39 research outputs found
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
Optimization and Performance Analysis of High Speed Mobile Access Networks
The end-to-end performance evaluation of high speed broadband mobile access networks is the main focus of this work. Novel transport network adaptive flow control and enhanced congestion control algorithms are proposed, implemented, tested and validated using a comprehensive High speed packet Access (HSPA) system simulator. The simulation analysis confirms that the aforementioned algorithms are able to provide reliable and guaranteed services for both network operators and end users cost-effectively. Further, two novel analytical models one for congestion control and the other for the combined flow control and congestion control which are based on Markov chains are designed and developed to perform the aforementioned analysis efficiently compared to time consuming detailed system simulations. In addition, the effects of the Long Term Evolution (LTE) transport network (S1and X2 interfaces) on the end user performance are investigated and analysed by introducing a novel comprehensive MAC scheduling scheme and a novel transport service differentiation model
An Optimal Energy Efficient Design of Artificial Noise for Preventing Power Leakage based Side-Channel Attacks
Side-channel attacks (SCAs), which infer secret information (for example
secret keys) by exploiting information that leaks from the implementation (such
as power consumption), have been shown to be a non-negligible threat to modern
cryptographic implementations and devices in recent years. Hence, how to
prevent side-channel attacks on cryptographic devices has become an important
problem. One of the widely used countermeasures to against power SCAs is the
injection of random noise sequences into the raw leakage traces. However, the
indiscriminate injection of random noise can lead to significant increases in
energy consumption in device, and ways must be found to reduce the amount of
energy in noise generation while keeping the side-channel invisible. In this
paper, we propose an optimal energy-efficient design for artificial noise
generation to prevent side-channel attacks. This approach exploits the sparsity
among the leakage traces. We model the side-channel as a communication channel,
which allows us to use channel capacity to measure the mutual information
between the secret and the leakage traces. For a given energy budget in the
noise generation, we obtain the optimal design of the artificial noise
injection by solving the side-channel's channel capacity minimization problem.
The experimental results also validate the effectiveness of our proposed
scheme
An Assessment of Indoor Geolocation Systems
Currently there is a need to design, develop, and deploy autonomous and portable indoor geolocation systems to fulfil the needs of military, civilian, governmental and commercial customers where GPS and GLONASS signals are not available due to the limitations of both GPS and GLONASS signal structure designs. The goal of this dissertation is (1) to introduce geolocation systems; (2) to classify the state of the art geolocation systems; (3) to identify the issues with the state of the art indoor geolocation systems; and (4) to propose and assess four WPI indoor geolocation systems. It is assessed that the current GPS and GLONASS signal structures are inadequate to overcome two main design concerns; namely, (1) the near-far effect and (2) the multipath effect. We propose four WPI indoor geolocation systems as an alternative solution to near-far and multipath effects. The WPI indoor geolocation systems are (1) a DSSS/CDMA indoor geolocation system, (2) a DSSS/CDMA/FDMA indoor geolocation system, (3) a DSSS/OFDM/CDMA/FDMA indoor geolocation system, and (4) an OFDM/FDMA indoor geolocation system. Each system is researched, discussed, and analyzed based on its principle of operation, its transmitter, the indoor channel, and its receiver design and issues associated with obtaining an observable to achieve indoor navigation. Our assessment of these systems concludes the following. First, a DSSS/CDMA indoor geolocation system is inadequate to neither overcome the near-far effect not mitigate cross-channel interference due to the multipath. Second, a DSSS/CDMA/FDMA indoor geolocation system is a potential candidate for indoor positioning, with data rate up to 3.2 KBPS, pseudorange error, less than to 2 m and phase error less than 5 mm. Third, a DSSS/OFDM/CDMA/FDMA indoor geolocation system is a potential candidate to achieve similar or better navigation accuracy than a DSSS/CDMA indoor geolocation system and data rate up to 5 MBPS. Fourth, an OFDM/FDMA indoor geolocation system is another potential candidate with a totally different signal structure than the pervious three WPI indoor geolocation systems, but with similar pseudorange error performance
Convergence of packet communications over the evolved mobile networks; signal processing and protocol performance
In this thesis, the convergence of packet communications over the evolved mobile networks is studied. The Long Term Evolution (LTE) process is dominating the Third Generation Partnership Project (3GPP) in order to bring technologies to the markets in the spirit of continuous innovation. The global markets of mobile information services are growing towards the Mobile Information Society.
