arXiv subjects

Abbas Mohammadi

Publications and source records attributed to Abbas Mohammadi.

12 recordsLinked to original sources

arXiv2025

Characterization of IRS-aided Indoor Wireless Virtual-Reality with Hybrid Beamforming

This paper introduces an optimum solution for a utility function that increases spectral efficiency in wireless Virtual Reality (VR) systems. This system uses Multi-user Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing (MU-MIMO OFDM) with hybrid beamforming in indoor Intelligent Reflecting Surface (IRS) based Downlink (DL) scenario. Given the critical need to maximize the rate for transmitting VR traffic to meet the low-latency requirements, a substantial bandwidth allocation is essential. This bandwidth is assumed to be in the mmWave band, according to the IEEE 802.11ad/ay standard. The proposed utility function takes into account various delays, including processing, transmission and queuing delays, on both DL and Uplink (UL). Moreover, the relation between transmission delay and the utility function is examined in different Signal-to-Noise Ratio (SNR) levels, using both mean and minimum channel gain metrics. An optimization approach is applied to iteratively determine the IRS phase shifts and effective channel gain. The simulation results are benchmarked against NS3 simulations, showing a high degree of consistency. With an average accuracy of 81.57% the calculated DL and UL rates match the NS3 results when considering the IRS. Also, our proposed method achieves superior performance in the case of complexity over the existing designs.

cs.IT↗

arXiv2025

Characterization of Using Hybrid Beamforming in mmWave Virtual Reality

Wireless Virtual Reality (VR) is increasingly in demand in Wireless LANs (WLANs). In this paper, a utility function for resource management in wireless VR is proposed. Maximizing the sum rate metric in transmitting VR audio or videos is an important factor for ascertaining low latency in obtaining QoS requirement of users in VR, so forth mmWave frequency band in WLAN technology should be used. This frequency band is presented in IEEE 802.11ad/ay. Resource access method in IEEE 802.11ay standard is MultiUser MIMO (MU-MIMO) with OFDM modulation. Operating at mmWave frequency band is equal to use massive number of antenna to enhance the received power in (Line of Sight) LoS direction by inducing sever propagation with small wavelength. Also for reducing the complexity of hardware in mmWave technology, designers should select some number of connected phase shifters to each antenna element by hybrid beamforming method. Processing delay, transmission delay and queue delay should be considered in acquiring QoS metric in terms of utility function. The optimal closed form expression of the multi-attribute utility function is based on these delays that are calculated by downlink and uplink rates in assistant with hybrid beamforming. Trends of transmission delay and multi-attribute utility function in various Es/N0 values and different scenarios are analyzed. Based on these results, 95.4% accuracy in comparison with ns3 in uplink and downlink channel modeling in IEEE 802.11ay standard's indoor environment has been reported. Also, it is shown that min channel gain consideration can cause reduction in the value of the utility function and incursion in transmission delay in VR.

cs.NI↗

arXiv2023

High-Entropy Hydrides for Fast and Reversible Hydrogen Storage at Room Temperature: Binding-Energy Engineering via First-Principles Calculations and Experiments

Despite high interest in compact and safe storage of hydrogen in the solid-state hydride form, the design of alloys that can reversibly and quickly store hydrogen at room temperature under pressures close to atmospheric pressure is a long-lasting challenge. In this study, first-principles calculations are combined with experiments to develop high-entropy alloys (HEAs) for room-temperature hydrogen storage. TixZr2-xCrMnFeNi (x = 0.4-1.6) alloys with the Laves phase structure and low hydrogen binding energies of -0.1 to -0.15 eV are designed and synthesized. The HEAs reversibly store hydrogen in the form of Laves phase hydrides at room temperature, while (de)hydrogenation pressure systematically reduces with increasing the zirconium fraction in good agreement with the binding energy calculations. The kinetics of hydrogenation are fast, the hydrogenation occurs without any activation or catalytic treatment, the hydrogen storage performance remains stable for at least 1000 cycles, and the storage capacity is higher than that for commercial LaNi5. The current findings demonstrate that a combination of theoretical calculations and experiments is a promising pathway to design new high-entropy hydrides with high performance for hydrogen storage.

cond-mat.mtrl-sci↗

arXiv2020

Energy Efficiency Optimization for Device-to-Device Communication Underlaying Cellular Networks in Millimeter-Wave

