Cyclic bit loading for adaptive OFDM in narrowband power line communications

Although Power Line Communication (PLC) is not a new technology, its use to support data transmission over low voltage (LV) distribution networks is still the focus of ongoing research. This thesis focuses on the channel modelling and performance evaluation of narrowband (NB) PLC system. First, the channel modelling approaches of PLC are studied. Then, the proposed PLC channel modelling method based on the bottom-up approach for LV narrowband PLC in a frequency band between 9 kHz and 490 kHz is presented. This proposed model employs the transmission and scattering matrix methods to calculate the transfer function of a typical LV PLC network which comprises two common cable types (copper cables and aluminium conductor steel reinforced). Unlike the top-down approaches, this model is scalable as the network complexity increases and can better describe the network behaviour as a function of physical parameters.In addition, the noise characteristics and popular noise reduction techniques of PLC are studied. The major impairment to the PLC is the impulsive noise which is mainly generated by the switching transient in the network. Hence, a new technique is proposed to mitigate the impact of impulsive noise on data transmission over power lines. This proposed technique is an optimal Clipping/Blanking nonlinearity technique which is based on the minimum bit error rate (BER) search. Results obtained from the simulation of this technique demonstrate that performance has been enhanced in the NB-PLC system. The performance of the narrowband PLC system is also evaluated in both physical (PHY) and medium access control (MAC) layers. Since Orthogonal Frequency Division Multiplexing (OFDM) is a suitable modulation scheme for hostile environment of the power line, it is used to evaluate the PHY layer performance. As a result of the PHY layer performance analyses, it is found that the BER performance between neighbouring points in the typical LV PLC network is reasonable, but communication beyond one hop have to rely on upper layer protocols. In the MAC layer performance evaluation of the PLC system, the widely known random access MAC protocol that uses the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) will be utilised. The MAC performance evaluation of the PLC system demonstrates a significant packet loss in LV PLC network even with a light traffic condition due to the noisy channel. Furthermore, the goodput declines abruptly once the individual transmission rate is high enough to block the network. In addition, the simulation results show that the channel errors can be reduced by adjusting the MAC parameters to allow the re-transmissions mechanisms to recoup the lost packets.

The characterization powerline networks and investigation of communicarion performances has been the interest of several research works. Despite of its complex noise scenario and variable attenuation, narrowband powerline communication (NB-PLC) systems are key element in smart grids which provide different applications such as remote meter reading, home automation and energy management. Mainly located at the last mile communication, NB-PLC systems participate in monitoring and controlling power consumption at different level from local utilities to final customers in conjunction with wireless technology. To provide a proper communication flow over powerlines, it is primordial to get efficient designed and proven PLC systems responding to smart grids requirements. After PLC system design and development, a major task is the infield test which is a heavy task, time consuming and does not give enough information about system performance and robustness. In one hand, test and verification result are as variable as channel conditions. So, it is not obvious to get relevant information from classical infield test. In the other hand, the behavior of existing industrial PLC systems behavior cannot be accurately reproduced in simulation environment. Therefore, getting a flexible standalone platform emulating NB-PLC channel phenomena allows overcoming verification process difficulty. In literature, few research works are interested in emulating narrowband powerline.First, the idea of emulating PLC channels using a stand-alone device has started in a broadband PLC by presenting a hardware platform based on a digital signal processor (DSP) and a field programmable gate array (FPGA). Then, algorithms have been developed and optimized to reduce complexity and improve real-time performance. Regarding NB-PLC, an emulator has been proposed for indoor channels in the frequency range between 95 and 148.5 kHz using analog to digital circuit for channel transfer function and noise scenario. More flexibility and accuracy in generating the NB-PLC channel behavior has been studied and extended to support frequencies up to 500 kHz. The main challenge was the definition of time varying reference channels and tunable sophisticated noise scenarios for emulation. Both proposed NB-PLC channel emulator only takes into consideration the attenuation as predefined function and noise phenomena. The ZC detection is supposed to be ideal that it does not affect the communication performance.The objective of this research work consists in proposing a flexible DSP based NB-PLC channel emulator encompassing the channel bottlenecks interfering during communication. The channel attenuation is deduced using bottom up approach and appropriate noise scenarios are defined to meet as much as possible realistic phenomena. The effect of zero crossing variation is also taken into account. The overall parameters are optimized to be embedded on a DSP platform.

The indoor narrowband power line communication (NB-PLC) suffers from noise impairments, which emanate from several end-user electrical devices connected across the PLC channel. These noise impairments result into burst errors, which consequently lead to data corruption. Therefore, in order to implement robust communication techniques that will thrive on the noisy PLC channel, a full knowledge and modeling of the noise that exists on the NB-PLC channel is inevitable. This paper thus reports a First-order Markov modeling of NB-PLC channel noise, based on experimental measurements. For the modeling, BPSK, DBPSK, QPSK and DQPSK modulation schemes were implemented using Universal Software Radio Peripheral (USRP). The resulting channel models are useful for improving the robustness of the above modulation schemes as well as designing forward error correction techniques for mitigating the effect of noise impairments. The results are also useful in optimizing NB-PLC system design, thereby, enhancing the accuracy and improving the overall PLC system performance.

