Optimal Blind APSK Detection in Polynomial Time

Amplitude/phase-shift keying (APSK) is a power- and bandwidth- efficient modulation technique that is robust against high-power- amplifier nonlinear distortion effects and has been adopted in the standard DVB-S2 for digital video broadcasting and interactive broadband satellite services. Differential APSK has been studied as a simple blind alternative that avoids channel estimation and tracking at the receiver. However, if the channel is unknown at the receiver end, then the optimal blind detector takes the form of a sequence detector and has exponential (in the sequence length) complexity when implemented through a conventional exhaustive search among all possible data sequences. In this work, we develop a novel algorithm that has polynomial complexity and performs optimal blind sequence detection of APSK.