9,220 research outputs found
Energy efficient transmitter design with compact antenna for future wireless communication systems
This thesis explores a novel technique for transceiver design in future wireless systems, which
is cloud radio access networks (CRANs) with single radio frequency (RF) chain antennas at
each remote radio head (RRH).
This thesis seeks to make three contributions.
Firstly, it proposes a novel algorithm to solve the oscillatory/unstable behaviour of electronically
steerable parasitic array radiators (ESPAR) when it provides multi-antenna functionality
with a single RF chain. This thesis formulates an optimization problem and derives closed-form
expressions when calculating the configuration of an ESPAR antenna (EA) for arbitrary
signals transmission. This results in simplified processing at the transmitter. The results
illustrate that the EA transmitter, when utilizing novel closed-form expressions, shows significant
improvement over the performance of the EA transmitter without any pre-processing.
It performs at nearly the same symbol error rate (SER) as standard multiple antenna systems.
Secondly, this thesis illustrates how a practical peak power constraint can be put into an
EA transceiver design. In an EA, all the antenna elements are fed centrally by a single power
amplifier. This makes it more probable that during use, the power amplifier reaches maximum
power during transmission. Considering limited power availability, this thesis proposes a new
algorithm to achieve stable signal transmission.
Thirdly, this thesis shows that an energy efficiency (EE) optimization problem can be formulated
and solved in CRANs that deploy single RF chain antennas at RRHs. The closed-form
expressions of the precoder and power allocation schemes to transmit desired signals are obtained
to maximise EE for both single-user and multi-user systems. The results show that
the CRANs with single RF chain antennas provide superior EE performance compared to the
standard multiple antenna based systems
PAR-Aware Large-Scale Multi-User MIMO-OFDM Downlink
We investigate an orthogonal frequency-division multiplexing (OFDM)-based
downlink transmission scheme for large-scale multi-user (MU) multiple-input
multiple-output (MIMO) wireless systems. The use of OFDM causes a high
peak-to-average (power) ratio (PAR), which necessitates expensive and
power-inefficient radio-frequency (RF) components at the base station. In this
paper, we present a novel downlink transmission scheme, which exploits the
massive degrees-of-freedom available in large-scale MU-MIMO-OFDM systems to
achieve low PAR. Specifically, we propose to jointly perform MU precoding, OFDM
modulation, and PAR reduction by solving a convex optimization problem. We
develop a corresponding fast iterative truncation algorithm (FITRA) and show
numerical results to demonstrate tremendous PAR-reduction capabilities. The
significantly reduced linearity requirements eventually enable the use of
low-cost RF components for the large-scale MU-MIMO-OFDM downlink.Comment: To appear in IEEE Journal on Selected Areas in Communication
Signal and System Design for Wireless Power Transfer : Prototype, Experiment and Validation
A new line of research on communications and signals design for Wireless
Power Transfer (WPT) has recently emerged in the communication literature.
Promising signal strategies to maximize the power transfer efficiency of WPT
rely on (energy) beamforming, waveform, modulation and transmit diversity, and
a combination thereof. To a great extent, the study of those strategies has so
far been limited to theoretical performance analysis. In this paper, we study
the real over-the-air performance of all the aforementioned signal strategies
for WPT. To that end, we have designed, prototyped and experimented an
innovative radiative WPT architecture based on Software-Defined Radio (SDR)
that can operate in open-loop and closed-loop (with channel acquisition at the
transmitter) modes. The prototype consists of three important blocks, namely
the channel estimator, the signal generator, and the energy harvester. The
experiments have been conducted in a variety of deployments, including
frequency flat and frequency selective channels, under static and mobility
conditions. Experiments highlight that a channeladaptive WPT architecture based
on joint beamforming and waveform design offers significant performance
improvements in harvested DC power over conventional
single-antenna/multiantenna continuous wave systems. The experimental results
fully validate the observations predicted from the theoretical signal designs
and confirm the crucial and beneficial role played by the energy harvester
nonlinearity.Comment: Accepted to IEEE Transactions on Wireless Communication
Waveform design for Wireless Power Transfer
Far-field Wireless Power Transfer (WPT) has attracted significant attention in recent years. Despite the rapid progress, the emphasis of the research community in the last decade has remained largely concentrated on improving the design of energy harvester (so-called rectenna) and has left aside the effect of transmitter design. In this paper, we study the design of transmit waveform so as to enhance the dc power at the output of the rectenna. We derive a tractable model of the nonlinearity of the rectenna and compare with a linear model conventionally used in the literature. We then use those models to design novel multisine waveforms that are adaptive to the channel state information (CSI). Interestingly, while the linear model favours narrowband transmission with all the power allocated to a single frequency, the nonlinear model favours a power allocation over multiple frequencies. Through realistic simulations, waveforms designed based on the nonlinear model are shown to provide significant gains (in terms of harvested dc power) over those designed based on the linear model and over nonadaptive waveforms. We also compute analytically the theoretical scaling laws of the harvested energy for various waveforms as a function of the number of sinewaves and transmit antennas. Those scaling laws highlight the benefits of CSI knowledge at the transmitter in WPT and of a WPT design based on a nonlinear rectenna model over a linear model. Results also motivate the study of a promising architecture relying on large-scale multisine multiantenna waveforms for WPT. As a final note, results stress the importance of modeling and accounting for the nonlinearity of the rectenna in any system design involving wireless power
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