STOCKHOLM, Jan 18 (Reuters) - Sweden"s Ericsson (ERICb.ST) has filed another set of patent infringement lawsuits against Apple (2788.T) in the latest salvo between the two companies over royalty payment for use of 5G wireless patents in iPhones. Both companies have already sued each other in the United States as negotiations failed over the renewal of a seven-year licensing contract for telecoms patents first struck in 2015. Ericsson sued first in October, claiming that Apple was trying to improperly cut down the royalty rates. The iPhone maker then filed a lawsuit in December accusing the Swedish company of using "strong-arm tactics" to renew patents. "Ericsson has refused to negotiate fair terms for renewing our patent licensing agreement, and instead has been suing Apple around the world to extort excessive royalties ... we are asking the court to help determine a fair price," an Apple spokesman said on Tuesday. Patent lawsuits are quite common among technology companies because every dollar saved could amount to significant amounts over the duration of the agreement, with companies such as Ericsson charging $2.50 to $5 for every 5G handset. "Since the prior agreement has expired, and we have been unable to reach agreement on the terms and scope of a new licence, Apple is now using our technology without a licence," an Ericsson spokesman said. The Swedish company invests about $5 billion a year in research, has a portfolio of more than 57,000 patents and royalties from its patent portfolio account for roughly a third of its operating profit. Last year Ericsson settled patent lawsuits with Samsung (005930.KS) after several months of court battles that temporarily hit its quarterly earnings. Pending dues are usually cleared after a settlement is reached. read more