Markus Stefer

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In adaptive time division duplex (TDD) broadcast multi-antenna orthogonal frequency division multiplexing (OFDM) systems, non-reciprocal transceiver chains at the base station (BS) cause multi-user interference. This is due to the inappropriate spatial filter design at the BS based on the reverse link estimate. Hence, BS transceiver calibration is required.(More)
The combination of OFDM with joint preprocessing in adaptive multi-antenna systems offers both an ease of equalization in frequency-selective channels and keeping the signal processing at the mobile stations simple. In addition, the spatial dimension can be efficiently exploited to ensure high system throughput. With the utilization of higher-order(More)
In this paper, the impact of nonreciprocal transceivers is demonstrated by measurement results for different adaptive transmission strategies in a time division duplex MIMO-OFDM system. These strategies rely on the channel state information (CSI) at the transmitter, thus requiring either appropriate feedback or reciprocity of both communication links. The(More)
In this paper, a hardware-based calibration scheme at the base station is used to mitigate the impact of the non-reciprocal transceivers in a time division duplex (TDD) multiple-input-multiple-output orthogonal-frequency-division-multiplexing (MIMOOFDM) system. The calibration setup consists of two single-pole-double-throw (SPDT) switches to bypass the(More)
In this paper, a framework is established to quantify the influence of hardware imperfections realizing a Direction-of-Arrival (DoA) estimation system using a circular antenna array. The latter exploits one transceiver and therefore samples the different antennas sequentially. To accomplish this, a Single-Pole-Multifold-Throw (SPMT) switch is needed to(More)
The performance of multiple-input multiple-output (MIMO) systems is affected by the spatial correlation properties, which depend on the array configuration and the channel characteristics. The configuration can be influenced by manipulating the radiation patterns of the antennas, the antenna spacing and the array geometry. To decrease the spatial(More)
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