A U.S. federal judge has issued a preliminary ruling that Qualcomm owes Apple nearly $1 billion in patent royalty rebate payments, though the decision is unlikely to result in Qualcomm writing a check to Apple because of other developments in the dispute.

Judge Gonzalo Curiel of the U.S. District Court for the Southern District of California on Thursday ruled that Qualcomm, the world's biggest supplier of mobile phone chips, was obligated to pay nearly $1 billion in rebate payments to Apple, which for years used Qualcomm's modem chips to connect iPhones to wireless data networks.

The payments were part of a business cooperation agreement between the two companies amid the peculiar patent licensing practices of the consumer electronics industry.

In general, the contract factories that built Apple's iPhones would pay Qualcomm billions of dollars per year for the use of Qualcomm's patented technology in iPhones, a cost that Apple would reimburse the contract factories for. Separately, Qualcomm and Apple had a cooperation agreement under which Qualcomm would pay Apple a rebate on the iPhone patent payments if Apple agreed not to attack in court or with regulators.