Ashraf Sharaqa

Performance evaluation of multiuser diversity in multiuser two-hop cooperative multi-relay wireless networks using maximal ratio combining over Rayleigh fading channels

Multiuser diversity MUD cooperative wireless networks combine the features of the MIMO systems without confronting the physical layer constraints by providing multiple copies of the transmitted signal from the source to the destination with the help of the relay node. Cooperative wireless networks have attracted the full attention in the last few years and are implemented widely in many wireless communication systems to adapt for the fading impairments, provide higher data rates, and improve the performance of the wireless communication systems. In this paper, we present an informative study for the reason of evaluating the performance of the MUD in the multiuser two-hop cooperative multi-relay networks using maximal ratio combining. Furthermore, we derive tight closed-form expressions of outage probability and symbol error probability for the amplify-and-forward and fixed decode-and-forward protocols with the MUD. Additionally, we conduct a simulation study to show to what extent our analytical and simulation results agree with each other. It is worthy to mention that our analytical and simulation results agree fairly with each other under high average signal-to-noise ratio, whereas they show that our proposed system with multiple relays provides significant improvements over those previously proposed systems having only one relay. Copyright

Design of linear and circular antenna arrays using biogeography based optimization

The design of linear and circular antenna arrays is one of the important electromagnetic optimization problems. In this paper, the problem of designing these arrays for specific radiation properties is dealt with. The biogeography based optimization (BBO) method, which represents a new evolutionary algorithm, is used in the optimization process. BBO is used to minimize the maximum side lobe level (SLL) and null control for isotropic linear antenna arrays by optimizing different array parameters (position, amplitude, and phase). Similarly, for non-uniform circular antenna arrays (CAA), BBO is used to determine an optimum set of weights and positions that provide a radiation pattern with maximum SLL reduction with the constraint of a fixed major lobe beam width. The results obtained show the effectiveness of BBO compared to other optimization methods.

Variable Z 0 applied to the optimal design of multi-stub matching network and a meander monopole

Variable Z0, a new concept in antenna design and optimization, is applied to two optimization problems: a multi-stub matching network (MSMN) using biogeography-based optimization (BBO), and an ultra wideband meander monopole antenna (MMA) using central force optimization (CFO). BBO is a newly-proposed stochastic global search and optimization evolutionary algorithm (EA) used to determine MSMN stub lengths and locations for optimum (minimum) reflection coefficient. CFO is a deterministic EA used to optimize the MMA’s impedance bandwidth (IBW) while maintaining good average gain without considering the radiation pattern in detail. Two cases are investigated for both problems: (a) fixed characteristic impedance Z0, and (b) variable characteristic impedance. In the first case, Z0 is a fixed user-specified parameter (the traditional methodology), whereas in the second, it is a true variable quantity whose value is determined by the optimization methodology, which is a new technology. Variable Z0 is a fundamentally different design approach in optimization problems. BBO’s fixed Z0 results for MSMN are compared to published data computed using Nelder–Mead optimization with BBO exhibiting better performance. BBO’s results are improved even more using Variable Z0 technology. A similar performance improvement is seen for Variable Z0 applied to the CFO-optimized MMA.

On the optimal design of non-uniform concentric circular antenna arrays

In this paper, the design of non-uniform concentric circular antenna arrays (CCAAs) of isotropic radiators with optimum side lobe level reduction is presented. The newly-proposed global evolutionary optimization methods; namely: the biogeography based optimization (BBO) is used to determine a set of weights that provides a radiation pattern with optimum side lobe level reduction with the constraint of a fixed major lobe beamwidth. The results obtained from BBO are compared with those obtained using the Matlab function Fmincon which uses a sequential quadratic programming (SQP) method. The comparison shows that the design of non-uniformly excited CCAAs using SQP method provides a side lobe level reduction that is better than that obtained using global stochastic optimization methods, indicating that global optimization techniques are not really needed in this problem.

BER analysis in relay-based DF cooperative diversity systems with relay & destination interferers

Incremental relaying has been recently introduced to overcome the problem with the restricted resources utilization associated with fixed relaying schemes in a pre-determined manner. Only when the direct path is not usable, the incremental relaying exploits the feedback from the destination to inform the relay about the necessity to send the source signal. In this paper, the performance analysis in terms of the bit error rate (BER) of the decode-and-forward (DF) incremental relaying over mixed fading channels is provided. The effects of the Co-channel interference near the destination and the relay caused respectively by the multiple L and N interferers are presented. Numerical results are provided to prove the solidity of our assumptions and compare the results of the system with and without the effects of the interference at the relay.

Closed-form expression for outage probability in relay-based cooperative diversity systems over Nakagami fading channels with interference

Incremental relaying was firstly introduced in order to compensate for the deficiencies associated with the regular cooperative schemes, namely, the fixed relaying schemes where the node helps the source in relaying its signal to the destination regardless of the channel conditions. In this paper, the performance of a two-hop Decode-and-Forward incremental relaying over Rayleigh fading channels with the presence of the multiple L interferers located near the destination which will degrade the overall behavior of the system taking into consideration that the fading channels from the interferers to the destination is assumed to be a sum of identically and independently distributed Rayleigh random variables is introduced.

Outage probability analysis in relay-based DF cooperative diversity systems with relay & destination interferers

Incremental relaying was firstly introduced in order to accommodate for the restriction associated with the fixed relaying schemes by using the intermediate relays only when they are needed by using a feedback from the destination to determine whether or not to use the relay which depends mainly on the usability of the direct path between the source and the relay. When the relay receives this negative feedback from the destination then it will send the signal to the destination within the second time slot which by then will be combined with the source signal using MRC, and by this, the system resources will be utilized efficiently. This paper provide the performance analysis of a decode-and-forward incremental relaying cooperative relaying over Rayleigh and Nakagami-m mixed fading channels with the presence of multiple interferers L and N near the destination and the relay respectively, which in turn will degrade the overall system performance and also compares the system performance with and without the presence of the interferers near the relay. Numerical results are provided to validate our assumptions.

Variable Z 0 applied to biogeography based optimized multi-stub matching network

Variable Z0 technology is applied to the problem of designing a multi-stub matching network (MSMN) using Biogeography Based Optimization (BBO). BBO is a newly-proposed stochastic global search and optimization evolutionary algorithm. It will be used to determine the lengths and locations of the stubs in a multi-stub matching network for optimum (minimum) reflection coefficient. Two cases are investigated: in the first case, Z0 is a fixed user-specified parameter (the traditional methodology), whereas in the second, it is a true variable quantity whose value is determined by the optimization methodology. BBOs fixed Z0 results are compared to published data with BBO exhibiting better performance. BBOs results are improved even more using Variable Z0 technology.