On cooperative coding for narrow band PLC networks

Advanced Metering Infrastructure (AMI) is the foundation of the Smart Grid system. One of the most important parts of AMI is smart meter communication. Power Line Communication (PLC) technology utilizes the existing power line network for communication media between smart meters and Data Collector Units (DCU). One of the biggest challenges of communication using PLC is the noise level due to residential loads. In this study, laboratory test set up to measure noise caused by PV rooftop and residential loads are observed. Each PLC frequency band was measured and observed to determine the suitable frequency for PLC communication which was the low noise level. Some experiments in the field were conducted to determine the performance of the PLC. Laboratory test measurement result shows the FCC band (150-490 kHz) was outside the range of PV rooftop and residential load noise. On the other hand, the Cenelec A (35-90 kHz) frequency range was in the range of noise signal. Therefore, NB-PLC G3 using FCC frequency band was proposed to achieve robust data communication and lower noise level. G3 PLC FCC band was tested in the real field residential area, the experimental results showed 97.62% successful rate within one-week data collection.

MIMO-OFDM narrowband-PLC in distribution systems: Impact of power transformers on achievable data rates

Non-stationary, non-Gaussian noise severely limits the performance of narrowband (NB) power line communication (PLC) systems. Due to the periodic mains voltage, substantial parts of the noise are known to show time-periodic features. Exploiting these features can significantly improve noise canceling methods and thus the overall performance of PLC systems. A prerequisite for this is an accurate estimation of the statistical properties of the power line noise which is also an important part of the channel characterization. In this work, we perform a spectral correlation analysis to evaluate the strongest cyclic frequencies of the noise encountered in low-voltage NB-PLC applications. Our analysis is based on time-synchronized noise measurements at five different locations with a total observation time of 24 hours. Our contribution includes the implementation and estimation of the cyclic coherence function up to 500 kHz, the extraction of the strongest cyclic frequencies, as well as a short- and long-term analysis of the cyclic features. Finally, we present a statistical analysis of the cyclic frequencies based on the complete set of measurements. This analysis shows that cyclostationarity can be observed in the complete NB frequency range and confirms that the dominant cyclic frequency is twice the mains voltage frequency.

Signal-to-noise ratio (SNR) is an important parameter for adaptive orthogonal frequency division multiplexing (OFDM) systems as it serves as a standard measure of signal quality. In this work, we present a novel SNR per subcarrier estimation scheme for wireless OFDM systems in frequency selective channels. The novel scheme can operate both in time and frequency, requiring only one previously known OFDM symbol. Firstly the noise variance per subcarrier estimate is obtained using the estimated channel coefficients and a novel analysis of its estimation error is provided. The noise variance per subcarrier estimate is used to obtain the SNR per subcarrier estimate. The estimation scheme takes under consideration the frequency selectivity of the channel and the variation of the noise statistics across the OFDM subcarrier index. The estimator's performance, in means of normalized mean square error (NMSE), is evaluated through simulations on a variety of channel models and is compared with another estimation scheme. The NMSE of the proposed scheme demonstrates its ability to identify the local statistics of the noise efficiently resulting into a reliable estimator in contrast with other similar approaches.

SummarySeveral techniques for a state‐of‐the‐art advanced metering infrastructure (AMI) within the smart grid are being extensively studied and evaluated around the world. Advanced metering infrastructure provides an enhanced and efficient energy management infrastructure that can facilitate the latest demands of electric utilities, consumers, and smart grid. In the past few years, standardization process for the implementation of AMI using narrowband power line communications (NB‐PLC) transceivers has been completed by ITU‐T and IEEE. This paper is focused on the utilization of CENELEC band of NB‐PLC for deployment aspects. The power transformer model of 200 and 75 kVA transformers for 9 to 90 kHz frequency range that lies in CENELEC‐A band of NB‐PLC is also proposed. The proposed model is more simple than previously presented models in the literature and has the capability to evaluate the transformers working not only under normal condition but also under resonance condition for frequency of interest. Moreover, the efficient procedure for field measurements that provides a generalized NB‐PLC channel model for low voltage access network to deploy AMI within Lahore, Pakistan, is presented. A Simulink model is developed to validate the results. The analysis of measured and simulated results illustrates a close agreement of channel transfer functions. This research work proposes an improved and more accurate NB‐PLC channel model especially for South Asian countries.

