J.T. Entrambasaguas

A channel model proposal for indoor power line communications

In this article, a channel model for broadband indoor Power Line Communications (PLC) is presented and discussed. The modeling approach is based on the physical structure of the electrical networks inside homes and small offices. The structure has been simplified to derive a parametric model that still preserves the essential behavior of these channels in the HF band (up to 30 MHz). The model provides realistic channels by setting values to a reduced number of physical parameters. In addition, statistical distributions for such parameters that allow generating ensembles of random channels are suggested. The validity of the generated channels is assessed by comparing their behavior to the one of channels measured at several indoor power networks. Hence, this model can be employed to estimate the performance of transmission techniques on PLC channels, to aid in the design of PLC systems or to make prototype conformance tests.

Broadband modelling of indoor power-line channels

The main purpose of this paper is to describe and model the characteristics of low voltage distribution lines inside consumer premises, when used as a broadband communication channel. Results from measurements performed both in the laboratory and in residential buildings, are presented and discussed. Also a channel model to simulate the behaviour of these lines for high bit-rate digital communications is proposed. The model contemplates the topology of the power grid and the characteristics of the wires and loads connected to them; it incorporates as well statistical time variation of the loads, so that the dynamic evolution of the channel performance can be evaluated.

Modeling and evaluation of the indoor power line transmission medium

The aim of this article is to outline the possibilities of indoor power lines when used to support local area networks in homes or small offices. For this purpose, the channel characteristics are described and a channel model is presented. This model is related to the physical nature of common indoor power lines, so its parameters can be defined in a straightforward way. Based on it, the performance of communication systems that use discrete multitone modulation, which appears to be the most suitable technique for these channels, is evaluated. Finally, a discussion about medium access control strategies is included.

Impact of channel estimation error on adaptive modulation performance in flat fading

Presented here is an approach to analyzing the effect of imperfect channel estimation on adaptive modulation. The sensitivity of the main performance parameters to short-term and long-term estimation error sources is summarized in a set of new formulas that are either closed-form expressions or simple to compute numerically.

Fundamentals of the cyclic short-time variation of indoor power-line channels

In this paper, indoor power-line channels properties are analyzed. The focus is put on the short-term variation that channel exhibits due to the behavior of electrical devices, which is influenced by the presence of mains voltage. Devices high-frequency parameters are time-varying and this makes the channel varies as well. To characterize this behavior it is proposed a model with an LPTV system and cyclostationary noise. In addition, examples of measurements corresponding to actual channels that illustrate these features are shown. More quantitative measurements results performed according to this channel model are presented in JA Cortes, et al. (2005).

A Channel Simulator for Indoor Power-line Communications

In this paper, a simulator for indoor power-line channels is presented. Its behavioral model includes both the long-and short-time variation of the channel. The long-time variation is due to the electrical appliances switching and is modeled in a statistical way. The cyclic short-time variation is related to the presence of the mains voltage and is characterized modeling the channel response as a linear periodically time-variant (LPTV) system and including an additive cyclostationary noise term. The cyclic model is simplified by using a slow variation approach, so that the channel can be modeled by means of a cyclic sequence of LTI systems with stationary noise terms. Channels according to the behavioral model are generated based on the physical structure of the network. The model for this physical structure comprises: the wiring, characterized as a set of terminated transmission lines connected in a tree-like fashion; and the electrical appliances, which are modeled as electric bipoles acting as impedances and noise sources. The simulator can perform the calculation of the channel frequency response and noise power spectral density at the receiver given a network topology. Afterwards, a channel simulation can be carried out using two banks of filters, one for the LPTV channel response and the other to obtain cyclostationary noise by filtering AWGN. Some test results for the channel generation and simulation are presented, and practical applications of this simulator are discussed.

Characterization of the cyclic short-time variation of indoor power-line channels response

Indoor power-line channels response exhibits a time-varying behaviour with a twofold nature. The first one is the well-known long-term variation caused by the connection and disconnection of electrical devices. The second one is a short-time variation, synchronous to the mains, whose origin is the dependence of the impedance presented by electrical devices on the mains voltage (Canete, FJ et al., 2005). The purpose of this paper is to assess the importance of this latter aspect in actual channels. To this end, a measurement procedure able to extract these short-time variations is described at first. Afterwards, a statistical analysis of the results obtained from a measurement campaign performed at different scenarios is given. Specifically, the delay spread, the peak excursion and the rate of change of the frequency response in the band from 1 MHz to 20 MHz are presented and discussed.

Optimum discrete-power adaptive QAM scheme for Rayleigh fading channels

In this letter, the utilization of a finite number of power levels per constellation in adaptive QAM schemes for flat fading channels is analyzed. Assuming a maximum target BER, the optimum switching thresholds in order to maximize the spectral efficiency are found for Rayleigh fading. Both analysis and simulation results show that a small number of power levels per constellation allows to obtain a good compromise between high spectral efficiency and low feedback information rate.

Multiuser Capacity and Fairness Evaluation of Channel/QoS-Aware Multiplexing Algorithms

In this work multiplexing of variable-rate sources over shared generic multiple fading channels is addressed. In general, the performance of existing multiplexing algorithms has been compared in very specific environments, making it difficult to draw general conclusions. In this article we propose a generic variable-rate multiuser and multichannel system model that can be applied to any orthogonal channel multiplexing mechanism (e.g., TDM, OFDM, CDM, or SDM) through parametric modeling. Based on the model, the performance of different multiplexing algorithms proposed in the literature is evaluated over moderately fast fading snared channels. Physical channel conditions, random traffic arrival, and QoS requirements are taken into consideration in the study. Multiuser capacity and fairness are assessed and evaluated for different channel-aware and/or QoS-aware user multiplexing algorithms. Results show the joint diversity gain and QoS in terms of the throughput and delay experienced by different user information flows

Performance evaluation of OFDMA wireless systems using WM-SIM platform

Orthogonal Frequency-Division Multiple Access (OFDMA) is becoming a very promising candidate for Long Term Evolution (LTE) and future Forth Generation (4G) technology specifications. This paper presents the work-in-progress development of an OFDMA wireless system model, which runs on top of the Wireless Mobile SIMulation platform (WM-SIM). The main physical (PHY) and Medium Access Control (MAC) functionalities at the radio interface have been implemented and evaluated. A multi-user downlink scheme, where a Base Station (BS) transmits variable-rate information to a set of mobile terminals, is assumed. Performance results show the accuracy of the simulations compared to theoretical estimations.