Polar codes based OFDM-PLC systems in the presence of middleton class-A noise

© 2016 IEEE. The performance of power line communication (PLC) systems suffer mainly from non-Gaussian noise, commonly referred to as impulsive noise. To reduce the effect of this noise, various channel coding techniques have been studied in the literature over PLC channels. Unlike existing works, in this paper we investigate the performance and robustness of polar codes over impulsive noise PLC channels for different codeword lengths and noise scenarios in orthogonal frequency division multiplexing (OFDM) systems. In particular, insightful comparisons between hard decision (HD) decoding and soft decision (SD) decoding for the proposed system are made. Furthermore, we investigate the blanking and clipping techniques with polar codes for impulsive noise mitigation. In addition, for the sake of comparison, results for LDPC coding are also presented. The results show that polar codes can considerably improve the performance of PLC systems. It will also be demonstrated that SD decoding offers better performance than HD decoding and that as the codeword length is increased, the performance can be further improved

Study of the operational SNR while constructing polar codes

Channel coding is commonly based on protecting information to be communicated across an unreliable medium, by adding patterns of redundancy into the transmission path. Also referred to as forward error control coding (FECC), the technique is widely used to enable correcting or at least detecting bit errors in digital communication systems. In this paper we study an original FECC known as polar coding which has proven to meet the typical use cases of the next generation mobile standard. This work is motivated by the suitability of polar codes for the new coming wireless era. Hence, we investigate the performance of polar codes in terms of bit error rate (BER) for several codeword lengths and code rates. We first perform a discrete search to find the best operating signal-to-noise ratio (SNR) at two different code rates, while varying the blocklength. We find in our extensive simulations that the BER becomes more sensitive to operating SNR (OSNR) as long as we increase the blocklength and code rate. Finally, we note that increasing blocklength achieves an SNR gain, while increasing code rate changes the OSNR domain. This trade-off sorted out must be taken into consideration while designing polar codes for high-throughput application

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

Polar codes combined with physical layer security on impulsive noise channels

Ph. D. ThesisThe need for secure communications is becoming more and more impor- tant in modern society as wired and wireless connectivity becomes more ubiquitous. Currently, security is achieved by using well established encryption techniques in the upper layers that rely on computational complexity to ensure security. However, processing power is continu- ally increasing and well-known encryption schemes are more likely to be cracked. An alternative approach to achieving secure communication is to exploit the properties of the communication channel. This is known as physical layer security and is mathematically proven to be secure. Phys- ical layer security is an active research area, with a significant amount of literature covering many different aspects. However, one issue that does not appear to have been investigated in the literature is the effect on physical layer security when the noise in the communication channel is impulsive. Impulsive noise adds large spikes to the transmitted signal for very short durations that can significantly degrade the signal. The main source of impulsive noise in wireless communications is electromag- netic interference generated by machinery. Therefore, this project will investigate the effect of impulsive noise on physical layer security. To ensure a high level of performance, advanced error-correcting codes are needed to correct the multiple errors due to this harsh channel. Turbo and Low-Density Parity-Check (LDPC) codes are capacity-approaching codes commonly used in current wireless communication standards, but their complexity and latency can be quite high and can be a limiting fac- tor when required very high data rates. An alternative error-correcting code is the polar code, which can actually achieve the Shannon capacity on any symmetric binary input discrete memoryless channel (B-DMC). Furthermore, the complexity of polar codes is low and this makes them an attractive error-correcting code for high data rate wireless commu- nications. In this project, polar codes are combined with physical layer security and the performance and security of the system is evaluated on impulsive noise channels for the first time. This project has three contributions: Polar codes designed for impulsive noise channels using density evo- lution are combined with physical layer security on a wire-tap chan- nel experiencing impulsive noise. The secrecy rate of polar codes is maximised. In the decoding of polar codes, the frozen bits play an important part. The posi- tions of the frozen bits has a significant impact on performance and therefore, the selection of optimal frozen bits is presented to opti- mise the performance while maintaining secure communications on impulsive noise wire-tap channels. Optimal puncturing patterns are investigated to obtain polar codes with arbitrary block lengths and can be applied to different modu- lation schemes, such as binary phase shift keying (BPSK) and M- ary Quadrature Amplitude Modulation (QAM), that can be rate compatible with practical communication systems. The punctured polar codes are combined with physical layer security, allowing the construction of a variety of different code rates while maintaining good performance and security on impulsive noise wire-tap chan- nels. The results from this work have demonstrated that polar codes are ro- bust to the effects of impulsive noise channel and can achieve secure communications. The work also addresses the issue of security on im- pulsive noise channels and has provided important insight into scenarios where the main channel between authorised users has varying levels of impulsiveness compared with the eavesdropper's channel. One of the most interesting results from this thesis is the observation that polar codes combined with physical layer security can achieve good perfor- mance and security even when the main channel is more impulsive than the eavesdropper's channel, which was unexpected. Therefore, this thesis concludes that the low-complexity polar codes are an excellent candidate for the error-correcting codes when combined with physical layer security in more harsh impulsive wireless communication channels

