  Next-generation systems aim to increase both the speed and responsiveness of
wireless communications, while supporting compelling applications such as edge
and cloud computing, remote-Health, vehicle-to-infrastructure communications,
etc. As these applications are expected to carry confidential personal data,
ensuring user privacy becomes a critical issue. In contrast to traditional
security and privacy designs that aim to prevent confidential information from
being eavesdropped upon by adversaries, or learned by unauthorized parties, in
this paper we consider designs that mask the users' identities during
communication, hence resulting in anonymous communications. In particular, we
examine the recent interest in physical layer (PHY) anonymous solutions. This
line of research departs from conventional higher layer anonymous
authentication, encryption and routing protocols, and judiciously manipulates
the signaling pattern of transmitted signals in order to mask the senders' PHY
characteristics. We first discuss the concept of anonymity at the PHY, and
illustrate a strategy that is able to unmask the sender's identity by analyzing
his or her PHY information only, i.e., signalling patterns and the inherent
fading characteristics. Subsequently, we overview the emerging area of
anonymous precoding to preserve the sender's anonymity, while ensuring high
receiver-side signal-to-interference-plus-noise ratio (SINR) for communication.
This family of anonymous precoding designs represents a new approach to
providing anonymity at the PHY, introducing a new dimension for
privacy-preserving techniques.
