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## Novas tecnicas de processamento espaço-temporal em transmissão conciliando diversidade e beamforming; New methods for transmit space-time processing combining diversity and beamforming

Fonte: Biblioteca Digital da Unicamp
Publicador: Biblioteca Digital da Unicamp

Tipo: Tese de Doutorado
Formato: application/pdf

Publicado em 01/11/2006
Português

Relevância na Pesquisa

59.00839%

#Processamento de sinal adaptativo#Sistemas de comunicação movel#Antenas ajustaveis#Telecomunicações#Smart antennas#Adaptive signal processing#Mobile communications systems#Telecommunications

O presente trabalho trata da utilização, em transmissão, de um arranjo de antenas na estação rádio-base de um sistema de comunicação celular. Na recepção, as soluções para explorar o arranjo são atualmente bem estabelecidas na literatura. Por outro lado, na transmissão, o problema se mantém aberto. Duas abordagens são possíveis: explorar o arranjo de antenas em beamforming ou em diversidade. Essas duas abordagens se opõem pelas hipóteses sobre a correlação dos canais, o que implica um maior ou menor espaçamento entre as antenas, de acordo com o ambiente de propagação. Na prática, essas hipóteses são muito difíceis de se respeitar. Nesta dissertação, pretendemos tratar esta questão na sua globalidade, conciliando diversidade e beamforming para melhor explorar o arranjo de antenas. Consideramos o contexto monousuário, assim como o caso multiusuário. No caso monousuário, propomos uma estrutura de transmissão composta por uma técnica de diversidade de transmissão clássica aplicada a antenas virtuais diretivas e idealmente independentes. Essas antenas virtuais são fabricadas por meio de filtros puramente espaciais aplicados às antenas reais. O conjunto desses filtros é chamado precoder e se intercala entre a diversidade de transmissão e o arranjo de antenas utilizado em transmissão. Esse precoder desempenha um duplo papel...

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## Utilização conjunta de técnicas de formtação de feixe, diversidade espacial e equalização na recepção de sinais

Fonte: Florianópolis
Publicador: Florianópolis

Tipo: Dissertação de Mestrado
Formato: 109 p.| il., grafs., tabs.

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#Engenharia eletrica#Sistemas de comunicação sem fio#Ondas de radio -#Propagacao#Processamento de sinais

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica.; Nesta dissertação, investiga-se a utilização conjunta de técnicas de formatação de feixe, diversidade espacial e equalização de canal para recepção de sinais em um sistema de comunicação sem fio. Utiliza-se um conjunto de arranjos de antenas (dois arranjos lineares) para obter tanto diversidade espacial como formatação de feixe. As antenas em cada arranjo são espaçadas segundo o critério de filtragem espacial (formatação de feixe), enquanto que os arranjos são espaçados buscando satisfazer o critério de diversidade espacial. Com a diversidade espacial, busca-se combater o desvanecimento plano, enquanto que com a formatação de feixe o desvanecimento seletivo em frequência. Tais fenômenos estão sempre presentes nos sistemas de comunicação sem fio, devido à propagação por múltiplos percursos do sinal transmitido. Três técnicas de combinação dos sinais na saída dos conformadores são apresentadas: seleção - escolhendo o sinal com menor ISI; soma não ponderada; e soma ponderada - enfatizando o sinal de maior potência. Um equalizador DFE é empregado na saída da técnica de combinação para mitigar a ISI residual. A estrutura do receptor em estudo é apresentada para operar de forma adaptativa...

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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

Português

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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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## Multi-sensor frequency domain multiple access interference canceller for DS-CDMA systems

Fonte: John Wiley and Sons
Publicador: John Wiley and Sons

Tipo: Artigo de Revista Científica

Português

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Direct sequence code division multiple access (DS-CDMA) signals exhibit cyclostationary properties which imply a redundancy between frequency components separated by multiples of the symbol rate. In this paper a multiple access interference canceller (frequency shift canceller) that explores this property is presented. This linear frequency domain canceller operates on the spread signal in such way that the interference and noise at its output is minimized (minimum mean squared error criterion). The frequency shift canceller (FSC) performance was evaluated for a UMTS-TDD scenario and multi-sensor configurations, where the cases of diversity and beamforming were considered. All these configurations are evaluated concatenated with a parallel interference canceller (PIC-2D). The results are benchmarked against the performance of the conventional RAKE-2D detector, the conventional PIC-2D detector and single user scenario, and we observe considerable performance gains with the FSC especially for the diversity case and a performance close to the single user case when it was evaluated jointly with PIC-2D.

