Raqibul Mostafa

Wideband air-to-ground radio channel measurements using an antenna array at 2 GHz for low-altitude operations

Wideband measurements were performed using a direct-sequence spread-spectrum measurement system in the air-to-ground radio environment to characterize propagation between an airborne transmitter and a ground-based receiving antenna array at a center frequency of 2.05 GHz. The transmitter was flown along constant-radius arcs at low altitudes around the receiver location to obtain measurement results for 7.5, 15, 22.5, and 30 degree elevation angles. An 80 megachip per second (Mcps) modulating PN sequence was transmitted by the airborne station. The receiver was located in a campus environment of four- to six-story buildings and rolling terrain. The receiver used a four-element antenna array and sampled received signals at 1 gigasample per second (Gsps) per channel. Power-delay profiles that approximated channel impulse responses were used to measure magnitude, phase, and delay of multipath signal components received at each element. Characterization parameters produced from the measurements include RMS delay spread, excess delay spread, multipath fading CDFs, antenna diversity gain, and gain achieved through spatial-temporal combining. The measurements presented here support analysis of wireless systems for intentional transmissions, such as data communications between ground nodes and low-altitude aircraft. In addition, these measurements support investigations into interference from ground sources to low-altitude aircraft (e.g., on instrument approaches) or interception of signals originating from ground sources.

Virginia Tech Space-Time Advanced Radio (VT-STAR)

With the integration of the Internet and multimedia applications in next generation wireless communications, the demand for reliable high data rate services is rapidly growing. Traditional wireless communications systems use a single input single output (SISO) channel, meaning one antenna at each side of the link. Information theory research has shown an enormous potential growth in the capacity of wireless systems by using multiple element array (MEA) technology at both ends of the link. Space-time coding exploits the spatialtemporal diversity provided by the multiple input multiple output (MIMO) channel, significantly increasing both the system capacity and the reliability of the wireless link. The Virginia Tech Space-Time Advanced Radio (VT-STAR) system presents a visual demonstration of the capabilities of space-time coding techniques. The VT-STAR system has integrated an MPEG-2 video stream to show a representation of the effect of the wireless channel on a video transmission in real-time. Core algorithms are implemented on Texas Instruments TMS320C67 Evaluation Modules (EVM). Data conversion between the digital and analog domains is performed by TI THS5661 EVM and TI THS1206 EVM for the transmitter and receiver, respectively. The radio frequency subsystem is composed of multi-channel transmitter and receiver chains implemented in hardware. The capabilities of the MIMO channel are demonstrated in a non-line of sight (NLOS) indoor environment. Real-time monitoring of physical layer parameters, such as the bit error rate and diversity advantage, as well as a video display are presented on an attached personal computer.

MIMO channel capacity measurements using the VT-STAR architecture

The Virginia Tech Space-Time Advanced Radio (VT-STAR) has been used to collect and process narrowband multiple-input multiple-output (MIMO) channel measurements in a non line-of-sight (NLOS) indoor environment. Following the description of the radio architecture we report here initial representative results of the capacity measured in our indoor laboratory settings. As part of the validation process, the effect of pattern distortion associated with the orientation of the antenna arrays is discussed. We compare the theoretical capacity results of [2] with the measured capacities obtained by a MIMO configuration, receive diversity (with single transmit antenna), transmit diversity (with single receive antenna) and a single-input single output (SISO) channel only.

Measurement of multipath signal component amplitude correlation coefficients versus propagation delay

This paper presents a technique for measuring and modeling multipath components in wideband vector channels. The technique is useful for analyzing and simulating channels for wideband receiver antenna array systems and wideband MIMO (multiple-input, multiple-output) systems. By performing wideband vector channel measurements, the strengths of the multipath components resolved within the bandwidth of the system are compared across the array. Diffuse scattering and summation of multipath with delay differences within the resolution of the receiver cause received multipath components to fade. Fading of components across the array can be compared and quantified using correlation coefficients. Developed through this research is a method of processing data that produces results useful for modeling, simulation, and characterization of wideband vector channels using measurements.

Proposed deployments to provide E-healthcare in Bangladesh: Urban and rural perspectives

E-healthcare or telemedicine applications are being widely deployed across the globe to provide healthcare to remote locations. This paper proposes E-healthcare deployments at the patient side that target urban and rural population in Bangladesh. In this regard, the paper addresses the existing healthcare facilities and socio-economic condition of these two population categories to identify the potential telemedicine applications. The core of the proposed deployments is a generic E-healthcare unit that is amenable to different requirements in different deployment scenarios. Provisions for individual and group deployments are discussed for both rural and urban scenarios. These deployments take into consideration the existing nationwide telecommunication infrastructure and services. The proposed deployments show that a customized E-healthcare solution can easily be developed for individuals or groups availing the existing array of telemedicine devices and the telecommunication link.

