Mehmet Bilim

Outage Probability Analysis of Dual-Hop Decode-and-Forward Relaying Over Mixed Rayleigh and Generalized Gamma Fading Channels

In this letter, outage probability of dual-hop decode-and-forward (DF) relaying scheme is analyzed over mixed Rayleigh and generalized Gamma fading channels. Cooperation model considered in this work consists of a source, a relay and a destination. It is assumed that source-relay and relay-destination channels experience Rayleigh fading and generalized Gamma fading, respectively. Exact outage probability expression is derived and outage performance is illustrated for both direct transmission and DF relaying scheme.

A Closed-Form Approximate BEP Expression for Cooperative IDMA Systems over Multipath Nakagami-

In this letter, a closed-form approximate bit error probability (BEP) expression is derived for cooperative interleave-division multiple access systems with decode-and forward relaying subject to multipath Nakagami-m fading channels. The BEP expression is obtained by using the exponential-type approximation of Gaussian Q-function. Then, the derived expression is used to analyze system performance for different parameters, such as number of relays and Nakagami-m fading parameter. The accuracy of theoretical derivation is extensively validated through comprehensive computer simulations. It is shown that the results obtained by the proposed expression are in well agreement with the simulation results.

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In an interleave-division multiple access (IDMA) system, interleavers have a crucial role for the system performance. This paper presents a new approach to random interleavers for traditional IDMA systems. The proposed interleaver uses a random variable which is defined by Rayleigh distribution for mapping. Simulation results demonstrate that the proposed interleaver approach improves the bit-error rate (BER) performance of the IDMA systems.

Fading Channels

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.

A new approach to random interleavers for traditional IDMA systems

In this paper, the performance of amplify-and-forward (AF) cooperative diversity is analyzed over asymmetric fading channels. The source–relay and the relay–destination links experience Rayleigh fading while the source–destination link is subject to generalized Gamma fading. First, the probability density function (PDF) and the moment generating function (MGF) of the source–relay–destination link and the MGF of the source–destination link are derived. Then, the symbol error rate (SER) is determined based on the MGF of the total end-to-end signal-to-noise ratio (SNR). Moreover, the SER performance of N-relay assisted AF cooperative diversity is illustrated for M-ary phase shift keying (M-PSK) and M-ary quadrature amplitude modulation (M-QAM). Based on the derived MGF expressions, the numerical results are obtained by varying the modulation types and channel parameters for different scenarios.

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

In this paper, a closed-form expression for the moment generating function (MGF) of the instantaneous signal to noise ratio (SNR) per symbol is derived for Weibull fading channels. The derived MGF is valid for the rational values of fading parameter and it is shown to be useful for analyzing the symbol error rate for the case of M-ary phase shift keying and M-ary quadrature amplitude modulation schemes. Also, the outage probability can be accurately evaluated by using the probability density function of instantaneous SNR considered in this work.

SER Performance of Amplify-and-Forward Cooperative Diversity Over Asymmetric Fading Channels

In this paper, approximate outage probability (OP) and average symbol error rate (SER) of cooperative direct-sequence code-division multiple access (DS-CDMA) systems with amplify-and-forward (AF) relaying are evaluated over asymmetric fading channels. Practically, the channels between source (S), relay (R) and destination (D) nodes in a DS-CDMA system can be subject to different fading due to the nature of wireless medium. Motivated by this reality, the SD path is assumed to be Nakagami-m distributed which is a general fading model for different types of channel conditions while SR and RD paths are considered to experience Rician fading in order to include line of sight conditions. First, closed-form solutions are obtained for both the cumulative distribution function and the probability density function of SRD paths. Then, a closed-form total moment generating function (MGF) of the considered system is derived. The lower bound of the OP is calculated with the help of the inverse Laplace transform of the derived MGF expression while average SER is analyzed by evaluating the integral over the derived MGF. Finally, an asymptotic MGF expression is proposed for high signal-to-noise ratio (SNR) analysis of AF DS-CDMA systems. The simulation results are provided to verify the correctness of the analytical derivations. It is shown that the approximate OP and average SER results are in well agreement with the simulations and the asymptotic results are tight from medium to high SNR regime.

A Closed-Form MGF Expression of Instantaneous SNR for Weibull Fading Channels

The inverse cumulative distribution function (CDF) appears in many important problems such as outage probability calculations in wireless communications. The Nakagami-m inverse CDF is difficult to compute numerically and is known to have no closed form. In this paper, we present a new and useful approximation to the Nakagami-m inverse CDF. The genetic algorithm is applied to optimize the coefficients of the proposed approximation. For typical cases in Nakagami-m wireless communication channels, it is shown through comprehensive computer simulations that the proposed method has high accuracy in most of the region of the exact CDF values.

Average symbol error rate and outage probability of DS-CDMA systems with AF relaying over asymmetric fading channels

A new multiple access technique so-called Interleave-Division Multiple Access (IDMA) is proposed for spread spectrum communications systems in recent years. Assignment of interleaver has an important role for the performance of IDMA technique. For that purpose, various structures of interleaver is proposed for IDMA in the literature. In this study, the bit error rate (BER) performance of the IDMA systems is investigated for Weibull interleaver which is a new random interleaver approach. Also the performance of mixed interleaver which was used for turbo codes previously is presented in IDMA systems. Simulation results show that the BER performance of Weibull interleaver mostly outperforms the Mixed and Random interleavers when the number of simultaneous user is large.

A New Nakagami-m Inverse CDF Approximation Based on the Use of Genetic Algorithm

In this work, outage probability of amplify-and-forward direct-sequence code-division multiple-access systems is derived with full selection diversity for α-η-μ fading channels. First, cumulative distribution function of α-η-μ distribution is derived and then, lower bound of the outage probability is obtained for the considered system. The outage probability performance of the considered system is presented for different number of relays and values of fading parameter with simulation results.