Some telecommunications stocks did not do as well as they could have last year, and J.P. Morgan thinks it knows why.

The bank said in an April note that some investors grew concerned in 2017 about returns — or the lack of them — on so-called 5G mobile network technology, which is designed to deliver faster data speeds.

J.P. Morgan analysts said they found "depressed valuation" for Chinese, Japanese, South Korea and Australian telecommunications stocks. Those markets are likely to be the first in the region to roll out 5G, according to the bank.

All told, companies in the Asian telecom sector underperformed the MSCI Asia Index by 18 percent in the 12 months to April 2018, the analysts said.