The thesis begins with the principles and theories of the multiple-access transmission schemes, transmitter receiver techniques and signal processing algorithms. Next, packet communications and Internet protocols are referred from the IETF standards with the characteristics of mobile communications in the focus. The mobile network architecture and protocols bind together the evolved packet system of Internet communications to the radio access network technologies. Specifics of the traffic models are shortly visited for their statistical meaning in the radio performance analysis. Radio resource management algorithms and protocols, also procedures, are covered addressing their relevance for the system performance. Throughout these Chapters, the commonalities and differentiators of the WCDMA, WCDMA/HSPA and LTE are covered. The main outcome of the thesis is the performance analysis of the LTE technology beginning from the early discoveries to the analysis of various system features and finally converging to an extensive system analysis campaign. The system performance is analysed with the characteristics of voice over the Internet and best effort traffic of the Internet. These traffic classes represent the majority of the mobile traffic in the converged packet networks, and yet they are simple enough for a fair and generic analysis of technologies. The thesis consists of publications and inventions created by the author that proposed several improvements to the 3G technologies towards the LTE. In the system analysis, the LTE showed by the factor of at least 2.5 to 3 times higher system measures compared to the WCDMA/HSPA reference. The WCDMA/HSPA networks are currently available with over 400 million subscribers and showing increasing growth, in the meanwhile the first LTE roll-outs are scheduled to begin in 2010. Sophisticated 3G LTE mobile devices are expected to appear fluently for all consumer segments in the following years
Characterization and modeling of the channel and noise for broadband indoor Power Line Communication (PLC) networks.
Doctor of Philosophy in Electronic Engineering. University of KwaZulu-Natal, Durban 2016Power Line Communication (PLC) is an interesting approach in establishing last mile broadband
access especially in rural areas. PLC provides an already existing medium for broadband
internet connectivity as well as monitoring and control functions for both industrial
and indoor usage. PLC network is the most ubiquitous network in the world reaching every
home. However, it presents a channel that is inherently hostile in nature when used for
communication purposes. This hostility is due to the many problematic characteristics of
the PLC from a data communicationsâ perspective. They include multipath propagation
due to multiple reflections resulting from impedance mismatches and cable joints, as well as
the various types of noise inherent in the channel. Apart from wireless technologies, current
high data rate services such as high speed internet are provided through optical fibre links,
Ethernet, and VDSL (very-high-bit-rate digital subscriber line) technology. The deployment
of a wired network is costly and demands physical effort. The transmission of high frequency
signals over power lines, known as power line communications (PLC), plays an important
role in contributing towards global goals for broadband services inside the home and office.
In this thesis we aim to contribute to this ideal by presenting a powerline channel modeling
approach which describes a powerline network as a lattice structure. In a lattice structure, a
signal propagates from one end into a network of boundaries (branches) through numerous
paths characterized by different reflection/transmission properties. Due to theoretically infinite
number of reflections likely to be experienced by a propagating wave, we determine the
optimum number of paths required for meaningful contribution towards the overall signal
level at the receiver. The propagation parameters are obtained through measurements and
other model parameters are derived from deterministic power system. It is observed that the
notch positions in the transfer characteristics are associated with the branch lengths in the
network. Short branches will result in fewer notches in a fixed bandwidth as compared to
longer branches. Generally, the channel attenuation increase with network size in terms of
number of branches. The proposed model compares well with experimental data. This work
presents another alternative approach to model the transfer characteristics of power lines
for broadband power line communication. The model is developed by considering the power
line to be a two-wire transmission line and the theory of transverse electromagnetic (TEM)
wave propagation. The characteristic impedance and attenuation constant of the power line
are determined through measurements. These parameters are used in model simplification
and determination of other model parameters for typical indoor multi-tapped transmission
line system. The transfer function of the PLC channel is determined by considering the
branching sections as parallel resonant circuits (PRC) attached to the main line. The model
is evaluated through comparison with measured transfer characteristics of known topologies
and it is in good agreement with measurements. Apart from the harsh topology of power
line networks, the presence of electrical appliances further aggravates the channel conditions
by injecting various types of noises into the system. This thesis also discusses the process
of estimating powerline communication (PLC) asynchronous impulsive noise volatility by
studying the conditional variance of the noise time series residuals. In our approach, we use
the Generalized Autoregressive Conditional Heteroskedastic (GARCH) models on the basis
that in our observations, the noise time series residuals indicate heteroskedasticity. By performing
an ordinary least squares (OLS) regression of the noise data, the empirical results
show that the conditional variance process is highly persistent in the residuals. The variance
of the error terms are not uniform, in fact, the error terms are larger at some portions of
the data than at other time instances. Thus, PLC impulsive noise often exhibit volatility
clustering where the noise time series is comprised of periods of high volatility followed by
periods of high volatility and periods of low volatility followed by periods of low volatility.
