Alexander Lampe

Alexander Lampe
Hochschule Mittweida | HSMW · Department of Mathematics

About

31
Publications
1,218
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653
Citations

Publications

Publications (31)
Article
Full-text available
In this contribution, we consider the classification of time series and similar functional data which can be represented in complex Fourier and wavelet coefficient space. We apply versions of learning vector quantization (LVQ) which are suitable for complex-valued data, based on the so-called Wirtinger calculus. It allows for the formulation of gra...
Preprint
Full-text available
This paper contains a feasibility study of deep neural networks for the classification of Euro banknotes with respect to requirements of central banks on the ATM and high speed sorting industry. Instead of concentrating on the accuracy for a large number of classes as in the famous ImageNet Challenge we focus thus on conditions with few classes and...
Chapter
This paper presents a technique to handle the problem of high peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems. The presented scheme is a combination of two well-known techniques, namely selected mapping (SLM) and clipping. In contrast to other hybrid schemes, where the mentioned techniques are perform...
Conference Paper
Massive multiple-input multiple-output (MIMO) is a key technology driving the 5G evolution. It relies on the use a large number of antennas at the base-station to improve network performance. The performance of massive MIMO systems is often limited by imperfect channel estimation because of pilot contamination. Recently, several channel estimation...
Chapter
This paper addresses the application of gradientdescentbased machine learning methods to complex-valued data. In particular, the focus is on classification using Learning Vector Quantization and extensions thereof. In order to apply gradient-based methods to complex-valued data we use the mathematical formalism of Wirtinger’s calculus to describe t...
Conference Paper
This paper presents a technique to handle the problem of high peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems. The presented scheme is a combination of two well-known techniques, namely selected mapping (SLM) and clipping. In contrast to other hybrid schemes, where the mentioned techniques are perform...
Conference Paper
Several contributions have been made on using Compressed Sensing (CS) for sparse channel estimation in wireless communications. Therein the focus is mainly set on designing transmission systems towards the application of CS channel estimation, which includes for example the proposal for random pilot patterns in OFDM systems. However, most state of...
Conference Paper
In mobile systems it is essential to estimate the channel response at the receiver. Since the multipath structure of the radio channel is generally sparse, this has recently proven in OFDM systems to be an application where insights from the theory of Compressed Sensing (CS) can be beneficial. Classical methods apply for example digital MMSE filter...
Conference Paper
This paper studies the robustness of spreading sequences designed for random code-division multiple-access (CDMA) schemes with continuous-time constant envelope (CE) against transmitter impairments. It is shown that by taking into account the impairments of a real implementation the investigated design algorithm finds a set of spreading waveforms w...
Article
This paper studies the spectral efficiency of code-division multiple access with constant envelope modulation in the large system limit. Despite the fact that continuous phase modulation is hit by a severe drawback in spectral efficiency as compared to quadrature amplitude modulation on a single user communication link, the gap in terms of spectral...
Article
In this paper, we develop receiver concepts for transmission with space-time block codes (STBCs) over frequency-selective fading channels. The focus lies on Alamouti's space-time block-coding scheme, but the results may be generalized to other STBCs as well. We show that a straightforward combination of conventional equalizers and a space-time bloc...
Article
In this paper, we develop receiver concepts for transmission with space--time block codes (STBC's) over frequency--selective fading channels. The focus lies on Alamouti's STBC, but the results may be generalized to related STBC's. We show that a straightforward combination of conventional equalizers and a space--time block decoder is only possible...
Article
In this paper, we develop receivers for transmission with space--time block codes (STBC's) over fading intersymbol interference (ISI) channels. The focus lies on Alamouti's STBC, but the results may be generalized to related codes. It turns out that a straightforward combination of conventional equalizers and a space--time block decoder is only pos...
Article
In this paper, we develop receiver concepts for transmission with space-time block codes (STBCs) over frequency-selective fading channels. The focus lies on Alamouti's space-time block-coding scheme, but the results may be generalized to other STBCs as well. We show that a straightforward combination of conventional equalizers and a space-time bloc...
