Regularized Neural Detection for One-Bit Massive MIMO Communication Systems

Detection for one-bit massive MIMO systems presents several challenges especially for higher order constellations. Recent advances in both model-based analysis and deep learning frameworks have resulted in several robust one-bit detector designs. Our work builds on the current state-of-the-art gradient descent (GD)-based detector. We introduce two novel contributions in our detector design: (i) We augment each GD iteration with a deep learning-aided regularization step, and (ii) We introduce a novel constellation-based loss function for our regularized DNN detector. This one-bit detection strategy is applied to two different DNN architectures based on algorithm unrolling, namely, a deep unfolded neural network and a deep recurrent neural network. Being trained on multiple randomly sampled channel matrices, these networks are developed as general one-bit detectors. The numerical results show that the combination of the DNN-augmented regularized GD and constellation-based loss function improve the quality of our one-bit detector, especially for higher order M-QAM constellations.Comment: Initially submitted to IEEE TMLCN in October 202

An Improved Analytical Model for Efficiency Estimation in Design Optimization Studies of a Refrigerator Compressor

The stack up of losses within a system gives an indication of its efficiency. In a refrigerator compressor, valves contribute to thermodynamic losses (pressure and cooling capacity) due to valve dynamics and mistiming. This paper proposes an improvement to an existing analytic closed form solution for efficiency estimation of such compressors by incorporating more detailed valve physics/ dynamics. For maximum energy efficiency ratio (EER), it is beneficial in certain variable capacity compressor architectures to drive the piston at a resonant frequency. In an oscillating system, this is typically determined by the mechanical spring-damper characteristics. This resonant frequency is usually a complex function of the geometry and operating conditions due to the gas-spring effect. A closed form solution for performance estimation of such a setup proposed earlier in literature (Choe & Kim) does not account for the effect of valve dynamics. However, the timing of valve operation influences the in-cylinder pressure build-up transients and thus modulates the gas-spring stiffness. While an accurate estimation of the resonant frequency requires a multi-physics simulation of the compressor, a detailed simulation of such complexity is time intensive especially when performing design optimization studies and hence analytical models would be preferred. The current work presents an improved equivalent analytic model for such optimization. Uncertainty analysis of the present approach is also discussed by comparing different performance parameters against full nonlinear model estimates, as relevant

Surgical Management of Optic Disc Pit Maculopathy with Outer Retinal Hole

Objective: To report the successful outcome of a rare optic pit-associated maculopathy with an outer retinal hole following 23 G vitrectomy, internal limiting membrane (ILM) peeling and fluid-gas exchange without additional endolaser. Method: Interventional case report. Results: This case report documents a 56-year-old male patient with complaints of progressive diminution of vision in the right eye more than in the left eye due to an optic disc pit with an outer retinal hole and a cataract. Optical coherence tomography confirmed the presence of an outer retinal hole. The case report shows the successful outcome of a rare optic pit-associated maculopathy with an outer retinal hole and a cataract following phacoemulsification with 23 G vitrectomy, ILM peeling and fluid-gas exchange without additional endolaser

Friction Model Development for a reciprocating compressor

Friction loss has a significant impact on the performance of a reciprocating compressor. Piston-cylinder friction is a major contributor compared to the other contributors like thrust bearing, piston pin and crank. In the present work,the piston–cylinder interaction inside a small hermetic compressor is modeled using the Reynolds equation which is solved using finite difference method. The model provides key compressor design parameters such as minimum oil film thickness, oil pressure distribution between piston-cylinder, normal forces and friction power loss. The model is validated against data from published literature. Using the above formulation, different concepts have been studied & compared against their friction loss characteristics. These include variable speed versus variable displacement for capacity control, piston-cylinder clearance for blow-by, cold start (high viscosity oil due to low temperature), lubricating fluids, viz. POE versus gas bearing

An Approach Towards Reed Valve Geometry Design

Pressure-actuated reed valves play an important role in the compression process of a refrigerator compressor. The material properties and geometrical parameters of the valve and geometrical properties of valve port determine the flow coefficient which in turn impacts the compressor efficiency. Also, the moving mass of the valve and its stiffness governs the transient response (valve flutter) which impacts life and reliability of the valve in operation. Therefore, it is imperative to carefully design the reed valves to maximize compressor performance while meeting the above requirements. The design of reed valves involves determining the geometrical parameters (length, width and thickness) and material properties (type of steel etc.). These properties are chosen such that they correspond to the desired mass and stiffness of the valve. This work mainly focuses on determining the basic valve topology (geometrical parameters) with the desired mass and stiffness of the reed valve as design constraints. In order to obtain the optimum reed valve mass and stiffness values, an in-house system level performance simulation model is used. An analytical finite element based model has been built that searches for geometrical parameters which meets both target valve parameters and material limitations for reliability and life. This provides multiple valve designs with different geometrical parameters and gives the designer the flexibility to choose the most suitable valve design for a targeted application. Additionally, the basic valve topology will facilitate a more detailed performance analyses, viz. flow-thermal simulations and flow-structure interaction

Synchronization in pairs of opto-thermally driven mechanically coupled micro-oscillators

We study the phenomenon of synchronization in pairs of doubly clamped, mechanically coupled silicon micro-oscillators. A continuous-wave laser beam is used to drive the micro-beams into limit cycle oscillations and to detect the oscillations using interferometry. Devices of different dimensions are used to introduce frequency detuning, and short silicon bridges connecting the micro-beams are used as mechanical coupling between the oscillators. The region of synchronization is plotted for the MEMS system in the detuning vs. coupling parameter space and compared with the numerical analysis of a corresponding, lumped-parameter model. Three states of oscillations are observed i.e. the drift state, quasi-periodic state, and the synchronized state. The numerical model also distinguishes between in-phase and out-of-phase synchronization where out-of-phase synchronization is observed at low coupling strengths and low frequency detuning. We also show that the experimentally measured frequency fluctuations of the system reduce with an increase in coupling strength.Comment: 8 pages, 7 figure