Following several recent service outages in Japan, NTT DoCoMo Inc. (NYSE: DCM) has increased the amount it plans to spend on certain network upgrades to ¥164 billion (US$2 billion) over the next three years and brought forward its investment schedule, according to company information.

Out of that total, ¥122 billion ($1.5 billion) has been earmarked for "further processing capability enhancement of packet switching" and "facility build-up to cope with increase in control signals." The goal is to add capacity to the packet switching system so that it can accommodate control signals from 50 million smartphones.

Smartphone signaling was the culprit of the last service outage Docomo suffered at the end of January that left 2.5 million customers in Tokyo without service for about four and a half hours. The operator was in the process of upgrading its network to cope with increased signaling traffic from smartphones, but the new system was not able to handle the amount of control signals, which is what led to the service disruption. (See Android Signaling Storm Rises in Japan .)

Docomo had already planned to invest ¥134 billion ($1.6 billion) over this three-year period on network upgrades, but as a result of the recent outages, the operator increased the planned spending by 30 billion ($373 million), according to an operator spokeswoman.

Other recent service problems were related to the operator's sp-mode service, which is described as an ISP service for smartphones. Of the total new investment, ¥40 billion ($498 million) has been allocated to upgrading that system.

Why this matters
While not all of Docomo's planned investment is related to smartphone signaling, the details the operator revealed about its spending plans provide some indication of what the cost of smartphone signaling can be for mobile operators.

For more
Here's the latest on how operators and smartphone makers are responding to the signaling storm:

— Michelle Donegan, European Editor, Light Reading Mobile