348 research outputs found
Linear Finite-Field Deterministic Networks With Many Sources and One Destination
We find the capacity region of linear finite-field deterministic networks
with many sources and one destination. Nodes in the network are subject to
interference and broadcast constraints, specified by the linear finite-field
deterministic model. Each node can inject its own information as well as relay
other nodes' information. We show that the capacity region coincides with the
cut-set region. Also, for a specific case of correlated sources we provide
necessary and sufficient conditions for the sources transmissibility. Given the
"deterministic model" approximation for the corresponding Gaussian network
model, our results may be relevant to wireless sensor networks where the
sensing nodes multiplex the relayed data from the other nodes with their own
data, and where the goal is to decode all data at a single "collector" node.Comment: 5 pages, 3 figures, submitted to ISIT 201
Caching and Coded Multicasting: Multiple Groupcast Index Coding
The capacity of caching networks has received considerable attention in the
past few years. A particularly studied setting is the case of a single server
(e.g., a base station) and multiple users, each of which caches segments of
files in a finite library. Each user requests one (whole) file in the library
and the server sends a common coded multicast message to satisfy all users at
once. The problem consists of finding the smallest possible codeword length to
satisfy such requests. In this paper we consider the generalization to the case
where each user places requests. The obvious naive scheme consists
of applying times the order-optimal scheme for a single request, obtaining
a linear in scaling of the multicast codeword length. We propose a new
achievable scheme based on multiple groupcast index coding that achieves a
significant gain over the naive scheme. Furthermore, through an information
theoretic converse we find that the proposed scheme is approximately optimal
within a constant factor of (at most) .Comment: 5 pages, 1 figure, to appear in GlobalSIP14, Dec. 201
The academic and industrial embrace of space-time methods
[Guest Editors introduction to: Special issue on space-time transmission, reception, coding and signal processing]
Every episode of the classic 1966–1969 television series Star Trek begins with Captain Kirk’s (played by William Shatner) famous words : “Space: The final frontier….” While space may not be the final frontier for the information and communication theory community, it is proving to be an important and fruitful one.
In the information theory community, the notion of space can be broadly defined as the simultaneous use of multiple, possibly coupled, channels. The notions of space–time and multiple-input multiple-output (MIMO) channels are therefore often used interchangeably. The connection between space and MIMO is most transparent when we view the multiple channels as created by two or more spatially separated antennas at a wireless transmitter or receiver.
A large component of the current interest in space–time methods can be attributed to discoveries in the late 1980s and early 1990s that a rich wireless scattering environment can be beneficial when multiple antennas are used on a point-to-point link. We now know that adding antennas in a rich environment provides proportional increases in point-to-point data rates, without extra transmitted power or bandwidth
Closed-form performance analysis of linear MIMO receivers in general fading scenarios
Linear precoding and post-processing schemes are ubiquitous in wireless
multi-input-multi-output (MIMO) settings, due to their reduced complexity with
respect to optimal strategies. Despite their popularity, the performance
analysis of linear MIMO receivers is mostly not available in closed form, apart
for the canonical (uncorrelated Rayleigh fading) case, while for more general
fading conditions only bounds are provided. This lack of results is motivated
by the complex dependence of the output signal-to-interference and noise ratio
(SINR) at each branch of the receiving filter on both the squared singular
values as well as the (typically right) singular vectors of the channel matrix.
