Augmenting Mobile 3G Using WiFi: Measurement, System Design, and Implementation

We investigate if WiFi access can be used to augment 3G capacity. To understand the feasibility of 3G augmentation, we conduct a detailed study of 3G and WiFi access from moving vehicles, in three different cities. We find that the average 3G and WiFi availability across the testbeds is 87% and 11%, respectively. We also find that, unlike stationary environments, WiFi throughput is lower than 3G throughput in mobile environments, and WiFi loss rates are higher. We then design a system, called Wiffler, that uses two key ideas—leveraging delay tolerance and fast switching. For delay tolerant applications, Wiffler uses a simple model of the environment to predict WiFi connectivity, and delays applications to offload more data on WiFi. But Wiffler delays applications only if it results in 3G savings. For applications that are extremely sensitive to delay or loss (e.g., VoIP), Wiffler quickly switches to 3G if WiFi is unable to successfully transmit the packet within a small time window. We implement and deploy Wiffler in our vehicular testbed. Both our implementation and trace-driven experiments show that Wiffler significantly increases 3G savings. For example, for a realistic workload, Wiffler reduces 3G usage by 45% for a delay tolerance of 60 seconds.