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Umberto Mengali

Bio: Umberto Mengali is an academic researcher from University of Pisa. The author has contributed to research in topics: Synchronization & Communication channel. The author has an hindex of 19, co-authored 72 publications receiving 2965 citations.


Papers
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Book
31 Oct 1997
TL;DR: The Principles, Methods and Performance Limits of Carrier Frequency Recovery with Linear Modulations and Timing Recovery with CPM Modulations are presented.
Abstract: Introduction. Principles, Methods and Performance Limits. Carrier Frequency Recovery with Linear Modulations. Carrier Frequency Recovery with CPM Modulations. Carrier Phase Recovery with Linear Modulations. Carrier Phase Recovery with CPM Modulations. Timing Recovery in Baseband Transmission. Timing Recovery with Linear Modulations. Timing Recovery with CPM Modulations. Index.

1,029 citations

Journal ArticleDOI
TL;DR: In this article, a pseudonoise sequence is used for carrier frequency estimation in orthogonal frequency division multiplexing (OFDM) systems, and the estimation range can be widened in proportion to L without the need of a second training symbol.
Abstract: An efficient algorithm has been proposed by Schmidl and Cox (see IEEE Trans. Commun., p.1613-21, 1997) for carrier frequency estimation in orthogonal frequency division multiplexing systems. The scheme is based on the transmission of a training symbol composed of two identical halves in the time domain. Its accuracy is close to the Cramer-Rao bound and its estimation range, which is originally limited to the distance between two adjacent subcarriers, can be widened by exploiting a second training symbol containing some suitable pseudonoise sequence. In this paper we extend this algorithm by considering a training symbol composed of L>2 identical parts. This makes it possible to achieve a better accuracy at the cost of some increase in computational load. Furthermore, the estimation range can be widened in proportion to L without the need of a second training symbol.

534 citations

Proceedings ArticleDOI
01 Jan 1999
TL;DR: This paper extends the proposed algorithm for carrier frequency estimation in orthogonal frequency division multiplexing systems by considering a training symbol composed of L>2 identical parts, which makes it possible to achieve a better accuracy at the cost of some increase in computational load.
Abstract: An efficient algorithm has been proposed by Schmidl and Cox (see IEEE Trans. Commun., p.1613-21, 1997) for carrier frequency estimation in orthogonal frequency division multiplexing systems. The scheme is based on the transmission of a training symbol composed of two identical halves in the time domain. Its accuracy is close to the Cramer-Rao bound and its estimation range, which is originally limited to the distance between two adjacent subcarriers, can be widened by exploiting a second training symbol containing some suitable pseudonoise sequence. In this paper we extend this algorithm by considering a training symbol composed of L>2 identical parts. This makes it possible to achieve a better accuracy at the cost of some increase in computational load. Furthermore, the estimation range can be widened in proportion to L without the need of a second training symbol.

265 citations

Journal ArticleDOI
01 Mar 1998
TL;DR: In this paper, the authors considered feed forward carrier frequency estimation methods in burst-mode digital transmission, with tutorial objectives foremost, and provided a framework within which current estimation methods can be evaluated.
Abstract: This paper considers feedforward carrier frequency estimation methods in burst-mode digital transmission, with tutorial objectives foremost. Assuming PSK modulation, two scenarios are envisaged in which frequency estimates are derived either from a preamble appended to the data block, or directly from the modulated signal. Several estimation algorithms are considered with different and somewhat contrasting characteristics. The characteristics we focus on are: estimation accuracy, estimation range, minimum operating signal-to-noise ratio (threshold), and implementation complexity. They provide a framework within which current estimation methods can be evaluated. The paper reviews and compares some prominent algorithms proposed in literature, trying to single out the best ones for a given application.

202 citations

Journal ArticleDOI
TL;DR: Two timing algorithms are proposed that exploit the samples of the received signal to estimate the start of the individual frames with respect to the receiver's clock and the location of the first frame in each symbol (symbol timing).
Abstract: This paper is concerned with timing recovery for ultra-wideband communication systems operating in a dense multipath environment. Two timing algorithms are proposed that exploit the samples of the received signal to estimate the start of the individual frames with respect to the receiver's clock (frame timing) and the location of the first frame in each symbol (symbol timing). Channel estimation comes out as a by-product and can be used for coherent matched filter detection. The proposed algorithms require sampling rates on the order of the inverse of the pulse duration. Their performance is assessed by simulating the operation of coherent and differential detectors. Their sensitivity to the sampling rate is discussed, and the effects of the multiple access interference are evaluated.

