Ibrahim Y. Abualhaol

Survey on device-to-device communications: Challenges and design issues

Device-to-Device (D2D) communications has been proposed to cellular networks in order to optimize spectrum efficiency and resources utilization. In D2D-assisted networks, the traditional cellular communication techniques are not applicable but rather need to be redesigned to fulfill new requirements. Therefore, new communication techniques are proposed to take the advantages of the D2D connectivity in the network. In this paper, we describe the concept of D2D communications. Then, we review the main challenges and design issues of D2D-assisted networks. This survey focuses on cooperative communications in D2D-assisted networks and addresses challenges which limit the performance of the cooperative D2D-assisted networks such as relay selection, power consumption and multi-casting. Moreover, design issues and approaches to overcome these limitations are explained.

Capacity Analysis of MIMO System Over Identically Independent Distributed Weibull Fading Channels

The capacity of multiple input multiple output (MIMO) system over wireless channels has been investigated analytically and by simulation over different types of wireless fading channels, such as Rayleigh and Nakagami-m fading channels. The capacity of MIMO system over Weibull fading channels has not been considered in the literature before because of the complexity in obtaining closed form expressions for either the probability of outage capacity or the average capacity. In this paper, finite mixture (FM) with expectation-maximization (EM) algorithm is utilized to derive simple approximate expression for the probability density function (pdf) of the capacity distribution over identically independent distributed (iid) Weibull fading channels. This approximation converts the complicated capacity distribution to a simple weighted sum of univariate normal distributions with appropriate weighting coefficients, means, and variances for a predefined system model and channel statistics. The resultant approximation simplifies the mathematical analysis of the average capacity and the outage capacity in terms of well known Q-functions.

Generalized average BER expression for SC and MRC reciever over Nakagami-m fading channels

This paper presents simple and accurate approximation of the normalized incomplete upper and lower gamma functions that frequently appear in Nakagami-m fading channels. Based on the proposed approximation and in conjunction with the approximation of the Q-function proposed by Chiani, Dardari, and Simon [1], simple and accurate generalized closed-form expressions for the average Bit Error Rate (BER) over Nakagami-m fading channels are derived for Selection Combining (SC) and Maximum Ratio Combining (MRC) receivers for any number of diversity branches. The derived expressions are applicable for any coherent modulation scheme with any constellation order for both Rayleigh and Nakagami-m fading channels. Monte Carlo simulation of the average BER curves for both SC and MRC using different digital modulation schemes with different constellation order over Nakagami-m fading channels are compared with the closed-forms. The closed-forms numerical results coincide with the Monte Carlo simulation for different values of the fading parameter m. These expressions are simple and can be used to analyze the average BER over Nakagami-m fading channels with high accuracy.

Outage Probability Analysis in a Cooperative UAVs Network Over Nakagami-m Fading Channels

The outage probability in a network of cooperative unmanned airborne vehicles (UAVs) is studied analytically. A master-slave topology with one ground control unit (GCU) is assumed where the GCU communicates directly with a master UAV. The master-slave and master-GCU links are assumed to satisfy a certain minimum data rate required by the application provided by the UAV. The outage probability of the system is defined as the probability that either the rate of transmission over any of the links drops below the predefined minimum value for that link, or the GCU-master link is not able to transmit the aggregate data from all UAVs besides the minimum rate achieved by the master UAV itself. The outage probability is considered over Nakagami-m fading channels. The resultant expression for the outage probability can be used to provide guidelines for system designers to minimize the outage probability of the cooperative UAVs network. In the same time, it could be used to maximize the system throughput with the constraint of not exceeding a certain outage probability limit.

General BER analysis over Nakagami-m fading channels

Based on the approximated expression of the Q-function by Chiani, Dardari, and Simon, a simple and accurate generalized closed-form expression for the bit error rate (BER) over Nakagami-m fading channel is derived. The expression is given as a product of the well-known gamma function and a finite sum of functions of the Nakagami-m fading parameter. The derived expression is applicable for any real m ≥ 0.5, and for any coherent modulation scheme of any order. Numerical results are used to validate the derived expressions using different combinations of modulation orders and Nakagami-m fading parameters.