Article
We propose several equalization schemes based on widely linear processing (WLP). The received signal and its complex conjugate are separately filtered and the results are linearly combined. It is shown that WLP yields a gain in performance if the (noiseless) received signal can be interpreted as the convolution of a real-valued data sequence and an...
Article
A practically interesting approach for iterative channel estimation, multiuser detection, and single-user decoding based on maximum a posteriori symbol-by-symbol estimation for direct sequence/code-division multiple-access (DS-CDMA) is proposed. The receiver relies on the output of a bank of matched filters for each user and each path, and combines...
Article
In this paper, a novel robust noncoherent receiver for MMSE interference suppression for DS-CDMA is proposed. The receiver consists of an MMSE filter and a decision-feedback differential detector (DF-DD). The performance of the proposed scheme is investigated analytically and by computer simulations. It is shown that the loss compared to coherent M...
Article
A novel multiuser detector for direct sequence code division multiple access is proposed. The receiver performs iterated soft decision interference cancellation (ISDIC) based on multiuser interference suppression filters designed for minimization of the mean-square error. Assuming a complex modulation format, we show that the multiuser interference...
Conference Paper
This paper presents a modified version of Tomlinson-Harashima type precoding applicable to a setting with decentralized receivers, e.g. in a DS-CDMA downlink scenario. Precoding, i.e., nonlinear pre-equalization, is an interesting strategy for significantly simplifying signal processing at the receiver side (mobile terminals) at only moderate addit...
Conference Paper
In this paper, Tomlinson-Harashima precoding, a nonlinear pre-equalization technique, is proposed for transmission over multiple-input/multiple-output channels. Instead of equalizing intersymbol interference (temporal equalization) here spatial equalization, i.e., equalization of multi-user interference is performed. If only a low-rate backward cha...
Conference Paper
We develop receivers for transmission with space-time block codes (STBCs) over fading intersymbol interference (ISI) channels. The focus lies on Alamouti's STBC, but the results may be generalized to related codes. It turns out that a straightforward combination of conventional equalizers and a space-time block decoder is only possible if at least...
Article
In this paper, two novel equalization algorithms applying soft-decision feedback, designed for quaternary phase-shift keying (QPSK) transmission are introduced. The first one uses a matched filter (MF) as a front end and is derived from [1] where it was originally developed for binary transmission. The second one is an improved version of the first...
Article
In this paper, we develop receiver concepts for transmission with space time block codes (STBC's) over frequency selective fading channels. The focus lies on Alamouti's space time block coding scheme, but the results may be generalized to other STBC's. We show that a straightforward combination of conventional equalizers and a space time block deco...
Article
In this paper, we investigate the transmission over time--variant multipath Rayleigh --fading channels employing Direct Sequence Code Division Multiple Access (DS--CDMA). In order to estimate the actual channel state as well as to detect the users' data symbols an iterated channel estimation scheme employing pilot symbols in conjunction with soft d...
Conference Paper
The concept of widely linear estimation is applied to the equalization problem. Widely linear equalizers and decision-feedback equalizers with widely linear feedforward filtering are presented. For mobile communication channels significant performance gains can be achieved compared to conventional equalizers
Conference Paper
We give the asymptotic signal-to-interference ratio for the so-called widely linear minimum mean-squared error multiuser receiver for transmission of multiple users to a common receiver with DS-CDMA. Observing that widely linear multiuser detection virtually doubles the spreading factor, we show that transmission with real-valued channel symbols ca...
Conference Paper
Coded transmission over time-variant multipath Rayleigh-fading channels employing direct sequence code division multiple access (DS-CDMA) is considered. Assuming ideal knowledge of the actual channel state and randomly chosen spreading sequences, the performance of iterative multiuser equalization based on adapted MMSE-filters combined with serial...
Conference Paper
Multi-cell CDMA systems with interference cancellation and powerful single-user channel coding close to the channel capacity are investigated for randomly chosen signature sequences and single cell site processing. Due to path loss and shadowing they show superior power and bandwidth efficiency on the AWGN channel compared with orthogonal multiple...

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