The burstiness of PLC impulsive noise is therefore not spread randomly across the time
period, but instead has a degree of autocorrelation. This provides evidence of time-varying
conditional second order moment of the noise time series. Based on these properties, the
noise time series data is said to suffer from heteroskedasticity. GARCH models addresses the
deficiencies of common regression models such as Autoregressive Moving Average (ARMA)
which models the conditional expectation of a process given the past, but regards the past
conditional variances to be constant. In our approach, we predict the time-varying volatility
by using past time-varying variances in the error terms of the noise data series. Subsequent
variances are predicted as a weighted average of past squared residuals with declining weights
that never completely diminish. The parameter estimates of the model indicates a high degree
of persistence in conditional volatility of impulsive noise which is a strong evidence of
explosive volatility. Parameter estimation of linear regression models usually employs least
squares (LS) and maximum likelihood (ML) estimators. While maximum likelihood remains
one of the best estimators within the classical statistics paradigm to date, it is highly reliant
on the assumption about the joint probability distribution of the data for optimal results.
In our work, we use the Generalized Method of Moments (GMM) to address the deficiencies
of LS/ML in order to estimate the underlying data generating process (DGP). We use
GMM as a statistical technique that incorporate observed noise data with the information in
population moment conditions to determine estimates of unknown parameters of the underlying
model. Periodic impulsive noise (short-term) has been measured, deseasonalized and
modeled using GMM. The numerical results show that the model captures the noise process
accurately. Usually, the impulsive signals originates from connected loads in an electrical
power network can often be characterized as cyclostationary processes. A cyclostationary
process is described as a non-stationary process whose statistics exhibit periodic time variation,
and therefore can be described by virtue of its periodic order. The focus of this chapter
centres on the utilization of cyclic spectral analysis technique for identification and analysis
of the second-order periodicity (SOP) of time sequences like those which are generated by
electrical loads connected in the vicinity of a power line communications receiver. Analysis
of cyclic spectrum generally incorporates determining the random features besides the periodicity
of impulsive noise, through the determination of the spectral correlation density
(SCD). Its effectiveness on identifying and analysing cyclostationary noise is substantiated
in this work by processing data collected at indoor low voltage sites
Characterization and modelling of the channel and noise for broadband indoor powerline communication (plc.) networks.
Masters degree. University of KwaZulu-Natal, Durban.Power Line Communication (PLC) is an interesting approach in establishing last mile broad band access especially in rural areas. PLC provides an already existing medium for broad band internet connectivity as well as monitoring and control functions for both industrial and indoor usage. PLC network is the most ubiquitous network in the world reaching every
home. However, it presents a channel that is inherently hostile in nature when used for
communication purposes. This hostility is due to the many problematic characteristics of
the PLC from a data communicationsâ perspective. They include multipath propagation
due to multiple reflections resulting from impedance mismatches and cable joints, as well as
the various types of noise inherent in the channel. Apart from wireless technologies, current
high data rate services such as high speed internet are provided through optical fibre links,
Ethernet, and VDSL (very-high-bit-rate digital subscriber line) technology. The deployment
of a wired network is costly and demands physical effort. The transmission of high frequency
signals over power lines, known as power line communications (PLC), plays an important
role in contributing towards global goals for broadband services inside the home and office.
In this thesis we aim to contribute to this ideal by presenting a powerline channel modeling
approach which describes a powerline network as a lattice structure. In a lattice structure, a
signal propagates from one end into a network of boundaries (branches) through numerous
paths characterized by different reflection/transmission properties. Due to theoretically infi nite number of reflections likely to be experienced by a propagating wave, we determine the
optimum number of paths required for meaningful contribution towards the overall signal
level at the receiver. The propagation parameters are obtained through measurements and
other model parameters are derived from deterministic power system. It is observed that the
notch positions in the transfer characteristics are associated with the branch lengths in the
network. Short branches will result in fewer notches in a fixed bandwidth as compared to
longer branches. Generally, the channel attenuation increase with network size in terms of
number of branches. The proposed model compares well with experimental data. This work
presents another alternative approach to model the transfer characteristics of power lines
for broadband power line communication. The model is developed by considering the power
line to be a two-wire transmission line and the theory of transverse electromagnetic (TEM)
wave propagation. The characteristic impedance and attenuation constant of the power line
v
are determined through measurements. These parameters are used in model simplification
and determination of other model parameters for typical indoor multi-tapped transmission
line system. The transfer function of the PLC channel is determined by considering the
branching sections as parallel resonant circuits (PRC) attached to the main line. The model
is evaluated through comparison with measured transfer characteristics of known topologies
and it is in good agreement with measurements. Apart from the harsh topology of power
line networks, the presence of electrical appliances further aggravates the channel conditions
by injecting various types of noises into the system. This thesis also discusses the process
of estimating powerline communication (PLC) asynchronous impulsive noise volatility by
studying the conditional variance of the noise time series residuals. In our approach, we use
the Generalized Autoregressive Conditional Heteroskedastic (GARCH) models on the basis
that in our observations, the noise time series residuals indicate heteroskedasticity. By per forming an ordinary least squares (OLS) regression of the noise data, the empirical results
show that the conditional variance process is highly persistent in the residuals. The variance
of the error terms are not uniform, in fact, the error terms are larger at some portions of
the data than at other time instances. Thus, PLC impulsive noise often exhibit volatility
clustering where the noise time series is comprised of periods of high volatility followed by
periods of high volatility and periods of low volatility followed by periods of low volatility.
