# A melhor ferramenta para a sua pesquisa, trabalho e TCC!

Página 18 dos resultados de 735 itens digitais encontrados em 0.002 segundos

## Soft Handoff and Uplink Capacity in a Two-Tier CDMA System

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 18/03/2005
Português

Relevância na Pesquisa

26.82907%

This paper examines the effect of soft handoff on the uplink user capacity of
a CDMA system consisting of a single macrocell in which a single hotspot
microcell is embedded. The users of these two base stations operate over the
same frequency band. In the soft handoff scenario studied here, both macrocell
and microcell base stations serve each system user and the two received copies
of a desired user's signal are summed using maximal ratio combining. Exact and
approximate analytical methods are developed to compute uplink user capacity.
Simulation results demonstrate a 20% increase in user capacity compared to hard
handoff. In addition, simple, approximate methods are presented for estimating
soft handoff capacity and are shown to be quite accurate.; Comment: To appear in IEEE Transactions on Wireless Communications

Link permanente para citações:

## Randomly Spread CDMA: Asymptotics via Statistical Physics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 23/03/2005
Português

Relevância na Pesquisa

26.82907%

This paper studies randomly spread code-division multiple access (CDMA) and
multiuser detection in the large-system limit using the replica method
developed in statistical physics. Arbitrary input distributions and flat fading
are considered. A generic multiuser detector in the form of the posterior mean
estimator is applied before single-user decoding. The generic detector can be
particularized to the matched filter, decorrelator, linear MMSE detector, the
jointly or the individually optimal detector, and others. It is found that the
detection output for each user, although in general asymptotically non-Gaussian
conditioned on the transmitted symbol, converges as the number of users go to
infinity to a deterministic function of a "hidden" Gaussian statistic
independent of the interferers. Thus the multiuser channel can be decoupled:
Each user experiences an equivalent single-user Gaussian channel, whose
signal-to-noise ratio suffers a degradation due to the multiple-access
interference. The uncoded error performance (e.g., symbol-error-rate) and the
mutual information can then be fully characterized using the degradation
factor, also known as the multiuser efficiency, which can be obtained by
solving a pair of coupled fixed-point equations identified in this paper. Based
on a general linear vector channel model...

Link permanente para citações:

## A CDMA multiuser detection algorithm based on survey propagation

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa

26.82907%

A computationally tractable CDMA multiuser detection algorithm is developed
based on survey propagation.; Comment: Abstract for my presentation at Randomness and Computation Joint
Workshop ``New Horizons in Computing'' and ``Statistical Mechanical Approach
to Probabilistic Information Processing'' (18-21 July, 2005, Sendai, Japan)

Link permanente para citações:

## Optimal Power Control for Multiuser CDMA Channels

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 14/09/2005
Português

Relevância na Pesquisa

26.82907%

In this paper, we define the power region as the set of power allocations for
K users such that everybody meets a minimum signal-to-interference ratio (SIR).
The SIR is modeled in a multiuser CDMA system with fixed linear receiver and
signature sequences. We show that the power region is convex in linear and
logarithmic scale. It furthermore has a componentwise minimal element. Power
constraints are included by the intersection with the set of all viable power
adjustments.
In this framework, we aim at minimizing the total expended power by
minimizing a componentwise monotone functional. If the feasible power region is
nonempty, the minimum is attained. Otherwise, as a solution to balance
conflicting interests, we suggest the projection of the minimum point in the
power region onto the set of viable power settings. Finally, with an
appropriate utility function, the problem of minimizing the total expended
power can be seen as finding the Nash bargaining solution, which sheds light on
power assignment from a game theoretic point of view. Convexity and
componentwise monotonicity are essential prerequisites for this result.; Comment: To appear in the proceedings of the 2005 IEEE International Symposium
on Information Theory, Adelaide...

