2,425 research outputs found
Simultaneous Transmission and Reception: Algorithm, Design and System Level Performance
Full Duplex or Simultaneous transmission and reception (STR) in the same
frequency at the same time can potentially double the physical layer capacity.
However, high power transmit signal will appear at receive chain as echoes with
powers much higher than the desired received signal. Therefore, in order to
achieve the potential gain, it is imperative to cancel these echoes. As these
high power echoes can saturate low noise amplifier (LNA) and also digital
domain echo cancellation requires unrealistically high resolution
analog-to-digital converter (ADC), the echoes should be cancelled or suppressed
sufficiently before LNA. In this paper we present a closed-loop echo
cancellation technique which can be implemented purely in analogue domain. The
advantages of our method are multiple-fold: it is robust to phase noise, does
not require additional set of antennas, can be applied to wideband signals and
the performance is irrelevant to radio frequency (RF) impairments in transmit
chain. Next, we study a few protocols for STR systems in carrier sense multiple
access (CSMA) network and investigate MAC level throughput with realistic
assumptions in both single cell and multiple cells. We show that STR can reduce
hidden node problem in CSMA network and produce gains of up to 279% in maximum
throughput in such networks. Finally, we investigate the application of STR in
cellular systems and study two new unique interferences introduced to the
system due to STR, namely BS-BS interference and UE-UE interference. We show
that these two new interferences will hugely degrade system performance if not
treated appropriately. We propose novel methods to reduce both interferences
and investigate the performances in system level.Comment: 20 pages. This manuscript will appear in the IEEE Transactions on
Wireless Communication
A 6-12 GHz Analogue Lag-Correlator for Radio Interferometry
Aims: We describe a 6-12 GHz analogue correlator that has been developed for
use in radio interferometers. Methods: We use a lag-correlator technique to
synthesis eight complex spectral channels. Two schemes were considered for
sampling the cross-correlation function, using either real or complex
correlations, and we developed prototypes for both of them. We opted for the
``add and square'' detection scheme using Schottky diodes over the more
commonly used active multipliers because the stability of the device is less
critical. Results: We encountered an unexpected problem, in that there were
errors in the lag spacings of up to ten percent of the unit spacing. To
overcome this, we developed a calibration method using astronomical sources
which corrects the effects of the non-uniform sampling as well as gain error
and dispersion in the correlator.Comment: 14 pages, 21 figures, accepted for publication in A&
A 6-12 GHz Analogue Lag-Correlator for Radio Interferometry
Aims: We describe a 6-12 GHz analogue correlator that has been developed for
use in radio interferometers. Methods: We use a lag-correlator technique to
synthesis eight complex spectral channels. Two schemes were considered for
sampling the cross-correlation function, using either real or complex
correlations, and we developed prototypes for both of them. We opted for the
``add and square'' detection scheme using Schottky diodes over the more
commonly used active multipliers because the stability of the device is less
critical. Results: We encountered an unexpected problem, in that there were
errors in the lag spacings of up to ten percent of the unit spacing. To
overcome this, we developed a calibration method using astronomical sources
which corrects the effects of the non-uniform sampling as well as gain error
and dispersion in the correlator.Comment: 14 pages, 21 figures, accepted for publication in A&
Design and Prototyping of Hybrid Analogue Digital Multiuser MIMO Beamforming for Non-Orthogonal Signals
To enable user diversity and multiplexing gains, a fully digital precoding
multiple input multiple output (MIMO) architecture is typically applied.
However, a large number of radio frequency (RF) chains make the system
unrealistic to low-cost communications. Therefore, a practical three-stage
hybrid analogue-digital precoding architecture, occupying fewer RF chains, is
proposed aiming for a non-orthogonal IoT signal in low-cost multiuser MIMO
systems. The non-orthogonal waveform can flexibly save spectral resources for
massive devices connections or improve data rate without consuming extra
spectral resources. The hybrid precoding is divided into three stages including
analogue-domain, digital-domain and waveform-domain. A codebook based beam
selection simplifies the analogue-domain beamforming via phase-only tuning.