The burstiness of PLC impulsive noise is therefore not spread randomly across the time
period, but instead has a degree of autocorrelation. This provides evidence of time-varying
conditional second order moment of the noise time series. Based on these properties, the
noise time series data is said to suffer from heteroskedasticity. GARCH models addresses the
deficiencies of common regression models such as Autoregressive Moving Average (ARMA)
which models the conditional expectation of a process given the past, but regards the past
conditional variances to be constant. In our approach, we predict the time-varying volatility
by using past time-varying variances in the error terms of the noise data series. Subsequent
variances are predicted as a weighted average of past squared residuals with declining weights
that never completely diminish. The parameter estimates of the model indicates a high de gree of persistence in conditional volatility of impulsive noise which is a strong evidence of
explosive volatility. Parameter estimation of linear regression models usually employs least
squares (LS) and maximum likelihood (ML) estimators. While maximum likelihood remains
one of the best estimators within the classical statistics paradigm to date, it is highly reliant
vi
on the assumption about the joint probability distribution of the data for optimal results.
In our work, we use the Generalized Method of Moments (GMM) to address the deficien cies of LS/ML in order to estimate the underlying data generating process (DGP). We use
GMM as a statistical technique that incorporate observed noise data with the information in
population moment conditions to determine estimates of unknown parameters of the under lying model. Periodic impulsive noise (short-term) has been measured, deseasonalized and
modeled using GMM. The numerical results show that the model captures the noise process
accurately. Usually, the impulsive signals originates from connected loads in an electrical
power network can often be characterized as cyclostationary processes. A cyclostationary
process is described as a non-stationary process whose statistics exhibit periodic time varia tion, and therefore can be described by virtue of its periodic order. The focus of this chapter
centres on the utilization of cyclic spectral analysis technique for identification and analysis
of the second-order periodicity (SOP) of time sequences like those which are generated by
electrical loads connected in the vicinity of a power line communications receiver. Analysis
of cyclic spectrum generally incorporates determining the random features besides the pe riodicity of impulsive noise, through the determination of the spectral correlation density
(SCD). Its effectiveness on identifying and analysing cyclostationary noise is substantiated
in this work by processing data collected at indoor low voltage sites
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Operational support systems for satellite communications
The role of satellite communications is changing from providing bandwidth linking network operators interconnections towards providing IP enabled communications to end users. This migration from few high-value routes towards many low-value routes means that integration and automation of processes with terrestrial networks becomes critical in driving down unit costs. Integration and automation is necessary on all planes: user, control and management. In satellite communications, management aspects, underpinned by Operational Support Systems (OSS) have received the least research attention, making this a valuable topic for study. In most areas, OSS for satellite systems are similar to other domains. However there are some notable areas of difference which have been the focus of this research. The eTOM business framework, developed by the TMF, has been used to highlight aspects of OSS unique to satellite. Since satellite capacity represents the highest operational cost of a satellite route, effective management while minimising the overhead traffic is critical. The transmission of IP packets is assumed and the real-time measurement of QoS parameters such as packet delay and loss emerged as the most important differences. A number of approaches to QoS measurement are feasible, however the use of trace packets is most promising especially for high network loads. An experiment compares the results from simulations, mathematical models and from a test network, using Poisson and self-similar traffic flows. The relationship between measurement accuracy and trace packet intensity is explored and the measurement response time to steps in traffic load is estimated. It is discovered that measurement accuracy improves as the queue load increases, in contrast to alternative approaches such as sampling of user packets. The response time to steps depends upon the degree of self-similarity and is generally longer than the times recommended by standards. A pragmatic approach to management of different modes is proposed where the measurement method is changed depending on the load