278 research outputs found
Improving ADSL Performance with Selective QAM Mapping and Hybrid ARQ
Asymmetric Digital Subscriber Line (ADSL) is a high-rate transmission standard used for broadband access. Error performance and bandwidth efficiency are the two main concerns in ADSL transmission, hence prompting the need for appropriate techniques to provide improved error protection and noise robustness in ADSL systems. This paper proposes an enhanced ADSL transmission model which incorporates Trellis Coded Modulation (TCM), selective or prioritised QAM constellation mapping and Hybrid Automatic Repeat reQuest HARQ with diversity combining. Simulation results demonstrate that the proposed scheme provides a significant gain of over 3 dB in Eb/No over a conventional ADSL system which does not use HARQ. It also achieves a 30 percent gain in throughput over a conventional ADSL which uses HARQ without diversity combining.Keywords: ADSL, Selective QAM, TCM, HARQ, Diversity Combining.Cite as:A B N Goolamhossen, T P Fowdur "Improving ADSL Performance with Selective QAM Mapping and Hybrid ARQ ", ADBU J.Engg.Tech., 2(1)(2015) 0021103(7pp
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
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
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
Single-Carrier Modulation versus OFDM for Millimeter-Wave Wireless MIMO
This paper presents results on the achievable spectral efficiency and on the
energy efficiency for a wireless multiple-input-multiple-output (MIMO) link
operating at millimeter wave frequencies (mmWave) in a typical 5G scenario. Two
different single-carrier modem schemes are considered, i.e., a traditional
modulation scheme with linear equalization at the receiver, and a
single-carrier modulation with cyclic prefix, frequency-domain equalization and
FFT-based processing at the receiver; these two schemes are compared with a
conventional MIMO-OFDM transceiver structure. Our analysis jointly takes into
account the peculiar characteristics of MIMO channels at mmWave frequencies,
the use of hybrid (analog-digital) pre-coding and post-coding beamformers, the
finite cardinality of the modulation structure, and the non-linear behavior of
the transmitter power amplifiers. Our results show that the best performance is
achieved by single-carrier modulation with time-domain equalization, which
exhibits the smallest loss due to the non-linear distortion, and whose
performance can be further improved by using advanced equalization schemes.
Results also confirm that performance gets severely degraded when the link
length exceeds 90-100 meters and the transmit power falls below 0 dBW.Comment: accepted for publication on IEEE Transactions on Communication
Bit-Error-Rate-Minimizing Channel Shortening Using Post-FEQ Diversity Combining and a Genetic Algorithm
In advanced wireline or wireless communication systems, i.e., DSL, IEEE 802.11a/g, HIPERLAN/2, etc., a cyclic prefix which is proportional to the channel impulse response is needed to append a multicarrier modulation (MCM) frame for operating the MCM accurately. This prefix is used to combat inter symbol interference (ISI). In some cases, the channel impulse response can be longer than the cyclic prefix (CP). One of the most useful techniques to mitigate this problem is reuse of a Channel Shortening Equalizer (CSE) as a linear preprocessor before the MCM receiver in order to shorten the effective channel length. Channel shortening filter design is a widely examined topic in the literature. Most channel shortening equalizer proposals depend on perfect channel state information (CSI). However, this information may not be available in all situations. In cases where channel state information is not needed, blind adaptive equalization techniques are appropriate. In wireline communication systems (such as DMT), the CSE design is based on maximizing the bit rate, but in wireless systems (OFDM), there is a fixed bit loading algorithm, and the performance metric is Bit Error Rate (BER) minimization. In this work, a CSE is developed for multicarrier and single-carrier cyclic prefixed (SCCP) systems which attempts to minimize the BER. To minimize the BER, a Genetic Algorithm (GA), which is an optimization method based on the principles of natural selection and genetics, is used. If the CSI is shorter than the CP, the equalization can be done by a frequency domain equalizer (FEQ), which is a bank of complex scalars. However, in the literature the adaptive FEQ design has not been well examined. The second phase of this thesis focuses on different types of algorithms for adapting the FEQ and modifying the FEQ architecture to obtain a lower BER. Simulation results show that this modified architecture yields a 20 dB improvement in BER
An improved channel model for ADSL and VDSL systems
This paper examines existing channel models used with xDSL systems and identifies a key shortcoming - namely, the implicit assumption that all impulse noise originates at the transmitter. Based on extensive data collected from the local loop, a new model is proposed which addresses this problem by combining a digital filter model of the transmission line with a distributed noise source. This better reflects the nature of a real telephone line, and thus provides a more solid basis for simulation and optimisation of xDSL systems
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