While the explicit knowledge of the statistics of the SINR can be circumvented
for some fading types in the analysis of the linear Minimum Mean-Squared Error
(MMSE) receiver, this does not apply to the less complex and widely adopted
Zero-Forcing (ZF) scheme. This work provides the first-to-date closed-form
expression of the probability density function (pdf) of the output ZF and MMSE
SINR, for a wide range of fading laws, encompassing, in particular,
correlations and multiple scattering effects typical of practically relevant
channel models.Comment: 16 pages, 2 figures, contents submitted to IEEE/VDE WSA 201
On the Effectiveness of OTFS for Joint Radar Parameter Estimation and Communication
We consider a joint radar parameter estimation and communication system using orthogonal time frequency space (OTFS) modulation. The scenario is motivated by vehicular applications where a vehicle (or the infrastructure) equipped with a mono-static radar wishes to communicate data to its target receiver, while estimating parameters of interest related to this receiver. Provided that the radar-equipped transmitter is ready to send data to its target receiver, this setting naturally assumes that the receiver has been already detected. In a point-to-point communication setting over multipath time-frequency selective channels, we study the joint radar and communication system from two perspectives, i.e., the radar parameter estimation at the transmitter as well as the data detection at the receiver. For the radar parameter estimation part, we derive an efficient approximated Maximum Likelihood algorithm and the corresponding Cramér-Rao lower bound for range and velocity estimation. Numerical examples demonstrate that multi-carrier digital formats such as OTFS can achieve as accurate radar estimation as state-of-the-art radar waveforms such as frequency-modulated continuous wave (FMCW). For the data detection part, we focus on separate detection and decoding and consider a soft-output detector that exploits efficiently the channel sparsity in the Doppler-delay domain. We quantify the detector performance in terms of its pragmatic capacity, i.e., the achievable rate of the channel induced by the signal constellation and the detector soft-output. Simulations show that the proposed scheme outperforms concurrent state-of-the-art solutions. Overall, our work shows that a suitable digitally modulated waveform enables to efficiently operate joint radar parameter estimation and communication by achieving full information rate of the modulation and near-optimal radar estimation performance. Furthermore, OTFS appears to be particularly suited to the scope
On the Average Performance of Caching and Coded Multicasting with Random Demands
For a network with one sender, receivers (users) and possible
messages (files), caching side information at the users allows to satisfy
arbitrary simultaneous demands by sending a common (multicast) coded message.
In the worst-case demand setting, explicit deterministic and random caching
strategies and explicit linear coding schemes have been shown to be order
optimal. In this work, we consider the same scenario where the user demands are
random i.i.d., according to a Zipf popularity distribution. In this case, we
pose the problem in terms of the minimum average number of equivalent message
transmissions. We present a novel decentralized random caching placement and a
coded delivery scheme which are shown to achieve order-optimal performance. As
a matter of fact, this is the first order-optimal result for the caching and
coded multicasting problem in the case of random demands.Comment: 5 pages, 3 figure, to appear in ISWCS 201
Implementation of a Bordeaux-Montreal community of practice: An option for optimal post-stroke care
Formation of giant polymer vesicles by simple double emulsification using block copolymers as the sole surfactant dagger
Comparation of the new rebound tonometer IOPen and the Goldmann tonometer, and their relationship to corneal properties
Purpose To compare the intraocular pressures
(IOPs) obtained with the IOPen rebound
tonometer, Goldmann applanation tonometer
(GAT) and the ocular response analyzer (ORA)
and investigate the effects of corneal
biomechanical properties on IOPen
measurements.
Methods A total of 198 normal eyes were
included in this cross-sectional and
randomized study. Three measurements were
taken using IOPen. Agreement between
tonometers was calculated using the Bland
and Altman limits of agreement (LoA)
analysis.
Results The median IOPen IOP was 3mmHg
below the GAT (Po0.001), 3mmHg below
the ORA IOP similar to Goldmann (IOPg),
and 3mmHg below the ORA IOP corrected
using corneal parameters (IOPcc)(Po0.01).
The LoA width between the IOPen and GAT
IOPs varied between 13.92 (mean IOPen IOP)
and 15.99mmHg (third IOPen measurement).
The central corneal thickness (CCT) was
unrelated to IOPen measurements (P40.05).
Corneal hysteresis (CH) and corneal rigidity
factor (CRF) were correlated with IOPen
and GAT.
Conclusions IOPen underestimated the IOP
compared with GAT and ORA. The effect of
measurement quality or measurement order on
IOPen was low. CCT did not affect the IOPen,
but the CH and CRF did. The LoA width
between the IOPen and GAT IOPs was higher
than between the ORA IOPg or ORA IOPcc
and GAT IOPs
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