Letter: A Simple Multilevel Block‐Coding Scheme with π/4‐QPSK Properties

Abstract

A multilevel block‐coded QPSK with a similar envelope and trajectories as π/4‐QPSK is proposed. Additionally, it is rotationally invariant and, thus, allows coherent detection. The asymptotic coding gain is 3 dB, whereas the effective coding gain at a bit‐error probability of 10−6 is around 2 dB against uncoded π/4‐QPSK. The corresponding trellis of a full maximum‐likelihood decoder has only four states, which results in a very low complexity.