588 research outputs found
Joint Spatial Multiplexing and Transmit Diversity in MIMO Ad Hoc Networks
This paper investigates the performance of MIMO ad hoc networks that employ
transmit diversity, as delivered by the Alamouti scheme, and/or spatial
multiplexing, according to the Vertical Bell Labs Layered Space-Time system
(V-BLAST). Both techniques are implemented in a discrete-event network
simulator by focusing on their overall effect on the resulting
signal-to-interference-plus-noise ratio (SINR) at the intended receiver. Unlike
previous works that have studied fully-connected scenarios or have assumed
simple abstractions to represent MIMO behavior, this paper evaluates MIMO ad
hoc networks that are not fully connected by taking into account the effects of
multiple antennas on the clear channel assessment (CCA) mechanism of CSMA-like
medium access control (MAC) protocols. In addition to presenting a performance
evaluation of ad hoc networks operating according to each individual MIMO
scheme, this paper proposes simple modifications to the IEEE 802.11 DCF MAC to
allow the joint operation of both MIMO techniques. Hence, each pair of nodes is
allowed to select the best MIMO configuration for the impending data transfer.
The joint operation is based on three operation modes that are selected based
on the estimated SINR at the intended receiver and its comparision with a set
of threshold values. The performance of ad hoc networks operating with the
joint MIMO scheme is compared with their operation using each individual MIMO
scheme and the standard SISO IEEE 802.11. Performance results are presented
based on MAC-level throughput per node, delay, and fairness under saturated
traffic conditions.Comment: 16 page
A Survey of Millimeter Wave (mmWave) Communications for 5G: Opportunities and Challenges
With the explosive growth of mobile data demand, the fifth generation (5G)
mobile network would exploit the enormous amount of spectrum in the millimeter
wave (mmWave) bands to greatly increase communication capacity. There are
fundamental differences between mmWave communications and existing other
communication systems, in terms of high propagation loss, directivity, and
sensitivity to blockage. These characteristics of mmWave communications pose
several challenges to fully exploit the potential of mmWave communications,
including integrated circuits and system design, interference management,
spatial reuse, anti-blockage, and dynamics control. To address these
challenges, we carry out a survey of existing solutions and standards, and
propose design guidelines in architectures and protocols for mmWave
communications. We also discuss the potential applications of mmWave
communications in the 5G network, including the small cell access, the cellular
access, and the wireless backhaul. Finally, we discuss relevant open research
issues including the new physical layer technology, software-defined network
architecture, measurements of network state information, efficient control
mechanisms, and heterogeneous networking, which should be further investigated
to facilitate the deployment of mmWave communication systems in the future 5G
networks.Comment: 17 pages, 8 figures, 7 tables, Journal pape
Density-aware Dynamic Mobile Networks: Opportunities and Challenges
We experience a major paradigm change in mobile networks. The infrastructure
of cellular networks becomes mobile as it is densified by using mobile and
nomadic small cells to increase coverage and capacity. Furthermore, the
innovative approaches such as green operation through sleep scheduling,
user-controlled small cells, and end-to-end slicing will make the network
highly dynamic. Mobile cells, while bringing many benefits, introduce many
unconventional challenges that we present in this paper. We have to introduce
novel techniques for adapting network functions, communication protocols and
their parameters to network density. Especially when cells on wheels or wings
are considered, static and man-made configurations will waste valuable
resources such as spectrum or energy if density is not considered as an
optimization parameter. In this paper, we present the existing density
estimators. We analyze the impact of density on coverage, interference,
mobility management, scalability, capacity, caching, routing protocols and
energy consumption. We evaluate nomadic cells in dynamic networks in a
comprehensive way and illustrate the potential objectives we can achieve by
adapting mobile networks to base station density. The main challenges we may
face by employing dynamic networks and how we can tackle these problems are
discussed in detail
Towards 1 Gbps/UE in Cellular Systems: Understanding Ultra-Dense Small Cell Deployments
Todays heterogeneous networks comprised of mostly macrocells and indoor small
cells will not be able to meet the upcoming traffic demands. Indeed, it is
forecasted that at least a 100x network capacity increase will be required to
