Space-Time Block Coding for MIMO Channels

Hamid Jafarkhani 에스케이텔레콤 (주) 2004 Telecommunications Review Vol.14 No.3

A Study of Connectivity in MIMO Fading Ad-Hoc Networks

Yousefi'zadeh, H.,Jafarkhani, H.,Kazemitabar, J. The Korea Institute of Information and Commucation 2009 Journal of communications and networks Vol.11 No.1

We investigate the connectivity of fading wireless ad-hoc networks with a pair of novel connectivity metrics. Our first metric looks at the problem of connectivity relying on the outage capacity of MIMO channels. Our second metric relies on a probabilistic treatment of the symbol error rates for such channels. We relate both capacity and symbol error rates to the characteristics of the underlying communication system such as antenna configuration, modulation, coding, and signal strength measured in terms of signal-to-interference-noise-ratio. For each metric of connectivity, we also provide a simplified treatment in the case of ergodic fading channels. In each case, we assume a pair of nodes are connected if their bi-directional measure of connectivity is better than a given threshold. Our analysis relies on the central limit theorem to approximate the distribution of the combined undesired signal affecting each link of an ad-hoc network as Gaussian. Supported by our simulation results, our analysis shows that (1) a measure of connectivity purely based on signal strength is not capable of accurately capturing the connectivity phenomenon, and (2) employing multiple antenna mobile nodes improves the connectivity of fading ad-hoc networks.

An Optimal Power-Throughput Tradeoff Study for MIMO Fading Ad-Hoc Networks

Yousefi'zadeh, Homayoun,Jafarkhani, Hamid The Korea Institute of Information and Commucation 2010 Journal of communications and networks Vol.12 No.4

In this paper, we study optimal tradeoffs of achievable throughput versus consumed power in wireless ad-hoc networks formed by a collection of multiple antenna nodes. Relying on adaptive modulation and/or dynamic channel coding rate allocation techniques for multiple antenna systems, we examine the maximization of throughput under power constraints as well as the minimization of transmission power under throughput constraints. In our examination, we also consider the impacts of enforcing quality of service requirements expressed in the form of channel coding block loss constraints. In order to properly model temporally correlated loss observed in fading wireless channels, we propose the use of finite-state Markov chains. Details of fading statistics of signal-to-interference-noise ratio, an important indicator of transmission quality, are presented. Further, we objectively inspect complexity versus accuracy tradeoff of solving our proposed optimization problems at a global as oppose to a local topology level. Our numerical simulations profile and compare the performance of a variety of scenarios for a number of sample network topologies.

A Study of Connectivity in MIMO Fading Ad-Hoc Networks

H. Yousefi’zadeh,H. Jafarkhani,J. Kazemitabar 한국통신학회 2009 Journal of communications and networks Vol.11 No.1

We investigate the connectivity of fading wireless ad-hoc networks with a pair of novel connectivity metrics. Our first metric looks at the problem of connectivity relying on the outage capacity of MIMO channels. Our second metric relies on a probabilistic treatment of the symbol error rates for such channels. We relate both capacity and symbol error rates to the characteristics of the underlying communication system such as antenna configuration, modulation, coding, and signal strength measured in terms of signal-to-interference-noise-ratio. For each metric of connectivity, we also provide a simplified treatment in the case of ergodic fading channels. In each case, we assume a pair of nodes are connected if their bi-directional measure of connectivity is better than a given threshold. Our analysis relies on the central limit theorem to approximate the distribution of the combined undesired signal affecting each link of an ad-hoc network as Gaussian. Supported by our simulation results, our analysis shows that (1) a measure of connectivity purely based on signal strength is not capable of accurately capturing the connectivity phenomenon, and (2) employing multiple antenna mobile nodes improves the connectivity of fading ad-hoc networks.

An Optimal Power-Throughput Tradeoff Study for MIMO Fading Ad-Hoc Networks

Homayoun Yousefi’zadeh,Hamid Jafarkhani 한국통신학회 2010 Journal of communications and networks Vol.12 No.4

In this paper, we study optimal tradeoffs of achievable throughput versus consumed power in wireless ad-hoc networks formed by a collection of multiple antenna nodes. Relying on adaptive modulation and/or dynamic channel coding rate allocation techniques for multiple antenna systems, we examine the maximization of throughput under power constraints as well as theminimization of transmission power under throughput constraints. In our examination, we also consider the impacts of enforcing quality of service requirements expressed in the form of channel coding block loss constraints. In order to properly model temporally correlated loss observed in fading wireless channels, we propose the use of finite-state Markov chains. Details of fading statistics of signal-to-interference-noise ratio, an important indicator of transmission quality, are presented. Further, we objectively inspect complexity versus accuracy tradeoff of solving our proposed optimization problems at a global as oppose to a local topology level. Our numerical simulations profile and compare the performance of a variety of scenarios for a number of sample network topologies.

