Applicability of Space-Time Block Codes for distributed cooperative broadcasting in MANETs with high node mobility

Mobile Ad-Hoc Networks (MANETs) are often characterized by high node mobility and rapid topology changes which in turn can cause high packet loss rates. In order to cope with this, MANETs typically rely on routing algorithms that try to efficiently distribute messages in the entire network. Such routing schemes introduce an overhead that limits the scalability of MANETs with respect to the number of nodes and/or mobility. Cooperative communication techniques have the potential to improve the efficiency of distributing messages and thus to increase the MANET scalability. In this paper, we propose an efficient cooperative broadcasting scheme based on distributed transmit diversity. To this end, we adapt Space-Time Block- Codes (STBCs), that were initially designed for a co-located setup in quasi-static environments, to a distributed setup with time-variant channels. We perform a comprehensive analysis based on bit error simulations to compare different STBC candidates and identify Linear-Scalable Dispersion Codes (LSDCs) to be a valuable option. For those, we propose an improvement of the inner-code for different channel models without the need for channel state information at the transmitter (CSIT). Besides, we validate the performance advantage of cooperative broadcasting by outage simulations in typical MANET scenarios

Distributed cooperative transmission in MANETs with multiple timing and carrier frequency offsets

Cooperative transmission is a promising approach to establish robust communication in Mobile Ad-Hoc Networks (MANETs). In low-complexity MANETs several transmitters (TX) can be aggregated to a virtual multiple input system. For such a setup, the impact of various timing and carrier frequency offsets (TO, CFO) has to be mitigated. We propose an effective, purely time-domain based equalizer structure that allows to establish cooperative transmission with a transmit diversity scheme in presence of aforementioned impairments and multipath channels. Exemplarily investigating the broadcast performance by outage simulations in a MANET scenario, we can demonstrate the benefits and indicate that the proposed structure is auspicious to improve the general scalability of MANETs

SDR-based demonstration system and applicability of SNR aggregation for multistage distributed cooperative communication in MANETs

Multistage or hierarchical distributed cooperative communication on the physical layer is a promising approach to overcome the scalability limitation of Mobile Ad-hoc Networks (MANETs). Standalone nodes that could successfully decode messages join transmission and support each other. They become a virtual transmit cluster and send simultaneously. While information theoretic research has demonstrated that an approximately linear scaling behaviour can be achieved, imperfections and constraints of practical systems have not been taken into account. Within this paper, we present a scalable and modular low-cost demonstration system based on software-defined radios (SDRs) to study distributed cooperative communication in practical MANETs. Furthermore, we apply SNR aggregation in combination with distributed cooperative transmission. To this end, we show a practical implementation approach and investigate the performance by measurements and simulations. Our results clearly highlight the advantages of combining distributed cooperative communication and SNR aggregation, e. g. to overcome larger distances in a distributed long haul multiple-input single-output (MISO) scenario or to enable a more efficient broadcast

Multi-carrier (OFDM) cooperative transmission in MANETs with multiple carrier frequency offsets

Cooperative transmission, realized by aggregating several nodes to a virtual multiple input system, is an auspicious approach to establish a more robust and effective communication in MANETs. In such a setup, impairments, i. e. multiple timing and carrier frequency offsets (TO, CFO) will occur. While multi-carrier schemes, e. g. Orthogonal Frequency Division Multiplexing (OFDM), are well-known to mitigate the impact of multipath propagation and TO, multiple CFO causes inter-carrier-interference (ICI) which typically degrades the performance significantly. Within this paper, we propose an effective code and equalizer structure that allows to overcome this limitation. It mitigates the impact of multiple CFO that can be significantly larger than the subcarrier spacing with a reasonable computational effort. For that, we utilize inherent code properties of Linear-Scalable Dispersion Codes (LSDCs) and propose a communication system composed of an equalizer structure in combination with LSDCs that enables multi-carrier distributed cooperative transmission for practical MANETs with high node mobility. We demonstrate the benefits of cooperative transmission in comparison to classical non-cooperative multi-hop or concurrent transmission by outage simulations, which clearly indicate that our proposal can be of crucial importance for the overall MANET scalability. Lastly, we compare our OFDM system with a recently proposed time-domain equalization single-carrier system and point out use cases, where the OFDM system can be more advantageous

