Fading Channel Model Research Articles

Dual-Polarized Spatial Modulation Over Correlated Fading Channels

We address multiple-input multiple-output (MIMO) communication employing spatial modulation (SM) with dual-polarized (DP) antennas. The proposed architecture adds the polarization dimension to the conventional SM mappings and offers performances, which are comparable to or under certain conditions even better than those of the uni-polarized systems while occupying half as much space. We consider the generalized spatially correlated Rayleigh and Rician fading channel models and present an average bit-error probability upper bounding framework for the proposed DP SM-MIMO system. The theoretical error analysis is also extended to the case where the channel coefficients are estimated with Gaussian estimation errors. This upper bounding method is also used to determine the conditions in which the dual-polarized SM is better than equivalent systems with uni-polarized antennas. Theoretical derivations are also validated by extensive simulations, both corroborating that SM combined with dual-polarization forms an attractive alternative not only for its improved multiplexing gains and space efficiency but also for performance gains over correlated channels.

Design and actualisation of the improved Jakes fading channel

Based on the original Jakes model, the authors have proposed a new design for an inexpensive fading channel simulator that can be easily actualised with fewer low-frequency oscillators than that used in existing structures. The major modifications from the original Jakes model include the generation of path gains under an improved distribution, and presetting the arrival angles and initial phases to be zero. These modifications not only reduce the hardware cost of the channel simulator, but also provide better statistic properties than the model proposed by Zheng and Xiao. Specifically, the improved Jakes fading channel model presented in this study needs only eight low-frequency oscillators. Simulation results have demonstrated that the proposed design exhibits improved first-order and second-order statistical properties.

Performance analysis of the clustering-based multihop wireless energy harvesting sensor networks over symmetric and asymmetric fading channels

In this work, we propose a clustering-based multihop relaying with the partial relay selection scheme for an energy harvesting relaying network and analyze the performance in the framework of the decode-and-forward relaying and adaptive power splitting protocol over symmetric and asymmetric fading channel models. In particular, we analyze the system performance in terms of the outage probability, effective transmission rate, and throughput. Through extensive numerical analysis, we show that the proposed scheme can substantially outperform the conventional multihop relaying without clustering as well as direct transmission, which suggests that the proposed scheme can be used to extend the network coverage without any extra energy from the network. We also demonstrate that the proposed scheme can compensate for the performance loss due to poor radio frequency to DC conversion efficiency as well as path loss by exploiting the gain associated with multihop relaying as well as the diversity gain achieved through the partial relay selection scheme. Moreover, we investigate the relationship between the total number of relay nodes in the network and the number of hops and show that there is an optimal number of hops that can maximize the throughput for a given transmission power of the source. The effect of the asymmetric channels in our clustering-based multihop relaying is also investigated and it is revealed that the existence of Rician fading will help improve the throughput at the destination side, rather than the source side, as opposed to the conventional multihop relaying scenarios without clustering.

Defining Spatial Secrecy Outage Probability for Exposure Region-Based Beamforming

With the increasing number of antennae in base stations, there is considerable interest in using beamforming to improve physical layer security, by creating an “exposure region” that enhances the received signal quality for a legitimate user and reduces the possibility of leaking information to a randomly located passive eavesdropper. This paper formalizes this concept by proposing a novel definition for the security level of such a legitimate transmission, called the spatial secrecy outage probability (SSOP). By performing a theoretical and numerical analysis, it is shown how the antenna array parameters can affect the SSOP and its analytic upper bound. While this approach may be applied to any array type and any fading channel model, it is shown here how the security performance of a uniform linear array varies in a Rician fading channel by examining the analytic SSOP upper bound.

On the Performance Analysis of Wireless Communication Systems over ???/??? Composite Fading Channels

The α - μ/α - μ fading channel model is the result of the product of two independent and non-identically distributed (i.n.i.d.) α - μ variates. As such, in order to study the performance of wireless communication systems in such fading model, the envelopes of the probability density function (pdf) and cumulative distribution function (cdf) must be obtained. To this end, simple and the general closed-form expressions for the pdf and cdf of the product of two independent and non-identically distributed (i.n.i.d.) α - μ variates are obtained. Then based on these expressions, we derive closed-form expressions for the outage probability, the average symbol error probability (SEP) and the nth moment of the signal-to-noise ratio (SNR), and the ergodic channel capacity. The derived expressions are then used to analyse the performance of a wireless communication system. Analytical results are sustained through Monte-Carlo simulations, and a perfect match is reported over a wide range of SNR values and for several values of fading parameters.

