Weibull Fading Channels Research Articles

On the performance of 2[formula omitted]2 DF relay mixed RF/FSO airborne system over Exponentiated Weibull fading channel

This paper discuses the performance of a mixed free space optical (FSO)/radio frequency (RF) airborne communication system which consists of a dual-input dual-output (DIDO) relay based on decode-and-forward (DF), single-antenna RF transmitter, and single-aperture optical receiver. The Nakagami-m fading channel and exponentiated Weibull fading channel are adopted for the RF channel and FSO link, respectively. The analytical expressions of probability density function (PDF) and cumulative distribution function (CDF) about the equivalent signal-to-noise ratio (SNR) are obtained. We also analyze the average bit-error-rate and outage probability of the mixed FSO/RF system and derive closed form expressions by the Meijer’s G function. To further verify the performance of the system, we simulate to compare the performance of the DIDO and single-input single-output (SISO) relay-based communication systems. The DIDO relay-based system outperforms the SISO relay system.

Analysis and Optimization Study of Antenna Selection in Dual Hop Relay Networks over Weibull Fading Channels

Field experiments show that Weibull distribution can be considered as the most suitable distribution to model weak to high signal power levels in indoor and outdoor environments. Recently, Exponentiated Weibull which is a special case of Weibull fading, have been widely adopted in free-space optical communication systems to model weak and high levels of turbulence effects. Motivated from the increasing use of Weibull distribution, this paper studies the popular dual-hop amplify-and-forward relay network with joint transmit and receive antenna selection where closed form ergodic capacity, symbol error rate and outage probability expressions are derived for Weibull fading channels. With the help of high SNR analysis, diversity gain, array gain and optimum relay location are obtained. Finally, theoretical findings are validated by simulation results.

Impact of pointing errors on the SER performance of free space optical communication system with two decision thresholds over exponentiated Weibull fading channels

The impact of pointing errors on the symbol error rate (SER) performance of multiple pulse-position modulation (MPPM) free space optical (FSO) system with optimized decision threshold (ODT) and dynamic decision threshold (DDT) is investigated over exponentiated Weibull atmospheric turbulence channels. The probability density function (PDF) of the aggregated channel model is derived on the basis of Meijer’s G-function and the closed-form SER expression is then obtained by Gauss–Laguerre quadrature function. The variations of SER performance with different jitter variances, beam width, aperture sizes, and turbulence strengths for these two decision threshold schemes are analyzed in detail. The study shows that the impact of jitter variances is more apparent for ODT than that for DDT scheme and the performance difference between ODT and DDT schemes decreases with the increase of beam width. Monte Carlo simulation is also provided to verify the correctness of the proposed SER models. This work is beneficial to the design of FSO system.

The effects of different noise types and mobility on error rate of digital modulation schemes over millimeter-wave Weibull fading channels

Millimeter (mm-wave) communication is a prominent candidate to support the evolution towards fifth generation (5G) wireless systems. As such, in this paper, we study the impact of different noise type and mobility on the performance of coherent binary digital modulation schemes in mm-wave Weibull fading channels. To this end, exact and new closed-form expressions are derived for the bit error rate of coherent digital modulation schemes in millimeter wave Weibull fading channels in the presence of additive non-Gaussian noise. In addition, new and exact closed-form expressions are obtained for the symbol error rate of square M-ary quadrature amplitude modulation scheme (M-AQM). The derived expressions take into consideration the mobility of the wireless receives. Besides, they are valid for integer and non-integer values of the fading and noise shaping parameters. Analytical results are supported by Monte-Carlo simulations to validate the accuracy of the obtained results.

Image transmission performance of direct sequence code division multiple access communication systems in Weibull fading channels

Image transmission performance of direct sequence code division multiple access communication systems in Weibull fading channels

On the performance of dual-hop mixed RF/FSO wireless communication system in urban area over aggregated exponentiated Weibull fading channels with pointing errors

The performance of decode-and-forward dual-hop mixed radio frequency / free-space optical system in urban area is studied. The RF link is modeled by the Nakagami-m distribution and the FSO link is described by the composite exponentiated Weibull (EW) fading channels with nonzero boresight pointing errors (NBPE). For comparison, the ABER results without pointing errors (PE) and those with zero boresight pointing errors (ZBPE) are also provided. The closed-form expression for the average bit error rate (ABER) in RF link is derived with the help of hypergeometric function, and that in FSO link is obtained by Meijer’s G and generalized Gauss–Laguerre quadrature functions. Then, the end-to-end ABERs with binary phase shift keying modulation are achieved on the basis of the computed ABER results of RF and FSO links. The end-to-end ABER performance is further analyzed with different Nakagami-m parameters, turbulence strengths, receiver aperture sizes and boresight displacements. The result shows that with ZBPE and NBPE considered, FSO link suffers a severe ABER degradation and becomes the dominant limitation of the mixed RF/FSO system in urban area. However, aperture averaging can bring significant ABER improvement of this system. Monte Carlo simulation is provided to confirm the validity of the analytical ABER expressions.

