Klaus Hugl

Device-to-device communication as an underlay to LTE-advanced networks

In this article device-to-device (D2D) communication underlaying a 3GPP LTE-Advanced cellular network is studied as an enabler of local services with limited interference impact on the primary cellular network. The approach of the study is a tight integration of D2D communication into an LTE-Advanced network. In particular, we propose mechanisms for D2D communication session setup and management involving procedures in the LTE System Architecture Evolution. Moreover, we present numerical results based on system simulations in an interference limited local area scenario. Our results show that D2D communication can increase the total throughput observed in the cell area.

LTE Capacity Compared to the Shannon Bound

In this paper we propose a modification to Shannon capacity bound in order to facilitate accurate benchmarking of UTRAN long term evolution (LTE). The method is generally applicable to wireless communication systems, while we have used LTE air-interface technology as a case study. We introduce an adjusted Shannon capacity formula, where we take into account the system bandwidth efficiency and the SNR efficiency of LTE. Separating these issues, allows for simplified parameter extraction. We show that the bandwidth efficiency can be calculated based on system parameters, while the SNR efficiency is extracted from detailed link level studies including advanced features of MIMO and frequency domain packet scheduling (FDPS). We then use the adjusted Shannon capacity formula combined with G-factor distributions for macro and micro cell scenarios to predict LTE cell spectral efficiency (SE). Such LTE SE predictions are compared to LTE cell SE results generated by system level simulations. The results show an excellent match of less that 5-10% deviation.

Interference-Aware Resource Allocation for Device-to-Device Radio Underlaying Cellular Networks

Future cellular networks such as IMT-Advanced are expected to allow underlaying direct Device-to-Device (D2D) communication for spectrally efficient support of e.g. rich multimedia local services. Enabling D2D links in a cellular network presents a challenge in radio resource management due to the potentially severe interference it may cause to the cellular network. We propose a practical and efficient scheme for generating local awareness of the interference between the cellular and D2D terminals at the base station, which then exploits the multiuser diversity inherent in the cellular network to minimize the interference. System simulations demonstrate that substantial gains in cellular and D2D performance can be obtained using the proposed scheme.

Device-to-Device Communication Underlaying Cellular Communications Systems

In this article we propose to facilitate local peer-to-peer communication by a Device-to-Device (D2D) radio that operates as an underlay network to an IMT-Advanced cellular network. It is expected that local services may utilize mobile peer-to-peer communication instead of central server based communication for rich multimedia services. The main challenge of the underlay radio in a multi-cell environment is to limit the interference to the cellular network while achieving a reasonable link budget for the D2D radio. We propose a novel power control mechanism for D2D connections that share cellular uplink resources. The mechanism limits the maximum D2D transmit power utilizing cellular power control information of the devices in D2D communication. Thereby it enables underlaying D2D communication even in interference-limited networks with full load and without degrading the performance of the cellular network. Secondly, we study a single cell scenario consisting of a device communicating with the base station and two devices that communicate with each other. The results demonstrate that the D2D radio, sharing the same resources as the cellular network, can provide higher capacity (sum rate) compared to pure cellular communication where all the data is transmitted through the base station.

Device-to-Device Communications; Functional Prospects for LTE-Advanced Networks

In this paper the possibility of device-to-device (D2D) communications as an underlay of an LTE-A network is introduced. The D2D communication enables new service opportunities and reduces the eNB load for short range data intensive peer-to-peer communication. The cellular network may establish a new type of radio bearer dedicated for D2D communications and stay in control of the session setup and the radio resources without routing the user plane traffic. The paper addresses critical issues and functional blocks to enable D2D communication as an add-on functionality to the LTE SAE architecture. Unlike 3G spread spectrum cellular and OFDM WLAN techniques, LTE-A resource management is fast and operates in high time-frequency resolution. This could allow the use of non-allocated time-frequency resources, or even partial reuse of the allocated resources for D2D with eNB controlled power constraints. The feasibility and the range of D2D communication, and its impact to the power margins of cellular communications are studied by simulations in two example scenarios. The results demonstrate that by tolerating a modest increase in interference, D2D communication with practical range becomes feasible. By tolerating higher interference power the D2D range will increase.

Interference-avoiding MIMO schemes for device-to-device radio underlaying cellular networks

An underlaying direct Device-to-Device (D2D) communication mode in future cellular networks, such as IMT-Advanced, is expected to provide spectrally efficient and low latency support of e.g. rich multi-media local services. Enabling D2D links in a cellular network presents a challenge in transceiver design due to the potentially severe interference between the cellular network and D2D radios. In this paper we propose MIMO transmission schemes for cellular downlink that avoid generating interference to a D2D receiver operating on the same time-frequency resource. System simulations demonstrate that substantial gains in D2D SINR of up to 15 dB and around 10% total cell capacity gains can be obtained by using the proposed scheme.

Wideband 3D characterization of mobile radio channels in urban environment

This paper describes three-dimensional (3D) radio channel measurements at the base station site in an urban environment. We introduce a measurement concept which combines an RF switched receiver array and a synthetic aperture technique and allows full 3D characterization of the channel. Additionally, dual-polarized patch antennas as array elements enable full determination of the polarization properties of the impinging signals. We describe measurements at over 70 different transmitter positions and three receiver array sites with different sectors and antenna heights. Our results show that the received energy is concentrated within identifiable clusters in the azimuth-elevation-delay domain. We demonstrate that the observed propagation mechanisms are mainly determined by the environment close to the base station. Street canyon propagation dominates also when the receiver array is at or even above rooftop level with the studied measurement distances. Thus, the azimuth spectrum at the BS site is fairly independent of the location of the mobile. Signal components propagating over the rooftop are often related to reflections from high-rise buildings in the surroundings.

Geometry-based directional model for mobile radio channels -principles and implementation

Adaptive antennas are used in mobile radio systems for improving coverage and increasing capacity. For realistic system design and simulation, channel models are required in order to assess the performance of such systems. We propose the so-called ‘geometry-based stochastic channel model’ (GSCM), which is easy to implement and has a low complexity even when the directional dimension of the channel is taken into account. In this model, we prescribe the probability density function (PDF) of the location of the scatterers. From this, the angularly resolved impulse response can be computed by a simple ray tracing. We then present various extensions of the model in urban environments, namely for diffraction losses and wave guiding by street canyons. We also discuss methods for efficiently implementing GSCM. Copyright

Downlink beamforming for frequency division duplex systems

We propose a downlink beamforming method for an adaptive antenna system utilizing our new spatial covariance matrix transformation (SCMT). Therefore we first estimate the azimuthal power spectrum (APS) of the received uplink data for all users within the same physical channel. Afterwards we modify the APS of the user and the interference to prevent beampointing errors for the desired user and improve the nulling capabilities. Finally we construct the spatial covariance matrices at the downlink frequency and use this spatial information for antenna weight calculation. The approach is applicable for any adaptive antenna system with FDD. It outperforms direction of arrival based methods by at least 10 dB in SNIR. Applying the SCMT we approach the upper downlink limit within 4 dB in urban environments.

Performance of linear multi-user MIMO precoding in LTE system

For scenarios with a large number of users to be served in one cell, high capacity gains can be achieved by transmitting independent data streams to different users sharing the same time-frequency resources. This technique is known as Multi-User MIMO (MU-MIMO). In this paper we investigate the performance of MU-MIMO operation in 3GPP LTE for different frequency granularities of the precoder at the OFDM transmitter. We also investigate the impact of channel correlation on the performance of the receiver when it is unaware of the interfererpsilas precoding vector. The performance is evaluated by means of semistatic system simulations.