Iftekhar Alam- firstname.lastname@example.org
Pune Institute of Engg and Technology
Shivajinagar, Pune; INDIA - 411 005
Popular version of paper 3aPP1
Presented Wednesday morning, May 18, 2005
Joint ASA/CAA Meeting, Vancouver, BC
Blindness is a sensory disability which is difficult to treat but can to some
extent be helped by artificial aids. This paper describes a method for enabling
blind persons to pinpoint objects in their environment to high accuracy by bouncing
ultrasound from them. Such "ultrasound eyeglasses" are called "sonoculars"
(sonic binoculars) and several systems have already been developed. However,
there is a way to improve their accuracy. In our work, we have developed a technique
in which sonoculars would be able to receive highly precise "direction
of arrival" (DoA) information of incoming echoes. In turn, such a capability
would allow visually impaired persons to localize (determine the location) of
nearby objects with higher precision than possible before.
Throughout history, the staff, or long cane, has provided visually impaired persons with information about their immediate surroundings. By using the sense of touch, such persons protect themselves against collisions with objects. But what has been most significantly missing in this form of travel is reliable information about objects farther away than 6 meters or so. In addition, it is also difficult for a blind person to judge the distance between nearby objects. Thus, it has been suggested that an ability to use ultrasound echoes leads to superior mobility in the blind. Some species--most notably bats--use this "echolocation" to decrease dependence on their poor vision when hunting and navigating at night.
The proposed visual aid acts as a "sonocular perception system," which is a vision substitution aid for enabling blind persons. The blind person wears "ultrasonic eyeglasses" which has an array of ultrasonic sensors embedded in it. The ultrasonic signal, covering a narrow frequency band, is reflected back by the objects, falling in the ultrasound beam and is received. The received signal is "massaged" and processed before being converted to audible sound signals sent to both ears at once.
To allow a blind person to have a near-visual experience, making it easier to avoid obstacles, the system must have the ability to detect weak echoes in the presence of strong echoes. This paper presents a technique for performing this necessary calculation. We have developed a robust algorithm for estimating the Direction of Arrival (DoA) of the ultrasound. Our algorithm separates the spatial ultrasound data into signal and noise components. In this paper, we propose and investigate this "subspace" DoA algorithm.. This technique/algorithm has been found to give good results in localizing objects and distinguishing between objects which are close together horizontally (i.e., they have a small azimuthal angle).
Using a computer simulation, we compared the performance of our DoA algorithm to another algorithm called MUSIC. The simulation results in figure 1 provide the following comparison-
Other Advantages over MUSIC Algorithm
The following are the other advantages of the proposed algorithm over the MUSIC algorithm:
(a) The bearing resolution (the resolution with which one can determine the angle between the wearer and the source) improves with increase in number of ultrasound input samples. For any given number of samples (N), the resolution achieved by the proposed algorithm is better as compared with MUSIC. Thus, for MUSIC algorithm the number of input samples required to achieve the required resolution is more.
(b) Our algorithm distinguishes very weak sound sources in the vicinity of strong ones and its resolution is not sensitively dependent upon the difference in echo level between two adjacent sources. It is also inferred from the simulations that MUSIC can distinguish between two targets with strong echo levels and a small amplitude difference between them.
Our DoA algorithm has achieved resolution better than that from the MUSIC algorithm. Several experiments have been carried out on actual subjects, by simulating 'auditory events' derived and mapped from this algorithm. The experiments carried out have provided very encouraging results. The results are indicated in figure 2.