interannual variability of statistics, such as the relative number of fades, is quantified and found to be low, except for the higher attenuation thresholds or the highest durations considered in this paper.

An Improved Dual-Hop Transmission Method for High Reliability in Wireless Communication Networks

In this paper, a new dual-hop transmission scheme based on MIMO-OFDM is proposed in order to enhance the performance of cooperative scheme. This paper proposes improved cooperative dual-hop scheme which handles transmission schemes for three areas of the cell by changing transmission symbols. Since performance of wireless communication depends on channel states of cell area, the transmission can have flaws because of deep fading or heavy shadowing. Therefore, in order to overcome these flaws, a cooperative dual-hop scheme is used to construct virtual MIMO system and get spatial diversity gain. In addition, the usage of CDD and STBC scheme redeems the cooperative dual-hop scheme by obtaining high reliability.

Channel Deviation-Based Power Control in Body Area Networks.

Internet enabled body area networks (BANs) will form a core part of future remote health monitoring and ambient assisted living technology. In BAN applications, due to the dynamic nature of human activity, the off-body BAN channel can be prone to deep fading caused by body shadowing and multipath fading. Using this knowledge, we present some novel practical adaptive power control protocols based on the channel deviation to simultaneously prolong the lifetime of wearable devices and reduce outage probability. The proposed schemes are both flexible and relatively simple to implement on hardware platforms with constrained resources making them inherently suitable for BAN applications. We present the key algorithm parameters used to dynamically respond to the channel variation. This allows the algorithms to achieve a better energy efficiency and signal reliability in everyday usage scenarios such as those in which a person undertakes many different activities (e.g., sitting, walking, standing, etc.). We also profile their performance against traditional, optimal, and other existing schemes for which it is demonstrated that not only does the outage probability reduce significantly, but the proposed algorithms also save up to average transmit power compared to the competing schemes.

Depolarisation studies of single trees at 20 GHz

This study addresses the characterisation of the polarisation states of the re-radiated signal from a natural tree performed in the vicinity around deep signal fades, at 20 GHz. The polarisation pattern method has been used to investigate the effects of depolarisation and to further characterise the changes in the polarisation state of the re-radiated signal occurring as a result of the currents induced in the trunk, branches and leaves, which are significantly influenced by the complex permittivities of the various materials making up the tree. Results presented in this study will explain the signal behaviour observed in the various regions around the tree. The results also show that depolarisation, in addition to absorption and scatter, is an important factor formulating accurate models for propagation in vegetation.

Fractionally Nyquist Sample Spaced ARMA Blind Equalizer for Direct Signal Recovery in Passive Bistatic Radar

This paper proposes a modified signal processing structure based on the fractionally Nyquist sample spaced structure for passive bistatic radar. To recover the direct signal from the multipath clutter, an equalizer of the Auto regressive moving average (ARMA) type is proposed based on the fractionally Nyquist sample spaced constant modulus algorithm. Compared with the conventional Nyquist sample spaced equalizer, the equalizer of the fractionally Nyquist sample spaced ARMA structure is more effective in dealing with deep fading multipath channels with zeros near the unit circle. Computer simulations and real data tests indicate that the proposed approach outperforms the conventional processing structure in terms of both clutter residual and mean square error.

Diversity Study of a Frequency Selective Surface Transponder for Wearable Applications

This communication presents a semipassive radio frequency identification system in the 2.45-GHz Industrial, Scientific and Medical band. The transponder (or tag) is based on a modulated frequency selective surface (FSS). The FSS is composed of dipoles loaded with varactor diodes that modulate the radar cross section. The FSS transponder is designed to work for wearable and on-body applications and is used for reading and transmitting information from different sensors placed on the body. Experimental results locating the FSS at different positions in real scenarios and also at different places on the body are provided. Multiple FSSs have been used to explore spatial and polarization diversity techniques in order to mitigate the deep fadings that can happen during communication. Noticeable diversity gain has been obtained in both the cases without using antenna diversity in the reader. Finally, this communication describes a proof-of-concept experiment of the communication where two FSSs send digital data using a frequency shift keying modulation.

