MOBILE SENSING: Retrospectives and Trends

It is difficult to think back to a time before smartphones existed, with their ubiquitous computing and communication capabilities, and with detailed location sensing easily available from Global Positioning Systems (GPS). In the late 1990s, when my research group began work on mobile sensing, smartphones had not yet been invented. While GPS did exist, GPS receivers were expensive, power-hungry and not widely available. Our first mobile computing project started as a powerefficiency study for a GPS-based interactive campus tour. GPS-based tour applications are familiar now, but were unheard of then, and the physical implementation was a challenge. We used a Palm Pilot PDA (personal digital assistant) connected to an external GPS receiver and an external Wi-Fi card. In those days, PDAs had neither GPS nor any wireless communication capability! Given the bulkiness of the various pieces of our "app," we carried them and their batteries around in a shoebox. Since both the GPS and the radio were quite high power (over 1W), they greatly impacted the system's battery life. Our power-efficiency work explored methods to locally cache maps on the PDA, and to power down modules when not in use.