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## Transmission strategies for MISO downlink MC-CDMA mobile systems

Fonte: Springer Verlag
Publicador: Springer Verlag

Tipo: Artigo de Revista Científica

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#Antenna array#FDD#MC-CDMA#MISO#Pre-filtering and downlink#SFBC#TDD#Pre-filtering#Antenna arrays#Code division multiple access#Computer terminals

This paper proposes two space-frequency schemes with a multi-user pre-filtering technique for downlink (DL) multicarrier code division multiple access (MC-CDMA) systems. We consider the use of antenna arrays at the base station (BS) and a single antenna at the mobile terminal (MT) and derive the proposed multi-user pre-filtering technique that modulates the transmitted signal to eliminate the effects of multiple access interference (MAI) and channel distortions at the mobile terminals, while maintaining low MT complexity. Two types of detectors are considered at the MT: simple despreading and single user equalizers. The performances of the proposed schemes are compared to those of other transmit signal design approaches that have been recently proposed for DL MC-CDMA, considering both typical indoor and pedestrian scenarios, and channel coding based on UMTS specifications. © Springer Science+Business Media, LLC. 2009.

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## Downlink space-frequency preequalization techniques for TDD MC-CDMA mobile radio systems

Fonte: SpringerOpen
Publicador: SpringerOpen

Tipo: Artigo de Revista Científica

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#Antenna array#Downlink#MC-CDMA#Preequalization#TDD#Algorithms#Antenna arrays#Electrocardiography#Mathematical models#Mobile telecommunication systems#Natural frequencies

The paper considers downlink space-frequency preequalizations techniques for time division duplex (TDD) MC-CDMA. We consider the use of antenna arrays at the base station (BS) and analytically derive different preequalization schemes for two different receiver configurations at the mobile terminal: a simple despread receiver without channel equalization and an equal-gain combiner (EGC) conventional receiver. We show that the space-frequency preequalization approach proposed allows to format the transmitted signals so that the multiple access interference at mobile terminals is reduced allowing to transfer the most computational complexity from mobile terminal to the BS. Simulation results are carried out to demonstrate the effectiveness of the proposed preequalization schemes.; European project IST-2001-32620 - MATRICE; FCT - POSI/CPS/46701/2002

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## Performance evaluation of space-frequency pre-filtering schemes for downlink TDD MC-CDMA systems

Fonte: IEEE
Publicador: IEEE

Tipo: Conferência ou Objeto de Conferência

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#Computational complexity#Natural frequencies#Signal interference#Signal processing#Signal receivers#Base station (BS)#Downlink channels#Mobile terminals (MT)#Code division multiple access

This paper deals with downlink space-frequency pre-filtering techniques for time division duplex MC-CDMA. We consider the use of antenna arrays at the base station (BS) and present different pre-filtering schemes for two different receiver configurations at the mobile terminal: a simple despreading receiver without channel equalization and an EGC conventional receiver. We show that the space-frequency pre-filtering approaches proposed allow to format the transmitted signals so that the multiple access interference at mobile terminals is reduced allowing to transfer the most computational complexity from mobile terminal (MT) to the base station. One important issue for all pre-filtering scheme is that their effectiveness relies on the accuracy of the uplink channel estimates in modeling the downlink channel. Therefore, we evaluate the performance of both schemes in scenarios where the channel changes between an uplink and downlink slot, in order to obtain the performance penalties as a function of the time separation between the uplink (UL) and downlink (DL) slots. ©2004 IEEE.; European projcct IST-2001-32620 MATRICE; FCT - POSI/CPS/46701/2002

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## Transmit space-frequency prefiltering technique for downlink TDD MC-CDMA systems

Fonte: IEEE
Publicador: IEEE

Tipo: Conferência ou Objeto de Conferência

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#Antenna array#Diversity and beamforming#Downlink#MC-CDMA#Pre-filtering#TDD#Algorithms#Antenna arrays#Computational complexity#Computer simulation#Packet networks

In this communication we present a space-frequency pre-filtering technique, for downlink time division duplex (TDD) MC-CDMA systems, where the base station is equipped with an antenna array. We show that the pre-filtering approach can considerably reduce the multiple access interference at the mobile terminals allowing to transfer a significant part of the computational complexity to the base station, using a very low complex receiver at mobile. This approach relies on the availability of the channel state information at transmission, i.e., uses the time division duplex channel reciprocity between alternative uplink and downlink to obtain the channel state information. Simulation results are presented to demonstrate the effectiveness of the proposed prefiltering algorithm. Moreover, the performance of the proposed pre-filtering algorithm is assessed in two distinct scenarios: beamforming and diversity.; European IST-2001-32620 MATRICE project (MC-CDMA Transmission Techniques for Integrated Broadband Cellular Systems); FCT

