Rüdiger Halfmann

LTE-Advanced Relaying for Outdoor Range Extension

Future cellular wireless networks based on MIMO- OFDM enable high data rates in outdoor scenarios. Limitations in coverage, especially at cell-edge, might be overcome by transmission over relays, which is therefore widely discussed for LTE-Advanced networks. Here, a multi-hop relay node is placed at the cell-edge or in a coverage hole in order to compensate for the penetration path loss caused by buildings. Relay nodes can be deployed in two modes, either as amplify and forward or as decode and forward relay. The later system may benefit from independent link adaptation which is a key concept especially under fading conditions in outdoor broadband wireless. This paper reports on first multi-hop relaying field trials in the LTE downlink. These field trials were carried out in a single-cell, single sector urban outdoor environment within the Berlin LTE- Advanced Testbed. Results show that outdoor relaying is a key concept to deliver high data rates to the cell edge. Furthermore, results show that rates above 60 Mbps are achievable and outdoor relaying yields for a 300 m range extension. In addition, results show that multi-hop relaying provides cell-edge users with a minimum data rate of at least 20 Mbps which is mandatory, especially if QoS constraints have to be met.

Interference map estimation using spatial interpolation of MDT reports in cognitive radio networks

An LTE-Advanced Radio Access Network (RAN) would be able to activate an additional component carrier in a Licensed Spectrum Access (LSA) channel, allowing the mobile network operator (MNO) to boost capacity and data rates. But such a dynamic spectrum access strategy requires an effective method for estimating the impact of the LTA-Advanced RAN operation on the primary user and minimizing it. LTE-Advanced provides a useful feature, namely the minimization of drive test (MDT) reporting system, wherein the network collects measurement data performed by the user equipment. Each report provides position and signal strength information. In this paper, we compare the performance of some spatial interpolation methods that would be used to reconstruct the interference map of an LTE-Advanced RAN based on the MDT reports. In this way, the MNO can determine if an LSA channel could be used without potential harm to the primary user operation just by checking the estimated interference map. Furthermore, the performance of different interpolation methods for establishment of interference map is analyzed, when the MDT reports containing errors in the values or locations of the reported measurements. Estimation accuracy is also evaluated respect to spatial correlation.

Interference protection mechanism for LTE-Advanced radio access networks supporting dynamic spectrum access

Spectrum licensing schemes are subject to fixed allocation, little sharing and long term holding, which is leading to the current problem of false scarcity. Considering current spectrum allocation methodologies and given the exponential growth of traffic demand, spectrum scarcity becomes problematic since in the near future current radio access technologies will not be able to cope with this traffic demand increase anymore. Thus, new licensing schemes must be designed to enable sharing of spectrum frequency, so that rarely used spectrum channels can be reallocated dynamically between primary users and mobile services. Cognitive radio based dynamic spectrum access is foreseen as a solution to this intricate problem. Further, simple dynamic spectrum access schemes could be integrated into an LTE-Advanced mobile network, making use of carrier aggregation and the standardized user equipment measurement reports. In this paper, we focus on geographical division of spectrum for an LTE-Advanced network, where the spectrum is classified into Frequency/Location/Time bundles. These bundles work as independent tradeable units that can be aggregated and tailored to the needs of the participants in spectrum adjudication. Geographic locations are divided into a square grid, where an estimation of the Radio Environment Map based on propagation parameters is used to assess the sets of tradeable units assigned to a given mobile network operator. Furthermore we make an analysis of how spectrum exclusion areas can be characterized and defined in order to coexist with the operators network.