The effect of Weibull fading channel on cooperative spectrum sensing network using an improved energy detector

This paper analyses the performance of proposed cooperative spectrum sensing (CSS) network in Weibull fading environment. First, we have derived the novel analytic expressions for probabilities of missed detection and false alarm in Weibull fading channel, assuming an improved energy detector (IED), selection combining diversity scheme and multiple antennas at each cognitive radio (CRs). Next, performance is analyzed using complementary receiver operating characteristics curves, total error rate, average channel throughput, and network utility function curves for the proposed CSS network. The optimal performance of CSS network is achieved by optimizing the CSS network parameters. The closed form of expressions for the optimum value of number of CRs, arbitrary power of received signal, and detection threshold at each CR are derived using OR-Rule and AND-Rule at fusion center (FC). The average channel throughput and network utility function analysis are evaluated using $$k=1+n$$ and $$k=N-n$$ fusion rules at FC. Finally, the impact of several network parameters such as, multiple antennas at each CR (M), number of CRs (N) in CSS network, Weibull fading parameter (V), arbitrary power of received signal (p), and sensing channel SNR ( $${\bar{\gamma }})$$ on the performance of proposed CSS network are investigated using the simulation results. The performance comparison between conventional energy detector and an IED has been highlighted with the simulations.

ABER Performance of LDPC-Coded OFDM Free-Space Optical Communication System Over Exponentiated Weibull Fading Channels With Pointing Errors

A low-density parity-check (LDPC)-coded free space optical (FSO) orthogonal frequency-division multiplexing (OFDM) communication system over aggregated exponentiated Weibull (EW) fading channels with pointing errors considered is investigated. On the basis of the probability density function and cumulative distribution function of the composite channel gain, the analytical expressions of average bit error rate (ABER) of this FSO-OFDM system with on–off keying, K -ary quadrature amplitude modulation (QAM) and phase shift keying (PSK) modulation schemes are derived by using generalized Gauss–Lagurre quadrature rule, respectively. Monte Carlo simulations are provided to verify the validity of these three expressions. Furthermore, LDPC codes are applied in the simulation to improve the ABER performance. The results show that the ABER performance of 16-QAM-OFDM is better than that of the 16-PSK-OFDM system over composite EW fading channels, regardless of the turbulence strengths. For the modulation schemes involved, the degradation due to the increase of atmospheric turbulence strength for turbulence only scenario is more severe when compared with pointing errors included case. The study also demonstrates that significant coding gain improvement can be achieved by LDPC codes over EW fading channels, especially under strong turbulence condition. With pointing errors, more coding gain can be obtained when the jitter increases or beamwidth decreases.

Performance Analysis of Cooperative Spectrum Sensing Network Using Optimization Technique in Different Fading Channels

Spectrum sensing is an important task to find out the spectrum holes in a given radio spectrum. Spectrum sensing performance is improved with the aid of multiple cognitive radios (CRs) in the network and each CR having multiple antennas in different fading channels (Rayleigh, Hoyt and Weibull fading channel). In this paper, we have considered that each CR having multiple antennas and improved energy detector (IED) scheme is used for detection of primary user. Imperfect channel is considered between CRs and fusion center (i.e. in reporting channel) with an error probability rate (r). We have derived the novel expression for missed detection probability (P m ), closed form of expression to find out optimal value of number of CR users (N opt ), closed form of expression and procedure to find an optimal value of normalized threshold value (λ n,opt ), expression for optimal value of arbitrary power of received signal (P opt ) and calculation of minimum value of total error in different fading channels are provided. Performance is evaluated to find out (N opt ), (λ n,opt ), (P opt ) and to calculate minimum error value for various network parameters like SNR, r, λ n and multiple number of antennas (M). It is observed that detection performance is improved by using multiple antennas at each CR. Comparison between conventional energy detector and IED, comparison among Rayleigh, Hoyt and Weibull fading channels also provided for different cases of network parameters.