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## Pre-filtering antenna array for downlink TDD MC-CMA systems

Fonte: IEEE
Publicador: IEEE

Tipo: Conferência ou Objeto de Conferência

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#Antenna array#Downlink#MC-CDMA#Pre-filtering#TDD#Antenna arrays#Code division multiple access#Orthogonal frequency division multiplexing#Radio interference#Signal receivers#Time division multiple access

This communication deals with downlink time division duplex MC-CDMA system, and presents a frequency domain pre-filtering technique, where the base station is equipped with an antenna array. We show that the space-filtering approach proposed allows to format the transmitted signals so that the multiple access interference at the mobile terminals is reduced allowing to transfer a significant part of the computational burden to the base station, and therefore enabling the use of a very low complex receiver at mobile. This approach uses the time division duplex channel reciprocity between uplink and downlink to obtain the channel state information. Simulation results are presented to demonstrate the effectiveness of the proposed pre-filtering algorithm.; European IST-2001-32620 MATRICE project (MC-CDMA Transmission Techniques for Integrated Broadband Cellular Systems); FCT

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## Prefiltering techniques using antenna arrays for downlink tdd mc-cdma systems

Fonte: Kluwer Academic Publishers
Publicador: Kluwer Academic Publishers

Tipo: Parte de Livro

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This paper deals with downlink time division duplex MC-CDMA system, and presents a space-frequency pre-filtering technique designed for two different receivers: an advanced one and an EGC conventional receiver, where the base station e equipped with an antenna array. We show that the space-frequency pre-filtering approach proposed allows to format the transmitted signals so that the multiple access interference at mobile terminals is reduced allowing to transfer the most computational burden to the base station. Simulations results are carried out to demonstrate the effectiveness of the proposed pre-filtering schemes.; European IST-2001-32620 MATRICE project

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## Single and multiple antenna relay-assisted techniques for uplink and downlink OFDM systems

Fonte: IARIA
Publicador: IARIA

Tipo: Artigo de Revista Científica

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In this paper we propose and assess the
performance of relay-assisted schemes designed for both the
uplink and downlink OFDM based systems, using efficient
distributed space-frequency block coding protocols. We
consider the use of an antenna array at the base station and a
single antenna at the user terminal. At the relay node we
consider either single antenna or an antenna array. We assume
that some of the user terminals deployed in a certain area
could act as relaying-able terminals for the communication of
other users. Two types of relay-assisted protocols are
considered: equalize-and-forward and decode-and-forward.
The optimal maximum ratio combining coefficients are derived
for the proposed relay-assisted schemes. The performance of
these cooperative schemes is evaluated under realistic
scenarios, considering typical pedestrian scenarios based on
WiMAX specifications and using channel convolutional turbo
code. The proposed schemes are also compared against the
non-cooperative OFDM based systems. +umerical results show
that the availability of antenna arrays at the relays
significantly improves the cooperative systems performance,
which outperform the non-cooperative ones in most studied
scenarios.

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## Downlink cognitive interference alignment for heterogeneous networks

Fonte: IEEE
Publicador: IEEE

Tipo: Conferência ou Objeto de Conferência

Português

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The deployment of small-cells along a macro-cell is considered to be an effective solution in order to increase the capacity and offload the traffic from the macro-cell system. In current heterogeneous configuration with large number of deployments, it is likely that the small-cells will coexist with macro cells over the same spectrum as additional spectrum licenses are difficult and expensive to acquire. The coexistence of these cells leads to considerable interference between the two systems. In this context, we propose an underlay downlink cognitive interference alignment approach in order to remove both the interference from small-cells to the macro-cell system and from macro-cell to the small-cells. In the proposed scheme the small-cells sense the unused resources in the space dimension of the macro-cell and then communicate without interfering with the macro-cell system. The simulation results show that the secondary system does not affect the performance of primary system. The proposed scheme also provides close to optimal performance with minor overheads.

