As wireless communications systems have to accommodate an ever-increasing number of data transfers, a lack of sufficient protocols for ensuring that data is transferred to the correct user could leave systems open to an attack.

Berk Akgun at the University of Arizona and his colleagues explored this type of attack in a recent study in IEEE Transactions on Information Forensics and Security. They found that in some cases, the transfer of data can be degraded by more than 50 percent when massive multiple-input multiple-output (MIMO) is used. Massive MIMO is considered one of the key enabling technologies for 5G networks. 

MIMO is a well-established technique in wireless communications whereby two or more transmitters and receivers send and receive data at once. But as base stations transition to massive MIMO, they become equipped with more and more antennas to transmit signals, and these signals are more likely to interfere with one another. To address this issue, smaller, periodic signals called pilots are assigned to and emitted from each user, which ensure that data is transferred to the correct person.

A major constraint of this approach, especially as the number of communication channels for each base station continues to grow, is the limited number of pilots available. Sometimes, users must be assigned the same pilot sequence, which can interfere with the proper transfer of data and lead to poor system performance. This is called pilot contamination. But this contamination can also be harnessed by an attacker to purposely interfere with data transfers.