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Publicações

Publicações por CTM

2006

Adaptive audio equalization of rooms based on a technique of transparent insertion of acoustic probe signals

Autores
Rocha, AF; Leite, A; Pinto, F; Ferreira, AJS;

Publicação
Audio Engineering Society - 120th Convention Spring Preprints 2006

Abstract
This paper presents a new method performing real-time adaptive equalization of room acoustics in the frequency domain. The developed method obtains the frequency response of the room by means of the transparent insertion of a certain number of acoustic probe signals into the main audio spectrum. The opportunities for the insertion of tones are identified by means of a spectral analysis of the audio signal and using a psychoacoustic model of frequency masking. This enhanced version of the adaptive equalizer will be explained as well as its real time implementation on a TMS320C6713 DSP based platform. Finally the results of the acoustic tests and conclusions about its performance will be presented.

2006

Audio communication coder

Autores
Ferreira, AJS; Sirilia, D;

Publicação
Audio Engineering Society - 120th Convention Spring Preprints 2006

Abstract
3G mobile and wireless communication networks elicit new ways of multimedia human interaction and communication, notably two-way high-quality audio communication. This is inline with both the consumer expectation of new audio experiences and functionalities, and with the motivation of Telecom Operators to offer consumers new services and communication modalities. In this paper we describe the design and optimization of a nioriophonic audio coder (Audio Communication Coder -ACC) that features low-delay coding (< 50 ms) and intrinsic error robustness, while minimizing complexity and achieving competitive coding gains and audio quality at bit rates around 32 kbit/s and higher. ACC source, perceptual and bandwidth extension tools are described and an emphasis is placed on ACC structural and operational features making it suitable for real-time, two-way audio communication. A few performance results are also presented. Audio demos are available at http://www.atc-labs.corn/acc/ .

2006

Dynamic and automatic connection of personal area networks to the global internet

Autores
Campos, R; Ricardo, M;

Publicação
Proceedings of the International Conference on Wireless Communications and Mobile Computing, IWCMC 2006, Vancouver, British Columbia, Canada, July 3-6, 2006

Abstract
In the Next Generation Networks (NGNs) users will carry multiple devices forming cooperative networks known as Personal Area Networks (PANs). Some existing technologies enable this type of networks, such as Bluetooth or IEEE 802.15.4, but a unified framework capable of self-organizing them dynamically in a full heterogeneous environment populated by these and other technologies still has to be defined. Also, these networks are envisioned to be connecting dynamically to the Internet, and may use two IP versions and their autoconfiguration mechanisms. In this paper we propose a new framework, the Autoconfiguration and Self-management of Personal Area Networks (ASPAN), which enables the automatic and dynamic deployment of PANs in the heterogeneous environments envisioned for NGNs and handles the automatic and dynamic connection of a PAN to the global Internet. Copyright 2006 ACM.

2006

Extending the coverage of a 4G telecom network using hybrid ad-hoc networks: A case study

Autores
Calcada, T; Ricardo, M;

Publicação
Challenges in AD HOC Networking

Abstract
Ad-hoc networks that are connected with the infrastructure Internet are named hybrid ad-hoc networks. In 4G communications scenarios, hybrid ad-hoc networks seem to be valuable since they may increase the coverage of wireless networks with minor costs. Using them, terminals out of range of an access point or a base station, or not having adequate network interfaces, may reach the operator's infrastructure via other terminals. This paper presents a hybrid ad-hoc network solution and a testbed implementation.

2006

XCP for shared-access multi-rate media

Autores
Abrantes, F; Ricardo, M;

Publicação
ACM SIGCOMM COMPUTER COMMUNICATION REVIEW

Abstract
The eXplicit Control Protocol (XCP) was developed to overcome some of the limitations of TCP, such as low utilization in high bandwidth delay product networks, unstable throughput, large queue build-up, and limited fairness. XCP, however, requires that each queue controller in a path knows the exact capacity of its link. In shared access media, e.g. IEEE 802.11, knowing the actual capacity of the channel is a difficult task. In this paper we propose modifications to the XCP algorithm that enable the utilization of XCP even when the capacity of a link is unknown. These modifications are validated through simulation. We also present the results of a comparison between the performance of the modified XCP and TCP, where XCP controlled flows result more stable, fairness increases, and the network delay becomes lower. In addition, as the bandwidth delay product increases, XCP is able to maintain near-maximum utilization while TCP decreases utilization.

2006

A low-power oscillation based LNA BIST scheme

Autores
da Silva, JM;

Publicação
IEEE DTIS: 2006 International Conference on Design & Test of Integrated Systems in Nanoscale Technology, Proceedings

Abstract
Test stimuli generation and power consumption are two Issues that jeopardize the design of built-in self test schemes. The LNA testing approach presented herein relies on converting the amplifier Into an oscillator and on using a low-power correlator to obtain a signature from the cross-correlation between the dynan-dc power supply current and the LNA's output voltage. In test mode a high fault coverage is obtained together with a low power consumption, while avoiding an extra stimulus generator. No significant performance degradation results from the added test circuitry. Concerning the Interface with the external tester, a digital signal is required to switch between normal and test modes, as well as a low frequency line to capture the correlator DC output voltage.

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