561 research outputs found
Investigation of non-binary trellis codes designed for impulsive noise environments
PhD ThesisIt is well known that binary codes with iterative decoders can achieve
near Shannon limit performance on the additive white Gaussian noise
(AWGN) channel, but their performance on more realistic wired or wireless
channels can become degraded due to the presence of burst errors
or impulsive noise. In such extreme environments, error correction alone
cannot combat the serious e ect of the channel and must be combined
with the signal processing techniques such as channel estimation, channel
equalisation and orthogonal frequency division multiplexing (OFDM).
However, even after the received signal has been processed, it can still
contain burst errors, or the noise present in the signal maybe non Gaussian.
In these cases, popular binary coding schemes such as Low-Density
Parity-Check (LDPC) or turbo codes may not perform optimally, resulting
in the degradation of performance. Nevertheless, there is still scope
for the design of new non-binary codes that are more suitable for these
environments, allowing us to achieve further gains in performance. In
this thesis, an investigation into good non-binary trellis error-correcting
codes and advanced noise reduction techniques has been carried out with
the aim of enhancing the performance of wired and wireless communication
networks in di erent extreme environments. These environments
include, urban, indoor, pedestrian, underwater, and powerline communication
(PLC). This work includes an examination of the performance
of non-binary trellis codes in harsh scenarios such as underwater communications
when the noise channel is additive S S noise. Similar work
was also conducted for single input single output (SISO) power line communication
systems for single carrier (SC) and multi carrier (MC) over
realistic multi-path frequency selective channels. A further examination
of multi-input multi-output (MIMO) wired and wireless systems on
Middleton class A noise channel was carried out. The main focus of the
project was non-binary coding schemes as it is well-known that they outperform
their binary counterparts when the channel is bursty. However,
few studies have investigated non-binary codes for other environments.
The major novelty of this work is the comparison of the performance
of non-binary trellis codes with binary trellis codes in various scenarios,
leading to the conclusion that non-binary codes are, in most cases,
superior in performance to binary codes. Furthermore, the theoretical
bounds of SISO and MIMO binary and non-binary convolutional coded
OFDM-PLC systems have been investigated for the rst time. In order
to validate our results, the implementation of simulated and theoretical
results have been obtained for di erent values of noise parameters and
on di erent PLC channels. The results show a strong agreement between
the simulated and theoretical analysis for all cases.University of
Thi-Qar for choosing me for their PhD scholarship and the Iraqi Ministry
of Higher Education and Scienti c Research (MOHESR) for granting me
the funds to study in UK. In addition, there was ample support towards
my stay in the UK from the Iraqi Cultural Attach e in Londo
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
Advanced Coding And Modulation For Ultra-wideband And Impulsive Noises
The ever-growing demand for higher quality and faster multimedia content delivery over short distances in home environments drives the quest for higher data rates in wireless personal area networks (WPANs). One of the candidate IEEE 802.15.3a WPAN proposals support data rates up to 480 Mbps by using punctured convolutional codes with quadrature phase shift keying (QPSK) modulation for a multi-band orthogonal frequency-division multiplexing (MB-OFDM) system over ultra wideband (UWB) channels. In the first part of this dissertation, we combine more powerful near-Shannon-limit turbo codes with bandwidth efficient trellis coded modulation, i.e., turbo trellis coded modulation (TTCM), to further improve the data rates up to 1.2 Gbps. A modified iterative decoder for this TTCM coded MB-OFDM system is proposed and its bit error rate performance under various impulsive noises over both Gaussian and UWB channel is extensively investigated, especially in mismatched scenarios. A robust decoder which is immune to noise mismatch is provided based on comparison of impulsive noises in time domain and frequency domain. The accurate estimation of the dynamic noise model could be very difficult or impossible at the receiver, thus a significant performance degradation may occur due to noise mismatch. In the second part of this dissertation, we prove that the minimax decoder in \cite, which instead of minimizing the average bit error probability aims at minimizing the worst bit error probability, is optimal and robust to certain noise model with unknown prior probabilities in two and higher dimensions. Besides turbo codes, another kind of error correcting codes which approach the Shannon capacity is low-density parity-check (LDPC) codes. In the last part of this dissertation, we extend the density evolution method for sum-product decoding using mismatched noises. We will prove that as long as the true noise type and the estimated noise type used in the decoder are both binary-input memoryless output symmetric channels, the output from mismatched log-likelihood ratio (LLR) computation is also symmetric. We will show the Shannon capacity can be evaluated for mismatched LLR computation and it can be reduced if the mismatched LLR computation is not an one-to-one mapping function. We will derive the Shannon capacity, threshold and stable condition of LDPC codes for mismatched BIAWGN and BIL noise types. The results show that the noise variance estimation errors will not affect the Shannon capacity and stable condition, but the errors do reduce the threshold. The mismatch in noise type will only reduce Shannon capacity when LLR computation is based on BIL
