The next public appearance by Apple CEO Tim Cook could be as a witness at his company's upcoming trial against Qualcomm. 

The executive is one of many possible witnesses listed in a joint filing from Apple and Qualcomm on Thursday as they prepare to face off in court next month over Qualcomm's licensing practices. The list includes top executives from Apple and Qualcomm -- such as both companies' CEOs -- as well as representatives from Apple's contract manufactures, third parties like Samsung and Motorola, and various experts.

The companies likely won't call everyone listed, partly because of time constraints. 

The San Diego trial starts April 15 and is slated to last for 20 days. There are billions of dollars at stake, with Apple's manufacturing partners asking for $27 billion in damages in the trial. The contract manufacturers -- which include Foxconn, formally known as Hon Hai Precision; Compal; Pegatron; and Wistron -- are involved in the case because they're the ones who license Qualcomm's patents on behalf of Apple. Apple and Qualcomm are also asking for damages.

Apple and Qualcomm have been fighting over patents and licensing since January 2017, when Apple filed suit against Qualcomm for roughly $1 billion, saying the maker of wireless chips didn't give fair licensing terms for its technology. Apple wants to pay a lower amount for using Qualcomm technology in its devices. Qualcomm, the world's biggest provider of mobile chips, responded by suing Apple for patent infringement and seeking a ban on iPhone sales.

Qualcomm maintains that no modern handset -- including the iPhone -- would've been possible without its cellular technologies. Because Qualcomm owns patents related to 3G, 4G and 5G phones -- as well as other features like software -- any handset makers building a device that connects to the networks has to pay it a licensing fee, even if they don't use Qualcomm's chips. Apple, in disputing Qualcomm's terms, ordered its manufacturing partners to stop paying Qualcomm. Qualcomm hasn't yet said how much it's requesting in damages in the trial.

Along with Cook, many other top Apple executives could be called to testify in next month's trial. That includes Operating Chief Jeff Williams; Phil Schiller, head of marketing; Bob Mansfield, the Apple engineer who previously oversaw hardware; Bruce Sewell, the company's former general counsel; and Tony Blevins, vice president of procurement.

From Qualcomm, CEO Steve Mollenkopf; President Cristiano Amon; Alex Rogers, the company's head of licensing; Derek Aberle, the company's former lead of licensing; and co-founder Irwin Jacobs are among the people who could appear on the stand.

Many of the executives testified during January's trial between the US Federal Trade Commission and Qualcomm. The FTC two years ago accused Qualcomm of operating a monopoly, forcing customers like Apple to work with it exclusively and charging excessive licensing fees for its technology. The two sides made their arguments during a trial in January and are waiting for a judge's ruling in the case.

Apple and Qualcomm also met in court over patents earlier this month, and a jury in San Diego determined that Apple violated three Qualcomm patents and should pay the chipmaker $31 million for infringing on its technology. Qualcomm had alleged that Apple used its technology without permission in some versions of the iPhone. The jury awarded Qualcomm the full amount it had requested at the start of the two-week trial.