| The ability to enter text on phones is crucial for utilizing the Short Message Service (SMS) of digital cellular networks. Standard 12-Button phone keypads are not naturally suited for text entry as each button on them encodes 3 or 4 letters. This thesis presents a new technique, Less-Tap, to enter text on a mobile phone keypad. The new method is similar to the traditional Multitap method in that it requires the user to press buttons repeatedly to get a required letter. However, in Less-Tap, the letters are rearranged within each button according to their frequency in the language. This way, the most common letters require only one key press. A user study was conducted to compare Less-Tap against Multitap . It shows that the proposed method is significantly faster than the traditional one.; The thesis also presents a new model for predicting text entry speed on 12-button mobile phone keypads. The model is of special interest as it can predict the performance of novice users. Like other models for text entry, the proposed model includes a movement component based on Fitts' law and a linguistic component based on letter digraph probabilities. It adds a mental preparation time before key presses and considers the fact that multiple presses of the same key cannot be modelled accurately by Fitts' law. Finally, the prediction of the model is compared to previously published experimental results. |
