Investors in Bharti Airtel are keenly waiting rival Idea Cellular Ltd's October-December earnings results due later in the day.

Idea is much smaller than Bharti in revenue terms, but both mobile carriers operate on GSM technology and have similar kinds of subscribers.

As well, both companies' mainstay is second-generation (2G) voice although there has been a greater push in recent months to increase revenue from mobile data.

That may help explain why Idea and Bharti shares have seen a correlation of 0.86 in the past three months.

"Idea's numbers would also answer whether the 2G industry is growing or not, which should have bearing on Bharti too," said an analyst tracking the sector.