The Cellular Relay Carpet: Distributed Cooperation with Ubiquitous Relaying

We consider the up- as well as downlink of a cellular network in which base stations (BSs) are supported by a large amount of relays spread over the entire area like a carpet. The BSs only see the static relays as the nodes they communicate with, which enables large antenna arrays at the BSs with sophisticated multi-user MIMO transmission. Together with a simple form of BS cooperation, the communication via the small relay cells allows to improve the data rates by distributed interference management and to reduce the complexity at the terminals. We investigate different types of relays as well as different relaying strategies for this relay carpet and compare them with respect to complexity, required channel state information (CSI), and performance in the interference-limited environment of dense cellular networks. The robustness of the different schemes with respect to channel estimation errors is studied and we conclude that especially relays of very low complexity are not sensitive to CSI imperfections. Relays can thus be applied in large numbers and enable massive MIMO at the BSs. The relay carpet proves thereby to be an efficient approach to enhance future generations of cellular networks significantly

Urology consultants versus large language models : potentials and hazards for medical advice in urology

Background Current interest surrounding large language models (LLMs) will lead to an increase in their use for medical advice. Although LLMs offer huge potential, they also pose potential misinformation hazards. Objective This study evaluates three LLMs answering urology-themed clinical case-based questions by comparing the quality of answers to those provided by urology consultants. Methods Forty-five case-based questions were answered by consultants and LLMs (ChatGPT 3.5, ChatGPT 4, Bard). Answers were blindly rated using a six-step Likert scale by four consultants in the categories: ‘medical adequacy’, ‘conciseness’, ‘coherence’ and ‘comprehensibility’. Possible misinformation hazards were identified; a modified Turing test was included, and the character count was matched. Results Higher ratings in every category were recorded for the consultants. LLMs' overall performance in language-focused categories (coherence and comprehensibility) was relatively high. Medical adequacy was significantly poorer compared with the consultants. Possible misinformation hazards were identified in 2.8% to 18.9% of answers generated by LLMs compared with <1% of consultant's answers. Poorer conciseness rates and a higher character count were provided by LLMs. Among individual LLMs, ChatGPT 4 performed best in medical accuracy (p < 0.0001) and coherence (p = 0.001), whereas Bard received the lowest scores. Generated responses were accurately associated with their source with 98% accuracy in LLMs and 99% with consultants. Conclusions The quality of consultant answers was superior to LLMs in all categories. High semantic scores for LLM answers were found; however, the lack of medical accuracy led to potential misinformation hazards from LLM ‘consultations’. Further investigations are necessary for new generations.Peer reviewe

Current Trends for 4D Space-Time Topology for Semantic Flow Segmentation

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High-resolution maps of Swiss apiaries and their applicability to study spatial distribution of bacterial honey bee brood diseases

Honey bees directly affect and are influenced by their local environment, in terms of food sources, pollinator densities, pathogen and toxin exposure and climate. Currently, there is a lack of studies analyzing these data with Geographic Information Systems (GIS) to investigate spatial relationships with the environment. Particularly for inter-colonial pathogen transmission, it is known that the likelihood of a healthy colony to become infested (e.g., Varroosis) or infected (e.g., American foulbrood—AFB, European foulbrood—EFB) increases with higher colony density. Whether these transmission paths can actually be asserted at apiary level is largely unknown. Here, we unraveled spatial distribution and high-resolution density of apiaries and bacterial honey bee brood diseases in Switzerland based on available GIS data. Switzerland as ‘model country’ offers the unique opportunity to get apiary data since 2010 owing to compulsory registration for every beekeeper. Further, both destructive bee brood diseases (AFB and EFB) are legally notifiable in Switzerland, and EFB has an epizootic character for the last decades. As governmental data sets have to be ameliorated, raw data from the cantonal agricultural or veterinary offices have been included. We found a mean density of 0.56 apiaries per km2, and high resolution spatial analyzes showed strong correlation between density of apiaries and human population density as well as agricultural landscape type. Concerning two bacterial bee brood diseases (AFB, EFB), no significant correlation was detectable with density of apiaries on cantonal level, though a high correlation of EFB cases and apiary density became obvious on higher resolution (district level). Hence, Swiss EFB epizootics seem to have benefited from high apiary densities, promoting the transmission of pathogens by adult bees. The GIS-based method presented here, might also be useful for other bee diseases, anthropogenic or environmental factors affecting bee colonies

Genes in the postgenomic era

We outline three very different concepts of the gene - 'instrumental', 'nominal', and 'postgenomic'. The instrumental gene has a critical role in the construction and interpretation of experiments in which the relationship between genotype and phenotype is explored via hybridization between organisms or directly between nucleic acid molecules. It also plays an important theoretical role in the foundations of disciplines such as quantitative genetics and population genetics. The nominal gene is a critical practical tool, allowing stable communication between bioscientists in a wide range of fields grounded in well-defined sequences of nucleotides, but this concept does not embody major theoretical insights into genome structure or function. The post-genomic gene embodies the continuing project of understanding how genome structure supports genome function, but with a deflationary picture of the gene as a structural unit. This final concept of the gene poses a significant challenge to conventional assumptions about the relationship between genome structure and function, and between genotype and phenotype