Link permanente para citações:

## Blind Adaptive Subcarrier Combining Technique for MC-CDMA Receiver in Mobile Rayleigh Channel

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 25/02/2011
Português

Relevância na Pesquisa

26.82907%

A new subcarrier combining technique is proposed for MC -CDMA receiver in
mobile Rayleigh fading channel. It exploits the structure formed by repeating
spreading sequences of users on different subcarriers to simultaneously
suppress multiple access interference (MAI) and provide implicit channel
tracking without any knowledge of the channel amplitudes or training sequences.
This is achieved by adaptively weighting each subcarrier in each symbol period
by employing a simple gradient descent algorithm to meet the constant modulus
(CM) criterion with judicious selection of step-size. Improved BER and user
capacity performance are shown with similar complexity in order of O(N)
compared with conventional maximum ratio combining and equal gain combining
techniques even under high channel Doppler rates.

Link permanente para citações:

## Bidirectional MMSE Algorithms for Interference Mitigation in CDMA Systems over Fast Fading Channels

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 10/06/2013
Português

Relevância na Pesquisa

26.82907%

This paper presents adaptive bidirectional minimum mean-square error (MMSE)
parameter estimation algorithms for fast-fading channels. The time correlation
between successive channel gains is exploited to improve the estimation and
tracking capabilities of adaptive algorithms and provide robustness against
time-varying channels. Bidirectional normalized least mean-square (NLMS) and
conjugate gradient (CG) algorithms are devised along with adaptive mixing
parameters that adjust to the time-varying channel correlation properties. An
analysis of the proposed algorithms is provided along with a discussion of
their performance advantages. Simulations for an application to interference
suppression in DS-CDMA systems show the advantages of the proposed algorithms.; Comment: 3 figures, ISWCS, 2012

Link permanente para citações:

## An Analysis of the DS-CDMA Cellular Uplink for Arbitrary and Constrained Topologies

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa

26.82907%

A new analysis is presented for the direct-sequence code-division multiple
access (DS-CDMA) cellular uplink. For a given network topology, closed-form
expressions are found for the outage probability and rate of each uplink in the
presence of path-dependent Nakagami fading and shadowing. The topology may be
arbitrary or modeled by a random spatial distribution with a fixed number of
base stations and mobiles placed over a finite area. The analysis is more
detailed and accurate than existing ones and facilitates the resolution of
network design issues including the influence of the minimum base-station
separation, the role of the spreading factor, and the impact of various
power-control and rate-control policies. It is shown that once power control is
established, the rate can be allocated according to a fixed-rate or
variable-rate policy with the objective of either meeting an outage constraint
or maximizing throughput. An advantage of variable-rate power control is that
it allows an outage constraint to be enforced on every uplink, which is
impossible when a fixed rate is used throughout the network.; Comment: IEEE Transactions on Communications, vol. 61, no. 8, pp. 3318 - 3326,
August 2013

Link permanente para citações:

## An Efficient Paging Algorithm for Multi-Carrier CDMA System

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 11/09/2011
Português

Relevância na Pesquisa

26.82907%

To cope with the increasing demand of wireless communication services
multi-carrier systems are being used. Radio resources are very limited and
efficient usages of these resources are inevitable to get optimum performance
of the system. Paging channel is a low-bandwidth channel and one of the most
important channels on which system performance depends significantly. Therefore
it is vulnerable to even moderate overloads. In this paper, an efficient paging
algorithm, Concurrent Search, is proposed for efficient use of paging channel
in Multi- carrier CDMA system instead of existing sequential searching
algorithm. It is shown by the simulation that the paging performance in
proposed algorithm is far better than the existing system.

Link permanente para citações:

## Adaptive Reduced-Rank Processing Using a Projection Operator Based on Joint Iterative Optimization of Adaptive Filters For CDMA Interference Suppression

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 27/05/2013
Português

Relevância na Pesquisa

26.82907%

This paper proposes a novel adaptive reduced-rank filtering scheme based on
the joint iterative optimization of adaptive filters. The proposed scheme
consists of a joint iterative optimization of a bank of full-rank adaptive
filters that constitutes the projection matrix and an adaptive reduced-rank
filter that operates at the output of the bank of filters. We describe minimum
mean-squared error (MMSE) expressions for the design of the projection matrix
and the reduced-rank filter and simple least-mean squares (LMS) adaptive
algorithms for its computationally efficient implementation. Simulation results
for a CDMA interference suppression application reveals that the proposed
scheme significantly outperforms the state-of-the-art reduced-rank schemes,
while requiring a significantly lower computational complexity.; Comment: 4 figures. Published in SSP 2010. arXiv admin note: substantial text
overlap with arXiv:1205.4390, arXiv:1304.7548

