Clothes, cars, trains, tractors, body sensors, and tracking tags. By the end of this decade, analysts say, 50 billion things such as these will connect to mobile networks. They'll consume 1000 times as much data as today's mobile gadgets, at rates 10 to 100 times as fast as existing networks can support. So as carriers rush to roll out 4G equipment, engineers are already beginning to define a fifth generation of wireless standards.