Repeat interval for minute reminder on a Windows phone

I have a program that starts a reminder after 30 minutes. I would like to change it so that the reminder starts every 30 minutes without any user interaction. I don’t want them to have to press a button to start a timer, as they currently are. Here is what I still have:

            Reminder r = new Reminder("REMINDER..");
            r.Title = "REMINDER..";
            r.Content = "YOU CAN SMOKE AT THIS TIME";
            r.BeginTime = DateTime.Now.AddMinutes(30);
            r.ExpirationTime = DateTime.Now.AddDays(1);
            ScheduledActionService.Add(r);