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In an acoustic communication system that employs orthogonal frequency division multiplexing (OFDM), the presence of considerable Doppler spread destroys the frequency orthogonality of OFDM, and thus inter-carrier interference (ICI) is introduced, which increases the bit error rate (BER). This work proposes a channel equalizer based on the BCJR algorithm (BCJRE) for mitigating ICI. Its performance...
Complementary sets of sequences (CSS) are widely used in communications field due to their good correlation properties. The use of multilevel CSS reduces the binary CSS limitations in length and number of sequences per set, giving more flexibility in their applications, but with a higher computational complexity in the implementation of the generation and/or correlation algorithms. Although efficient...
Complementary Set of Sequences (CSS) are being widely used in communications due to the ideal correlation properties and the availability of efficient correlators that significantly reduce the number of computations in the detection process. In this paper, the performance of the acoustic signals encoded by multilevel CSS in an underwater horizontal link is analysed. For that, a channel propagation...
In the past few years, the use of Complementary Set of Sequences (CSS) had a considerable impact on several applications, such as: OFDM or quasi-synchronous CDMA communication systems, multiuser active sensing systems, or the development of non-destructive testing (NDT). Their use is attractive due to the ideal aperiodic correlation properties of the sequences. There are efficient architectures to...
The computation of relative positions among mobile objects is a useful information when are not constrained to a specific environment and they cannot depend on an external infrastructure to obtain their location information. The resolution of this kind of problems cannot be treated separately for each object. Thus, it is necessary to use ranging mechanisms that allow to simultaneously measuring the...
The use of Ultra -WideBand (UWB) techniques is considered an attractive solution for indoor Local Positioning Systems (LPS). In this case, the positioning is usually performed by hyperbolic trilateration techniques measuring the time difference of arrival (TDOA) between the received signals coming from the beacons placed in the environment. The detection of the true arrival instant for the used encoded...
In this paper the design of an underwater acoustic link using the model for a short vertical channel is presented. From the specifications of the link, it is possible to determine the optimum operating frequency, modulation scheme and transmit power, information that will be useful to perform a selection of the appropriate acoustic transducer. For that purpose, a brief description of the channel model...
Accurate distance estimation is a key part for certain active sensing systems as ultrasonic Indoor Positioning Systems (IPSs). In these systems, receive filters play a key role for the achievement of robust and accurate position estimations. For that reason, this paper carries out the performance comparison of different receive filters, namely matched-filter, generalized cross-correlation function,...
Underwater Wireless Sensor Network applications require the design of efficient communications links due to the rough environment. Acoustic signals make feasible the data transmission based on Direct Sequence Code Division Multiple Access (DS-CDMA) techniques, because compensates the multipath effect and allow receivers to simultaneously distinguish among multiple independent emitters. For that purpose,...
The underwater channel is a highly variable medium due to the influence of several effects on the acoustic signal, and the physical variability of the environment. This behavior makes the underwater channel a very difficult one to model, and also a complex environment to work with. In acoustic-based positioning or sonar systems, where it is important to know accurately the time-of-flights of the signals,...
Underwater acoustic channel modeling keeps being an active field of research, despite the fact that the physical effects are known since decades ago. The great variability that is found in this kind of channel makes modeling a difficult task, being highly dependent on a particular environment. For high frequencies, ray tracing is a simple and reliable solution, giving a good approximation and a lot...
This work proposes several techniques to validate the detection of objects in railway environments. The system for obstacle detection is based on an infrared emitting barrier and another of receivers placed on opposing side in the railway, establishing different optical links between them. The system is located at the segments of the railroads where it is desired to know the existence of objects,...
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