Deborah Gold

Indoor Tracking and Navigation Using Received Signal Strength and Compressive Sensing on a Mobile Device

An indoor tracking and navigation system based on measurements of received signal strength (RSS) in wireless local area network (WLAN) is proposed. In the system, the location determination problem is solved by first applying a proximity constraint to limit the distance between a coarse estimate of the current position and a previous estimate. Then, a Compressive Sensing-based (CS--based) positioning scheme, proposed in our previous work , , is applied to obtain a refined position estimate. The refined estimate is used with a map-adaptive Kalman filter, which assumes a linear motion between intersections on a map that describes the users path, to obtain a more robust position estimate. Experimental results with the system that is implemented on a PDA with limited resources (HP iPAQ hx2750 PDA) show that the proposed tracking system outperforms the widely used traditional positioning and tracking systems. Meanwhile, the tracking system leads to 12.6 percent reduction in the mean position error compared to the CS-based stationary positioning system when three APs are used. A navigation module that is integrated with the tracking system provides users with instructions to guide them to predefined destinations. Thirty visually impaired subjects from the Canadian National Institute for the Blind (CNIB) were invited to further evaluate the performance of the navigation system. Testing results suggest that the proposed system can be used to guide visually impaired subjects to their desired destinations.

Perspectives on low vision service in Canada: A pilot study

BACKGROUND A review of the literature and current practice patterns for vision rehabilitation care in Canada provide a basis for this pilot study, which was undertaken to explore related issues from the perspectives of older adults and low vision service providers. The pilot study was overseen by a number of collaborators whose names are listed at the end of this paper. METHODS Thirty people aged 60 years or older who had vision impairments and were clients of the Canadian National Institute for the Blind were surveyed by telephone. Ophthalmologists, optometrists, and opticians completed a mail questionnaire. Vision rehabilitation practitioners and nurses, ophthalmic technicians, and service providers for low vision technical aids were surveyed by e-mail. RESULTS Ophthalmologists are a primary source of referrals to low vision services, but low functional vision does not always trigger such referrals, nor are referrals always timely. Optometrists are primary providers of low vision services, including dispensing of low vision aids, but such aids are expensive, and inadequate training in their use may contribute to noncompliance. Costs associated with providing low vision assessments and services are higher than compensation to vision service providers, whose capacity to meet increasing demand is limited. In addition, there are disparities between rural and urban areas and among provinces in the availability of, and funding for, services and aids. INTERPRETATION On the basis of the findings, an emergent theory is proposed on the consequences resulting from lack of planning and standards for vision rehabilitation care. The implications of this study form the basis for further research.

Prevalence of Visual Impairment and Uncorrected Refractive Error – Report from a Canadian Urban Population-based Study

Abstract Purpose: The prevalence of visual impairment due to uncorrected refractive error has not been previously studied in Canada. A population-based study was conducted in Brantford, Ontario. Methods: The target population included all people 40 years of age and older. Study participants were selected using a randomized sampling strategy based on postal codes. Presenting distance and near visual acuities were measured with habitual spectacle correction, if any, in place. Best corrected visual acuities were determined for all participants who had a presenting distance visual acuity of less than 20/25. Results: Population weighted prevalence of distance visual impairment (visual acuity <20/40 in the better eye) was 2.7% (n = 768, 95% confidence interval (CI) 1.8–4.0%) with 71.8% correctable by refraction. Population weighted prevalence of near visual impairment (visual acuity <20/40 with both eyes) was 2.2% (95% CI 1.4–3.6) with 69.1% correctable by refraction. Multivariable adjusted analysis showed that the odds of having distance visual impairment was independently associated with increased age (odds ratio, OR, 3.56, 95% CI 1.22–10.35; ≥65 years compared to those 39–64 years), and time since last eye examination (OR 4.93, 95% CI 1.19–20.32; ≥5 years compared to ≤2 years). The same factors appear to be associated with increased prevalence of near visual impairment but were not statistically significant. Conclusions: The majority of visual impairment found in Brantford was due to uncorrected refractive error. Factors that increased the prevalence of visual impairment were the same for distance and near visual acuity measurements.

Anonymous Indoor Navigation System on Handheld Mobile Devices for Visually Impaired

An indoor positioning and navigation system based on measurements of received signal strength in wireless local area network is proposed. In the system, the location determination problem is solved by applying compressive sensing, which offers recovery of sparse signals from a small number of noisy measurements by solving an ℓ1-minimization problem. The refined estimate is then used with a map-adaptive Kalman filter for real-time tracking. A navigation module integrated with the tracking system guides users to pre-defined destinations with voice instructions. Experimental results with a system that was implemented on a PDA shows that the proposed tracking system is lightweight so that it can be used on a resource constrained platform while outperforming the widely used traditional positioning and tracking systems. A pilot study was carried out with 30 visually impaired subjects from the Canadian National Institute for the Blind. Testing results show that the proposed system can be used to guide visually impaired subjects to their desired destinations with a very high success rate.