Orthogonal frequency division multiplexing (OFDM) signals with rectangular pulses exhibit low spectral confinement. Shaping their power spectral density (PSD) is imperative in the increasingly overcrowded spectrum to benefit from the cognitive radio (CR) paradigm. However, since the available spectrum is non-contiguous and its occupancy changes with time, the spectral shaping solution has to be dynamically adapted. This work proposes a framework that allows using a reduced set of preoptimized pulses to shape the spectrum of OFDM signals, irrespective of its spectral width and location, by means of simple transformations. The employed pulses combine active interference cancellation (AIC) and adaptive symbol transition (AST) terms in a transparent way to the receiver. They can be easily adapted online by the communication device to changes in the location or width of the transmission band, which contrasts with existing methods of the same type that require solving NP-hard optimization problems.

Orthogonal frequency division multiplexing (OFDM) signals with rectangularly windowed pulses exhibit low spectral confinement. Two approaches usually referred to as pulse-shaping and active interference cancellation are classically employed to reduce the out-of-band emission (OOBE) without affecting the receiver. This paper proposes a spectral shaping method that generalizes and unifies these two strategies. To this end, the OFDM carriers are shaped with novel pulses, referred to as generalized pulses, that consist of the ones used in conventional OFDM systems plus a series of cancellation terms aimed at reducing the OOBE of the former. Hence, each generalized pulse embeds all the terms required to reduce its spectrum in the desired bands. This leads to a data-independent optimization problem that notably simplifies the implementation complexity and allows the analytical calculation of the resulting power spectral density (PSD), which in most methods found in the literature can only be estimated by means of simulations. As an example of its performance, the proposed technique allows complying with the stringent PSD mask imposed by the EN 50561-1 with a data carrier loss lower than 4%. By contrasts, 28% of the data carriers have to be nulled when pulse-shaping is employed in this scenario.

This note corrects a recurrent erratum in Section VII of our paper “An MTL-based channel model for indoor broadband mimo power line communications”[1]. Errors are concerned with the quantification of the spatial correlation of MIMO channels by means of the condition number of the channel matrix. According to the definition given in expression (25) of the paper, the higher the condition number, the higher the spatial correlation. However, Section VII is written as if high condition numbers correspond to low spatially correlated channels. Hence,whenever it is said that a given fact reduces the spatial correlation or, equivalently, that it yields lower spatially correlated channels, it should say exactly the opposite, i.e, the referred fact increases the spatial correlation or yields higher spatially correlated channels; and vice versa.

The recent release of indoor power line communication (PLC) standards with multiple-input multiple-output (MIMO) capabilities has led to the need for channel models that reflect the multiconductor nature of the grid. This paper proposes a model, based on the multiconductor transmission line theory, along with a random PLC channel generator operating in the frequency range from 1 to 100 MHz. Its distinctive features are the modeling of three key elements: the asymmetry in the layout caused by the derivations to the light switches, the impedance of the devices connected to the three wires of the grid, and the variable distance between the conductors in loose wiring deployments. The influence of these elements in the spatial correlation between the streams of the MIMO links is studied and compared with measurements.

In this work, a network simulator for power line communications based in the Homeplug-AV technology is presented. The simulator implements both the physical and the MAC layers, along with an in-home power line channel generator, which makes it very useful in a wide variety of network optimization procedures. To the authors' knowledge, performance evaluation of the MAC layer of Homeplug-AV by means of simulations has been always accomplished assuming excessively simplistic channel conditions. Therefore, this simulator represents an important contribution, as it includes a realistic physical model along with the CSMA/CA protocol described in the standard. In this paper, the proposed simulator is employed to evaluate the performance of the Homeplug-AV standard in an in-home network. The obtained results are then applied to video services planning in networks based in this standard.

This paper presents a statistical characterization of in-vehicle power lines, based on channel measurements carried out in a automobile. In particular, the impact of the engine speed on the characteristics of the channels is analyzed. Performance of an Orthogonal Frequency-Division Multiplexing (OFDM) system is assessed using the channel measurements.

In this paper, an FPGA-based channel emulator for indoor power line communications (PLC) is described. It has been designed for a band up to 30 MHz and is able to emulate time-varying channels and to generate a great variety of disturbances.

In the near future, several radio access technologies will coexist in Beyond 3G mobile networks (B3G) and they will be eventually transformed into one seamless global communication infrastructure. Self-managing systems (i.e. those that self-configure, self-protect, self-heal and self-optimize) are the solution to tackle the high complexity inherent to these networks. In this context, this paper proposes a system for auto-diagnosis in the Radio Access Network (RAN) of wireless systems. The malfunction of the RAN may be due not only to a hardware fault, but also (and more difficult to identify) to a bad configuration. The proposed system is based on the analysis of Key Performance Indicators (KPIs) in order to isolate the cause of the network malfunction. In this paper, two alternative probabilistic systems are compared, which differ on how KPIs are modelled (continuous or discrete variables). Experimental results are examined in order to support the theoretical concepts, based on data from a live network. The drawbacks and benefits of both systems are studied and some conclusions on the scenarios under which each model should be used are presented.

