Efficient Implementation of a Symbol Timing Estimator for Broadband PLC

It has been shown that power line communication (PLC) in the high frequency (HF) band is a feasible data transmission method for a future smart grid concept — a low-voltage direct current (LVDC) distribution system. Furthermore, PLC is proposed as a basis of the data network architecture in the LVDC system. In the analysis of the communication channel characteristics and the design of the communication system, channel modeling plays an essential role. A PLC channel model in the LVDC system is presented and analyzed in this paper. The channel model is implemented with a circuit simulator, which provides several advantages for the modeling; for instance, channel characteristics can be analyzed and modeled both in the time and frequency domain. In this paper, the PLC channel gain (including signal attenuation in the power cable) in the LVDC system is modeled in the frequency domain. The channel model is verified by and compared with measurements carried out in the PLC channel in an LVDC laboratory system.

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.

Unpredictable characteristics of power line communication (PLC) channels seriously affect the performance of the communication systems. Among these unpredictable characteristics, noise is considered to be the main source of errors in data transmission in PLC systems. Unlike conventional communication systems in which noise is usually modeled as additive white Gaussian noise (AWGN), its definition in PLC channels has a more complicated form. In order to design reliable PLC systems, it is essential to understand the features of noise in power line networks. Since the impulsive noise generated by electrical house appliances is one of the most significant noise types in PLC channel, it is very important to analyze these electrical devices with respect to their noise characteristics. In this paper, impulsive noise characteristics of various house appliances are analyzed over the frequency range of 30kHz-50MHz.

Power line communication (PLC) uses the highly developed infrastructure of the electrical energy distribution network for data transmission. Measurements are showing that a broadband use of PLC channels is possible. So, PLC is of interest to future broadband communication systems. Such systems will be heterogeneous in several respects, for example relative to the used transmission channel but also relative to the complexity of the participant nodes. Wittneben and Kuhn (see block VTC 2002 - Spring) presented a new class of space-time block codes for radio channels. These codes meet the requirements of future communication systems. They are highly flexible and can be adapted to the particular requests of the transmission. In this paper a PLC application of these codes is investigated. They are used as a basis for a scalable and efficient PLC channel coding scheme. This shows that this class of codes can be used as a generic coding scheme for heterogeneous networks. Alternatively, the PLC application can be considered as an example of the usage of the codes on a frequency selective channel with coloured noise. The applied linear block code optimally uses the diversity of the frequency selective channels in combination with OFDM. This leads to significant gains in performance in case of very frequency selective channels; for barely frequency selective channels or for an AWGN channel the performance is slightly better or not affected respectively. These performance results are presented for measured PLC channels.

Exponential demand for broadband applications has elicited renewed interest in characterizing noise in power line communication (PLC) networks for optimal error performance analysis. PLC is economical and ubiquitous, however due to multipath phenomena and nonstationary impulsive noise, the PLC channel is very harsh to signal transmission. Recent studies reveal that PLC noise is cyclostationary and modelling its characteristic should exploit the spectral and temporal redundancy. In addition, preliminary research shows that PLC noise exhibits self-similarity and can be predicted by fractal theory. In modelling noise employing fractal theory, the Hausdorff dimension (D) needs to be approximated. D is related to Hurst parameter (H), which is a measure of self-similarity. Hence, it is important to estimate H for accurate noise prediction using fractal theory. H parameter estimators assume stationarity in time series data. Therefore, preprocessing is required for the case of PLC noise before estimating H to make it stationary as periodicity and nonstatioanrity affects the H estimators. In this study, we remove the periodicity hidden in the PLC noise obtained from measurement campaign within several university offices, workshops and laboratories. Then long-range dependence is estimated from this pre-processed noise data by employing three estimation algorithms: R/S (rescaled adjusted range) method, aggregated variance method and absolute values of aggregated series method. Results from the said estimation methods though not the same, show that the Hurst parameters obtained from various noise measurements are greater than 0.5, implying presence of self-similarity with long-term memory. Results from this study will find valuable applications in PLC noise modelling using fractal and chaos theory and in error performance analysis in both narrowband and broadband PLC systems.

Advanced communication technologies has allowed the power-line communication (PLC) channel to be a transmission medium that enables the transferring of high-speed digital data over the classical indoor electrical wires. The development of PLC systems for Internet, voice, and data services requires measurement-based models of the transfer characteristics of the power-line network suitable for performance analysis by simulation. In this paper, a statistical-based and deterministic PLC channel frequency model was proposed. This model has the advantage of using only one parameter: the channel class. Related software is also developed. In this paper, this model is further improved to represent the measured impulse responses, and related software is developed. First, a PLC channel classification is realized, and an average magnitude and phase channel model by class is proposed. Second, the multipath behaviour of the PLC channel is introduced: a statistical-based channel magnitude generator is built, and a refined phase model is suggested. Finally, the related software is briefly described.

Power Line Communications have been the subject of an important research work. At the same time, the growing demand for multimedia communications provides a good prospect for PLC as a promising transmission technique for the “last mile” access network. Orthogonal Frequency Division Multiplexing (OFDM) is a spectrally efficient multicarrier modulation technique for high speed data transmission over multipath fading channels. High Peak-to-Average Power Ratio (PAPR) is a major drawback of OFDM. The high PAR of the OFDM signal has to be considered when setting the range of the digital-to-analog converter (DAC) and dimensioning the line-driver. This paper introduced an improved PAPR reduction scheme using constant envelope modulation. Furthermore, by utilizing continuous phase modulation (CPM) in a CE-OFDM system, the PAPR can be effectively reduced to 0 dB. The paper describes a CE-OFDM based modem for Power Line Communications (PLC) over the low voltage distribution network. Relying on a preliminary characterization of a PLC network, a complete description of the modem is given.