Link permanente para citações:

## Joint SIC and Relay Selection for Cooperative DS-CDMA Systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 01/10/2014
Português

Relevância na Pesquisa

26.82907%

In this work, we propose a cross-layer design strategy based on a joint
successive interference cancellation (SIC) detection technique and a
multi-relay selection algorithm for the uplink of cooperative direct-sequence
code-division multiple access (DS-CDMA) systems. We devise a low-cost greedy
list-based SIC (GL-SIC) strategy with RAKE receivers as the front-end that can
approach the maximum likelihood detector performance. %Unlike prior art, the
proposed GL-SIC algorithm %exploits the Euclidean distance between users of
interest, multiple %ordering and their constellation points to build an
effective list %of detection candidates. We also present a low-complexity
multi-relay selection algorithm based on greedy techniques that can approach
the performance of an exhaustive search. %A cross-layer %design strategy that
brings together the proposed GL-SIC algorithm %and the greedy relay selection
is then developed. Simulations show an excellent bit error rate performance of
the proposed detection and relay selection algorithms as compared to existing
techniques.; Comment: 5 figures, conference

Link permanente para citações:

## Performance Improvement of Iterative Multiuser Detection for Large Sparsely-Spread CDMA Systems by Spatial Coupling

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa

26.82907%

Kudekar et al. proved that the belief-propagation (BP) performance for
low-density parity check (LDPC) codes can be boosted up to the
maximum-a-posteriori (MAP) performance by spatial coupling. In this paper,
spatial coupling is applied to sparsely-spread code-division multiple-access
(CDMA) systems to improve the performance of iterative multiuser detection
based on BP. Two iterative receivers based on BP are considered: One receiver
is based on exact BP and the other on an approximate BP with Gaussian
approximation. The performance of the two BP receivers is evaluated via density
evolution (DE) in the dense limit after taking the large-system limit, in which
the number of users and the spreading factor tend to infinity while their ratio
is kept constant. The two BP receivers are shown to achieve the same
performance as each other in these limits. Furthermore, taking a continuum
limit for the obtained DE equations implies that the performance of the two BP
receivers can be improved up to the performance achieved by the symbol-wise MAP
detection, called individually-optimal detection, via spatial coupling.
Numerical simulations show that spatial coupling can provide a significant
improvement in bit error rate for finite-sized systems especially in the region
of high system loads.; Comment: submitted to IEEE Trans. Inf. Theory

Link permanente para citações:

## Energy-Efficient Power Control in Multipath CDMA Channels via Large System Analysis

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 19/07/2008
Português

Relevância na Pesquisa

26.82907%

This paper is focused on the design and analysis of power control procedures
for the uplink of multipath code-division-multiple-access (CDMA) channels based
on the large system analysis (LSA). Using the tools of LSA, a new decentralized
power control algorithm aimed at energy efficiency maximization and requiring
very little prior information on the interference background is proposed;
moreover, it is also shown that LSA can be used to predict with good accuracy
the performance and operational conditions of a large network operating at the
equilibrium over a multipath channel, i.e. the power,
signal-to-interference-plus-noise ratio (SINR) and utility profiles across
users, wherein the utility is defined as the number of bits reliably delivered
to the receiver for each energy-unit used for transmission. Additionally, an
LSA-based performance comparison among linear receivers is carried out in terms
of achieved energy efficiency at the equilibrium. Finally, the problem of the
choice of the utility-maximizing training length is also considered. Numerical
results show a very satisfactory agreement of the theoretical analysis with
simulation results obtained with reference to systems with finite (and not so
large) numbers of users.; Comment: Proceedings of the IEEE International Symposium on Personal...