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## Enhanced Handoff Scheme for Downlink-Uplink Asymmetric Channels in Cellular Systems

Fonte: Hindawi Publishing Corporation
Publicador: Hindawi Publishing Corporation

Tipo: Artigo de Revista Científica

Publicado em 31/12/2013
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In the latest cellular networks, data services like SNS and UCC can create asymmetric packet generation rates over the downlink and uplink channels. This asymmetry can lead to a downlink-uplink asymmetric channel condition being experienced by cell edge users. This paper proposes a handoff scheme to cope effectively with downlink-uplink asymmetric channels. The proposed handoff scheme exploits the uplink channel quality as well as the downlink channel quality to determine the appropriate timing and direction of handoff. We first introduce downlink and uplink channel models that consider the intercell interference, to verify the downlink-uplink channel asymmetry. Based on these results, we propose an enhanced handoff scheme that exploits both the uplink and downlink channel qualities to reduce the handoff-call dropping probability and the service interruption time. The simulation results show that the proposed handoff scheme reduces the handoff-call dropping probability about 30% and increases the satisfaction of the service interruption time requirement about 7% under high-offered load, compared to conventional mobile-assisted handoff. Especially, the proposed handoff scheme is more efficient when the uplink QoS requirement is much stricter than the downlink QoS requirement or uplink channel quality is worse than downlink channel quality.

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## Receivers with chip-level decision feedback equalizer for CDMA downlink channels

Fonte: Institute of Electrical Electronics Engineers Inc (IEEE)
Publicador: Institute of Electrical Electronics Engineers Inc (IEEE)

Tipo: Artigo de Revista Científica

Publicado em //2004
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#Code-division multiple-access (CDMA)#decision feedback equalizer (DFE)#downlink#interference suppression#iterative technique

For the code division multiple access (CDMA) downlink channel, we investigate the decision feedback equalizer (DFE) at chip-level to effectively suppress multiple-access interference (MAI) when the spreading sequences are orthogonal. The structure of the receiver with the chip-level DFE has been investigated and the minimum mean-square error solution has been derived. Due to the inherent structure of the chip-level DFE, some iterative techniques with hard and soft decisions have been proposed. It is shown that the proposed receivers with the chip-level DFE can provide satisfactory performance. In comparison with the adaptive chip-level linear equalizer, the number of users can be doubled by using adaptive chip-level DFE at a bit-error rate of 10/sup -3/. Throughout the paper, we assume that scrambled orthogonal codes are used for spreading sequences.; Jinho Choi, Seong Rag Kim and Cheng-Chew Lim

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## Finite Backlog Effects on Downlink Scheduling

Fonte: Universidade Rice
Publicador: Universidade Rice

Tipo: Conference paper

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Conference Paper; In a multi-user downlink system, the use of channel estimates in the scheduling process can significantly improve the spectral efficiency. Recent work has shown that from a sum rate capacity standpoint, and assuming infinite queue backlogs, the optimal transmission scheme is to select the user with the largest instantaneous channel gain. A more realistic scenario is considered in this work, in which the downlink scheduling problem with finite queue backlogs is analyzed. It is shown that although time division scheduling is optimal for infinite backlogs, this is not the case for finite buffer sizes. In fact, a simple broadcast scheduler is shown to be more power efficient than the maximum rate time division scheduler under such a scenario.

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## An Efficient Circulant MIMO Equalizer for CDMA Downlink: Algorithm and VLSI Architecture

Fonte: Hindawi Publishing Corporation
Publicador: Hindawi Publishing Corporation

Tipo: Artigo de Revista Científica

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We present an efficient circulant approximation-based MIMO equalizer architecture for the CDMA downlink. This reduces the direct matrix inverse (DMI) of size (NF×NF) with O((NF)3) complexity to some FFT operations with O(NF log2(F)) complexity and the inverse of some (N×N) submatrices.We then propose parallel and pipelined VLSI architectures with Hermitian optimization and reduced-state FFT for further complexity optimization. Generic VLSI architectures are derived for the (4×4) high-order receiver from partitioned (2 × 2) submatrices. This leads to more parallel VLSI design with 3× further complexity reduction. Comparative study with both the conjugate-gradient and DMI algorithms shows very promising performance/complexity tradeoff. VLSI design space in terms of area/time efficiency is explored extensively for layered parallelism and pipelining with a Catapult C high-level-synthesis methodology.

