4G LTE may be approaching respectable coverage and speeds in the U.S. these days, but that's nothing to the kind of blazing downloads that some Japanese and South Korean operators have been introducing.

NTT Docomo Inc. says it will "pre-launch" its upgraded "Xi" (pronounced "crossy") LTE service with maximum download speeds of 150 Mbit/s on Tuesday in Kawasaki, Kanagawa Prefecture.

The operator plans to start offering the service in parts of Tokyo, Osaka and Nagoya from October 2013. Maximum upload speeds could hit 50 Mbit/s, Docomo claims.

Docomo says it will have its first handsets ready to support the faster service from October as well. The operator started with its Xi 4G service in December 2010 with 75 Mbit/s downloads. From March this year it has been updating the network so that it is capable of theoretical maximum downlinks of 112.5 Mbit/s.

The claimed 150 Mbit/s peak speeds match similar boasts from South Korean operator SK Telecom , which launched its LTE-Advanced network with bandwidth aggregation in June. Docomo, however, isn't planning to move to LTE-Advanced until sometime around 2015. (See Docomo Chooses LTE-Advanced Partners.)

Docomo's claimed 150 Mbit/s downloads are, of course, theoretical maximum downlinks unlikely to ever be achieved on a loaded network. Average downlink speeds available with the upgrade should, however, be 30 Mbit/s or greater, roughly twice those offered by nearly all other 4G service providers.

— Dan Jones, Site Editor, Light Reading Mobile