Improved Scheduling Mechanisms for Synchronous Information and Energy Transmission.

Wireless energy collecting technology can effectively reduce the network time overhead and prolong the wireless sensor network (WSN) lifetime. However, the traditional energy collecting technology cannot achieve the balance between ergodic channel capacity and average collected energy. In order to solve the problem of the network transmission efficiency and the limited energy of wireless devices, three improved scheduling mechanisms are proposed: improved signal noise ratio (SNR) scheduling mechanism (IS2M), improved N-SNR scheduling mechanism (INS2M) and an improved Equal Throughput scheduling mechanism (IETSM) for different channel conditions to improve the whole network performance. Meanwhile, the average collected energy of single users and the ergodic channel capacity of three scheduling mechanisms can be obtained through the order statistical theory in Rayleig, Ricean, Nakagami-m and Weibull fading channels. It is concluded that the proposed scheduling mechanisms can achieve better balance between energy collection and data transmission, so as to provide a new solution to realize synchronous information and energy transmission for WSNs.

Optimization Analysis of Improved Energy Detection based Cooperative Spectrum Sensing Network in Nakagami-m and Weibull Fading Channels

Optimization Analysis of Improved Energy Detection based Cooperative Spectrum Sensing Network in Nakagami-m and Weibull Fading Channels

Performance Modeling of Link Duration in Vehicular Ad Hoc Networks Under Weibull Fading Channel Conditions

This paper presents an analytical model for the probability density function of link duration in vehicular ad hoc networks by considering the vehicle-to-vehicle channel to undergo Weibull fading. Assuming free flow traffic state and the vehicle speed to be uniformly distributed, we analyse the dependence of various parameters on link duration and its PDF. We perform Kolmogorov–Smirnov test and establish that the probability distribution of link duration can be approximated as exponential.

PERFORMANCE COMPARISON OF DUAL-BRANCH AND TRIPLE-BRANCH SELECTION DIVERSITY RECEIVER BASED ON DESIRED SIGNAL ALGORITHM OVER CORRELATED WEIBULL FADING CHANNELS

As an important performance measure, in this paper the outage probability of dual- and triple-branch selection combining (SC) diversity system is compared. The analyzed system works over correlated Weibull fading channels in the presence of cochannel interference (CCI) where the output signal choice is done using desired signal algorithm. Results are graphically presented showing the influence of number of diversity branches, correlation coefficient and ratio of average powers of desired and interference signal.

Cooperative IDMA systems with regenerative relays over Weibull fading channels: outage probability and error analysis

Cooperative communications has recently been introduced into multiple-access networks to combat the signal attenuation caused by fading and therefore improve the network performance. This study proposes the outage probability and error analysis of cooperative interleave-division multiple-access (IDMA) networks with regenerative relays over Weibull fading channels. The main contribution of this study relies on deriving a moment-generating function (MGF) of the total signal-to-noise ratio with the help of Pade approximation for IDMA with regenerative relaying. The derived MGF expression is employed to evaluate the outage probability of the considered system. Moreover, a closed-form asymptotic expression for the error probability of the considered system is derived and then comprehensive computer simulations have been performed to validate the accuracy of the authors’ analytical results. It is shown that results obtained by the proposed MGF and asymptotic error expressions are in good agreement with their corresponding simulation results.

Performance analysis for mixed FSO/RF Nakagami-m and Exponentiated Weibull dual-hop airborne systems

In this paper, the performances of mixed free-space optical (FSO)/radio frequency (RF) systems are presented based on the decode-and-forward relaying. The Exponentiated Weibull fading channel with pointing error effect is adopted for the atmospheric fluctuation of FSO channel and the RF link undergoes the Nakagami-m fading. We derived the analytical expression for cumulative distribution function (CDF) of equivalent signal-to-noise ratio (SNR). The novel mathematical presentations of outage probability and average bit-error-rate (BER) are developed based on the Meijer's G function. The analytical results show an accurately match to the Monte-Carlo simulation results. The outage and BER performance for the mixed system by decode-and-forward relay are investigated considering atmospheric turbulence and pointing error condition. The effect of aperture averaging is evaluated in all atmospheric turbulence conditions as well.