Performance Evaluation of Underwater Wireless Optical Communications Links in the Presence of Different Air Bubble Populations

We experimentally evaluate the performance of underwater wireless optical communication (UWOC) links in the presence of different air bubbles. Air bubbles of different sizes and densities are generated by using an air pipe in conjunction with a submersible water pump of variable flow rate that helps break up large bubbles into smaller bubbles. Received signal intensity measurements show that bubbles significantly degrade the performance of UWOC links. Large bubbles completely obstruct the optical beam and cause a deep fade. However, as the bubble size decreases, the level of deep fade also decreases because the optical beam is less susceptible to complete obstruction, and more light reaches the detector. We also show that beam expansion could help mitigate the performance degradation due to the deep fade caused by air bubbles scatters in the channel.

Transmission Power Adaption for Full-Duplex Relay-Aided Device-to-Device Communication

Device-to-device (D2D) communications bring significant improvements of spectral efficiency by underlaying cellular networks. However, they also lead to a more deteriorative interference environment for cellular users, especially the users in severely deep fading or shadowing. In this paper, we investigate a relay-based communication scheme in cellular systems, where the D2D communications are exploited to aid the cellular downlink transmissions by acting as relay nodes with underlaying cellular networks. We modeled two-antenna infrastructure relays employed for D2D relay. The D2D transmitter is able to transmit and receive signals simultaneously over the same frequency band. Then we proposed an efficient power allocation algorithm for the base station (BS) and D2D relay to reduce the loopback interference which is inherent due to the two-antenna infrastructure in full-duplex (FD) mode. We derived the optimal power allocation problem in closed form under the independent power constraint. Simulation results show that the algorithm reduces the power consumption of D2D relay to the greatest extent and also guarantees cellular users’ minimum transmit rate. Moreover, it also outperforms the existing half-duplex (HD) relay mode in terms of achievable rate of D2D.

Cross‐polarisation discrimination studies of single trees at 20 and 62.4 GHz

This study addresses the characterisation of cross-polarisation discrimination of re-radiated signals from natural trees performed in the vicinity around deep signal fades. Results presented in this study will explain the signal behaviour observed in the various regions around the tree. This has been addressed in this study through a combination of analytical and experimental modelling based on thorough examination of the re-radiation functions of single trees and appropriate measurements performed under controlled environments, at 20 and 62.4 GHz. The identification of three distinct regions of interest in the scatter (re-radiated) field is discussed in this study, where it is shown that depolarisation, in addition to absorption and scatter, is an important factor formulating accurate models for propagation in vegetation media.

Opportunistic Routing and Scheduling for Wireless Networks

In spatial time division multiple access wireless mesh networks, not all links can be activated simultaneously, as links scheduled for transmission must satisfy the specified SINR requirements. Previously, slot assignment has been done on a link basis, where a set of links is selected for transmission in a given slot. However, if selected links are in deep fade or have no traffic to transmit, the slot is wasted. Thus, a node-based scheme was proposed, where a set of nodes is selected for transmission. Which link to be used by a node depends on the links’ instantaneous traffic load. Although this allows us to exploit multi-user diversity, it creates a planning discrepancy: slot assignment is designed based on long-term channel statistics, but scheduling on short-term channel fading conditions. Consequently, the performance gain of the node-based scheme is not consistent: it is marginal under certain scenarios. To avoid the design discrepancy, we develop a new slot-assignment and routing framework in this paper. The new approach incorporates short-term channel fading statistics to optimize the long term slot assignment, routing and scheduling simultaneously. Hence, multi-user diversity can be exploited more efficiently. Not only is the performance gain of the resulting system significant (can be as much as 64% higher throughput than the scheme introduced by Chen and Lea), it is also less topology dependent compared with the one by Chen and Lea.

