[kbaker]

It does seem like WAAS at first glance, but I actually think they are creating their own GPS-compatible satellites:

> To put it simply, with QZSS it is like the number of GPS satellites has been increased. Because QZSS has interoperability with GPS, the number of satellites that can transmit satellite signals at the same time is increased, which makes stable positioning possible. This also decreases the positioning errors as described. [1]

With L1 and L5 carriers on GPS now, you can definitely get down to cm-level positioning already. I think they are just launching more satellites in Japan-specific orbits so they have better, faster GPS coverage above Japan, and especially in dense cities where you need a high angle of elevation for positioning satellites.

The farming systems are more real-time kinematic GPS, which broadcast local corrections from a dedicated reference statiion. [2]

[1] http://www.qzs.jp/en/services/index.html

[2] http://en.wikipedia.org/wiki/Real_Time_Kinematic