Peter Fertl

Location dependent resource allocation for mobile device-to-device communications

Device-to-device (D2D) communication as an underlay to future cellular networks has been recently considered as an efficient cell offloading and capacity increasing solution. In this paper, we propose to use the D2D underlay as a carrier for automotive safety applications with very strict quality of service and reliability requirements. We propose a location dependent resource allocation scheme (LDRAS) for mobile D2D communications that fulfills the requirements of such services, while reducing the signaling overhead and guaranteeing a certain maximum interference level within the primary network and the D2D underlay, respectively. The former is ensured by applying persistent resource allocation to the vehicular D2D network. The latter is achieved with a spatial reuse scheme with fixed resource reservation, exploiting the localized nature of vehicle-to-vehicle communications. Initial simulation results, comparing the proposed LDRAS to a state-of-the-art radio resource management algorithm, are provided as a proof-of-concept and illustrate the benefits of our solution.

Quantization for soft-output demodulators in bit-interleaved coded modulation systems

We study quantization of log-likelihood ratios (LLR) in bit-interleaved coded modulation (BICM) systems in terms of an equivalent discrete channel. We propose to design the quantizer such that the quantizer outputs become equiprobable. We investigate semi-analytically and numerically the ergodic and outage capacity over single- and multiple-antenna channels for different quantizers. Finally, we show bit error rate simulations for BICM systems with LLR quantization using a rate 1/2 low-density parity-check code.

Capacity-based performance comparison of MIMO-BICM demodulators

This paper provides a performance comparison of multiple-input multiple-output (MIMO) demodulators for bit-interleaved coded modulation (BICM) systems with non-iterative demodulation and decoding. We propose to use the capacity of an equivalent ldquomodulationrdquo channel as a performance measure that has the advantage of not depending on the outer error correcting code. Based on this approach, we conclude that a universal ranking of MIMO (soft and hard) demodulation algorithms is not possible. This result is confirmed via bit error rate simulations for a practical system involving low-density parity-check codes. Our approach also allows to derive practical guidelines for MIMO-BICM system design.

On the generalized mutual information of BICM systems with approximate demodulation

We consider a generic bit-interleaved coded modulation (BICM) systems with an approximate demodulator or log-likelihood ratio (LLR) computer. The performance of a BICM system with optimal demodulation has previously been characterized by Caire et al. in terms of the capacity of an independent parallel-channel model with binary inputs and (continuous) LLRs as outputs, and by Martinez et al. in terms of the generalized mutual information (GMI) where the BICM decoder is viewed as a mismatched decoder. Whereas GMI and capacity of the parallel-channel model coincide under optimal demodulation, they differ in general for the case of an approximate demodulator. Herein we show (i) that augmenting approximate BICM demodulators with scalar LLR correction increases the GMI and (ii) that the GMI of the LLR-corrected system coincides with the capacity of the parallel-channel model with binary inputs and outputs given by the approximate LLRs.

Performance evaluation of automotive off-board applications in LTE deployments

The new cellular communication standard 3GPP Long Term Evolution (LTE) promises high throughputs and low latencies, thus enabling even more bandwidth-demanding and real-time critical services for end-users. This is of particular interest for vehicle manufacturers who in the future intend to offer a huge variety of cooperative driver assistance services with different quality of service (QoS) settings. In this paper we analyze the suitability of LTE for future automotive off-board services in terms of transmission delays and reliability under various QoS settings. Our investigations are based on extensive LTE system-level simulations under different load conditions and network deployments as well as on a theoretical delay analysis. The results show that an accurate selection of the LTE QoS parameters is crucial in order to meet the delay and reliability requirements of future automotive applications, especially in high-load network conditions.

Performance Assessment of MIMO-BICM Demodulators Based on Mutual Information

We provide a comprehensive performance comparison of soft-output and hard-output demodulators in the context of non-iterative multiple-input multiple-output bit-interleaved coded modulation (MIMO-BICM). Coded bit error rate (BER), widely used in literature for demodulator comparison, has the drawback of depending strongly on the error correcting code being used. This motivates us to propose the mutual information of the equivalent modulation channel (comprising modulator, wireless channel, and demodulator) as a code-independent performance measure. We present extensive numerical results for spatially independent identically distributed (i.i.d.) ergodic and quasi-static fading channels under perfect and imperfect channel state information. These results reveal that the performance ranking of MIMO demodulators is rate-dependent and provide new insights regarding MIMO-BICM system design, i.e., the choice of antenna configuration, symbol constellation, and demodulator for a given target rate.

Perturbation-Based Distributed Beamforming for Wireless Relay Networks

This paper deals with distributed beamforming techniques for wireless networks with half-duplex amplify-and- forward relays. Existing schemes optimize the beamforming weights based on the assumption that channel state information (CSI) is available at the relays. We propose to use adaptive beamforming based on deterministic perturbations and limited feedback (1-bit) from the destination to the relays in order to avoid CSI at the relays. Two scalable perturbation schemes are considered and practical implementation aspects are addressed. Simulation results confirm that the proposed techniques closely approach optimum performance and have satisfactory tracking properties in time-varying environments.

Towards the METIS 5G concept: First view on Horizontal Topics concepts

METIS is developing a 5G system concept that meets the requirements of the beyond-2020 connected information society and supports new usage scenarios. To meet the objectives METIS uses Horizontal Topics (HT) that addresses a key new challenge, identifies necessary new functionalities and proposes HT-specific concepts. This paper presents an initial view of the HT-specific concepts for each of the METIS HTs: Direct Device-to-Device Communication, Massive Machine Communication, Moving Networks, Ultra-Dense Networks, and Ultra-Reliable Communication. It also describes how the HT-specific concepts will be integrated into one overall METIS 5G concept.

Availability indication as key enabler for ultra-reliable communication in 5G

Due to its flexibility, cost-efficiency, and the ability to support mobility, wireless connectivity is seen today as a key enabler for a wide range of applications beyond classical mobile communications. A significant part of these applications depends on the capability of the wireless communication system to provide reliable connectivity. However, due to the randomness of the wireless propagation channel, reliability is still a critical issue in these systems. Some applications, such as vehicular and industrial applications, demand a level of reliability that wireless communication systems typically are not able to guarantee. This paper provides a framework that enables these applications to make use of wireless connectivity only if the transmission conditions are favorable enough. The concept is based on the idea that - despite the fact that it is practically impossible to ensure error-free wireless communication - it is feasible to derive boundary conditions for the transmission success. To this end, the paper introduces a novel metric for Ultra-Reliable Communication (URC) referred to as “Availability”, that determines the expected presence or absence of link reliability at the time of transmission. The availability is signaled by means of an Availability Indicator (AI) to the applications. Moreover, we develop the system model for computing the AI and illustrate the potential benefits of the new reliability metric by means of a possible implementation for automotive scenarios.

Channel Estimation in Wireless OFDM Systems With Irregular Pilot Distribution

This paper addresses pilot-assisted channel estimation for wireless orthogonal frequency division multiplexing (OFDM) systems with irregular pilot arrangements. Using nonuniform sampling techniques, we propose a novel channel estimator that is based on conjugate gradient iterations and features very low computational complexity. We investigate the impact of the pilot arrangement on the channel estimation mean square error and we provide a heuristic stopping criterion for early termination of the conjugate gradient iterations. One-dimensional and two-dimensional channel estimator implementations and applications of our method to multiple-antenna and multiuser OFDM systems are discussed. Extensive numerical simulations corroborate that the proposed method performs similarly to computationally much more expensive minimum mean square error estimators.