Stevens Institute of Technology

About: Stevens Institute of Technology is a education organization based out in Hoboken, New Jersey, United States. It is known for research contribution in the topics: Computer science & Cognitive radio. The organization has 5440 authors who have published 12684 publications receiving 296875 citations. The organization is also known as: Stevens & Stevens Tech.

Cognitive Radio Architecture Evolution

Abstract: The radio research community has aggressively embraced cognitive radio for dynamic radio spectrum management to enhance spectrum usage, e.g., in ISM bands and as secondary users in unused TV bands, but the needs of the mobile wireless user have not been addressed as thoroughly on the question of high quality of information (QoI) as a function of place, time, and social setting (e.g. commuting, shopping, or in need of medical assistance). This paper considers the evolution of cognitive radio architecture (CRA) in the context of motivating use cases such as public safety and sentient spaces to characterize CRA with an interdisciplinary perspective where machine perception in visual, acoustic, speech, and natural language text domains provide cues to the automatic detection of stereotypical situations, enabling radio nodes to select from among radio bands and modes more intelligently and enabling cognitive wireless networks to deliver higher QoI within social and technical constraints, made more cost effective via embedded and distributed computational intelligence.

Quantum cascade lasers: ultrahigh-speed operation, optical wireless communication, narrow linewidth, and far-infrared emission

Abstract: Following an introduction to the history of the invention of the quantum cascade (QC) laser and of the band-structure engineering advances that have led to laser action over most of the mid-infrared (IR) and part of the far-IR spectrum, the paper provides a comprehensive review of recent developments that will likely enable important advances in areas such as optical communications, ultrahigh resolution spectroscopy and applications to ultrahigh sensitivity gas-sensing systems We discuss the experimental observation of the remarkably different frequency response of QC lasers compared to diode lasers, ie, the absence of relaxation oscillations, their high-speed digital modulation, and results on mid-IR optical wireless communication links, which demonstrate the possibility of reliably transmitting complex multimedia data streams Ultrashort pulse generation by gain switching and active and passive modelocking is subsequently discussed Recent data on the linewidth of free-running QC lasers (/spl sim/150 kHz) and their frequency stabilization down to 10 kHz are presented Experiments on the relative frequency stability (/spl sim/5 Hz) of two QC lasers locked to optical cavities are discussed Finally, developments in metallic waveguides with surface plasmon modes, which have enabled extension of the operating wavelength to the far IR are reported

Carbonate effects on hexavalent uranium adsorption by iron oxyhydroxide.

Abstract: Carbonate dramatically affects the adsorption of uranium (U(VI)) onto iron hydroxides and its mobility in the natural environment. Batch tests, zeta potential measurements, and Fourier transform infrared (FTIR) spectroscopic studies were utilized to characterize the nature of U(VI) adsorption on ferrihydrite. Adsorption isotherms demonstrated that carbonate had a negative effect on U(VI) adsorption on ferrihydrite at pH >6. Zeta potential measurements indicated that U(VI) was adsorbed as a cationic species (SO−UO2+) in the absence of carbonate and as anionic U(VI) complexes in the presence of carbonate at neutral pH. FTIR spectroscopic measurement of adsorbed U(VI) suggested that it was retained as uranyl carbonate complexes in the presence of carbonate. An increase in carbonate concentration caused a shift in the antisymmetric stretching vibration of the uranyl (UO22+) U−O bond toward lower wavenumbers, which indicated an increasing carbonate effect in the adsorbed uranyl carbonate complexes. The adsorbe...

Deterministic multiuser carrier-frequency offset estimation for interleaved OFDMA uplink

Abstract: In orthogonal frequency-division multiple access (OFDMA), closely spaced multiple subcarriers are assigned to different users for parallel signal transmission. An interleaved subcarrier-assignment scheme is preferred because it provides maximum frequency diversity and increases the capacity in frequency-selective fading channels. The subcarriers are overlapping, but orthogonal to each other such that there is no intercarrier interference (ICI). Carrier-frequency offsets (CFOs) between the transmitter and the receiver destroy the orthogonality and introduces ICI, resulting in multiple-access interference. This paper exploits the inner structure of the signals for CFO estimation in the uplink of interleaved OFDMA systems. A new uplink signal model is presented, and an estimation algorithm based on the signal structure is proposed for estimating the CFOs of all users using only one OFDMA block. Diversity schemes are also presented to improve the estimation performance. Simulation results illustrate the high accuracy and efficiency of the proposed algorithm.