483 research outputs found
A Traffic Model for Machine-Type Communications Using Spatial Point Processes
A source traffic model for machine-to-machine communications is presented in
this paper. We consider a model in which devices operate in a regular mode
until they are triggered into an alarm mode by an alarm event. The positions of
devices and events are modeled by means of Poisson point processes, where the
generated traffic by a given device depends on its position and event
positions. We first consider the case where devices and events are static and
devices generate traffic according to a Bernoulli process, where we derive the
total rate from the devices at the base station. We then extend the model by
defining a two-state Markov chain for each device, which allows for devices to
stay in alarm mode for a geometrically distributed holding time. The temporal
characteristics of this model are analyzed via the autocovariance function,
where the effect of event density and mean holding time are shown.Comment: Accepted at the 2017 IEEE 28th Annual International Symposium on
Personal, Indoor, and Mobile Radio Communications (PIMRC) - Workshop WS-07 on
"The Internet of Things (IoT), the Road Ahead: Applications, Challenges, and
Solutions
Code-Expanded Random Access for Machine-Type Communications
The random access methods used for support of machine-type communications
(MTC) in current cellular standards are derivatives of traditional framed
slotted ALOHA and therefore do not support high user loads efficiently.
Motivated by the random access method employed in LTE, we propose a novel
approach that is able to sustain a wide random access load range, while
preserving the physical layer unchanged and incurring minor changes in the
medium access control layer. The proposed scheme increases the amount of
available contention resources, without resorting to the increase of system
resources, such as contention sub-frames and preambles. This increase is
accomplished by expanding the contention space to the code domain, through the
creation of random access codewords. Specifically, in the proposed scheme,
users perform random access by transmitting one or none of the available LTE
orthogonal preambles in multiple random access sub-frames, thus creating access
codewords that are used for contention. In this way, for the same number of
random access sub-frames and orthogonal preambles, the amount of available
contention resources is drastically increased, enabling the support of an
increased number of MTC users. We present the framework and analysis of the
proposed code-expanded random access method and show that our approach supports
load regions that are beyond the reach of current systems.Comment: 6 Pages, 7 figures, This paper has been submitted to GC'12 Workshop:
Second International Workshop on Machine-to-Machine Communications 'Key' to
the Future Internet of Thing
On a User-Centric Base Station Cooperation Scheme for Reliable Communications
In this paper, we describe CoMP2flex, a user-centric base station (BS)
cooperation scheme that provides improvements in reliability of both uplink
(UL) and downlink (DL) communications of wireless cellular networks. CoMP2flex
supports not only cooperation of two BSs with same direction of traffic but
also cooperation of two BSs serving bidirectional traffic. The reliability
performance of CoMP2flex is shown with numerical simulations and analytical
expressions. We quantify and numerically validate the performance of the greedy
BS pairing algorithm by comparing maximum weight matching methods, implemented
as the Edmonds matching algorithm for weighted graphs.Comment: to be presented in IEEE VTC 2017 Sprin
Ribosome specificity of archaebacterial elongation factor 2 Studies with hybrid polyphenylalanine synthesis systems
AbstractPolyphenylalanine synthesis with ribosomes and two separated, partially purified elongation factors (EF) was measured in cell-free systems from the archaebacteria Thermoplasma acidophilum and Methanococcus vannielii, in an eukaryotic system from rat liver and an eubacterial one with Escherichia coli ribosomes and factors from Thermus thermophilus. By substitution of heterologous EF-2 or EF-G, respectively, for the homologous factors, ribosome specificity was shown to be restricted to factors from the same kingdom. In contrast EF-1 from T. thermophilus significantly cooperated with ribosomes from T. acidophilum
CoMPflex: CoMP for In-Band Wireless Full Duplex
In this letter we consider emulation of a Full Duplex (FD) cellular base
station (BS) by using two spatially separated and coordinated half duplex (HD)
BSs. The proposed system is termed CoMPflex (CoMP for In-Band Wireless Full
Duplex) and at a given instant it serves two HD mobile stations (MSs), one in
the uplink and one in the downlink, respectively. We evaluate the performance
of our scheme by using a geometric extension of the one-dimensional Wyner
model, which takes into account the distances between the devices. The results
show that CoMPflex leads to gains in terms of sum-rate and energy efficiency
with respect to the ordinary FD, as well as with respect to a baseline scheme
based on unidirectional traffic.Comment: 4 pages, 4 figure
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