arXiv subjects

Muhammad Asad Ullah

Publications and source records attributed to Muhammad Asad Ullah.

11 recordsLinked to original sources

arXiv2026

Direct-to-Device Connectivity for Integrated Communication, Navigation and Surveillance

Sixth-generation (6G) communication systems are expected to support direct-to-device (D2D) connectivity, enabling standard user equipment (UE) to seamlessly transition to non-terrestrial network (NTN), particularly satellite communication mode, when operating beyond terrestrial network (TN) coverage. This D2D concept does not require hardware modifications to conventional UEs and eliminates the need for dedicated satellite ground terminals. D2D-capable UEs can be mounted on both manned and unmanned aircraft, however, they are especially well-suited for low-altitude unmanned aircraft due to their compact form factor, lightweight design, energy efficiency, and TN-NTN roaming capabilities. D2D can also enable beyond-visual-line-of-sight operation by providing NTN support for Communications, Navigation, and Surveillance (CNS) services during TN outages or congestion. This paper investigates the capabilities and limitations of D2D connectivity for low-altitude unmanned aircraft operating in urban environments. We analyze the variation in line-of-sight probability for both TN and NTN links as a function of aircraft altitude. We further compute path loss and received signal strength while accounting for a representative TN deployment with down-tilted antennas. The results show that the TN and NTN links complement each other, significantly improving the availability of the CNS service at low altitudes. These findings provide insights to support the design and optimization of future 6G-enabled integrated CNS services.

cs.NI↗

arXiv2025

A First Look at Starlink In-Flight Performance: An Intercontinental Empirical Study

Starlink delivers Internet services to users across terrestrial, maritime, and aviation domains. The prior works have studied its performance at fixed sites and in-motion vehicles, while an in-depth analysis of in-flight performance remains absent. With major airlines now offering Starlink Internet onboard, there is a growing need to evaluate and improve its performance for aviation users. This paper addresses this shortcoming by conducting in-flight measurements over the Baltic Sea and the Pacific Ocean. Our measurement results show that a single user device experiences median throughputs of 64 Mbps and 24 Mbps for the downlink and uplink, respectively. The median uplink throughput is approximately 33 Mbps when the aircraft maintains an altitude above 17,000 feet. However, a significant reduction in uplink performance is observed during the aircraft descent phase, with the median throughput dropping to around 20 Mbps at lower altitudes. Round-trip time (RTT) is highly dependent on the location of the ground station being pinged and the use of inter-satellite links (ISLs). We dive deeper into 5.5 hours of ping measurements collected over the Pacific Ocean and investigate factors influencing RTT, hypothesizing that ISLs routing, data queuing at satellites, and feeder link congestion contribute to deviations from theoretical values. For comparative analysis, we evaluate the Starlink ground terminal and in-flight connectivity performance from the perspectives of a residential user and an airline passenger, respectively.

cs.NI↗

arXiv2025

Doppler Estimation and Compensation Techniques in LoRa Direct-to-Satellite Communications

Within the LPWAN framework, the LoRa modulation adopted by LoRaWAN technology has garnered significant interest as a connectivity solution for IoT applications due to its ability to offer low-cost, low-power, and long-range communications. One emerging use case of LoRa is DtS connectivity, which extends coverage to remote areas for supporting IoT operations. The satellite IoT industry mainly prefers LEO because it has lower launch costs and less path loss compared to Geostationary orbit. However, a major drawback of LEO satellites is the impact of the Doppler effect caused by their mobility. Earlier studies have confirmed that the Doppler effect significantly degrades the LoRa DtS performance. In this paper, we propose four frameworks for Doppler estimation and compensation in LoRa DtS connectivity and numerically compare the performance against the ideal scenario without the Doppler effect. Furthermore, we investigate the trade-offs among these frameworks by analyzing the interplay between spreading factor, and other key parameters related to the Doppler effect. The results provide insights into how to achieve robust LoRa configurations for DtS connectivity.