Discrete multitone (DMT) modulation is a suitable technique to cope with main impairments of broadband indoor power-line channels: spectral selectivity and cyclic time variations. To attain higher bit rates, in those subbands with good transmission conditions a high number of bits per symbol must be allocated and, hence, synchronization issues become an important concern. This paper analyzes the performance of a conventional DMT timing recovery scheme designed for linear time-invariant (LTI) channels, like digital subscriber lines, when employed over indoor power-lines. The influence of the channel short-time variations and the sampling jitter on the synchronization scheme performance is assessed. Proper parameterization of the timing recovery scheme is provided on the basis of reducing the impact of channel time variations while maintaining the ability to track the sampling jitter.

In the forthcoming years, different radio access technologies (GSM, GPRS, UMTS, etc.) will have to coexist within the same cellular network. In this scenario of increasingly complex networks, automated management is becoming a crucial issue to provide high-quality services. In this paper, a system for automatic fault diagnosis of the radio access part of a mobile communication system is presented. For this purpose, a probabilistic diagnosis model based on discrete Bayesian Networks (BNs) is proposed. There is always a trade-off between accuracy and complexity of the model. Hence, two alternative structures to code the dependencies among elements in the model are compared with regard to their simplicity and performance. Empirical results are examined, based on data from a live GSMIGPRS network. Taking into account the experiments, a BN structure is selected for diagnosis in cellular networks.

The purpose of this paper is to analyze the properties of indoor power line communications channels when they are used for broadband transmission. It will be shown that these channels exhibit a short-term variation, due to the fact that high-frequency parameters of electrical devices depend on the instantaneous amplitude of mains voltage. This phenomenon leads to a channel model proposal based on a linear periodically time-varying system and cyclostationary random noise. A measurement system, designed to capture these time variations in real power networks, and some of the most significant results obtained with it, are presented. In addition, a statistical analysis of the measurements performed in several indoor power line scenarios is included, so that the relevance of time variations in actual channels can be evaluated.

Frequency plans (FPs) based on mobile measurements present several advantages compared to those based on propagation predictions. These FPs use interference matrices (IMs) created from measurement reports (MMRs). MMRs, as described in the GSM specifications, present some limitations: quantization and truncation of measured values, only six strongest neighbours reported and BSIC (base station identity code) decoding procedure. In addition, different types of IMs, depending on the processing of the raw data, can be considered. In this paper, MMRs limitations and their impact on different types of IMs are analyzed. Simulations for macrocell and microcell scenarios have been carried out to reinforce the conclusions.

Discrete multitone (DMT) modulation is a multicarrier technique that allows the transmission of high speed data over band limited channels. This type of system is very sensitive to synchronization errors when used in digital subscriber loop applications (xDSL), due to the high number of carriers and high density constellations involved. This paper addresses the topic of all-digital timing error correction in a DMT system for xDSL applications, where the timing error correction procedure is based entirely on signal interpolation. An analytical study of the interpolator filter performance is carried out, arriving at an expression for the signal-to-distortion ratio (SDR) at the output of the receiver, as a merit figure. In this derivation, the fixed frequency domain equalizer (FEQ) plays an important role since it compensates for a great part of the distortion introduced by the interpolator. From this study, the design of the optimal interpolator filter in terms of SDR, based on a multirate approach with Kaiser window, is presented. Specific designs for ASIC and for DSP-based implementations are obtained. Performance results are excellent, yielding SDR values above 50 dB for all carriers while keeping the computational cost low.

We describe a communication terminal called Tiche. Tiche was designed for achieving privacy when fax or speech are transmitted over the public switching telephone network, PSTN. It is composed of three main functional blocks: a speech coder, an encryption algorithm and a digital modem. When Tiche is connected to a telephone set and to the PSTN, the modem tries to communicate at the higher rate possible for the given channel and selects the speech coder according to that, it selects one of the bit rates available with the standard V32 (4800 or 9600 bps). When it transmits fares Tiche detects the communication standard: V27, V29 or V17 and selects the corresponding modem. The ciphering system is based on both public key and private key algorithms. The overall system is digital and was programmed using DSP.>

A review is presented of several classical equalizers for data transmission, showing that they are special cases of a general time-delay neural net (TDNN). It is shown that the solution to the deconvolution problem for many transmission channel types, including linear and nonlinear distortions, can be solved by means of TDNN. Alternatively, TDNN can be seen as a generalization of currently used equalizers and as tools for discovering new ones.>