Leadsled, what are you talking about CDMA broadband? ADS-B systems use the 1090 MHz Extended Squitter (1090ES) data link.
First off, the ADS message is limited to 56 bits. The issue has been, how much data from the ac can be braodcast in 56 bits. Note that currently S mode is 56 bits total.
Second, the bandwidth issue is well known, the FAA calls it congestion. Currently, ADSB uses 1090 Mhz, but the FAA is looking at using 978 Mhz below 18,000. Congestion is caused by the bandwidth being used up, and the system will drop aircraft.
Encription, again, well known issue..
"At the Black Hat and Defcon security conference this week in Las Vegas, two security researchers plan to give separate talks on the same troubling issue: By 2020, a new system known as Automated Dependent Surveillance-Broadcast or ADS-B will be required as the primary mode of aircraft tracking and control for commercial aircraft in the U.S.–earlier in other countries such as Australia. And both researchers say that ADS-B lacks both the encryption necessary to keep those communications private and the authentication necessary to prevent spoofed communications from mixing with real ones, potentially allowing hackers to fabricate messages and even entire aircraft with radio tools that are cheaper and more accessible than ever before.
“Anyone can technically transmit these messages,” says Andrei Costin, a Ph.D. candidate at the French security institute Eurecom who plans to give a talk called “Ghosts In The Air (Traffic)” at Black Hat. “It’s practically possible for a medium-technical savvy person to mount an attack and impersonate a plane that’s not there.”
Next-Gen Air Traffic Control Vulnerable To Hackers Spoofing Planes Out Of Thin Air