Digital-domain precoding can fine-tune the codebook shaped beam and resolve
multiuser interference in terms of both signal amplitude and phase. In the end,
the waveform-domain precoding manages the self-created inter carrier
interference (ICI) of the non-orthogonal signal. This work designs over-the-air
signal transmission experiments for fully digital and hybrid precoding systems
on software defined radio (SDR) devices. Results reveal that waveform precoding
accuracy can be enhanced by hybrid precoding. Compared to a transmitter with
the same RF chain resources, hybrid precoding significantly outperforms fully
digital precoding by up to 15.6 dB error vector magnitude (EVM) gain. A fully
digital system with the same number of antennas clearly requires more RF chains
and therefore is low power-, space- and cost- efficient. Therefore, the
proposed three-stage hybrid precoding is a quite suitable solution to
non-orthogonal IoT applications
First generation of optical fiber phase reference distribution system for TESLA
This report describes the design of a phase stable Fiber Optic (FO) link for the TESLA technology based projects. The concept of this long optical link, with a feedback system suppressing long term drifts of the RF signal phase is described. Stability requirements are given and most important design issues affecting the system performance are discussed. The technical design issues of system components like laser transmitter and optical phase shifter are described in detail. Last sections depict the software developed for system control and experimental results obtained after system was assembled
Investigation of high bandwith biodevices for transcutaneous wireless telemetry
PhD ThesisBIODEVICE implants for telemetry are increasingly applied today in various areas
applications. There are many examples such as; telemedicine, biotelemetry, health care,
treatments for chronic diseases, epilepsy and blindness, all of which are using a wireless
infrastructure environment. They use microelectronics technology for diagnostics or monitoring
signals such as Electroencephalography or Electromyography. Conceptually the biodevices are
defined as one of these technologies combined with transcutaneous wireless implant telemetry
(TWIT). A wireless inductive coupling link is a common way for transferring the RF power and
data, to communicate between a reader and a battery-less implant. Demand for higher data rate
for the acquisition data returned from the body is increasing, and requires an efficient modulator
to achieve high transfer rate and low power consumption. In such applications, Quadrature Phase
Shift Keying (QPSK) modulation has advantages over other schemes, and double the symbol rate
with respect to Binary Phase Shift Keying (BPSK) over the same spectrum band. In contrast to
analogue modulators for generating QPSK signals, where the circuit complexity and power
dissipation are unsuitable for medical purposes, a digital approach has advantages. Eventually a
simple design can be achieved by mixing the hardware and software to minimize size and power
consumption for implantable telemetry applications. This work proposes a new approach to
digital modulator techniques, applied to transcutaneous implantable telemetry applications;
inherently increasing the data rate and simplifying the hardware design. A novel design for a
QPSK VHDL modulator to convey a high data rate is demonstrated. Essentially, CPLD/FPGA
technology is used to generate hardware from VHDL code, and implement the device which
performs the modulation. This improves the data transmission rate between the reader and
biodevice. This type of modulator provides digital synthesis and the flexibility to reconfigure and
upgrade with the two most often languages used being VHDL and Verilog (IEEE Standard)
being used as hardware structure description languages. The second objective of this thesis is to
improve the wireless coupling power (WCP). An efficient power amplifier was developed and a
new algorithm developed for auto-power control design at the reader unit, which monitors the
implant device and keeps the device working within the safety regulation power limits (SAR). The proposed system design has also been modeled and simulated with MATLAB/Simulink to
validate the modulator and examine the performance of the proposed modulator in relation to its
specifications.Higher Education Ministry in Liby
A high-speed tunable beam splitter for feed-forward photonic quantum information processing
We realize quantum gates for path qubits with a high-speed,
polarization-independent and tunable beam splitter. Two electro-optical
modulators act in a Mach-Zehnder interferometer as high-speed phase shifters
and rapidly tune its splitting ratio. We test its performance with heralded
single photons, observing a polarization-independent interference contrast
above 95%. The switching time is about 5.6 ns, and a maximal repetition rate is
2.5 MHz. We demonstrate tunable feed-forward operations of a single-qubit gate
of path-encoded qubits and a two-qubit gate via measurement-induced interaction
between two photons
Beam loading
We begin by giving a description of the radio-frequency generator-cavity-beam
coupled system in terms of basic quantities. Taking beam loading and cavity
detuning into account, expressions for the cavity impedance as seen by the
generator and as seen by the beam are derived. Subsequently methods of
beam-loading compensation by cavity detuning, radio-frequency feedback and
feedforward are described. Examples of digital radio-frequency phase and
amplitude control for the special case of superconducting cavities are also
given. Finally, a dedicated phase loop for damping synchrotron oscillations is
discussed.Comment: 25 pages, contribution to the CAS - CERN Accelerator School: Course
on High Power Hadron Machines; 24 May - 2 Jun 2011, Bilbao, Spai
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