412 research outputs found
Calculation of the Performance of Communication Systems from Measured Oscillator Phase Noise
Oscillator phase noise (PN) is one of the major problems that affect the
performance of communication systems. In this paper, a direct connection
between oscillator measurements, in terms of measured single-side band PN
spectrum, and the optimal communication system performance, in terms of the
resulting error vector magnitude (EVM) due to PN, is mathematically derived and
analyzed. First, a statistical model of the PN, considering the effect of white
and colored noise sources, is derived. Then, we utilize this model to derive
the modified Bayesian Cramer-Rao bound on PN estimation, and use it to find an
EVM bound for the system performance. Based on our analysis, it is found that
the influence from different noise regions strongly depends on the
communication bandwidth, i.e., the symbol rate. For high symbol rate
communication systems, cumulative PN that appears near carrier is of relatively
low importance compared to the white PN far from carrier. Our results also show
that 1/f^3 noise is more predictable compared to 1/f^2 noise and in a fair
comparison it affects the performance less.Comment: Accepted in IEEE Transactions on Circuits and Systems-I: Regular
Paper
Low-Complexity OFDM Spectral Precoding
This paper proposes a new large-scale mask-compliant spectral precoder
(LS-MSP) for orthogonal frequency division multiplexing systems. In this paper,
we first consider a previously proposed mask-compliant spectral precoding
scheme that utilizes a generic convex optimization solver which suffers from
high computational complexity, notably in large-scale systems. To mitigate the
complexity of computing the LS-MSP, we propose a divide-and-conquer approach
that breaks the original problem into smaller rank 1 quadratic-constraint
problems and each small problem yields closed-form solution. Based on these
solutions, we develop three specialized first-order low-complexity algorithms,
based on 1) projection on convex sets and 2) the alternating direction method
of multipliers. We also develop an algorithm that capitalizes on the
closed-form solutions for the rank 1 quadratic constraints, which is referred
to as 3) semi-analytical spectral precoding. Numerical results show that the
proposed LS-MSP techniques outperform previously proposed techniques in terms
of the computational burden while complying with the spectrum mask. The results
also indicate that 3) typically needs 3 iterations to achieve similar results
as 1) and 2) at the expense of a slightly increased computational complexity.Comment: Accepted in IEEE International Workshop on Signal Processing Advances
in Wireless Communications (SPAWC), 201
Beamforming in MISO Systems: Empirical Results and EVM-based Analysis
We present an analytical, simulation, and experimental-based study of
beamforming Multiple Input Single Output (MISO) systems. We analyze the
performance of beamforming MISO systems taking into account implementation
complexity and effects of imperfect channel estimate, delayed feedback, real
Radio Frequency (RF) hardware, and imperfect timing synchronization. Our
results show that efficient implementation of codebook-based beamforming MISO
systems with good performance is feasible in the presence of channel and
implementation-induced imperfections. As part of our study we develop a
framework for Average Error Vector Magnitude Squared (AEVMS)-based analysis of
beamforming MISO systems which facilitates comparison of analytical,
simulation, and experimental results on the same scale. In addition, AEVMS
allows fair comparison of experimental results obtained from different wireless
testbeds. We derive novel expressions for the AEVMS of beamforming MISO systems
and show how the AEVMS relates to important system characteristics like the
diversity gain, coding gain, and error floor.Comment: Submitted to IEEE Transactions on Wireless Communications, November
200
A Quantitative Assessment of the Compatibility of Ultra Wideband with Broadband Wireless Access and Radar Services
In July 2008, following a request made by the Radio Spectrum Policy Unit in DG INFSO (Unit B4), a pilot phase of twelve months was agreed with Member States representatives in the Radio Spectrum Committee. During this time the Institute for the Protection and Security of the Citizen of the EC Joint Research Centre (IPSC-JRC) has been mandated to provide testing facilities to support the development of Community spectrum legal measures under the Radio Spectrum Decision (676/2002/EC). In the frame of this pilot phase, IPSC-JRC has successfully completed the implementation and extensive testing of both a state-of-the-art laboratory test-bed and a simulation tool, which have been specifically designed for two different coexistence studies. Firstly, the coexistence between broadband wireless access (BWA) and ultra wideband (UWB) services in the 3.5 GHz frequency band; and secondly, the coexistence between radiolocation (i.e. radar) and UWB services in the 3.1-3.4 GHz frequency band. The selection of these two coexistence scenarios is not casual and has been made based on the fact that they have been considered highly relevant in the CEPT-ECC studies on UWB mandated by the European Commission.JRC.G.6-Security technology assessmen
Self-interference cancellation enabling high-throughput short-reach wireless full-duplex communication
