11 research outputs found
Iterative receiver based on SAGE algorithm for crosstalk cancellation in upstream vectored VDSL
We propose the use of an iterative receiver based on the Space Alternating Generalized Expectation maximization (SAGE) algorithm for crosstalk cancellation in upstream vectored VDSL. In the absence of alien crosstalk, we show that when initialized with the frequency-domain equalizer (FEQ) output, the far-end crosstalk (FEXT) can be cancelled with no more real-time complexity than the existing linear receivers. In addition, the suggested approach does not require offline computation of the channel inverse and thus reduces the receiver complexity. In the presence of alien crosstalk, there is a significant gap between the rate performance of the linear receivers as compared with the single-user bound (SUB). The proposed receiver is shown to successfully bridge this gap while requiring only a little extracomplexity. Computer simulations are presented to validate the analysis and confirm the performance of the proposed receiver
Performance of Coded Multi-Line Copper Wire for G.fast Communications in the Presence of Impulsive Noise
In this paper, we focus on the design of a multi-line
copper wire (MLCW) communication system. First, we construct
our proposed MLCW channel and verify its characteristics based
on the Kolmogorov-Smirnov test. In addition, we apply Middleton
class A impulsive noise (IN) to the copper channel for further
investigation. Second, the MIMO G.fast system is adopted utilizing
the proposed MLCW channel model and is compared to a single
line G-fast system. Second, the performance of the coded system
is obtained utilizing concatenated interleaved Reed-Solomon (RS)
code with four-dimensional trellis-coded modulation (4D TCM), and
compared to the single line G-fast system. Simulations are obtained
for high quadrature amplitude modulation (QAM) constellations
that are commonly used with G-fast communications, the results
demonstrate that the bit error rate (BER) performance of the coded
MLCW system shows an improvement compared to the single line
G-fast systems
Оценка защищенности цифровых систем передачи информации с отводным каналом
В статье предложен новый подход к оценке защищенности цифровых систем передачи информации с отводным каналом. Он основан на их представлении в виде многополюсной микроволновой цепи. Предложены алгоритмы расчета отводных каналов с использованием S-матриц в независимости от технологий передачи
информации и для различных физических каналов (проводных и беспроводных), что позволяет с единых позиций проводить анализ беспроводных и проводных ЦСПИ
ОЦЕНКА ЗАЩИЩЕННОСТИ ЦИФРОВЫХ СИСТЕМ ПЕРЕДАЧИ ИНФОРМАЦИИ С ОТВОДНЫМ КАНАЛОМ
В статье предложен новый подход к оценке защищенности цифровых систем передачи информации с отводным каналом. Он основан на их представлении в виде многополюсной микроволновой цепи. Предложены алгоритмы расчета отводных каналов с использованием S-матриц в независимости от технологий передачи информации и для различных физических каналов (проводных и беспроводных), что позволяет с единых позиций проводить анализ беспроводных и проводных ЦСПИ
Mitigation of impulsive noise for SISO and MIMO G.fast system
To address the demand for high bandwidth data transmission over telephone transmission lines, International Telecommunication Union (ITU)
has recently completed the fourth generation broadband (4GBB) copper
access network technology, known as G.fast.
Throughout this thesis, extensively investigates the wired broadband
G.fast coding system and the novel impulsive noise reduction technique
has been proposed to improve the performance of wired communications
network in three different scenarios: single-line Discrete Multiple Tone
(DMT)- G.fast system; a multiple input multiple-output (MIMO) DMTG.fast system, and MIMO G.fast system with different crosstalk cancellation methods. For each of these scenarios, however, Impulsive Noise
(IN) is considered as the main limiting factor of performance system.
In order to improve the performance of such systems, which use higher
order QAM constellation such as G.fast system, this thesis examines the
performance of DMT G.fast system over copper channel for six different
higher signal constellations of M = 32, 128, 512, 2048, 8192 and 32768 in
presence of IN modelled as the Middleton Class A (MCA) noise source.
In contrast to existing work, this thesis presents and derives a novel
equation of Optimal Threshold (OT) to improve the IN frequency domain mitigation methods applied to the G.fast standard over copper
channel with higher QAM signal constellations. The second scenario,
Multi-Line Copper Wire (MLCW) G.fast is adopted utilizing the proposed MLCW Chen model and is compared to a single line G-fast system
by a comparative analysis in terms of Bit-Error-Rate(BER) performance
of implementation of MLCW-DMT G.fast system. The third scenario,
linear and non-linear crosstalk crosstalk interference cancellation methods are applied to MLCW G.fas and compared by a comparative analysis
in terms of BER performance and the complexity of implementation.University of
Technology for choosing me for their PhD scholarship and The Higher
Committee For Education Development in Iraq(HCED
Analysis of the impact of impulse noise in digital subscriber line systems
In recent years, Digital subscriber line (DSL) technology has been gaining popularity as a high speed
network access technology, capable of the delivery of multimedia services. A major impairment for
DSL is impulse noise in the telephone line. However, evaluating the data errors caused by this noise is
not trivial due to its complex statistical nature, which until recently had not been well understood, and
the complicated error mitigation and framing techniques used in DSL systems. This thesis presents a
novel analysis of the impact of impulse noise and the DSL framing parameters on transmission errors,
building on a recently proposed impulse noise model. It focuses on errors at higher protocol layers, such
as asynchronous transfer mode (ATM), in the most widely used DSL version, namely Asymmetric DSL
(ADSL).