Measurement-Based Multiple-Scattering Model of Small-Scale Fading in High-Speed Railway Cutting Scenarios

In this letter, the fading statistics of wireless channels in high-speed railway cutting scenarios are characterized based on measurements. A multiple scattering model called second-order scattering fading (SOSF) is used to model the small-scale fading considering the influence of cuttings and bridges. The SOSF model can offer the possibility of analytical estimation for different fading severities via a simple moment-based estimator. It is demonstrated that Ricean fading is the dominant fading distribution in cutting scenarios, but deep fades also occur. The fading process is therefore described by a hidden Markov model, which is validated statistically by measurement data.

Opportunistic channel access with repetition time diversity and switching cost: a block multi-armed bandit approach

In this paper, we investigate the channel access problem considering switching cost in the block fading channels with unknown information of channel occupation and quality. We formulate this problem as a multi-armed bandit (MAB) problem with the goal of minimizing the outage rate and avoiding frequent channel switching. To achieve this goal, a block based multi-armed bandit (BMAB) learning algorithm is proposed. Furthermore, the BMAB algorithm is extended to cope with the short-term deep channel fading, by exploiting the repetition time diversity (RTD). The regrets of the proposed two algorithms are proved to be logarithmic in time. Performance analysis and simulation results show that the proposed algorithms outperform standard SMAB algorithm in average system outage rate, switching cost and throughput. In addition, the repetition time diversity multi-armed bandit (RTDMAB) algorithm is better than BMAB algorithm in the presence of deep channel fading at the cost of receiving complexity .

Characterization of 300-GHz Wireless Channel on a Computer Motherboard

This paper presents characterization of 300-GHz wireless channel on a computer motherboard, where several different measurement scenarios have been considered. Results indicate that the presence of the ground plane and/or vertical parallel-plate structures in the channel introduces multipath that, if constructively superimposed, may create a path loss lower than free-space propagation path loss. In addition, it has been found that a few centimeters of vertical misalignment between the transmitter and the receiver result in a path loss greater than 5 dB. Furthermore, the results indicate that vertical components such as dual in-line memory modules with reflection coefficient close to one for all incident angles can be used to create directed non-line-of-sight (LoS) links with wide coherence bandwidth. Finally, for LoS propagation obstructed by large objects, such as a heatsink, the path-loss exponent of 1.77 is found, while the rotating fan causes periodic fading in the received power, indicating that channel equalization techniques will be needed to overcome deep fades. All these results indicate that optimal communications can be achieved by carefully positioning the antennas with respect to the motherboard layout.

Performance Analysis of 32 QAPM System with SC Diversity in Rician Fading Channel

Objectives: Due to demand QoS Service according to advancing the IOT technique, it is necessary to study a new modulation technique to improve the data throughput while maintaining the property of IEEE 802.15.4 radio. Methods/Statistical Analysis: To improve the data throughput of low-power radio, a proposed method adopts QAPM modulation and SC diversity. It makes the radio possible to enhance BER by reducing the influence of white noise and deep fading without additional power consumption. Findings: A core of proposed method is securing the hamming distance by degrading modulation level, reducing the influence of fading by selecting the superior signal and saving the power by having a silenceperiod for a half period of symbol. As a result, the proposed method makes it possible to achieve BER enhancement and power gain. Especially, the proposed method has the advantage that a BER performance can be further improved with increasing fading depth. Improvements/Applications: By introducing proposed method, it is expected to improve the utilization of QoS service in near field communication like WBAN.

Influence of Cobalt and Sodium Doping on MnO/CNT Composite Anode Materials for Li-Ion Batteries

