Received Signal Envelope Research Articles

A Unification of LoS, Non-LoS, and Quasi-LoS Signal Propagation in Wireless Channels

The modeling of wireless communication channels is often broken down into two distinct states, defined according to the optical viewpoints of the transmitter (TX) and receiver (RX) antennas, namely, line-of-sight (LoS) and non-LoS (NLoS). Movement of the TX, RX, both and/or objects in the surrounding environment means that channel conditions may transition between LoS and NLoS leading to a third state of signal propagation, namely, quasi-LoS (QLoS). Unfortunately, this state is largely ignored in the analysis of signal propagation in wireless channels. We, therefore, propose a new statistical framework that unifies signal propagation for LoS, NLoS, and QLoS channel conditions, leading to the creation of the three-state model (TSM). The TSM has a strong physical motivation, whereby the signal propagation mechanisms underlying each state are considered to be similar to those responsible for Rician fading. However, in the TSM, the dominant signal component, if present, can be subject to shadowing. To support the use of the TSM, we develop novel formulations for the probability density functions of the in-phase and quadrature components of the complex received signal, the received signal envelope, and the received signal phase. In addition, we derive an expression for the complex autocorrelation function of the TSM, which will be of particular importance in understanding and simulating its time correlation properties. Finally, we show that the TSM provides a good fit to field measurements obtained for two different body-centric wireless channels operating at 2.45 GHz, which are known to be subject to the phenomena underlying the TSM.

Second-Order Statistics for IRS-Assisted Multiuser Vehicular Network With Co-Channel Interference

In this paper, we consider a downlink multi-user vehicular communication network empowered by an intelligent reflecting surface (IRS) with the base station (BS) employing the orthogonal frequency division multiple access (OFDMA) scheme. The performance of the considered system is evaluated in terms of second-order statistics (SOS) in the presence of multiple co-channel interferers with varying powers and speeds. In particular, we develop the analytical expressions of level crossing rate (LCR) and average outage duration (AOD) of the received signal envelope at a desired vehicle by considering a generalized fading model as - distribution. The impact of various system and channel parameters such as number of reflecting elements, amplitude of reflection coefficients, number of interferers, Doppler frequencies of desired and interfering vehicles, and different channel fading environments has been shown on the LCR and AOD performances. Moreover, we derive an expression for asymptotic LCR under high transmit power conditions. It has been shown that the asymptotic LCR is independent of the threshold and transmit power. In addition, we consider a stop and wait automatic repeat request (SW-ARQ) protocol for reliable data packet transmission and derive the expressions for packet error rate (PER) and throughput by utilizing the finite-state Markov channel (FSMC) model. The optimal packet length is also determined which maximizes the throughput under SW-ARQ protocol. The impact of various system parameters is also shown on the PER and throughput performances.

Effects of Solar Radio Emissions on Outdoor Radio Propagation at 38 GHz Bands for D2D Communications

This letter presents empirical data documenting the effects of solar radio emissions on outdoor radio propagation at 38 GHz millimeter-wave (mmWave) band for both line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios. Comparing the measurement data collected during a sunny day with the counterpart data collected at night, higher path loss exponent (PLE) values were observed during the day compared to nighttime. This is attributable to the decrease in the carrier-to-noise ratio for day-time signal propagation in sunny sky compared to nighttime. About 4% and 25% increase in PLE values was observed during the day for LOS and NLOS scenarios, respectively. This translates into corresponding decrease in the radio coverage of the wireless transmitter during the day compared to nighttime. Time-domain waveforms were also examined, and it was found that the average received signal envelope was 103 times below a given threshold during the day, and 19 times below the same threshold at night. This, thus, shows that the received signal envelope fades out many more times during the day compared to nighttime.

A Theoretical Channel Model for Spatial Fading in Retrodirective Backscatter Channels

The round-trip nature of backscatter communications subjects the radio link to unusually severe small-scale fading. Over fading channels, the received signal envelope in backscatter-based systems such as radio-frequency identification (RFID) systems fades worse than a standard one-way communication. In this paper, we study spatial fading of the received signal envelope in an important class of backscatter systems using retrodirective transponders that allow microwave and mm-wave communications at extraordinarily low-power consumption by an RF tag. Our comparative study shows that the use of retrodirective RF tags changes the backscatter channel statistics from being doubly faded to singly faded, resembling a conventional, one-way radio channel. Surprisingly, fading in retrodirective backscatter channels is highly varied and sensitive to the fine structure of the diffuse multipath waves in the radio environment in ways that fading in conventional radio links are not.