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## WCDMA downlink capacity of cigar-shaped microcells using soft hand-over with SIR-based power control for over-ground train service

Fonte: Elsevier BV
Publicador: Elsevier BV

Tipo: Artigo de Revista Científica

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This is the author’s version of a work that was accepted for publication in Computer Communications. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Computer Communications, 31, 1 (2008) DOI: 10.1016/j.comcom.2007.10.014; In this paper, the downlink sector capacity of a cigar-shaped microcells using wideband code-division multiple-access (WCDMA) with soft hand-over (SHO) mode is analyzed. The two-slope propagation loss with log-normal shadowing is used in the analysis where a model of eight cigar-shaped microcells is utilized to calculate the downlink sector capacity. The performance of the downlink is studied for different sector radii, standard deviations of the shadowing and propagation exponents. It is found that, for a sector range higher than 940 m, increasing the sector range will reduce the downlink sector capacity. Also it is found that increasing the value of the propagation parameters will reduce the downlink sector capacity. In many cases, the downlink sector capacity will be code limited since the theoretical downlink sector capacity is higher than the number of codes assigned to each sector. The high theoretical downlink sector capacity is due to the low value (0.06–0.1) of the WCDMA orthogonality factor of rural zone microcells.

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## Implementation of Iterative Channel Equalization for MIMO Systems in WCDMA Downlink

Fonte: Universidade Rice
Publicador: Universidade Rice

Tipo: Conference paper; Text; Text

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#MIMO#WCDMA#Downlink#Equalization#Conjugate Gradient#1xEV-DV#fixed-point#MIMO#WCDMA#Downlink#Equalization

Conference Paper; In downlink transmission, channel multipaths destroy the orthogonality between users causing Multiple Access Interference (MAI). In order to restore the orthogonality between the users, chip-level channel equalization based on the iterative conjugate-gradient (CG) algorithm has been proposed in [Heikkilla '02]. We extend this approach to the multiple transmit antenna case and propose 16-bit fixed point implementation. Simulations show the robustness of the fixed point implementation of the proposed algorithm. Moreover, this approach outperforms RAKE receiver in all cases.; Texas Instruments; Nokia; National Science Foundation

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## Comparison between Performances of Channel Estimation Techniques for CP-LTE and ZP-LTE Downlink Systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 09/08/2012
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In this paper, we propose to evaluate the performance of channel estimation
techniques for Long Term Evolution (LTE) Downlink systems based on Zero Padding
technique (ZP) instead of Cyclic Prefixing (CP). LTE Downlink system is a
multiuser system based on a MIMO-OFDMA technology. Usually, in OFDM systems, a
guard interval is inserted in order to mitigate both inter-carrier interference
(ICI) and inter-symbol interference (ISI). LTE Downlink systems are based on
CP-OFDM technique which consists of a copy a last OFDM symbols inserted at the
beginning of each transmitted OFDM symbol. Although this technique shows good
performances, the CP-LTE system suffers from a power efficiency loss.With the
number of present OFDM symbols in LTE Downlink radio frame, the bandwidth loss
becomes more important. Instead of CP, we propose to evaluate the performance
of ZP-LTE systems in order to avoid the power efficiency .In this paper, we
interest to evaluate the performance of channel estimation techniques for the
two LTE Downlink systems. Simulations results show that although ZP-LTE systems
outperform CP-LTE Downlink systems in terms of power efficiency, the CP-LTE
systems show better performance than ZP-LTE systems and especially for high SNR
values. MATLAB Monte-Carlo simulations are used to evaluate the performance of
LS...

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## Uplink Downlink Rate Balancing in Cooperating Cellular Networks

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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Broadcast MIMO techniques can significantly increase the throughput in the
downlink of cellular networks, at the price of channel state information (CSI)
feedback from the mobiles, sent over the uplink. Thus, it creates a mechanism
that can tradeoff some uplink capacity for increased downlink capacity. In this
work we quantify this tradeoff and study the exchange ratio between the
feedback rate (over the uplink) and the downlink rate. We study both finite and
infinite networks, and show that for high enough (but finite) SNR, the uplink
rate can be exchanged for increased downlink rate with a favorable exchange
ratio. This exchange ratio is an increasing function of the channel coherence
time, and a decreasing function of the number of measured base stations. We
also show that devoting a constant fraction of the uplink to CSI feedback can
increase the downlink multiplexing gain continuously from 0 to 1, in finite
networks. On the other hand, in infinite networks (with infinite connectivity)
our bounds can only show doubly logarithmic scaling of the rate with SNR. The
presented results prove that the adaptation of the feedback rate can control
the balance between the uplink and downlink rates. This capability is very
important in modern cellular networks...