Li ion batteries (LIBs) have been the leading technology in the portable electronics market since their discovery by Sony in the 1990s. Commercially, their setup is constituted by a graphite anode, a lithium metal oxide cathode and LiPF6 dissolved in a mixture of carbonates as electrolyte, characterized by a maximum energy specific density 150 Wh/Kg [1]. However, the needs of newer and cleaner forms of energy is pushing lithium ion batteries towards higher scale applications, such as the electric grid or automotive, requiring the energy and power density to be at least doubled in the near future. Materials advances at both sides of the cell have been actively investigated for several years. The cathodic side of the cell presents very few choices of materials that are suitable to be used in LIBs (LiCoO2, LiMnO2, LiFeO4), all with a theoretical capacity lower than 300 mAh/g, and even lower practically achievable capacity. At the anode, there is a much wider choice of active materials. Silicon has been one of the most widely investigated options in recent years because of its very high theoretical capacity (>3000 mAh/g) and availability. However, pure silicon materials show very rapid deep capacity fade due to the large volumetric expansion occurring during the alloying/dealloying electrochemical reaction (more than 250% of the initial volume). To mitigate this, several materials and operational adjustments have been made and modern silicon composites are only able to achieve a capacity ca. 1000 mAh/g, only 1/3 of the theoretical capacity [2]. Moreover, reference [3] showed that, due to the cathodic limitation of the cell, there is a “capacity penalty” when the anode material capacity is too much larger than the cathode material, and the anode capacity should only be around 700 mAh/g (until new cathode materials are discovered) to fully realize improvements to the overall cell performance. This opens up the periodic table to a wide number of available chemistries including metal oxides [4] which have been the focus of many electrochemical studies so far because of their higher capacity relative to graphite and environmental friendliness. Among the metal oxides, manganese oxides are attractive because they are inexpensive and highly available [5]. Unfortunately, to date few studies have been shown with acceptable capacity and retention have been reported, particularly under realistic operating conditions. In this work, our team will discuss the synthesis of a novel bi-metallic Mn/Co oxide active material imbedded into a low loading multiwalled carbon nanotubes matrix, as shown in Figure 1. We will show the impact of cobalt doping on half-cell performance. Different Cobalt dopant contents (0%,5%,10%,15% and 20%) were prepared and their electrochemical performance was tested, including capacity retention (Figure 2) and rate capability up to 1600 mA/g. Lastly, Na was used as a doping as well, increasing the performance of the manganese active material, which can be tied to enhancement in the electronic conductivity. References. M.M. Thackeray, C. Wolverton and E.D. Isaacs, Energy and Environmental Science, 5, (2012), 7854.T. Osaka, H. Nara, T. Momma and T. Yokoshima, J. Mater. Chem. A, 2, (2014) 883. M. Karulkar, J. Power Sources, 273 (2015) 1194-1201. N. Spinner, L. Zhang and W.E. Mustain, J. Mat. Chem. A, 2(6) (2014) 1627.L. Li, A.R.O. Raji and J.M. Tour, Advanced Materials, 25, (2013), 6298. Figure 1

Implementation of Advanced Carrier Tracking Algorithm Using Adaptive-Extended Kalman Filter for GNSS Receivers

Use of Global Navigation Satellite Systems (GNSS) receivers for real-time applications has improved significantly all over the world. The main problem with the designed receivers is their failure to function under harsh environmental conditions because of the structured phase-locked loop (PLL) architecture. One of the most critical phenomena that cause signal degradation in GNSS receiver is ionospheric scintillations, which create disturbances in amplitude and phase of the received signal. The problem in signal acquisition and tracking, even in the severe canonical fades (deep amplitude fading correlated with reference to half cycle phase jumps), can be mitigated using robust and adaptive carrier tracking algorithms. The autoregressive exogenous modeling parameters are useful in estimating the amplitude and phase scintillations. The proposed adaptive-extended Kalman filter (AEKF) approach works as an effective carrier tracking algorithm maintaining a balance in dual problems faced by PLL-based receivers, i.e., (estimation versus mitigation) and (dynamics versus noise reduction) tradeoff. The developed AEKF algorithm performed well for synthetic Cornell scintillation monitor data and for Global Positioning System L1 PRN 12 data collected around 21.30 H (local time) on October 24, 2012, in Rio de Janeiro, Brazil, with GNSS Software Navigation Receiver.

