Browsing by Subject "Millimeter wave"

Now showing 1 - 3 of 3

Open Access
60 GHz wireless data center networks: A survey
(Elsevier BV * North-Holland, 2021-02-11) Terzi, Çağlar; Körpeoğlu, İbrahim
Data centers (DCs) became an important part of computing today. A lot of services in Internet are run on DCs. Meanwhile a lot of research is done to tackle the challenges of high-performance and energy-efficient data center networking (DCN). Hot node congestion, cabling complexity/cost, and cooling cost are some of the important issues about data centers that need further investigation. Static and rigid topology in wired DCNs is an other issue that hinders flexibility. Use of wireless links for DCNs to eliminate these disadvantages is proposed and is an important research topic. In this paper, we review research studies in literature about the design of radio frequency (RF) based wireless data center networks. RF wireless DCNs can be grouped into two as hybrid (wireless and wired) and completely wireless data centers. We investigate both. We also compare wireless DCN solutions in the literature with respect to various aspects. Open areas and research ideas are also discussed.
Open Access
An overview of physical layer security with finite-alphabet signaling
(Institute of Electrical and Electronics Engineers Inc., 2019) Aghdam, Sina Rezaei; Nooraiepour, A.; Duman, Tolga M.
Providing secure communications over the physical layer with the objective of achieving secrecy without requiring a secret key has been receiving growing attention within the past decade. The vast majority of the existing studies in the area of physical layer security focus exclusively on the scenarios where the channel inputs are Gaussian distributed. However, in practice, the signals employed for transmission are drawn from discrete signal constellations such as phase shift keying and quadrature amplitude modulation. Hence, understanding the impact of the finite-alphabet input constraints and designing secure transmission schemes under this assumption is a mandatory step toward a practical implementation of physical layer security. With this motivation, this paper reviews recent developments on physical layer security with finite-alphabet inputs. We explore transmit signal design algorithms for single-antenna as well as multi-antenna wiretap channels under different assumptions on the channel state information at the transmitter. Moreover, we present a review of the recent results on secure transmission with discrete signaling for various scenarios including multi-carrier transmission systems, broadcast channels with confidential messages, cognitive multiple access and relay networks. Throughout the article, we stress the important behavioral differences of discrete versus Gaussian inputs in the context of the physical layer security. We also present an overview of practical code construction over Gaussian and fading wiretap channels, and discuss some open problems and directions for future research.
Open Access
Theoretical study and experimental realization of a low-loss metamaterial operating at the millimeter-wave regime: demonstrations of flat-and prism-shaped samples
(IEEE, 2009-10-23) Alici, K. B.; Özbay, Ekmel
We designed a low-loss double-negative composite metamaterial that operates at the millimeter-wave regime. A negative passband with a peak transmission value of 2.7 dB was obtained experimentally at 100 GHz. We performed transmission-based qualitative effective medium theory analysis numerically and experimentally to prove the double-negative nature of the metamaterial. These results were supported by the standard retrieval analysis method and the study was extended by reporting the fractional bandwidth and loss of the metamaterial as the number of layers in the propagation direction increased. We numerically calculated 2-D field map and experimentally confirmed far-field radiation response of horn antenna and metamaterial lens composite. Finally, we demonstrated that the effective index of the metamaterial was negative by performing far-field angular scanning measurements for a metamaterial prism. We simulated the prism by using the DrudeLorentz model and obtained the scattered field map in two dimensions at millimeter-wavelengths.