The planned purchase of Motorola Mobility for $12.5 billion is the largest acquisition to date by Google. It will serve to defend and promote the Android ecosystem, not only for mobile handsets and tablets but also for set-top boxes. Google will also own the leading provider of set-top boxes by revenue worldwide. That does not mean that Google will be welcomed into the living room by either service or programming providers.

In a surprise move, Google announced a definitive agreement to purchase Motorola Mobility at a 63% premium on the share price. The deal is expected to close late 2011 or early 2012, subject to regulatory approval.

Motorola Mobility was separated from Motorola as an independent public company in January 2011. As well as selling smart phones and tablets, it has end-to-end capabilities in the video domain, from headends through network equipment infrastructure to set-top boxes for cable and internet protocol television.

The company recently launched its first video gateway device, its Medios Xperience platform for interactive television services, and Televation, a broadband video device enabling consumers to watch live television on any connected IP device anywhere around the home.

“Motorola is also a market leader in the home devices and video solutions business,” wrote Larry Page, the chief executive of Google. “With the transition to internet protocol, we are excited to work together with Motorola and the industry to support our partners and cooperate with them to accelerate innovation in this space.”

As he went on to explain, the move is partly about using patents to help defend the Android ecosystem: “Our acquisition of Motorola will increase competition by strengthening Google’s patent portfolio, which will enable us to better protect Android from anti-competitive threats from Microsoft, Apple and other companies.”

A consortium including Microsoft and Apple recently purchased 6,000 patents from bankrupt Nortel for $4.5 billion. Motorola Mobility has 17,000 patents and a further 7,500 pending.

Google published a number of strangely similar quotes from Android partners welcoming the defence of the Android ecosystem, including senior executives from Samsung, HTC, LG, and Sony Ericsson.

Google will run Motorola as a separate business and the Android platform will remain open, with Motorola as a licensee.

Motorola was a founding member of the Open Handset Alliance formed to promote Android and switched to the Linux based Java environment as the sole operating system for its smartphones in 2008.

There are more than 150 million activated Android devices worldwide, with over half a million more added every day.

Google TV, also based on the Android operating system, has so far been less successful to date. Announced in May 2010 as a partnership between Google, Intel, Sony and Logitech, it appeared half-baked. ABC, CBS, NBC and Hulu promptly blocked access to Google TV products. Logitech was inundated with product returns and slashed the price of its Revue from $249 to $99 to clear inventory.

A relaunch of Google TV is expected soon and the addition of Motorola to the mix in a significant development.

Motorola is one of the leading set-top box suppliers in the United States, supplying Comcast, AT&T and Verizon. The potential to add Google TV technology to these devices is intriguing but would be highly disruptive to the relationships between service operators and programming providers.

Speaking to analysts, Sanjay Jha, the chief executive of Motorola Mobility, pointed to the transition from traditional set-top boxes to internet protocol devices. “There is a great convergence happening between the mobile world and the content that enters the homes with a set-top box. Working with our carriers, we’ll be able to accelerate that convergence and deliver products, which will delight customers, quite frankly.”

The 12.5 billion dollar question is whether Android could yet have a similar effect on the set-top box market as it has in the mobile handset world.

Years have been spent developing and promoting OCAP, latterly branded as Tru2Way, as a standard platform for cable television, based on a similar Java-based environment.

So far neither Tru2Way nor Google TV has resulted in a television revolution, but the combination of tablets, smartphones and smart televisions promises to transform the television user experience and Android could be an important part of that.

As Andrew Burke, the chief executive of Amino, wrote: “A revised Google TV solution could be a classic ‘cuckoo’s egg’ — planted in the home to offer an Internet video value-add but over time becomes the dominantly viewed device that pushes out the incumbent Pay-TV solution from the living room.”

We are still waiting to see how Google will disrupt the television world. An indication of how that world is changing is that Google chairman Dr Eric Schmidt is due to provide the keynote at the annual Edinburgh International Television Festival. It will be the first time the prestigious MacTaggart lecture has been given by someone from outside the industry.