The impulse noise is characterised statistically through its amplitudes, duration, inter-arrival times,
and frequency spectrum, using the British Telecom / University of Edinburgh / Deutsche Telekom
(BT/UE/DT) model. This model is broadband, considers both the time and the frequency domains,
and accounts for the impulse clustering. It is based on recent measurements in two different telephone
networks (the UK and Germany) and therefore is the most complete model available to date and suited
for DSL analysis. A new statistical analysis of impulse noise spectra from DT measurements shows
that impulse spectra can be modelled with three spectral components with similar bandwidth statistical
distributions. Also, a novel distribution of the impulse powers is derived from the impulse amplitude
statistics.
The performance of a generic ADSL modem is investigated in an impulse noise and crosstalk environment
for different bit rates and framing parameters. ATM cell and ADSL frame error rates, and
subjective MPEG2 video quality are used as performance metrics. A new modification of a bit loading
algorithm is developed to enable stable convergence of the algorithm with trellis coding and restricted
subtone constellation size. It is shown that while interleaving brings improvement if set at its maximum
depth, at intermediate depths it actually worsens the performance of all considered metrics in comparison
with no interleaving. No such performance degradation is caused by combining several symbols in a
forward error correction (FEC) codeword, but this burst error mitigation technique is only viable at low
bit rates. Performance improvement can also be achieved by increasing the strength of FEC, especially
if combined with interleaving. In contrast, trellis coding is ineffective against the long impulse noise
error bursts. Alien as opposed to kindred crosstalk degrades the error rates and this is an important issue
in an unbundled network environment. It is also argued that error free data units is a better performance
measure from a user perspective than the commonly used error free seconds.
The impact of impulse noise on the errors in DSL systems has also been considered analytically. A
new Bernoulli-Weibull impulse noise model at symbol level is proposed and it is shown that other models
which assume Gaussian distributed impulse amplitudes or Rayleigh distributed impulse powers give
overly optimistic error estimates in DSL systems. A novel bivariate extension of the Weibull impulse
amplitudes is introduced to enable the analysis of orthogonal signals. Since an exact closed-form expression
for the symbol error probability of multi-carrierQAM assuming Bernoulli-Weibull noise model
does not exist, this problem has been solved numerically. Multi-carrier QAM is shown to perform better
at high signal-to-noise ratio (SNR), but worse at low SNR than single carrier QAM, in both cases because
of the spreading of noise power between subcarriers. Analytical expressions for errors up to frame
level in the specific case of ADSL are then derived from the impulse noise model, with good agreement
with simulation results. The Bernoulli-Weibull model is applied to study the errors in single-pair highspeed
DSL (SHDSL). The performance of ADSL is found to be better when the burst error mitigation
techniques are used, but SHDSL has advantages if low bit error rate and low latency are required
The effect of heterogeneity on decorrelation mechanisms in spiking neural networks: a neuromorphic-hardware study
High-level brain function such as memory, classification or reasoning can be
realized by means of recurrent networks of simplified model neurons. Analog
neuromorphic hardware constitutes a fast and energy efficient substrate for the
implementation of such neural computing architectures in technical applications
and neuroscientific research. The functional performance of neural networks is
often critically dependent on the level of correlations in the neural activity.
In finite networks, correlations are typically inevitable due to shared
presynaptic input. Recent theoretical studies have shown that inhibitory
feedback, abundant in biological neural networks, can actively suppress these
shared-input correlations and thereby enable neurons to fire nearly
independently. For networks of spiking neurons, the decorrelating effect of
inhibitory feedback has so far been explicitly demonstrated only for
homogeneous networks of neurons with linear sub-threshold dynamics. Theory,
however, suggests that the effect is a general phenomenon, present in any
system with sufficient inhibitory feedback, irrespective of the details of the
network structure or the neuronal and synaptic properties. Here, we investigate
the effect of network heterogeneity on correlations in sparse, random networks
of inhibitory neurons with non-linear, conductance-based synapses. Emulations
of these networks on the analog neuromorphic hardware system Spikey allow us to
test the efficiency of decorrelation by inhibitory feedback in the presence of
hardware-specific heterogeneities. The configurability of the hardware
substrate enables us to modulate the extent of heterogeneity in a systematic
manner. We selectively study the effects of shared input and recurrent
connections on correlations in membrane potentials and spike trains. Our
results confirm ...Comment: 20 pages, 10 figures, supplement