L. De Nardis

Modeling and optimization of UWB communication networks through a flexible cost function

The traditional design of communication networks has rarely been able to focus on the optimization of global network properties. Ultra-wideband (UWB) radio is emerging as an attractive physical layer for wireless communication networks offering new opportunities for the principled design and optimization of network properties. We develop a framework for the principled design of UWB wireless networks based on a flexible cost function that can be tailored and scaled to a wide range of networks and applications, ranging from sensor networks to voice and data wireless networks. The function comprises cost terms associated with transmission, connection setup, interference, and quality-of-service. Multihop routing strategies are associated with admissible paths of minimal cost that are computable in linear time. The cost function together with the overall level of requests determine the dynamics of the connections and the equilibrium topology of the network. We report simulation results in the case of simple ring and square lattice networks.

Overview of the IEEE 802.15.4/4a standards for low data rate Wireless Personal Data Networks

The IEEE 802.15.4 standard provides a framework for low data rate communications systems, typically sensor networks. The 802.15.4a revision introduces new options for the physical layer, in order to support higher data rates and accurate ranging capability, enabling new applications based on information on distance and positions of the devices in the network. In this paper the differences among physical layers of 802.15.4 vs. 802.15.4a are briefly reviewed. Next, the MAC layer of 802.15.4 vs. 802.15.4a are reviewed and compared. Device functionalities, network topologies as well as access strategies in both standards are described, and the impact of the new physical layer features on MAC and higher layers are discussed, with particular attention to the ranging scheme adopted in the new revision of the standard.

UWB ad-hoc networks

We propose a new strategy for path selection in a UWB based ad-hoc network which by minimizing a power-dependent global cost function, can potentially lead to an optimal network organization characterized by low emitted power levels and high network performance.

UWB ranging accuracy in high- and low-data-rate applications

The Cramer-Rao lower bound (CRLB) was determined for different ultra-wideband (UWB) signal formats and, in particular, for the two UWB high-data-rate (HDR) signal formats proposed within the IEEE 802.15.3a Task Group, that is, the impulsive direct-sequence UWB (DS-UWB) and the nonimpulsive multiband orthogonal frequency-division multiplexing (MB-OFDM), and an impulsive time hopping (TH) UWB format close to the format for UWB low data rate (LDR) of the forthcoming IEEE 802.15.4a standard. The analysis was carried out for both ideal and multipath channels under power constraints as set by emission masks. Results obtained for HDR formats showed that DS-UWB has better ranging accuracy than does MB-OFDM, thanks to its potentially larger bandwidth and higher frequency of operation. In addition, the degree of multipath strongly affected ranging accuracy, although differently for DS-UWB versus MB-OFDM. When incorporating a correlation receiver structure as well as an Early Late gate synchronizer in the model, ranging performance proved to be related to features of the synchronization sequence. For specific synchronization sequences, in particular, the best ranging accuracy was obtained with MB-OFDM. In the case of LDR, the study analyzed the effect of pulse shape on CRLB. Results showed that a suboptimal choice of the pulse shape reduces the ranging accuracy achievable by TH-UWB signals.

Multi user interference in power-unbalanced ultra wide band systems: analysis and verification

Validity of the standard Gaussian approximation (SGA) for modeling multi user interference (MUI) in impulse radio ultra wide band (IR-UWB) systems which do not implement power control is investigated. Analysis focuses on the case of UWB systems adopting binary pulse position modulation (2PPM) with a time hopping (TH) code division multiple access scheme. Theoretical predictions are compared vs. simulation outputs in order to quantify limitations of the SGA hypothesis.

Radio frequency interference issues in impulse radio multiple access communication systems

Impulse radio systems use very short pulses. Consequently, the spectrum of the transmitted signal spreads over several gigahertz and overlaps with RF bands occupied by other communication systems. As a result, radio frequency interference (RFI) affects the received signal. We present an analysis of the effects of RFI to a victim UWB receiver. Conditions for RFI cancellation for a large class of interfering signals are derived and it is shown that accurate frequency estimation of the interfering signal is necessary in order to provide interference cancellation. Finally, we give the level of accuracy that guarantees that the theoretical results hold in practice.

A position based routing strategy for UWB networks

In this paper a position based routing strategy which exploits the high precision ranging capabilities offered by ultra-wide band (UWB) is presented. It is shown that if a position-aware routing protocol and a power-aware routing metric based on ranging measurements are adopted, emitted power levels as well as multi-user interference are significantly reduced. The position-aware strategy is compared with standard solutions based on the minimization of the number of hops and on-demand routing. Results are presented for various transmission ranges, i.e. network connectivity conditions. Both power efficiency and routing performance are taken into account in the analysis and trade-offs between these two features are finally discussed.

Power limits fulfilment and MUI reduction based on pulse shaping in UWB networks

Pulse shaping in ultra-wide band (UWB) networks based on impulse radio (IR) is a viable way for adapting the power spectral density (PSD) of transmitted signals to spectral requirements. The proposed pulse shaping method is based on linear combination of a set of base waveforms obtained by differentiation of the Gaussian pulse. Strategies for selecting linear combination coefficients are proposed and approximation of emission masks for UWB indoor systems based on linear combination of the above base functions is analyzed. It is shown that linear combination of base waveforms fulfils spectral requirements with higher efficiency than that achieved by a single waveform. The adoption of pulse shaping in the reduction of multiuser interference (MUI) between different UWB networks is finally proposed and evaluated by means of simulations.

Power-aware design of MAC and routing for UWB networks

Ultra wide band (UWB) radio is considered as a valuable candidate for the deployment of large-scale, low data rate networks, thanks to its large bandwidth allowing for a high number of simultaneous communications. The specific characteristics of UWB, such as ranging capability and severe power limitations, call however for innovative solutions not only at the physical layer, but also at MAC and network layers as well. In this paper an integrated strategy for MAC and routing in UWB networks is proposed, which combines the multiple access capabilities and the ranging information provided by this transmission technique. The strategy exploits the distance information for reducing the power emission in the network, leading to a longer network lifetime and low multi user interference (MUI), thanks to the combination of a distance-based routing metric with a location-aware routing protocol, enabled by the adoption of a distributed positioning protocol. The effectiveness of the proposed solution is evaluated by means of simulations.

Cognitive routing models in UWB networks

This paper investigates the effect of introducing cognitive mechanisms in the routing module of a wireless network. A routing cost function that incorporates measurements of both internal network status and instantaneous behavior of external world is described. The proposed cost function is analyzed by simulation in the framework of IEEE 802.15.4a-like low data rate and low cost networks for mixed indoor/outdoor communications. The analysis focuses on the impact of MUI modeling on network performance. Results indicate that MUI-awareness, as provided by the proposed cognitive cost function, may improve network performance in terms of network lifetime. Based on this analysis, a mechanism for learning from previous routing decisions and adapting the routing cost function to MUI conditions is introduced.