Investigation of Orthogonal Frequency Division Multiplexing Based Power Line Communication Systems
Power Line Communication (PLC) has the potential to become the preferred technique for providing broadband to homes and offices with the advantage of eliminating the need for new wiring infrastructure and reducing the cost. Power line grids, however, present a hostile channel for data communication, since the fundamental purpose of the power line channel was only the transmission of electric power at 50/60 Hz frequencies. The development of PLC systems for providing broadband applications requires an adequate knowledge of the power line channel characteristics. Various types of noise and multipath effects are some of the limitations for power line channels which need to be considered carefully in designing PLC systems. An effect of an impulsive noise characterized with short durations is identified as one of the major impairment in PLC system. Orthogonal Frequency Division Multiplexing (OFDM) technique is one of the modulation approaches which has been regarded as the modulation technique for PLC systems by most researchers in the field and is used in this research study work. This is because it provides high robustness against impulsive noise and minimizes the effects of multipath. In case of impulsive noise affecting the OFDM system, this effect is spread over multiple subcarriers due to Discrete Fourier Transform (DFT) at the receiver. Hence, each of the transmitted communication symbols is only affected by a fraction of the impulsive noise. In order to achieve reliable results for data transmission, a proper power line channel with various noise models must be used in the investigations. In this research study work, a multipath model which has been widely accepted by many researchers in the field and practically proven in the Tanzanian power line system is used as the model for the power line channel.
The effects of different scenarios such as variations in direct path length, path number, branch length and load on the channel frequency response are investigated in this research work. Simulation results indicate the suitability of multi-carrier modulation technique such as an OFDM over the power line channels. To represent the actual noise scenario in the power line channel, an impulsive noise and background noise are classified as the two main noise sources. A Middleton class A noise is modelled as an impulsive noise, whereas the background noise is modelled as an Additive White Gaussian Noise (AWGN). The performance of PLC system based on OFDM is investigated under Middleton Class A and AWGN noise scenarios. It is observed that Bit Error Rate (BER) for the impulsive noise is higher than the background noise. Since channel coding can enhance the transmission in a communication system, Block code and convolutional codes have been studied in this research work. The hamming code chosen as a type of the block code, whereas the Trellis Coded Modulation (TCM) selected from the category of the convolutional channel codes and modelled in Matlab2013b. Although TCM code produces improvements in the Signal-to-Noise Ratio (SNR), they do not perform well with Middleton class A noise. A rectangular 16-QAM TCM based on OFDM provides better BER rate compared to the general TCM
Iterative decoding combined with physical-layer network coding on impulsive noise channels
PhD ThesisThis thesis investigates the performance of a two-way wireless relay channel (TWRC)
employing physical layer network coding (PNC) combined with binary and non-binary
error-correcting codes on additive impulsive noise channels. This is a research topic that
has received little attention in the research community, but promises to offer very
interesting results as well as improved performance over other schemes. The binary
channel coding schemes include convolutional codes, turbo codes and trellis bitinterleaved
coded modulation with iterative decoding (BICM-ID). Convolutional codes
and turbo codes defined in finite fields are also covered due to non-binary channel
coding schemes, which is a sparse research area. The impulsive noise channel is based on
the well-known Gaussian Mixture Model, which has a mixture constant denoted by α.
The performance of PNC combined with the different coding schemes are evaluated with
simulation results and verified through the derivation of union bounds for the theoretical
bit-error rate (BER). The analyses of the binary iterative codes are presented in the form
of extrinsic information transfer (ExIT) charts, which show the behaviour of the iterative
decoding algorithms at the relay of a TWRC employing PNC and also the signal-to-noise
ratios (SNRs) when the performance converges. It is observed that the non-binary coding
schemes outperform the binary coding schemes at low SNRs and then converge at higher
SNRs. The coding gain at low SNRs become more significant as the level of
impulsiveness increases. It is also observed that the error floor due to the impulsive noise
is consistently lower for non-binary codes. There is still great scope for further research
into non-binary codes and PNC on different channels, but the results in this thesis have
shown that these codes can achieve significant coding gains over binary codes for
wireless networks employing PNC, particularly when the channels are harsh
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