This paper studies energy efficiency maximization in device-to-device (D2D) communications underlaying cellular networks in millimeter-wave (mm-wave) band. A stochastic geometry framework has been used to extract the results. First, cellular and D2D users are modeled by independent homogeneous Poisson point process; then, exact expressions for successful transmission probability of D2D and cellular users have been derived. Furthermore, the average sum rate and energy efficiency for a typical D2D scenario have been presented. An optimization problem subject to transmission power and quality of service constraints for both cellular and D2D users has been defined and energy efficiency of D2D communication is maximized. Simulation results reveal that by working in millimeter-wave, significant energy efficiency improvement can be attained, e.g., 20\% energy efficiency improvement compared to Rayleigh distribution in the practical scenarios by considering circuit power. Finally, to verify our analytical expressions, the simulation studies are carried out and the excellent agreements have been achieved.

eess.SP↗

arXiv2019

Energy Efficient Power Allocation for Device-to-Device Communications Underlaid Cellular Networks Using Stochastic Geometry

In this paper, we study an energy efficiency maximization problem in uplink for D2D communications underlaid with cellular networks on multiple bands. Utilizing stochastic geometry, we derive closed-form expressions for the average sum rate, successful transmission probability, and energy efficiency of cellular and D2D users. Then, we formulate an optimization problem to jointly maximize the energy efficiency of D2D and cellular users and obtain optimum transmission power of both D2D and cellular users. In the optimization problem, we guarantee the QoS of users by taking into account the success transmission probability on each link. To solve the problem, first we convert the problem into canonical convex form. Afterwards, we solve the problem in two phases, energy efficiency maximization of devices and energy efficiency maximization of cellular users. In the first phase, we maximize the energy efficiency of D2D users and feed the solution to the second phase where we maximize the energy efficiency of cellular users. Simulation results reveal that significant energy efficiency can be attained e.g., 10% energy efficiency improvement compared to fix transmission power in high density scenario.

eess.SP↗

arXiv2019

The comparison of the healing performance of polyurethane-modified bitumen mixtures

Considering much distresses occurring at the surface of the asphalt roads, self-healing phenomenon attracted much attention because of reducing the road surface distresses and its benefits. The use of polymers, which are mainly used to improve the properties of asphalt mixtures, is one of the ways to increase self-healing properties. In this study, four polymer-modified bitumen mixtures were made applying the most common polyurethanes (by combining three different types of polymers and a nanographene particle). Then the mixtures were exposed to long-term aging under PAV to be evaluated in situations where less healing occurs. Finally, by performing a time sweep test and measuring the shear complex modulus (G *) before and after the rest period, the healing rate of these mixtures was measured and compared. By examining the results, it was found that the TDI-CO polymer-modified mixture is the best mixture for bitumen healing.

physics.app-ph↗

arXiv2018

Spectral Analysis of GFDM Modulated Signal under Nonlinear Behavior of Power Amplifier

General frequency division multiplexing (GFDM) is a flexible non-orthogonal waveform candidate for 5G which can offer some advantages such as low out-of-band (OOB) emission and high spectral efficiency. In this paper, the effects of nonlinear behavior of practical PAs on GFDM signal are studied. In the first step, a closed form expression for power spectral density (PSD) of GFDM signal is extracted. Then, the PSD at the output of PA as a function of input power and the coefficients of nonlinear polynomial PA model is derived. In addition, the adjacent channel power (ACP) and ACP ratio, as two important performance metrics, are evaluated. The simulation results confirm the accuracy of derived analytical expressions. Moreover, to validate the performance of GFDM modulation after nonlinear PA, it is compared with OFDM modulation.

eess.SP↗

arXiv2017

Secure two-way communication via a wireless powered untrusted relay and friendly jammer

In this paper, we propose a self-dependent two-way secure communication where two sources exchange confidential messages via a wireless powered untrusted amplify-and-forward (AF) relay and friendly jammer (FJ). By adopting the time switching (TS) architecture at the relay, the data transmission is accomplished in three phases: Phase I) Energy harvesting by the untrusted relay and the FJ through non-information transmissions from the sources, Phase II) Information transmission by the sources and jamming transmissions from the FJ to reduce information leakage to the untrusted relay; and Phase III) Forwarding the scaled version of the received signal from the untrusted relay to the sources. For the proposed system, we derive a new closed-form lower bound expression for the ergodic secrecy sum rate (ESSR). Numerical examples are provided to demonstrate the impacts of different system parameters such as energy harvesting time, transmit signal-to-noise ratio (SNR) and the relay/FJ location on the secrecy performance. The numerical results illustrate that the proposed network with friendly jamming (WFJ) outperforms traditional one-way communication and the two-way without friendly jamming (WoFJ) policy.

