797 research outputs found

    Analysis Framework for Opportunistic Spectrum OFDMA and its Application to the IEEE 802.22 Standard

    Full text link
    We present an analytical model that enables throughput evaluation of Opportunistic Spectrum Orthogonal Frequency Division Multiple Access (OS-OFDMA) networks. The core feature of the model, based on a discrete time Markov chain, is the consideration of different channel and subchannel allocation strategies under different Primary and Secondary user types, traffic and priority levels. The analytical model also assesses the impact of different spectrum sensing strategies on the throughput of OS-OFDMA network. The analysis applies to the IEEE 802.22 standard, to evaluate the impact of two-stage spectrum sensing strategy and varying temporal activity of wireless microphones on the IEEE 802.22 throughput. Our study suggests that OS-OFDMA with subchannel notching and channel bonding could provide almost ten times higher throughput compared with the design without those options, when the activity and density of wireless microphones is very high. Furthermore, we confirm that OS-OFDMA implementation without subchannel notching, used in the IEEE 802.22, is able to support real-time and non-real-time quality of service classes, provided that wireless microphones temporal activity is moderate (with approximately one wireless microphone per 3,000 inhabitants with light urban population density and short duty cycles). Finally, two-stage spectrum sensing option improves OS-OFDMA throughput, provided that the length of spectrum sensing at every stage is optimized using our model

    Generic wireless sensor network for dynamic monitoring of a new generation of building material

    Get PDF
    Existing testing methods for building materials before deployment include a series of procedures as stipulated in British Standards, and most tests are performed in a controlled laboratory environment. Types of equipment used for measurements, data logging, and visualisation are commonly bulky, hard-wired, and consume a significant amount of power. Most of the off-the-shelf sensing nodes have been designed for a few specific applications and cannot be used for general purpose applications. This makes it difficult to modify or extend the sensing features when needed. This thesis takes the initiative of designing and implementing a low-powered, open-source, flexible, and small-sized Generic wireless sensor network (GWSN) that can continuously monitor the building materials and building environment, to address the limitations of the conventional measurement methods and the technological gap. The designed system is comprised of two custom-made sensor nodes and a gateway, as well as purpose designed firmware for data collection and processing. For the proof of concept and experimental studies, several measurement strategies were designed, to demonstrate, evaluate, and validate the effectiveness of the system. The data was collected from selected case study areas in the School of Energy, Geoscience, Infrastructure and Society (EGIS) laboratories by measuring and monitoring building structures and indoor environment quality parameters using the designed GWSN. The measured data includes heat flux through the material, surface and air temperatures on both sides of the material/structure, moisture variation, ambient temperature, relative humidity, carbon dioxide, volatile organic compounds, particulate matter, and sound/acoustic levels. The initial results show the potential of the designed system to become the new benchmark for tracking the variation of building materials with the environment and investigating the impact of variation of building materials on indoor environment quality. Based on the estimates of the thermal performance data, the sample used in the experiment had a typical U-value between 4.8 and 5.8 W/m2K and a thermal resistance value of 0.025m2 ·K/W[1][2]. Thermal resistance values from the GWSN real-time measurement were between 0.025 and 0.03 m2K/W, with an average of 0.025 m2K/W, and thermal transmission values varied between 4.55 and 5.11 W/m2K. Based on the data obtained, the results are within the range of typical values[3]. For thermal comfort measurements, the results of humidity and temperature from GWSN were compared to values in the Kambic climatic chamber in the EGIS laboratory, and the accuracies were 99 % and 98 % respectively. For the IAQ measurements, the values of CO2 and TVOCs were compared to the commercial off-the-shelf measuring system, and the accuracies were 98 %, and 97 %. Finally, the GWSN was tested for acoustic measurements in the range of 55 dB to 106 dB. The results were compared to class one Bruel & Kjaer SLM. The accuracy of GWSN was 97 %. The GWSN can be used for in lab and in-situ applications, to measure and analyse the thermal physical properties of building materials/building structures (thermal transmittance, thermal conductivity, and thermal resistance). The system can also measure indoor air quality, thermal comfort, and airborne sound insulation of the building envelope. The key point here is to establish a direct link between how building materials vary with the environment and how this impacts indoor environment quality. Such a link is essential for long-term analysis of building materials, which cannot be achieved using current methods. Regarding increasing the power efficient of the implemented GWSN as well as its performance and functionality, a new sensing platforms using backscatter technology have been introduced. The theory of modulation and spread spectrum technique used in backscattering has been explored. The trade-off between hardware complexity/power consumption and link performance has been investigated. Theoretical analysis and simulation validation of the new sensing technique, using backscatter communication, has been performed. A novel multicarrier backscatter tag compatible with Wireless Fidelity has been implemented and an IEEE 802.11g OFDM preamble was synthesized by simulation. The tag consists of only two transistors with current consumption no larger than 0.2 ΌA at voltage of less than 0.6 V. Novel harmonic suppression approaches for frequency-shifted backscatter communication has been proposed and demonstrated. The proposed approaches independently manipulate mirror harmonics and higher order harmonics whereby; specified higher order harmonics can be removed by carefully designing the real-valued (continuous and discrete) reflection coefficients-based backscatter tags. When successfully implemented, the backscatter system will reduce sensor node power consumption by shifting the power-consuming radio frequency carrier synthesis functions to carrier emitters.Engineering and Physical Sciences Research Council (EPSRC) Funding EP/H009612/

