129 results
Now showing1 - 10 of 129
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Mixed block markov superposition transmission codes(2026-06-15); ; ; Block Markov superposition transmission (BMST) codes provide a flexible framework for constructing codes with near-capacity performance and low-complexity sliding-window decoding. However, existing BMST variants show contrasting performance limitations: recursive BMST (rBMST) codes suffer from error propagation but avoid high error floors, whereas non-recursive BMST codes exhibit the opposite behavior. Motivated by these complementary characteristics, we combine recursive and non-recursive components through parallel and serial concatenation, yielding mixed BMST (mBMST) codes. The proposed framework subsumes existing BMST variants and enables new BMST structures. Simulations show that these structures improve FER and BER performance with lower memory requirements than rBMST.Publicationtype: Preprint66 29 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Fast window decoding of BMST codes via step adjustment and universal parity-Check terminationBlock Markov Superposition Transmission (BMST) codes are a class of spatially coupled codes, that achieve excellent error correction performance via superposition of simple constituent codes. A BMST encoder consists of an outer basic code and an inner rate-one block-convolutional shift register. The resulting graph representation of the encoder allows slidingwindow decoding, similarly to spatially coupled Low-Density Parity-Check codes. This paper proposes a method to reduce the decoding complexity by adjusting the step size of the sliding window. Furthermore, a low-complexity parity-check-based early termination criterion is introduced, which can be universally applied to recursive BMST structures.Publicationtype: Conference Paper93 44 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Hybrid receive combining for scalable cell-free massive MIMO with multiple CPUs and latency-constrained midhaul linksWe propose a new way of operating a cell-free massive multiple-input multiple-output (MIMO) system with multiple central processing units (CPUs). In scalable cell-free massive MIMO systems, each user equipment (UE) is served by a cluster of access points (APs). The required coordination of the APs is often modeled to be done at a single cloud CPU, but in practice this cloud CPU consists of many physical entities which can be distributed over a large geographical area. Contrary to other works, in this work we explicitly model the cloud CPU as multiple physical CPUs, where each AP is connected to one of these CPUs via a low-latency fronthaul link. The CPUs are connected via midhaul links which may have a much higher latency. Hence, extensive cooperation between APs connected to the same CPU is possible while cooperation between APs connected to different CPUs is limited. We outline a joint initial access, pilot assignment, and clustering procedure in such a network. Further, we propose a new hybrid receive combining approach that takes advantage of this structure and allows for a scalable implementation of the system. We compare the performance of our proposed hybrid cell-free system with multiple CPUs to both the idealized centralized cloud CPU version and to the fully distributed cell-free system. Our results show that the proposed system can achieve a performance close to the idealized cloud CPU system while being practically feasible. Furthermore, our hybrid approach substantially outperforms a cellular Distributed Antenna System (DAS) with no CPU cooperation.Publicationtype: Conference Paper107 80 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Wideband channel modeling for wireless avionics intra-communications(IEEE, 2025-07); ; ; Wireless Avionics Intra-Communications (WAIC) has been proposed to partially replace costly wiring in future generations of aircraft. Besides the allocation of a frequency range and several performance figures, there is no standardized transmission scheme so far. For the design of suitable physical layer techniques, comprehensive models are required to perform realistic link-level simulations for the aircraft environment. This paper presents a wideband channel model for in-cabin WAIC systems, derived from channel measurements performed in an Airbus A321 cabin. The model is validated by comparing experimentally measured and simulated frame error rates using the proposed model in an IEEE 802.11a-based OFDM transmission.Publicationtype: Conference Paper51 35 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , 21 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Collaborative relative positioning in underwater environments using acoustic communication and two-way ranging(2025-03); ; 31 17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Region-Specific Coarse Quantization with Check Node Awareness in 5G-LDPC
Decoding(2025-02-11); This paper presents novel techniques for improving the error correction performance and reducing the complexity of coarsely quantized 5G LDPC decoders. The proposed decoder design supports arbitrary message-passing schedules on a base-matrix level by modeling exchanged messages with entry-specific discrete random variables. Variable nodes (VNs) and check nodes (CNs) involve compression operations designed using the information bottleneck method to maximize preserved mutual information between code bits and quantized messages. We introduce alignment regions that assign the messages to groups with aligned reliability levels to decrease the number of individual design parameters. Group compositions with degree-specific separation of messages improve performance by up to 0.4 dB. Further, we generalize our recently proposed CN-aware quantizer design to irregular LDPC codes and layered schedules. The method optimizes the VN quantizer to maximize preserved mutual information at the output of the subsequent CN update, enhancing performance by up to 0.2 dB. A schedule optimization modifies the order of layer updates, reducing the average iteration count by up to 35 %. We integrate all new techniques in a rate-compatible decoder design by extending the alignment regions along a rate-dimension. Our complexity analysis shows that 2-bit decoding can double the area efficiency over 4-bit decoding at comparable performance.Publicationtype: Journal Article57 150 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Memory-Assisted Quantized LDPC DecodingWe enhance coarsely quantized LDPC decoding by reusing computed check node messages from previous iterations. Typically, variable and check nodes update and replace old messages every iteration. We show that, under coarse quantization, discarding old messages entails a significant loss of mutual information. The loss is avoided with additional memory, improving performance by up to 0.23 dB. We optimize quantization with a modified information bottleneck algorithm that considers the statistics of old messages. A simple merge operation reduces memory requirements. Depending on channel conditions and code rate, memory assistance enables up to 32% better area efficiency for 2-bit decoding.Publicationtype: Journal Article86 47 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Wideband channel modeling for wireless avionics intra-communicationsWireless Avionics Intra-Communications (WAIC) has been proposed to partially replace costly wiring in future generations of aircraft. Besides the allocation of a frequency range and several performance figures, there is no standardized transmission scheme so far. For the design of suitable physical layer techniques, comprehensive models are required to perform realistic link-level simulations for the aircraft environment. We present a wideband channel model for in-cabin WAIC systems, that has been derived from channel measurements performed in an Airbus A321 cabin. The model is validated by comparing physically measured frame error rates to simulated error ratesusing the proposed model in an OFDM transmission based on IEEE 802.11a applied to the WAIC frequency band.Publicationtype: Conference Poster not in Proceedings51 32 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , On neural network data predistortion and constellation shaping for satellite channels(2025); In communication over transparent satellite payloads, traveling wave-tube amplifier (TWTA) cause nonlinear distortion to the transmit signal. Together with filters involved in the transmission chain, the TWTA causes distorted decision regions (warping) and intersymbol interference (ISI) at the matched filter output. This nonlinear channel can be compensated by means of data predistortion. The remaining interference results can be interpreted as a channel and the transmit constellation can be optimized for the joint channel with influences from additive white Gaussian noise (AWGN) and phase noise. This work shows how constellation shaping and data predistortion can be designed using neural networks. Particularly, a novel data predistortion algorithm based on a recurrent neural network (RNN) which accounts for the ISI is presented. For constellation shaping, different constrained optimization techniques are presented, including quadrant-symmetric optimization, spiral constellations and amplitude and phase-shift keying (APSK) constellations. All constellations are shaped by implementing the communication chain as an autoencoder, which is trained on a channel with the abovementioned impairments, which occur in satellite links. Resulting constellations are presented together with data predistortion, bit error rate (BER) and information rates.Publicationtype: Conference Poster not in Proceedings32 27