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## Blind Adaptive MIMO Receivers for Space-Time Block-Coded DS-CDMA Systems in Multipath Channels Using the Constant Modulus Criterion

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 29/12/2012
Português

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We propose blind adaptive multi-input multi-output (MIMO) linear receivers
for DS-CDMA systems using multiple transmit antennas and space-time block codes
(STBC) in multipath channels. A space-time code-constrained constant modulus
(CCM) design criterion based on constrained optimization techniques is
considered and recursive least squares (RLS) adaptive algorithms are developed
for estimating the parameters of the linear receivers. A blind space-time
channel estimation method for MIMO DS-CDMA systems with STBC based on a
subspace approach is also proposed along with an efficient RLS algorithm.
Simulations for a downlink scenario assess the proposed algorithms in several
situations against existing methods.; Comment: 4 figures, IEEE Transactions on Communications, 2010

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## Performance Analysis of Wavelet Based MC-CDMA System with Implementation of Various Antenna Diversity Schemes

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 16/07/2012
Português

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The impact of using wavelet based technique on the performance of a MC-CDMA
wireless communication system has been investigated. The system under proposed
study incorporates Walsh Hadamard codes to discriminate the message signal for
individual user. A computer program written in Mathlab source code is developed
and this simulation study is made with implementation of various antenna
diversity schemes and fading (Rayleigh and Rician) channel. Computer simulation
results demonstrate that the proposed wavelet based MC-CDMA system outperforms
in Alamouti (two transmit antenna and one receive antenna) under AWGN and
Rician channel.

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## Channel Estimation for MIMO MC-CDMA Systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 09/12/2011
Português

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The concepts of MIMO MC-CDMA are not new but the new technologies to improve
their functioning are an emerging area of research. In general, most mobile
communication systems transmit bits of information in the radio space to the
receiver. The radio channels in mobile radio systems are usually multipath
fading channels, which cause inter-symbol interference (ISI) in the received
signal. To remove ISI from the signal, there is a need of strong equalizer. In
this thesis we have focused on simulating the MIMO MC-CDMA systems in MATLAB
and designed the channel estimation for them.

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## The Size of Optimal Sequence Sets for Synchronous CDMA Systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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The sum capacity on a symbol-synchronous CDMA system having processing gain
$N$ and supporting $K$ power constrained users is achieved by employing at most
$2N-1$ sequences. Analogously, the minimum received power (energy-per-chip) on
the symbol-synchronous CDMA system supporting $K$ users that demand specified
data rates is attained by employing at most $2N-1$ sequences. If there are $L$
oversized users in the system, at most $2N-L-1$ sequences are needed. $2N-1$ is
the minimum number of sequences needed to guarantee optimal allocation for
single dimensional signaling. $N$ orthogonal sequences are sufficient if a few
users (at most $N-1$) are allowed to signal in multiple dimensions. If there
are no oversized users, these split users need to signal only in two dimensions
each. The above results are shown by proving a converse to a well-known result
of Weyl on the interlacing eigenvalues of the sum of two Hermitian matrices,
one of which is of rank 1. The converse is analogous to Mirsky's converse to
the interlacing eigenvalues theorem for bordering matrices.; Comment: 18 pages, 2 figures, technical report

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## Bounds for the Sum Capacity of Binary CDMA Systems in Presence of Near-Far Effect

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 28/03/2010
Português

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In this paper we are going to estimate the sum capacity of a binary CDMA
system in presence of the near-far effect. We model the near-far effect as a
random variable that is multiplied by the users binary data before entering the
noisy channel. We will find a lower bound and a conjectured upper bound for the
sum capacity in this situation. All the derivations are in the asymptotic case.
Simulations show that especially the lower bound is very tight for typical
values Eb/N0 and near-far effect. Also, we exploit our idea in conjunction with
the Tanaka's formula [6] which also estimates the sum capacity of binary CDMA
systems with perfect power control.

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## Randomness and metastability in CDMA paradigms

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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Code Division Multiple Access (CDMA) in which the signature code assignment
to users contains a random element has recently become a cornerstone of CDMA
research. The random element in the construction is particularly attractive in
that it provides robustness and flexibility in application, whilst not making
significant sacrifices in terms of multiuser efficiency. We present results for
sparse random codes of two types, with and without modulation. Simple
microscopic consideration on system samples would suggest differences in the
phase space of the two models, but we demonstrate that the thermodynamic
results and metastable states are equivalent in the minimum bit error rate
detector. We analyse marginal properties of interactions and also make
analogies to constraint satisfiability problems in order to understand
qualitative features of detection and metastable states. This may have
consequences for developing algorithmic methods to escape metastable states,
thus improving decoding performance.; Comment: 5 pages, 3 figures, prepared IEEE.cls, accepted physcomnet-08

