NEW DELHI—India's largest cellular operator, Bharti Airtel Ltd., plans to spend $9 billion to improve its mobile data network in the country, the company said Monday.

Much of this money will be invested in laying fiber optic cables and improving network signals in congested areas.

Despite Airtel spending hundreds of millions of dollars to rent bandwidth from the Indian government, "there are still problems with the network," said Gopal Vittal, the company's chief executive.

While smartphone ownership is rising rapidly in India, the country's network of cellphone towers has struggled to keep pace.

For example, Airtel says it has roughly half the number of towers it needs in the heart of New Delhi to provide full coverage there.

Mobile network operators say that they haven't been able to improve network coverage in India because of the high fees they pay the government for the right to offer cellular broadband services.

During the latest auction in March, companies agreed to pay $17.6 billion for broadband spectrum rights.

That left little money to spend on enhancing the networks, these companies say.

Airtel said it would take on debt to fund its improvements.

Write to Sean McLain at sean.mclain@wsj.com

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(END) Dow Jones Newswires

November 30, 2015 04:25 ET (09:25 GMT)