2,810 research outputs found
Building accurate radio environment maps from multi-fidelity spectrum sensing data
In cognitive wireless networks, active monitoring of the wireless environment is often performed through advanced spectrum sensing and network sniffing. This leads to a set of spatially distributed measurements which are collected from different sensing devices. Nowadays, several interpolation methods (e.g., Kriging) are available and can be used to combine these measurements into a single globally accurate radio environment map that covers a certain geographical area. However, the calibration of multi-fidelity measurements from heterogeneous sensing devices, and the integration into a map is a challenging problem. In this paper, the auto-regressive co-Kriging model is proposed as a novel solution. The algorithm is applied to model measurements which are collected in a heterogeneous wireless testbed environment, and the effectiveness of the new methodology is validated
Non-Orthogonal Multiplexing of Ultra-Reliable and Broadband Services in Fog-Radio Architectures
The fifth generation (5G) of cellular systems is introducing Ultra-Reliable
Low-Latency Communications (URLLC) services alongside more conventional
enhanced Mobile BroadBand (eMBB) traffic. Furthermore, the 5G cellular
architecture is evolving from a base station-centric deployment to a fog-like
set-up that accommodates a flexible functional split between cloud and edge. In
this paper, a novel solution is proposed that enables the non-orthogonal
coexistence of URLLC and eMBB services by processing URLLC traffic at the Edge
Nodes (ENs), while eMBB communications are handled centrally at a cloud
processor as in a Cloud-Radio Access Network (C-RAN) system. This solution
guarantees the low-latency requirements of the URLLC service by means of edge
processing, e.g., for vehicle-to-cellular use cases, as well as the high
spectral efficiency for eMBB traffic via centralized baseband processing. Both
uplink and downlink are analyzed by accounting for the heterogeneous
performance requirements of eMBB and URLLC traffic and by considering practical
aspects such as fading, lack of channel state information for URLLC
transmitters, rate adaptation for eMBB transmitters, finite fronthaul capacity,
and different coexistence strategies, such as puncturing.Comment: Submitted as Journal Pape
Geo-Based Scheduling for C-V2X Networks
Cellular Vehicle-to-Everything (C-V2X) networks can operate without cellular
infrastructure support. Vehicles can autonomously select their radio resources
using the sensing-based Semi-Persistent Scheduling (SPS) algorithm specified by
the Third Generation Partnership Project (3GPP). The sensing nature of the SPS
scheme makes C-V2X communications prone to the well-known hidden-terminal
problem. To address this problem, this paper proposes a novel geo-based
scheduling scheme that allows vehicles to autonomously select their radio
resources based on the location and ordering of neighboring vehicles on the
road. The proposed scheme results in an implicit resource selection
coordination between vehicles (even with those outside the sensing range) that
reduces packet collisions. This paper evaluates analytically and through
simulations the proposed scheduling scheme. The obtained results demonstrate
that it reduces packet collisions and significantly increases the C-V2X
performance compared to when using the sensing-based SPS scheme
Cryptographic protection for military radio communications
Protecting the confidentiality, integrity and availability of information is very important in any telecommunications system. Information protection requires use of necessary physical, personal, information and communication technologies and above all – electromagnetic and cryptographic security measures. Equipment and tools for cryptographic protection should be examined and assessed in terms of resistance to known threats. Additional requirements are put on information protection for radio communication, especially military, where radio transmission is characterized by uncertainty of establishing and maintaining connections, bit rates are relatively low, often without full duplex. All this has an impact on the methods of cryptographic synchronization and implementation of cryptographic functions. A different approach to information protection is required by classic narrowband radio communications, a different one in time-division multi-access modes, and another one in broadband packet data transmission. Systems designed for information protection in radio communications implement appropriate operating modes of operation for cryptographic algorithms and protocols. Latest threats from quantum computers pose new challenges, especially in systems using public-key cryptography, because there are algorithms that can be used to attack these schemes with polynomial complexity
Cryptographic protection for military radio communications
Protecting the confidentiality, integrity and availability of information is very important in any telecommunications system. Information protection requires use of necessary physical, personal, information and communication technologies and above all – electromagnetic and cryptographic security measures. Equipment and tools for cryptographic protection should be examined and assessed in terms of resistance to known threats. Additional requirements are put on information protection for radio communication, especially military, where radio transmission is characterized by uncertainty of establishing and maintaining connections, bit rates are relatively low, often without full duplex. All this has an impact on the methods of cryptographic synchronization and implementation of cryptographic functions. A different approach to information protection is required by classic narrowband radio communications, a different one in time-division multi-access modes, and another one in broadband packet data transmission. Systems designed for information protection in radio communications implement appropriate operating modes of operation for cryptographic algorithms and protocols. Latest threats from quantum computers pose new challenges, especially in systems using public-key cryptography, because there are algorithms that can be used to attack these schemes with polynomial complexity
Network Management and Control for mmWave Communications
Millimeter-wave (mmWave) is one of the key technologies that enables the next wireless
generation. mmWave offers a much higher bandwidth than sub-6GHz communications
which allows multi-gigabit-per-second rates. This also alleviates the scarcity of spectrum
at lower frequencies, where most devices connect through sub-6GHz bands. However new
techniques are necessary to overcome the challenges associated with such high frequencies.
