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In the preceding chapter, we have seen that data-dependent beamformers can be efficiently realized in GSC structures. However, GSCs, or more general LCLSE/LCMV beamformers, are sensitive to steering errors, to array perturbations and to reverberation w.r.t. the desired signal. Therefore, the performance of LCLSE/LCMV beamformers may decrease in realistic implementations: The desired signal may be distorted, a nd/or interference rejection may be reduced. In order to overcome these problems and to fully profit from the advantages of the GSC, we derive in this chapter a robust version of the GSC (RGSC). The problems of LCLSE/LCMV beamformers are resolved by using time-varying spatio-temporal constraints instead of purely spatial constraints [HK02a, HK03]. In contrast to spatial constraints, these s patiotemporal constraints explicitly take multi-pat h propagation w.r.t. the desired source into account by modeling the propagation by room impulse responses, such that the direct signal path and the secondary signal paths are cancelled at the output of the blocking matrix of the RGSC. Therefore, the RGSC is robust against cancellation of the desired signal in reverberant acoustic environments. In Chap. 2, it was shown that not only the propagation in a reflective environment can be modeled by impulse responses, but that n on-perfect transducer characteristics, i.e., directional-dependent and time-varying tolerances of the complex gain of the transducers, can be captured in impulse responses, too. Therefore, the RGSC is robust against tolerances of the characteristics or positions of the transducers without requiring explicit calibration. Timevarying spatio-temporal constraints take into account the temporal variations of the impulse responses between the desired source and the sensor signals due to speaker movements, changes in the acoustic environment, or time-varying complex gains of the sensors. [ABSTRACT FROM AUTHOR]

In cooperative amplify-and-forward (AF) system using spatially distributed relays, there exist some relay paths degrading performance because of noise enhancement. In order to alleviate the deteriorating effect of such paths, we propose adaptive generalized selection combining (GSC)/MRC and iterative GSC/MRC switching techniques based on cyclic-redundancy-check (CRC) error detection. The adaptive GSC (with order N)/MRC switching with K relays operates as follows: the destination performs initial data detection by combining the strongest N ( < K + 1) paths, and CRC is checked for error detection. If an error is detected, MRC with all the K + 1 paths is then performed. To further generalize, the iterative GSC/MRC is employed in an iterative manner conditioned on successive error detection. Our simulation results show that the proposed schemes show better diversity performance than conventional one in terms of the bit-error rate (BER), when an appropriate CRC generator polynomial is used depending on the frame size. The diversity gain of the proposed schemes become far prominent when imperfect channel estimation is assumed at the destination. [ABSTRACT FROM AUTHOR]

A definition of the term "GSC Bus" is presented. It stands for Gecko System Connect Bus, also knowm as Gonzo System Connect and General System Connect. It is a bus used in many of the HP 9000 workstations and services. It was 32-bit and reached 40MHz in its final iterations.

The decline in duodenal ulcer disease and the new endoscopic therapeutic techniques (endoscopic submucosal dissection, ESD) for early-stage gastric cancers have diminished the need for gastric surgery. In the other side, gastric surgery is improving progressively in the field of bariatric surgery. Data from literature with long-term follow-up reports a variable risk of gastric cancer after gastric surgery both for benign and malignant diseases. Since the bariatric surgery has recently introduced in clinical practice, few reports have been published on endoscopic follow-up after bariatric surgery. [ABSTRACT FROM AUTHOR]

In active sonar system, the detection of bottom object in shallow water is usually a difficult task since the reverberation, which consisting of a large number of spurious echoes, and generates a lot of false alarm. The propagation channel exhibits time-spreading distortion(TSD) and fast fading distortion(FFD) in ocean. The distortion mechanisms degrade optimum detector performance and reduce the performance of high resolution detector in shallow water. The recursive adaptive beamforming based on the recursive least square(RLS) and the generalized sidelobe canceller(GSC) structure is constructed for uniform circular receiving array application. Then we combined detectors based TSD/FFD channel model with RLS-GSC, to enhance bottomed object detection performance in littoral area. The approach is evaluated experimentally using real-data set and in simulation test. It improves detection signal-to-reverberation ratio(SRR) and also reduce false alarm probability in real conditions. [ABSTRACT FROM AUTHOR]