24,483 research outputs found
Wideband digital phase comparator for high current shunts
A wideband phase comparator for precise measurements of phase difference of
high current shunts has been developed at INRIM. The two-input digital phase
detector is realized with a precision wideband digitizer connected through a
pair of symmetric active guarded transformers to the outputs of the shunts
under comparison. Data are first acquired asynchronously, and then transferred
from on-board memory to host memory. Because of the large amount of data
collected the filtering process and the analysis algorithms are performed
outside the acquisition routine. Most of the systematic errors can be
compensated by a proper inversion procedure.
The system is suitable for comparing shunts in a wide range of currents, from
several hundred of milliampere up to 100 A, and frequencies ranging between 500
Hz and 100 kHz. Expanded uncertainty (k=2) less than 0.05 mrad, for frequency
up to 100 kHz, is obtained in the measurement of the phase difference of a
group of 10 A shunts, provided by some European NMIs, using a digitizer with
sampling frequency up to 1 MHz. An enhanced version of the phase comparator
employs a new digital phase detector with higher sampling frequency and
vertical resolution. This permits to decrease the contribution to the
uncertainty budget of the phase detector of a factor two from 20 kHz to 100
kHz. Theories and experiments show that the phase difference between two high
precision wideband digitizers, coupled as phase detector, depends on multiple
factors derived from both analog and digital imprint of each sampling system.Comment: 20 pages, 9 figure
Fundamental Limits of Wideband Localization - Part II: Cooperative Networks
The availability of positional information is of great importance in many
commercial, governmental, and military applications. Localization is commonly
accomplished through the use of radio communication between mobile devices
(agents) and fixed infrastructure (anchors). However, precise determination of
agent positions is a challenging task, especially in harsh environments due to
radio blockage or limited anchor deployment. In these situations, cooperation
among agents can significantly improve localization accuracy and reduce
localization outage probabilities. A general framework of analyzing the
fundamental limits of wideband localization has been developed in Part I of the
paper. Here, we build on this framework and establish the fundamental limits of
wideband cooperative location-aware networks. Our analysis is based on the
waveforms received at the nodes, in conjunction with Fisher information
inequality. We provide a geometrical interpretation of equivalent Fisher
information for cooperative networks. This approach allows us to succinctly
derive fundamental performance limits and their scaling behaviors, and to treat
anchors and agents in a unified way from the perspective of localization
accuracy. Our results yield important insights into how and when cooperation is
beneficial.Comment: To appear in IEEE Transactions on Information Theor
On the Outage Capacity of Correlated Multiple-Path MIMO Channels
The use of multi-antenna arrays in both transmission and reception has been
shown to dramatically increase the throughput of wireless communication
systems. As a result there has been considerable interest in characterizing the
ergodic average of the mutual information for realistic correlated channels.
Here, an approach is presented that provides analytic expressions not only for
the average, but also the higher cumulant moments of the distribution of the
mutual information for zero-mean Gaussian (multiple-input multiple-output) MIMO
channels with the most general multipath covariance matrices when the channel
is known at the receiver. These channels include multi-tap delay paths, as well
as general channels with covariance matrices that cannot be written as a
Kronecker product, such as dual-polarized antenna arrays with general
correlations at both transmitter and receiver ends. The mathematical methods
are formally valid for large antenna numbers, in which limit it is shown that
all higher cumulant moments of the distribution, other than the first two scale
to zero. Thus, it is confirmed that the distribution of the mutual information
tends to a Gaussian, which enables one to calculate the outage capacity. These
results are quite accurate even in the case of a few antennas, which makes this
approach applicable to realistic situations.Comment: submitted for publication IEEE Trans. Information Theory; IEEEtran
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Advanced Quantizer Designs for FDD-Based FD-MIMO Systems Using Uniform Planar Arrays
Massive multiple-input multiple-output (MIMO) systems, which utilize a large
number of antennas at the base station, are expected to enhance network
throughput by enabling improved multiuser MIMO techniques. To deploy many
antennas in reasonable form factors, base stations are expected to employ
antenna arrays in both horizontal and vertical dimensions, which is known as
full-dimension (FD) MIMO. The most popular two-dimensional array is the uniform
planar array (UPA), where antennas are placed in a grid pattern. To exploit the
full benefit of massive MIMO in frequency division duplexing (FDD), the
downlink channel state information (CSI) should be estimated, quantized, and
fed back from the receiver to the transmitter. However, it is difficult to
accurately quantize the channel in a computationally efficient manner due to
the high dimensionality of the massive MIMO channel. In this paper, we develop
both narrowband and wideband CSI quantizers for FD-MIMO taking the properties
of realistic channels and the UPA into consideration. To improve quantization
quality, we focus on not only quantizing dominant radio paths in the channel,
but also combining the quantized beams. We also develop a hierarchical beam
search approach, which scans both vertical and horizontal domains jointly with
moderate computational complexity. Numerical simulations verify that the
performance of the proposed quantizers is better than that of previous CSI
quantization techniques.Comment: 15 pages, 6 figure
Ultra Wideband Impulse Radio Systems with Multiple Pulse Types
In an ultra wideband (UWB) impulse radio (IR) system, a number of pulses,
each transmitted in an interval called a "frame", is employed to represent one
information symbol. Conventionally, a single type of UWB pulse is used in all
frames of all users. In this paper, IR systems with multiple types of UWB
pulses are considered, where different types of pulses can be used in different
frames by different users. Both stored-reference (SR) and transmitted-reference
(TR) systems are considered. First, the spectral properties of a multi-pulse IR
system with polarity randomization is investigated. It is shown that the
average power spectral density is the average of the spectral contents of
different pulse shapes. Then, approximate closed-form expressions for the bit
error probability of a multi-pulse SR-IR system are derived for RAKE receivers
in asynchronous multiuser environments. The effects of both inter-frame
interference (IFI) and multiple-access interference (MAI) are analyzed. The
theoretical and simulation results indicate that SR-IR systems that are more
robust against IFI and MAI than a "conventional" SR-IR system can be designed
with multiple types of ultra-wideband pulses. Finally, extensions to
multi-pulse TR-IR systems are briefly described.Comment: To appear in the IEEE Journal on Selected Areas in Communications -
Special Issue on Ultrawideband Wireless Communications: Theory and
Application
Mathematical modeling of ultra wideband in vivo radio channel
This paper proposes a novel mathematical model for an in vivo radio channel at ultra-wideband frequencies (3.1–10.6 GHz), which can be used as a reference model for in vivo channel response without performing intensive experiments or simulations. The statistics of error prediction between experimental and proposed model is RMSE = 5.29, which show the high accuracy of the proposed model. Also, the proposed model was applied to the blind data, and the statistics of error prediction is RMSE = 7.76, which also shows a reasonable accuracy of the model. This model will save the time and cost on simulations and experiments, and will help in designing an accurate link budget calculation for a future enhanced system for ultra-wideband body-centric wireless systems
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