Current Issue : October - December Volume : 2012 Issue Number : 4 Articles : 5 Articles
The problem of designing robust systems to track global navigation satellite system (GNSS) signals in harsh environments has\r\ngained high attention. The classical closed loop architectures, such as phase locked loops, have been used for many years for\r\ntracking, but in challenging applications their design procedure becomes intricate. This paper proposes and demonstrates the use\r\nof a quasi-open loop architecture to estimate the time varying carrier frequency of GNSS signals. Simulation results show that this\r\nscheme provides an additional degree of freedom to the design of the whole architecture. In particular, this additional degree of\r\nfreedom eases the design of the loop filter in harsh environments....
An episode of relatively thick (till ~3 km) aerosol formation over the urban area of Sofia city was observed by lidar at a wavelength\r\nof 1064 nm. The lidar is part of Sofia lidar station at the Institute of Electronics of Bulgarian Academy of Sciences. Analysis of the\r\nweather conditions during the measurement period explains the stable persistence of such formation of human-activity aerosol\r\nover the town for the days of observation 20, 21, 23, and 24 June, 2011. The estimated top of the Planetary Boundary Layer for the\r\nmeasurement dated 23 June showed unusually high altitude ~2200m above ground. The results are presented in terms of vertical\r\natmospheric backscatter coefficient profiles and color maps of the aerosol stratification evolution...
Carrier phase estimation in real-time Global Navigation Satellite System (GNSS) receivers is usually performed by tracking loops\r\ndue to their very low computational complexity. We show that a careful design of these loops allows them to operate properly\r\nin high-dynamics environments, that is, accelerations up to 40 g or more. Their phase and frequency discriminators and loop\r\nfilter are derived considering the digital nature of the loop inputs. Based on these ideas, we propose a new loop structure named\r\nUnambiguous Frequency-Aided Phase-Locked Loop (UFA-PLL). In terms of tracking capacity and noise resistance UFA-PLL has\r\nthe same advantages of frequently used coupled-loop schemes, but it is simpler to design and to implement. Moreover, it can keep\r\nphase lock in situations where other loops cannot. The loop design is completed selecting the correlation time and loop bandwidth\r\nthat minimize the pull-out probability, without relying on typical rules of thumb. Optimal and efficient ways to smooth the phase\r\nestimates are also presented. Hence, high-quality phase measurementsââ?¬â?usually exploited in offline and quasistatic applicationsââ?¬â?\r\nbecome practical for real-time and high-dynamics receivers. Experiments with fixed-point implementations of the proposed loops\r\nand actual radio signals are also shown....
The paper exploits the outlier detection techniques for wireless-sensor-network- (WSN-) based localization problem and proposes\r\nan outlier detection scheme to cope with noisy sensor data. The cheap and widely available measurement techniqueââ?¬â?received\r\nsignal strength (RSS)ââ?¬â?is usually taken into account in the indoor localization system, but the RSS measurements are known to be\r\nsensitive to the change of the environment. The paper develops an outlier detection scheme to deal with abnormal RSS data so as\r\nto obtain more reliable measurements for localization. The effectiveness of the proposed approach is verified experimentally in an\r\nindoor environment....
Motion detection in the fly is extremely fast with low computational requirements. Inspired from the fly�s vision system, we focus\r\non a real-time flight control on a miniquadrotor with fast visual feedback. In this work, an elaborated elementary motion detector\r\n(EMD) is utilized to detect local optical flow. Combined with novel receptive field templates, the yaw rate of the quadrotor is\r\nestimated through a lookup table established with this bioinspired visual sensor. A closed-loop control system with the feedback of\r\nyaw rate estimated by EMD is designed. With the motion of the other degrees of freedom stabilized by a camera tracking system,\r\nthe yaw-rate of the quadrotor during hovering is controlled based on EMD feedback under real-world scenario. The control\r\nperformance of the proposed approach is compared with that of conventional approach. The experimental results demonstrate\r\nthe effectiveness of utilizing EMD for quadrotor control....
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