3,540 research outputs found
Millimeter Wave Cellular Networks: A MAC Layer Perspective
The millimeter wave (mmWave) frequency band is seen as a key enabler of
multi-gigabit wireless access in future cellular networks. In order to overcome
the propagation challenges, mmWave systems use a large number of antenna
elements both at the base station and at the user equipment, which lead to high
directivity gains, fully-directional communications, and possible noise-limited
operations. The fundamental differences between mmWave networks and traditional
ones challenge the classical design constraints, objectives, and available
degrees of freedom. This paper addresses the implications that highly
directional communication has on the design of an efficient medium access
control (MAC) layer. The paper discusses key MAC layer issues, such as
synchronization, random access, handover, channelization, interference
management, scheduling, and association. The paper provides an integrated view
on MAC layer issues for cellular networks, identifies new challenges and
tradeoffs, and provides novel insights and solution approaches.Comment: 21 pages, 9 figures, 2 tables, to appear in IEEE Transactions on
Communication
An Efficient Uplink Multi-Connectivity Scheme for 5G mmWave Control Plane Applications
The millimeter wave (mmWave) frequencies offer the potential of orders of
magnitude increases in capacity for next-generation cellular systems. However,
links in mmWave networks are susceptible to blockage and may suffer from rapid
variations in quality. Connectivity to multiple cells - at mmWave and/or
traditional frequencies - is considered essential for robust communication. One
of the challenges in supporting multi-connectivity in mmWaves is the
requirement for the network to track the direction of each link in addition to
its power and timing. To address this challenge, we implement a novel uplink
measurement system that, with the joint help of a local coordinator operating
in the legacy band, guarantees continuous monitoring of the channel propagation
conditions and allows for the design of efficient control plane applications,
including handover, beam tracking and initial access. We show that an
uplink-based multi-connectivity approach enables less consuming, better
performing, faster and more stable cell selection and scheduling decisions with
respect to a traditional downlink-based standalone scheme. Moreover, we argue
that the presented framework guarantees (i) efficient tracking of the user in
the presence of the channel dynamics expected at mmWaves, and (ii) fast
reaction to situations in which the primary propagation path is blocked or not
available.Comment: Submitted for publication in IEEE Transactions on Wireless
Communications (TWC
Integration of Satellites in 5G through LEO Constellations
The standardization of 5G systems is entering in its critical phase, with
3GPP that will publish the PHY standard by June 2017. In order to meet the
demanding 5G requirements both in terms of large throughput and global
connectivity, Satellite Communications provide a valuable resource to extend
and complement terrestrial networks. In this context, we consider a
heterogeneous architecture in which a LEO mega-constellation satellite system
provides backhaul connectivity to terrestrial 5G Relay Nodes, which create an
on-ground 5G network. Since large delays and Doppler shifts related to
satellite channels pose severe challenges to terrestrial-based systems, in this
paper we assess their impact on the future 5G PHY and MAC layer procedures. In
addition, solutions are proposed for Random Access, waveform numerology, and
HARQ procedures.Comment: Submitted to IEEE Global Communications Conference (GLOBECOM) 201
Performance Analysis of Physical Layer Network Coding for Two-way Relaying over Non-regenerative Communication Satellites
Two-way relaying is one of the major applications of broadband communication
satellites, for which an efficient technique is Physical Layer Network Coding
(PLNC). Earlier studies have considered satellites employing PLNC with onboard
processing. This paper investigates the performance of PLNC over
non-regenerative satellites, as a majority of the operational and planned
satellites have no onboard processing. Assuming that the channel magnitudes of
the two users are equal, two operating conditions are considered with
uncoded-QPSK relaying. In the first condition, both users are completely
synchronized in phase and transmit power, and in the second condition, phase is
not synchronized. The peak power constraint imposed by the satellite amplifier
is considered and the error performance bounds are derived for both the
conditions. The simulation results for end-to-end Bit Error Rate (BER) and
throughput are provided. These results shall enable communication system
designers to decide system parameters like power and linearity, and perform
tradeoff analysis between different relaying schemes.Comment: 9 pages and 13 figure
Hybrid Millimeter-Wave Systems: A Novel Paradigm for HetNets
Heterogeneous Networks (HetNets) are known to enhance the bandwidth
efficiency and throughput of wireless networks by more effectively utilizing
the network resources. However, the higher density of users and access points
in HetNets introduces significant inter-user interference that needs to be
mitigated through complex and sophisticated interference cancellation schemes.
Moreover, due to significant channel attenuation and presence of hardware
impairments, e.g., phase noise and amplifier nonlinearities, the vast bandwidth
in the millimeter-wave band has not been fully utilized to date. In order to
enable the development of multi-Gigabit per second wireless networks, we
introduce a novel millimeter-wave HetNet paradigm, termed hybrid HetNet, which
exploits the vast bandwidth and propagation characteristics in the 60 GHz and
70-80 GHz bands to reduce the impact of interference in HetNets. Simulation
results are presented to illustrate the performance advantage of hybrid HetNets
with respect to traditional networks. Next, two specific transceiver structures
that enable hand-offs from the 60 GHz band, i.e., the V-band to the 70-80 GHz
band, i.e., the E-band, and vice versa are proposed. Finally, the practical and
regulatory challenges for establishing a hybrid HetNet are outlined.Comment: 12 pages, 5 Figures, IEEE Communication Magazine. In pres
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