Link permanente para citações:

## Blind Adaptive MIMO Receivers for CDMA Systems with Space-Time Block-Codes and Low-Cost Algorithms

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 20/10/2014
Português

Relevância na Pesquisa

26.82907%

In this paper we present low-complexity blind multi-input multi-output (MIMO)
adaptive linear multiuser receivers for direct sequence code division multiple
access (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 and
low-complexity stochastic gradient (SG) adaptive algorithms are developed for
estimating the parameters of the space-time linear receivers. The receivers are
designed by exploiting the unique structure imposed by both spreading codes and
STBC. A blind space-time channel estimation scheme for STBC systems based on a
subspace approach is also proposed along with an efficient SG algorithm.
Simulation results for a downlink scenario assess the receiver structures and
algorithms and show that the proposed schemes achieve excellent performance,
outperforming existing methods.; Comment: 10 pages, 4 figures, Signal Processing, 2012

Link permanente para citações:

## Energy Efficiency in Multi-Hop CDMA Networks: a Game Theoretic Analysis Considering Operating Costs

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 23/01/2008
Português

Relevância na Pesquisa

26.82907%

A game-theoretic analysis is used to study the effects of receiver choice and
transmit power on the energy efficiency of multi-hop networks in which the
nodes communicate using Direct-Sequence Code Division Multiple Access
(DS-CDMA). A Nash equilibrium of the game in which the network nodes can choose
their receivers as well as their transmit powers to maximize the total number
of bits they transmit per unit of energy spent (including both transmit and
operating energy) is derived. The energy efficiencies resulting from the use of
different linear multiuser receivers in this context are compared for the
non-cooperative game. Significant gains in energy efficiency are observed when
multiuser receivers, particularly the linear minimum mean-square error (MMSE)
receiver, are used instead of conventional matched filter receivers.; Comment: To appear in the Proceedings of the 2008 IEEE International
Conference on Acoustics, Speech and Signal Processing, Las Vegas, NV, March
30 -- April 4, 2008

Link permanente para citações:

## Large-System Analysis of Joint Channel and Data Estimation for MIMO DS-CDMA Systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa

26.82907%

This paper presents a large-system analysis of the performance of joint
channel estimation, multiuser detection, and per-user decoding (CE-MUDD) for
randomly-spread multiple-input multiple-output (MIMO) direct-sequence
code-division multiple-access (DS-CDMA) systems. A suboptimal receiver based on
successive decoding in conjunction with linear minimum mean-squared error
(LMMSE) channel estimation is investigated. The replica method, developed in
statistical mechanics, is used to evaluate the performance in the large-system
limit, where the number of users and the spreading factor tend to infinity
while their ratio and the number of transmit and receive antennas are kept
constant. The performance of the joint CE-MUDD based on LMMSE channel
estimation is compared to the spectral efficiencies of several receivers based
on one-shot LMMSE channel estimation, in which the decoded data symbols are not
utilized to refine the initial channel estimates. The results imply that the
use of joint CE-MUDD significantly reduces rate loss due to transmission of
pilot signals, especially for multiple-antenna systems. As a result, joint
CE-MUDD can provide significant performance gains, compared to the receivers
based on one-shot channel estimation.; Comment: The paper was resubmitted to IEEE Trans. Inf. Theory

Link permanente para citações:

## Performance Analysis of Uplink & Downlink Transmission in CDMA System

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 25/02/2010
Português

Relevância na Pesquisa

26.82907%

CDMA is a multiple access method in which the user's uses spread spectrum
techniques and occupy the entire spectrum whenever they transmit. In wireless
communication signal-to-noise ratio (SNR) is the very important parameter that
influences the system performance. Any mode of mobile transmission is not free
from channel impairment such as noise, interference and fading. This channel
impairment caused signal distortion and degradation in SNR.Also there are
differences between uplink (forward channel) and downlink (reverse
channel).Along with these differences, both the links use different codes for
chanellizing the individual users. This paper simulates the expressions for the
pdfs of the SNR for both uplink and downlink transmission assuming that the
system is operating at an average signal-to-noise ratio is 6dB per information
bit.; Comment: Journal of Telecommunications,Volume 1, Issue 1, pp84-86, February
2010

