22,886 research outputs found
Fronthaul-Constrained Cloud Radio Access Networks: Insights and Challenges
As a promising paradigm for fifth generation (5G) wireless communication
systems, cloud radio access networks (C-RANs) have been shown to reduce both
capital and operating expenditures, as well as to provide high spectral
efficiency (SE) and energy efficiency (EE). The fronthaul in such networks,
defined as the transmission link between a baseband unit (BBU) and a remote
radio head (RRH), requires high capacity, but is often constrained. This
article comprehensively surveys recent advances in fronthaul-constrained
C-RANs, including system architectures and key techniques. In particular, key
techniques for alleviating the impact of constrained fronthaul on SE/EE and
quality of service for users, including compression and quantization,
large-scale coordinated processing and clustering, and resource allocation
optimization, are discussed. Open issues in terms of software-defined
networking, network function virtualization, and partial centralization are
also identified.Comment: 5 Figures, accepted by IEEE Wireless Communications. arXiv admin
note: text overlap with arXiv:1407.3855 by other author
Asymptotically-Optimal Incentive-Based En-Route Caching Scheme
Content caching at intermediate nodes is a very effective way to optimize the
operations of Computer networks, so that future requests can be served without
going back to the origin of the content. Several caching techniques have been
proposed since the emergence of the concept, including techniques that require
major changes to the Internet architecture such as Content Centric Networking.
Few of these techniques consider providing caching incentives for the nodes or
quality of service guarantees for content owners. In this work, we present a
low complexity, distributed, and online algorithm for making caching decisions
based on content popularity, while taking into account the aforementioned
issues. Our algorithm performs en-route caching. Therefore, it can be
integrated with the current TCP/IP model. In order to measure the performance
of any online caching algorithm, we define the competitive ratio as the ratio
of the performance of the online algorithm in terms of traffic savings to the
performance of the optimal offline algorithm that has a complete knowledge of
the future. We show that under our settings, no online algorithm can achieve a
better competitive ratio than , where is the number of
nodes in the network. Furthermore, we show that under realistic scenarios, our
algorithm has an asymptotically optimal competitive ratio in terms of the
number of nodes in the network. We also study an extension to the basic
algorithm and show its effectiveness through extensive simulations
Delay Performance of MISO Wireless Communications
Ultra-reliable, low latency communications (URLLC) are currently attracting
significant attention due to the emergence of mission-critical applications and
device-centric communication. URLLC will entail a fundamental paradigm shift
from throughput-oriented system design towards holistic designs for guaranteed
and reliable end-to-end latency. A deep understanding of the delay performance
of wireless networks is essential for efficient URLLC systems. In this paper,
we investigate the network layer performance of multiple-input, single-output
(MISO) systems under statistical delay constraints. We provide closed-form
expressions for MISO diversity-oriented service process and derive
probabilistic delay bounds using tools from stochastic network calculus. In
particular, we analyze transmit beamforming with perfect and imperfect channel
knowledge and compare it with orthogonal space-time codes and antenna
selection. The effect of transmit power, number of antennas, and finite
blocklength channel coding on the delay distribution is also investigated. Our
higher layer performance results reveal key insights of MISO channels and
provide useful guidelines for the design of ultra-reliable communication
systems that can guarantee the stringent URLLC latency requirements.Comment: This work has been submitted to the IEEE for possible publication.
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