Online Throughput Maximization for Energy Harvesting Communication Systems with Battery Overflow

Energy harvesting communication system enables energy to be dynamically harvested from natural resources and stored in capacitated batteries to be used for future data transmission. In such a system, the amount of future energy to harvest is uncertain and the battery capacity is limited. As a consequence, battery overflow and energy dropping may happen, causing energy underutilization. To maximize the data throughput by using the energy efficiently, a rate-adaptive transmission schedule must address the trade-off between a high-rate transmission which avoids energy overflow and a low-rate transmission which avoids energy shortage. In this paper, we study an online throughput maximization problem without knowing future information. To the best of our knowledge, this is the first work studying the fully-online transmission rate scheduling problem for battery-capacitated energy harvesting communication systems. We consider the problem under two models of the communication channel, a static channel model that assumes the channel status is stable, and a fading channel model that assumes the channel status varies. For the former, we develop an online algorithm that approximates the offline optimal solution within a constant factor for all possible inputs. For the latter, that the channel gains vary in range $[h_{min},h_{max}]$ , we propose an online algorithm with a proven $\Theta (\log (\frac{h_{max}}{h_{min}}))$ -competitive ratio. Our simulation results further validate the efficiency of the proposed online algorithms.

Blind FrFT-OFDM signal parameters estimation for underlay cognitive radio based on second-order cyclo-stationarity feature

Fractional Fourier transform (FrFT) OFDM scheme has been proposed previously in order to alleviate the problem of high peak to average power ratio (PAPR) of OFDM and its immunity against inter carrier interference. The cyclo-stationarity property of FrFT-OFDM is often neglected in the literature. In this paper, this missing analysis is provided and a blind algorithm for FrFT-OFDM signal parameters estimation is proposed. Novel mathematical formulas for the autocorrelation function of the FrFT-OFDM signal over both AWGN and fading channels are derived. These mathematical formulas show that the FrFT-OFDM signal has a cyclo-stationarity property. Also, novel mathematical formulas are derived for cyclic autocorrelation function of the FrFT-OFDM signal over both AWGN and fading channel models. Simulation results for the cyclic autocorrelation function show that signal detection and parameters estimation based on FrFT-OFDM cyclo-stationarity are feasible. The case of underlay cognitive radio is also investigated.

Modeling of Non-WSSUS Double-Rayleigh Fading Channels for Vehicular Communications

This paper deals with the modeling of nonstationary time-frequency (TF) dispersive multipath fading channels for vehicle-to-vehicle (V2V) communication systems. As a main contribution, the paper presents a novel geometry-based statistical channel model that facilitates the analysis of the nonstationarities of V2V fading channels arising at a small-scale level due to the time-varying nature of the propagation delays. This new geometrical channel model has been formulated following the principles of plane wave propagation (PWP) and assuming that the transmitted signal reaches the receiver antenna through double interactions with multiple interfering objects (IOs) randomly located in the propagation area. As a consequence of such interactions, the first-order statistics of the channel model’s envelope are shown to follow a worse-than-Rayleigh distribution; specifically, they follow a double-Rayleigh distribution. General expressions are derived for the envelope and phase distributions, four-dimensional (4D) TF correlation function (TF-CF), and TF-dependent delay and Doppler profiles of the proposed channel model. Such expressions are valid regardless of the underlying geometry of the propagation area. Furthermore, a closed-form solution of the 4D TF-CF is presented for the particular case of the geometrical two-ring scattering model. The obtained results provide new theoretical insights into the correlation and spectral properties of small-scale nonstationary V2V double-Rayleigh fading channels.

Second-Order Statistics for Indoor Wireless Joint Fading/Shadowing Channels

In this letter, we consider the joint fading and two-path shadowing (JFTS) channel model, which has been found suitable for characterizing indoor large open office environments with low mobility and stationary users. We derive useful expressions of fundamental channel statistics such as the number of level crossings in time, frequency, and space as well as average fade duration, bandwidth, and length for the JFTS faded/shadowed link. We also compare numerical results and their impact on system design over a variety of realistic propagation scenarios, which can be modeled by varying the JFTS parameters.