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## On Optimum Asymptotic Multiuser Efficiency of Randomly Spread CDMA

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/10/2014
Português

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We extend the result by Tse and Verd\'{u} on the optimum asymptotic multiuser
efficiency of randomly spread CDMA with Binary Phase Shift Keying (BPSK) input.
Random Gaussian and random binary antipodal spreading are considered. We obtain
the optimum asymptotic multiuser efficiency of a $K$-user system with spreading
gain $N$ when $K$ and $N\rightarrow\infty$ and the loading factor,
$\frac{K}{N}$, grows logarithmically with $K$ under some conditions. It is
shown that the optimum detector in a Gaussian randomly spread CDMA system has a
performance close to the single user system at high Signal to Noise Ratio (SNR)
when $K$ and $N\rightarrow\infty$ and the loading factor, $\frac{K}{N}$, is
kept less than $\frac{\log_3K}{2}$. Random binary antipodal matrices are also
studied and a lower bound for the optimum asymptotic multiuser efficiency is
obtained. Furthermore, we investigate the connection between detecting matrices
in the coin weighing problem and optimum asymptotic multiuser efficiency. We
obtain a condition such that for any binary input, an $N\times K$ random matrix
whose entries are chosen randomly from a finite set, is a detecting matrix as
$K$ and $N\rightarrow \infty$.; Comment: 19 pages, 1 figure, submitted to Transaction on Information Theory

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## Improved Algorithm for Throughput Maximization in MC-CDMA

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 14/09/2012
Português

Relevância na Pesquisa

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The Multi-Carrier Code Division Multiple Access (MC-CDMA) is becoming a very
significant downlink multiple access technique for high-rate data transmission
in the fourth generation wireless communication systems. By means of efficient
resource allocation higher data rate i.e. throughput can be achieved. This
paper evaluates the performance of criteria used for group (subchannel)
allocation employed in downlink transmission, which results in throughput
maximization. Proposed algorithm gives the modified technique of sub channel
allocation in the downlink transmission of MC-CDMA systems. Simulation are
carried out for all the three combining schemes, results shows that for the
given power and BER proposed algorithm comparatively gives far better results; Comment: 12 pages

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## Secure CDMA Sequences

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 20/12/2012
Português

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Single sequences like Legendre have high linear complexity. Known CDMA
families of sequences all have low complexities. We present a new method of
constructing CDMA sequence sets with the complexity of the Legendre from new
frequency hop patterns, and compare them with known sequences. These are the
first families whose normalized linear complexities do not asymptote to 0,
verified for lengths up to 6x108. The new constructions in array format are
also useful in watermarking images. We present a conjecture regarding the
recursion polynomials. We also have a method to reverse the process, and from
small Kasami/No-Kumar sequences we obtain a new family of 2n doubly periodic
(2n+1)x(2n-1) frequency hop patterns with correlation 2.; Comment: 10 pages, 8 figures

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## Relay-Assisted Partial Packet Recovery with IDMA Method in CDMA Wireless Network

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 14/04/2010
Português

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Automatic Repeat Request (ARQ) is an effective technique for reliable
transmission of packets in wireless networks. In ARQ, however, only a few
erroneous bits in a packet will cause the entire packet to be discarded at the
receiver. In this case, it's wasteful to retransmit the correct bit in the
received packet. The partial packet recovery only retransmits the unreliable
decoded bits in order to increase the throughput of network. In addition, the
cooperative transmission based on Interleave-division multiple-access (IDMA)
can obtain diversity gains with multiple relays with different locations for
multiple sources simultaneously. By exploring the diversity from the channel
between relay and destination, we propose a relay-assisted partial packet
recovery in CDMA wireless network to improve the performance of throughput. In
the proposed scheme, asynchronous IDMA iterative chip-by-chip multiuser
detection is utilized as a method of multiple partial recovery, which can be a
complementarity in a current CDMA network. The confidence values' concept is
applied to detect unreliable decoded bits. According to the result of
unreliable decoded bits' position, we use a recursive algorithm based on cost
evaluation to decide a feedback strategy. Then the feedback request with
minimum cost can be obtained. The simulation results show that the performance
of throughput can be significantly improved with our scheme...