Link permanente para citações:

## Errorless Codes for Over-loaded CDMA with Active User Detection

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 04/10/2008
Português

Relevância na Pesquisa

26.82907%

In this paper we introduce a new class of codes for over-loaded synchronous
wireless CDMA systems which increases the number of users for a fixed number of
chips without introducing any errors. In addition these codes support active
user detection. We derive an upper bound on the number of users with a fixed
spreading factor. Also we propose an ML decoder for a subclass of these codes
that is computationally implementable. Although for our simulations we consider
a scenario that is worse than what occurs in practice, simulation results
indicate that this coding/decoding scheme is robust against additive noise. As
an example, for 64 chips and 88 users we propose a coding/decoding scheme that
can obtain an arbitrary small probability of error which is computationally
feasible and can detect active users. Furthermore, we prove that for this to be
possible the number of users cannot be beyond 230.

Link permanente para citações:

## Performance Estimation of 2*3 MIMO-MC-CDMA using Convolution Code

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 12/03/2014
Português

Relevância na Pesquisa

26.82907%

In this paper we estimate the performance of 2by3 MIMOMCCDMA system using
convolution code in MATLAB which highly reduces BER by increasing the
efficiency of system. MIMO and MCCDMA system combination is used to reduce bit
error rate and also for forming a new system called MCCDMA which is multi user
and multiple access schemes used to increase the performance of the system.
MCCDMA system is a narrowband flat fading in nature which converts frequency
selective to numerous narrowband flat fading multiple parallel sub-carriers to
increase the efficiency of the system. Now this MCCDMA system can also be
enhanced by grouping with 2by3 MIMO system which utilizes ZF decoder at the
receiver to decrease BER in which half rate convolutionally encoded Alamouti
STBC block code is used for channel encoding scheme as transmit diversity of
MIMO with multiple transmit antenna. And convolution encoder is also used as
source encoder or FEC encoder in MIMOMCCDMA. Advantage of using MIMO-MC-CDMA
using convolution code is due to reduce complexity of system and also for
reducing BER and finally to increase gain of system. Now after this we examine
system in various modulation techniques like, 8PSK, 16QAM, QPSK, 32QAM, 8QAM
and 64QAM using MATLAB in Rayleigh fading channel.; Comment: 5 pages...

Link permanente para citações:

## Point-to-point and Point-to-multipoint CDMA Access Network with Enhanced Security

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa

26.82907%

We propose a network implementation with enhanced security at the physical
layer by means of time-hopping CDMA, supporting cryptographically secure
point-to-point and point-to-multipoint communication. In particular, we analyze
an active star topology optical network implementation capable of supporting
128 simultaneous users up to 20 km apart. The feasibility of the proposed
scheme is demonstrated through numerical simulation.

Link permanente para citações:

## A New Analysis of the DS-CDMA Cellular Uplink Under Spatial Constraints

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 28/04/2013
Português

Relevância na Pesquisa

26.82907%

A new analysis is presented for the direct-sequence code-division multiple
access (DS-CDMA) cellular uplink. For a given network topology, closed-form
expressions are found for the outage probability and rate of each uplink in the
presence of path-dependent Nakagami fading and log-normal shadowing. The
topology may be arbitrary or modeled by a random spatial distribution for a
fixed number of base stations and mobiles placed over a finite area with the
separations among them constrained to exceed a minimum distance. The analysis
is more detailed and accurate than existing ones and facilitates the resolution
of network design issues, including the influence of the minimum base-station
separation, the role of the spreading factor, and the impact of various
power-control and rate-control policies. It is shown that once power control is
established, the rate can be allocated according to a fixed-rate or
variable-rate policy with the objective of either meeting an outage constraint
or maximizing throughput. An advantage of the variable-rate policy is that it
allows an outage constraint to be enforced on every uplink, whereas the
fixed-rate policy can only meet an average outage constraint.; Comment: 6 pages, 6 figures, to appear at International Conference on
Communications (ICC) 2013

Link permanente para citações: