Daniela Maniezzo

Coherent acoustic array processing and localization on wireless sensor networks

Advances in microelectronics, array processing, and wireless networking have motivated the analysis and design of low-cost integrated sensing, computing, and communicating nodes capable of performing various demanding collaborative space–time processing tasks. In this paper, we consider the problem of coherent acoustic sensor array processing and localization on distributed wireless sensor networks. We first introduce some basic concepts of beamforming and localization for wide-band acoustic sources. A review of various known localization algorithms based on time-delay followed by least-squares estimations as well as the maximum–likelihood method is given. Issues related to practical implementation of coherent array processing, including the need for fine-grain time synchronization, are discussed. Then we describe the implementation of a Linux-based wireless networked acoustic sensor array testbed, utilizing commercially available iPAQs with built-in microphones, codecs, and microprocessors, plus wireless Ethernet cards, to perform acoustic source localization. Various field-measured results using two localization algorithms show the effectiveness of the proposed testbed. An extensive list of references related to this work is also included.

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.

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.

A cross-layer framework for wireless LAN QoS support

The IEEE 802.11x based wireless LAN technologies are leading the indoor Internet distribution in education, business and home environments. They are usually deployed as wireless extension of a broadband access to the network (i.e. DSL, cable modem, etc). These technologies are based on CSMA/CA media access with a positive MAC layer acknowledgement and a retransmission mechanism that aids noisy channel propagation condition and eventual undetected collisions. While TCP traffic benefits from a layer 2 retransmission policy the multimedia traffic experiences large delays and jitter resulting in a poor user experience. We satisfy the emerging user need of a MAC layer Quality of Service (QoS) support by taking advantage from layers 4-7 information. We believe the concepts and the architectural design presented are suitable to enhance QoS support in wireless technologies.

Energetic trade-off between computing and communication resource in multimedia surveillance sensor network

In recent years, advances in microelectronics have allowed the development of low-power, low-cost, and small devices with sensing, computing, and wireless communication capabilities. An important criterion on the design and operation of these devices is their energy consumption. Two factors that affect the energy consumption of the sensor network are computation and communication. The simple strategy of locally processing the acquired data and transmitting it, is not optimal from the energy consumption point of view, relative to other strategies based on distributed processing and successive transmission of partially processed data. In this paper, we analyze the energy tradeoff between computation and communication resources in order to minimize the total energy consumption. We propose a heuristic solution to the stated sensor network problem for a multimedia application using Strong Arm RISC processors to perform a certain data compression algorithm.

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.

DSP implementation of a distributed acoustical beamformer on a wireless sensor platform

In this paper, we consider the use of a Compaq iPAQ 3760s, equipped with a built-in microphone and an external wireless card, for acoustic acquisition and processing to perform a distributed acoustical beamforming. Time synchronization among the microphones is achieved by the reference-broadcast synchronization method. Two beamforming algorithms, based on the time difference of arrivals (TDOA) among the microphones followed by a least-squares estimation, and the maximum-likelihood (ML) parameter estimation method, are used to perform source detection, enhancement, localization, delay-steered beamforming, and direction-of-arrival estimation. Experimental beamforming results using the iPAQs and the wireless network are reported.

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.

Fast-FMS: fast multimedia across 3g mobile networks

Fast-FMS is a new network protocol designed to support fast and effective multimedia delivery in 3G networks. In particular, Fast-FMS provides a reliable session between two mobile customers that want to transmit multimedia and data while on a voice conversation. The protocol leverages the multi-RAB feature of 2.5+ cellular networks to provide a new almost-real-time class of services that fill the gap between the costly circuit-switched video-call service and the basic services based on MMS. 1. Fast-FMS Description