Bengali text input interface design for mobile devices

Text entry has become one of the most frequent activities performed using mobile devices such as PDAs. Virtual keyboards (VK), which allow text to be entered by tapping keys displayed on the screen, are among the predominant mode of text input for such devices. It is important to design VK layouts in a way such that the users can achieve high text entry speed with high accuracy. Several layouts, primarily in English and also in some other languages, have been proposed to achieve the twin objectives. However, no such work has been reported for Bengali, the second and fifth most popular language of India and the world, respectively. The existing methods cannot be applied directly to Bengali VK design due to the problem of accommodating the large Bengali alphabet (more than 60 characters) on a small display area. In order to resolve the resulting usability-performance trade-off, this paper proposes a two-level design. Five two-level VKs representing three design paradigms (alphabetic, frequency-based and adaptive) have been designed and compared in an empirical study. The study results show that for mobile devices, the two-level adaptive design is expected to give best performance in terms of text entry rate and accuracy. The layouts as well as the procedure and results of the study are discussed in this paper.