Sabah Badri-Hoeher

Single-antenna co-channel interference cancellation for TDMA cellular radio systems

Co-channel interference cancellation is particularly challenging in the downlink of cellular radio systems because usually only one receive antenna is available at the mobile terminal. This tutorial provides an overview of promising a single-antenna co-channel interference cancellation techniques. Focus is on the downlink of time-division multiple access systems. The results may, however, be extended to related applications, including interference suppression in multiple-input multiple-output systems.

Single antenna interference cancellation (SAIC) for cellular TDMA networks by means of joint delayed-decision feedback sequence estimation

In this letter, single antenna co-channel interference cancellation for cellular time-division multiple access (TDMA) networks by means of joint delayed-decision feedback sequence estimation is studied. The performance is increased by a novel adaptive state allocation technique

Single Antenna Interference Cancellation (SAIC) for Cellular TDMA Networks by Means of Decoupled Linear Filtering/Nonlinear Detection

In this paper, a receiver structure suitable for single-antenna cochannel interference cancellation in cellular TDMA networks is studied. The receiver under investigation consists of a novel linear prefilter followed by a nonlinear detector. The task of the prefilter is to suppress non-Gaussian interference and - simultaneously - to shorten the overall impulse response, whereas the task of the nonlinear detector is to cancel intersymbol interference. The prefilter is designed according to the principle of minimum mean square error estimation, without solving an eigenvalue problem. Optionally the prefilter can be designed utilizing available knowledge of all cochannels, knowledge of the channel of a desired user only, or with no channel knowledge at all. The nonlinear detector may be an arbitrary nonlinear equalizer, in the simplest case a memoryless detector. The receiver structure under investigation is compatible with conventional TDMA receivers ignoring cochannel interference. Performance results are presented for synchronous and asynchronous GSM/GPRS networks

Trellis-based equalization for sparse ISI channels revisited

Sparse intersymbol-interference (ISI) channels are encountered in a variety of high-data-rate communication systems. Such channels have a large channel memory length, but only a small number of significant channel coefficients. In this paper, trellis-based equalization of sparse ISI channels is revisited. Due to the large channel memory length, the complexity of maximum-likelihood detection, e.g., by means of the Viterbi algorithm (VA), is normally prohibitive. In the first part of the paper, a unified framework based on factor graphs is presented for complexity reduction without loss of optimality. In this new context, two known reduced-complexity algorithms for sparse ISI channels are recapitulated: The multi-trellis VA (M-VA) and the parallel-trellis VA (P-VA). It is shown that the M-VA, although claimed, does not lead to a reduced computational complexity. The P-VA, on the other hand, leads to a significant complexity reduction, but can only be applied for a certain class of sparse channels. In the second part of the paper, a unified approach is investigated to tackle general sparse channels: it is shown that the use of a linear filter at the receiver renders the application of standard reduced-state trellis-based equalizer algorithms feasible, without significant loss of optimality. Numerical results verify the efficiency of the proposed receiver structure

Joint delayed-decision feedback sequence estimation with adaptive state allocation

Single antenna co-channel interference cancellation for cellular TDMA networks by means of joint delayed-decision feedback sequence estimation is proposed. The performance can be increased by a novel adaptive state allocation technique.

Characterization of maritime RF/FSO channel

The growing demand on high speed data transmission as well as the bandwidth limitation of microwave (RF) transmission has stimulated the development of free-space optical (FSO) laser communication links during the last years. Making the data transmission reliable is one of the challenging problems that have to be solved to establish a communication system suitable for commercial usage. Optical transmission is highly impacted by different channel conditions, leading from signal damping to turbulence effects due to the atmosphere. In this paper a hybrid RF/FSO maritime channel is investigated. The link distance under investigation is about 14 km. Transmitted data collected during a 6 months measurement campaign is evaluated and theoretically analyzed. The correlation between weather and atmospheric impacts to the large amount of RF and FSO transmission data available, will provide an insight into the capability of estimating channel quality.