eess.SP↗

arXiv2025

Impact of Weather on Satellite Communication: Evaluating Starlink Resilience

Satellite communications have emerged as one of the most feasible solutions to provide global wireless coverage and connect the unconnected. Starlink dominates the market with over 7,000 operational satellites in low Earth orbit (LEO) and offers global high-speed and low-latency Internet service for stationary and mobile use cases, including in-motion connectivity for vehicles, vessels, and aircraft. Starlink terminals are designed to handle extreme weather conditions. Starlink recommends a flat high performance (FHP) terminal for users living in areas with extreme weather conditions. The earlier studies evaluated Starlink's FHP throughput for stationary and in-motion users without providing a detailed analysis of how weather affects its performance. There remains a need to investigate the impact of weather on FHP's throughput. In this paper, we address this shortcoming by analyzing the impact of weather on Starlink's performance in Oulu, Finland, a city located in Northern Europe near the Arctic Circle. Our measurements reveal that rain degrades median uplink and downlink throughput by 52.27% and 37.84%, respectively. On the contrary, there was no noticeable impact on the round-trip time. Additionally, we also examine the impact of cloud cover on the Starlink throughput. The linear regression analysis reveals the negative relationship between throughput and cloud cover. The cloud cover of up to 12.5% has around 20% greater throughput than the cloud cover of 87.5%

cs.ET↗

arXiv2025

Starlink in Northern Europe: A New Look at Stationary and In-motion Performance

Starlink has introduced the Flat High Performance (FHP) terminal, specifically designed to support the vehicles and the vessels in motion as well as the high-demand stationary users. The research on FHP terminal throughput analysis remains limited, only a few existing studies evaluate FHP, focusing on the limited parameters and scenarios. This paper evaluates the FHP terminal's performance in Finland, Northern Europe. We examine round-trip time (RTT), uplink, and downlink throughput for both stationary and in-motion use. We measure network efficiency across six geographically diverse servers and get insights of network routing strategies. Our results show that Starlink provides high-speed, low-RTT connectivity, however, the throughput experiences fluctuations with slight degradation when in motion. Additionally, we compare Starlink and terrestrial network RTT and possible routing paths.

cs.NI↗

arXiv2025

5G Integrated Communications, Navigation, and Surveillance: A Vision and Future Research Perspectives

Communication, Navigation, and Surveillance (CNS) is the backbone of the Air Traffic Management (ATM) and Unmanned Aircraft System (UAS) Traffic Management (UTM) systems, ensuring safe and efficient operations of modern and future aviation. Traditionally, the CNS is considered three independent systems: communications, navigation, and surveillance. The current CNS system is fragmented, with limited integration across its three domains. Integrated CNS (ICNS) is a contemporary concept implying that those systems are provisioned through the same technology stack. ICNS is envisioned to improve service quality, spectrum efficiency, communication capacity, navigation predictability, and surveillance capabilities. The 5G technology stack offers higher throughput, lower latency, and massive connectivity compared to many existing communication technologies. This paper presents our 5G ICNS vision and network architecture and discusses how 5G technology can support integrated CNS services using terrestrial and non-terrestrial networks. We also discuss key 5G radio access technologies for delivering integrated CNS services at low altitudes for Innovative Air Mobility (IAM) and Advanced Air Mobility (AAM) operations. Finally, we present relevant challenges and potential research directions for further studies.

cs.NI↗

arXiv2024

Deterministic generation of frequency-bin-encoded microwave photons

A distributed quantum computing network requires a quantum communication channel between spatially separated processing units. In superconducting circuits, such a channel can be implemented based on propagating microwave photons to encode and transfer quantum information between an emitter and a receiver. However, traveling microwave photons can be lost during the transmission, leading to the failure of information transfer. Heralding protocols can be used to detect such photon losses. In this work, we propose such a protocol and experimentally demonstrate a frequency-bin encoding method of microwave photonic modes using superconducting circuits. We deterministically encode the quantum information from a superconducting qubit by simultaneously emitting its information into two photonic modes at different frequencies, with a process fidelity of 90.4%. The frequency-bin-encoded photonic modes can be used, at the receiver processor, to detect the occurrence of photon loss. Our work thus provides a reliable method to implement high-fidelity quantum state transfer in a distributed quantum computing network, incorporating error detection to enhance performance and accuracy.

