https://hdl.handle.net/20.500.12761/1 2026-09-11T01:53:31Z 2026-09-11T01:53:31Z Eleftherakis, Stavros Giustiniano, Domenico Zhao, Yuxin Jiang, Xiaolin Lindmark, Gustav Gunnarsson, Fredrik https://hdl.handle.net/20.500.12761/2068 2026-09-11T00:00:11Z 2026-07-01T00:00:00Z

From 5G Single-Cell Signals to Pervasive Smartphone Positioning: A Real-World Study Eleftherakis, Stavros; Giustiniano, Domenico; Zhao, Yuxin; Jiang, Xiaolin; Lindmark, Gustav; Gunnarsson, Fredrik Accurate and reliable positioning is a cornerstone of pervasive computing. However, GNSS is not always available for pervasive services while cellular-network-based alternatives have proven unsuccessful, due to coarse position accuracy or complex network setup. In this work, we investigate 5G singlecell positioning by leveraging Timing Advance and Angle of Arrival measurements, two key indicators already used in 5G NR for communication. Our approach does not require tight network synchronization among base stations, unlike other 5G positioning techniques. We present the first real-world study of single-cell positioning in a 5G network with a commercial gNB and an off-the-shelf smartphone moving up to 461 meters away from the gNB across four urban trajectories. Our analysis reveals two key challenges: coarse angular and timing resolution, and severe angle and range errors under Non-Line-of-Sight (NLOS) conditions. To overcome these challenges, we present a framework that (i) synthesizes higher-resolution Angle-ofArrival estimates from real 5G beam patterns, (ii) classifies LOS/NLOS conditions with a Convolutional Neural Network trained on beam signal-strength heatmaps, and (iii) refines angle and ranging using multipath-aware corrections. Our system reduces the median positioning error from 86.8 m to 16.5 m with a single gNB, without the aid of external sensors.

2026-07-01T00:00:00Z Goultiaev Tolstokorov, Alexandr Mouratidis, Kyriakos Dogani, Javad Laoutaris, Nikolaos https://hdl.handle.net/20.500.12761/2067 2026-09-10T00:00:27Z 2026-10-01T00:00:00Z

Rent-a-RAG: Embedding-Space Watermarks for Auditing Third-Party RAG Goultiaev Tolstokorov, Alexandr; Mouratidis, Kyriakos; Dogani, Javad; Laoutaris, Nikolaos Third-party retrieval-augmented generation (RAG) marketplaces create a new auditing problem: data providers may license corpora to a RAG operator, yet later have no visibility into whether their documents are being reused without compensation. Auditing this misuse is difficult because the operator is non-cooperative, answers are paraphrased by the generator, and one response may combine evidence from many providers. We propose DirBucket, a provider-side semantic watermarking and black-box auditing framework for document-level reuse in multi-provider RAG. DirBucket watermarks documents by meaning-preserving paraphrases whose embeddings are biased toward provider-bucket secret directions, enabling detection from black-box answers while preserving retrieval utility. On a challenging benchmark that reflects mixed-provider reuse under black-box access, DirBucket is the only method that consistently achieves strong target detection with no non-target activation, detecting non-compliance in every audit within 23 audited answers on our primary benchmark. The watermark survives adversarial post-answer laundering, and none of the evaluated evasion strategies simultaneously defeats detection while preserving user-perceived answer quality. Detection transfers unchanged to a second benchmark built from real clinical, cyber-threat-intelligence, and legal provider corpora. These results suggest that embedding-space watermarking can make document reuse in third-party RAG statistically auditable.

2026-10-01T00:00:00Z de Andrés Hernández, David Alhamwy, Yasin Wagner, Daniel Stephan, Maximilian Wichtlhuber, Matthias Hohlfeld, Oliver https://hdl.handle.net/20.500.12761/2066 2026-08-29T00:00:18Z 2026-08-11T00:00:00Z

LARS: Keeping Local Traffic Local with Latency-Aware Route Servers at IXPs de Andrés Hernández, David; Alhamwy, Yasin; Wagner, Daniel; Stephan, Maximilian; Wichtlhuber, Matthias; Hohlfeld, Oliver Internet Exchange Points facilitate traffic exchange through Route Servers that use BGP for path selection without considering latency. This paper presents LARS, the first system to enable latency-aware path optimization at IXP route servers. It requires no changes to BGP and no bilateral coordination among members, thus directly enabling latency-aware routing for all IXP members. LARS continuously probes the route-server RIB, annotates routes with RTT-derived BGP communities, and enables members to (i) enforce a configurable latency radius that suppresses high-latency routes and (ii) prefer lower-latency alternatives when multiple paths exist. We evaluate LARS at a very large IXP using a production-level prototype that demonstrates stable latency estimation, effective tail-latency control via selective redistribution, and potential to optimize BGP best paths.

2026-08-11T00:00:00Z Jörnell, Carl Perez, Vicente Saguillo, Oriol https://hdl.handle.net/20.500.12761/2065 2026-08-29T00:00:14Z 2026-09-01T00:00:00Z

Opening Wide, Moving Fast: Polymarket Spread Dynamics Jörnell, Carl; Perez, Vicente; Saguillo, Oriol Polymarket creates a new market for every event it lists, and each contract begins with an empty order book: no inherited orders, no assigned market maker, and no opening auction. Every contract there- fore has a clear opening moment and an early period during which its trading conditions are still forming. Using roughly 160,000 contracts cre- ated between October 2025 and March 2026, we study what it costs to trade in a market’s first hours of life and how that cost behaves across different kinds of events. Over the first twenty-four hours of each market, the genesis window, we measure how wide spreads start and how quickly they narrow, how much it actually costs to trade immediately, and how much of that cost stays with the liquidity provider versus reflecting the price moving after- wards. We compare these patterns across eight event categories. Trading costs are strongly category-dependent from the very first trade: sports markets open cheaply with deep, balanced books, while other categories open much wider and take longer to settle, with most of the narrowing happening within the first hour. Centrally, we document a dissociation: ranking categories by how expensive they are to trade and by how much early trades move the price produces two orderings that do not agree. These are separate properties, not two views of the same thing

2026-09-01T00:00:00Z