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## MIMO processing techniques for 4G systems; Técnicas de processamento MIMO para sistemas 4G

Fonte: Universidade de Aveiro
Publicador: Universidade de Aveiro

Tipo: Dissertação de Mestrado

Português

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#Engenharia electrónica#Comunicações móveis#Comunicações de acesso múltiplo#Multiplexagem#Sistemas de antenas#4G#LTE#MIMO#Diversidade#Multiplexagem Espacial#Beamforming

The theme of this dissertation work is focused in one of the key technologies
specified in the last 4G cellular standards, which are the MIMO systems. In this
context, the MIMO (Multiple Input Multiple Output) acronym is used to define a
communication system where multiple antennas are used, therefore using this
type of systems jointly with specific signal processing techniques, we can use
the spatial dimension in order to generate multiplexing, diversity and
beamforming gains.
The aim of this work is to show the type of signal processing techniques that
must be applied in order to achieve the gains referenced above, as well the
optimal channel conditions in which these gains are maximized.Therefore,
beyond the presentation of the theoretical background related with these type of
techniques, we will present the MIMO transmission modes specified on 4G-LTE,
having not only the aiming of show the type of practical constraints verified in a
practical implementation, but also present the solutions used to solve that kind
of constraints.
In the last part of this work is presented a simulation platform implemented for
one of the spatial multiplexing modes specified on LTE, which is the mode 4.
The numerical results obtained allowed to see the advantage in the use of SIC
(Successive Interference Cancelation) equalizers for multi-layer transmission
modes...

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## An Innovations-Based Noise Cancelling Technique on Inverse Kepstrum Whitening Filter and Adaptive FIR Filter in Beamforming Structure

Fonte: Molecular Diversity Preservation International (MDPI)
Publicador: Molecular Diversity Preservation International (MDPI)

Tipo: Artigo de Revista Científica

Publicado em 29/06/2011
Português

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This paper presents an acoustic noise cancelling technique using an inverse kepstrum system as an innovations-based whitening application for an adaptive finite impulse response (FIR) filter in beamforming structure. The inverse kepstrum method uses an innovations-whitened form from one acoustic path transfer function between a reference microphone sensor and a noise source so that the rear-end reference signal will then be a whitened sequence to a cascaded adaptive FIR filter in the beamforming structure. By using an inverse kepstrum filter as a whitening filter with the use of a delay filter, the cascaded adaptive FIR filter estimates only the numerator of the polynomial part from the ratio of overall combined transfer functions. The test results have shown that the adaptive FIR filter is more effective in beamforming structure than an adaptive noise cancelling (ANC) structure in terms of signal distortion in the desired signal and noise reduction in noise with nonminimum phase components. In addition, the inverse kepstrum method shows almost the same convergence level in estimate of noise statistics with the use of a smaller amount of adaptive FIR filter weights than the kepstrum method, hence it could provide better computational simplicity in processing. Furthermore...

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## Transmit Diversity with Channel Feedback

Fonte: Universidade Rice
Publicador: Universidade Rice

Tipo: Conference paper

Português

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Conference Paper; Transmit diversity in the presence of channel feedback at the transmitter is analyzed in this paper. We first consider perfect channel feedback and summarize the beamforming solution which minimizes the codeword error probability. We note that the error probability minimizing scheme is different from the mutual information maximizing scheme. We then present a scheme with partial channel feedback in the form of relative phases of channel vectors. This scheme achieves performance comparable to the beamforming with much less information about the channel, which in turn requires less resources for feedback. The new scheme presented in this paper is a generalization of a well known scheme for two transmit and one receive antenna, using the phase difference of the channel coefficients.

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## On Beamforming with Finite Rate Feedback in Multiple Antenna Systems

Fonte: Universidade Rice
Publicador: Universidade Rice

Tipo: Artigo de Revista Científica

Português

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Journal Paper; In this paper, we study a multiple antenna system where the transmitter is equipped with quantized information about instantaneous channel realizations. Assuming that the transmitter uses the quantized information for beamforming, we derive a universal lower bound on the outage probability for any finite set of beamformers. The universal lower bound provides a concise characterization of the gain with each additional bit of feedback information regarding the channel. Using the bound, it is shown that finite information systems approach the perfect information case as (t-1)2

^{-B/(t-1)}, where*B*is the number of feedback bits and*t*is the number of transmit antennas. The geometrical bounding technique, used in the proof of the lower bound, also leads to a design criterion for good beamformers, whose outage performance approaches the lower bound. The design criterion minimizes the maximum inner product between any two beamforming vectors in the beamformer codebook, and is equivalent to the problem of designing unitary space time codes under certain conditions. Finally, we show that good beamformers are good packings of 2-dimensional subspaces in a 2*t*-dimensional real Grassmannian manifold with chordal distance as the metric.Link permanente para citações:

## Distributed Beamforming in Wireless Multiuser Relay-Interference Networks with Quantized Feedback

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/07/2010
Português

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We study quantized beamforming in wireless amplify-and-forward
relay-interference networks with any number of transmitters, relays, and
receivers. We design the quantizer of the channel state information to minimize
the probability that at least one receiver incorrectly decodes its desired
symbol(s). Correspondingly, we introduce a generalized diversity measure that
encapsulates the conventional one as the first-order diversity. Additionally,
it incorporates the second-order diversity, which is concerned with the
transmitter power dependent logarithmic terms that appear in the error rate
expression. First, we show that, regardless of the quantizer and the amount of
feedback that is used, the relay-interference network suffers a second-order
diversity loss compared to interference-free networks. Then, two different
quantization schemes are studied: First, using a global quantizer, we show that
a simple relay selection scheme can achieve maximal diversity. Then, using the
localization method, we construct both fixed-length and variable-length local
(distributed) quantizers (fLQs and vLQs). Our fLQs achieve maximal first-order
diversity, whereas our vLQs achieve maximal diversity. Moreover, we show that
all the promised diversity and array gains can be obtained with arbitrarily low
feedback rates when the transmitter powers are sufficiently large. Finally...

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## Optimized Training for Net Energy Maximization in Multi-Antenna Wireless Energy Transfer over Frequency-Selective Channel

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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This paper studies the training design problem for multiple-input
single-output (MISO) wireless energy transfer (WET) systems in
frequency-selective channels, where the frequency-diversity and
energy-beamforming gains can be both reaped to maximize the transferred energy
by efficiently learning the channel state information (CSI) at the energy
transmitter (ET). By exploiting channel reciprocity, a new two-phase channel
training scheme is proposed to achieve the diversity and beamforming gains,
respectively. In the first phase, pilot signals are sent from the energy
receiver (ER) over a selected subset of the available frequency sub-bands,
through which the ET determines a certain number of "strongest" sub-bands with
largest antenna sum-power gains and sends their indices to the ER. In the
second phase, the selected sub-bands are further trained by the ER, so that the
ET obtains a refined estimate of the corresponding MISO channels to implement
energy beamforming for WET. A training design problem is formulated and
optimally solved, which takes into account the channel training overhead by
maximizing the net harvested energy at the ER, defined as the average harvested
energy offset by that consumed in the two-phase training. Moreover...

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## On the feasibility of beamforming in millimeter wave communication systems with multiple antenna arrays

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 20/10/2014
Português

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The use of the millimeter (mm) wave spectrum for next generation (5G) mobile
communication has gained significant attention recently. The small carrier
wavelengths at mmwave frequencies enable synthesis of compact antenna arrays,
providing beamforming gains that compensate the increased propagation losses.
In this work, we investigate the feasibility of employing multiple antenna
arrays to obtain diversity/multiplexing gains in mmwave systems, where each of
the arrays is capable of beamforming independently. Considering a codebook
based beamforming system (e.g., to facilitate limited feedback), we observe
that the complexity of \emph{jointly} optimizing the beamforming directions
across the multiple arrays is highly prohibitive, even for very reasonable
system parameters. To overcome this bottleneck, we develop reduced complexity
algorithms for optimizing the choice of beamforming directions, premised on the
sparse multipath structure of the mmwave channel. Specifically, we reduce the
cardinality of the joint beamforming search space, by restricting attention to
a small set of dominant candidate directions. To obtain the set of dominant
directions, we develop two complementary approaches: (a) based on computation
of a novel spatial power metric; a detailed analysis of this metric shows that...

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## Network Beamforming Using Relays with Perfect Channel Information

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 07/04/2008
Português

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This paper is on beamforming in wireless relay networks with perfect channel
information at relays, the receiver, and the transmitter if there is a direct
link between the transmitter and receiver. It is assumed that every node in the
network has its own power constraint. A two-step amplify-and-forward protocol
is used, in which the transmitter and relays not only use match filters to form
a beam at the receiver but also adaptively adjust their transmit powers
according to the channel strength information. For a network with any number of
relays and no direct link, the optimal power control is solved analytically.
The complexity of finding the exact solution is linear in the number of relays.
Our results show that the transmitter should always use its maximal power and
the optimal power used at a relay is not a binary function. It can take any
value between zero and its maximum transmit power. Also, this value depends on
the quality of all other channels in addition to the relay's own channels.
Despite this coupling fact, distributive strategies are proposed in which, with
the aid of a low-rate broadcast from the receiver, a relay needs only its own
channel information to implement the optimal power control. Simulated
performance shows that network beamforming achieves the maximal diversity and
outperforms other existing schemes. Then...