New closed-form expressions for SNR estimates of Nakagami fading channels by the method of moments

Method of moments has been a parameter estimation technique appropriate to calculate signal-to-noise ratio (SNR) estimates in fading channel models in which an optimal technique like maximum likelihood estimation is not mathematically tractable. In this article, the ratio of the second moment squared to the fourth moment of the received signal envelope is considered to calculate an exact expression for the SNR estimate in Nakagami-m fading channel for M-QAM and $$\theta $$ -MQAM modulations as well as expressions to evaluate the variance and the mean of the estimate. The paper presents two useful contributions for SNR estimation theory on Nakagami fading. Besides the exact algebraic expression for the estimate for a generalized QAM modulation scheme, its performance is evaluated through a statistical linearization argument.

English

Fading is commonly used to describe the properties of the communication channel. Large efforts have been made to describe characteristics of the channel in wireless communication system. The performance of wireless signal propagation in a conventional environment needs Doppler fading channel schemes by assuming a perfect knowledge about the channel frequency response at both the transmitter and the receiver sides. Two models were used to depict the characteristics of Doppler fading channel in term of source velocity,  where the first  is free space transmission model consists of two antennas at a given distance (r) to calculate the received signal strength for transmission links at relative motion between the transmitter and receiver antennas. The second model is simulation based on Matlab (2013B) to compute and plot the received signal envelope taking into account the source velocity over the multipath fading. The analysis and employing the information of Doppler fading can enhance the characteristics of channel estimation.   Key words: Doppler, fading, frequency, receiver, transmitter.

Joint Parameter Estimation for the Two-Wave with Diffuse Power Fading Model.

Wireless sensor networks deployed within metallic cavities are known to suffer from a very severe fading, even in strong line-of-sight propagation conditions. This behavior is well-captured by the Two-Wave with Diffuse Power (TWDP) fading distribution, which shows great fit to field measurements in such scenarios. In this paper, we address the joint estimation of the parameters K and Δ that characterize the TWDP fading model, based on the observation of the received signal envelope. We use a moment-based approach to derive closed-form expressions for the estimators of K and Δ, as well as closed-form expressions for their asymptotic variance. Results show that the estimation error is close to the Cramer-Rao lower bound for a wide range of values of the parameters K and Δ. The performance degradation due to a finite number of observations is also analyzed.

Inverse Gaussian‐based composite channel model and time series generator for land mobile satellite systems under tree shadowing

In this study, a new composite channel model for land mobile satellite (LMS) systems under tree shadowing is proposed utilising the inverse Gaussian (IG) distribution to model the shadowing component. Using the experimental data of received power under tree shadowing at L-band, which were carried out at Stromovka Park in Prague, the Czech Republic, the assumption of the IG distribution for the description of the first-order statistics of large-scale effects is investigated and validated. A new LMS channel model is developed as a sum of a signal experiencing IG shadowing and a signal under Rayleigh multipath effects. Moreover, a methodology to generate accurate time series of the received signal envelope using the IG distribution is presented. Such methodology and generally time series generators can be used for the evaluation of system's performance and for end-to-end simulations. Finally, it is shown that the proposed time series generator reproduces the first-order and second-order statistics of the LMS channel model with a very good accuracy.

The Gamma-Gamma Channel Model - A Survey

Background: In Free space optical communication medium, the received signal envelope is affected by various impairments. The most dominating effect is turbulence induced fading. To model the turbulence there are fading channel models. Findings: In this paper the Gamma-gamma fading model is reviewed which gives impressive results under all types of turbulence conditions. The Gamma-gamma channel model statistics and its performance with spatial diversity techniques under correlation are reviewed. It has been shown that the Gamma-gamma channel model is able to perform better under correlation than other fading channel models. Improvements: The performance analysis of Gamma-gamma channel under pointing errors and its working with recent techniques in which FSO systems works with RF systems (Hybrid RF/FSO system) are also included in this paper.

LCR of SC receiver output signal over α-κ-μ multipath fading channels

Wireless mobile communication system with selection combining (SC) diversity receiver is investigated in this paper. Received signal envelope experiences ?-?-? short term fading resulting in system performance degradation. Level crossing rate (LCR) and average fade duration (AFD) of SC receiver output signal envelope are obtained as rapidly converging infinite series expressions. Numerically evaluated results are presented graphically, in order to discuss the effects of transmission parameters: multipath fading severity, dominant component power and nonlinearity propagation parameter on observed LCR performance of dual SC.

Modulation Identification Using Moment Features for Communications via Ricean Fading SIMO Channels

Modulation identification (MI) of an unknown communication signal plays a key role in various civilian and military applications, such as cognitive radio, spectrum surveillance, and electronic warfare systems. In this paper, a new MI algorithm for Ricean fading channel signals in wireless single input multiple output systems is proposed, which employs high-order moments as features for identification. The second-order moment and the fourth-order cross-moment matrix of the received signal envelope are used to estimate the moments of the transmitted data. The performance of the proposed algorithm is investigated through numerical simulations and compared with the MI algorithm in the literature.