cs.CR↗

arXiv2017

Optimal Power Allocation and Secrecy Sum Rate in Two-Way Untrusted Relaying

In this paper, we examine the secrecy performance of two-way relaying between a multiple antenna base station (BS) and a single antenna mobile user (MU) in the presence of a multiple antenna friendly jammer (FJ). We consider the untrusted relaying scenario where an amplify-and-forward relay is both a necessary helper and a potential eavesdropper. To maximize the instantaneous secrecy sum rate, we derive new closed-form solutions for the optimal power allocation (OPA) between the BS and MU under the scenario of relaying with friendly jamming (WFJ). Based on the OPA solution, new closed-form expressions are derived for the ergodic secrecy sum rate (ESSR) with Rayleigh fading channel. Furthermore, we explicitly determine the high signal-to-noise ratio slope and power offset of the ESSR to highlight the benefits of friendly jamming. Numerical examples are provided to demonstrate the impact of the FJ's location and number of antennas on the secrecy performance.

cs.CR↗

arXiv2017

Optimal Power Allocation by Imperfect Hardware Analysis in Untrusted Relaying Networks

By taking a variety of realistic hardware imperfections into consideration, we propose an optimal power allocation (OPA) strategy to maximize the instantaneous secrecy rate of a cooperative wireless network comprised of a source, a destination and an untrusted amplify-and-forward (AF) relay. We assume that either the source or the destination is equipped with a large-scale multiple antennas (LSMA) system, while the rest are equipped with a single antenna. To prevent the untrusted relay from intercepting the source message, the destination sends an intended jamming noise to the relay, which is referred to as destination-based cooperative jamming (DBCJ). Given this system model, novel closed-form expressions are presented in the high signal-to-noise ratio (SNR) regime for the ergodic secrecy rate (ESR) and the secrecy outage probability (SOP). We further improve the secrecy performance of the system by optimizing the associated hardware design. The results reveal that by beneficially distributing the tolerable hardware imperfections across the transmission and reception radio-frequency (RF) front ends of each node, the system's secrecy rate may be improved. The engineering insight is that equally sharing the total imperfections at the relay between the transmitter and the receiver provides the best secrecy performance. Numerical results illustrate that the proposed OPA together with the most appropriate hardware design significantly increases the secrecy rate.

cs.CR↗

arXiv2017

Joint Relay Selection and Power Allocation in Large-Scale MIMO Systems with Untrusted Relays and Passive Eavesdroppers

In this paper, a joint relay selection and power allocation (JRP) scheme is proposed to enhance the physical layer security of a cooperative network, where a multiple antennas source communicates with a single-antenna destination in presence of untrusted relays and passive eavesdroppers (Eves). The objective is to protect the data confidentially while concurrently relying on the untrusted relays as potential Eves to improve both the security and reliability of the network. To realize this objective, we consider cooperative jamming performed by the destination while JRP scheme is implemented. With the aim of maximizing the instantaneous secrecy rate, we derive a new closed-form solution for the optimal power allocation and propose a simple relay selection criterion under two scenarios of non-colluding Eves (NCE) and colluding Eves (CE). For the proposed scheme, a new closed-form expression is derived for the ergodic secrecy rate (ESR) and the secrecy outage probability as security metrics, and a new closed-form expression is presented for the average symbol error rate (SER) as a reliability measure over Rayleigh fading channels. We further explicitly characterize the high signal-to-noise ratio slope and power offset of the ESR to highlight the impacts of system parameters on the ESR. In addition, we examine the diversity order of the proposed scheme to reveal the achievable secrecy performance advantage. Finally, the secrecy and reliability diversity-multiplexing tradeoff of the optimized network are provided. Numerical results highlight that the ESR performance of the proposed JRP scheme for NCE and CE cases is increased with respect to the number of untrustworthy relays.

cs.IT↗

arXiv2016

Characterization of Effective Capacity in Antenna Selection MIMO Systems

In this Paper, the effective capacity of a multiple-input multiple-output (MIMO) system in two different cases with receive antenna selection (RAS) and transmit antenna selection (TAS) schemes is investigated. A closed-form solution for the maximum constant arrival rate of this network with statistical delay quality of service (QoS) constraint is extracted in the quasi-static fading channel. This study is conducted in two different cases. When channel state information (CSI) is not available at the MIMO transmitter, implementation of TAS is difficult. Therefore, RAS scheme is employed and one antenna with the maximum instantaneous signal to noise ratio (SNR) is chosen at the receiver. On the other hand, when CSI is available at the transmitter, TAS scheme is executed. In this case one antenna is selected at the transmitter. Moreover, an optimal power-control policy is applied to the selected antenna and the effective capacity of the MIMO system is derived. Finally, this optimal power adaptation and the effective capacity are investigated in two asymptotic cases with the loose and strict QoS requirements. In particular, we show that in the TAS scheme with the loose QoS restriction, the effective capacity converges to the ergodic capacity. Then, an exact closed-form solution is obtained for the ergodic capacity of the channel here.

cs.IT↗