A Novel Non-Stationary Multipath Fading Channel Model Based on Propagation Measurements Using SDR and FPGA

A Novel Non-Stationary Multipath Fading Channel Model Based on Propagation Measurements Using SDR and FPGA

A Novel Non-Stationary Multipath Fading Channel Model Based on Propagation Measurements Using SDR and FPGA

A Novel Non-Stationary Multipath Fading Channel Model Based on Propagation Measurements Using SDR and FPGA

Network Service Method under Cloud Environment of Wireless Sensor Networks in Disaster Situation

The sensor networks are characterized by tiny, inexpensive, and advanced communication technology. However, wireless ad-hoc sensor networks (WASNs) have some issues such as the limited amount of energy, multipath fading, and some other issues when they applied in disaster situations. For reducing power consumption, we show mathematical analysis of energy saving, and enhanced error symbol probability. The simulation results prove our analysis. As for the multipath fading, we also show the mathematical analysis of fading channel characteristics and channel model, as well as how to mitigate the multipath fading by modulation and diversity techniques. From the simulation results, we prove the proposed system with amplify-and-forward (AF) relaying can achieve a 2.5 dB performance gain the BER 10-4 whereas the achievable improvement is almost a 4 dB at the BER 10-5 when using maximal ratio combining.

Study on performance of coherent orthogonal frequency division multiplexing system in exponential atmospheric turbulent channel

We analyze the performance of a coherent orthogonal frequency division multiplexing (OFDM) system and a serial decode and forward relay transmission multihop coherent free-space optical OFDM system using an exponential distribution atmospheric turbulence model under the circumstance of strong atmospheric turbulence. The attenuation of the atmospheric channel fading model mainly considers the light intensity scintillation caused by atmospheric turbulence and interaction between the path consumption, the transmitter and the receiver. The OFDM signal mapping method uses quadrature amplitude modulation. We also derive the formulas of the outage probability and symbol error rate of the coherent OFDM and multihop system, respectively, under the conditions described above. In addition, a simulation is performed, which is essential to evaluate the influence of key factors including coherent detection in a number of relay nodes, the mapping orders, and the number of subcarriers, which have a significant effect on the outage performance and the bit error performance of the OFDM-FSO system under the strong atmospheric turbulence.

A New Simulation Model of Rician Fading Channel

In this paper, a new simulation model of Rician fading channel is proposed. Based on an existing Rayleigh fading channel model, the new Rician model takes a zero-mean sinusoid with random phase as its line-of-sight component. First, the statistical properties of the new model are analyzed. It is shown that the probability density function of the Rician fading envelope and phase are independent of time, and they are in accordance with the reference model. The simulation results show that the second-order statistics of the new model approach the reference model and one existing Rician model with a small finite number of propagation paths and any Rician factor.

Cross‐layer queueing analysis for aggregated ON–OFF arrivals with adaptive modulation and coding

Packet loss and delay in wireless networks is a function of both the traffic characteristics (e.g. load, burstiness) and the characteristic behaviour of the fading channel. In this study, the authors propose and analyse a new queue model in which the server process is controlled by the adaptive modulation and coding (AMC) algorithm, and with aggregated ON–OFF packet arrivals to a finite buffer. In the scenarios, where users require multiple services, aggregated ON–OFF arrivals approximate bursty behaviour better than the Poisson arrivals analysed in many earlier queueing models. They focus on the packet drop probability, the packet loss probability, the average queueing delay and the throughput, showing significant differences in these metrics between the cross-layer models using aggregated ON–OFF arrivals and Poisson arrivals. This indicates that in wireless packet network performance evaluation, the traffic model is at least as important as the effect of the fading channel modelling.

Optimizing Unlicensed Spectrum Sharing for LTE-U and WiFi Network Coexistence

Long-term evolution in unlicensed spectrum (LTE-U) is an emerging technology for expanding cellular network capacity without additional spectrum cost. This paper investigates effective spectrum sharing for coexisting Wi-Fi and LTE-U services. Based on a novel hyper access point (HAP) we introduced for effectively embedding LTE-U in unlicensed Wi-Fi band, LTE-U can directly take advantage of the Wi-Fi point coordination function protocol. To facilitate the coexistence, our HAP dedicates a contention-free period to LTE-U users and allows a contention period (CP) for traditional Wi-Fi users. We investigate the optimization of joint user association and resource allocation to further improve system throughput and user fairness. We formulate a network utility maximization problem based on the Nash bargaining solution (NBS), for which we derive a closed-form expression for the optimal CP length under a given user association. We analyze this NBS-based utility maximization and the performance of the proposed algorithm under log-normal fading, Rayleigh fading, and Rician fading channel models, respectively. Our numerical results corroborate our analysis and demonstrate effective improvement of the system performance by the proposed HAP algorithm against traditional LTE-U deployment.