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## Bounds on the Sum Capacity of Synchronous Binary CDMA Channels

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa

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In this paper, we obtain a family of lower bounds for the sum capacity of
Code Division Multiple Access (CDMA) channels assuming binary inputs and binary
signature codes in the presence of additive noise with an arbitrary
distribution. The envelope of this family gives a relatively tight lower bound
in terms of the number of users, spreading gain and the noise distribution. The
derivation methods for the noiseless and the noisy channels are different but
when the noise variance goes to zero, the noisy channel bound approaches the
noiseless case. The behavior of the lower bound shows that for small noise
power, the number of users can be much more than the spreading gain without any
significant loss of information (overloaded CDMA). A conjectured upper bound is
also derived under the usual assumption that the users send out equally likely
binary bits in the presence of additive noise with an arbitrary distribution.
As the noise level increases, and/or, the ratio of the number of users and the
spreading gain increases, the conjectured upper bound approaches the lower
bound. We have also derived asymptotic limits of our bounds that can be
compared to a formula that Tanaka obtained using techniques from statistical
physics; his bound is close to that of our conjectured upper bound for large
scale systems.; Comment: to be published in IEEE Transactions on Information Theory

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## Partial Cross-Correlation of D-Sequences based CDMA System

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 18/04/2008
Português

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Like other pseudorandom sequences, decimal sequences may be used in designing
a Code Division Multiple Access (CDMA) system. They appear to be ideally suited
for this since the cross-correlation of d-sequences taken over the LCM of their
periods is zero. But a practical system will not, in most likelihood, satisfy
the condition that the number of chips per bit is equal to the LCM for all
sequences that are assigned to different users. It is essential, therefore, to
determine the partial cross-correlation properties of d-sequences. This paper
has performed experiments on d-sequences and found that the partial
cross-correlation is less than for PN sequences, indicating that d-sequences
can be effective for use in CDMA.; Comment: 6 pages

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## Joint Receiver and Transmitter Optimization for Energy-Efficient CDMA Communications

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 09/12/2007
Português

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This paper focuses on the cross-layer issue of joint multiuser detection and
resource allocation for energy efficiency in wireless CDMA networks. In
particular, assuming that a linear multiuser detector is adopted in the uplink
receiver, the case considered is that in which each terminal is allowed to vary
its transmit power, spreading code, and uplink receiver in order to maximize
its own utility, which is defined as the ratio of data throughput to transmit
power. Resorting to a game-theoretic formulation, a non-cooperative game for
utility maximization is formulated, and it is proved that a unique Nash
equilibrium exists, which, under certain conditions, is also Pareto-optimal.
Theoretical results concerning the relationship between the problems of SINR
maximization and MSE minimization are given, and, resorting to the tools of
large system analysis, a new distributed power control algorithm is
implemented, based on very little prior information about the user of interest.
The utility profile achieved by the active users in a large CDMA system is also
computed, and, moreover, the centralized socially optimum solution is analyzed.
Considerations on the extension of the proposed framework to a multi-cell
scenario are also briefly detailed. Simulation results confirm that the
proposed non-cooperative game largely outperforms competing alternatives...

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## Optimization of sequences in CDMA systems: a statistical-mechanics approach

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 01/10/2008
Português

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Statistical mechanics approach is useful not only in analyzing macroscopic
system performance of wireless communication systems, but also in discussing
design problems of wireless communication systems. In this paper, we discuss a
design problem of spreading sequences in code-division multiple-access (CDMA)
systems, as an example demonstrating the usefulness of statistical mechanics
approach. We analyze, via replica method, the average mutual information
between inputs and outputs of a randomly-spread CDMA channel, and discuss the
optimization problem with the average mutual information as a measure of
optimization. It has been shown that the average mutual information is
maximized by orthogonally-invariant random Welch bound equality (WBE) spreading
sequences.; Comment: 17pages, submitted to Special Issue on Interdisciplinary Paradigms
for Networking in International Journal of Computer and Telecommunications
Networking

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## Counting solutions for the CDMA multiuser MAP demodulator

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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We evaluate the average number of locally minimal solutions for maximum-{\it
a-posteriori} (MAP) demodulation in code-division multiple-access (CDMA)
systems. For this purpose, we use a sophisticated method to investigate the
ground state properties for the Sherrington-Kirkpatrick-type (i.e. fully
connected) spin glasses established by Tanaka and Edwards in 1980. We derive
the number of locally minimal solutions as a function of several parameters
which specify the CDMA multiuser MAP demodulator. We also calculate the
distribution function of the normalized-energies for the locally minimum
states. We find that for a small number of chip intervals (or equivalently a
large number of users) and large noise level at the base station, the number of
local minimum solutions becomes larger than that of the SK model. This provides
us with useful information about the computational complexity of the MAP
demodulator.; Comment: 23pages, 4figures, using jpsj2.cls, 2 figures were replaced

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## Guard Zones and the Near-Far Problem in DS-CDMA Ad Hoc Networks