    FPGA-based architectures for acoustic beamforming with microphone arrays : trends, challenges and research opportunities

    Get PDF
    Over the past decades, many systems composed of arrays of microphones have been developed to satisfy the quality demanded by acoustic applications. Such microphone arrays are sound acquisition systems composed of multiple microphones used to sample the sound field with spatial diversity. The relatively recent adoption of Field-Programmable Gate Arrays (FPGAs) to manage the audio data samples and to perform the signal processing operations such as filtering or beamforming has lead to customizable architectures able to satisfy the most demanding computational, power or performance acoustic applications. The presented work provides an overview of the current FPGA-based architectures and how FPGAs are exploited for different acoustic applications. Current trends on the use of this technology, pending challenges and open research opportunities on the use of FPGAs for acoustic applications using microphone arrays are presented and discussed

    The personal hearing system- A software hearing aid for a personal communication system

    Get PDF
    A concept and architecture of a personal communication system (PCS) is introduced that integrates audio communication and hearing support for the elderly and hearing-impaired through a personal hearing system (PHS). The concept envisions a central processor connected to audio headsets via a wireless body area network (WBAN). To demonstrate the concept, a prototype PCS is presented that is implemented on a netbook computer with a dedicated audio interface in combination with a mobile phone. The prototype can be used for field-testing possible applications and to reveal possibilities and limitations of the concept of integrating hearing support in consumer audio communication devices. It is shown that the prototype PCS can integrate hearing aid functionality, telephony, public announcement systems, and home entertainment. An exemplary binaural speech enhancement scheme that represents a large class of possible PHS processing schemes is shown to be compatible with the general concept. However, an analysis of hardware and software architectures shows that the implementation of a PCS on future advanced cell phone-like devices is challenging. Because of limitations in processing power, recoding of prototype implementations into fixed point arithmetic will be required and WBAN performance is still a limiting factor in terms of data rate and delay

    Advanced sensors technology survey

    Get PDF
    This project assesses the state-of-the-art in advanced or 'smart' sensors technology for NASA Life Sciences research applications with an emphasis on those sensors with potential applications on the space station freedom (SSF). The objectives are: (1) to conduct literature reviews on relevant advanced sensor technology; (2) to interview various scientists and engineers in industry, academia, and government who are knowledgeable on this topic; (3) to provide viewpoints and opinions regarding the potential applications of this technology on the SSF; and (4) to provide summary charts of relevant technologies and centers where these technologies are being developed

