Luca Reggiani

Pseudo-chaotic time hopping for UWB impulse radio

In this paper, we propose a pseudo-chaotic modulation suitable for ultrawide-bandwidth impulse-radio communication systems. The coding scheme is based upon controlling the symbolic dynamics of a chaotic map for encoding the digital information to be transmitted. The pseudo-chaotic time hopping enhances the spread-spectrum characteristics of the system, by removing most periodic components from the transmitted signal. A maximum-likelihood detector for the proposed scheme is presented and its scalability features are illustrated. Finally, theoretical performance bounds for both soft and hard Viterbi decoding are derived and compared with the simulation results.

Rapid search algorithms for code acquisition in UWB impulse radio communications

Ultrawideband (UWB) impulse radio is an emerging technology suitable for high-rate tactical wireless communications. One of the crucial challenges for a connecting station remains the initial code acquisition, in a hostile propagation environment (e.g., urban combat). In this paper, we address the coarse acquisition of pseudonoise (PN) codes and propose algorithms for speeding up the acquisition process and/or reducing the complexity of the acquisition algorithm itself. Also, in the case of energy detection, we show that the front-end sampling rate may be reduced. An in-depth analysis, supported by simulations in the presence of multipath is presented, and the results discussed.

A reduced-complexity acquisition algorithm for UWB impulse radio

UWB (ultra-wideband) is a promising technology for short-range wireless communications, like in WPAN (wireless personal area networks) applications. In the context of UWB impulse radio, one of the crucial challenges remains the acquisition of synchronization in terms of time, precision and number of operations. In this paper, we present a novel strategy for reducing the number of operations required for the coarse acquisition of pseudo-noise sequences (at the chip level), thus speeding up the overall synchronization process. Also, we discuss the trade-off between computational load and synchronization performance.

An Algorithm for Positioning Relays and Point Scatterers in Wireless Systems

In this letter, we discuss the problem of positioning an unknown number of amplify-and-forward relays or point scatterers using a wireless network of wideband transceivers. We propose to model this positioning problem as an assignment problem. In doing so, we avoid the problems associated with an exhaustive gridsearch approach, which has recently been proposed to solve the problem. Numerical simulations show promising results in terms of performance and robustness.

Ultra-wide band sensor networks for tracking point scatterers or relays

In this paper we investigate the possible benefits and drawbacks of using a previously proposed “soft” ranging algorithm for tracking moving objects in indoor scenarios. The objects considered in this work could be either passive point scatterers or active relays. A number of ultra-wide band transceivers are deployed throughout the environment, and they are used to estimate multi-path propagation delays, that constitute the input data to the tracking algorithm. The motivation behind this work is that “soft” ranging algorithm enables both estimation of ranging error on a measurement-by-measurement basis, and also a straight-forward approach to multiple-hypotheses testing (MHT). Thus, this type of ranging algorithm is likely to fit well into a filter-bank tracking system. Computer simulations based on Ray-tracing propagation data indicates that the proposed approach enables both more robust and also more accurate positioning than when a more conventional threshold-based technique is used for ranging.

Probability density functions of soft information

It is well known that soft decoding algorithms are based on the use of reliability measures for binary and nonbinary symbols. We consider an analytical estimation of the distributions of reliability measures after soft decoding of block and convolutional codes or intersymbol interference (ISI) channels. This estimation, based on a simple geometric interpretation of reliability measures, allows the observation of different distributions for correct and incorrect symbols, and could be helpful for the analysis of soft decoding algorithms.

On the acquisition time for serial and parallel code search in UWB impulse radio

UWB (ultra-wideband) is an emerging technology for short-range wireless communications, such as WPAN (wireless personal area networks). In the context of UWB (ultra-wideband) impulse radio, one of the crucial challenges remains the acquisition of synchronization in terms of time, precision and number of operations. In this paper, we present a study on the acquisition time, for different code acquisition strategies, when considering the channel model adopted by IEEE 802.15.3a. Finally, we propose a simplified implementation of the acquisition algorithm based upon a coarser time frame quantization.

Hybrid active and passive localization for small targets

Ultra-Wideband (UWB) is an emerging technology for short-range wireless communications. Due to the high bandwidth of UWB signals, accurate ranging is possible, which is one of many reasons why UWB is a candidate physical layer for wireless sensor networks (WSNs). Reliable position information, obtained with a reasonable complexity overhead and possibly low energy consumption, is often paramount for a successful operation of these networks. The paper concerns a novel approach for improving the trade-off between energy consumption and performance in a localization tracking process. The scenario of application is common: a set of fixed beacons is used for tracking the position of a target that is moving in a limited indoor environment. The principle behind the proposed approach is relatively simple: tracking a small target device is realized by mixing active signal transmissions, which allow using standard techniques for deriving distances and locations, as well as passive signal receptions, which exploit scattering caused by small targets during signal propagation. The entire tracking process exploits the combination of these two types of transmissions with the advantage of possibly saving energy in the target device. The algorithm performance is highlighted by computer simulations using channel models adopted by the IEEE 802.15.4a working group.

Least Squares Channel Estimation for IEEE 802.16e Systems Based on Adaptive Taps Selection

IEEE 802.16 is an emerging technology for broadband cellular wireless communications. In the context of high capacity systems for mobile terminals, implementation issues like channel estimation become more challenging because of the sparsity of the pilots grid (w.r.t. the channel coherence bandwidth) and the time varying nature of the channel. This paper proposes a novel algorithm for channel estimation that is characterized by a good trade-off between complexity and performance. The algorithm, that is suitable for pilot-aided OFDM transmission, is applied here to IEEE 802.16e systems. Numerical results show that a meaningful performance gain (in terms of mean squared error and error probability) is provided by this estimation procedure, especially in the low SNR (Signal to Noise Ratio) region.

Coherent vs. Non-Coherent Detection for Orthogonal Convolutional Modulation: A Trade-Off Analysis

In the context of low data-rate UWB (ultra-wideband) networks, relying upon impulse radio-based devices, it has emerged the need of devising coding/modulation schemes amenable of both coherent and non-coherent detection. The rationale being the potential coexistence of different classes of devices characterized by different complexity/performances. In this work, we consider several orthogonal convolutional modulation (OCM) schemes and study the corresponding trade-offs in terms of coherent vs. non-coherent detection performance. Our theoretical predictions are supported by numerical simulations, thus confirming the results, based on which we provide some general design guidelines