Alexander Kocian

Joint time-frequency linear equalization for OFDM signals

Within the context of high-data rate transmissions over time varying multipath fading channels, this article presents a new receiver design for orthogonal frequency division multiplexing (OFDM) systems. The received signal is processed jointly in time and frequency domains. A Discrete Wavelet Transform is applied to the received signal before equalization which is based on the minimum mean square error (MMSE) principle. The paper shows that the proposed receiver is able to work also in highly time-variant channels where a traditional frequency domain equalizer gets very bad performance. Moreover, it is shown that this joint time-frequency equalization is able to exploit time diversity without coding. The performance of the proposed equalizer are shown both in case of perfect channel estimation and in presence of a MMSE linear channel estimator.

Development and realization of an artificial patient with hearing impairment

The paper proposes a narrowband stochastic system model for auditory signal processing. The parameters are ipsilateral, contralateral and interaural hearing losses, false positive and false negative responses, and patient response time. The auditory model is then used to realize a patient simulator (artificial patient), comprising out of two microphones, a skull simulator, sound cards and a noiseless personal computer. A locally stored database contains the simulated and the recorded patient data. First field trials in an audiometric test room at the University Medical Center, Utrecht, The Netherlands, indicate that the artificial patient resembles the behavior of a real patient within a band of 10 dB-HL over the entire audiometric frequency range.

Intelligent Smartphone Audiometry

The continuously aging population in the majority of industrialized nations challenges the healthcare providers to maintain quality of healthcare services at status quo. To make health care sustainable, the paradigm Ambient Intelligence can be used to exploit information and telecommunication technology for the development of autonomous healthcare services. Following this approach, we design and implement a virtual audiologist dubbed ViA, performing air-conduction and bone-conduction hearing tests based on a standard in contrast to existing solutions. The software platform is Android. In this paper, we present the system architecture of ViA with focus on the Android platform and discuss calibration issues. First test results in office environment indicate that a large range of hearing thresholds can be reproduced on different smartphones within a band of 9 dB. ViA has the potential to identify individuals with correctable hearing loss without putting extra load on the healthcare providers.

A novel look at FDE multicarrier and single carrier transmission schemes

In this paper, main Single Carrier (SC) and Multicarrier (MC) systems with Frequency Domain Equalization (FDE) are reviewed with the objective to identify key features of the evolution path of air interfaces towards 4G. In particular, this paper shows that the FFT/IFFT operation can be seen as the concatenation of two operations: S/P conversion and spreading. We show that the transmitter of an OFDMA system performs a S/P conversion and a multiplication with specific complex spreading codes. By replacing the orthogonal complex spreading codes of this equivalent OFDMA system, with traditional orthogonal spreading codes that are used in DS-CDMA systems, for instance Walsh-Hadamard codes, we achieve a novel multicode-CDMA system. The comparison of this novel SC transmission scheme with other SC and MC systems shows that the novel SC system has almost the same performance as OFDMA and also similar PAPR. On the other hand, it has a pretty different behavior wrt other SC systems such as IFDMA and DS-CDMA with FDE.

Joint Bayesian soft multiuser decoding and multichannel estimation based on the variational IEM algorithm

The paper presents an iterative scheme that incrementally minimizes the Kullback-Leibler divergence between joint posterior and nuisance parameter distribution, and directly minimizes the Kullback-Leibler divergence between joint posterior and parameter-of-interest distribution in alternating order. This so-called variational Bayes incremental expectation maximization (VB-IEM) algorithm has two virtues: first, it non-decreases an objective function at each iteration and secondly, it adopts the convergence properties of the exact EM algorithm if the parameter estimate is consistent and maximum a posteriori. When the VB-IEM algorithm is applied to joint multi-user decoding and multi-channel estimation in flat Rayleigh fading, Monte Carlo simulations show that the proposed scheme supports extremely high effective system loads.