How We Tested and What the Ratings Mean
We decided to test the three major 3G cellular wireless broadband providers in 13 U.S. cities that we judged to be broadly representative of the locales where most customers are likely to use these services. In each city, we randomly chose 20 test locations, evenly distributed over the metropolitan area. We performed all of our tests inside a parked car.
We created a 1-minute stress test to evaluate the quality and performance of the wireless service. We tested network delay, upload speed, download speed, and reliability, as well as the correlation between "bars of service" and network performance.
We conducted the tests using industry-standard wireless-testing software (Ixia Chariot) running on a Windows XP SP3 laptop. We tested on a laptop, rather than on a smartphone, because we needed the laptop's processing power to run Ixia's rigorous 1-minute tests, and because a laptop can test the strengths and weaknesses of the network more accurately than a cell phone can. To connect to each network, we used the latest USB modem from each vendor: AT&T's USBConnect Option Quicksilver, Sprint's Sierra Wireless USB 598, and Verizon Wireless's Novatel Wireless USB 727. All of the client adapters we used came from the respective vendors and were recommended by the outlets where we purchased them.
Download speed: the average speed (in kilobits per second) at which we downloaded random data from a known Internet server during a 1-minute streaming test.
Upload speed: the average speed (in kilobits per second) at which we uploaded random data to a known Internet server during a 1-minute streaming test.
Reliability: the percentage of tests for a given city in which we could detect a signal, connect at a reasonable speed (faster than dial-up), and sustain an uninterrupted connection for the duration of a 1-minute streaming test.
Illustrations by Keith Negley.