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Item type:Publication, Access status: without files , 21 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Recurrent Neural Network Data Predistortion for Transparent Satellite Channels(2024-12); Satellite transponders operate with traveling wavetube amplifiers (TWTAs) which nonlinearly distort the transmit signal, particularly when transmission power close to amplifier saturation is desired. Hence, the concatenation of pulse shaping filter, input multiplexer (IMUX) filter, TWTA, output multiplexer (OMUX) filter and receive filter causes distorted decision regions and severe intersymbol interference (ISI) at the receive filter output. The standards DVB-S2 and DVB-S2X recommend setups for transparent satellite channels. Here, the distortion is traditionally compensated using a lookup tablebased centroid data predistortion algorithm. In this work, we propose an improved approach for data predistortion based on bidirectional recurrent neural networks (BRNNs). We show the superiority of BRNN data predistortion over centroidbased predistortion by comparing information rates and bit error rates on recommended setups from the DVB-S2 standard. Furthermore, we show how BRNN predistortion enables ISI compensation for high order modulations from DVB-S2X, where the traditional lookup table approach fails due to infeasible memory requirements.Publicationtype: Conference Paper69 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Finite alphabet fast list decoders for polar codesThe so-called fast polar decoding schedules are meant to improve the decoding speed of the sequential-natured successive cancellation list decoders. The decoding speedup is achieved by replacing various parts of the serial decoding process with efficient special-purpose decoder nodes. This work incorporates the fast decoding schedules for polar codes into their quantized finite alphabet decoding. In a finite alphabet successive cancellation list decoder, the log-likelihood ratio computations are replaced with lookup operations on low-resolution integer messages. The lookup tables are designed using the information bottleneck method. It is shown that the finite alphabet decoders can also leverage the special decoder nodes found in the literature. Besides their inherent decoding speed improvement, the use of these special decoder nodes drastically reduces the number of lookup tables required to perform the finite alphabet decoding. In order to perform quantized decoding using lookup operations, the proposed decoders require up to 93% less unique lookup tables as compared to the ones that use the conventional successive cancellation schedule. Moreover, the proposed decoders exhibit negligible loss in error correction performance without necessitating alterations to the lookup table design process.Publicationtype: Conference Paper23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Unrolled and pipelined decoders based on look-up tables for polar codes(IEEE, 2023-10-10); ; Unrolling a decoding algorithm allows to achieve extremely high throughput at the cost of increased area. Lookup tables (LUTs) can be used to replace functions otherwise implemented as circuits. In this work, we show the impact of replacing blocks of logic by carefully crafted LUTs in unrolled decoders for polar codes. We show that using LUTs to improve key performance metrics (e.g., area, throughput, latency) may turn out more challenging than expected. We present three variants of LUT-based decoders and describe their inner workings as well as circuits in detail. The LUT-based decoders are compared against a regular unrolled decoder, employing fixed-point representations for numbers, with a comparable error-correction performance. A short systematic polar code is used as an illustration. All resulting unrolled decoders are shown to be capable of an information throughput of little under 10 Gbps in a 28 nm FD-SOI technology clocked in the vicinity of 1.4 GHz to 1.5 GHz. The best variant of our LUT-based decoders is shown to reduce the area requirements by 23% compared to the regular unrolled decoder while retaining a comparable error-correction performance.Publicationtype: Conference Paper23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Hidden node-aware dynamic spectrum access using deep learning for coexisting aeronautical communication systems(IEEE, 2023-10); ; ; ; We propose a novel approach based on deep learning to address the hidden node problem which occurs in the coexistence of aeronautical communication standards. The modern aeronautical communication standard L-band Digital Aeronautical Communications System (LDACS) in Air-Air (A/A) mode needs to share spectrum with the Distance Measuring Equipment (DME), which is a legacy system. As DME is safety-critical, causing interference on it must be avoided for all newly proposed aeronautical systems spectrally coexisting with it. Recently, cognitive radio techniques have been proposed for LDACS A/A to access spectrum dynamically and to overcome the limitations of static approaches. For this, a Recurrent Neural Network (RNN) was trained to