125 research outputs found
Network-Assisted Device-to-Device (D2D) Direct Proximity Discovery with Underlay Communication
Device-to-Device communications are expected to play an important role in
current and future cellular generations, by increasing the spatial reuse of
spectrum resources and enabling lower latency communication links. This
paradigm has two fundamental building blocks: (i) proximity discovery and (ii)
direct communication between proximate devices. While (ii) is treated
extensively in the recent literature, (i) has received relatively little
attention. In this paper we analyze a network-assisted underlay proximity
discovery protocol, where a cellular device can take the role of: announcer
(which announces its interest in establishing a D2D connection) or monitor
(which listens for the transmissions from the announcers). Traditionally, the
announcers transmit their messages over dedicated channel resources. In
contrast, inspired by recent advances on receivers with multiuser decoding
capabilities, we consider the case where the announcers underlay their messages
in the downlink transmissions that are directed towards the monitoring devices.
We propose a power control scheme applied to the downlink transmission, which
copes with the underlay transmission via additional power expenditure, while
guaranteeing both reliable downlink transmissions and underlay proximity
discovery.Comment: Accepted for presentation at Globecom 201
Zero-Outage Cellular Downlink with Fixed-Rate D2D Underlay
Two of the emerging trends in wireless cellular systems are Device-to-Device
(D2D) and Machine-to-Machine (M2M) communications. D2D enables efficient reuse
of the licensed spectrum to support localized transmissions, while M2M
connections are often characterized by fixed and low transmission rates. D2D
connections can be instrumental in localized aggregation of uplink M2M traffic
to a more capable cellular device, before being finally delivered to the Base
Station (BS). In this paper we show that a fixed M2M rate is an enabler of
efficient Machine-Type D2D underlay operation taking place simultaneously with
another \emph{downlink} cellular transmission. In the considered scenario, a BS
transmits to a user , while there are Machine-Type Devices (MTDs)
attached to , all sending simultaneously to and each using the same rate
. While assuming that knows the channel , but not the interfering
channels from the MTDs to , we prove that there is a positive downlink rate
that can always be decoded by , leading to zero-outage of the downlink
signal. This is a rather surprising consequence of the features of the multiple
access channel and the fixed rate . We also consider the case of a
simpler, single-user decoder at with successive interference cancellation.
However, with single-user decoder, a positive zero-outage rate exists only when
and is zero when . This implies that joint decoding is
instrumental in enabling fixed-rate underlay operation.Comment: Revised versio
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
Massive M2M Access with Reliability Guarantees in LTE Systems
Machine-to-Machine (M2M) communications are one of the major drivers of the
cellular network evolution towards 5G systems. One of the key challenges is on
how to provide reliability guarantees to each accessing device in a situation
in which there is a massive number of almost-simultaneous arrivals from a large
set of M2M devices. The existing solutions take a reactive approach in dealing
with massive arrivals, such as non-selective barring when a massive arrival
event occurs, which implies that the devices cannot get individual reliability
guarantees. In this paper we propose a proactive approach, based on a standard
operation of the cellular access. The access procedure is divided into two
phases, an estimation phase and a serving phase. In the estimation phase the
number of arrivals is estimated and this information is used to tune the amount
of resources allocated in the serving phase. Our results show that the
proactive approach is instrumental in delivering high access reliability to the
M2M devices.Comment: Accepted for presentation in ICC 201
Random Access for Machine-Type Communication based on Bloom Filtering
We present a random access method inspired on Bloom filters that is suited
for Machine-Type Communications (MTC). Each accessing device sends a
\emph{signature} during the contention process. A signature is constructed
using the Bloom filtering method and contains information on the device
identity and the connection establishment cause. We instantiate the proposed
method over the current LTE-A access protocol. However, the method is
applicable to a more general class of random access protocols that use
preambles or other reservation sequences, as expected to be the case in 5G
systems. We show that our method utilizes the system resources more efficiently
and achieves significantly lower connection establishment latency in case of
synchronous arrivals, compared to the variant of the LTE-A access protocol that
is optimized for MTC traffic. A dividend of the proposed method is that it
allows the base station (BS) to acquire the device identity and the connection
establishment cause already in the initial phase of the connection
establishment, thereby enabling their differentiated treatment by the BS.Comment: Accepted for presentation on IEEE Globecom 201
A Tractable Model of the LTE Access Reservation Procedure for Machine-Type Communications
A canonical scenario in Machine-Type Communications (MTC) is the one
featuring a large number of devices, each of them with sporadic traffic. Hence,
the number of served devices in a single LTE cell is not determined by the
available aggregate rate, but rather by the limitations of the LTE access
reservation protocol. Specifically, the limited number of contention preambles
and the limited amount of uplink grants per random access response are crucial
to consider when dimensioning LTE networks for MTC. We propose a low-complexity
model of LTE's access reservation protocol that encompasses these two
limitations and allows us to evaluate the outage probability at click-speed.
The model is based chiefly on closed-form expressions, except for the part with
the feedback impact of retransmissions, which is determined by solving a fixed
point equation. Our model overcomes the incompleteness of the existing models
that are focusing solely on the preamble collisions. A comparison with the
simulated LTE access reservation procedure that follows the 3GPP
specifications, confirms that our model provides an accurate estimation of the
system outage event and the number of supported MTC devices.Comment: Submitted, Revised, to be presented in IEEE Globecom 2015; v3: fixed
error in eq. (4
Closed-Form Derivations of ISI and MUI for Time-Reversed Ultra Wideband
Through transmitter pre-filtering, a time reversed UWB system is capable if harnessing a multipath channel to achieve temporal and spatial focusing. Unfortunately, large RMS channel delay spread leads to significant intersymbol and multiuser interference. This paper presents closed-form expressions for self and multi-user interference for a UWB system utilizing a time-reversed approach. The influence of user multiplexing codes is taken to account through incorporation of a ‘separation probability’, which characterizes a family of hopping sequences. The standardized IEEE 802.15.3a channel model is applied, and the derived performances are compared with that of a simulated time hopped time-reversed UWB system
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