Soft Output M ‐Algorithm Based Quantum Data Detection for Polar Coded Wireless Quantum Optical Multipath Communications

ABSTRACT

Entanglement‐based quantum communication schemes, such as quantum teleportation, rely on classical communication links, which introduce significant transmission overhead and limit the achievable quantum advantage. To address this issue, this work investigates a non–entanglement‐based quantum communication concept. The proposed laser‐based physical layer (PHY) model accommodates a multipath quantum channel and receiver impairments, including intersymbol interference (ISI) caused by multipath propagation, thermal background noise, decoherence, the absence of phase coherence between transmitter and receiver, photon‐counting reception, dark counts and quantum efficiency. Because optimum full state sequence detection becomes increasingly complex with increasing channel memory, a reduced‐complexity trellis‐based, suboptimum yet practical sequence detection approach considering the ‐algorithm is applied. By extending this algorithm to generate soft outputs, a soft‐output ‐algorithm (SOMA) is obtained, enabling improved channel decoding. Two SOMA variants are introduced: a straightforward ‘post‐processing (PP)’‐SOMA and a more advanced ‘simple rule (SR)’‐SOMA. Results indicate that, particularly with SR‐SOMA, the proposed concept substantially reduces transmission overhead while ensuring reliable reception performance. Furthermore, the integration of classical channel coding, such as 3GPP 5G/new radio (5G/NR) polar codes, enhances overall system robustness. The proposed architecture can operate as a stand‐alone communication system without entanglement and may additionally convey the classical feed‐forward information required by entanglement‐based protocols.