Indoor Broadband Power Line Communications Research Articles

Channel estimation for OFDM-based indoor broadband power line communication systems

State-of-the-art indoor broadband power line communications (PLC) systems use orthogonal frequency division multiplexing (OFDM) signals with constellations up to 10 bits/symbol, which makes channel estimation a key aspect. This paper focuses on the initial channel estimation used in the payload, which might be further adapted by means of a decision-directed strategy. This initial estimate has to be computed on a per-frame basis and can be accomplished from the preamble, the header symbol (assuming that it has been correctly decoded) or from a combination of both. This work proposes simple channel estimation techniques for this problem and derives their most appropriate parameters. They are compared with the linear minimum mean squared-error (LMMSE) estimator and others commonly used in wireless scenarios by considering both their performance and computational complexity. The factors limiting the performance of the estimators based on the preamble and the header symbols are analyzed and the implications of the differences between PLC and wireless channels, such as the absence of fading, in the design of estimation techniques that require knowledge of the channel statistics are discussed. A performance analysis of the considered techniques is accomplished in a set of 171 measured indoor PLC channels. Obtained results indicate that estimators from the header perform better than those based on the preamble symbols and we provide a computationally simple estimator that gives nearly optimum performance by combining estimates from both the preamble and the header symbols.

Efficient Access Control for Broadband Power Line Communications in Home Area Networks

In this paper, we address the problem of improving the medium access control (MAC) layer efficiency in indoor broadband power line communication networks. Several overheads in the MAC layer, like random back-offs and collision recovery, degrade the MAC efficiency. To reduce these overheads, we apply in-band full-duplexing (IBFD), which enables medium-aware transmission at all the network nodes. Specifically, we propose two new schemes called contention-free pre-sensing and mutual preamble detection to minimize the time spent during contentions and collisions. Considering the non-idealities of IBFD, we analytically show the feasibility of our solutions. We further design a comprehensive simulation model with multiple priority data frames and Poisson network traffic arrival to emulate a real in-home network traffic. We then present numerical results for both the classical saturated network model and the comprehensive traffic model, to show through OMNeT++ simulations that our presented solutions achieve over 95% of the optimum MAC efficiency that can only be attained in the idealized case of no contentions or collisions.

Performance analysis of orthogonal frequency division multiplexing systems in dispersive indoor power line channels inflicting asynchronous impulsive noise

Hidden semi-Markov modelling of the asynchronous impulsive noise (IN) encountered in indoor broadband power line communications (PLCs) is investigated by considering the statistical distributions of both the inter-arrival time and the duration of asynchronous IN components. Then, the bit error ratio (BER) of orthogonal frequency division multiplexing systems using Q-ary quadrature amplitude modulation is analysed with the aid of the proposed noise model, when communicating over dispersive indoor power line channels inflicting asynchronous IN in addition to the background noise. The authors’ simulation results confirm the accuracy of the analysis and quantify the impact of various factors on the achievable BER performance. The grave impact of asynchronous IN on indoor broadband PLCs suggests that efficient techniques have to be designed for mitigating its effects.

Multi‐way relaying for cooperative indoor power line communications

Sustaining high data rates over an indoor broadband power line communication (PLC) link is a challenging task due to the significant attenuation of high frequency signals transmitted over power cables. Repeaters are often used to alleviate the problem of signal attenuation, however, this comes at a loss of multiplexing gain. On the other hand, modern relaying concepts, as used in wireless systems, are not as effective in PLC setups due to the absence of diversity improvement. In this study, the authors address this issue and propose a new approach to improve the multiplexing gain of relay-aided PLC systems. The authors consider a multi-user indoor PLC scenario where all users want to share their data. For this setup, the authors then advocate the application of amplify-and-forward (AF) multi-way relaying (MWR). Considering the practical constraints of an indoor PLC system, the authors study the achievable data rates of AF MWR, and compare them to those achievable with direct (non-cooperative) transmission and conventional relaying schemes. The simulations demonstrate that depending on the network topology, MWR can result in significant performance improvement. The authors further discuss how their rate analysis can be exploited to decrease the energy consumption in the system.

Compressed Impairment Sensing-Assisted and Interleaved-Double-FFT-Aided Modulation Improves Broadband Power Line Communications Subjected to Asynchronous Impulsive Noise

