Olivier Rousseaux

Estimation and equalization of doubly selective channels using known symbol padding

This paper considers the situation where users that experience high-mobility transmit data over frequency-selective channels, resulting in a doubly selective channel model (i.e., time- and frequency-selective channels) and this within the framework of Known Symbol Padding (KSP) transmission. KSP is a recently proposed block transmission technique where short sequences of known symbols acting as guard bands are inserted between successive blocks of data symbols. This paper proposes three novel channel estimation methods that allow for an accurate estimation of the time-varying transmission channel solely relying on the knowledge of the redundant symbols introduced by the KSP transmission scheme. The first method is a direct adaptive one while the others rely on a recently proposed model, the Basis Expansion Model (BEM), where the doubly selective channel is approximated with high accuracy using a limited number of complex exponentials. An important characteristic of the proposed methods is that they exploit all the received symbols that contain contributions from the training sequences and blindly filter out the contribution of the unknown surrounding data symbols. Besides these channel identification methods, the classical KSP equalizers are adapted to the context of doubly selective channels, which allows evaluation of the bit-error-rate (BER) performance of a KSP transmission system relying on the proposed channel estimation methods in the context of doubly selective channels. Simulation results show that KSP transmission is indeed a suitable transmission technique toward the delivery of high data rates to users experiencing a high mobility, when adapted KSP equalizers are used in combination with the proposed channel estimation methods.

UWB Radio Transceivers For Ultra Low Power and Low Data Rate Communications

Radio transceivers relying on impulsed radio UWB signals show a strong potential for low data rate communications at an ultra low power consumption. They are for instance proposed by the IEEE 802.15.4a low-rate wireless personal area networks standard (LR-WPAN) to support low data rates, low power and low complexity short-range radio communications. In this paper, we give an overview of our recent UWB radio front-end designs along with new system simulation results, and derive specifications for a 15.4a receiver. The system simulations are used to balance the partitioning of gain, noise and distortion for next generation transceivers and allow to analyze the expected communication range of IEEE 802.15.4a systems in various channel conditions. The free-space wireless channel loss as well as 9 propagation scenarios are taken into account.

Gaussian maximum-likelihood channel estimation with short training sequences

In this paper, we address the problem of identifying convolutive channels using a Gaussian maximum-likelihood (ML) approach when short training sequences (possibly shorter than the channel impulse-response length) are periodically inserted in the transmitted signal. We consider the case where the channel is quasi-static (i.e., the sampling period is several orders of magnitude smaller than the coherence time of the channel). Several training sequences can thus be used in order to produce the channel estimate. The proposed method can be classified as semiblind and exploits all channel-output samples containing contributions from the training sequences (including those containing contributions from the unknown surrounding data symbols). Experimental results show that the proposed method closely approaches the Cramer-Rao bound and outperforms existing training-based methods (which solely exploit the channel-output samples containing contributions from the training sequences only). Existing semiblind ML methods are tested as well and appear to be outperformed by the proposed method in the considered context. A major advantage of the proposed approach is its computational complexity, which is significantly lower than that of existing semiblind methods.

Tuning of a decoupling controller for a 2×2 system using iterative feedback tuning

Iterative feedback tuning is used to tune a decoupling controller for a 2 x 2 multivariable system. The tuning is carried out in two steps. In the first step the coefficients of two proportional decoupling controllers are tuned, and in the second step two PD-controllers are tuned. The approach is evaluated on a nonlinear simulation model of a two-link manipulator. The evaluation is carried out using two different reference trajectories and also in the presence of friction. The resulting closed loop systems show satisfactory behavior in all three cases

Iterative Feedback Tuning Applied to Robot Joint Controllers

Tuning of robot joint controllers using iterative feedback tuning (IFT) is considered. Using a simulation model of a two-link robot arm the applicability of IFT is investigated for a nonlinear and ...

A suboptimal Iterative Method for Maximum-Likelihood Sequence Estimation in a Multipath Context

We present an iterative semiblind suboptimal maximum-likelihood sequence estimation (MLSE) method for single-carrier block transmission over stationary multipath channels. This suboptimal ML detector is based on an iterative least squares with projection (ILSP) algorithm exploiting both the finite alphabet properties of the transmitted signal and its cyclic prefixed structure in order to approach ML detection in a cheap way. Since the initial channel estimate is crucial for the convergence speed of the ILSP algorithm, we propose a new low-complexity stochastic method for providing an initial channel estimate. We therefore rely on some known symbols that are provided by a variant of cyclic prefix only (CP-Only) transmission, known as the known symbol padding only (KSP-Only) technique. The resulting channel model is sufficiently accurate to be used as a starting point for the iterations. The final result is a direct symbol estimation method that is characterised by its low computational complexity and its promising results in terms of bit error rate (BER).

Direct semi-blind design of serial linear equalizers for doubly-selective channels

Recently, serial linear equalizers (SLEs) and serial decision feedback equalizers (SDFEs) have been proposed to mitigate the doubly-selective channel effects. To design the SLE/SDFE and to model the doubly-selective channel, a so-called finite impulse response basis expansion model (FIR-BEM) is used. Initially, the FIR-BEM coefficients of the SLE/SDFE were designed based on the exact knowledge of the FIR-BEM coefficients of the doubly-selective channel. In practice, we can use a direct SLE/SDFE design procedure, which avoids an intermediate channel estimation step. In this paper, we describe this idea for the SLE and focus on direct semi-blind design of the FIR- BEM coefficients of the SLE. Simulation results demonstrate the validity of the proposed approach.

A stochastic method for training based channel identification

In this paper, we propose a new iterative stochastic method to identify convolutive channels when training sequences are inserted in the transmitted signal. We consider the case where the channel is quasistatic (i.e. the sampling period is several orders of magnitude below the coherence time of the channel). There are no requirements on the length of the training sequences and all the received symbols that contain contributions from the training symbols are exploited. The interference from the unknown data symbols surrounding the training sequences is considered as additive noise colored by the transmission channel. An iterative weighted least squares approach is used to filter out the contribution of both this interference term and the additive white gaussian noise term.

Ultra Wide Band in Medical Applications

Ultra Wide Band (UWB) technology has been developed in the last years in the framework of short-range low data rate communications. Due to the wide channels bandwidth and low power characteristics it provides a very different approach to wireless technologies compared to conventional narrow band systems. This makes it interesting in medicine area with many potential applications. In this chapter, the discussion is focused on the application of this technology in medical monitoring, and Wireless Body Area Networks.

RF and Base-Band circuit blocks for LR-UWB receivers

Low Data Rate Ultra-Wideband (LR-UWB) systems have an enormous potential and compare favorably to other communication systems, in terms of capacity and low-complexity. This stems from the channels located at rather high frequencies (3.5 GHz-10 GHz), which offer each a large signal bandwidth (500MHz). However, these aggressive broadband frequency properties of UWB systems make the design of low-power receivers quite challenging. In this paper the circuit blocks that constitute an LR-UWB receiver are illustrated. They are designed in CMOS 90nm technology. The RF section, including LNAs and oscillators is considered first. Secondly, the problems and the circuit solutions related to the base-band section, including filters and programmable gain amplifiers are addressed.