Aspects regarding the use of the INFREP network for identifying possible seismic precursors

In the last decades, one of the main research directions in identifying seismic precursors involved monitoring VLF (Very Low Frequency) and LF (Low Frequency) radio waves and analysing their propagation characteristics. Essentially this method consists of monitoring different available VLF and LF transmitters from long distance reception points. The received signal has two major components: the ground wave and the sky wave, where the sky wave propagates by reflection on the lower layers of the ionosphere. It is assumed that before and during major earthquakes, unusual changes may occur in the lower layers of the ionosphere, such as the modification of the charged particles number density and the altitude of the reflection zone. Therefore, these unusual changes in the ionosphere may generate unusual variations in the received signal level.The International Network for Frontier Research on Earthquake Precursors (INFREP) was developed starting with 2009 and consists of several dedicated VLF and LF radio receivers used for monitoring various radio transmitters located throughout Europe. The receivers’ locations were chosen so that the propagation path from these VLF/LF stations would pass over high seismicity regions while others were chosen to obtain different control paths.The monitoring receivers are capable of continuously measuring the received signal amplitude from the VLF/LF stations of interest. The recorded data is then stored and sent to an INFREP database, which is available on the Internet for scientific researchers. By processing and analysing VLF and LF data samples, collected at different reception points and at different periods of the year, one may be able to identify some distinct patterns in the envelope of the received signal level over time. Significant deviations from these patterns may have local causes such as the electromagnetic pollution at the monitoring point, regional causes like existing electrical storms over the propagation path or even global causes generated by high-intensity solar flares. As a consequence, classifying these perturbations and minimizing them (when possible) would represent an important step towards identifying significant pattern deviations caused by seismic activities.Taken into consideration some of the issues mentioned above, this paper intends to present some aspects meant to improve the overall performance of the existing INFREP network. The signal-to-noise ratio improvement of the monitoring receiver may be achieved by relocating the antenna (or even the entire monitoring system if possible) in areas with less electromagnetic pollution within the VLF and LF bands. Other solution may involve replacing the existing electric “whip” antennas with magnetic loop antennas.Regarding the measuring method, long-term averaging of the received signal to reduce the electromagnetic noise should be carefully applied. If the averaging time is too long, there is a risk that, during a seismic event, the details of the received signal envelope would be lost. Moreover, this may reduce the possibility of making correlations between the monitored stations and INFREP receivers in case of sudden ERP (Effective Radiated Power) variations of the VLF/LF stations. For the same reason, the time synchronization of the recorded data using (for instance) GPS technology is highly recommended.Other aspects related to the overall performance improvement of the INFREP network consist of monitoring other VLF/LF stations such as the Krasnodar station (south of Russia), part of the ALPHA/RSDN-20 VLF navigation system, or the 77.5kHz DCF77 time signal transmitter (near Frankfurt am Main, Germany). Moreover, the installation of a new reception point in Romania (near Cluj-Napoca) for monitoring the Vrancea area (within the Carpathians Mountains) and the Adriatic region will provide complementary scientific data within the network.

The Gamma-Gamma Signal Fading Model: A Survey [Wireless Corner

In a wireless communication medium, the received signal envelope fluctuates randomly due to the scattering nature of these channels. This paper is intended to present a comprehensive literature review on the gamma-gamma signal fading model and its use in the performance analysis of different communication systems, with more elaboration on wireless radio-frequency (RF) communication networks, including cellular and relay networks, and wireless optical networks. First, the different communication channels where the gamma-gamma distribution is used to model the signal-fading phenomena are described. Second, the reported results on the statistics for the gamma-gamma distribution, including the product, the quotient, the sum, and the order statistics are presented. Finally, the performance analyses carried out in the open literature for wireless RF systems, relay networks, and wireless optical systems are summarized, and some possible directions for future research are highlighted.

Modeling of First-Order Statistics of the MIMO Dual Polarized Channel at 2 GHz for Land Mobile Satellite Systems Under Tree Shadowing

The Land Mobile Satellite (LMS) channel at 2 GHz is examined and the first order statistics are modeled using experimental data for two tree shadowing scenarios. Considering that the first order statistics of the channel are used as input to channel models as well as for the calculation of the system margins, the modeling of the probability density function (PDF) and the cumulative distribution function (CDF) of the received signal envelope is of great importance for the design of LMS systems. Experimental data from measurements performed in Prague, the Czech Republic, are presented for two scenarios, a Heavy Tree Shadowing one and an Intermediate Tree Shadowing one. Four of the most widely used distributions, Rayleigh, Rice, Loo and lognormal, are considered for the modeling of the CDF of the signal envelope. Loo and Rice distributions out of the four considered distributions provide the best fit with reference to the measured data. Moreover, analytical empirical expressions are given for the parameters of the Loo distributions as a function of the elevation angle, to be used for the modeling of the LMS channel under tree shadowing. It is found that the expressions for the estimation of the distributions' parameters provide a good fit to the experimental data.