predict idle time slots on those frequency bands, where both systems operate. By exploiting patterns in the spectrum access of DME, a promising amount of idle resources could be predicted. However, previous approaches would perform poorly in a real-world deployment, as they did not take the hidden node problem into account.This paper formulates the hidden node problem for the case that an LDACS A/A user is within communication range of a DME ground station, but not within range of all airborne DME users connected to it. Through statistical analysis, we underline the problem's significance in practical cases. We simulate the coexistence of the two systems from a channel access perspective, taking signal propagation and the behavior of the ground station into account. Further, we present an RNN that is able to predict the channel access of hidden nodes. The key idea of our algorithm is to exploit the fact that while DME request pulses from airborne users may appear as hidden, response pulses from the ground station will be visible. Our results show that by inferring DME request channel activity from the response channel, the hidden node problem can be overcome effectively. By using our approach, nearly the same performance can be achieved as in the idealized case where all nodes are visible.Publicationtype: Conference Paper28 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Space-efficient quantized polar decoders designed using the information Bottleneck methodQuantized successive cancellation list decoders can be designed by incorporating the information bottleneck method into the density evolution of polar codes. All operations, except the path metric update, in the information bottleneck successive cancellation list decoders are simple table lookups of unsigned integers. The number of lookup tables required for decoding depends on the codeword length such that a larger number of tables are used in decoding longer codewords. These lookup tables add to the space complexity of the quantized decoder and it is, therefore, desirable to reduce the number of lookup tables required for decoding. In this work, an information bottleneck based polar decoder design is proposed that uses the minsum rule to design the lookup tables beside the information bottleneck method. In the proposed decoder, the number of required decoding tables is halved since the min-sum lookup tables need not to be stored due the availability of their hardwareefficient implementation. Additionally, the design SNR of the information bottleneck decoders are optimized to improve their error correction performance.Publicationtype: Conference Paper28 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Underwater Distance Estimation Using the JANUS Communication Standard(2023-03); Distance estimation is an integral part of localization in Euclidean space and the first step of any localization algorithm. In the underwater domain the distance is estimated by measuring the propagation delay of a pressure wave in the acoustic frequency range. In the process a known waveform is correlated with a received signal in order to determine the time instance of the wave incident at a receiver, thus the correlation properties of the known waveform are of upmost importance. This paper evaluates the suitability of the communication standard called JANUS for the generation of waveforms for distance estimation while still adhering to the standard. Additionally the correlation properties of the resulting waveforms are compared to slight adaptations to the JANUS standard and less restricted FH-FSK waveforms commonly used in continuous wave sonar and radar systemsPublicationtype: Conference Paper135 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Uniform vs. Non-Uniform Coarse Quantization in Mutual Information Maximizing LDPC Decoding(2022-12); Recently, low-resolution LDPC decoders have been introduced that perform mutual information maximizing signal processing. However, the optimal quantization in variable and check nodes requires expensive non-uniform operations. Instead, we propose to use uniform quantization with a simple hardware structure, which reduces the complexity of individual node operations approximately by half and shortens the decoding delay significantly. Our analysis shows that the loss of preserved mutual information resulting from restriction to uniform quantization is very small. Furthermore, the error rate simulations with regular LDPC codes confirm that the uniform quantization causes only minor performance degradation within 0.01 dB compared to the non-uniform alternative. Due to the complexity reduction, especially the proposed 3-bit decoder is a promising candidate to replace 4-bit conventional decoders.Publicationtype: Conference Paper46 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Deep Learning-Based Dynamic Spectrum Access for Coexistence of Aeronautical Communication SystemsPublicationtype: Conference Paper124 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Forney Observation Models for Faster-Than-Nyquist Signaling on Nonlinear Satellite Links(2022-09); ; Publicationtype: Conference Paper52