Amidst all of Aribtron’s problems administering the new PPM system, seems competitors are seeing an opportunity in it all to kick the ratings giant from the top spot during the confusion. The Nielsen Company is re-entering the radio ratings business in the U.S. and Cumulus Media announced today that they will be on board for the services. The radio broadcaster will start relying on Nielsen’s measurements of 50 of its small and midsize markets in the third quarter of 2009. iHeartmedia (formerly Clear Channel) Radio will use the Nielsen data for 17 of the markets. Nielsen, perhaps best known for television ratings, already measures radio audiences in other countries. In the United States, Nielsen will be in direct competition with Arbitron , the country’s leading supplier of radio ratings data. Stations use ratings to sell advertising time. Nielsen will produce ratings the old way by collecting diaries from respondents. Arbitron’s effort to gradually replace diaries with an electronic form of measurement, personal people meters, has led some station owners to complain.