Artificial-Noise-Aided Secure Multi-Antenna Transmission with Limited Feedback

We present an optimized secure multi-antenna transmission approach based on artificial-noise-aided beamforming, with limited feedback from a desired single-antenna receiver. To deal with beamformer quantization errors as well as unknown eavesdropper channel characteristics, our approach is aimed at maximizing throughput under dual performance constraints - a connection outage constraint on the desired communication channel and a secrecy outage constraint to guard against eavesdropping. We propose an adaptive transmission strategy that judiciously selects the wiretap coding parameters, as well as the power allocation between the artificial noise and the information signal. This optimized solution reveals several important differences with respect to solutions designed previously under the assumption of perfect feedback. We also investigate the problem of how to most efficiently utilize the feedback bits. The simulation results indicate that a good design strategy is to use approximately 20% of these bits to quantize the channel gain information, with the remainder to quantize the channel direction, and this allocation is largely insensitive to the secrecy outage constraint imposed. In addition, we find that 8 feedback bits per transmit antenna is sufficient to achieve approximately 90% of the throughput attainable with perfect feedback.Comment: to appear in IEEE Transactions on Wireless Communication

Constructing packings in Grassmannian manifolds via alternating projection

This paper describes a numerical method for finding good packings in Grassmannian manifolds equipped with various metrics. This investigation also encompasses packing in projective spaces. In each case, producing a good packing is equivalent to constructing a matrix that has certain structural and spectral properties. By alternately enforcing the structural condition and then the spectral condition, it is often possible to reach a matrix that satisfies both. One may then extract a packing from this matrix. This approach is both powerful and versatile. In cases where experiments have been performed, the alternating projection method yields packings that compete with the best packings recorded. It also extends to problems that have not been studied numerically. For example, it can be used to produce packings of subspaces in real and complex Grassmannian spaces equipped with the Fubini--Study distance; these packings are valuable in wireless communications. One can prove that some of the novel configurations constructed by the algorithm have packing diameters that are nearly optimal.Comment: 41 pages, 7 tables, 4 figure

Density of non-residues in Burgess-type intervals and applications

We show that for any fixed \eps>0, there are numbers $\delta>0$ and $p_0\ge 2$ with the following property: for every prime $p\ge p_0$ and every integer $N$ such that p^{1/(4\sqrt{e})+\eps}\le N\le p, the sequence $1,2,...,N$ contains at least $\delta N$ quadratic non-residues modulo $p$. We use this result to obtain strong upper bounds on the sizes of the least quadratic non-residues in Beatty and Piatetski--Shapiro sequences.Comment: In the new version we use an idea of Roger Heath-Brown (who is now a co-author) to simply the proof and improve the main results of the previous version, 14 page

Distribution and Status of the Brazilian Free-tailed Bat (Tadarida brasiliensis cynocephala) in Arkansas

Investigations of building infestations, mist netting activities, and specimens submitted to the Arkansas Department of Health document the Brazilian free-tailed bat to be found in 14 Arkansas counties. Both overwintering and maternity colonies were examined. Numbers of individuals ranged from one to several thousand

Descriptive Epidemiology of Physical Activity in Adolescents

This paper reviews the descriptive epidemiology of physical activity in adolescents. Large population-based studies were reviewed, along with smaller studies using objective monitoring of physical activity. Estimates showed that adolescents engage in physical activity of any intensity for a mean of one hour per day. Approximately two thirds of males and one quarter of females participate in moderate to vigorous activity for 20 min 3 or more days per week. Activity levels decline with increasing age across adolescence, and this decrease is more marked in females than in males. Comparison of these data to physical activity guidelines for adolescents suggests the vast majority are meeting the guideline of accumulating physical activity. However, a substantial number of males, and the majority of females, are not meeting the guideline for moderate to vigorous physical activity

Coverage and Rate of Joint Communication and Parameter Estimation in Wireless Networks

From an information theoretic perspective, joint communication and sensing (JCAS) represents a natural generalization of communication network functionality. However, it requires the re-evaluation of network performance from a multi-objective perspective. We develop a novel mathematical framework for characterizing the sensing and communication coverage probability and ergodic rate in JCAS networks. We employ a formulation of sensing parameter estimation based on mutual information to extend the notions of coverage probability and ergodic rate to the radar setting. We define sensing coverage probability as the probability that the rate of information extracted about the parameters of interest associated with a typical radar target exceeds some threshold, and sensing ergodic rate as the spatial average of the aforementioned rate of information. Using this framework, we analyze the downlink sensing and communication coverage and rate of a mmWave JCAS network employing a shared waveform, directional beamforming, and monostatic sensing. Leveraging tools from stochastic geometry, we derive upper and lower bounds for these quantities. We also develop several general technical results including: i) a generic method for obtaining closed form upper and lower bounds on the Laplace Transform of a shot noise process, ii) a new analog of H{\"o}lder's Inequality to the setting of harmonic means, and iii) a relation between the Laplace and Mellin Transforms of a non-negative random variable. We use the derived bounds to numerically investigate the performance of JCAS networks under varying base station and blockage density. Among several insights, our numerical analysis indicates that network densification improves sensing SINR performance -- in contrast to communications.Comment: 87 pages, 5 figures. Published in IEEE Transactions on Information Theor

Seasonal copepod lipid pump promotes carbon sequestration in the deep North Atlantic

Physical, chemical and biological processes can mediate carbon transfer from surface ocean waters to below the permanent pycnocline and so promote ocean carbon sequestration. Passive sinking of organic and carbonate-rich biogenic particles - the ‘biological pump’ -has been estimated to account for a sequestration flux of 2 - 8 gC m-2 yr-1 at around 1000m depth. Here we identify a comparably important mechanism for sequestering carbon in the North Atlantic and other sub-polar seas. We estimate that as a result of the annual vertical migration of overwintering copepods, between 2 and 6 gC m-2 yr-1 are actively transported to below the permanent pycnocline as lipids. Only 25 - 50% of these lipids are carried back to the surface in spring with the surviving copepods, resulting in a sequestration flux of 1 to 4 gC m-2 yr-1. This ’lipid pump’ has gone largely un-recorded in either direct measurements of carbon sequestration, or estimates based on surface production and export flux. In addition, elemental ratios of nitrogen, phosphorus, silicon and iron to carbon are extremely low or zero in lipids, so the lipid pump does not strip the surface ocean of limiting nutrients, and decouples the carbon sink from nutrient replenishment rates