This paper deals with the analysis of the timing acquisition (synchronization) process in Impulse Radio (IR-) Ultra Wide Band (UWB) systems based on Differential Trans- mitted Reference (DTR) receiver architectures. The fundamen- tal contribution includes a theoretical framework for timing acquisition analysis, which is not only able to describe the first moment (Mean Acquisition Time, MAT), and the second moment (standard deviation of the acquisition time) of the acquisition process, but which also provides a consistent and comprehensive analysis of the probability mass function of the acquisition time, i.e., Acquisition Time Mass Probability. In particular, the specific novelty insights of this paper are as follows: i) the proposal of a new synchronization algorithm, which is based on a two-step approach and relies on the specific characteristics and peculiarities of DTR receivers, as well as the analysis of its performance via a framework based on the theory of Markov processes; ii) the exploitation of the LATTICE- POISSON algorithm to accurately estimate the Acquisition Time nization, differential transmitted reference receiver, mean acqui- sition time, acquisition time mass probability, multipath channels. I. INTRODUCTION AND MOTIVATIONS IMPULSE RADIO (IR) [1]-[3] is a particular form of UWB technology that is characterized by the transmission of very short pulses occupying a large frequency bandwidth. This large bandwidth allows UWB signals to finely resolve multipath components and to exploit multipath diversity, thus making UWB a viable candidate for communications in harsh reference scenarios, such as industrial/factory indoor and forest/sub-urban outdoor environments. Moreover, due to their fine delay resolution properties, UWB signals are robust against fading, and are potentially able to provide accurate ranging and synchronization capabilities [4]-[6]. Timing acquisition is one of the most critical aspects to enable the unique benefits of UWB communication. Never- theless, although synchronization represents a key challenge in any digital communication systems, its difficulty is exac- erbated in IR-UWB due to the distinguishing feature of these systems, i.e., ultrashort low-duty-cycle pulse transmissions operating at a very low power spectral density [7]. The main consequences of pulse-based transmissions can be summarized as follows. i) Timing recovery is required not only at the frame level (i.e., to find when the first frame in each symbol starts), but also at the pulse level (i.e., to find where a pulse is located within a frame) [8], and ii) timing errors as small as a fraction of nanosecond may be responsible for pronounced system performance (e.g., Bit Error Probability, BEP) degradation, [9]-[11]. As a consequence, timing acquisition may turn out to be a very long process in the UWB context. Furthermore, UWB timing acquisition in multipath channels has to consider that, due to the very large number of resolvable multipath components, different delays may lead to a successful acqui- sition [12] (multipath-aided timing acquisition). This aspect is instead almost neglected in traditional Spread Spectrum (SS) systems [13], [14] with the exception of a few contributions (see, e.g., [15], [16] and references therein, [17]-[19]. The reader can also refer to [20] for an in-depth analysis of acquisition modeling in SS fading channels). Mass Probability and Overall Acquisition Probability (P(ov)), D i.e., the probability to get synchronized before a given time; iii) the performance analysis and comparison of one-step and two-step solutions with respect to the acquisition threshold; and iv) the analysis of two approaches to estimate MAT and P(ov) D in multipath fading channels, i.e., “Tacq Average” and “Pd Average’, which are shown to lead to different results in different scenarios. We observe that restricting the analysis to the MAT may lead to hasty conclusions about the effect of the acquisition threshold on the design of DTR receivers, thus substantiating the need for a more general analysis using P(ov), as well as D the necessity of specifying the characteristics of the wireless channel (e.g., quasi-static, slowly- or fast-fading) for an accurate performance analysis.
A Novel Class of Algorithms for Timing Acquisition of Differential Transmitted Reference (DTR) Ultra Wide Band (UWB) Receivers - Architecture, Performance Analysis and System Design
GRAZIOSI, FABIO;SANTUCCI, FORTUNATO
2008-01-01
Abstract
This paper deals with the analysis of the timing acquisition (synchronization) process in Impulse Radio (IR-) Ultra Wide Band (UWB) systems based on Differential Trans- mitted Reference (DTR) receiver architectures. The fundamen- tal contribution includes a theoretical framework for timing acquisition analysis, which is not only able to describe the first moment (Mean Acquisition Time, MAT), and the second moment (standard deviation of the acquisition time) of the acquisition process, but which also provides a consistent and comprehensive analysis of the probability mass function of the acquisition time, i.e., Acquisition Time Mass Probability. In particular, the specific novelty insights of this paper are as follows: i) the proposal of a new synchronization algorithm, which is based on a two-step approach and relies on the specific characteristics and peculiarities of DTR receivers, as well as the analysis of its performance via a framework based on the theory of Markov processes; ii) the exploitation of the LATTICE- POISSON algorithm to accurately estimate the Acquisition Time nization, differential transmitted reference receiver, mean acqui- sition time, acquisition time mass probability, multipath channels. I. INTRODUCTION AND MOTIVATIONS IMPULSE RADIO (IR) [1]-[3] is a particular form of UWB technology that is characterized by the transmission of very short pulses occupying a large frequency bandwidth. This large bandwidth allows UWB signals to finely resolve multipath components and to exploit multipath diversity, thus making UWB a viable candidate for communications in harsh reference scenarios, such as industrial/factory indoor and forest/sub-urban outdoor environments. Moreover, due to their fine delay resolution properties, UWB signals are robust against fading, and are potentially able to provide accurate ranging and synchronization capabilities [4]-[6]. Timing acquisition is one of the most critical aspects to enable the unique benefits of UWB communication. Never- theless, although synchronization represents a key challenge in any digital communication systems, its difficulty is exac- erbated in IR-UWB due to the distinguishing feature of these systems, i.e., ultrashort low-duty-cycle pulse transmissions operating at a very low power spectral density [7]. The main consequences of pulse-based transmissions can be summarized as follows. i) Timing recovery is required not only at the frame level (i.e., to find when the first frame in each symbol starts), but also at the pulse level (i.e., to find where a pulse is located within a frame) [8], and ii) timing errors as small as a fraction of nanosecond may be responsible for pronounced system performance (e.g., Bit Error Probability, BEP) degradation, [9]-[11]. As a consequence, timing acquisition may turn out to be a very long process in the UWB context. Furthermore, UWB timing acquisition in multipath channels has to consider that, due to the very large number of resolvable multipath components, different delays may lead to a successful acqui- sition [12] (multipath-aided timing acquisition). This aspect is instead almost neglected in traditional Spread Spectrum (SS) systems [13], [14] with the exception of a few contributions (see, e.g., [15], [16] and references therein, [17]-[19]. The reader can also refer to [20] for an in-depth analysis of acquisition modeling in SS fading channels). Mass Probability and Overall Acquisition Probability (P(ov)), D i.e., the probability to get synchronized before a given time; iii) the performance analysis and comparison of one-step and two-step solutions with respect to the acquisition threshold; and iv) the analysis of two approaches to estimate MAT and P(ov) D in multipath fading channels, i.e., “Tacq Average” and “Pd Average’, which are shown to lead to different results in different scenarios. We observe that restricting the analysis to the MAT may lead to hasty conclusions about the effect of the acquisition threshold on the design of DTR receivers, thus substantiating the need for a more general analysis using P(ov), as well as D the necessity of specifying the characteristics of the wireless channel (e.g., quasi-static, slowly- or fast-fading) for an accurate performance analysis.Pubblicazioni consigliate
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