ECG feature extraction in temporal domain and detection of various heart conditions

Diagnosis of cardiac conditions is greatly dependent on ECG analysis. The current trend is to automate analysis and diagnosis through adopting various signal processing techniques. This paper presents a temporal feature extraction method for ECG feature extraction and detection of various heart conditions. This is achieved by extracting ECG features such as P, T wave, QRS complex, PR, QT, RR, ST intervals and ST segment deviations. The real time ECG data used for this study has been obtained from the MIT-BIH arrhythmia and European ST-T databases. The cardiac arrhythmias that this algorithm can successfully detect are Sinus Tachycardia, Sinus Bradycardia, Premature Atrial Contraction (PAC) and First-Degree Atrioventricular block. Target application for the proposed simple temporal extraction can be portable device for ECG signal acquisition and diagnosis for telemedicine applications in rural areas and also for personal cardio-care.

Design and implementation of a DSP-based MIMO system prototype for real-time demonstration and indoor channel measurements

The design and implementation of the Virginia Tech Space-Time Advanced Radio (VT-STAR), a multiple antenna element space-time (ST) processing prototype testbed, is presented. The testbed is a research tool for comparing practical and theoretical performance metrics (e.g., throughput, link reliability) in different wireless channel conditions. The prototype builds around software-defined radio (SDR) concepts on a DSP platform and provides the flexibility to implement various forms of ST techniques. Different components of the system are described in detail, including the software implementation, I/O schemes with custom hardware, and data transfer mechanisms between the DSP and the host PC. Two different example realizations are presented, a real-time demonstration and an offline measurement tool. Finally, some representative measurement results obtained in indoor environments are presented. These results show VT-STAR to be a promising tool for performing MIMO experiments and generating channel measurements that can complement simulation studies in this area.

Suicidal Ideation Is Associated with Altered Variability of Fingertip Photo-Plethysmogram Signal in Depressed Patients

Physiological and psychological underpinnings of suicidal behavior remain ill-defined and lessen timely diagnostic identification of this subgroup of patients. Arterial stiffness is associated with autonomic dysregulation and may be linked to major depressive disorder (MDD). The aim of this study was to investigate the association between arterial stiffness by photo-plethysmogram (PPG) in MDD with and without suicidal ideation (SI) by applying multiscale tone entropy (T-E) variability analysis. Sixty-one 10-min PPG recordings were analyzed from 29 control, 16 MDD patients with (MDDSI+) and 16 patients without SI (MDDSI−). MDD was based on a psychiatric evaluation and the Mini-International Neuropsychiatric Interview (MINI). Severity of depression was assessed using the Hamilton Depression Rating Scale (HAM-D). PPG features included peak (systole), trough (diastole), pulse wave amplitude (PWA), pulse transit time (PTT) and pulse wave velocity (PWV). Tone (Diastole) at all lags and Tone (PWA) at lags 8, 9, and 10 were found to be significantly different between the MDDSI+ and MDDSI− group. However, Tone (PWA) at all lags and Tone (PTT) at scales 3–10 were also significantly different between the MDDSI+ and CONT group. In contrast, Entropy (Systole), Entropy (Diastole) and Tone (Diastole) were significantly different between MDDSI− and CONT groups. The suicidal score was also positively correlated (r = 0.39 ~ 0.47; p < 0.05) with systolic and diastolic entropy values at lags 2–10. Multivariate logistic regression analysis and leave-one-out cross-validation were performed to study the effectiveness of multi-lag T–E features in predicting SI risk. The accuracy of predicting SI was 93.33% in classifying MDDSI+ and MDDSI− with diastolic T-E and lag between 2 and 10. After including anthropometric variables (Age, body mass index, and Waist Circumference), that accuracy increased to 96.67% for MDDSI+/− classification. Our findings suggest that tone-entropy based PPG variability can be used as an additional accurate diagnostic tool for patients with depression to identify SI.

Proposed Framework for the Deployment of Telemedicine Centers in Rural Bangladesh

This paper presents a unique and comprehensive framework for the deployment of effective telemedicine centers in diverse locations in Bangladesh. The framework employs a top-down analysis and design approach by properly organizing the key elements comprising it. The elements include a nationwide analysis of demographics along with current healthcare scenario as well location-specific pre-deployment studies and the recommended telemedicine solution. This framework will be a valuable guide to deploy effective and long-term telemedicine center at any given location. Towards this goal, the paper presents the framework along with a detailed discussion of the constituent elements, and analyzes several case studies to demonstrate the application of the framework to provide site-specific telemedicine solutions at some selected test sites. All the previous telemedicine projects in Bangladesh suffered from a lack of sustainability and it is expected that deployments based on the proposed framework will be effective, scalable, and long-lasting in bringing e-healthcare to the target population in Bangladesh.

A novel smart metering system for loss reduction and efficient load management in the power distribution sector of Bangladesh

This paper presents a prototype implementation of smart meter that facilitates the migration of our existing conventional distribution systems towards the smart distribution system. This is a step forward towards implementation of smart grid system. The proposed smart meter that establishes a two-way wireless communication link between the consumer premise and service provider can provide a number of advantages and add-on features, such as, establishing flexible dynamic multirate tariff planning, identifying and locating the premise of system loss, and full time monitoring and subsequent decision-making. In particular, an improvement of the load shedding scenario in Bangladesh is proposed based on the analysis of the load shedding data furnished by Dhaka Power Distribution Company (DPDC). It is observed that a particular feeder can be operated with less frequent load shedding if the individual customer is allowed to operate within a reduced limit monitored by the novel smart meter.