69 research outputs found
Optimum Header Positioning in Successive Interference Cancellation (SIC) based Aloha
Random Access MAC protocols are simple and effective when the nature of the
traffic is unpredictable and sporadic. In the following paper, investigations
on the new Enhanced Contention Resolution ALOHA (ECRA) are presented, where
some new aspects of the protocol are investigated. Mathematical derivation and
numerical evaluation of the symbol interference probability after SIC are here
provided. Results of the optimum header positioning which is found to be in the
beginning and in the end of the packets, are exploited for the evaluation of
ECRA throughput and Packet Error Rate (PER) under imperfect knowledge of
packets positions. Remarkable gains in the maximum throughput are observed for
ECRA w.r.t. Contention Resolution ALOHA (CRA) under this assumption.Comment: Accepted for publication in the IEEE International Conference on
Communications (ICC) 201
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
Detection and Combining Techniques for Asynchronous Random Access with Time Diversity
Asynchronous random access (RA) protocols are particularly attractive for
their simplicity and avoidance of tight synchronization requirements. Recent
enhancements have shown that the use of successive interference cancellation
(SIC) can largely boost the performance of these schemes. A further step
forward in the performance can be attained when diversity combining techniques
are applied. In order to enable combining, the detection and association of the
packets to their transmitters has to be done prior to decoding. We present a
solution to this problem, that articulates into two phases. Non-coherent
soft-correlation as well as interference-aware soft-correlation are used for
packet detection. We evaluate the detection capabilities of both solutions via
numerical simulations. We also evaluate numerically the spectral efficiency
achieved by the proposed approach, highlighting its benefits.Comment: 6 pages, 7 figures. Work has been submitted to the 11th International
ITG Conference on Systems, Communications and Coding 201
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
From 5G to 6G: Has the Time for Modern Random Access Come?
This short paper proposes the use of modern random access for IoT
applications in 6G. A short overview of recent advances in uncoordinated medium
access is provided, highlighting the gains that can be achieved by leveraging
smart protocol design intertwined with advanced signal processing techniques at
the receiver. The authors' vision on the benefits such schemes can yield for
beyond-5G systems is presented, with the aim to trigger further discussion.Comment: 2 pages, 1 figure, presented at 6G Summit, Levi, Finland, 201
Relay-aided Slotted Aloha for Optical Wireless Communications
We consider a relay-aided Slotted ALOHA solution for uplink random access for
an Optical Wireless Communications (OWC)-based Internet of Things (IoT). The
first phase of uplink, the one between IoT devices and the relays, is realized
using indoor OWC, while the second phase, between the relays and a base
station, represents the long-range RF transmission based on low-power wide area
network such as LoRaWAN and occurs outdoors. The throughput performance
dependence on the OWC and RF channel conditions is observed. The behavior of
the performance gain due to adding relays is highlighted and investigated under
different channel and traffic conditions.Comment: Published in: 2020 12th International Symposium on Communication
Systems, Networks and Digital Signal Processing (CSNDSP
Cache Placement Optimization for Layered Video Content
In this work, we investigate cache placement strategies for layered video content. We consider a library of video
files that can be requested in different quality levels, according
to a specific distribution. The study involves formulating and
solving two distinct optimization problems to determine the most
effective approach to cache placement. Our aim is to compare the
following strategies: placement strategy which reduces congestion
on the backhaul link by minimizing the number of transmissions
necessary to meet user requests, and placement strategy which
maximizes the probability of users being fully served from cached
content. As shown in the solutions, these two performance metrics
lead to different solutions for content that needs to be cached
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