Reliability-Based Hybrid Automated Repeat reQuest (RB-HARQ) strongly improves the throughput of a communications system by identifying and retransmitting the symbols deemed most unreliable after decoding the initial transmission. Additional soft-value processing, large feedback messages and many retransmissions are required to achieve a high throughput. We compare a variant of RB-HARQ designed for limited feedback with a new low-overhead, clustered Parity-Based Partial-Retransmission (PBPR) HARQ scheme. The new scheme selects symbols connected to unsatisfied parity checks and intersects this set with a subset of all symbols consisting of uniformly distributed information or parity symbols to improve the throughput. Since clustered HARQ schemes work best with codes exhibiting high intra-codeword correlations, we use Spatially-Coupled Low-Density Parity-Check (SC-LDPC) codes for evaluation.

We study the end-to-end steering problem using visual input data from an onboard vehicle camera. An empirical comparison between spatial, spatio-temporal and multimodal models is performed assessing each concept's performance from two points of evaluation. First, how close the model is in predicting and imitating a real-life driver's behavior, second, the smoothness of the predicted steering command. The latter is a newly proposed metric. Building on our results, we propose a new recurrent multimodal model. The suggested model has been tested on a custom dataset recorded by BMW, as well as the public dataset provided by Udacity. Results show that it outperforms previously released scores. Further, a steering correction concept from off-lane driving through the inclusion of correction frames is presented. We show that our suggestion leads to promising results empirically.

The iterative algorithms employed to decode Low-Density Parity-Check (LDPC) codes are not guaranteed to converge to a valid code word for every receive word. The goal of Early Termination (ET) is to prevent the waste of resources in such cases. In this paper, we conduct an analysis of the suitability of ET criteria by tracking the evolution of parameters available from decoder-internal states. We find that the commonly selected parameters, e.g., the mean Log-Likelihood Ratio (LLR) magnitude or the fraction of satisfied parity checks, result in similar probabilities of detecting non-converging receive words. We propose a novel criterion for Early Give-Up (EGU) and evaluate its performance using a cost metric based on the retransmission of individual code blocks initiated by higher-layer protocols.

The multiple antenna channel coding problem in orthogonal frequency-division multiplexing is reconsidered, because with frequency interleaving the effective channel characteristic across tones is rather fast fading and does not comply with the quasi-static channel model widely assumed for space-time codes. We study the fast-fading multiple transmit and receive antenna channel via evaluation of the capacity of the ergodic channel. Capacity comparisons give guidelines on how to adjust coding rate and modulation cardinality jointly. Simulations show that bit-based coding outperforms space-time codes in fast fading and, furthermore, offers greater flexibility in rate adaptation.

Preamble schemes with periodic signal repetitions are often used for synchronization purposes in transmission over dispersive media. We describe a sandamble, being a splitted repetition preamble with reduced training overhead, and compare its frame and frequency synchronization performance in burst transmission to the performance of a conventional repetition preamble like standardized IEEE 802.11a or HiperLAN/2 wireless modems. Optimum frame position and frequency offset estimation from a sandamble structure is treated and the Cramer-Rao lower bound for frequency estimation is derived. Though the fundamental idea is independent from the specific modulation scheme, we show results for orthogonal frequency-division multiplexing (OFDM).

Conventional orthogonal frequency-division multiplexing receivers disregard the guard interval in channels with small dispersion even though its unconsumed portion can be exploited for improved demodulation by applying a Nyquist-shaped window in the receiver. The transmitter does not need to be modified, subcarrier orthogonality in the receiver is preserved, and the receiver discrete Fourier transform size can be retained. Windowing can mitigate the joint effect of additive noise and intercarrier interference among subcarriers caused by the carrier frequency offset. A closed solution for optimum window coefficients suited to this scenario is derived.

Selected mapping (SLM) peak power reduction is distortionless as it selects the actual transmit signal from a set of alternative signals, which all represent the same information. Usually, the specific signal generation information needs to be transmitted and carefully protected against bit errors. Here, we propose an extension of SLM, which employs scrambling and refrains from transmitting explicit side information. Some additional complexity and nearly vanishing redundancy is introduced to achieve markedly improved transmit signal statistics. Even though SLM is applicable with any modulation, we concentrate on orthogonal frequency-division multiplexing (OFDM).

Two types of repetition preambles are compared concerning frequency synchronization in burst transmission. A near-optimum frequency estimation algorithm with scalable lock-in range is proposed in conjunction with a reduced-overhead synchronization preamble, the so-called sandamble. Even though the fundamental ideas are independent from the specific modulation scheme, we study the algorithms in an orthogonal frequency-division multiplexing (OFDM) system.

Conventional orthogonal frequency-division multiplexing (OFDM) receivers disregard oversized guard intervals. An (adaptive) Nyquist-shaped receive window could exploit signal samples in its unconsumed portion to improve demodulation. The OFDM transmitter is not modified, subcarrier orthogonality is preserved, and the DFT size may be retained. In this paper, we optimize the window shape by considering additive noise and intercarrier interference due to carrier frequency offsets, jointly.

Commonly, a repetition preamble is proposed as a burst training sequence to allow frame- and carrier frequency synchronization in digital transmission over unknown, severely dispersive channels. In this paper the preamble is composed of one repeated data-carrying-and therefore random-orthogonal frequency division multiplexing (OFDM) symbol. The current literature suggests several metrics to detect repetition preambles for coarse frame synchronization so we provide a ranking of four different metrics proposed by Chevillat, Maiwald and Ungerboeck (1987), Sandell, van de Beek and Borjesson (1995), Schmidl and Cox (see IEEE Trans. on Commun., vol.45, no.12, p.1613-21, 1997), and Keller and Hanzo (see Proceedings of the International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC'96), p.963-67, Taipei, Taiwan, 1996) via a simulative assessment. Furthermore, a probability-based motivation for the metric of Chevillat et al is given.

An efficient and distortionless scheme for peak power reduction in orthogonal frequency division multiplexing (OFDM) is proposed, which introduces some additional complexity but nearly vanishing redundancy. The approach is very flexible and works with arbitrary numbers of subcarriers and without restriction on the type of modulation applied in them. The core of the approach is the coordination of appropriately phase rotated signal parts to minimize the peak power of the multiplex signal. The improved statistics of peak power in the optimized transmit signal are demonstrated by simulation results. Finally, it is shown that this scheme is close to the theoretical limit curve of redundancy versus minimum peak-to-average power ratio (PAR).