This keynote discusses the behavior of noise in indoor power line communications (PLC) channels. Some ideas to improve system performance based on the knowledge of PLC noise are also introduced. The power-line noise at an outlet is the sum of noise waveforms produced and emitted to the lines from the appliances connected to the power-line network. In the design and the analysis of wireless communication systems, stationary additive white Gaussian noise (AWGN) is often assumed. In PLC systems, however, the statistical behavior of the man-made noise is quite different from that of the stationary AWGN. The fact that the noise in power-lines is not AWGN is often believed to be a cause of low quality of communications. However, Gaussian is the distribution of the largest entropy, and communications under non-Gaussian noise may achieve better performance if the system is designed to adapt the noise statistics. In other words, PLC systems retain large potential for performance improvement if the behavior of the noise is clarified and taken into account in the system design. For narrow-band indoor PLC, we have a mathematically tractable and accurate model based on experimental measurements. In this model, the noise is expressed as a Gaussian process whose instantaneous variance is a periodic time function. With this assumption and representation, the cyclostationary features of power-line noise can be described in close form formula with a small set of parameters. In wide-band indoor PLC, we have made measurements with high speed sampling (50MHz) with long observation duration (10.4s).

Modern hospitals are beginning to adopt E-HEALTH as efficient complements to the traditional healthcare services. To support the E-HEALTH services, a locatable, radiation-free and high-capacity communication system is urgently needed in hospitals. Power line communication (PLC) system can use the ubiquitous power line network to power the light-emitting diode (LED) lights while serving as the backbone network for the indoor visible light communication (VLC) systems naturally. In this paper, an integrated broadband power line and visible light communication systems with OFDM modulation is proposed for the indoor hospital applications. This gives a brand-new solution to replace the conventional wireless communication systems in hospitals.

Direct sequence code division multiple access (DS-CDMA) and M-ary frequency shift keying (MFSK) are two viable modulation schemes for broadband power line communication (PLC) channels, for multi-carrier and single carrier cases respectively. In this paper, we study the bit error rate (BER) performance of a synchronous DS-CDMA system and an MFSK system employing coherent detection for a PLC channel. The background noise present in PLC channel is assumed to follow Nakagami-m distribution as suggested by earlier works. Thereafter a comparison is drawn between the two modulation schemes. In order to draw the comparison at an equal level, we analyse the BER performances of the two systems having the same degree of transmitter/ receiver complexity along with the criteria of same bandwidth occupation, same transmission power as well as the same PLC channel characteristics. The study provides an insight as to how a small change in the parameter of a random variable (RV) describing the background power line noise has a marked influence on the BER performances of the two modulation schemes mentioned above. Also from the simulation results obtained it is quite evident that for a single user case, the MFSK system outperforms the DS-CDMA system at similar data rates.

Power Line Communication (PLC) channel is a very challenging environment, this is due to the fact that severe impairments adhering this medium. A more realistic and accurate noise model based symmetric alpha-stable distribution (SαS) is considered in this paper to better fit the properties of real noise inherent in power grid system. In this paper we study the impact of the degree of impulsiveness based SαS model on the performance of MIMO over PLC channel. Results show the improvement reached in PLC by using MIMO-OFDM, and reveal the effectiveness of considering a more realistic noise model.

Broadband PLC (power line communication) has become one of the most important communication technologies for Smart Gird applications, especially for AMI (Advanced Metering Infrastructure) and HAN (Home Area Network). Currently, most broadband PLC products are based on OFDM, DMT or Spread-Spectrum technologies. Their performances differ from each other on certain circumstances. This paper proposes a performance testing model to test PLC devices' Transmitting Capacity and Noise Tolerance. Four PLC devices using different modulation technologies respectively are tested. In addition, the performances of different technologies are analyzed and some discussions are made. To reduce the affection of noise brought in by electric appliances, an "isolating socket" is introduced, which can filter the noises on the appliance side.

This paper investigates the physical layer security of in-home and broadband power line communications (PLC) systems threatened by colluding wireless communication (WLC) eavesdroppers, which are localized near or far from the transmitter and operate in the same frequency band. In this regard, we show that PLC and hybrid PLC-WLC channels can be considered as uncorrelated random processes. In the sequel, we confirm the severity of a WLC eavesdropper or a group of them located near the transmitter. Also, we show that a group of colluding WLC eavesdroppers located far from the transmitter poses the same security risk of only one WLC eavesdropper located near the transmitter. Finally, a discussion of wiretap code rates for achieving effective secrecy throughput is presented.

Highly reliable LDPC coded data transfer in home networks by using Canete’s PLC channel model

Power Line Communications (PLC) is regarded as the promising home networking technology for smart grid application since the PLC technology enables data transmission via the existing power line. The cooperation between PLC and Wireless Local Area Network (WLAN) will be an effective hybrid solution for Home Area Networks (HANs). In this paper, we consider that Transmission Control Protocol (TCP) packets are transmitting in heterogenous communications network based on PLC and WLAN. The existing TCP congestion control has low effectiveness due to the error-prone power line channel. Therefore, we propose an adaptive rate control to improve TCP performance in the hybrid PLC/WLAN HANs. We exploit the communications mechanism of WLAN to improve the PLC link utilization. The methodology of Heuristic Dynamic Programming (HDP) is employed to obtain the optimal rate policy. The bottleneck link capacity is estimated by neural network training. The sending rate is adapted according to the long-term quality of service (QoS) of applications. Simulation results illustrate that the proposed rate control effectively filters out the negative impact from the instantaneous impulse noise in PLC channel and outperforms the existing TCP.