117 research outputs found
Design and analysis for TCP-friendly window-based congestion control
The current congestion control mechanisms for the Internet date back to the early 1980âs and were
primarily designed to stop congestion collapse with the typical traffic of that era. In recent years the
amount of traffic generated by real-time multimedia applications has substantially increased, and the
existing congestion control often does not opt to those types of applications. By this reason, the Internet
can be fall into a uncontrolled system such that the overall throughput oscillates too much by a single
flow which in turn can lead a poor application performance. Apart from the network level concerns,
those types of applications greatly care of end-to-end delay and smoother throughput in which the
conventional congestion control schemes do not suit. In this research, we will investigate improving the
state of congestion control for real-time and interactive multimedia applications. The focus of this work
is to provide fairness among applications using different types of congestion control mechanisms to get
a better link utilization, and to achieve smoother and predictable throughput with suitable end-to-end
packet delay
On Ability of Troubleshooting by Observing Some Physical Layer Parameters of xDSL Transceivers
This article presents a review of the investigation of the possibility of increasing the efficiency of existing line test solutions for troubleshooting testing for IPTV over xDSL, by the results of experimental research on real system under commercial exploitation. At the beginning of this article the main weaknesses of the existing troubleshooting testing are described. In the continuation of the article the physical layer parameters of xDSL transceiver are listed. In the reset this article provides a few specific examples of xDSL lines with their physical layer parameters of xDSL transceivers followed by analysis how they can be used for the purposes of more efficient measurement of parameters of copper pairs
Reducing Internet Latency : A Survey of Techniques and their Merit
Bob Briscoe, Anna Brunstrom, Andreas Petlund, David Hayes, David Ros, Ing-Jyh Tsang, Stein Gjessing, Gorry Fairhurst, Carsten Griwodz, Michael WelzlPeer reviewedPreprin
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
Fifty Years of Noise Modeling and Mitigation in Power-Line Communications.
Building on the ubiquity of electric power infrastructure, power line communications (PLC) has been successfully used in diverse application scenarios, including the smart grid and in-home broadband communications systems as well as industrial and home automation. However, the power line channel exhibits deleterious properties, one of which is its hostile noise environment. This article aims for providing a review of noise modeling and mitigation techniques in PLC. Specifically, a comprehensive review of representative noise models developed over the past fifty years is presented, including both the empirical models based on measurement campaigns and simplified mathematical models. Following this, we provide an extensive survey of the suite of noise mitigation schemes, categorizing them into mitigation at the transmitter as well as parametric and non-parametric techniques employed at the receiver. Furthermore, since the accuracy of channel estimation in PLC is affected by noise, we review the literature of joint noise mitigation and channel estimation solutions. Finally, a number of directions are outlined for future research on both noise modeling and mitigation in PLC
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
OFDM Technique in Packet Captured Slotted Aloha Mobile Communication Systems
School of Electrical and Computer Engineerin
Adaptive multilevel quadrature amplitude radio implementation in programmable logic
Emerging broadband wireless packet data networks are increasingly employing spectrally efficient modulation methods like Quadrature Amplitude Modulation (QAM) to increase the channel efficiency and maximize data throughput. Unfortunately, the performance of high level QAM modulations in the wireless channel is sensitive to channel imperfections and throughput is degraded significantly at low signal-to-noise
ratios due to bit errors and packet retransmission. To obtain a more ârobustâ physical
layer, broadband systems are employing multilevel QAM (M-QAM) to mitigate this reduction in throughput by adapting the QAM modulation level to maintain acceptable packet error rate (PER) performance in changing channel conditions.
This thesis presents an adaptive M-QAM modem hardware architecture, suitable for use as a modem core for programmable software defined radios (SDRs) and broadband wireless applications. The modem operates in âburstâ mode, and can reliably synchronize to different QAM constellations âburst-by-burstâ.
Two main improvements exploit commonality in the M-QAM constellations to minimize the redundant hardware required. First, the burst synchronization functions (carrier, clock, amplitude, and modulation level) operate reliably without prior knowledge of the QAM modulation level used in the burst. Second, a unique bit stuffing and shifting technique is employed which supports variable bit rate operation, while reducing the core signal processing functions to common hardware for all constellations. These features make this architecture especially attractive for implementation with Field Programmable Gate Arrays (FPGAs) and Application-Specific Integrated Circuits (ASICs); both of
which are becoming popular for highly integrated, cost-effective wireless transceivers
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