Apple PUSH notification is not a good solution
1) You can only package a limited amount of data to it
2) It may be difficult to figure out if users have the app launched, or exited. If you keep sending PUSH even after users exit the app, they will end up with lots of spam. If you try to send something to the server to indicate that users have closed the app so it should stop sending PUSH, it may not work when the app crashes.
I suggest you use Sockets.
Or just use a scheduled loop to make requests every minute.
.....
But I wonder if you can just send a PUSH without alert body and sound, and just sending a 0 badge. If app it opened, it will be able to feedback to the server to continue sending update. If there is no feedback, stop sending push .