meet the traffic demands in 2020. As a result, vendors and operators are now
looking at using every tool at hand to improve network capacity. In this epic
campaign, three paradigms are noteworthy, i.e., network densification, the use
of higher frequency bands and spectral efficiency enhancement techniques. This
paper aims at bringing further common understanding and analysing the potential
gains and limitations of these three paradigms, together with the impact of
idle mode capabilities at the small cells as well as the user equipment density
and distribution in outdoor scenarios. Special attention is paid to network
densification and its implications when transitioning to ultra-dense small cell
deployments. Simulation results show that network densification with an average
inter site distance of 35 m can increase the cell- edge UE throughput by up to
48x, while the use of the 10GHz band with a 500MHz bandwidth can increase the
network capacity up to 5x. The use of beamforming with up to 4 antennas per
small cell base station lacks behind with cell-edge throughput gains of up to
1.49x. Our study also shows how network densifications reduces multi-user
diversity, and thus proportional fair alike schedulers start losing their
advantages with respect to round robin ones. The energy efficiency of these
ultra-dense small cell deployments is also analysed, indicating the need for
energy harvesting approaches to make these deployments energy- efficient.
Finally, the top ten challenges to be addressed to bring ultra-dense small cell
deployments to reality are also discussed
Transmission Capacity of Ad Hoc Networks with Spatial Diversity
This paper derives the outage probability and transmission capacity of ad hoc
wireless networks with nodes employing multiple antenna diversity techniques,
for a general class of signal distributions. This analysis allows system
performance to be quantified for fading or non-fading environments. The
transmission capacity is given for interference-limited uniformly random
networks on the entire plane with path loss exponent in which nodes
use: (1) static beamforming through sectorized antennas, for which the
increase in transmission capacity is shown to be if the antennas
are without sidelobes, but less in the event of a nonzero sidelobe level; (2)
dynamic eigen-beamforming (maximal ratio transmission/combining), in which the
increase is shown to be ; (3) various transmit
antenna selection and receive antenna selection combining schemes, which give
appreciable but rapidly diminishing gains; and (4) orthogonal space-time block
coding, for which there is only a small gain due to channel hardening,
equivalent to Nakagami- fading for increasing . It is concluded that in
ad hoc networks, static and dynamic beamforming perform best, selection
combining performs well but with rapidly diminishing returns with added
antennas, and that space-time block coding offers only marginal gains.Comment: 16 pages, 10 figures, to appear in IEEE Transactions on Wireless
Communication
On the Design of MAC Protocols for Multi-Packet Communication in IEEE 802.11 Heterogeneous Networks Using Adaptive Antenna Arrays
This paper discusses the design requirements for enabling multiple simultaneous peer-to-peer communications in IEEE 802.11 asynchronous networks in the presence of adaptive antenna arrays, and proposes two novel access schemes to realize multipacket communication (MPC). Both presented solutions, which rely on the information acquired by each node during the monitoring of the network activity, are suitable for distributed and heterogeneous scenarios, where nodes equipped with different antenna systems can coexist. The first designed scheme, called threshold access MPC (TAMPC), is based on a threshold on the load sustainable by the single-node, while the second protocol, called signal-to-interference ratio (SIR) access MPC (SAMPC), is based on an accurate estimation of the SIR and on the adoption of low density parity check codes. Both protocols, which are designed to be backward compatible with the 802.11 standard, are numerically tested in realistic scenarios. Furthermore, the performance of the two schemes is compared to the theoretical one and to that of the 802.11n extension in a mobile environment
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
MAC Protocols for Wireless Mesh Networks with Multi-beam Antennas: A Survey
Multi-beam antenna technologies have provided lots of promising solutions to
many current challenges faced in wireless mesh networks. The antenna can
establish several beamformings simultaneously and initiate concurrent
transmissions or receptions using multiple beams, thereby increasing the
overall throughput of the network transmission. Multi-beam antenna has the
ability to increase the spatial reuse, extend the transmission range, improve
the transmission reliability, as well as save the power consumption.
