The proceeding in a Seattle federal court will determine how much of a royalty Microsoft Corp should pay Google Inc for a license to some of Motorola's patents. Google bought Motorola for $12.5 billion, partly for its library of communications patents.
If U.S. District Judge James Robart decides Google deserves only a small royalty, then its Motorola patents would be a weaker bargaining chip for Google to negotiate licensing deals with rivals.
Apple Inc and Microsoft have been litigating in courts around the world against Google and partners like Samsung Electronics Co Ltd, which use the Android operating system on their mobile devices.
Apple contends that Android is basically a copy of its iOS smartphone software, and Microsoft holds patents that it contends cover a number of Android features.
Motorola had sought up to $4 billion a year for its wireless and video patents, while Microsoft argues its rival deserves just over $1 million a year. A federal judge in Wisconsin last week threw out a similar case brought by Apple against Google just before trial.
In court on Tuesday Microsoft called Jon DeVaan, a veteran software manager in the Windows division, as its first witness. He said Motorola's wireless and video patents at issue covered only a small part of the overall Windows architecture.
During the run-up to trial in Seattle, both Microsoft and Google asked Robart to keep secret a range of financial details about the two companies, including licensing deals and sales revenue projections. Google requested that Robart clear the courtroom when witnesses discuss those details.
However, in an order on Monday, Robart rejected that request. The public will not be able to view the documents describing patent deals or company sales during trial, Robart ruled, but testimony will be in open court.
"If a witness discloses pertinent terms, rates or payments, such information will necessarily be made public," the judge wrote.
Additionally, any documents the judge relies on for his final opinion will be disclosed, Robart wrote on Monday.
Before trial began on Tuesday, Robart said in court that he wanted to take the most "expansive" interpretation of the public's right to know. Several outside companies besides Microsoft and Motorola, like Research in Motion Inc , have also asked him to keep secret their royalty deals.
Robart said he would consider a request to refer to those third party companies by code names, known only to the lawyers and the judge.
The case in U.S. District Court, Western District of Washington is Microsoft Corp. vs. Motorola Inc., 10-cv-1823.
© Thomson Reuters 2012