Performance analysis of cooperative multi-carrier relay-based UAV networks over generalized fading channels

The outage probability in a network of cooperative unmanned airborne vehicles (UAVs) over generalized fading channels is studied analytically using finite mixture with expectation maximization technique. A relay-based topology with one ground control unit (GCU) is considered, where the cooperative UAVs can communicate with the GCU directly or through relay. The application the UAV is assigned for specifies the minimum required transmission rate the UAV should achieve. The outage probability of the system is defined as the probability that either the transmission rate over any of the links drops below a predefined minimum threshold for that link or the Relay-GCU link is not able to transmit the aggregate data from all relayed UAVs and the minimum rate required by the relay UAV itself. Throughout the paper, expressions for the outage probability and the average achievable bit rate of a cooperative multi-carrier system are derived over generalized fading channels. Finite mixture with expectation maximization algorithm is utilized to derive a simple approximate expression for the probability density function (pdf) of the achievable bit rate assuming adaptive M-ary quadrature amplitude modulation (M-QAM). This pdf is used to derive closed-form expressions for the outage probability and the average bit rate. Copyright

Subchannel-Division Adaptive Resource Allocation Technique for Cooperative Relay-Based MIMO/OFDM Wireless Communication Systems

In this paper, we propose cooperative division relay- based allocation technique jointly with adaptive bit/power loading for multiple-input-multiple-output/orthogonal frequency division multiplexing (MIMO/OFDM) system. In this cooperative division technique, the transmitted stream of bits is divided into two parts. The first part is sent directly from the source to the destination, whereas the second part is relayed to the destination through an indirect link. The sub-channel division is jointly optimized with adaptive bit/power loading among different sub-channels to maximize the overall MIMO/OFDM received signal in the relay- based system according to the channel state information (CSI). The bit error rate (BER) performance using this cooperative division technique is presented and compared with non-cooperative one. The use of this type of cooperative technique in relay- based MIMO/OFDM system has shown high BER performance improvement. Such improvement comes from the fact that this technique jointly with adaptive bit/power loading, in relay-based system, enables us to exploit the inherent system diversities in the frequency, space, and time to maximize the system power efficiency, and to guarantee the fulfillment of the required quality of service (QoS) including BER and transmission rate. It is noticed that the advantage of cooperation in terms of BER increases as the order of MIMO system increases.

Throughput optimization of cooperative UAVs using adaptive channel assignment

The wireless link represents the bottleneck in the communication of a group of cooperative unmanned airborne vehicles (UAVs). Due to the high speed of the UAVs, the nature of the environments where they are usually deployed and the possible intentional jamming that might exist, the effect of phenomena such as multipath propagation and Doppler spread is more pronounced. In this paper, we propose an adaptive channel assignment (ACA) strategy for allocating the available bandwidth, which is divided into a number of sub-channels, over a number of communications links in a network of UAVs. The proposed ACA algorithm has two main advantages over the static channel assignment (SCA) approach. First, it maximizes the overall throughput of the UAVs network and second, it significantly reduces the probability of outage in the system defined as the percentage of time the links are incapable of supporting a minimum required transmission rate that is determined by the application. The ACA approach is formulated in terms of a binary optimization problem that is solved using the branch-and-bound method. We assume that the links in the network are Rayleigh faded and we use a finite state Markov chain (FSMC) for their modeling. Using Monte Carlo simulations, we show that the proposed channel assignment approach provides a significant gain in the overall throughput and reduction in the outage probability compared to the SCA

Enhanced channel estimation technique in MIMO-OFDM system

Multiple Input Multiple Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM), MIMO-OFDM, is considered as a spectrally efficient approach to achieve high throughput communications. This paper investigates the performance of MIMO-OFDM system using the proposed NLMS adaptive equalizer and the developed Singular Value Decomposition (SVD) technique in estimating the channel. The performances of using various values of the NLMS algorithms step-size were also investigated and an optimum value, based on a trade-off between the convergence speed and the steady state noise floor, was chosen. Then, the bit error rate (BER) performance of the NLMS adaptive receiver is compared with that of the SVD algorithm. It is clear that the SVD gives better performance over the NLMS adaptive filter.

Capacity analysis of cooperative relay-based communication system

In this paper, we consider the analysis of a cooperative relay-based amplify-and-forward system in terms of average and outage capacity over fading channels. We first optimize the relay gain with the objective of maximizing the received signal-to-noise-ratio (SNR) at the destination, given that the fading statistics of the links in the cooperative system are known at the relay node. The Gaussian finite mixture with an expectation maximization algorithm is utilized to approximate the fading pdf expression in a simple and unified closed-form for the pdfs of Rayleigh, Nakagami-m, and Weibull fading channels. Using this technique, the average capacity and the outage capacity are derived. Monte Carlo simulation results are presented to validate the derived expressions.