| 1. |
- Bohge, Mathias, et al.
(författare)
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A New Optimization Model for Dynamic Power and Sub-Carrier Allocations in Packet-Centric OFDMA Cells
- 2007
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Ingår i: Frequenz. - : FACHVERLAG SCHIELE SCHON. - 0016-1136 .- 2191-6349. ; 61:1-2, s. 35-38
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that applying dynamic resource allocation to down-link transmissions of OFDMAsystems provides a significant performance increase, by taking advantage of diversity effects. In order toquantify the maximum possible gain achievable by applying dynamic mechanisms, several optimizationproblems have been suggested for studying a dynamic system's optimal behaviour. However, so far theseoptimization approaches do not take sophisticated system requirements into account, as there are differentpacket-arrival processes, buffering constraints, scheduling policies, as well as QoS requirements per serviceclass. In this paper we present a new optimization model that is based on a packet-centric system view andincludes the system requirements mentioned above. We compare the performance results of the conventionaland the new approach and study the impact of dynamic power allocation in both cases.
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| 2. |
- Eddine Lamri, I., et al.
(författare)
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Design and development of a graphene-based reconfigurable patch antenna array for THz applications
- 2023
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Ingår i: Frequenz. - : Walter de Gruyter GmbH. - 0016-1136 .- 2191-6349. ; 77:3-4, s. 219-228
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a graphene-based antenna array for terahertz (THz) applications. The suggested antenna array has four radiating square shaped patches fed by a coplanar waveguide (CPW) technique. The proposed antenna array operates at the three frequencies with operational bandwidths of 1.173-1.210 THz (at 1.19 THz), 1.270-1.320 THz (at 1.3 GHz), and 1.368-1.346 THz (at 1.4 GHz). The total area of the antenna array is reported as 1000 × 1000 μm2, printed on a Silicon substrate with a thickness of 20 μm and a dielectric constant of ϵ r = 11.9. To enhance the structure's performance and optimize the feeding network, a parametric analysis was performed using the FDTD technique. Furthermore, the key properties of the proposed antenna array, such as resonance frequency, peak gain, and radiation efficiency, may be changed by adjusting the chemical potentials of the graphene in the antenna array. The use of graphene's chemical potential tuneability yields exceptional results comparing to the recent research outputs, with a peak gain and radiation efficiency of 10.45 dB and 70%, respectively. These results show the performance of the suggested design for constructing antenna arrays for use in THz applications.
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| 3. |
- Ejaz, A., et al.
(författare)
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Towards durable and efficient antenna with SAR reduction analysis for on-body applications
- 2022
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Ingår i: Frequenz. - : Walter de Gruyter GmbH. - 0016-1136 .- 2191-6349. ; 76:7-8, s. 429-439
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Tidskriftsartikel (refereegranskat)abstract
- This paper is focused on providing a viable solution to wearable antenna performance disconcertment caused by the underlying human body. Direct placement of the antenna on the body yields undesired results owing to the frequency detuning effect. The simplest possible way out is to make use of a metallic reflector. Hence, a reflector backed antenna is presented for 5.8 GHz ISM band with total lateral dimensions of 28 × 28 × 13.58 mm3. The reflector makes use of a conformal high dielectric laminate coated with a thin copper layer owing to which the assembled design achieves low SAR (Specific Absorption Rate). The prototype provides excellent results at the cost of some extra volume occupation in an off-body direction. Another AMC (Artificial Magnetic Conductor) backed technique is followed and implemented separately to have the structural compactness lacking in the former case. The antenna at hand is backed by a 2 × 2 array of AMC unit cells. The overall design dimensions are reduced. The reflector backed design achieves 8.2 dB gain, above 90% efficiency, and 99% bandwidth overlap with the primary antenna. The AMC backed design provides good spectrum coverage from 5.73 to 5.94 GHz with high gain. Free space response, on-body performance, and investigation of SAR analysis of the proposed designs substantiate effective wireless data transfer in body-centric communication.
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| 4. |
- Naghibi, Farshad, et al.
(författare)
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Performance Prediction Model for Interference-limited Dynamic OFDMA Systems
- 2010
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Ingår i: Frequenz. - 0016-1136 .- 2191-6349. ; 64:9-10, s. 159-163
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a performance model for dynamic resource allocation in interference-limited OFDMA-based cellular networks. Specifically, we derive an analytical framework by which it is possible to estimate the VoIP capacity of the cell per downlink frame, purely based on the average SINR per terminal. Hence, this framework can be used for admission control. The major difficulty to overcome is to predict the impact of dynamic resource allocations on the system performance in the presence of multiple interfering cells. We show that dynamic resource allocations transform the distribution of subcarrier SINR and derive an approximate, closed-form representation of these transformed distributions. Based on these derivations, we obtain rate probability mass functions per terminal which predict system performance up to a gap of about 26 % compared to optimal system performance.
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| 5. |
- Perea-Tamayo, Robert, et al.
(författare)
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Investigation of GaN-HEMT Based Switches for Hybrid Switching Amplifier Supply-Modulators
- 2012
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Ingår i: Frequenz. - : Walter de Gruyter GmbH. - 0016-1136 .- 2191-6349. ; 66:11-12, s. 339-345
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Tidskriftsartikel (refereegranskat)abstract
- An investigation of GaN-HEMT based switching stages in hybrid switching amplifiers (HSA) for wide-bandwidth supply modulation of RF power amplifiers is presented. The HSA is designed for maximum 15 V supply voltage, 1 A supply current and 10 MHz bandwidth. GaN-HEMT switch designs with alternative gate drive circuitry are investigated with regard to power, efficiency and linearity under different load conditions using simulations and measurements of the fabricated circuits. The full HSA showed an efficiency of 49.7% for a WCDMA envelope. A modified switching stage with improved gate-drive circuitry shows 85% efficiency in a 15 V buck-converter test-circuit for a 10 V conversion at 1 MHz over a 15 Ω load.
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| 6. |
- Gevorgian, Spartak, 1948, et al.
(författare)
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Electronically scanning beamformers based on ferroelectric technology
- 2005
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Ingår i: Frequenz. - 0016-1136. ; 59:1-2, s. 40-48
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Tidskriftsartikel (refereegranskat)abstract
- Basic properties and the potential of ferroelectrics for applications in electronically scanned beamformers are discussed. Low drive power consumption, relatively low losses, high speed, and the possibilities of realisation cost effective beamformers are the main advantages offered by ferroelectric technology. A brief review of ferroelectric scanning antennas is also given.
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| 7. |
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