Imaging sonar-based fish detection in shallow waters

Traditionally, fish stock assessment is a time-consuming, expensive, and invasive task, since fish are caught and counted using research vessels. Therefore, in a joint project a non-invasive, acoustic-optical Underwater Fish Observatory (UFO) is proposed and developed. The UFO counts and classifies fish utilizing a stereo camera system and a sonar system in order to observe the available biomass. In this paper, we first give an overview of the whole system. Afterwards, we focus on the acoustic part of the system, which utilizes an imaging sonar in order to detect, track, and classify fish. The sonar is mounted on a fixed lander and collects data over long periods of time for the study of fish behavior. It is also intended to trigger cameras for more detailed analysis, when fish are detected in the visibility range of the cameras. The work describes the first processing steps of sonar images for parameter estimation and segmentation. The performance of the fish detector is evaluated using a set of manually annotated sonar images. The detection results show good agreement with the annotations, although some challenges for future improvement of the detector still remain.

A novel method for surface to subsea localization utilizing a modified hough transform

A new approach for acoustic localization of a fixed subsea transponder using a surface vessel equipped with a transceiver and global positioning system (GPS) based on a modified Hough transform (MHT) is presented. The MHT developed in this work is used to determine the latitude and longitude coordinates of a transponder utilizing acoustic range and GPS data gathered by the surface vessel while traveling a particular route. Various survey scenarios for a single seabed transponder have been simulated and studied considering both, accurate and inaccurate ranging, as well as realistic conditions such as different route lengths and inexactly geometrical routes (inter alia ellipse-shaped routes). The MHT-based localization approach may particularly find use in the survey of long baseline transponders. The fixed seabed transponders are provided to enable exploration tasks by acoustic networking in various fields, from science and research covering the seas and oceans (e.g. oceanography, marine biology and geology) to industrial use (e.g. exploration of deep-sea resources and minerals, monitoring of offshore constructions). The simulation results demonstrate that the proposed approach can localize the transponder unambiguously and precisely for accurate ranging. Concerning the impact of uniform ranging uncertainties, e.g. arising from spatio-temporally coherent sound speed variations, it can be concluded that full circle and ellipse routes enable a precise estimate while half and quarter circle as well as ellipse routes enable a positioning accuracy within the millimeter range. In the presence of noisy range measurements, e.g. impacted by GPS errors, the approach can provide root mean squared errors from less than 5 mm to 5 m for ranging with a standard deviation of 7.5 mm and 7.5 m, respectively. The proposed positioning approach outperforms the least-squares estimation when shortened survey routes such as half and quarter ellipse are considered. These route forms accelerate the data gathering process, which are motivated by the reduction of the vessel time and cost for the transponder survey.

Impact of speed of sound uncertainties on model-based positioning

In this paper, the impact of speed of sound uncertainties on ray-tracing based acoustic underwater positioning is investigated. Therefore, the model-based positioning approach recently proposed by the authors in [1] is simplified in sound ranging. Based on the new method the impact of different sound speed values in the distance estimate is studied. Furthermore, we analyze the effect of recording of a few measured values of the sound speed profile (SSP) on the ranging accuracy using the model-based approach. Altogether, it can be concluded that the resolution of the SSP has a significant influence on the accuracy of the distance estimation. A challenging effect is the nonlinearity in the SSP, which is addressed and discussed. Taking into account the nonlinearity in the distance estimate, investigations for a deep-water environment show promising results.

Impulse response shortening for multiple co-channels

In this paper, a novel design of a receiver-side FIR prefilter is proposed which is able to jointly shorten the impulse responses of multiple co-channels given just one receive antenna. The prefilter coefficients are computed without explicitly solving an eigenvalue problem. In conjunction with a reduced-complexity multiuser detector, a good error performance can be achieved. As a possible application, co-channel interference cancellation for the EDGE system is studied. The prefilter, however, is also suitable for interference suppression in MIMO systems, for crosstalk suppression, or for reducing the length of the cyclic prefix in multitone systems, among other applications.