Truncated Turbo Equalizer with SIC for OTFS

Orthogonal time frequency space (OTFS) is a promising candidate waveform for the next generation wireless communication systems. OTFS places data in the delay-Doppler (DD) domain, which simplifies channel estimation in highmobility scenarios. However, due to the 2-D convolution effect of the time-varying channel in the DD domain, equalization is still a challenge for OTFS. Existing equalizers for OTFS are either highly complex or they do not consider intercarrier interference present in high-mobility scenarios. Hence, in this paper, we propose a novel two-stage detection technique for coded OTFS systems. Our proposed detector brings orders of magnitude computational complexity reduction compared to existing methods. At the first stage, it truncates the channel by considering only the significant coefficients along the Doppler dimension and performs turbo equalization. To reduce the computational load of the turbo equalizer, our proposed method deploys the modified LSQR (mLSQR) algorithm. At the second stage, with only two successive interference cancellation (SIC) iterations, our proposed detector removes the residual interference caused by channel truncation. To evaluate the performance of our proposed truncated turbo equalizer with SIC (TTE-SIC), we set the minimum mean squared error (MMSE) equalizer without channel truncation as a benchmark. Our simulation results show that the proposed TTE-SIC technique achieves about the same bit error rate (BER) performance as the benchmark

Turbulent-like fluctuations in quasistatic flow of granular media

We analyze particle velocity fluctuations in a simulated granular system subjected to homogeneous quasistatic shearing. We show that these fluctuations share the following scaling characteristics of fluid turbulence in spite of their different physical origins: 1) Scale-dependent probability distribution with non-Guassian broadening at small time scales; 2) Power-law spectrum, reflecting long-range correlations and the self-affine nature of the fluctuations; 3) Superdiffusion with respect to the mean background flow

Fuga de radiação de unidades de radiologia pediátrica

Em radiologia pediátrica, é necessário que uma pessoa segure os pacientes durante a exposição, já gue os pacientes são crianças e recém-nascidos. Portanto, torna-se importante uma apropriada determinação e minimização da radiação de fuga das unidades de radiodiagnóstico. Fez-se medidas de radiação de fugas em cinco unidades de raios X, sendo quatro unidades produzidas pela mesma companhia. Três das quatro unidades produzidas pela mesma companhia apresentaram uma contribuição anormal da radiação de fuga. Discute-se a não-adequação dos atuais cabeçotes para radiologia pediátrica e apresenta-se sugestões para um novo enfoque em radiação pediátrica.In pediatric radiology, it is necessary that a person stay with the patients, as they are children and newly bom, during radiation exposure. Therefore, the proper evaluation and minimization of radiation leakage from radiodiagnostic units becomes important. Measurements of leakage radiation were carried out in five X-ray units, where four of which are manufactured by the same company. Three of the four units produced by the same company, showed an abnormal contribution of the leakage radiation. The inadequacy of the presently available housing tubes for pediatric radiology is discussed. Suggestions regarding new approach in pediatric radiology are presented

Pre-avalanche instabilities in a granular pile

We investigate numerically the transition between static equilibrium and dynamic surface flow of a 2D cohesionless granular system driven by a continuous gravity loading. This transition is characterized by intermittent local dynamic rearrangements and can be described by an order parameter defined as the density of critical contacts, e.g. contacts where the friction is fully mobilized. Analysis of the spatial correlations of critical contacts shows the occurence of ``fluidized'' clusters which exhibit a power-law divergence in size at the approach of the stability limit. The results are compatible with recent models that describe the granular system during the static/dynamic transition as a multi-phase system.Comment: 9 pages, 6 figures, submitted to Phys. Rev. Let