Asymptotics of Transmit Antenna Selection: Impact of Multiple Receive Antennas

Consider a fading Gaussian MIMO channel with $N_\mathrm{t}$ transmit and $N_\mathrm{r}$ receive antennas. The transmitter selects $L_\mathrm{t}$ antennas corresponding to the strongest channels. For this setup, we study the distribution of the input-output mutual information when $N_\mathrm{t}$ grows large. We show that, for any $N_\mathrm{r}$ and $L_\mathrm{t}$, the distribution of the input-output mutual information is accurately approximated by a Gaussian distribution whose mean grows large and whose variance converges to zero. Our analysis depicts that, in the large limit, the gap between the expectation of the mutual information and its corresponding upper bound, derived by applying Jensen's inequality, converges to a constant which only depends on $N_\mathrm{r}$ and $L_\mathrm{t}$. The result extends the scope of channel hardening to the general case of antenna selection with multiple receive and selected transmit antennas. Although the analyses are given for the large-system limit, our numerical investigations indicate the robustness of the approximated distribution even when the number of antennas is not large.Comment: 6 pages, 4 figures, ICC 201

Rapid soft X-ray fluctuations in solar flares observed with the X-ray polychromator

Three flares observed by the Soft X-Ray Polychromator on the Solar Maximum Mission were studied. Flare light curves from the Flat Crystal Spectrometer and Bent Crystal Spectrometer were examined for rapid signal variations. Each flare was characterized by an initial fast (less than 1 min) burst, observed by the Hard X-Ray Burst Spectrometer (HXRBS), followed by softer gradual X-ray emission lasting several minutes. From an autocorrelation function analysis, evidence was found for quasi-periodic fluctuations with rise and decay times of 10 s in the Ca XIX and Fe XXV light curves. These variations were of small amplitude (less than 20%), often coincided with hard X-ray emissions, and were prominent during the onset of the gradual phase after the initial hard X-ray burst. It is speculated that these fluctuations were caused by repeated energy injections in a coronal loop that had already been heated and filled with dense plasma associated with the initial hard X-ray burst

On Robustness of Massive MIMO Systems Against Passive Eavesdropping under Antenna Selection

In massive MIMO wiretap settings, the base station can significantly suppress eavesdroppers by narrow beamforming toward legitimate terminals. Numerical investigations show that by this approach, secrecy is obtained at no significant cost. We call this property of massive MIMO systems `secrecy for free' and show that it not only holds when all the transmit antennas at the base station are employed, but also when only a single antenna is set active. Using linear precoding, the information leakage to the eavesdroppers can be sufficiently diminished, when the total number of available transmit antennas at the base station grows large, even when only a fixed number of them are selected. This result indicates that passive eavesdropping has no significant impact on massive MIMO systems, regardless of the number of active transmit antennas.Comment: 7 pages, 2 figures; To be presented in IEEE Global Communications Conference (Globecom) 2018 in Abu Dhabi, UA

Optimal Number of Transmit Antennas for Secrecy Enhancement in Massive MIMOME Channels

This paper studies the impact of transmit antenna selection on the secrecy performance of massive MIMO wiretap channels. We consider a scenario in which a multi-antenna transmitter selects a subset of transmit antennas with the strongest channel gains. Confidential messages are then transmitted to a multi-antenna legitimate receiver while the channel is being overheard by a multi-antenna eavesdropper. For this setup, we approximate the distribution of the instantaneous secrecy rate in the large-system limit. The approximation enables us to investigate the optimal number of selected antennas which maximizes the asymptotic secrecy throughput of the system. We show that increasing the number of selected antennas enhances the secrecy performance of the system up to some optimal value, and that further growth in the number of selected antennas has a destructive effect. Using the large-system approximation, we obtain the optimal number of selected antennas analytically for various scenarios. Our numerical investigations show an accurate match between simulations and the analytic results even for not so large dimensions.Comment: 6 pages, 4 figures, IEEE GLOBECOM 201

Reflectance of an absorbing substrate for incident light of arbitrary polarization: appearance of a secondary maximum at oblique incidence