Robust wireless sensor network for smart grid communication : modeling and performance evaluation

Our planet is gradually heading towards an energy famine due to growing population and industrialization. Hence, increasing electricity consumption and prices, diminishing fossil fuels and lack significantly in environment-friendliness due to their emission of greenhouse gasses, and inefficient usage of existing energy supplies have caused serious network congestion problems in many countries in recent years. In addition to this overstressed situation, nowadays, the electric power system is facing many challenges, such as high maintenance cost, aging equipment, lack of effective fault diagnostics, power supply reliability, etc., which further increase the possibility of system breakdown. Furthermore, the adaptation of the new renewable energy sources with the existing power plants to provide an alternative way for electricity production transformed it in a very large and complex scale, which increases new issues. To address these challenges, a new concept of next generation electric power system, called the "smart grid", has emerged in which Information and Communication Technologies (ICTs) are playing the key role. For a reliable smart grid, monitoring and control of power system parameters in the transmission and distribution segments are crucial. This necessitates the deployment of a robust communication network within the power grid. Traditionally, power grid communications are realized through wired communications, including power line communication (PLC). However, the cost of its installation might be expensive especially for remote control and monitoring applications. More recently, plenty of research interests have been drawn to the wireless communications for smart grid applications. In this regard, the most promising methods of smart grid monitoring explored in the literature is based on wireless sensor network (WSN). Indeed, the collaborative nature of WSN brings significant advantages over the traditional wireless networks, including low-cost, wider coverage, self-organization, and rapid deployment. Unfortunately, harsh and hostile electric power system environments pose great challenges in the reliability of sensor node communications because of strong RF interference and noise called impulsive noise. On account of the fundamental of WSN-based smart grid communications and the possible impacts of impulsive noise on the reliability of sensor node communications, this dissertation is supposed to further fill the lacking of the existing research outcomes. To be specific, the contributions of this dissertation can be summarized as three fold: (i) investigation and performance analysis of impulsive noise mitigation techniques for point-to-point single-carrier communication systems impaired by bursty impulsive noise; (ii) design and performance analysis of collaborative WSN for smart grid communication by considering the RF noise model in the designing process, a particular intension is given to how the time-correlation among the noise samples can be taken into account; (iii) optimal minimum mean square error (MMSE)estimation of physical phenomenon like temperature, current, voltage, etc., typically modeled by a Gaussian source in the presence of impulsive noise. In the first part, we compare and analyze the widely used non-linear methods such as clipping, blanking, and combined clipping-blanking to mitigate the noxious effects of bursty impulsive noise for point-to-point communication systems with low-density parity-check (LDPC) coded single-carrier transmission. While, the performance of these mitigation techniques are widely investigated for multi-carrier communication systems using orthogonal frequency division multiplexing (OFDM) transmission under the effect of memoryless impulsive noise, we note that OFDM is outperformed by its single-carrier counterpart when the impulses are very strong and/or they occur frequently, which likely exists in contemporary communication systems including smart grid communications. Likewise, the assumption of memoryless noise model is not valid for many communication scenarios. Moreover, we propose log-likelihood ratio (LLR)-based impulsive noise mitigation for the considered scenario. We show that the memory property of the noise can be exploited in the LLR calculation through maximum a posteriori (MAP) detection. In this context, provided simulation results highlight the superiority of the LLR-based mitigation scheme over the simple clipping/blanking schemes. The second contribution can be divided into two aspects: (i) we consider the performance analysis of a single-relay decode-and-forward (DF) cooperative relaying scheme over channels impaired by bursty impulsive noise. For this channel, the bit error rate (BER) performances of direct transmission and a DF relaying scheme using M-PSK modulation in the presence of Rayleigh fading with a MAP receiver are derived; (ii) as a continuation of single-relay collaborative WSN scheme, we propose a novel relay selection protocol for a multi-relay DF collaborative WSN taking into account the bursty impulsive noise. The proposed protocol chooses the N’th best relay considering both the channel gains and the states of the impulsive noise of the source-relay and relay-destination links. To analyze the performance of the proposed protocol, we first derive closed-form expressions for the probability density function (PDF) of the received SNR. Then, these PDFs are used to derive closed-form expressions for the BER and the outage probability. Finally, we also derive the asymptotic BER and outage expressions to quantify the diversity benefits. From the obtained results, it is seen that the proposed receivers based on the MAP detection criterion is the most suitable one for bursty impulsive noise environments as it has been designed according to the statistical behavior of the noise. Different from the aforementioned contributions, talked about the reliable detection of finite alphabets in the presence of bursty impulsive noise, in the thrid part, we investigate the optimal MMSE estimation for a scalar Gaussian source impaired by impulsive noise. In Chapter 5, the MMSE optimal Bayesian estimation for a scalar Gaussian source, in the presence of bursty impulsive noise is considered. On the other hand, in Chapter 6, we investigate the distributed estimation of a scalar Gaussian source in WSNs in the presence of Middleton class-A noise. From the obtained results we conclude that the proposed optimal MMSE estimator outperforms the linear MMSE estimator developed for Gaussian channel