Jan Mietzner

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The use of multiple antennas for wireless communication systems has gained overwhelming interest during the last decade both in academia and industry. Multiple antennas can be utilized in order to accomplish a multiplexing gain, a diversity gain, or an antenna gain, thus enhancing the bit rate, the error performance, or the signal-to-noise-plus-interference(More)
In this paper, we propose two novel pre–equalization schemes for multiple–input single–output (MISO) direct– sequence ultra–wideband (DS–UWB) systems with pre–Rake combining and symbol–by–symbol detection. The first scheme employs one pre–equalization filter (PEF) per transmit antenna, whereas in the second scheme, the simplified PEF (S–PEF) scheme, all(More)
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(More)
The probabilistic data association (PDA) decoder is investigated for use in codedmultiple-input multiple-output (MIMO) systems and its strengths and weaknesses are determined. The conventional PDA decoder includes two approximations. The received symbols are assumed to be statistically independent and a Gaussian approximation is applied for the interference(More)
In this paper, we consider a relay-assisted wideband cognitive-radio (CR) system under the assumption that the frequency band chosen by the CR relay network for unlicensed spectrum usage overlaps with one or more bands dedicated to primary (e.g., licensed) narrowband links. Our objective is to optimize the performance of the CR system while limiting the(More)
The application of distributed space-time coding schemes in a simulcast network is considered, and a key challenge is addressed which arises in the downlink: Since the local oscillators employed at the individual transmitting nodes may independently differ from the nominal carrier frequency, frequency offsets will occur between the individual transmission(More)
We address the issue of optimal transmit power allocation in relay-assisted cognitive-radio (CR) systems. In particular, we assume that the frequency band chosen for unlicensed spectrum usage is not completely unoccupied, but contains one or more licensed narrowband users. For such a setting, we develop distributed transmit power allocation schemes, which(More)
Space-time codes (STC) are wireless transmission techniques utilizing multiple transmit antennas (and optionally multiple receive antennas) and have recently gained much interest. The efficiency of STC in fading environments is based on a diversity gain: Given sufficient antenna spacing, the nTnR transmission paths from the nT transmit (Tx) antennas to the(More)
In this paper, we propose a novel multi-hop relaying scheme to improve the performance and coverage of impulseradio-based ultra-wideband (IR-UWB) systems. With regard to a simple practical realization, we focus on a non-coherent system setup in conjunction with amplify-and-forward (A&F) relaying. In particular, we propose to employ a multiple-differential(More)
We consider practicable subsampling for sub- Nyquist radar systems based on a set of parallel bandpass filters for extracting range information of sparse target objects. Based on a compressed sensing framework, the corresponding measurement matrix composed of blockwise selected rows from a Fourier matrix is optimized, using sparse rulers known from(More)