Statistical Modeling and Simulation of Short-Range Device-to-Device Communication Channels at Sub-THz Frequencies

A 2-D geometrical propagation model for short-range device-to-device desktop communication channels at sub-terahertz (sub-THz) frequencies is proposed. Based on the geometrical model, a parametric reference model for short-range sub-THz multipath fading channels is developed. From the reference model, the corresponding frequency correlation function and the power delay profile (PDP) are derived and compared with the measured data. The results show good agreement between the measured and theoretical PDPs. Finally, a new sum-of-sinusoids-based simulation model for wideband sub-THz channels is proposed. The statistics of the reference model are verified by simulation. The results show that the simulation model is a good approximation of the reference model.

Design of complete software GPS signal simulator with low complexity and precise multipath channel model

The need for GPS data simulators have become important due to the tremendous growth in the design of versatile GPS receivers. Commercial hardware and software based GPS simulators are expensive and time consuming. In this work, a low cost simple novel GPS L1 signal simulator is designed for testing and evaluating the performance of software GPS receiver in a laboratory environment. A typical real time paradigm, similar to actual satellite derived GPS signal is created on a computer generated scenario. In this paper, a GPS software simulator is proposed that may offer a lot of analysis and testing flexibility to the researchers and developers as it is totally software based primarily running on a laptop/personal computer without the requirement of any hardware. The proposed GPS simulator allows provision for re-configurability and test repeatability and is developed in VC++ platform to minimize the simulation time. It also incorporates Rayleigh multipath channel fading model under non-line of sight (NLOS) conditions. In this work, to efficiently design the simulator, several Rayleigh fading models viz. Inverse Discrete Fourier Transform (IDFT), Filtering White Gaussian Noise (FWFN) and modified Sum of Sinusoidal (SOS) simulators are tested and compared in terms of accuracy of its first and second order statistical metrics, execution time and the later one is found to be as the best appropriate Rayleigh multipath model suitable for incorporating with GPS simulator. The fading model written in ‘MATLAB’ engine has been linked with software GPS simulator module enable to test GPS receiver’s functionality in different fading environments.

Joint Relay and Antenna Selection in MIMO PLNC Inter-vehicular Communication Systems over Cascaded Fading Channels

We investigate the joint relay and antenna selection performance in a multiple input multiple output (MIMO) Vehicle-to-Vehicle (V2V) communication system employing physical layer network coding (PLNC) with amplify-and-forward (AF) scheme at the relay antenna. Analytic results are derived under the cascaded Nakagami-m fading channel model assumption, which covers cascaded Rayleigh and conventional cellular channel models as well. We evaluate the performance of the system in terms of joint outage probability of sources and derive closed-form expressions for lower and upper bounds while an exact expression is found as a single integral form. Besides, the asymptotic diversity order is analyzed and quantified as a function of number of relays and antennas installed on the source and relay vehicles, and channel parameters. Finally, we verify the analytic derivations by computer simulations. Our results show that the outage probability performance decreases with the increasing cascading degrees of the channels but joint relay and antenna selection enhances the performance of the system superbly with the increasing number of relays and antennas. Also it is shown throughout all the simulation results, the lower bound for the joint outage probability seems to consistently be well tight for large SNR. Therefore it can be used for practical design of inter-vehicular communication systems which contain multiple relays and antennas.

Outdoor FSO Communications Under Fog: Attenuation Modeling and Performance Evaluation

Fog is considered to be a primary challenge for free space optics (FSO) systems. It may cause attenuation that is up to hundreds of decibels per kilometer. Hence, accurate modeling of fog attenuation will help telecommunication operators to engineer and appropriately manage their networks. In this paper, we examine fog measurement data coming from several locations in Europe and the United States and derive a unified channel attenuation model. Compared with existing attenuation models, our proposed model achieves a minimum of 9 dB, which is lower than the average root-mean-square error (RMSE). Moreover, we have investigated the statistical behavior of the channel and developed a probabilistic model under stochastic fog conditions. Furthermore, we studied the performance of the FSO system addressing various performance metrics, including signal-to-noise ratio (SNR), bit-error rate (BER), and channel capacity. Our results show that in communication environments with frequent fog, FSO is typically a short-range data transmission technology. Therefore, FSO will have its preferred market segment in future wireless fifth-generation/sixth-generation (5G/6G) networks having cell sizes that are lower than a 1-km diameter. Moreover, the results of our modeling and analysis can be applied in determining the switching/thresholding conditions in highly reliable hybrid FSO/radio-frequency (RF) networks.