A tight approximate analytical framework for performance analysis of equal gain combining receiver over independent Weibull fading channels

In this paper, a method for approximating the probability distribution of sum of independent and identical Weibull random variables is adopted to analyze the performance of equal gain combiner (EGC) receiver over non-identical Weibull fading channel (WFC). Our main result is to derive a generalized expression of the probability density function (PDF) of the signal-to-noise ratio (SNR) at the EGC output in the case of non-identical WFC. Based on this PDF, accurate approximation of significant performance criteria, such as outage probability (OP), the amount of fading (AoF), and average symbol/bit error probability (ASEP/ABEP), are derived. In addition, we derived the analytical expressions for channel capacities under various adaptation policies such as optimal rate adaptation (ORA), optimal simultaneous power and rate adaptation (OPRA), channel inversion with fixed rate (CIFR), and truncated channel inversion with fixed rate (TCIFR). The proposed mathematical analysis is complemented by several numerical results and validated using Monte Carlo simulation method.

Symbol error rate performance analysis of soft-decision decoded MPPM free space optical system over exponentiated Weibull fading channels

The symbol error rate (SER) performance of a multipulse pulse-position modulation (MPPM) free space optical (FSO) system under the combined effect of turbulence-induced fading modeled by exponentiated Weibull (EW) distribution and pointing errors with a soft-decision detector is investigated systematically. Particularly, the theoretical conditional SER (CSER) of soft-decision decoded MPPM is derived. The corresponding closed-form CSER is obtained via curve fitting with the Levenberg–Marquardt method. The analytical SER expression over the aggregated fading channels is then achieved in terms of Laguerre integration. Monte Carlo simulation results are also offered to corroborate the validity of the proposed SER model.

Impact of nonzero boresight pointing errors on the performance of a relay-assisted free-space optical communication system over exponentiated Weibull fading channels.

The impact of nonzero boresight pointing errors on the system performance of decode-and-forward protocol-based multihop parallel optical wireless communication systems is studied. For the aggregated fading channel, the atmospheric turbulence is simulated by an exponentiated Weibull model, and pointing errors are described by one recently proposed statistical model including both boresight and jitter. The binary phase-shift keying subcarrier intensity modulation-based analytical average bit error rate (ABER) and outage probability expressions are achieved for a nonidentically and independently distributed system. The ABER and outage probability are then analyzed with different turbulence strengths, receiving aperture sizes, structure parameters (P and Q), jitter variances, and boresight displacements. The results show that aperture averaging offers almost the same system performance improvement with boresight included or not, despite the values of P and Q. The performance enhancement owing to the increase of cooperative path (P) is more evident with nonzero boresight than that with zero boresight (jitter only), whereas the performance deterioration because of the increasing hops (Q) with nonzero boresight is almost the same as that with zero boresight. Monte Carlo simulation is offered to verify the validity of ABER and outage probability expressions.

A very tight approximate results of MRC receivers over independent Weibull fading channels

In this paper, we study the performance of L-branch maximal-ratio combining (MRC) receivers operating over independent Weibull-fading channels. Our main result is a very tight approximation of the probability density function (PDF) of the signal-to-noise ratio (SNR) at the output of the combiner. Based on this result, accurate approximation of significant performance criteria, such as outage probability and average symbol error rate (ASER) are derived. We also evaluate the average bit error rate (ABER) for several coherent and non-coherent modulation schemes, using a closed-form expression for the moment-generating function (MGF) of the output SNR for MRC receivers. In addition, we derive some analytical expressions for channel capacity under various adaptation policies such as optimal rate adaptation (ORA), Optimal simultaneous power and rate adaptation (OPRA), Channel inversion with fixed rate (CIFR), and Truncated channel inversion with fixed rate (TCIFR). The proposed mathematical analysis is complemented by numerous numerical results, which point out the effects of fading severity on the overall system performance. Computer simulations are also performed to verify the validity and the accuracy of the proposed theoretical approach.

Outage performance of multihop free-space optical communication system over exponentiated Weibull fading channels with nonzero boresight pointing errors

The outage performance of the multihop free-space optical (FSO) communication system with decode-and-forward (DF) protocol is studied by considering the joint effects of nonzero boresight pointing errors and atmospheric turbulence modeled by exponentiated Weibull (EW) distribution. The closed-form analytical expression of outage probability is derived, and the results are validated through Monte Carlo simulation. Furthermore, the detailed analysis is provided to evaluate the impacts of turbulence strength, receiver aperture size, boresight displacement, beamwidth and number of relays on the outage performance for the studied system.