Analysis of Selected Earth-Space Rain Attenuation Models for a Tropical Station

The restrained use of millimeter bands is due to severe rain attenuation. Attenuation is caused when rain cells intersects radio wave’s propagation path; resulting in deep fades. The effect of rainfall is more severe in tropical regions characterized by heavy rainfall intensity and large raindrops; hence, rain attenuation analyses are essential to study rain fade characteristics for use in earth-space link budget analysis, for outage prediction resulting from rain attenuation. Tropical regions are particularly challenged with signal outage, necessitating the formulation and development of suitable prediction model(s) for the region. Therefore, extensive knowledge of the propagation phenomena mitigating system availability and signal quality in these bands are required. Daily rainfall data were collected from the Nigerian Meteorological Services for Lagos for spanning January to December 2010. Results showed that although, the ITU-R model out-performed the other prediction models under consideration, none of prediction models matched the measurement data.

Photometric activity of UX orionis stars and related objects in the near infrared and optical: CO Ori, RR Tau, UX Ori, and VV Ser

This paper continues a study of the photometric activity of UX Ori stars in the optical and near-infrared (JHKLM bands) initiated in 2000. For comparison, the list of program stars contains two Herbig Ae stars that are photometrically quiet in the optical: MWC480 andHD179218. Fadings ofUXOri stars in the optical (V band) due to sporadic increases of the circumstellar extinction are also observed in the infrared (IR), but with decreasing amplitude. Two stars, RR Tau and UX Ori, displayed photometric events when V -band fadings were accompanied by an increase in IR fluxes. Among the two Herbig Ae stars that are photometrically quiet in the optical, MWC 480 proved to be fairly active in the IR. Unlike the UX Ori stars, the variation amplitude of MWC 480 increases from the J band to the M band. In the course of the observations, no deep fadings in the IR bands were detected. This indicates that eclipses of the program stars have a local nature, and are due to extinction variations in the innermost regions of the circumstellar disks. The results presented testify to an important role of the alignment of the circumstellar disks relative to the direction towards the observer in determining the observed IR variability of young stars.

Exploring Smart Pilot for Wireless Rate Adaptation

Rate adaptation is an essential component in today’s wireless standards, which help approach the channel capacity and maximize the throughput. However, how to estimate the optimal data rate in a fluctuated channel remains of great concern. Previous wisdoms leverage PHY layer information for rate estimation, including confidence information like SoftPHY hints, and channel state information (CSI) measurements. However, when experiencing rapid time varying and frequency selective fading channel, the above metrics can be inaccurate. The reason roots from the fact that there are not enough cost-efficient pilots, which are pre-known symbols inserted in a packet for channel estimation. In this paper, we observe that by digging into both PHY layer decoder and upper layer protocol headers, more reliable data bits with high confidence level can be exploited. These data bits, termed smart pilot, can be used to calibrate the channel estimation measurements cost-efficiently. Based on the calibrated estimation, we further propose a novel greedy rate selection algorithm to track the optimal data rate, which successfully avoids the impact of deep fading subcarriers in both legacy 802.11a/g and 802.11n MIMO systems. Our experiments on GNU radio testbed show that SmartPilot quickly tracks the link variance, and improve the channel estimation accuracy by 87%. Furthermore, the trace driven simulation reveals that greedy rate selection algorithm predicts the data rate as good as the optimal rate adaptation algorithms for 802.11 standards.

Energy Efficient Cooperative Spectrum Sensing in Cognitive Radio

Sensing in cognitive radio (CR) protects the primary user (PU) from bad interference. Therefore, it is assumed to be a requirement. However, sensing has two main challenges; first the CR is required to sense the PU under very low signal to noise ratios which will take longer sensing time, and second, some CR nodes may suffer from deep fading and shadowing effects. Cooperative spectrum sensing (CSS) is supposed to solve these challenges. However, CSS adds extra energy consumption due to CRs send the sensing result to the fusion center and receive the final decision from the fusion center. This is in addition to the sensing energy itself. Therefore, CSS may consume considerable energy out of the battery of the CR node. Therefore in this paper, we try to find jointly the sensing time required from each CR node and the number of CR nodes who should perform sensing such that the energy and energy efficiency (i.e., ratio of throughput to energy consumed) are optimized. Simulation results show that the joint optimization achieves better in terms of energy efficiency than other approaches that perform separate optimization.