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## Interference-Nulling Time-Reversal Beamforming for mm-Wave Massive MIMO in Multi-User Frequency-Selective Indoor Channels

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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Millimeter wave (mm-wave) and massive MIMO have been proposed for next
generation wireless systems. However, there are many open problems for the
implementation of those technologies. In particular, beamforming is necessary
in mm-wave systems in order to counter high propagation losses. However,
conventional beamsteering is not always appropriate in rich scattering
multipath channels with frequency selective fading, such as those found in
indoor environments. In this context, time-reversal (TR) is considered a
promising beamforming technique for such mm-wave massive MIMO systems. In this
paper, we analyze a baseband TR beamforming system for mm-wave multi-user
massive MIMO. We verify that, as the number of antennas increases, TR yields
good equalization and interference mitigation properties, but inter-user
interference (IUI) remains a main impairment. Thus, we propose a novel
technique called interference-nulling TR (INTR) to minimize IUI. We evaluate
numerically the performance of INTR and compare it with conventional TR and
equalized TR beamforming. We use a 60 GHz MIMO channel model with spatial
correlation based on the IEEE 802.11ad SISO NLoS model. We demonstrate that
INTR outperforms conventional TR with respect to average BER per user and
achievable sum rate under diverse conditions...

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## Collaborative Randomized Beamforming for Phased Array Radio Interferometers

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 14/11/2014
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The Square Kilometre Array (SKA) will form the largest radio telescope ever
built and such a huge instrument in the desert poses enormous engineering and
logistic challenges. Algorithmic and architectural breakthroughs are needed.
Data is collected and processed in groups of antennas before transport for
central processing. This processing includes beamforming, primarily so as to
reduce the amount of data sent. The principal existing technique points to a
region of interest independently of the sky model and how the other stations
beamform.
We propose a new collaborative beamforming algorithm in order to maximize
information captured at the stations (thus reducing the amount of data
transported). The method increases the diversity in measurements through
randomized beam- forming. We demonstrate through numerical simulation the
effectiveness of the method. In particular, we show that randomized beamforming
can achieve the same image quality while producing 40% less data when compared
to the prevailing method matched beamforming.; Comment: 9 pages, 8 figures

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## Diversity Analysis of Bit-Interleaved Coded Multiple Beamforming with Orthogonal Frequency Division Multiplexing

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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For broadband wireless communication systems, Orthogonal Frequency Division
Multiplexing (OFDM) has been combined with Multi-Input Multi-Output (MIMO)
techniques. Bit-Interleaved Coded Multiple Beamforming (BICMB) can achieve both
spatial diversity and spatial multiplexing for flat fading MIMO channels. For
frequency selective fading MIMO channels, BICMB with OFDM (BICMB-OFDM) can be
applied to achieve both spatial diversity and multipath diversity, making it an
important technique. However, analyzing the diversity of BICMB-OFDM is a
challenging problem. In this paper, the diversity analysis of BICMB-OFDM is
carried out. First, the maximum achievable diversity is derived and a full
diversity condition RcSL <= 1 is proved, where Rc, S, and L are the code rate,
the number of parallel steams transmitted at each subcarrier, and the number of
channel taps, respectively. Then, the performance degradation due to the
correlation among subcarriers is investigated. Finally, the subcarrier grouping
technique is employed to combat the performance degradation and provide
multi-user compatibility.; Comment: accepted to journal

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## Full-Diversity Precoding Design of Bit-Interleaved Coded Multiple Beamforming with Orthogonal Frequency Division Multiplexing

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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Multi-Input Multi-Output (MIMO) techniques have been incorporated with
Orthogonal Frequency Division Multiplexing (OFDM) for broadband wireless
communication systems. Bit-Interleaved Coded Multiple Beamforming (BICMB) can
achieve both spatial diversity and spatial multiplexing for flat fading MIMO
channels. For frequency selective fading MIMO channels, BICMB with OFDM
(BICMB-OFDM) can be employed to provide both spatial diversity and multipath
diversity, making it an important technique. In our previous work, the
subcarrier grouping technique was applied to combat the negative effect of
subcarrier correlation. It was also proved that full diversity of BICMB-OFDM
with Subcarrier Grouping (BICMB-OFDM-SG) can be achieved within the condition
R_cSL<=1, where R_c, S, and L are the code rate, the number of parallel streams
at each subcarrier, and the number of channel taps, respectively. The full
diversity condition implies that if S increases, R_c may have to decrease to
maintain full diversity. As a result, increasing the number of parallel streams
may not improve the total transmission rate. In this paper, the precoding
technique is employed to overcome the full diversity restriction issue of
R_cSL<=1 for BICMB-OFDM-SG. First, the diversity analysis of precoded
BICMB-OFDM-SG is carried out. Then...

