雷神公司

The harsh propagation environment at millimeter-wave (mmW) frequencies can be countered by using large antenna arrays, which can be steered electronically to create directional beams. Knowledge of the key channel characteristics in this environment, including the delay spread, the coherence time, and the coherence bandwidth, plays a significant role in optimal adaptation of the transmission waveform. In this paper, we focus on analyzing the delay spread of a directional mmW channel. A high delay spread causes inter-symbol interference (ISI), which can be mitigated by concatenating cyclic prefixes (CPs) to data symbols at the expense of lower spectral efficiency. Considering a single mmW link, whose transmitter (Tx) and receiver (Rx) are equipped with uniform planar arrays (UPAs), we study the impact of various beamforming attributes (e.g., antenna-array size, beamwidth, beam direction, and beam misalignment) on the average and root-mean-square delay spread. We use detailed simulations with accurate 3GPP channel models and conduct extensive experiments using a $4\times 8$ UPA at 28 GHz to verify our analysis. Based on this analysis, we study the optimal beamforming configuration at the Rx for a given Tx beamformer so as to maximize the spectral efficiency. Our proposed beam selection method finds the best Rx beam direction that results in a low delay spread and high signal-to-noise ratio (SNR). Our extensive simulation and experimental results verify that this method significantly improves the spectral efficiency, almost doubling the data rate in some cases.

Near infrared spectroscopy (NIRS) is capable of detecting and monitoring acute changes in cerebral blood volume and oxygenation associated with traumatic brain injury (TBI). Wavelength selection, source-detector separation, optode density, and detector sensitivity are key design parameters that determine the imaging depth, chromophore separability, and, ultimately, clinical usefulness of a NIRS instrument. We present simulation results of NIR light propagation in a digital head model as it relates to the ability to detect intracranial hematomas and monitor the peri-hematomal tissue viability. These results inform NIRS instrument design specific to TBI diagnosis and monitoring.

There is a debate within the information fusion community whether situation and threat assessment (SA/TA) are separate as called out in the Joint Directors of the Lab (JDL) or interlinked in the Data Fusion Information Group (DFIG) Model. Situation assessment seeks a geospatial and temporal acknowledgement of the environment while threat assessment determines the impacts from the situation. Three types of impacts exist: entities (e.g., objects), environments (e.g. natural disasters), and relationships (interactions among entities). While object assessment can be determined from Bayes and/or evidential reasoning, it is also extended to threat assessment through a prior effects and world modeling. In this paper, we bring together the discussions of context as related to the discussion on SA/TA contextual analysis. While it is inherent that context plays a role in TA; we seek to highlight some of the assumptions, difficulties, and needs for TA — most notably stemming from requirements for sensor, user, and mission (SUM) management. SA and TA can be separate, linked, or serial, depending on the circumstance. An example is presented that highlights the need for context assessment in threat analysis as related to the changing situation.

Quad Flat non-leaded (QFN) devices are one of the fastest growing package types in the electronics industry. QFN acceptance in long-life devices exposed to harsh environments is currently limited due to reliability concerns. The large area heat sink associated with the QFN design, floods the perimeter of QFN in the soldering process with flux residue making the QFN one of today’s toughest cleaning challenges. Un-cleaned flux residues trapped under the QFN have the potential to be hydroscopic and conductive. Concentrated ionic levels lower dielectric strength and can result in dendrite growth. From a cleaning perspective, many designers have poor insight into factors that assure a cleanable design. Variables such as solder paste, reflow conditions, component placement, component clearance (standoff), cleaning agent and cleaning equipment are important factors. Collaboration between process engineers, assembly designers, solder materials, cleaning agent and cleaning equipment experts can improve integration of the QFN design and assembly. Circuit board design plays an important role when cleaning is required. The purpose of this research is to study QFN ground pad and circuit board solder mask definition strategies. Past studies find that high levels of Z-Axis clearance result in less residue surrounding pads. Removal of solder mask opens flow channels that enable better cleaning. The designed experiment will study QFN cleaning effects and report data findings for current and improved design strategies.