812 research outputs found
Grant-Free Access: Machine Learning for Detection of Short Packets
In this paper, we explore the use of machine learning methods as an efficient
alternative to correlation in performing packet detection. Targeting
satellite-based massive machine type communications and internet of things
scenarios, our focus is on a common channel shared among a large number of
terminals via a fully asynchronous ALOHA protocol to attempt delivery of short
data packets. In this setup, we test the performance of two algorithms, neural
networks and random forest, which are shown to provide substantial improvements
over {traditional} techniques. Excellent performance is demonstrated in terms
of detection and false alarm probability also in the presence of collisions
among user transmissions. The ability of machine learning to extract further
information from incoming signals is also studied, discussing the possibility
to classify detected preambles based on the level of interference they undergo
Random access techniques for satellite communications
The effective coverage of satellites and the technology behind have motivated many actors to develop efficient communications for Internet access, television and telephony. For a long time, reservation resources of Demand Assignment Multiple Access (DAMA) techniques have been largely deployed in the return link of satellite communications, occupying most of the frequency bandwidth. However, these resources cannot follow the technological growth with big users communities in applications like the Internet of Things and Machine to Machine communications. Especially because the Round Trip Time is significant in addition to a potential underuse of the resources. Thus, access protocols based on ALOHA took over a big part of the Random Access (RA) research area and have considerably evolved lately. CRDSA have particularly put its fingerprint in this domain, which inspired many different techniques. In this context, a complementary method, called MARSALA comes to unlock CRDSA when packets can no longer be retrieved. This actually involves a correlation complexity related to packet localization which is necessary for replicas combinations that results in a potentially higher signal power. Accordingly, the main goal of this PhD research is to seek for effective and less complex alternatives. More precisely, the core challenge focuses on the way to manage multi-user transmissions and solve interference at reception, with the smallest complexity. In addition, the loop phenomenon which occur when multiple users transmit their packets at the same positions is tackled as it creates an error floor at the packet loss ratio performance. Synchronous and asynchronous solutions are proposed in this thesis, mainly based on providing the transmitter and the receiver with a shared prior information that could help reduce the complexity, mitigate the loop phenomenon and enhance the system performance. An in-depth description and analysis of the proposed techniques are presented in this dissertation
Modern Random Access for Satellite Communications
The present PhD dissertation focuses on modern random access (RA) techniques.
In the first part an slot- and frame-asynchronous RA scheme adopting replicas,
successive interference cancellation and combining techniques is presented and
its performance analysed. The comparison of both slot-synchronous and
asynchronous RA at higher layer, follows. Next, the optimization procedure, for
slot-synchronous RA with irregular repetitions, is extended to the Rayleigh
block fading channel. Finally, random access with multiple receivers is
considered.Comment: PhD Thesis, 196 page
Grant-Free Access: Machine Learning for Detection of Short Packets
In this paper, we explore the use of machine learning
methods as an efficient alternative to correlation in performing
packet detection. Targeting satellite-based massive machine type
communications and internet of things scenarios, our focus is on
a common channel shared among a large number of terminals
via a fully asynchronous ALOHA protocol to attempt delivery of
short data packets. In this setup, we test the performance of two
algorithms, neural networks and random forest, which are shown
to provide substantial improvements over traditional techniques.
Excellent performance is demonstrated in terms of detection
and false alarm probability also in the presence of collisions
among user transmissions. The ability of machine learning to
extract further information from incoming signals is also studied,
discussing the possibility to classify detected preambles based on
the level of interference they underg
Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)
Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression
A Survey on Wireless Security: Technical Challenges, Recent Advances and Future Trends
This paper examines the security vulnerabilities and threats imposed by the
inherent open nature of wireless communications and to devise efficient defense
mechanisms for improving the wireless network security. We first summarize the
security requirements of wireless networks, including their authenticity,
confidentiality, integrity and availability issues. Next, a comprehensive
overview of security attacks encountered in wireless networks is presented in
view of the network protocol architecture, where the potential security threats
are discussed at each protocol layer. We also provide a survey of the existing
security protocols and algorithms that are adopted in the existing wireless
network standards, such as the Bluetooth, Wi-Fi, WiMAX, and the long-term
evolution (LTE) systems. Then, we discuss the state-of-the-art in
physical-layer security, which is an emerging technique of securing the open
communications environment against eavesdropping attacks at the physical layer.
We also introduce the family of various jamming attacks and their
counter-measures, including the constant jammer, intermittent jammer, reactive
jammer, adaptive jammer and intelligent jammer. Additionally, we discuss the
integration of physical-layer security into existing authentication and
cryptography mechanisms for further securing wireless networks. Finally, some
technical challenges which remain unresolved at the time of writing are
summarized and the future trends in wireless security are discussed.Comment: 36 pages. Accepted to Appear in Proceedings of the IEEE, 201
A dynamic distributed multi-channel TDMA slot management protocol for ad hoc networks
With the emergence of new technologies and standards for wireless communications and an increase in application and user requirements, the number and density of deployed wireless ad hoc networks is increasing. For deterministic ad hoc networks, Time-Division Multiple Access (TDMA) is a popular medium access scheme, with many distributed TDMA scheduling algorithms being proposed. However, with increasing traffic demands and the number of wireless devices, proposed protocols are facing scalability issues. Besides, these protocols are achieving suboptimal spatial spectrum reuse as a result of the unsolved exposed node problem. Due to a shortage of available spectrum, a shift from fixed spectrum allocation to more dynamic spectrum sharing is anticipated. For dynamic spectrum sharing, improved distributed scheduling protocols are needed to increase spectral efficiency and support the coexistence of multiple co-located networks. Hence, in this paper, we propose a dynamic distributed multi-channel TDMA (DDMC-TDMA) slot management protocol based on control messages exchanged between one-hop network neighbors and execution of slot allocation and removal procedures between sender and receiver nodes. DDMC-TDMA is a topology-agnostic slot management protocol suitable for large-scale and high-density ad hoc networks. The performance of DDMC-TDMA has been evaluated for various topologies and scenarios in the ns-3 simulator. Simulation results indicate that DDMC-TDMA offers near-optimal spectrum utilization by solving both hidden and exposed node problems. Moreover, it proves to be a highly scalable protocol, showing no performance degradation for large-scale and high-density networks and achieving coexistence with unknown wireless networks operating in the same wireless domain
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