Detecting an object which is located at seabed is an important issue for various areas. This paper presents an approach to detection of an object that is placed at seabed in the shallow water. A conventional scheme is to employ a side-scan sonar to obtain images of a detection area and to use image processing schemes to recognize an object. Since this approach relies on high frequency signals to get clear images, its detection range becomes shorter and the processing time is getting longer. In this paper, we consider an active sonar system that is repeatedly sending a linear frequency modulated signal of 6～20 kHz in the shallow water of 100m depth. The proposed approach is to model consecutively received reflected signals and to measure their modeling error magnitudes which decide the existence of an object placed on seabed depending on relative magnitude with respect to threshold value. The feature of this approach is to only require an assumption that the seabed consists of an homogeneous sediment, and not to require a prior information on the specific properties of the sediment. We verify the proposed approach in terms of detection probability through computer simulation.

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Super-resolution near-field structure (super-RENS) read-out samples are affected by a nonlinear and noncausal channel, which results in intersymbol interference. Some of these nonlinearities are caused by domain bloom or asymmetry, which is an imperfection in the disc. In this study, we investigate the effect of the domain bloom on the super-RENS read-out signal. For this, we employ the asymmetric symbol conversion scheme to generate asymmetric symbols corresponding to a bit pattern and apply the linear modeling approach to model the read-out channel with a finite impulse response filter. The modeling performance is verified with the causal and noncausal filters in terms of normalized mean square error. The performance of the approach considered here is compatible with that of the Volterra filter, whereas the approach maintains a lower complexity than the Volterra filter.

Satellite communication has a broadband property and wide area coverage. It is also vulnerable to jamming because of the utilization of open channels. In this paper, a satellite transponder adopts a polyphase filter bank structure, which allows flexible frequency management while a nulling scheme was applied to remove narrowband interference signal of a filter bank sub-channel. For this satellite transponder, jamming, polyphase filter bank and nulling scheme are introduced, and in the simulation, we evaluate the performance of the anti-jamming system in terms of BER and PSNR by transceiving random data and images under various jamming environments.