Measurement, Characterization, and Modeling of the Helicopter Satellite Communication Radio Channel

The satellite-to-helicopter radio channel is measured, characterized, analyzed, and modelled. We used a sweep time delay cross correlation sounder operating at 14.25 GHz and actual helicopters for the experiment. From the measurements, signal fading, delay and Doppler spread are estimated. Wideband radio channel results show that the signal delay spread is small enough, so 32 MHz satellite transponders could be used with no need of equalization. We also observed two important propagation impairments on the received signal envelope, both of them caused by the main rotor blades. The first one is the power attenuation produced when the LoS is obstructed by the blades. We demonstrate that this effect could be mitigated by using spatial or polarization diversity technique in the receiver end. The second one is the presence of multipath propagation leading to a power level oscillation dependent on the amplitude of the received multipath components. An UTD-based 3-D ray tracing model was used to conclude that the main multipath components are generated by diffraction on the rotor blade edges.

Use of Shadowing Moments to Statistically Model Mobile Satellite Channels in Urban Environments

The performance of mobile satellite networks in built up areas is liable to deterioration since the wireless channel variations significantly affect the link availability over time. Previous statistical models which employ empirical data for estimation of fading parameters, are reliable only for specific environments. In this paper, we incorporate simple physical-statistical characteristics of urban canyons into estimation of shadowing moments which describe the received signal envelope. Our flexible model utilizes analytic fading parameters and accounts for azimuth and elevation angles hence, it facilitates simulation of low earth orbit (LEO) satellite links with good accuracy in areas where channel measurements are not available. Moreover, our novel approach can be effectively used for evaluation of the quality of service (QoS) in terms of bit error outage probability.

On the Advantages of Frequency-Only MIMO Radar

This paper deals with the advantages of the frequency based MIMO radars for target parameter estimation. When a moving target exists, the received signal includes Doppler frequency shift in which the target position, velocity and direction information exist. Hence, especially when the envelope of the received signal is destroyed densely, these unknown target parameters can be estimated efficiently by estimating the Doppler frequency of the returned signal. In this paper, the advantages of the frequency based MIMO radar are analyzed especially at low SNR values and when the target fluctuations exist.

A New Suboptimal Selection Combining With Enhanced Performance for BPSK Over Rayleigh Fading Channels

A new suboptimal selection combining (SC) scheme is proposed and is denoted by (α+ | <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> |)-SC, where α is the fading factor, and | <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> | is the received signal envelope. The (α+ | <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> |)-SC scheme has lower complexity than the optimal SC scheme and outperforms other existing suboptimal SC schemes such as the traditional signal-to-noise-ratio (SNR)-SC (denoted by α-SC) and | <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> |-SC schemes. To choose a diversity branch for signal reception, the suboptimal SNR-SC and | <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> |-SC schemes use SNR and | <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> | as their selection statistics, respectively, and the branch with the maximal selection statistic is selected. For the branch selection of (α+ | <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> |)-SC, basically, each diversity branch uses the linear sum of the selection statistics of α-SC and | <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> |-SC schemes as a new selection statistic. Unlike the optimal SC or maximal ratio combining (MRC) scheme that requires multipliers to form the selection or combining statistic, the (α+ | <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> |)-SC scheme only uses adders to generate the selection statistic, which makes (α+ | <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> |)-SC faster and more power-saving than the optimal SC or MRC. For performance comparisons, the bit error rate (BER) of binary phase-shift keying (BPSK) over independent but not necessarily identical ( i.n.d.) Rayleigh fading channels is derived. Numerical results show that the suboptimal (α+ | <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> |)-SC and optimal SC schemes have very close BER performance.

Some integral characteristics of MRC receiver in Nakagami-m fading environment

In this paper, maximal ratio combining (MRC) technique over Nakagami–m fading channel is described and some statistical characteristics of received signal envelope are analysed. For analytical and numerical evaluation of system performance, the probability density functions (PDF) of received signal envelope after MRC are analysed like particular solutions of corresponding differential equation, while the existence of singular solution is considered and analysed under different conditions.

The Inverse Gaussian Distribution in Wireless Channels: Second-Order Statistics and Channel Capacity

In this paper, we introduce the Inverse Gaussian (IG) fading distribution to model the envelope and the power of the received signal in radio propagation fading channels and free-space optical (FSO) channels. The joint distribution of the IG process and its derivative and the marginal distribution of the derivative are developed. The obtained formulas are then used to derive the second-order statistics of the received signal envelope and the channel capacity under IG and Nakagami-IG (NIG) fading distributions. Numerical results sustaining our analysis are provided, and the impacts of various parameters on the system performance are investigated.