Google will have arch-rival Apple to thank for a huge chunk of its mobile revenue in 2012.

The search giant's licensing deals with Apple over its Maps and Search apps have been a healthy cash cow since the iPhone debuted in 2007. This year will be no exception.

In an investors note released yesterday, Piper Jaffray analyst Gene Munster said he expects Google to generate around $4.5 billion in mobile sales this year. And iOS will kick in the largest or close to the largest chunk of that.

iOS will account for around 40 percent of Google's total mobile search revenue, or $1.6 billion, estimates Munster, which ultimately means iOS will generate around 2 percent of Google's total sales for the year.

But what happens if Apple replaces Google Maps with its own in-house map app? Recent reports suggest that Apple has already cooked up a 3D Maps app set to replace Google's app as the default on iOS devices. Regardless, Munster doesn't expect any significant changes to the numbers.

Google Maps will still live on in the App Store, freely available for any person to download, the analyst said. Google recently revealed that its Maps service has attracted more than 1 billion users across the world. Google offers a host of other apps for iOS users, but the Maps app could prove to be the most popular among them even if it's no longer the iOS default.

And Google isn't standing still with Maps.

The company unveiled yesterday a host of innovations to the service, including 3D images, offline use, and more shots of Street View.

Still, the move by Apple to replace Google Maps as the default may be just the latest attempt to squeeze out the search giant.

"Moving forward, we expect a continued tug-of-war between Apple and Google," Munster said. "We believe Google is likely to push more of its apps through the App Store, including Chrome, while Apple will continue to innovate around discovery on the iPhone through Siri. Net-net, we believe the core user experience on iOS will remain largely unchanged even if Google Maps is replaced."