Traditional Medium Access Control (MAC) protocols for wireless network largely
relied on the IEEE 802.11 Distributed Coordination Function(DCF) mechanism,
however, IEEE 802.11 DCF cannot take the advantages of these unique
capabilities provided by multi-beam antennas. This paper surveys the MAC
protocols for wireless mesh networks with multi-beam antennas. The paper first
discusses some basic information in designing multi-beam antenna system and MAC
protocols, and then presents the main challenges for the MAC protocols in
wireless mesh networks compared with the traditional MAC protocols. A
qualitative comparison of the existing MAC protocols is provided to highlight
their novel features, which provides a reference for designing the new MAC
protocols. To provide some insights on future research, several open issues of
MAC protocols are discussed for wireless mesh networks using multi-beam
antennas.Comment: 22 pages, 6 figures, Future of Information and Communication
Conference (FICC) 2019, https://doi.org/10.1007/978-3-030-12388-8_
Unified Stochastic Geometry Model for MIMO Cellular Networks with Retransmissions
This paper presents a unified mathematical paradigm, based on stochastic
geometry, for downlink cellular networks with multiple-input-multiple-output
(MIMO) base stations (BSs). The developed paradigm accounts for signal
retransmission upon decoding errors, in which the temporal correlation among
the signal-to-interference plus-noise-ratio (SINR) of the original and
retransmitted signals is captured. In addition to modeling the effect of
retransmission on the network performance, the developed mathematical model
presents twofold analysis unification for MIMO cellular networks literature.
First, it integrates the tangible decoding error probability and the abstracted
(i.e., modulation scheme and receiver type agnostic) outage probability
analysis, which are largely disjoint in the literature. Second, it unifies the
analysis for different MIMO configurations. The unified MIMO analysis is
achieved by abstracting unnecessary information conveyed within the interfering
signals by Gaussian signaling approximation along with an equivalent SISO
representation for the per-data stream SINR in MIMO cellular networks. We show
that the proposed unification simplifies the analysis without sacrificing the
model accuracy. To this end, we discuss the diversity-multiplexing tradeoff
imposed by different MIMO schemes and shed light on the diversity loss due to
the temporal correlation among the SINRs of the original and retransmitted
signals. Finally, several design insights are highlighted
Hybrid Satellite-Terrestrial Communication Networks for the Maritime Internet of Things: Key Technologies, Opportunities, and Challenges
With the rapid development of marine activities, there has been an increasing
number of maritime mobile terminals, as well as a growing demand for high-speed
and ultra-reliable maritime communications to keep them connected.
Traditionally, the maritime Internet of Things (IoT) is enabled by maritime
satellites. However, satellites are seriously restricted by their high latency
and relatively low data rate. As an alternative, shore & island-based base
stations (BSs) can be built to extend the coverage of terrestrial networks
using fourth-generation (4G), fifth-generation (5G), and beyond 5G services.
Unmanned aerial vehicles can also be exploited to serve as aerial maritime BSs.
Despite of all these approaches, there are still open issues for an efficient
maritime communication network (MCN). For example, due to the complicated
electromagnetic propagation environment, the limited geometrically available BS
sites, and rigorous service demands from mission-critical applications,
conventional communication and networking theories and methods should be
tailored for maritime scenarios. Towards this end, we provide a survey on the
demand for maritime communications, the state-of-the-art MCNs, and key
technologies for enhancing transmission efficiency, extending network coverage,
and provisioning maritime-specific services. Future challenges in developing an
environment-aware, service-driven, and integrated satellite-air-ground MCN to
be smart enough to utilize external auxiliary information, e.g., sea state and
atmosphere conditions, are also discussed
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