Miguel P. Pereira

Vital Signs Monitoring System Based on EMFi Sensors and Wavelet Analysis

The paper presents a monitoring system for non-obtrusive measuring of vital signs such as respiration and heart activity. Two sensing channels including electromechanical film sensors (EMFi sensor) tapped on an office chair are used to obtain the ballistocardiographyc (BCG) signals from human subjects. The conditioning circuits include amplification stages (charge amplifier, programmable gain amplifier) and 20 Hz low-pass and 50 Hz notch active filters used to improve the signal-to-noise ratio (SNR). The gain control and analog-to-digital conversion is performed using a multifunction I/O device USB compatible connected to a laptop PC. The digital processing of the acquired signals is an important part of the work. It includes digital filtering, based on Stationary Wavelet Transform, and signal decomposition, based on Discrete Wavelet Transform, in order to extract the respiration and heart rate based on BCG signal analyze. A practical approach concerning the dependence of the used wavelet type on vital signs estimation accuracy is reported. The results on respiration rate and heart rate using BCG signal and the implemented algorithms are compared with the values of these parameters measured through ECG and spirometry analysis.

Frequency-domain multipacket detection: a high throughput technique for SC-FDE systems

The traditional approach to cope with collisions is to discard the packets involved in it and to ask for their retransmission. However, since the signal associated to a collision has important information concerning the packets involved, we can efficiently resolve collisions with proper retransmissions. In this paper we consider severely time-dispersive channels and we propose a technique that allows efficient packet separation. We employ SC-FDE schemes (single-carrier with frequency-domain equalization) and we propose an iterative frequency-domain multi-packet detection. Since our technique requires uncorrelated channels for different retransmissions, we also propose an SP technique (Shifted Packets) for retransmissions in fixed channels. Since the total number of transmissions is equal to the number of packets involved in the collision (even when the channel remains fixed for the retransmissions), our technique allows high throughputs. The analysis of our detection technique combined with the NMDA (network-assisted diversity multiple access) MAC (medium access control) protocol shows significant throughput and delay improvements for low Eb/N0 values compared to a TDMA (time division multiple access) approach, where collisions are avoided. This technique is particularly appealing for the uplink of broadband wireless systems, since we consider SC-FDE schemes and the complexity is concentrated in the receiver. By employing the SP scheme we can use the same channel for the retransmissions, with only a small performance degradation.

Flow meters: Part 1

This tutorial has focused on the importance of accurate measurement by flow meters in industrial applications and what is necessary to provide accuracy. The properties of fluid flow are discussed in relation to how these properties affect the measurement by flow meters. The diagrams, formulas and graphs illustrate the important factors in the use of volumetric, mass and smart flow meters.

A virtual instrument to test smart transducer interface modules (stims)

This paper reports the hardware and software of virtual instruments and the tests conducted on a microcontroller-based smart transducer interface module (STIM) to check both STIMs performance and the suitability of a network capable application processor (NCAP) implemented in LabVIEW. The tests include the characterization of a digitizing channel of the STIM and the performance analysis of the system when the STIM simultaneously operates its digital outputs and its analog inputs.

A brief tutorial on the IEEE 1451.1 Standard - Part 13 in a series of tutorials in instrumentation and measurement

The 1451.1 standard addresses the definition of a network capable application processor (NCAP). The NCAP is a piece of hardware and software that acts as a bridge between transducers and the communication network. On the field side, an abstraction layer provides high-level functionality to communicate with transducers. On the network side, an abstraction layer provides high-level functionality to handle network requests. In the middle, the control routine adds intelligence to the NCAP by running algorithms that process the data received by both sides (the field and the network) and decide the next state of the system. The software architecture of the 1451.1 Std. is based on an information model, a data model, and two network communication models.The diversity of fieldbuses and network protocols leads a manufacturer to closed, less-flexible, and generally more-expensive solutions.