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## Variable-Length Channel Quantizers for Maximum Diversity and Array Gains

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 27/01/2013
Português

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We consider a $t \times 1$ multiple-antenna fading channel with quantized
channel state information at the transmitter (CSIT). Our goal is to maximize
the diversity and array gains that are associated with the symbol error rate
(SER) performance of the system. It is well-known that for both beamforming and
precoding strategies, finite-rate fixed-length quantizers (FLQs) cannot achieve
the full-CSIT diversity and array gains. In this work, for any function
$f(P)\in\omega(1)$, we construct variable-length quantizers (VLQs) that can
achieve these full-CSIT gains with rates $1+(f(P) \log P)/P$ and $1+f(P)/P^t$
for the beamforming and precoding strategies, respectively, where $P$ is the
power constraint of the transmitter. We also show that these rates are the best
possible up to $o(1)$ multipliers in their $P$-dependent terms. In particular,
although the full-CSIT SER is not achievable at any (even infinite) feedback
rate, the full-CSIT diversity and array gains can be achieved with a feedback
rate of 1 bit per channel state asymptotically.

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## Bit-Interleaved Coded Multiple Beamforming with Perfect Coding

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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When the Channel State Information (CSI) is known by both the transmitter and
the receiver, beamforming techniques employing Singular Value Decomposition
(SVD) are commonly used in Multiple-Input Multiple-Output (MIMO) systems.
Without channel coding, there is a trade-off between full diversity and full
multiplexing. When channel coding is added, both of them can be achieved as
long as the code rate Rc and the number of employed subchannels S satisfy the
condition RcS<=1. By adding a properly designed constellation precoder, both
full diversity and full multiplexing can be achieved for both uncoded and coded
systems with the trade-off of a higher decoding complexity, e.g., Fully
Precoded Multiple Beamforming (FPMB) and Bit-Interleaved Coded Multiple
Beamforming with Full Precoding (BICMB-FP) without the condition RcS<=1.
Recently discovered Perfect Space-Time Block Code (PSTBC) is a full-rate
full-diversity space-time code, which achieves efficient shaping and high
coding gain for MIMO systems. In this paper, a new technique, Bit-Interleaved
Coded Multiple Beamforming with Perfect Coding (BICMB-PC), is introduced.
BICMB-PC transmits PSTBCs through convolutional coded SVD systems. Similar to
BICMB-FP, BICMB-PC achieves both full diversity and full multiplexing...

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## Optimized Training Design for Multi-Antenna Wireless Energy Transfer in Frequency-Selective Channel

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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This paper studies the optimal training design for a multiple-input
single-output (MISO) wireless energy transfer (WET) system in
frequency-selective channels, where the frequency-diversity and
energy-beamforming gains can be both achieved by properly learning the channel
state information (CSI) at the energy transmitter (ET). By exploiting channel
reciprocity, a two-phase channel training scheme is proposed to achieve the
diversity and beamforming gains, respectively. In the first phase, pilot
signals are sent from the energy receiver (ER) over a selected subset of the
available frequency sub-bands, through which the sub-band that exhibits the
largest sum-power over all the antennas at the ET is determined and its index
is sent back to the ER. In the second phase, the selected sub-band is further
trained for the ET to estimate the multi-antenna channel and implement energy
beamforming. We propose to maximize the net energy harvested at the ER, which
is the total harvested energy offset by that used for the two-phase channel
training. The optimal training design, including the number of sub-bands
trained and the energy allocated for each of the two phases, is derived.; Comment: submitted for possible conference publication

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## A Novel Method of Beamforming to Improve the Space Diversity

Fonte: Instituto Politécnico Nacional, Centro de Innovación y Desarrollo Tecnológico en Cómputo
Publicador: Instituto Politécnico Nacional, Centro de Innovación y Desarrollo Tecnológico en Cómputo

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/12/2012
Português

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At present, the systems of mobile communications demand major capacity in the services, therefore optimum space diversity is needed. In this paper, we propose a new method of beam-forming to improve the space diversity and achieve frequency reuse. Our proposal consists in solving a system of linear equations from an 8-elements linear antenna array that increases the size of the side lobes. This method is compared with the algorithm of Dolph-Chebyshev. Our method shows competitive results in increasing the space diversity.

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