In power line communications (PLCs), the multipath-induced dispersion and the impulsive noise are the two fundamental impediments in the way of high-integrity communications. The conventional orthogonal frequency-division multiplexing (OFDM) system is capable of mitigating the multipath effects in PLCs, but it fails to suppress the impulsive noise effects. Therefore, in order to mitigate both the multipath effects and the impulsive effects in PLCs, in this paper, a compressed impairment sensing (CIS)-assisted and interleaved-double-FFT (IDFFT)-aided system is proposed for indoor broadband PLC. Similar to classic OFDM, data symbols are transmitted in the time-domain, while the equalization process is employed in the frequency domain in order to achieve the maximum attainable multipath diversity gain. In addition, a specifically designed interleaver is employed in the frequency domain in order to mitigate the impulsive noise effects, which relies on the principles of compressed sensing (CS). Specifically, by taking advantage of the interleaving process, the impairment impulsive samples can be estimated by exploiting the principle of CS and then cancelled. In order to improve the estimation performance of CS, we propose a beneficial pilot design complemented by a pilot insertion scheme. Finally, a CIS-assisted detector is proposed for the IDFFT system advocated. Our simulation results show that the proposed CIS-assisted IDFFT system is capable of achieving a significantly improved performance compared with the conventional OFDM. Furthermore, the tradeoffs to be struck in the design of the CIS-assisted IDFFT system are also studied.

Joint terminals and relay optimization for two-way power line information exchange systems with QoS constraints

The quality-of-service (QoS) criteria (measured in terms of the minimum capacity requirement in this paper) are very important to practical indoor power line communication (PLC) applications as they greatly affect the user experience. With a two-way multicarrier relay configuration, in this paper we investigate the joint terminals and relay power optimization for the indoor broadband PLC environment, where the relay node works in the amplify-and-forward (AF) mode. As the QoS-constrained power allocation problem is highly non-convex, the globally optimal solution is computationally intractable to obtain. To overcome this challenge, we propose an alternating optimization (AO) method to decompose this problem into three convex/quasi-convex sub-problems. Simulation results demonstrate the fast convergence of the proposed algorithm under practical PLC channel conditions. Compared with the conventional bidirectional direct transmission (BDT) system, the relay-assisted two-way information exchange (R2WX) scheme can meet the same QoS requirement with less total power consumption.

Analysis and Comparison of Deterministic Power Line Channel Modeling Methods

Indoor broadband power line communications (PLC) use home grid as communication media. Many applications exist such as data sharing and internet access. However, the performances achieved differ widely from a home to another because of differences in electrical installations. A software tool able to qualify any household grid versus power line might be developed. There is no today undeniable model and many frameworks exist. To make an informed choice, this paper analyzes and compares frequent deterministic modeling: chain matrices, multipath, infinite impulse response (IIR) filters, and electrical circuits. Multipath model proved to be the most accurate despite its implementation challenge. Chain matrices and electrical circuits are very sensitive to the uncertainty of the propagation coefficient and the impedance characteristic of power cables. Chain matrices and IIR filters based methods are unable to predict accurately the level of a fading due to both two derivations.

Channel Modeling for Indoor Broadband Power-Line Communications Networks With Arbitrary Topologies by Taking Adjacent Nodes Into Account

We develop a general channel model in broadband power-line communications (BPLC) network using infinite geometric series and the description matrices. The developed general channel model can handle arbitrary PLC channel links easily; thus, we can calculate accurate channel characteristics without increasing computing complexity. For considering the effect of the various branches of the network, we investigate the characteristics of the channel links with adjacent nodes composed of multiple branches. We conduct the simulations by varying the degree of distantness of the adjacent nodes and the number of branches at the nodes. Our simulation results suggest that we should consider adjacent nodes with a degree of distantness up to one for the arbitrary channel links; these were not considered in previous studies. This enables us to calculate accurate channel responses of the arbitrary channel links of indoor BPLC networks.

Feasibility Study of a New Injection Method for EMI Reduction in Indoor Broadband PLC Networks

This paper proposes a new signal-injection technique which utilizes the earth wire that is present in the electrical system to reduce electromagnetic-interference (EMI) radiation from indoor broadband power-line communication (PLC) networks. The new signal injection method is compared with the typical signal-injection technique used in PLC modems today. The method is also compared with an alternative signal-injection technique proposed by other researchers. For a balanced network, the proposed new signal-injection technique allows for a significant reduction in the level of radiated electric field of up to 40 dB in the frequency range from 1 to 30 MHz when compared to the typical signal-injection technique. The feasibility and practicality of using the new signal-injection technique for the reduction of EMI radiation are discussed.

Link-Adaptive Physical Layer for Indoor Broadband Power-Line Communications

Increasing interest in smart home automation systems or home networks has driven the use of low-voltage power lines as a high-speed data channel. Since this type of power line is not designed for communication purposes, the channel exhibits unfavorable transmission properties. In this paper, a novel orthogonal frequency-division multiplexing-based physical-layer architecture for indoor broadband power-line communications is proposed. For the design of the layer, a new constellation for bit-mapping (or modulation) is introduced to increase the transmission rate over a sudden phase-shift-prone channel. In addition, a simple bit-loading scheme is adopted and a new preamble for a packet-based power-line communication system is proposed. The proposed layer is implemented as a type of testbed, and is field-tested in labs and in residential homes. The test results demonstrate that the proposed system has good channel adaptivity and achieves high transmission rates.