64 research outputs found
Convolutive superposition for multicarrier cognitive radio systems
Recently, we proposed a spectrum-sharing paradigm for single-carrier
cognitive radio (CR) networks, where a secondary user (SU) is able to maintain
or even improve the performance of a primary user (PU) transmission, while also
obtaining a low-data rate channel for its own communication. According to such
a scheme, a simple multiplication is used to superimpose one SU symbol on a
block of multiple PU symbols.The scope of this paper is to extend such a
paradigm to a multicarrier CR network, where the PU employs an orthogonal
frequency-division multiplexing (OFDM) modulation scheme. To improve its
achievable data rate, besides transmitting over the subcarriers unused by the
PU, the SU is also allowed to transmit multiple block-precoded symbols in
parallel over the OFDM subcarriers used by the primary system. Specifically,
the SU convolves its block-precoded symbols with the received PU data in the
time-domain, which gives rise to the term convolutive superposition. An
information-theoretic analysis of the proposed scheme is developed, which
considers different amounts of network state information at the secondary
transmitter, as well as different precoding strategies for the SU. Extensive
simulations illustrate the merits of our analysis and designs, in comparison
with conventional CR schemes, by considering as performance indicators the
ergodic capacity of the considered systems.Comment: 29 pages, 8 figure
Equalization Techniques of Control and Non-Payload Communication Links for Unmanned Aerial Vehicles
In the next years, several new applications involving unmanned aerial vehicles (UAVs) for public and commercial uses are envisaged. In such developments, since UAVs are expected to operate within the public airspace, a key issue is the design of reliable control and non-payload communication (CNPC) links connecting the ground control station to the UAV. At the physical layer, CNPC design must cope with time- and frequency-selectivity (so-called double selectivity) of the wireless channel, due to lowaltitude operation and flight dynamics of the UAV. In this paper, we consider the transmission of continuous phase modulated (CPM) signals for UAV CNPC links operating over doubly-selective channels. Leveraging on the Laurent representation for a CPM signal, we design a two-stage receiver: the first one is a linear time-varying (LTV) equalizer, synthesized under either the zero-forcing (ZF) or minimum mean-square error (MMSE) criterion; the second one recovers the transmitted symbols from the pseudo-symbols of the Laurent representation in a simple recursive manner. In addition to LTV-ZF and LTV-MMSE equalizers, their widely-linear versions are also developed, to take into account the possible noncircular features of the CPM signal. Moreover, relying on a basis expansion model (BEM) of the doubly-selective channel, we derive frequency-shift versions of the proposed equalizers, by discussing their complexity issues and proposing simplified implementations. Monte Carlo numerical simulations show that the proposed receiving structures are able to satisfactorily equalize the doubly-selective channel in typical UAV scenarios
Enabling and Emerging Sensing Technologies for Crowd Management in Public Transportation Systems: A Review
Management of crowd information in public transportation (PT) systems is
crucial to foster sustainable mobility, by increasing the user's comfort and
satisfaction during normal operation, as well as to cope with emergency
situations, such as pandemic crises, as recently experienced with COVID-19
limitations. This paper presents a taxonomy and review of sensing technologies
based on Internet of Things (IoT) for real-time crowd analysis, which can be
adopted in various segments of the PT system (buses/trams/trains,
railway/subway stations, and bus stops). To discuss such technologies in a
clear systematic perspective, we introduce a reference architecture for crowd
management, which employs modern information and communication technologies
(ICT) in order to: (i) monitor and predict crowding events; (ii) adapt in
real-time PT system operations, by modifying service frequency, timetables,
routes, and so on; (iii) inform in realtime the users of the crowding status of
the PT system, by means of electronic displays installed inside vehicles or at
bus stops/stations, and/or by mobile transport applications. It is envisioned
that the innovative crowd management functionalities enabled by ICT/IoT sensing
technologies can be incrementally implemented as an add-on to traditional
intelligent transportation system (ITS) platforms, which are already in use by
major PT companies operating in urban areas. Moreover, it is argued that, in
this new framework, additional services can be delivered, such as, e.g.,
on-line ticketing, vehicle access control and reservation in severely crowded
situations, and evolved crowd-aware route planning.Comment: 15 pages, 2 figures, 2 tables, submitted to IEEE Sensors Journa
Anti-Jamming Beam Alignment in Millimeter-Wave MIMO Systems
In millimeter-wave (MMW) multiple-input multiple-output (MIMO)
communications, users and their corresponding base station (BS) have to align
their beam during both initial access and data transmissions to compensate for
the high propagation loss. The beam alignment (BA) procedure specified for 5th
Generation (5G) New Radio (NR) has been designed to be fast and precise in the
presence of non-malicious interference and noise. A smart jammer might exploit
this weakness and may launch an attack during the BA phase in order to degrade
the accuracy of beam selection and, thus, adversely impacting the end-to-end
performance and quality-of-service experienced by the users. In this paper, we
study the effects of a jamming attack at MMW frequencies during the BA
procedure used to perform initial access for idle users and adaptation/recovery
for connected users. We show that the BA procedure adopted in 5G NR is
extremely vulnerable to a smart jamming attack and, consequently, we propose a
countermeasure based on the idea of randomized probing, which consists of
randomly corrupting the probing sequence transmitted by the BS in order to
reject the jamming signal at the UE via a subspace-based technique based on
orthogonal projections and jamming cancellation. Numerical results corroborate
our theoretical findings and show the very satisfactory accuracy of the
proposed anti-jamming approach.Comment: 17 pages, 10 figures, 3 tables, accepted in IEEE Transactions on
Communication
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