Stephan Saur

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.

Radio access protocols and preamble design for machine type communications in 5G

Machine-type communications is seen as one of the main drivers of 5G. In this paper we compare one-stage and two- stage radio access protocol options for sporadic transmissions of small data packets in uplink with respect to throughput and delay requirements. An important aspect is robust and resource efficient preamble design to minimize missed detection and false alarm probabilities of service requests. Also the tradeoff between performance and necessary amount of downlink feedback bits is taken into account in our analysis. The final evaluation is done with computer simulation of a multi-cell system.

Diffusion LMS localization and tracking algorithm for wireless cellular networks

We propose a distributed least-mean squares (LMS) procedure based on a diffusion strategy for localization and tracking of mobile terminals in cellular networks. In the proposed algorithm, collaborating base stations measure two sets of parameters, namely, the received signal strength (RSS) and the signal propagation time (SPT) to estimate mobile locations. The proposed algorithm has a simple operational structure, offers agile tracking performance and helps the network to save energy and radio resources by benefiting from its decentralized and adaptive signal processing features.

Comparison of Collision-Free and Contention-Based Radio Access Protocols for the Internet of Things

The fifth-generation (5G) cellular networks will face the challenge of integrating the traditional broadband services with the Internet of Things (IoT), which is characterized by sporadic uplink transmissions of small data packets. Indeed, the access procedure of the previous generation cellular network (4G) is not able to support IoT traffic efficiently, because it requires a large amount of signaling for the connection setup before the actual data transmission. In this context, we introduce two innovative radio access protocols for sporadic transmissions of small data packets, which are suitable for 5G networks, because they provide a resource-efficient packet delivery exploiting a connectionless approach. The core of this paper resides in the derivation of an analytical framework to evaluate the performance of all the aforementioned protocols. The final goal is the comparison between 4G and 5G radio access solutions employing both our analytical framework and computer simulations. The performance evaluation results show the benefits of the protocols envisioned for 5G in terms of signaling overhead and access latency.