quant-ph↗

arXiv2024

Experiment-based Models for Air Time and Current Consumption of LoRaWAN LR-FHSS

Long Range - Frequency Hopping Spread Spectrum (LR-FHSS) is an emerging and promising technology recently introduced into the LoRaWAN protocol specification for both terrestrial and non-terrestrial networks, notably satellites. The higher capacity, long-range and robustness to Doppler effect make LR-FHSS a primary candidate for direct-to-satellite (DtS) connectivity for enabling Internet-of-things (IoT) in remote areas. The LR-FHSS devices envisioned for DtS IoT will be primarily battery-powered. Therefore, it is crucial to investigate the current consumption characteristics and Time-on-Air (ToA) of LR-FHSS technology. However, to our knowledge, no prior research has presented the accurate ToA and current consumption models for this newly introduced scheme. This paper addresses this shortcoming through extensive field measurements and the development of analytical models. Specifically, we have measured the current consumption and ToA for variable transmit power, message payload, and two new LR-FHSS-based Data Rates (DR8 and DR9). We also develop current consumption and ToA analytical models demonstrating a strong correlation with the measurement results exhibiting a relative error of less than 0.3%. Thus, it confirms the validity of our models. Conversely, the existing analytical models exhibit a higher relative error rate of -9.2 to 3.4% compared to our measurement results. The presented in this paper results can be further used for simulators or in analytical studies to accurately model the on-air time and energy consumption of LR-FHSS devices.

cs.ET↗

arXiv2024

Entanglement of photonic modes from a continuously driven two-level system

The ability to generate entangled states of light is a key primitive for quantum communication and distributed quantum computation. Continuously driven sources, including those based on spontaneous parametric downconversion, are usually probabilistic, whereas deterministic sources require accurate timing of the control fields. Here, we experimentally generate entangled photonic modes by continuously exciting a quantum emitter, a superconducting qubit, with a coherent drive, taking advantage of mode matching in the time and frequency domain. Using joint quantum state tomography and logarithmic negativity, we show that entanglement is generated between modes extracted from the two sidebands of the resonance fluorescence spectrum. Because the entangled photonic modes are perfectly orthogonal, they can be transferred into distinct quantum memories. Our approach can be utilized to distribute entanglement at a high rate in various physical platforms, with applications in waveguide quantum electrodynamics, distributed quantum computing, and quantum networks.

quant-ph↗

arXiv2023

Energy Efficiency Optimization for Subterranean LoRaWAN Using A Reinforcement Learning Approach: A Direct-to-Satellite Scenario

The integration of subterranean LoRaWAN and non-terrestrial networks (NTN) delivers substantial economic and societal benefits in remote agriculture and disaster rescue operations. The LoRa modulation leverages quasi-orthogonal spreading factors (SFs) to optimize data rates, airtime, coverage and energy consumption. However, it is still challenging to effectively assign SFs to end devices for minimizing co-SF interference in massive subterranean LoRaWAN NTN. To address this, we investigate a reinforcement learning (RL)-based SFs allocation scheme to optimize the system's energy efficiency (EE). To efficiently capture the device-to-environment interactions in dense networks, we proposed an SFs allocation technique using the multi-agent dueling double deep Q-network (MAD3QN) and the multi-agent advantage actor-critic (MAA2C) algorithms based on an analytical reward mechanism. Our proposed RL-based SFs allocation approach evinces better performance compared to four benchmarks in the extreme underground direct-to-satellite scenario. Remarkably, MAD3QN shows promising potentials in surpassing MAA2C in terms of convergence rate and EE.

cs.IT↗

arXiv2021

Self-Guided Quantum State Learning for Mixed States

We provide an adaptive learning algorithm for tomography of general quantum states. Our proposal is based on the simultaneous perturbation stochastic approximation algorithm and is applicable on mixed qudit states. The salient features of our algorithm are efficient ($O \left( d^3 \right)$) post-processing in the dimension $d$ of the state, robustness against measurement and channel noise, and improved infidelity performance as compared to the contemporary adaptive state learning algorithms. A higher resilience against measurement noise makes our algorithm suitable for noisy intermediate-scale quantum applications.

quant-ph↗