Spectrum security and enforcement is one of the major challenges that need to be addressed before spectrum sharing technologies can be adopted widely. The problem of rogue transmitters is a major threat to the viability of spectrum sharing. One approach for deterring rogue transmissions is to enable receivers to authenticate or uniquely identify transmitters. Although cryptographic mechanisms at the higher layers have been widely used to authenticate transmitters, the ability to authenticate transmitters at the physical (PHY) layer has a number of key advantages over higher layer approaches. In existing schemes, the authentication signal is added to the message signal in such a way that the authentication signal appears as noise to the message signal and vice versa. Hence, existing schemes are constrained by a fundamental tradeoff between the message signal’s signal-to-noise ratio (SNR) and the authentication signal’s SNR. In this paper, we extend the precoded duobinary signaling (P-DS) technique to devise a new PHY-layer authentication scheme called P-DS for authentication (P-DSA). P-DSA exploits the redundancy introduced by P-DS to embed the authentication signal into the message signal. P-DSA is not constrained by the aforementioned tradeoff between the message and authentication signals. Our results show that P-DSA improves the detection performance compared with the prior art without sacrificing message throughput or increasing transmission power.