A year after Nielsen nixed a venture with Arbitron to measure out-of-home viewing with its Portable People Meter, the company is moving forward with its own system to measure away-from-home TV viewing.

The ratings company says it will launch its new system in September, using cell phone tracking technology developed by Integrated Media Measurement of San Mateo, Calif.

Nielsen and IMMI will offer both national and local out of home TV ratings for New York, Chicago, Los Angeles, Miami, Denver and Houston. The local ratings will be taken from a sample of 500 in each city, and the national ratings will be based on 2,500 total participants.

The participants will carry mobile phones with meter technology developed by IMMI, which passively collects digital signals sent out from television telecasts that match to audio signatures collected by IMMI.

The new system will measure viewing in bars, hotel rooms, gyms, airports and more, viewing that until now has not been included in Nielsen samples culled from paper diaries and local people meters.

Media people and the networks have long complained about this segment of missing data, arguing that a huge amount of TV viewership is being left out that could have a big impact on where advertisers run their commercials.

Indeed, a study released earlier this week by Arbitron, based on its PPM device, found that a third of the television audience is watching more than two hours of television per day outside the home.

And it's not all in bars, contrary to a widely held perception. Seventy percent of respondents in the study said they watched at someone else’s house, 30 percent at restaurants and bars, 19 percent at work, 13 percent in hotels or vacation homes, and 33 percent somewhere else.

When Nielsen pulled out of the venture with Arbitron last year, after investing six years in the project, it promised to come up with an out-of-home measuring system of its own, but the initiative took some time to develop.

In a March 2006 letter to clients, Nielsen promised to not only begin OOH measurement but also to figure out a way to include iPod and mobile video TV watching in its numbers.

This is all part of Nielsen’s Anytime Anywhere Media Measurement initiative, which aims to provide ratings for all TV platforms, responding to critics who say the company’s way of measuring ratings are out of touch with today’s rapidly expanding technology.

The company also has begun measuring viewing on digital video recorders over the past 16 months, and plans to begin issuing commercial ratings later this year.