A research group at Virginia Tech has pointed out major flaws in 4G networks where a simple jamming device can take out entire regions of LTE signals. If the LTE network were to fall then 2G and 3G would still work but because such networks are being phased out and new customers are being pushed onto the newer network, such weak points in the network could allow for potential issues.
The director of the group Jeff Reed points out that the LTE network has 8 weak points all of which can be exploited by inexpensive means. The LTE network itself consists of many subsystems and all that is required is that one subsystem has to fail to take out the entire station. Reed goes on to say that the tools required to perform such an action would be a laptop and an inexpensive software-defined radio unit (costing less than $650). Due to the LTE standard being published publicly the knowledge of how the system works can be found and with expenses so low, someone with the knowledge or will can bring down the network.