An Internet and microcontroller-based remote operation multi-sensor system for water quality monitoring

The paper presents the architecture of a microcontroller-based multi-sensor able to measure different quantities used to characterize water quality and, at the same time, to disseminate data over the Internet. The architecture of the system includes a sensitive unit (that performs pH, temperature and turbidity measurements), a data acquisition, processing and communication unit, (16F877 microcontroller), and a RTL8019 LAN controller. The system also incorporates GSM communication capabilities in order to allow stand-alone operation in places such as river basin waters.

Performance of Packet Combining ARQ Error Control in a TDMA SC-FDE System

This paper considers the use of SC modulations (Single-Carrier) with FDE (Frequency-Domain Equalization) with low-complexity soft combining ARQ schemes (Automatic Repeat reQuest). With our technique, packets associated to different transmission attempts are combined in a soft way, allowing improved performances. Its low complexity makes it particularly interesting for the uplink of wireless systems. This paper proposes an accurate analytical model for a TDMA (Time Division Multiple Access) scheme where packet combining ARQ is applied. It evaluates the uplink non-saturated packet delay and goodput for a generic message arrival process. Our analytical results are validated using physical and MAC layer simulations.

A MAC Protocol for Mobile Wireless Sensor Networks with Bursty Traffic

This paper proposes the Mobile MH-MAC (Multimode Hybrid - Medium Access Control) protocol, an extension of MH-MAC with enhanced support for mobility on wireless sensor networks. It provides an asynchronous mode for energy efficiency during idle (unconnected) periods, and a synchronous mode for high throughput periods. Mode change is controlled by the application in a cross-layer approach. MMH-MAC was specially designed to tolerate asyn- chronous mobile nodes in the neighborhood of synchronous nodes, providing fast transition and interference mitigation mechanisms. Current MAC protocols rely on a passive method to associate a mobile node to a static cluster, triggered by the reception of a beacon. We propose an active approach that allows a mobile node to start sending data packets shortly after entering into data range of a static node, with negligible data loss in existing synchronous data connections. MMH-MAC was implemented in TinyOS and tested on TelosB motes and TOSSIM simulator.

Delay Optimization on a p-Persistent MAC Protocol for a Multi-Packet Detection in SC-FDE System

This paper deals with multi-packet detection for SC modulations (Single-Carrier) with FDE (Frequency- Domain Equalization). We consider iterative frequency-domain receivers that jointly perform equalization, multi-packet separation and channel decoding operations, for up to Qmax mobile terminals transmitting in one slot. In this paper we propose an accurate analytical model for a p-persistent random access MAC protocol, designed to handle a total number of mobile terminals J above Qmax. It evaluates the uplink non-saturated packet delay and calculates the optimal configuration for the packet transmission probability associated to each mobile terminal that minimizes the delay. Our analytical results are validated using physical and MAC layer simulations.

Performance of Diversity Combining ARQ Error Control in a TDMA SC-FDE System

The Quality of Service (QoS) requirements for modern broadband wireless systems can be very high, with small error rates and delays. Packets with errors are usually discarded and need to be retransmitted, leading to performance degradation. An alternative to simple retransmissions like Automatic Repeat reQuest (ARQ) schemes, that can minimize the degradation is to combine the signals associated to different transmission attempts, usually called diversity combining techniques. This paper considers the use of Single-Carrier (SC) modulations with Frequency-Domain Equalization (FDE) and low-complexity soft combining ARQ schemes. The time diversity combining technique presented in this paper, allows packets associated to different transmission attempts to be combined in a soft way so as to improve the performance. This technique is employed in a Time Division Multiple Access (TDMA) scheme. An accurate analytical model is proposed for the evaluation of the uplink packet delay in non-saturated traffic condition, and for the systems throughput (goodput) considering a generic packet arrival process. Physical (PHY) layer (packet error rates) and system-level (goodput and packet delay considering both PHY and Medium Access Control (MAC) layers) results are presented and validated by simulations for two distinctive arrival processes: Poisson and Geometric.