In-band full-duplex (FD) wireless communication allows the simultaneous transmission and reception of data at the same frequency band, effectively doubling the spectral efficiency and data rate while reducing the latency. Previously published designs mostly target the self-interference (SI) cancellation in conventional wireless systems. In this paper, we focus on real-time SI cancellation for short-reach wireless FD systems. The superior signal quality of a point-to-point short-reach wireless system, allows the utilization of wideband communications to achieve a high throughput. Besides, in such wireless systems, the impacts of phase noise and nonlinear distortions are largely reduced, easing the SI cancellation. Moreover, the degradation of signal reception quality due to FD operation is experimentally evaluated in different environments. Experimental results of a prototype implementation show that a combination of antenna isolation and digital cancellation can already achieve an overall SI cancellation performance of 72.5 dB over a bandwidth of 123 MHz. This prototype can support a high-data-rate FD communication link of close to 1 Gbps up to 300 cm with an error vector magnitude lower than -26 dB in a typical indoor environment
Zero Padding or Cyclic Prefix: Evaluation for Non-Orthogonal Signals
The debate of using zero padding (ZP) instead of a cyclic prefix (CP) for enhancing channel estimation and equalization performance is a recurring topic. This is particularly true for orthogonal signals, such as orthogonal frequency division multiplexing (OFDM). Yet, there are far fewer studies evaluating the impact of ZP and CP in non-orthogonal systems. Such systems have the added complexity of self-induced interference rendering channel estimation and equalization more challenging. For this reason, this work proposes a new channel estimation and equalization technique for non-orthogonal systems, which combines ZP with an orthogonal demodulator. Results show that the multipath components that appear in the ZP part can be used to enhance performance when compared to the CP approach
Enhanced Receivers for OFDM signals with super-QAM constellations
Nowadays, there is a high demand for wireless communication systems with higher through-
put. One popular technique widely used in current and developing wireless technologies is
Orthogonal Frequency-Division Multiplexing (OFDM) due to its robustness against fre-
quency selective fading and high spectral efficiency. To further extend OFDM capacity
to meet the near future’s expected demanding needs, OFDM systems with very large
Quadrature Amplitude Modulation (QAM) constellations, the so-called super-QAM, are
being proposed. However, OFDM signals are prone to nonlinear distortion effects due to
their high envelope fluctuations which reduces the system’s performance and this issue
is aggravated by the increase in the size of the constellation. For the implementation of
effective super-QAM OFDM systems, it is crucial to develop receivers that expect and
mitigate the nonlinear distortion on the transmitted signal.
In this work, nonlinear distortion on OFDM small QAM and super-QAM constellations
signals is studied, along with distortion models and methods to estimate them solely
from the transmitted signal, and application of Bussgang noise cancellation receivers and
analysis of their performance over a wide range of scenarios.Nos dias de hoje, há uma grande necessidade de criar sistemas de telecomunicação com
maior ritmo de dados. Uma técnica popular em tecnologias de telecomunicação atuais e
em desenvolvimento é Ortogonal Frequency-Devision Multiplexing (OFDM) devido à sua
robustez contra atenuação seletiva na frequência e alta eficiência espectral. Para aumentar
ainda mais a capacidade do OFDM de forma a preparar para ritmos ainda mais altos que
são expectáveis num futuro próximo, estão a ser propostos sistemas OFDM com enormes
constelações de Quadrature Amplitude Modulation (QAM), o chamado super-QAM. O
problema é que sinais OFDM são suscetÃveis a efeitos de distorção não linear devido à s
altas flutuações de envolvente e que traz pior desempenho do sistema, sendo esse problema
agravado pelo aumento do tamanho da constelação. Para a implementação de sistemas
super-QAM OFDM eficazes é crucial desenvolver recetores que mitiguem a distorção não
linear no sinal transmitido.
Neste trabalho, estuda-se a distorção não linear em sinais OFDM de pequenas cons-
telações QAM e super-QAM, modelos de distorção e métodos para estimá-los a partir do
sinal transmitido, aplicação de recetores de cancelamento de ruÃdo Bussgang e análise de
seu desempenho em diversos cenários
Achievable Sum Rates of Half- and Full-Duplex Bidirectional OFDM Communication Links
While full-duplex (FD) transmission has the potential to double the system
capacity, its substantial benefit can be offset by the self-interference (SI)
and non-ideality of practical transceivers. In this paper, we investigate the
achievable sum rates (ASRs) of half-duplex (HD) and FD transmissions with
orthogonal frequency division multiplexing (OFDM), where the non-ideality is
taken into consideration. Four transmission strategies are considered, namely
HD with uniform power allocation (UPA), HD with non-UPA (NUPA), FD with UPA,
and FD with NUPA. For each of the four transmission strategies, an optimization
problem is formulated to maximize its ASR, and a (suboptimal/optimal) solution
with low complexity is accordingly derived. Performance evaluations and
comparisons are conducted for three typical channels, namely symmetric
frequency-flat/selective and asymmetric frequency-selective channels. Results
show that the proposed solutions for both HD and FD transmissions can achieve
near optimal performances. For FD transmissions, the optimal solution can be
obtained under typical conditions. In addition, several observations are made
on the ASR performances of HD and FD transmissions.Comment: To appear in IEEE TVT. This paper solves the problem of sum
achievable rate optimization of bidirectional FD OFDM link, where joint time
and power allocation is involve
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