Authenticated and encrypted radio communications (Non-Internet or TCP/IP)
Public-key cryptography has only one advantage in the topology of the question (central server): it allows initial setup across a channel assumed secure from an integrity standpoint only (rather than also confidentiality). But public-key cryptography comes with complexity and performance issues; assuming ability to securely inject a secret key in slave devices, and the slave devices tailored to a single central server, plain old secret-key cryptography seems a good choice.

That would be with a master secret key in the central server, with each slave device assigned an ID and a "diversified" secret key derived from the master secret key and device ID, using some Key Derivation Function (HMAC will do nicely). These long-term keys can then be used to derive session keys, much like long-term public/private key pairs are used to derive session keys. Upon initiating communication with a device giving its ID, the central server can quickly find the slave device's secret key, by applying the KDF.