In visible light communications (VLCs), adaptive Orthogonal Frequency Division Multiplexing (OFDM) systems can adjust the transmission parameters according to channel estimation results to improve the system performance. Filtered-OFDM (F-OFDM) is a new flexible and adaptive technology based on OFDM systems and can further improve the system performance. In F-OFDM scheme, the out-of-band emission of OFDM signal is greatly inhibited by using the filter and the guard interval of the two subbands is reduced to save the spectrum resources. In this paper, we creatively apply the F-OFDM technology to visible light OFDM systems and derive the specific signal expression. Simulation results show that as the number of quadrature amplitude modulation (QAM) increases, the bit error rate (BER) performance of the F-OFDM system gets worse. Compared with asymmetrically clipped optical OFDM (ACO-OFDM) and direct current biased OFDM (DCO-OFDM) in VLCs, F-OFDM has better BER performance in 4QAM, 16QAM, and 64QAM schemes.

Broadband low-voltage power line communication (PLC) has many advantages including less investment cost, construction speed, and convenient access. Since the orthogonal frequency division multiplexing (OFDM) technology has strong anti-jamming and anti-frequency selective fading characteristics naturally it becomes a better low voltage power line communication solution. We proposed an OFDM channel estimation method based on compressed sensing (CS) technique according to the channel characteristics of low-voltage power lines. CS algorithm in OFDM system was discussed and an orthogonal matching pursuit (OMP) algorithm was applied to reconstruct the PLC channel information. The simulation results showed that the communication channel estimation method based on CS technique was feasible in PLC system, and the validity of information transmission in OFDM systems can be enhanced.

In recent times, power line communication (PLC) has an ability of communicating the signals and messages making use of the existing power lines without going for new mediums such as optical fibers or radio waves. Considering the voltage, electrical networks are rated as low (1 kV), medium (1–100 kV), and high (>100 kV) networks and the communication problems in these networks increase with increase in voltage. In order to establish high-speed data communications with data rates in the range of megabit/s over power line networks, dedicated communication systems considering the hostile channel properties are required. In addition to signal distortion, losses in cables and multipath propagation, noise from the system also plays a key role to alter the digital communication over power line networks which is dealt in this project. In this work, the signals are obtained with less bit error rate (BER) using Rayleigh fading channel improving the efficiency of the whole system. Different modulation techniques are compared in narrowband power line communication (PLC) systems, and some suggestions are made for the improvement of data transmission in narrowband systems. The best compromise for single-carrier PLC modules between efficiency and architecture complexity is being investigated in this project.

Narrowband (NB) powerline communication (PLC) is extensively adopted by utilities for the communication in advanced metering infrastructure (AMI) systems. PLC technology needs to overcome channel disturbances present in certain grid segments. This study analyzes improvement proposals of the physical layer of the main narrowband PLC technologies approved by international communication organizations that are currently deployed in Europe: Powerline Intelligent Metering Evolution (PRIME) 1.3.6, PRIME 1.4, and G3-PLC, in order to improve PLC performance under channel disturbances. This thorough study is based on simulations carried out by an innovative ad hoc Virtual PLC Lab, developed by the authors, applied in replicable, fully-automated, and cost reduced test scenarios. The analysis is performed by applying standardized test methods and metrics, and by evaluating the influence of a set of representative channel disturbances defined by the European Telecommunications Standards Institute (ETSI) and selected noises generated by distributed energy resources (DER) in normal operation. PLC performance improvements in terms of equalizer curve fitting, error correction codes, and noisy subcarrier suppression mechanisms are presented. The performance gain due to each physical improvement proposal is accurately measured and compared under the same conditions in a replicable and automated test environment in order to evaluate the use of the proposals in the evolution of future PLC technologies.

Power Line Communication is becoming more common each passing day. Narrowband Power Line Communication systems use a frequency range from 3 kHz to 500 kHz. Nonlinear loads are common in residences and unfortunately they produce harmonics. It is possible that some harmonics produced by the nonlinear loads may interact with the power line communication system. AC dimmers produce impulse noise. In this study, Fourier series of an AC chopper is computed and its current harmonics magnitudes which is in Narrowband Power Line Communication frequencies are examined with and without a smoothing inductor. Their harmonic magnitudes in the power line communication frequencies are compared. It has been found that the smoothing inductor performs well to decrease the AC chopper harmonics within the Narrowband power line frequencies.

Advanced Metering Infrastructure (AMI) is a key enabler of the Smart Grid. Narrowband Power Line Communication (PLC) technology is currently the preferred choice for many AMI use cases. Different PHY/MAC standards and dedicated routing protocols are emerging. New trustworthy models and simulation tools are needed for their evaluation in large scale deployments. This paper presents a realistic model for the latest generation of OFDM-based narrowband PLC standards. The model has been implemented in a popular network simulator - OPNET. Furthermore, the model and the simulator are validated against a real-world testbed. Finally, we present the calibration process and the scalability of the simulator. The results show that it is possible to simulate large topologies of up to 1000 smart meters under a proactive (RPL) or reactive (LOAD) packet routing.