110 citations


Cited by
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Journal ArticleDOI
TL;DR: An in-depth view of Terahertz Band (0.1-10 THz) communication, which is envisioned as a key technology to satisfy the increasing demand for higher speed wireless communication, is provided.

1,206 citations

Journal ArticleDOI
TL;DR: This tutorial overviews the state-of-the-art UWB in channel modeling, transmitters, and receivers of UWB radios, and outlines the research directions and challenges that needs to be overcome.
Abstract: Ultra-wideband (UWB) radio is a fast emerging technology with many unique attractive features that promotes major advances in wireless communications, networking, radar, imaging, and positioning systems. Research in UWB is still in its infancy stages, offering limited resources in handling the challenges facing the UWB communications. Understanding the unique properties and challenges of UWB communications as well as its application in competent signal processing techniques are vital in conquering the obstacles towards developing exciting UWB applications. UWB research and development has to cope with the challenges that limit their performance, capacity, throughput, network flexibility, implementation complexity, and cost. This tutorial focuses on UWB wireless communications at the physical layer. It overviews the state-of-the-art UWB in channel modeling, transmitters, and receivers of UWB radios, and outlines the research directions and challenges that needs to be overcome. Since a signal processing expertise is expected to have major impact in research and development of UWB systems, emphasis is placed on the DSP aspects.

1,199 citations

Journal ArticleDOI
TL;DR: Numerical results show that by optimizing the trajectory of the relay and power allocations adaptive to its induced channel variation, mobile relaying is able to achieve significant throughput gains over the conventional static relaying.
Abstract: In this paper, we consider a novel mobile relaying technique, where the relay nodes are mounted on unmanned aerial vehicles (UAVs) and hence are capable of moving at high speed. Compared with conventional static relaying, mobile relaying offers a new degree of freedom for performance enhancement via careful relay trajectory design. We study the throughput maximization problem in mobile relaying systems by optimizing the source/relay transmit power along with the relay trajectory, subject to practical mobility constraints (on the UAV’s speed and initial/final relay locations), as well as the information-causality constraint at the relay. It is shown that for the fixed relay trajectory, the throughput-optimal source/relay power allocations over time follow a “staircase” water filling structure, with non-increasing and non-decreasing water levels at the source and relay, respectively. On the other hand, with given power allocations, the throughput can be further improved by optimizing the UAV’s trajectory via successive convex optimization. An iterative algorithm is thus proposed to optimize the power allocations and relay trajectory alternately. Furthermore, for the special case with free initial and final relay locations, the jointly optimal power allocation and relay trajectory are derived. Numerical results show that by optimizing the trajectory of the relay and power allocations adaptive to its induced channel variation, mobile relaying is able to achieve significant throughput gains over the conventional static relaying.

1,079 citations

Book
31 Oct 1997
TL;DR: The Principles, Methods and Performance Limits of Carrier Frequency Recovery with Linear Modulations and Timing Recovery with CPM Modulations are presented.
Abstract: Introduction. Principles, Methods and Performance Limits. Carrier Frequency Recovery with Linear Modulations. Carrier Frequency Recovery with CPM Modulations. Carrier Phase Recovery with Linear Modulations. Carrier Phase Recovery with CPM Modulations. Timing Recovery in Baseband Transmission. Timing Recovery with Linear Modulations. Timing Recovery with CPM Modulations. Index.

1,029 citations

Journal ArticleDOI
TL;DR: This paper addresses basic OFDM and related modulations, as well as techniques to improve the performance of OFDM for wireless communications, including channel estimation and signal detection, time- and frequency-offset estimation and correction, peak-to-average power ratio reduction, and multiple-input-multiple-output (MIMO) techniques.
Abstract: Orthogonal frequency-division multiplexing (OFDM) effectively mitigates intersymbol interference (ISI) caused by the delay spread of wireless channels. Therefore, it has been used in many wireless systems and adopted by various standards. In this paper, we present a comprehensive survey on OFDM for wireless communications. We address basic OFDM and related modulations, as well as techniques to improve the performance of OFDM for wireless communications, including channel estimation and signal detection, time- and frequency-offset estimation and correction, peak-to-average power ratio reduction, and multiple-input-multiple-output (MIMO) techniques. We also describe the applications of OFDM in current systems and standards.

915 citations