Joint Routing, Scheduling and Power Control for Large Interference Wireless Networks

Javad Kazemitabar,Vahid Tabatabaee,Hamid Jafarkhani 한국통신학회 2017 Journal of communications and networks Vol.19 No.4

We consider the problem of joint routing, scheduling andpower control in multi-hop wireless networks. We use a linear relationbetween link capacity and signal to interference noise ratio inour formulation. In a previous work, using a duality approach, theoptimal link scheduling and power control that minimizes the totalaverage transmission power is found. We formulate this problemas a linear programming problem with exponential number of constraints. To cope with the exponential number of constraints, wepropose an iterative algorithm based on the cutting plane method. The separation oracle for the cutting plane algorithm turns out tobe an element-wise concave optimization problem that can be effectivelysolved using branch and bound algorithm. We extend thesame method to find the optimal routing scheduling and powercontrol. Simulation results show that this methodology is more efficientand scalable compare to the previously proposed algorithm.

Simulation and in vitro evaluations of microfluidically-fabricated clarithromycin-poly (e-caprolactone) nanoparticles

Beeta Tavana,Alireza Khatibi,Saeed Jafarkhani,Payam Zahedi,Mohammad Hossein Zamani,Seyed Hassan Jafari,Mohammad Najafi 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.124 No.-

Clarithromycin (CLR)-loaded poly (e-caprolactone) (PCL) nanoparticles (NPs) were synthesized usingmicrofluidics (MF) with square-shaped (MF1), and three-channel (MF2), geometries as well as conventionalbulk mixing (BM). Based on Comsol simulation results of MF chips, the flow rate ratio, nonsolventphase flow rate, and polymer solution concentration were optimized 0.05, 50 mL h1, and 0.2(%w/v), respectively; thereby, representing MF1 geometry with highest homogenous mixing. Characterization studies indicated that MF1-based NPs possessed smaller average diameter (91 nm),narrower polydispersity index (0.13) and higher zeta potential (-44 mV) compared to those NPs synthesizedby MF2 and BM methods. Moreover, MF1-aided synthesis of NPs exhibited the encapsulation efficiencyof approximately 81% and loading capacity of around 13%. Investigating CLR release behavior atdifferent pHs also demonstrated that the MF1-based NPs experienced the most controlled release, followedthe Fickian diffusion mechanism. The controlled release of MF1-based NPs was confirmed by evaluatingtheir inhibitory effect against specific cytokines on BEAS-2B as bronchitis cell line via a series ofin vitro experiments including real time-polymerase chain reaction and flow cytometry. Eventually, theantibacterial properties of the samples were studied on two prevalent bacterial strains and the obtainedobservations revealed that MF1-based NPs encompassed the best performance in controlled release ofCLR with respect to the other samples.

Sodium alginate/xanthan-based nanocomposite hydrogels containing 5-fluorouracil: Characterization and cancer cell death studies in presence of halloysite nanotube

Shadi Zolfagharian,Payam Zahedi,Mehdi Shafiee Ardestani,Alireza Khatibi,Saeed Jafarkhani 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.120 No.-

This work was aimed to synthesize 5-fluorouracil (5-FU)-loaded sodium alginate (SA)/xanthan gum (Xan)hydrogels containing sulfuric acid-treated halloysite nanotube (tHNT) using free radical polymerizationand evaluate their apoptosis against HeLa cells in cervical cancer therapy. The nanocomposite hydrogelincluding tHNT (SA/Xan: tHNT, 1:1) showed a rough surface with cross-linking density of 171.9 10-4mol/cm3 compared to tHNT-free sample (62.5 10-4 mol/cm3). The 5-FU encapsulation efficiency ofthe samples in the presence and absence of tHNT was obtained approximately 60 % and 76 %, respectively. Moreover, the drug release of the samples with and without tHNT were measured 72 % and93 % in acidic medium as well as 32 % and 57 % in basic environment after 72 h. Finally, the cytotoxicityresults revealed the minimum cell viability (3.3 %) for tHNT-loaded hydrogel sample on the 4th day, andflow cytometry assessments also exhibited that the apoptosis rate of HeLa cells for this sample was85.4 %, resulting in its remarkable potential for destroying this cancerous cell line.