Most of these challenges come from the high spatial attenuation at the mmWave band,
which requires new paradigms that differ from sub-6GHz communications. Most notably
mmWave telecommunications are characterized by the need to be directional in order to
extend the operational range. This is achieved by using electronically steerable antenna
arrays, that focus the energy towards the desired direction by combining each antenna
element constructively or destructively. Additionally, most of the energy comes from
the Line Of Sight (LOS) component which gives mmWave a quasi-optical behaviour
where signals can reflect off walls and still be used for communication. Some other
challenges that directional communications bring are mobility tracking, blockages and
misalignments due to device rotation. The IEEE 802.11ad amendment introduced wireless
telecommunications in the unlicensed 60 GHz band. It is the first standard to address
the limitations of mmWave. It does so by introducing new mechanisms at the Medium
Access Control (MAC) and Physical (PHY) layers. It introduces multi-band operation,
relay operation mode, hybrid channel access scheme, beam tracking and beam forming
among others.
In this thesis we present a series of works that aim to improve mmWave
telecommunications. First we give an overview of the intrinsic challenges of mmWave
telecommunications, by explaining the modifications to the MAC and PHY layers. This
sets the base for the rest of the thesis. Then do a comprehensive study on how mmWave
behaves with existing technologies, namely TCP. TCP is unable to distinguish losses
caused by congestion or by transmission errors caused by channel degradation. Since
mmWave is affected by blockages more than sub-6GHz technologies, we propose a set
of parameters that improve the channel quality even for mobile scenarios. The next job
focuses on reducing the initial access overhead of mmWave by using sub-6GHz information
to steer towards the desired direction. We start this work by doing a comprehensive High Frequency (HF) and Low Frequency (LF) correlation, analyzing the similarity of
the existing paths between the two selected frequencies. Then we propose a beam
steering algorithm that reduces the overhead to one third of the original time. Once
we have studied how to reduce the initial access overhead, we propose a mechanism
to reduce the beam tracking overhead. For this we propose an open platform based
on a Field Programmable Gate Arrays (FPGA) where we implement an algorithm that
completely removes the need to train on the Station (STA) side. This is achieved by
changing beam patterns on the STA side while the Access Point (AP) is sending the
preamble. We can change up to 10 beam patterns without losing connection and we reduce
the overhead by a factor of 8.8 with respect to the IEEE 802.11ad standard. Finally
we present a dual band location system based on Commercial-Off-The-Shelve (COTS)
devices. Locating the STA can improve the quality of the channel significantly, since the
AP can predict and react to possible blockages. First we reverse engineer existing 60
GHz enabled COTS devices to extract Channel State Information (CSI) and Fine Timing
Measurements (FTM) measurements, from which we can estimate angle and distance.
Then we develop an algorithm that is able to choose between HF and LF in order to
improve the overall accuracy of the system. We achieve less than 17 cm of median error
in indoor environments, even when some areas are Non Line Of Sight (NLOS).This work has been supported by IMDEA Networks Institute.Programa de Doctorado en IngenierÃa Telemática por la Universidad Carlos III de MadridPresidente: Matthias Hollick.- Secretario: Vincenzo Mancuso.- Vocal: Paolo Casar
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