Low-power wearable system for asthmatic wheeze detection

doctoral thesis

• Title (croatian): Nosivi sustav za detekciju asmatskih fićuka s malom potrošnjom energije
• Author: Dinko Oletić
• Mentor: Vedran Bilas (mentor)
• Committee member: Vedran Bilas (član povjerenstva)
• Granter: University of Zagreb; Faculty of Electrical Engineering and Computing; (Department of Electronic Systems and Information Processing); Zagreb
• Defense date and country: 2016, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Computing; Data Processing
• Universal decimal classification (UDC): 621.3 - Electrical engineering

Abstract

Area of this research is minimization of energy consumption of electronic systems for long-term monitoring of common symptom of chronic asthma - asthmatic wheezing. The proposed electronic sensor system consists of a wearable sensor measuring the mechanical vibrations on skin surface originating from respiration, and a wireless mobile device (smartphone). The system conducts automatic recognition of respiratory sounds. The essential design requirement is energy consumption at which the sensor system is able to quantify symptoms. In this context, research compared two system architectures: with asthmatic wheeze detection on the wearable sensor, and the architecture in which information capture on occurrence of wheeze is distributed between a sensor and a mobile device. Firstly, the problem of power-efficient asthmatic wheeze detection on-board wearable sensor was addressed. Building up on the literature state-of-the-art, four algorithms based on features drawn from STFT time-frequency decomposition have been compared on an low-power audio processing DSP. Best trade-off between classification performance and execution speed was obtained by STFT spectral crest shapes tracking algorithm yielding 87.51% sensitivity (SE), 93.42% specificity (SP), and 92.53% accuracy (ACC) at less than 3% of DSP’s active time. Secondly, application of compressed sensing (CS) was evaluated in a distributed sensing system as a mean of simultaneous reduction of power consumption of sensor, and the data-rate reduction in wireless communication. A prototype was demonstrated, implementing a combination of a time-domain subsampling CS encoder on the sensor, and the real-time DFT/DCT spectra CS reconstruction OMP algorithm on smartphone. Compression ratios of 4x to 5.33x were proved feasible. A robust algorithm for wheeze detection from CS reconstructed spectra, based on HMM, was proposed. It enabled for up to SE of 89.99%, SP of 94.03%, and 93.45% ACC at the CS compression rate of 4x, at the processing cost comparable to spectral crest shapes tracking algorithm. Finally, system-level power analysis confirmed that lowest system-level power, estimated from 328 to 428 uW, may be achieved in architecture with wheeze detection on-board wearable sensor. However, in the distributed architecture, CS enables for the lowest sensor power (216 - 357 uW), while simultaneously keeping the total system power (775 - 2605 uW) lower or equal to streaming of the uncompressed signal.

Abstract (croatian)

Područje ovog istraživanja je minimizacija potrošnje energije elektroničkih sustava za dugotrajno praćenje učestalog simptoma kronične astme - astmatskih fićuka. Predloženi elektronički senzorski sustav sastoji se od nosivog senzora koji mjeri vibracije na površini kože koje potječu od disanja, i bežičnog mobilnog uređaja (pametnog telefona). Sustav automatski raspoznaje zvukove disanja. Esencijalni konstrukcijski zahtjev odnosi se na količinu energije potrebne sustavu za kvantifikaciju simptoma. U tom kontekstu, istraživanje uspoređuje dvije arhitekture sustava: s detekcijom astmatskih fićuka na senzoru i arhitekturu u kojoj je dohvat informacije o pojavi fićuka raspodijeljen između senzora i mobilnog uređaja. Najprije je obrađen problem energetski učinkovite detekcije fićuka na procesoru nosivog senzora. Krećući od postojećeg stanja tehnike opisanog u literaturi, četiri algoritma temeljena na značajkama izvađenim iz kratkotrajne Fouriereove transformacije (engl. STFT) su uspoređena na audio procesoru za digitalnu obradu signala niske potriošnje. Najbolji odnos performansi klasifikacije i brzine izvođenja je dobiven algoritmom za praćenje spektralnih vrhova STFT-a dajući osjetljivost od 87,51%, specifičnost od 93,42% i točnost od 92,53%, pri manje od 3% aktivnog vremena procesora. Nadalje, primjena sažetog otipkavanja (engl. CS) je evaluirana u raspodijeljenom senzorskom sustavu kao način simultanog smanjenja potrošnje nosivog senzora te za smanjenje količine podatkovnog prometa u bežičnoj komunikaciji. Demonstriran je prototip koji implementira kombinaciju enkodera za sažeto otipkavanje s podotipkavanjem u vremenskoj domeni na senzoru i OMP algoritam implementiran na pametnom telefonu koji rekonstruira DFT/DCT spektar sažeto otipkanog signala. Pokazano je da se mogu ostvariti omjeri kompresije od 4x do 5,33x puta. Predložen je robustan algoritam detekcije fićuka iz rekonstruiranog spektra sažeto otipkanog signala, baziran na skrivenom Markovljevom modelu (engl. HMM). Algoritam omogućava osjetljivost do 89,99%, specifičnost do 94,03% i točnost do 93,45% pri omjeru kompresije 4x, uz trošak procesorske obrade sumjerljiv algoritmu za praćenje spektralnih vrhova u STFT-u. Konačno, analiza potrošnje na razini sustava potvrdila je da je najmanja srednja potrošnja, estimirana između 328 i 428 uW, ostvariva u arhitekturi s detekcijom fićuka na nosivom senzoru. Ipak, u raspodijeljenoj arhitekturi, sažeto otipkavanje omogućava najmanju potrošnju nosivog senzora (216 - 357 uW), uz simultano održavanje ukupne potrošnje senzorskog sustava (775 - 2605 uW) nižom ili podjednakom slučaju kontinuiranog prijenosa nekomprimiranog signala.

• Keywords: biomedical sensors; wireless sensor networks; electronic auscultation; asthmatic wheeze detection; short-term Fourier transform (STFT); compressed sensing (CS); hidden Markov model (HMM); low-power electronic design
• Keywords (croatian): biomedicinski senzori; bežične senzorske mreže; elektronička auskultacija; detekcija astmatskih fićuka; kratkotrajna Fourierova transformacija; sažeto otipkavanje; skriveni Markovljev model; elektronički dizajn uz nisku potrošnju energije
• Language: english
• URN:NBN: urn:nbn:hr:168:945084
• Study programme: Title: Electrical Engineering and Computing; Study programme type: university; Study level: postgraduate; Academic / professional title: Doktor znanosti elektrotehnike i računarstva (Doktor znanosti elektrotehnike i računarstva)
• Type of resource: Text
• Extent: 165 str. ; 30 cm.
• File origin: Born digital
• Access conditions: Closed access
• Created on: 2019-04-10 15:10:46