The stringent requirements of ultra-reliable low-latency communications (URLLC) require rethinking of the physical layer transmission techniques. Massive antenna arrays are seen as an enabler of the emerging 5th generation systems, due to increases in spectral efficiency and degrees of freedom for transmissions, which can greatly improve reliability under demanding latency requirements. Massive array coherent processing relies on accurate channel state information (CSI) in order to achieve high reliability. In this paper, we investigate the impact of imperfect CSI in a single-input multiple-output (SIMO) system on the coherent receiver. An amplitude-phase keying (APK) symbol constellation is proposed, where half of the symbols are transmitted with a lower power, and half with a higher power, such that there exist two energy levels. The symbols are demodulated using a dual non-coherent and coherent detection strategy, in order to improve symbol reliability. Simulation results show that for inaccurate CSI, the proposed scheme enhances receiver performance.