Hardy Halbauer

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.

Exploring the vertical dimension of dynamic beam steering

This paper investigates the properties of a cellular mobile radio system with the capability to dynamically adapt the downtilt at the base station on a per terminal basis. We compare several realization options of this vertical beam steering and explore the impacts of downtilt, vertical half-power beam width (HPBW) and inter-site distance (ISD) on spectral efficiency and cell coverage. We show that our approach improves performance in single-cell environment and can achieve a significant amount of interference avoidance already without any kind of coordination between cells.

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.

Interference-Avoidance Techniques: Improving Ubiquitous User Experience

This article presents interference- avoidance schemes developed in the Advanced Radio Interface Technologies for [Fourth Generation (4G)] Systems (ARTIST4G) Project for three scenarios targeting the deployment of Third-Generation Partnership Project (3GPP), long-term evolution (LTE)-advanced networks, and beyond. In the first scenario, we propose three-dimensional (3-D) beamforming as a flexible technology for taking the best benefit from the internode cooperation, constrained by the core network infrastructure. The second scenario addresses a long-term deployment with nonconstrained internodes cooperation link based on an interference-shaping strategy that allows for exploiting at its maximum the coordinated multipoint concept. Finally, we investigate interference coordination mechanisms for protecting the macro network from a massive deployment of small cells that provides a network capacity increase by high offloading capabilities.

A Preliminary Study on Waveform Candidates for 5G Mobile Radio Communications above 6 GHz

This paper provides an overview and preliminary comparison of several multi-carrier and single-carrier waveforms that are potential candidates for future 5G mobile radio communications above 6 GHz. The waveforms are assessed primarily based on the established and known results as well as recent findings keeping in view the design requirements that are relevant to using frequencies above 6 GHz, especially the millimeter wave frequencies. The Key Performance Indicators and degrees of freedom in the design of different waveforms and their potential applications for mm-wave communications are discussed. Certain features that are particularly interesting for mm-wave communication and require further investigations are also highlighted. Furthermore, a common framework for synthesizing different waveform candidates has been developed. Finally, a preliminary qualitative comparison of different multi-carrier and single carrier waveforms has been derived.

On the Impact of Mobility on the Channel Estimation in WIMAX OFDMA-Uplink

The demand for wireless broadband access systems supporting mobility of the individual users has dramatically increased in recent years. To this end, we analyze the impact of user-mobility in the uplink of an OFDMA system on the performance of pilot-aided channel estimation. We analyze the mean square error (MSE) performance of two pilot-aided channel estimation schemes, the simple Gauss-Markov estimator and the optimal LMMSE estimator. We derive closed-form expressions for the MSE taking into account the impact of intercarrier-interference and time-variations of the channel. Different pilot allocation strategies are analyzed and their performances are compared. Finally, the results are illustrated by numerical simulations based on the WiMax 802.16e specifications

Performance Evaluation of Analog Beamforming with Hardware Impairments for mmW Massive MIMO Communication in an Urban Scenario.

The use of massive multiple-input multiple-output (MIMO) techniques for communication at millimeter-Wave (mmW) frequency bands has become a key enabler to meet the data rate demands of the upcoming fifth generation (5G) cellular systems. In particular, analog and hybrid beamforming solutions are receiving increasing attention as less expensive and more power efficient alternatives to fully digital precoding schemes. Despite their proven good performance in simple setups, their suitability for realistic cellular systems with many interfering base stations and users is still unclear. Furthermore, the performance of massive MIMO beamforming and precoding methods are in practice also affected by practical limitations and hardware constraints. In this sense, this paper assesses the performance of digital precoding and analog beamforming in an urban cellular system with an accurate mmW channel model under both ideal and realistic assumptions. The results show that analog beamforming can reach the performance of fully digital maximum ratio transmission under line of sight conditions and with a sufficient number of parallel radio-frequency (RF) chains, especially when the practical limitations of outdated channel information and per antenna power constraints are considered. This work also shows the impact of the phase shifter errors and combiner losses introduced by real phase shifter and combiner implementations over analog beamforming, where the former ones have minor impact on the performance, while the latter ones determine the optimum number of RF chains to be used in practice.

An efficient Cholesky Decomposition based multiuser MIMO detection algorithm

This paper presents an efficient multiuser Multiple Input Multiple Output (MU-MIMO) detection algorithm. It introduces Cholesky Decomposition (CLD) and deploys Successive Interference Cancellation (SIC) detection. This study reveals that the proposed algorithm delivers equivalent performance to the QR Decomposition (QRD) based detection algorithm, with adequately lower complexity. As well, the CLD based detection algorithm can be straightforwardly adapted to other QRD based algorithm variants to reduce the computational effort.

On OFDM and SC-FDE Transmissions in Millimeter Wave Channels with Beamforming

The air interface for millimeter wave (mmWave) communications must be designed by properly taking into account the specific characteristics of the wireless channel at higher frequencies. In this work, we start by considering a channel model recently proposed in the literature for mmWave communications in outdoor urban scenarios. First, on top of this channel model we implement a sectorized beamforming model necessary to compensate the large path-loss at mmWave range and study how channel statistics, namely, delay spread and angle spread, are influenced by employing different beamwidths. Subsequently, adopting this beamforming model in the mmWave channel, orthogonal frequency division multiplexing (OFDM) and single carrier frequency domain equalization (SC-FDE) systems are compared. Extensive link level simulations are performed by considering different beamwidths, line-of-sight (LOS) coverage and channel coding. Numerical results show that SC-FDE using minimum mean square error (MMSE) equalization performs close to OFDM in coded systems. However, SC-FDE might be beneficial in practice due to much lower peak to average power ratio (PAPR) than OFDM.