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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The central issue in direct-sequence code-division multiple-access (DS-CDMA)
ad hoc networks is the prevention of a near-far problem. This paper considers
two types of guard zones that may be used to control the near-far problem: a
fundamental exclusion zone and an additional CSMA guard zone that may be
established by the carrier-sense multiple-access (CSMA) protocol. In the
exclusion zone, no mobiles are physically present, modeling the minimum
physical separation among mobiles that is always present in actual networks.
Potentially interfering mobiles beyond a transmitting mobile's exclusion zone,
but within its CSMA guard zone, are deactivated by the protocol. This paper
provides an analysis of DS-CSMA networks with either or both types of guard
zones. A network of finite extent with a finite number of mobiles is modeled as
a uniform clustering process. The analysis uses a closed-form expression for
the outage probability in the presence of Nakagami fading, conditioned on the
network geometry. By using the analysis developed in this paper, the tradeoffs
between exclusion zones and CSMA guard zones are explored for DS-CDMA and
unspread networks.; Comment: to appear at Milcom-2012

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## Equalization with oversampling in multiuser CDMA systems

Fonte: Instituto de Tecnologia da Califórnia
Publicador: Instituto de Tecnologia da Califórnia

Tipo: Article; PeerReviewed
Formato: application/pdf

Publicado em /05/2005
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Some of the major challenges in the design of new-generation wireless mobile systems are the suppression of multiuser interference (MUI) and inter-symbol interference (ISI) within a single user created by the multipath propagation. Both of these problems were addressed successfully in a recent design of A Mutually Orthogonal Usercode-Receiver (AMOUR) for asynchronous or quasisynchronous code division multiple access (CDMA) systems. AMOUR converts a multiuser CDMA system into parallel single-user systems regardless of the multipath and guarantees ISI mitigation, irrespective of the channel locations. However, the noise amplification at the receiver can be significant in some multipath channels. In this paper, we propose to oversample the received signal as a way of improving the performance of AMOUR systems. We design Fractionally Spaced AMOUR (FSAMOUR) receivers with integral and rational amounts of oversampling and compare their performance with the conventional method. An important point that is often overlooked in the design of zero-forcing channel equalizers is that sometimes, they are not unique. This becomes especially significant in multiuser applications where, as we will show, the nonuniqueness is practically guaranteed. We exploit this flexibility in the design of AMOUR and FSAMOUR receivers and achieve noticeable improvements in performance.

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## Optical-CDMA in InP

Fonte: Instituto de Tecnologia da Califórnia
Publicador: Instituto de Tecnologia da Califórnia

Tipo: Article; PeerReviewed
Formato: application/pdf

Publicado em /09/2007
Português

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This paper describes the InP platforms for photonic integration and the development on these platforms of an optical code division multiple access (O-CDMA) system for local area networks. We demonstrate three building blocks of this system: an optical pulse source, an encoder/decoder pair, and a threshold detector. The optical pulse source consists of an integrated colliding pulse-mode laser with nearly transform-limited 10 Gb/s pulses and optical injection locking to an external clock for synchronization. The encoder/decoder pair is based on arrayed waveguide gratings. Bit-error-rate measurements involving six users at 10 Gb/s showed error-free transmission, while O-CDMA codes were calibrated using frequency resolved optical gating. For threshold detection after the decoder, we compared two Mach--Zehnder interferometer (MZI)-based optical thresholding schemes and present results on a new type of electroabsorber-based MZI.

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## Optimal CDMA signature sequences, inverse eigenvalue problems and alternating minimization

Fonte: IEEE
Publicador: IEEE

Tipo: Book Section; PeerReviewed
Formato: application/pdf

Publicado em 15/09/2003
Português

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This paper describes the matrix-theoretic ideas known as Welch-bound-equality sequences or unit-norm tight frames that are used to alternate minimizing the total squared correlation. This paper shows the construction of an optimal signature sequences for the synchronous code-division multiple-access (S-CDMA) channel in the presence of white noise and uniform received powers to solve inverse eigenvalue problems that maximize the sum capacity of the S-CDMA channel.

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## Downlink interference analysis in DS-CDMA for unequal power requirements: The dirty user problem

Fonte: Conference Organising Committee
Publicador: Conference Organising Committee

Tipo: Conference paper

Português

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Downlink interference analysis within direct-sequence code-division multiple-access (DS-CDMA) systems is considered in this paper. Although orthogonal codes are used at the base-station transmitter, multi-path and different power requirements of terminals mean that substantial multiple access interference is suffered at the terminals. With the multitude of terminals available for 2G and 3G systems, inefficient terminal design leads to the "Dirty User Problem", that is, where a terminal requests more power from the base-station than an alternate terminal located at the same position. A "dirty user" causes higher interference on all other users in the cell and ultimately limits the capacity of the downlink link of a DS-CDMA system. This paper investigates this affect by determining the performance degradation in terms of the percentage of dirty users and their power requirement, compared to a conventional receiver.

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