15,711 research outputs found
Multicast Multigroup Precoding and User Scheduling for Frame-Based Satellite Communications
The present work focuses on the forward link of a broadband multibeam
satellite system that aggressively reuses the user link frequency resources.
Two fundamental practical challenges, namely the need to frame multiple users
per transmission and the per-antenna transmit power limitations, are addressed.
To this end, the so-called frame-based precoding problem is optimally solved
using the principles of physical layer multicasting to multiple co-channel
groups under per-antenna constraints. In this context, a novel optimization
problem that aims at maximizing the system sum rate under individual power
constraints is proposed. Added to that, the formulation is further extended to
include availability constraints. As a result, the high gains of the sum rate
optimal design are traded off to satisfy the stringent availability
requirements of satellite systems. Moreover, the throughput maximization with a
granular spectral efficiency versus SINR function, is formulated and solved.
Finally, a multicast-aware user scheduling policy, based on the channel state
information, is developed. Thus, substantial multiuser diversity gains are
gleaned. Numerical results over a realistic simulation environment exhibit as
much as 30% gains over conventional systems, even for 7 users per frame,
without modifying the framing structure of legacy communication standards.Comment: Accepted for publication to the IEEE Transactions on Wireless
Communications, 201
V2X Meets NOMA: Non-Orthogonal Multiple Access for 5G Enabled Vehicular Networks
Benefited from the widely deployed infrastructure, the LTE network has
recently been considered as a promising candidate to support the
vehicle-to-everything (V2X) services. However, with a massive number of devices
accessing the V2X network in the future, the conventional OFDM-based LTE
network faces the congestion issues due to its low efficiency of orthogonal
access, resulting in significant access delay and posing a great challenge
especially to safety-critical applications. The non-orthogonal multiple access
(NOMA) technique has been well recognized as an effective solution for the
future 5G cellular networks to provide broadband communications and massive
connectivity. In this article, we investigate the applicability of NOMA in
supporting cellular V2X services to achieve low latency and high reliability.
Starting with a basic V2X unicast system, a novel NOMA-based scheme is proposed
to tackle the technical hurdles in designing high spectral efficient scheduling
and resource allocation schemes in the ultra dense topology. We then extend it
to a more general V2X broadcasting system. Other NOMA-based extended V2X
applications and some open issues are also discussed.Comment: Accepted by IEEE Wireless Communications Magazin
Dependable Distributed Computing for the International Telecommunication Union Regional Radio Conference RRC06
The International Telecommunication Union (ITU) Regional Radio Conference
(RRC06) established in 2006 a new frequency plan for the introduction of
digital broadcasting in European, African, Arab, CIS countries and Iran. The
preparation of the plan involved complex calculations under short deadline and
required dependable and efficient computing capability. The ITU designed and
deployed in-situ a dedicated PC farm, in parallel to the European Organization
for Nuclear Research (CERN) which provided and supported a system based on the
EGEE Grid. The planning cycle at the RRC06 required a periodic execution in the
order of 200,000 short jobs, using several hundreds of CPU hours, in a period
of less than 12 hours. The nature of the problem required dynamic
workload-balancing and low-latency access to the computing resources. We
present the strategy and key technical choices that delivered a reliable
service to the RRC06
Random Linear Network Coding for 5G Mobile Video Delivery
An exponential increase in mobile video delivery will continue with the
demand for higher resolution, multi-view and large-scale multicast video
services. Novel fifth generation (5G) 3GPP New Radio (NR) standard will bring a
number of new opportunities for optimizing video delivery across both 5G core
and radio access networks. One of the promising approaches for video quality
adaptation, throughput enhancement and erasure protection is the use of
packet-level random linear network coding (RLNC). In this review paper, we
discuss the integration of RLNC into the 5G NR standard, building upon the
ideas and opportunities identified in 4G LTE. We explicitly identify and
discuss in detail novel 5G NR features that provide support for RLNC-based
video delivery in 5G, thus pointing out to the promising avenues for future
research.Comment: Invited paper for Special Issue "Network and Rateless Coding for
Video Streaming" - MDPI Informatio
Frame Based Precoding in Satellite Communications: A Multicast Approach
In the present work, a multibeam satellite that employs aggressive frequency
reuse towards increasing the offered throughput is considered. Focusing on the
forward link, the goal is to employ multi-antenna signal processing techniques,
namely linear precoding, to manage the inter-beam interferences. In this
context, fundamental practical limitations, namely the rigid framing structure
of satellite communication standards and the on-board per-antenna power
constraints, are herein considered. Therefore, the concept of optimal frame
based precoding under per-antenna constraints, is discussed. This consists in
precoding the transmit signals without changing the underlying framing
structure of the communication standard. In the present work, the connection of
the frame based precoding problem with the generic signal processing problem of
conveying independent sets of common data to distinct groups of users is
established. This model is known as physical layer multicasting to multiple
co-channel groups. Building on recent results, the weighted fair per-antenna
power constrained multigroup multicast precoders are employed for frame based
precoding. The throughput performance of these solutions is compared to
multicast aware heuristic precoding methods over a realistic multibeam
satellite scenario. Consequently, the gains of the proposed approach are
quantified via extensive numerical results.Comment: Accepted for presentation at the IEEE ASMS 201
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
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Bandwidth Borrowing Schemes for Instantaneous Video-on-Demand Systems
A controlled multicast scheme provides instantaneous service, but limited server bandwidth causes some user requests to be either delayed or rejected when insufficient free bandwidth is available. Two borrowing schemes are proposed for instantaneous video-on-demand (VOD) that reduce the user request blocking rate by borrowing bandwidth from ongoing video streams when there is insufficient free bandwidth for the server to deliver a new video stream. Both these new schemes have proved to be successful in reducing blocking rate and increasing bandwidth utilization at the expense of temporarily degrading the video quality
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