Pierpaolo Bergamo

Localization in sensor networks with fading and mobility

In sensor networks the device localization is an interesting topic due to its relationship with routing and energy consumption. We propose a scheme to perform localization, based on the estimation of the power received by only two beacons placed in known positions. By starting from the received powers, eventually averaged on a given window to counteract interference and fading, the actual distance between the sensor and the beacons is derived and the position obtained by means of triangulation. The paper shows the effectiveness of this approach in different environments, by including the possible disturbance due to fading channels and sensor mobility.

Distributed power control for energy efficient routing in ad hoc networks

In this paper, distributed power control is proposed as a means to improve the energy efficiency of routing algorithms in ad hoc networks. Each node in the network estimates the power necessary to reach its own neighbors, and this power estimate is used both for tuning the transmit power (thereby reducing interference and energy consumption) and as the link cost for minimum energy routing. With reference to classic routing algorithms, such as Dijkstra and Link State, as well as more recently proposed ad hoc routing schemes, such as AODV, we demonstrate by extensive simulations that in many cases of interest our scheme provides substantial transmit energy savings while introducing limited degradation in terms of throughput and delay.

Collaborative sensor networking towards real-time acoustical beamforming in free-space and limited reverberance

Wireless sensor networks have been attracting increasing research interest given the recent advances in microelectronics, array processing, and wireless networking. Consisting of a large collection of small, wireless, low-cost, integrated sensing, computing and communicating nodes capable of performing various demanding collaborative space-time processing tasks, wireless sensor network technology poses various unique design challenges, particularly for real-time operation. We review the approximate maximum-likelihood (AML) method for source localization and direction-of-arrival (DOA) estimation. Then, we consider the use of least-squares method (LS) method applied to DOA bearing crossings to perform source localization. A novel virtual array model applicable to the AML-DOA estimation method is proposed for reverberant scenarios. Details on the wireless acoustical testbed are given. We consider the use of Compaq iPAQ 3760s, which are handheld, battery-powered device normally meant to be used as personal organizers (PDAs), as sensor nodes. The iPAQ provide a reasonable balance of cost, availability, and functionality. It has a build in StrongARM processor, microphone, codec for acoustic acquisition and processing, and a PCMCIA bus for external IEEE 802.11b wireless cards for radio communication. The iPAQs form a distributed sensor network to perform real-time acoustical beamforming. Computational times and associated real-time processing tasks are described. Field measured results for linear, triangular, and square subarrays in free-space and reverberant scenarios are presented. These results show the effective and robust operation of the proposed algorithms and their implementations on a real-time acoustical wireless testbed.Wireless sensor networks have been attracting increasing research interest given the recent advances in microelectronics, array processing, and wireless networking. Consisting of a large collection of small, wireless, low-cost, integrated sensing, computing and communicating nodes capable of performing various demanding collaborative space-time processing tasks, wireless sensor network technology poses various unique design challenges, particularly for real-time operation. We review the approximate maximum-likelihood (AML) method for source localization and direction-of-arrival (DOA) estimation. Then, we consider the use of least-squares method (LS) method applied to DOA bearing crossings to perform source localization. A novel virtual array model applicable to the AML-DOA estimation method is proposed for reverberant scenarios. Details on the wireless acoustical testbed are given. We consider the use of Compaq iPAQ 3760s, which are handheld, battery-powered device normally meant to be used as personal organizers (PDAs), as sensor nodes. The iPAQ provide a reasonable balance of cost, availability, and functionality. It has a build in StrongARM processor, microphone, codec for acoustic acquisition and processing, and a PCMCIA bus for external IEEE 802.11b wireless cards for radio communication. The iPAQs form a distributed sensor network to perform real-time acoustical beamforming. Computational times and associated real-time processing tasks are described. Field measured results for linear, triangular, and square subarrays in free-space and reverberant scenarios are presented. These results show the effective and robust operation of the proposed algorithms and their implementations on a real-time acoustical wireless testbed.

Performance comparison of routing protocols for ad hoc networks

Routing protocols for ad hoc networks are currently a hot research topic and when a lot of metrics are jointly considered, some nontrivial conclusions can be drawn. In this work, we make a comparison of link state, AODV and DSR protocols for two different traffic classes, in a selected environment. The classic Dijkstra is also reported as comparison term. As performance metric, packet delivery fraction, throughput, average delay and energy are considered. We show that AODV and DSR perform well when the network load is moderate, while, if the traffic load is heavy, simple link state outperforms the reactive protocols and becomes a good candidate to be used.

Interference aware (IA) MAC: an enhancement to IEEE802.11b DCF

The IEEE802.11 has been devised explicitly for low mobility and single access point scenarios, so its effectiveness is impaired in conditions with not negligible interference in ad hoc and/or in infrastructure modes. Well known problems typical of these scenarios are the so called hidden and exposed terminals. In this paper we propose and test a novel MAC layer for wireless LANs, able to improve the performance of IEEE802.11 DCF (distributed coordination function) in environments with high interference levels. The key point is to insert information about received power and interference levels into MAC control packets. By computing an estimation of the interference increasing due to an eventual transmission (forbidden with IEEE802.11 because blocked by the virtual carrier sensing), the number of parallel transmissions can grow significantly.

MAC and routing solution for energy saving in ad hoc networks: distributed power control

Many important issues are involved when ad hoc networking is concerned. Energy is certainly one of the most critical aspects. Several solutions for energy saving are proposed in literature. In this work, we focus on the energy saving performed by the distributed power control (DPC), a mechanism that involves routing and MAC layers jointly. Simulations by means of SAM (simple ad hoc simulator) show that in fixed scenarios the energy saving is very high.

Security issues based on chaotic systems

A new encryption algorithm based on subblock processing in which one-way mixing functions obtained from a dynamic chaotic system, is presented and analyzed. The algorithm is based on an expansion of the Feistel cipher scheme, where the round function operates on a more grained subblock and both the key generations and the round functions are obtained from the quantized trajectory of chaotic systems. The paper gives details on the algorithm implementation and proposes a differential cryptanalysis investigation showing the algorithm robustness as a function of the used chaotic map. A final comparison with DES-like cryptosystem shows the effectiveness of our proposal in terms of minimum number of steps required to break the system.

Real-time caption streaming over WiFi network

The use of laptop and handheld computers in educational environments has changed the nature of teaching, introducing new ways for students to interact with materials, teachers, and their classmates. Technological advances allow handheld devices to be equipped with faster processors and wireless interfaces, making the performance comparable to laptop computers. We propose a simple but effective scheme according to which each student can visualize in realtime and store the captions of the ongoing lecture. The system is based on IEEE 802.11b multicast protocols and implements a redundant transmission mechanism to mitigate the errors due to the unreliable wireless channel.

Performance investigation of distributed power control for AODV routing protocol

The distributed power control (DPC) proposed and tested in various works has been applied to an ad hoc network using AODV as routing scheme. To test the performance of the power controlled version of AODV several simulations have been performed by considering two different kinds of traffic sources and different mobility conditions. Even if in the Dijkstra and Link State case. DPC showed good results in terms of delivery percentage, delivery time and energy saving in several system conditions, in this paper we outline that in the AODV case, its effectiveness is only performed in some operative conditions as a consequence of the intrinsic structure of the routing protocol.

Real time implementation of acoustical beamforming

Abstract Sensor networks are gaining great attention because of their large range of applications. The main purpose of a sensor network is to monitor an area including detecting, identifying, localizing, and tracking one or more objects of interest. These networks may be used by the military in surveillance, reconnaissance, and combat scenarios or around the perimeter of a manufacturing plant for intrusion detection. Such systems should be very ready to catch and signal the event. Real time issues are critical. Fortunately, nowadays the integrated circuit technology provides low-cost sensor nodes with signal processing and wireless communication capabilities. In this paper, we consider the use of simple PDAs (Personal Digital Assistant) equiped with built-in microphones and external IEEE802.11b wireless cards for radio communication. The purpose is to realize an audio localization system with some real-time constraints in term of computational delay.