Johannes Koppenborg

3D beamforming trials with an active antenna array

Beamforming techniques for mobile wireless communication systems like LTE using multiple antenna arrays for transmission and reception to increase the signal-to-noise-and-interference ratio (SINR) are state of the art. The increased SINR is not only due to a larger gain in the direction of the desired user, but also due to a better control of the spatial distribution of interference in the cell. To further enhance the system performance not only the horizontal, but also the vertical dimension can be exploited for beam pattern adaptation, thus giving an additional degree of freedom for interference avoidance among adjacent cells. This horizontal and vertical beam pattern adaptation is also referred to as 3D beamforming in the following. This paper describes investigations of the potential of 3D beamforming with lab and field trial setups and provides initial performance results.

3D beamforming: Performance improvement for cellular networks

The beam pattern of a mobile communication base station has significant impact on the performance of a cellular network. Three-dimensional (3D) beamforming combines the horizontal beam pattern adaptation, as applied for beamforming and multiple input multiple output (MIMO) schemes, with a vertical antenna pattern adaptation. The recent availability of new flexible antenna techniques enables a fully dynamic antenna pattern adaptation which can be specified per resource block and user equipment (UE), and makes 3D beamforming practically feasible. This paper describes the basic principles of 3D beamforming, including the impact of downtilt adaptation on the physical layer as well as the potential of its combination with beam coordination involving the media access control (MAC) layer. Our investigations assumed the vertical main lobe of the beam pattern was geometrically pointed towards the UE. We discuss a number of different realization options and simulation results including a Bell Labs field trial with vertical beam steering. Using wireless systems with state of the art Long Term Evolution (LTE) signal format and including the lightRadio™ antenna array, our trials in the Stuttgart testbed verified the basic predicted properties and potential advantages of 3D beamforming.

Interference avoidance with dynamic vertical beamsteering in real deployments

This paper gives an overview on the possibilities and potential of dynamic vertical beamsteering in a cellular mobile radio system with focus on the interference limited macro-cell scenario. Different realization options for dynamic terminal specific downtilt adaptation at the base station (eNB) are introduced and simulated performance figures are given. Beam coordination methods for interference avoidance without and with the requirement for inter-eNB communications are considered. The impact of the most important system parameters like downtilt angle variation and coordination algorithm parameter setting is investigated. Basic measurements in real environment for proof of concept are introduced and their relation to simulation results are discussed. Finally the major conclusions and an outlook for future investigations are given.

Hardware experiments on multi-carrier waveforms for 5G

Emerging new applications, such as Internet of Things (IoT), gigabit wireless connectivity, tactile internet, and many more are expected to impose new and diverse requirements on the design of the fifth generation (5G) of cellular communication systems. In recent years, many alternative multicarrier waveforms are being investigated with the aim to identify to what extent it would be possible to better address these diverse requirements compared to Cyclic Prefix (CP) OFDM, which is currently adopted by LTE/LTE-Advanced. However, most of these investigations considered in many research activities have focused on theoretical considerations or simulations and mainly with emphasis on only one alternative waveform. In this paper, we present ongoing work based on measurement results where real hardware experiments are conducted to investigate the performance of three waveform families: CP-OFDM, filter bank multicarrier with offset quadrature amplitude modulation (FBMC/OQAM) and universal-filtered OFDM (UF-OFDM). FBMC/OQAM has the benefit of very low sidelobes leading to less inter-carrier interference in asynchronous and high mobility scenarios, whereas the typically long filter leads to low efficiency for short blocks and the use of OQAM makes it nontrivial to adopt certain schemes well-developed for CP-OFDM. UF-OFDM combines the benefits of CP-OFDM with the advantage of significantly lower out-of-band radiation while avoiding the drawbacks of FBMC/OQAM. In this paper we compare the performance of these alternative waveforms under several 5G targeted scenarios.

Performance assessment of multi user inter cell interference alignment with measured channels

It has been shown that in a multi-user multi-cell network, the Multi User Inter Cell Interference Alignment (MUI-CIA) based transmit precoding outperforms the non-alignment based state of the art precoding schemes. The theory of MUICIA is based on the assumption that the partial and stale inter-cell interference (ICI) information is still useful. This ICI is used by the transmitter to design he precoding such that the ICI and the multi-user interference (MUI) are aligned at the receiver. In this paper, we provide the proof of this concept with the help of measured channels. By using a measurement test-bed, we demonstrate that in slow time variant channels, the partial ICI contains useful information. Our outcomes are based on two different indoor scenarios for a multi user multi cell system with multiple antenna users. We also take into account the impact of training overhead on the performance in order to realize the feasibility of MUICIA with nominal overhead. Moreover, we compare the performance of MUICIA with other non-alignment based multi user precoding schemes. The results show that the concept of MUICIA is valid and it provides higher gains in a multi cell setup than other non-alignment based precodings with high as well as nominal training overhead.