    Towards understanding the role of central processing in release from masking

    Get PDF
    People with normal hearing have the ability to listen to a desired target sound while filtering out unwanted sounds in the background. However, most patients with hearing impairment struggle in noisy environments, a perceptual deficit which current hearing aids and cochlear implants cannot resolve. Even though peripheral dysfunction of the ears undoubtedly contribute to this deficit, surmounting evidence has implicated central processing in the inability to detect sounds in background noise. Therefore, it is essential to better understand the underlying neural mechanisms by which target sounds are dissociated from competing maskers. This research focuses on two phenomena that help suppress background sounds: 1) dip-listening, and 2) directional hearing. When background noise fluctuates slowly over time, both humans and animals can listen in the dips of the noise envelope to detect target sound, a phenomenon referred to as dip-listening. Detection of target sound is facilitated by a central neuronal mechanism called envelope locking suppression. At both positive and negative signal-to-noise ratios (SNRs), the presence of target energy can suppress the strength by which neurons in auditory cortex track background sound, at least in anesthetized animals. However, in humans and animals, most of the perceptual advantage gained by listening in the dips of fluctuating noise emerges when a target is softer than the background sound. This raises the possibility that SNR shapes the reliance on different processing strategies, a hypothesis tested here in awake behaving animals. Neural activity of Mongolian gerbils is measured by chronic implantation of silicon probes in the core auditory cortex. Using appetitive conditioning, gerbils detect target tones in the presence of temporally fluctuating amplitude-modulated background noise, called masker. Using rate- vs. timing-based decoding strategies, analysis of single-unit activity show that both mechanisms can be used for detecting tones at positive SNR. However, only temporal decoding provides an SNR-invariant readout strategy that is viable at both positive and negative SNRs. In addition to dip-listening, spatial cues can facilitate the dissociation of target sounds from background noise. Specifically, an important cue for computing sound direction is the time difference in arrival of acoustic energy reaching each ear, called interaural time difference (ITD). ITDs allow localization of low frequency sounds from left to right inside the listener\u27s head, also called sound lateralization. Models of sound localization commonly assume that sound lateralization from interaural time differences is level invariant. Here, two prevalent theories of sound localization are observed to make opposing predictions. The labelled-line model encodes location through tuned representations of spatial location and predicts that perceived direction is level invariant. In contrast, the hemispheric-difference model encodes location through spike-rate and predicts that perceived direction becomes medially biased at low sound levels. In this research, through behavioral experiments on sound lateralization, the computation of sound location with ITDs is tested. Four groups of normally hearing listeners lateralize sounds based on ITDs as a function of sound intensity, exposure hemisphere, and stimulus history. Stimuli consists of low-frequency band-limited white noise. Statistical analysis, which partial out overall differences between listeners, is inconsistent with the place-coding scheme of sound localization, and supports the hypothesis that human sound localization is instead encoded through a population rate-code

    Content Suggestions for Universally Designed Hearing Aids

    Get PDF
    Nearly 80% of those who could benefit from wearing a hearing aid choose not to use one. This study, completed by an interdisciplinary team for the Victorian Deaf Society in Melbourne, Australia, addresses the social attitudes and other limitations of hearing aids which result in poor market penetration. Based on the principles of universal design, specific recommendations are presented to improve the function and style of hearing aids. Additionally, the study recommends implementation of hearing assistive devices for the hearing

    Electroacoustic and Behavioural Evaluation of Hearing Aid Digital Signal Processing Features

    Get PDF
    Modern digital hearing aids provide an array of features to improve the user listening experience. As the features become more advanced and interdependent, it becomes increasingly necessary to develop accurate and cost-effective methods to evaluate their performance. Subjective experiments are an accurate method to determine hearing aid performance but they come with a high monetary and time cost. Four studies that develop and evaluate electroacoustic hearing aid feature evaluation techniques are presented. The first study applies a recent speech quality metric to two bilateral wireless hearing aids with various features enabled in a variety of environmental conditions. The study shows that accurate speech quality predictions are made with a reduced version of the original metric, and that a portion of the original metric does not perform well when applied to a novel subjective speech quality rating database. The second study presents a reference free (non-intrusive) electroacoustic speech quality metric developed specifically for hearing aid applications and compares its performance to a recent intrusive metric. The non-intrusive metric offers the advantage of eliminating the need for a shaped reference signal and can be used in real time applications but requires a sacrifice in prediction accuracy. The third study investigates the digital noise reduction performance of seven recent hearing aid models. An electroacoustic measurement system is presented that allows the noise and speech signals to be separated from hearing aid recordings. It is shown how this can be used to investigate digital noise reduction performance through the application of speech quality and speech intelligibility measures. It is also shown how the system can be used to quantify digital noise reduction attack times. The fourth study presents a turntable-based system to investigate hearing aid directionality performance. Two methods to extract the signal of interest are described. Polar plots are presented for a number of hearing aid models from recordings generated in both the free-field and from a head-and-torso simulator. It is expected that the proposed electroacoustic techniques will assist Audiologists and hearing researchers in choosing, benchmarking, and fine-tuning hearing aid features

    Design of large polyphase filters in the Quadratic Residue Number System

    Full text link
    • 

    corecore