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## Degrees of Freedom of Uplink-Downlink Multiantenna Cellular Networks

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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An uplink-downlink two-cell cellular network is studied in which the first
base station (BS) with $M_1$ antennas receives independent messages from its
$N_1$ serving users, while the second BS with $M_2$ antennas transmits
independent messages to its $N_2$ serving users. That is, the first and second
cells operate as uplink and downlink, respectively. Each user is assumed to
have a single antenna. Under this uplink-downlink setting, the sum degrees of
freedom (DoF) is completely characterized as the minimum of
$(N_1N_2+\min(M_1,N_1)(N_1-N_2)^++\min(M_2,N_2)(N_2-N_1)^+)/\max(N_1,N_2)$,
$M_1+N_2,M_2+N_1$, $\max(M_1,M_2)$, and $\max(N_1,N_2)$, where $a^+$ denotes
$\max(0,a)$. The result demonstrates that, for a broad class of network
configurations, operating one of the two cells as uplink and the other cell as
downlink can strictly improve the sum DoF compared to the conventional uplink
or downlink operation, in which both cells operate as either uplink or
downlink. The DoF gain from such uplink-downlink operation is further shown to
be achievable for heterogeneous cellular networks having hotspots and with
delayed channel state information.; Comment: 22 pages, 11 figures, in revision for IEEE Transactions on
Information Theory

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## Linear Transceiver design for Downlink Multiuser MIMO Systems: Downlink-Interference Duality Approach

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 25/11/2013
Português

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This paper considers linear transceiver design for downlink multiuser
multiple-input multiple-output (MIMO) systems. We examine different transceiver
design problems. We focus on two groups of design problems. The first group is
the weighted sum mean-square-error (WSMSE) (i.e., symbol-wise or user-wise
WSMSE) minimization problems and the second group is the minimization of the
maximum weighted mean-squareerror (WMSE) (symbol-wise or user-wise WMSE)
problems. The problems are examined for the practically relevant scenario where
the power constraint is a combination of per base station (BS) antenna and per
symbol (user), and the noise vector of each mobile station is a zero-mean
circularly symmetric complex Gaussian random variable with arbitrary covariance
matrix. For each of these problems, we propose a novel downlink-interference
duality based iterative solution. Each of these problems is solved as follows.
First, we establish a new mean-square-error (MSE) downlink-interference
duality. Second, we formulate the power allocation part of the problem in the
downlink channel as a Geometric Program (GP). Third, using the duality result
and the solution of GP, we utilize alternating optimization technique to solve
the original downlink problem. For the first group of problems...

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## Interference Management with Partial Uplink/Downlink Spectrum Overlap

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 19/11/2015
Português

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Simultaneous reuse of spectral resources by uplink and downlink, denoted as
in-band full duplex (FD) communication, is promoted to double the spectral
efficiency when compared to its half-duplex (HD) counterpart. Interference
management, however, remains challenging in FD cellular networks, especially
when high disparity between uplink and downlink transmission powers exists. The
uplink performance can be particularly deteriorated when operating on channels
that are simultaneously occupied with downlink transmission. This paper
considers a cellular wireless system with partial spectrum overlap between the
downlink and uplink. The performance of the system becomes, therefore, a
function of the overlap fraction, as well as the power level of both the uplink
and downlink transmissions. The paper considers the problem of maximizing an
overall network utility to find the uplink/downlink transmission powers and the
spectrum overlap fraction between the uplink and downlink spectrum in each
cell, and proposes solving the problem using interior point method. Simulations
results confirm the vulnerability of the uplink performance to the FD
operation, and show the superiority of the proposed scheme over the FD and HD
schemes. The results further show that explicit uplink and downlink performance
should be considered for efficient design of cellular networks with overlapping
uplink/downlink resources.

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## Joint Rate and SINR Coverage Analysis for Decoupled Uplink-Downlink Biased Cell Associations in HetNets

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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Load balancing by proactively offloading users onto small and otherwise
lightly-loaded cells is critical for tapping the potential of dense
heterogeneous cellular networks (HCNs). Offloading has mostly been studied for
the downlink, where it is generally assumed that a user offloaded to a small
cell will communicate with it on the uplink as well. The impact of coupled
downlink-uplink offloading is not well understood. Uplink power control and
spatial interference correlation further complicate the mathematical analysis
as compared to the downlink. We propose an accurate and tractable model to
characterize the uplink SINR and rate distribution in a multi-tier HCN as a
function of the association rules and power control parameters. Joint
uplink-downlink rate coverage is also characterized. Using the developed
analysis, it is shown that the optimal degree of channel inversion (for uplink
power control) increases with load imbalance in the network. In sharp contrast
to the downlink, minimum path loss association is shown to be optimal for
uplink rate. Moreover, with minimum path loss association and full channel
inversion, uplink SIR is shown to be invariant of infrastructure density. It is
further shown that a decoupled association---employing differing association
strategies for uplink and downlink---leads to significant improvement in joint
uplink-downlink rate coverage over the standard coupled association in HCNs.

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