130 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
Fast Cell Discovery in mm-wave 5G Networks with Context Information
The exploitation of mm-wave bands is one of the key-enabler for 5G mobile
radio networks. However, the introduction of mm-wave technologies in cellular
networks is not straightforward due to harsh propagation conditions that limit
the mm-wave access availability. Mm-wave technologies require high-gain antenna
systems to compensate for high path loss and limited power. As a consequence,
directional transmissions must be used for cell discovery and synchronization
processes: this can lead to a non-negligible access delay caused by the
exploration of the cell area with multiple transmissions along different
directions.
The integration of mm-wave technologies and conventional wireless access
networks with the objective of speeding up the cell search process requires new
5G network architectural solutions. Such architectures introduce a functional
split between C-plane and U-plane, thereby guaranteeing the availability of a
reliable signaling channel through conventional wireless technologies that
provides the opportunity to collect useful context information from the network
edge.
In this article, we leverage the context information related to user
positions to improve the directional cell discovery process. We investigate
fundamental trade-offs of this process and the effects of the context
information accuracy on the overall system performance. We also cope with
obstacle obstructions in the cell area and propose an approach based on a
geo-located context database where information gathered over time is stored to
guide future searches. Analytic models and numerical results are provided to
validate proposed strategies.Comment: 14 pages, submitted to IEEE Transaction on Mobile Computin
Improving the Performance of Medium Access Control Protocols for Mobile Adhoc Network with Smart Antennas
Requirements for high quality links and great demand for high throughput in Wireless
LAN especially Mobile Ad-hoc Network has motivated new enhancements and work in
Wireless communications such as Smart Antenna Systems. Smart (adaptive) Antennas
enable spatial reuse, increase throughput and they increase the communication range
because of the increase directivity of the antenna array. These enhancements quantified
for the physical layer may not be efficiently utilized, unless the Media Access Control
(MAC) layer is designed accordingly.
This thesis implements the behaviours of two MAC protocols, ANMAC and MMAC
protocols in OPNET simulator. This method is known as the Physical-MAC layer
simulation model. The entire physical layer is written in MATLAB, and MATLAB is
integrated into OPNET to perform the necessary stochastic physical layer simulations.
The aim is to investigate the performance improvement in throughput and delay of the
selected MAC Protocols when using Smart Antennas in a mobile environment. Analytical
methods were used to analyze the average throughput and delay performance of the
selected MAC Protocols with Adaptive Antenna Arrays in MANET when using spatial
diversity. Comparison study has been done between the MAC protocols when using
Switched beam antenna and when using the proposed scheme.
It has been concluded that the throughput and delay performance of the selected protocols
have been improved by the use of Adaptive Antenna Arrays. The throughput and delay
performance of ANMAC-SW and ANMAC-AA protocols was evaluated in details
against regular Omni 802.11 stations. Our results promise significantly enhancement over
Omni 802.11, with a throughput of 25% for ANMAC-SW and 90% for ANMC-AA.
ANMAC-AA outperforms ANMAC-SW protocol by 60%. Simulation experiments
indicate that by using the proposed scheme with 4 Adaptive Antenna Array per a node,
the average throughput in the network can be improved up to 2 to 2.5 times over that
obtained by using Switched beam Antennas. The proposed scheme improves the
performances of both ANMAC and MMAC protocols but ANMAC outperforms MMAC
by 30%
A survey on wireless ad hoc networks
A wireless ad hoc network is a collection of wireless nodes that can dynamically self-organize into an arbitrary and temporary topology to form a network without necessarily using any pre-existing infrastructure. These characteristics make ad hoc networks well suited for military activities, emergency operations, and disaster recoveries.
Nevertheless, as electronic devices are getting smaller, cheaper, and more powerful, the mobile market is rapidly growing and, as a consequence, the need of seamlessly internetworking people and devices becomes mandatory. New wireless technologies enable easy deployment of commercial applications for ad hoc networks. The design of an ad hoc network has to take into account several interesting and difficult problems due to noisy, limited-range, and insecure wireless transmissions added to mobility and energy constraints. This paper presents an overview of issues related to medium access control (MAC), routing, and transport in wireless ad hoc networks and techniques proposed to improve the performance of protocols. Research activities and problems requiring further work are also presented. Finally, the paper presents a project concerning an ad hoc network to easily deploy Internet services on low-income habitations fostering digital inclusion8th IFIP/IEEE International conference on Mobile and Wireless CommunicationRed de Universidades con Carreras en Informática (RedUNCI
Exploiting Device-to-Device Communications to Enhance Spatial Reuse for Popular Content Downloading in Directional mmWave Small Cells
With the explosive growth of mobile demand, small cells in millimeter wave
(mmWave) bands underlying the macrocell networks have attracted intense
interest from both academia and industry. MmWave communications in the 60 GHz
band are able to utilize the huge unlicensed bandwidth to provide multiple Gbps
transmission rates. In this case, device-to-device (D2D) communications in
mmWave bands should be fully exploited due to no interference with the
macrocell networks and higher achievable transmission rates. In addition, due
to less interference by directional transmission, multiple links including D2D
links can be scheduled for concurrent transmissions (spatial reuse). With the
popularity of content-based mobile applications, popular content downloading in
the small cells needs to be optimized to improve network performance and
enhance user experience. In this paper, we develop an efficient scheduling
scheme for popular content downloading in mmWave small cells, termed PCDS
(popular content downloading scheduling), where both D2D communications in
close proximity and concurrent transmissions are exploited to improve
transmission efficiency. In PCDS, a transmission path selection algorithm is
designed to establish multi-hop transmission paths for users, aiming at better
utilization of D2D communications and concurrent transmissions. After
transmission path selection, a concurrent transmission scheduling algorithm is
designed to maximize the spatial reuse gain. Through extensive simulations
under various traffic patterns, we demonstrate PCDS achieves near-optimal
performance in terms of delay and throughput, and also superior performance
compared with other existing protocols, especially under heavy load.Comment: 12 pages, to appear in IEEE Transactions on Vehicular Technolog
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