The reflectance of an absorbing substrate Rθ(ɸ) is considered as a function of the angle of incidence ϕ and an incident polarization parameter θ, where cos2θ and sin2θ give the power fractions of incident radiation that are p-and s-polarized, respectively. Taking GaAs as an example, we find that at certain wavelengths (e.g., 0.248 and 0.620 µm), the Rθ vs ɸ curve becomes oscillatory in a narrow range of θ \u3e 45° with an unexpected secondary maximum appearing at oblique incidence. The extrema of the function Rθ(ɸ) are determined numerically, and their angular positions and reflectance levels are plotted vs θ for GaAs at photon energies of 1, 2, and 5 eV

THE EFFECT OF METFORMIN 0N CYTOKINES IN IRAQI PATIENTS WITH TYPE 2 DIABETES

Type 2diabetes mellitus (T2DM) is the most common form of diabetes and is characterized by disorders of insulin action and insulin secretion, and associated with increase problem of insulin resistant. High plasma levels of insulin and glucose due to insulin resistance often lead tometabolic syndrome. Chronic inflammation associated with metabolic and immune system involves a network of cellular andsystemic responses that integrates many complex signaling pathways infiltration of inflammation cells in adipose tissue , abnormal pro-inflammatory cytokinesproduction(IL-8,TNF-α). The study is designed to measure glycosylated hemoglobin (HbA1c),IL-8 and TNF-α.These parameters and measures applied for thirty newly diagnosed  patients with diabetes before and after treatment divided into 3 group.Three groups of (10) patients each newly diagnosed withT2DM;group(1) receives:500mg metformin for 3 months with (HbA1c=9.54±1.95,IL-8=13.85±6.15,TNF-α=260.1±123.7).                                                      group(2)receives:1000mg metformin for 3 months with (HbA1c=9.16±1.55,IL-8=15.02±6.28,TNF-α=230.86±49.26).    group(3)receives:1500mg metformin for 3 months with(HbA1c=9.80±1.94,IL-8=14.41±4.61,TNF-=207.42±40.45).                       Blood samples were withdrawn from the patients at pretreatment,then after 3 months of treatment. After 3 months of  treatment, patient who received metformin 1500mg had greater reduction in  HbA1c,IL-8 and TNF-α(27,9percent,44.20percent and49.75percent respectively),compared with patient who received metformin 1000mg(18.3percent,15.77percent,34.42percent respectively)and to metformin 500mg(10.3percent.12.56percent and 4.72percent).Metformin monotherapy are effective as an initial treatment of newly diagnosed diabetic patients in The national  diabetes center / University of Al-Mustansiriyah, Iraq.Metformin has significant reduction effect on these three group, had significant reduction in HbA1c and also significant reduction in cytokines in the three dose in different percent.Keywords,metformin,cytokines,diabete

Maximum rate of change of the differential reflection phase shift with respect to the angle of incidence for light reflection at the surface of an absorbing medium

The differential reflection phase shift, Δ = δp - δs, associated with the external reflection of monochromatic light at the surface of an absorbing medium is a monotonically decreasing function of the angle of incidence ø which is determined by the complex dielectric function ε. A new special angle of incidence, denoted by øΔ′max, is defined at which the slope Δ′ = ∂Δ/∂ø of the Δ-ø curve is maximum negative, Δ′max, and a transcendental equation is derived that determines this angle. øΔ′max differs from the principal angle øp at which Δ = 90°. As an example, øΔ′max is calculated by numerical iteration for light reflection at the air-Si interface for photon energies hv from 1.7 to 5.6eV in steps of 0.1eV, and is plotted, along with the associated maximum slope Δ′max, vs wavelength λ. It is noted that øΔ′max\u3eøp at every λ, a result that may hold in general. Also, for 4.5 ≤ hv ≤ 5.6 eV, øΔ′max = 90°, so that a maximum negative slope occurs at grazing incidence in this spectral range. Another interesting observation is that, when |ε| \u3e\u3e 1 (e.g., for metals in the IR), Δ′(90°) is a direct measure of the extinction coefficient k = Imε½