277 research outputs found
Torii-HLMAC: A distributed, fault-tolerant, zero configuration fat tree data center architecture with multiple tree-based addressing and forwarding
Proceedings of: IEEE Global Communications Conference (GLOBECOM 2012). Anaheim, California, USA. December 03-07, 2012.This paper describes Torii-HLMAC, a scalable, fault-tolerant, zero-configuration data center network fabric architecture protocol as a fully distributed alternative to PortLand for similar multiple tree network topologies. It uses multiple, fixed, tree-based positional MAC addresses for multiple path and table-free forwarding. Addresses are assigned by a simple extension of the Rapid Spanning Tree Protocol. Torii-HLMAC enhances the PortLand protocol advantages of scalability, zero configuration and high performance and adds instant path recovery, fully distributed routing and address assignment. ARP Proxy may be used to avoid ARP broadcast messages.This work was supported in part by grants from Comunidad de Madrid and Comunidad de Castilla la Mancha through Projects MEDIANET-CM (S-2009/TIC-1468) and EMARECE (PII1I09-0204-4319).Publicad
Energy Efficient Relay-Assisted Cellular Network Model using Base Station Switching
Cellular network planning strategies have tended to focus on peak traffic scenarios rather than energy efficiency. By exploiting the dynamic nature of traffic load profiles, the prospect for greener communications in cellular access networks is evolving. For example, powering down base stations (BS) and applying cell zooming can significantly reduce energy consumption, with the overriding design priority still being to uphold a minimum quality of service (QoS). Switching off cells completely can lead to both coverage holes and performance degradation in terms of increased outage probability, greater transmit power dissipation in the up and downlinks, and complex interference management, even at low traffic loads. In this paper, a cellular network model is presented where certain BS rather than being turned off, are switched to low-powered relay stations (RS) during zero-to-medium traffic periods. Neighbouring BS still retain all the baseband signal processing and transmit signals to corresponding RS via backhaul connections, under the assumption that the RS covers the whole cell. Experimental results demonstrate the efficacy of this new BS-RS Switching technique from both an energy saving and QoS perspective, in the up and downlinks
On the Performance of Millimeter Wave-based RF-FSO Links with HARQ Feedback
This paper studies the performance of hybrid radio-frequency (RF) and
free-space optical (FSO) links in the cases with and without hybrid automatic
repeat request (HARQ). Considering millimeter wave (mmwave) characteristics in
the RF link and pointing errors in the FSO link, we derive closed-form
expressions for the message decoding probabilities as well as the throughput
and the outage probability of the RF-FSO setups. We also evaluate the effect of
various parameters such as power amplifiers efficiency, different transmission
techniques in the FSO link, pointing errors in the FSO link as well as
different coherence times/symbol rates of the RF and the FSO links on the
throughput and outage probability. The results show the efficiency of the
RF-FSO links in different conditions. Moreover, the HARQ can effectively
improve the outage probability/energy efficiency, and compensate the effect of
hardware impairments in RF-FSO links.Comment: Under review in PIMRC'201
Spectral Efficiency and Energy Efficiency of OFDM Systems: Impact of Power Amplifiers and Countermeasures
In wireless communication systems, the nonlinear effect and inefficiency of
power amplifier (PA) have posed practical challenges for system designs to
achieve high spectral efficiency (SE) and energy efficiency (EE). In this
paper, we analyze the impact of PA on the SE-EE tradeoff of orthogonal
frequency division multiplex (OFDM) systems. An ideal PA that is always linear
and incurs no additional power consumption can be shown to yield a decreasing
convex function in the SE-EE tradeoff. In contrast, we show that a practical PA
has an SE-EE tradeoff that has a turning point and decreases sharply after its
maximum EE point. In other words, the Pareto-optimal tradeoff boundary of the
SE-EE curve is very narrow. A wide range of SE-EE tradeoff, however, is desired
for future wireless communications that have dynamic demand depending on the
traffic loads, channel conditions, and system applications, e.g.,
high-SE-with-low-EE for rate-limited systems and high-EE-with-low-SE for
energy-limited systems. For the SE-EE tradeoff improvement, we propose a PA
switching (PAS) technique. In a PAS transmitter, one or more PAs are switched
on intermittently to maximize the EE and deliver an overall required SE. As a
consequence, a high EE over a wide range SE can be achieved, which is verified
by numerical evaluations: with 15% SE reduction for low SE demand, the PAS
between a low power PA and a high power PA can improve EE by 323%, while a
single high power PA transmitter improves EE by only 68%.Comment: to be published, IEEE J. Sel. Areas Commu
Delay Reduction in Multi-Hop Device-to-Device Communication using Network Coding
This paper considers the problem of reducing the broadcast decoding delay of
wireless networks using instantly decodable network coding (IDNC) based
device-to-device (D2D) communications. In a D2D configuration, devices in the
network can help hasten the recovery of the lost packets of other devices in
their transmission range by sending network coded packets. Unlike previous
works that assumed fully connected network, this paper proposes a partially
connected configuration in which the decision should be made not only on the
packet combinations but also on the set of transmitting devices. First, the
different events occurring at each device are identified so as to derive an
expression for the probability distribution of the decoding delay. The joint
optimization problem over the set of transmitting devices and the packet
combinations of each is, then, formulated. The optimal solution of the joint
optimization problem is derived using a graph theory approach by introducing
the cooperation graph and reformulating the problem as a maximum weight clique
problem in which the weight of each vertex is the contribution of the device
identified by the vertex. Through extensive simulations, the decoding delay
experienced by all devices in the Point to Multi-Point (PMP) configuration, the
fully connected D2D (FC-D2D) configuration and the more practical partially
connected D2D (PC-D2D) configuration are compared. Numerical results suggest
that the PC-D2D outperforms the FC-D2D and provides appreciable gain especially
for poorly connected networks
Solar energy for self-contained power supply
Solar energy relevance in self-contained utility system as well as economic feasibility for each class of consumers considered. The article will outline utilising features of self-contained photovoltaic stations in Middle East and Northern Africa
On the Performance of Millimeter Wave-based RF-FSO Multi-hop and Mesh Networks
This paper studies the performance of multi-hop and mesh networks composed of
millimeter wave (MMW)-based radio frequency (RF) and free-space optical (FSO)
links. The results are obtained in cases with and without hybrid automatic
repeat request (HARQ). Taking the MMW characteristics of the RF links into
account, we derive closed-form expressions for the networks' outage probability
and ergodic achievable rates. We also evaluate the effect of various parameters
such as power amplifiers efficiency, number of antennas as well as different
coherence times of the RF and the FSO links on the system performance. Finally,
we determine the minimum number of the transmit antennas in the RF link such
that the same rate is supported in the RF- and the FSO-based hops. The results
show the efficiency of the RF-FSO setups in different conditions. Moreover,
HARQ can effectively improve the outage probability/energy efficiency, and
compensate for the effect of hardware impairments in RF-FSO networks. For
common parameter settings of the RF-FSO dual-hop networks, outage probability
of 10^{-4} and code rate of 3 nats-per-channel-use, the implementation of HARQ
with a maximum of 2 and 3 retransmissions reduces the required power, compared
to cases with open-loop communication, by 13 and 17 dB, respectively.Comment: Submitted to IEEE Transactions on Wireless Communication
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